Download HUMAN BIOCHEMISTRY

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Option B – Human Biochemistry
I.
Diet
Requirements of the human body for a healthy diet
 The function of food is to keep the body functioning and healthy.
 It provides energy and replenishes chemicals.
 Good health requires a balanced diet that includes all the essential nutrients taken from as
wide a variety of foods as possible.
 Nutrients can be divided into six main groups: proteins, carbohydrates, fats, vitamins,
minerals, and water.
 The amount of each required depends on several factors, such as age, weight, gender, and
occupation.
 A well-balanced diet consists of about 60% carbohydrate, 20-30% protein, and 10-20%
fat.
 Foods containing these three components will also provide the essential vitamins and the
fifteen essential minerals, which include calcium, magnesium, sodium, iron, and sulfur,
along with trace elements like iodine and chromium.
 In addition, a daily intake of about 2 dm3 (2 liters) of water is required.
 Malnutrition can occur when either too little or too much of these essential components
are taken.
 Other sources recommend eating a balanced diet with less than 30% of daily calories from all
fats and less than 10% of daily calories from saturated fats.
 Not all fats are created equal:
 Monounsaturated fats can help decrease LDL (bad) cholesterol levels and increase
HDL (good) cholesterol levels when part of a low-fat diet. Olive and canola oils are
the best oils to use. Avocados, while high in calories and fat, are another great source
of monounsaturated fat.
 Polyunsaturated fats can help decrease LDL (bad) cholesterol levels when part of a
healthy diet. Safflower, sunflower, corn and soybean oils contain the highest amounts
of polyunsaturated fats. Nuts and fatty fish such as salmon, tuna, mackerel and
herring are also good sources.
 Saturated fats are responsible for raising LDL (bad) cholesterol levels. They are
usually solid at room temperature and come primarily from animal sources such as
meat, poultry, butter and whole milk. Coconut, palm and palm kernel oils are also
high in saturated fats.
 Check food labels. When choosing margarine, choose a soft tub margarine that has
liquid oil listed as the first ingredient.
 Adding unsaturated fats (polyunsaturated and monounsaturated) can be good for you.
Since fat can help you feel full, eating the right amount of good fat can help you
reduce your total calorie intake if you eat lots of high-calorie, carbohydrate-rich
foods.
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 Guidelines for a healthy eating:
1) Eat a variety of foods.
2) Maintain a healthy weight.
3) Eat a diet low in fat, saturated fat, and cholesterol.
4) Include plenty of fruit and vegetables.
5) Use salt and sugar sparingly.
6) Moderate the intake of alcohol.
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 Nutritional information for a 37.5 g serving of a typical wheat breakfast cereal:
Energy
Protein
Carbohydrate
(of which sugar)
Fat
(of which saturated)
Fiber
(soluble)
(insoluble)
540 kJ
(128 kcal)
4.2 g
25.4 g
(1.8 g)
1.0 g
(0.2 g)
3.9 g
(1.2 g)
(2.7 g)
Sodium
Vitamins
thiamin (B1)
riboflavin (B2)
niacin
folic acid
Iron
0.1 g
0.4 mg (32% RDA)
0.5 mg (32% RDA)
5.7 mg (32% RDA)
63.8 g (32% RDA)
4.5 mg (32% RDA)
(RDA = recommended daily allowance)
 The daily calorific intake for a moderately active woman is about 8400 kJ (2000 kcal) per day
 For an adult male undertaking physical work this increases to about 14,700 kJ(3500 kcal)
 Energy is provided by fats, carbohydrates, and proteins.
 Carbohydrates provide the main source of energy, but (like proteins) are already partially
oxidized, and so do not provide as much energy, gram-for-gram as fats, which are also
used to store energy.
Food Calorimetry
 The energy content of a food can be found in a food calorimeter.
 A known mass of the food is heated electrically and burned in a supply of oxygen.
 The heat produced is transferred through a copper spiral to water, and the temperature
increase of the water recorded.
 The ‘water equivalent’ of the whole system is calibrated and the calorific value of the
food determined.
 Calorific values are typically recorded as kcal per 100g or more commonly as kJ per
100g. 1 kcal = 4.18 kJ
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cross-section of a bomb calorimeter
 Sample calculation:
37.5 g of the breakfast cereal quoted above gives 540 kJ of energy. Calculate the temperature
rise in a food calorimeter with a water equivalent of 626 g if 1.00 g of the breakfast cereal is
burned completely.
Benefits and Concerns of Genetically Modified Foods
 Crops and animals can be genetically modified to provide more food, be more resistant to
disease, or be more tolerant to heavy metals (among many other characteristics).
 Genetic engineering involves the process of selecting a single gene for a single characteristic
and transferring that stretch of DNA from one organism to another.
 An example of genetically modified food is the FlavrSavr tomato.
 In normal tomatoes, a gene is triggered when they ripen to produce a chemical that
makes the fruit go soft and eventually rot.
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

In the FlavrSavr tomato, the gene has been modified to ‘switch off’ the chemical so
that the fruit can mature longer on the vine for a fuller taste and have a longer shelf
life.
Due to quality control problems with the FlavrSavr. Calgene did not have access to
the best cultivars, so the genetic sequence was inserted into a cultivar that lacked
consistent production qualities. The resulting tomatoes sometimes fell below the
marketing standards set for the FlavrSavr label. FlavrSavr tomatoes were available
sporadically for several years, but eventually production was discontinued.
 Nutrients per 100 g of tomatoes:
Protein
Flavr Savr®
tomato
0.85 g ± 0.015 g 0.75-1.14 g
Conventional tomatoes
(controls)
0.53-1.05 g
Vitamin A
Vitamin B1 (thiamine)
Vitamin B2 (riboflavin)
Vitamin B6
Vitamin C
Niacin (nicotinic acid)
Calcium
Magnesium
Phosphorus
Sodium
Iron
192-1667 IU
16-80 µg
20-78 µg
50-150 µg
8.4-59 mg
0.3-0.85 mg
4.0-21 mg
5.2-20.4 mg
7.7-53 mg
1.2-32.7 mg
0.2-0.95 mg
420-2200 IU
39-64 µg
24-36 µg
10-140 µg
12.3-29.2 mg
0.43-0.76 mg
10-12 mg
9-13 mg
29-38 mg
2-3 mg
0.26-0.42 mg
Ingredient
Natural range
330-1600 IU
38-72 µg
24-36 µg
86-150 µg
15.3-29.2 mg
0.43-0.70 mg
9-13 mg
7-12 mg
25-37 mg
2-5 mg
0.2-0.41 mg
 Benefits of GM foods:
 Increase crop yields.
 Improve flavour, texture, nutritional value, and shelf life of food.
 Could incorporate anti-cancer substances and reduce exposure to less healthy fats.
 Make plants more resistant to disease, herbicides, and insect attack.
 Make plants more resistant to environmental conditions such as drought, salinity, heavy
metals in the soil.
 Concerns of GM foods:
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 Outcome of alterations uncertain, as not enough is known about how genes operate.
 May cause disease as antibiotic-resistant genes could be passed to harmful
microorganisms.
 Genetically engineered genes may escape to contaminate normal crops with unknown
effects.
 May alter the balance of delicate ecosystems as food chains become altered.
II.
Proteins
Structure
 2-amino acids (-amino acids) are the building blocks for proteins.
 All 2-amino acids have the same general structural formula (an amino group, attached to the
carbon next to the carboxylic acid group):
NH2
CHCOOH
X
The group X can stand for many different groups, for example:
H- (glycine)
CH3- (alanine)
NH2CH2CH2CH2CH2- (lysine)
HOCH2- (serine)
HSCH2- (cysteine)
CH2
N
(tryptophan)
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 Of the 20 amino acids commonly found in living organisms, 8 have non-polar (hydrophobic)
R groups, and the other 12 have polar (hydrophilic) R groups.
The amino acids vary in their side chains (indicated in blue in the diagram).
The eight amino acids in the orange area are nonpolar and hydrophobic.
The other amino acids are polar and hydrophilic ("water loving").
The two amino acids in the magenta box are acidic ("carboxy" group in the side chain).
The three amino acids in the light blue box are basic ("amine" group in the side chain).
 All amino acids contain both a carboxylic acid and an amino group in the same molecule.
Within the molecule of an amino acid, a proton is actually transferred from the acidic group
(the carboxylic acid) to the basic group (the amine). In some books you may see amino acids
shown as neutral molecules. More accurately, they may be shown as dipolar ions, often
referred to as zwitterions.
+
NH2
CHCOOH
NH3
CHCOO
X
X
neutral molecule
zwitterion (dipolar ion)
Per 1 Mon Jan 4Formation of Polypeptides By Condensation Reaction of Amino Acids
 Having 2 functional groups (a carboxylic acid and an amine) allows for the formation of
polypeptides.
 When amino acids join together, they are always bonded using the COOH of one molecule
and the NH2 of another.
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 Water is formed by “clipping off” the H from the amine, and the OH from the carboxylic
acid. Hence the term condensation or dehydration polymerization.
 Here are the possible combinations of the amino acids alanine and serine:
alanine
serine
alanylserine
O
O
NH2CHCOOH + NH2CHCOOH
CH3
serylalanine
H2O+ NH2CHCNHCHCOOH or NH2CHCNHCHCOOH
CH3
OH
OH
OH
CH3
 Two different compounds can be formed by combining two different amino acids, differing
only in the order of the amino acids. Compounds containing relatively small numbers of
amino acids are called peptides. The two examples above could more precisely be called
dipeptides. As the name implies, polypeptides consist of longer chains of amino acids –
usually chains of ten or more amino acids. Proteins contain large numbers of amino acids.
There is no general agreement on the distinction, in terms of numbers of amino acids,
between peptides and proteins (some definitions suggest that proteins are chains of amino
acids with molecular weights greater than 10,000).
 The link joining two amino acids is identical to that in an amide. In peptides and proteins it is
called the peptide bond.
In the portion of a peptide or protein shown at the left,
the peptide link is enclosed within dotted lines.
O
NHCH CNH
CHC
Levels of Protein Structure
 There are four basic levels of protein structure:
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 Primary structure is simply the sequence of amino acids in the protein chain.
 The sequence of amino acids affects all the other levels of structure, since they are a
consequence of interactions between R group of the amino acids.
 Polar R groups interact with other polar R groups further down the chain.
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
Likewise non-polar R groups interact with each other.
 -endorphin is a protein consisting of a single polypeptide chain of 31 amino acids,
which acts as a neurotransmitter in the brain. The primary structure of -endorphin is:
Alanine – Isoleucine – Isoleucine – Lysine – Asparagine – Alanine – Histidine – Lysine –
Lysine – Glycine – Glutamine – Tyrosine – Glycine – Glycine – Phenylalanine –
Methionine – Threonine – Serine – Glutamic Acid – Lysine – Serine – Glutamine –
Threonine – Proline – Leucine – Valine – Threonine – Leucine – Phenylalanine – Lysine
– Asparagine
 Secondary structures are the regular, repeating coils/folds (-helices and -pleated sheets)
stabilized by hydrogen bonds between groups in the polypeptide chain.
 Proteins have both polar and non-polar side chains.
 In an aqueous environment (water being polar), proteins will fold up so that the nonpolar side chains face inside and polar side chains face outward toward the water.
 While the conformation of each protein is unique, there are two regular patterns among
proteins, in terms of secondary structure: -helices and  -sheets.
 -helices occur when a single polypeptide chain coils up around itself in a regular
pattern producing a helix (like DNA).
 Each peptide bond in an -helix is hydrogen-bonded to another nearby peptide bond.
(The amide hydrogen atom in one peptide bond and the carbonyl oxygen atom in
another peptide bond).
 In aqueous environments, an isolated -helix is usually not stable on its own. Two
identical -helices (with a repeating arrangement of non-polar side chains) will twist
around each other to form a stable structure (a coiled-coil), which is held together by
disulfide bonds (S – S bonds).

-sheets (also called Beta-pleated sheets) are formed when an extended polypeptide
chain folds back and forth upon itself. The sheet is stabilized by hydrogen bonds
between the chains. There are no disulfide bonds (S – S bonds) between adjacent
chains – only hydrogen bonds holding it together.


These two types of secondary structures and (-helices and -sheets) are often
formed because they permit extensive hydrogen-bonding between the backbone
atoms, which stabilizes the structure.
Other parts of the structure are not highly stable and so adopt a random coil
formation, also part of the 2 structure.
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 As we just discussed, there are two main types of secondary structure:
 alpha helices ( helices) – delicate coils held together by H-bonds every 4th amino
acid

beta pleated sheets ( pleated sheets) – two regions of a polypeptide chain lie
parallel to each other & H-bonds between O or N
and H in the parallel chains hold them together
 In many proteins, parts of the polypeptide form secondary structures & other parts do not.
 In fact, in some proteins, 2 structures do not form at all. Whereas, in a few proteins,
almost all of the polypeptide forms 2 structures.
 Almost all of myosin molecules is -helix and almost all of fibroin (silk protein) is
-pleated sheet.
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Figure showing 2 and 3
structure of a protein.
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 Tertiary structure is the three dimensional conformation (shape) of a polypeptide.
 Tertiary structure is formed as the polypeptide folds up after being produced by
translation. Folding is caused by interactions of the amino acid R groups.
 Amino acids with non-polar side chains tend to aggregate in the middle of the
protein, away from water (since non-polar side chains are hydrophobic).
 Amino acids with polar (hydrophilic) side chains tend to be found on the outside of
the protein, where they may interact with water.
 Tertiary structure is stabilized by the intramolecular bonds formed between amino acids
in the polypeptide, especially between their R groups (as mentioned above).
 These bonds form between amino acids widely separated in the protein’s primary
structure, but which are brought together during the folding process.
 Types of intramolecular bonds include: ionic bonds (between + and – charged side
chains), hydrogen bonds, hydrophobic interactions, and disulfide bridges.
 Disulfide bridges are formed when two cysteine amino acids (which have sulfhydryl
groups in their side chains) form a covalent S-S bond.
disulfide bridges in bovine Ribonuclease A
 Bonds between ions serving as cofactors (non-protein molecules or ions required for the
proper functioning of an enzyme) and the side chains of certain amino acids may also be
responsible for folds in the polypeptide.
 See hemoglobin below as one such example.
 Globular proteins, which have a globular (folded) shape, illustrate 3 structure in
proteins
 Examples of globular proteins include the globin polypeptides in hemoglobin (four of
them, shown below), enzymes & microtubules ( = structural globular proteins).
the digestive
enzyme pepsin
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 Quaternary structure is the linking together of two or more polypeptides to form a single
functional protein.
 Large globular proteins (such as the overall hemoglobin molecule shown above) are often
made of several polypeptide chains and illustrate quaternary structure.
 The different polypeptide chains are held together by hydrogen bonds, ionic bonds,
van der Waal’s forces (between non-polar side chains), and disulfide bridges (or any
combination of these. Cofactors may also play a role in quaternary structure.
 Hemoglobin consists of 4 polypeptide subunits bound together, insulin consists of 2
polypeptides, and collagen consists of 3 polypeptides.
hemoglobin, composed of 4 myoglobin
polypeptides
 Together with the greater variety of amino acids, quaternary structure causes a great
range of biological activity.
 Quaternary structure may involve the binding of a prosthetic group to form a conjugated
protein.
 Conjugated proteins are proteins which contain chemical groups besides amino
acids. These chemical groups are called prosthetic groups.
 Prosthetic groups are the non-protein part of a conjugated protein. Metal ions and a
variety of organic molecules (e.g., vitamins, sugars, lipids) can serve as prosthetic
groups. Prosthetic groups are usually bound covalently to their proteins.
 Examples of conjugated proteins include hemoglobin (each of the four polypeptide
subunits is bound to a prosthetic heme group, containing iron), lipoproteins (whose
prosthetic groups are lipids), and glycoproteins (whose prosthetic groups are
carbohydrates).
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Protein Function (Per 1,3 Wed Jan 6)
 Proteins have many different functions in the body, from providing structure, to enzymes, to
energy sources. We will consider several of them here.
(1) Enzymes: All enzymes are globular proteins which catalyze biochemical reactions
 Amylase is an enzyme which catalyzes the breakup of starch into maltose and glucose.
 Catalase catalyzes the conversion of hydrogen peroxide (a toxic waste product of
metabolism) into water and oxygen.
(2) Hormones: Hormones are one type chemical signal which circulate in body fluids which
coordinate various parts and activities of an organism.
 Some hormones are proteins, while others are steroids.
 An example of a protein hormone is insulin, which helps vertebrate cells remove glucose
from the blood, regulating the concentration of blood sugar.
(3) Defense: Immunoglobulins are globular proteins which act as antibodies, binding antigens,
thus protecting an organism against foreign particles (viruses and bacteria).
 Part of the immunoglobulins molecule can vary, so that an almost endless variety of
different antibodies can be produced.
 Below is a diagram of an antibody, illustrating the quaternary structure of the protein
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(4) Structural Proteins: Structural proteins provide structure and support to the cell.
 Collagen is fibrous, structural protein which strengthens connective tissue in our skin,
bones, ligaments, tendons and other body parts.
 These tissues all produce tough collagen fibres in the spaces between their cells.
 Collagen accounts for 40% of the protein in the human body.
 Hair and nails consist almost entirely of polypeptides coiled into -helices.
(5) Transport: Some proteins transport other substances through the body.
 Hemoglobin is a protein which easily binds to oxygen due to the heme group in each of
its four subunits.
 The iron atom at the center of the heme group actually binds the oxygen.
(6) Movement: Some proteins facilitate movement in organisms.
 Myosin is a fibrous protein whose function (together with another protein called actin) is
to cause contraction in muscle fibers. This can result in movement in animals.
(7) Proteins form part of the cell membrane where they have several roles.
 The most common role is facilitating transport across the membrane.
 Cell membrane proteins may also play a role:
 as enzymes, catalyzing a biochemical reaction
 in signal transduction, having a shape that fits a chemical messenger (e.g. a hormone)
 in joining adjacent cells together
 cell-cell recognition (certain glycoproteins)
 attachment to the cytoskeleton (inside the cell), and to the extracellular matrix
A glycoprotein cell receptor
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Protein Analysis
 The primary structure of proteins (their amino acid sequence) can be determined either by
paper chromatography or by electrophoresis.
 In both cases, the peptide bonds in the protein must first be hydrolysed by hydrochloric
acid (HCl) to successively release the amino acids.
 The 3-dimensional structure of the complete protein can be confirmed by X-ray
crystallography.
 Chromatography
 To analyse proteins via paper chromatography, the peptide bonds holding amino acids
together must first be hydrolysed by HCl to separate individual amino acids.
 (This is similar to the paper chromatography you did in Chem 1, using ink pens, to
separate out the different colored pigments/dyes in black inks)
 The hydrolysed mixture of amino acids is applied to the baseline (origin) near the bottom
of the piece of chromatography paper and allowed to dry.
 Separate spots of known amino acids can be placed alongside to serve as references.
 Then the paper is placed in a solution containing a mixture of two or more solvents
(eluents), which begin to flow slowly up the paper by capillary action (recall that the
baseline must remain above the level of the solvent at the beginning of the experiment)
 A typical example of the two solvent mixture might be water and an alcohol.
 The solvents are selected so that one solvent is held more strongly than the other by
the paper, and forms a stationary solvent layer adsorbed on its surface.
 The other solvent is held less strongly and moves more freely up the paper.
 The different amino acids in the sample move up the chromatography paper at different
rates, according to their relative solubilities in the two solvents.
 The movement of amino acids that are most soluble in the strongly adsorbed solvent
is retarded, because they spend more time in the “stationary” layer.
 The amino acids that are more soluble in the other solvent move farther up the paper.
 After several hours (when the eluent has nearly reached the top of the paper), the sheet is
removed from the tank, dried, and stained with an organic dye (ninhydrin) to develop the
chromatogram by coloring the acids. This allows the amino acids to be located.
 The amino acid sequence can be determined by visual comparison to the amino acids
run alongside as reference markers.
 If samples of known amino acids are not available to use as reference markers, the Rf
value (retention factor value) can be measured and compared with a chart of known
Rf values of amino acids, since each amino acid has a different Rf value.
 It is possible that two amino acids will have the same Rf value in a particular solvent,
but different values in a different solvent. If this is the case, the chromatogram can
be turned 90 and run again using a second solvent.
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chromatography
paper
sample at
origin
Two-dimensional paper chromatography of normal (Hemoglobin A) and mutant (sickle cell,
Hemoglobin S) hemonglobins. The encircled in red spot represents the position of the peptide.
Stryer, Biochemistry, 1995
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Above: E. coli proteins analyzed
by SDS polyacrylamide
gel electrophoresis
Right: SDS-PAGE analysis of
Staphylococcus aureus
proteins
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 Electrophoresis
 Electrophoresis is a method of separating similarly sized molecules on the basis of their
charge.
 Proteins usually have a net positive or negative charge depending on the mixture of
charged amino acids they contain.
 If an electric field is applied to a solution containing a protein, the protein will
migrate at a rate that depends on its net charge, size, and shape.
 In two-dimensional gel electrophoresis, proteins are first separated on the basis of their
intrinsic charge.
 The sample is dissolved in a small volume of a nonionic (uncharged) detergent,
mercaptoethanol, and a denaturing urea agent. This solution solubilizes, denatures
(unfolds), and dissociates (separates) all the polypeptide chains, but does not change
their intrinsic charge.
 The polypeptide chains are then separated by isoelectric focusing, which depends on the
fact that the net charge on a protein varies with the pH of the surrounding solution.
 Amino acid structure changes at different pH values: at low pH, the amine group
will be protonated (gain a proton); at high pH, the carboxylic acid will lose a proton.
 For any protein, there is a unique pH value, called its isoelectric point, at which the
amino acid exists as a zwitterion.
+
NH2
CHCOOH
X
neutral molecule
NH3
CHCOO
X
zwitterion (dipolar ion)
As a zwitterion, the amino acid has no net charge and therefore will not migrate in an
electric field.
 The medium on which electrophoresis is carried out is usually a polyacrylamide gel.
Thus the process is known as PAGE (polyacrylamide gel electrophoresis).
 The sample of amino acids is placed in the middle of the gel, and a potential
electrical difference is applied across it.
 Using a mixture of special buffers, a stable pH gradient is established in the gel,
running from basic to acidic.
 In isoelectric focusing, depending on the pH of the buffer, the different amino acids
will move at different rates toward the positive and negative electrodes. The proteins
will move to a point in the pH gradient that corresponds to its isoelectric point (where
its charges are balanced) and stay there.
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 In the second step, the gel is turned 90 (at a right angle to the direction of the first step),
and the proteins are again electrophoresed.
 A detergent called SDS is added, and this time, the proteins are separated according
to their size – smaller molecules moving farther.
 When separation is complete, the acids can be sprayed with ninhydrin and identified by
comparing the distance they have traveled with standard samples, or from a comparison
of their isoelectric points.
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III. Carbohydrates
 The term carbohydrates includes both sugars and polymers of sugars.
 Carbohydrates can be classified as monosaccharides, disaccharides, and polysaccharides
1) monosaccharides – (aka simple sugars) are the simplest carbohydrates, having the basic
formula CH2O
 examples: glucose (C6H12O6), fructose (C6H12O6), and ribose (C5H10O5)
 Monosaccharides have between 3 and 6 carbons.
 Monosaccharides with the general formula C5H10O5 are called pentoses.
Monosaccharides with the general formula C6H12O6 are called hexoses.
 Straight chain monosaccharides have a carbonyl group (C = O), and at least two hydroxyl
groups (–OH). However, many structural isomers of monosaccharides are possible.
 Several carbon atoms are chiral, thus optical isomers are possible.
 Monosaccharides (and sugars, in general) also often occur in ring structures. As ring
structures, the carbonyl group (C = O) becomes an ether (C – O – C). See below.
 Monosaccharides have only one ring structure.
 D-glucose is the natural form of glucose. D-glucose can exist as a straight chain (with
ketone), or as a ring structure.
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
The ring structure of D-glucose can exist in 2 separate crystalline forms,  and .
(-D-glucose and -D-glucose). The only difference between them is the position of
the –OH group on the first carbon. These differences are diagrammed below:

Let's explain the terms alpha and beta. Notice the alpha and beta forms of glucose in
the diagram.
The  – form has the -OH on carbon #1 pointed down
the  – form has the -OH on carbon #1 pointed up.
Remember that in the real world, this is a 3-dimensional molecule and so it will make
a difference which way the -OH group points.



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 ribose – a 5-carbon sugar which forms part of the backbone of DNA
 monosaccharide functions: monosaccharides provide energy to cells
 Glucose is a major energy provider to cells.
 Cells burn energy (stored in glucose) during cellular respiration.
 Glucose is produced during photosynthesis in plants, then stored for later use in
respiration. Humans can obtain this glucose when they consume plants (or anything
else containing sugars).
 Glucose can be used immediately by the body for energy or stored in muscles in the
form of glycogen (a polysaccharide).
 Glucose is carried by the blood to transport energy to cells throughout the body.
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2) disaccharides – form an ester linkage between two monosaccharides, via a dehydration
reaction
 examples: sucrose (C12H22O11) formed by the condensation of glucose and fructose;
maltose (C12H22O11) formed by the condensation of glucose and glucose;
lactose (C12H22O11) formed by the condensation of glucose and galactose
 Thus, disaccharides have two ring structures.


The diagram below illustrates the formation of sucrose from glucose and fructose.
Specifically, sucrose is formed by a condensation reaction between -D-glucose and
-D-fructose.
Note the dehydration that has taken place for the bond to form:


The diagram below illustrates the formation of maltose from two glucose molecules.
Note the dehydration that has taken place for the bond to form:
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

The diagram below illustrates the formation of lactose from glucose and galactose.
Specifically, lactose is formed by a dehydration reaction between -D-galactose and
-D-glucose.
Note the dehydration that has taken place for the bond to form:
lactose
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
a second diagram of maltose:

lactose:

sucrose, again:
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3) polysaccharides – form ester linkages between several monosaccharides
 Polysaccharides have more than two ring structures.
 There are three major classes of polysaccharides with which you need be familiar:
starch, glycogen, and cellulose.
1. Starches are polysaccharides consisting entirely of glucose molecules connected by
-1,4 linkages between glucose molecules. (note the alpha linkages in the diagram
below – formed by condensation rxns!) Starch is the principal food reserve in plants
and the main source of carbohydrates in the human diet. There are two different
types of starch: amylose (-amylose) and amylopectin.







-amylose starch constitutes about 20-25 per cent of ordinary starch.
Amylose is a linear polymer of several thousand glucose residues (C6H10O5 after
the condensation process joining them together) linked by (14) bonds.
The glucoses are arranged in a continuous but curled chain somewhat like a coil
of rope. Hydrogen bonding between the oxygen atoms of sequential glucose
residues tends to encourage this helical conformation. These helical structures
are relatively stiff and may present contiguous hydrophobic surfaces.
The interior of the amylose helix is non-polar allowing them to trap oils and fats
inside the helix.
Amylose molecules consist of single mostly-unbranched chains with 500-20,000
(14) D-glucose units (depending on source).
A very few (16) branches and linked phosphate groups may be found, but
these have little influence on the molecule's relative non-polarity.
Before these starches can enter (or leave) cells, they must be digested
(hydrolyzed) by amylases. Amylases, allow water molecules to enter at the -1,4
linkages, breaking the chain and producing a mixture of glucose and maltose.
(amylose starch polysaccharide – note -1,4 linkages)

In the second kind of starch, amylopectin, considerable side-branching of the
molecule occurs. Amylopectin consists mainly of (14)-linked glucose units
but additionally contains (16)-branch points every 24 to 30 glucose
molecules on average, yielding a polysaccharide with a highly branched
structure. This non-random branching is determined by branching enzymes that
leave each chain with up to 30 glucose residues.
30

Each amylopectin molecule contains a million or so residues (up to about 2
million), about 5% of which form the branch points. Amylopectin, in contrast
with amylose, is water soluble.
A look at amylopectin structure on three levels (close up, then zooming out…):
Amylopectin is a branched polymer held together by both the linear
1,4'-a-glycoside bonds and the branched 1,6'-a-glycoside bonds.
These branches occur approximately every 35 glucose units.
Amylose Content of Various Starches
Starch Source
Waxy Rice
% Amylose
0
31
Corn
Wheat
Sweet Potato
Potato
28
26
18
20
2. Cellulose is formed by -1,4 linkages between glucose molecules.
 So, the main structural difference between starch and cellulose is the  vs. 
linkages:
 the -linkages make starch a flexible energy storage material
 the -linkages make cellulose a stiff, structural material

Function: Cellulose is found in cell walls (found only in plants, fungi, green algae,
dinoflagellates, and bacteria), where it plays a structural role.
 Here’s one more set of diagrams to help illustrate the difference in linkages:
32
3. The storage polysaccharide of animals, glycogen has a structure very similar to
amylopectin, but glycogen is more highly branched than amylopectin, with branch
points every 8 to 12 glucose residues.
 The body does not immediately use all the glucose absorbed from digestion of
starch, but converts most of it to glycogen, much of which is stored in the liver.
 Glycogen is present in all cells but most prevalent in skeletal muscle & liver cells.
 As the body requires glucose, hydrolysis of glycogen releases it into the
bloodstream.
 Glycogen provides an energy reserve for animals just as ordinary starch does for
plants.
 Glycogen is only a minor component of the human nutrition since the major
compounds for long-term energy storage in animals are the triglycerides of fat.
 Glycogen is different from both starch and cellulose in that the Glucose chain is
branched or "forked". See the diagram below for a comparison of the structures:
 mono-, di-, and polysaccharides are illustrated below together for comparison:
33
Recap: Major Functions of Polysaccharides in the Body
 Carbohydrates are used by humans:
 To provide energy
 Foods such as bread, biscuits, cakes, potatoes, and cereals are all high in
carbohydrates.
 To store energy (energy reserves)
 Starch is stored in the livers of animals in the form of glycogen (animal starch).
 Glycogen has almost the same chemical structure as amylopectin.
 As precursors for other biologically important molecules
 For example, carbohydrates are components of nucleic acids and thus play an
important role in the biosynthesis of proteins.
 Although humans cannot digest cellulose, it plays an important role in the structure
of plants. A high fiber diet (roughage) has been shown to prevent bowel cancer.
34
IV. Fats
Composition of Fats & Oils
 fats and oils are both made up of a molecule of glycerol and three fatty acid molecules
 glycerol – also called propan-1,2,3-triol
 fatty acids – consist of a long hydrocarbon chain with a carboxyl group at one end
35
 Fats and oils can be formed by clipping off the H from all the alcohol groups on the glycerol,
and the -OH groups from three fatty acids, to form a triester (also called a triglyceride).
 As the fatty acids are formed, the H and the OH (which were just clipped off) combine to
form a water molecule as a byproduct (three water molecules for every triester formed).
 So the term “dehydration” or “condensation” reaction is often applied to this process
Saturated vs. Unsaturated Fats
 There are two types of fats, both of which are illustrated below:
 Saturated fats, which contain only single bonds (most animal fats are saturated).
 Unsaturated fats, which contain at least one double bond (most fish & plant fats).
(A monounsaturated fat contains only one double bond; a polyunsaturated fat contains
two or more double bonds.)
 Here is a second illustration of a fat (triglyceride), containing both saturated and
unsaturated fatty acids:
36

These fats and oils are also often known as triglycerides, since (by definition)
glycerides are the esters formed by glycerol and one or more fatty acids.
 The essential chemical difference between fats and oils is in the fatty acid groups:
 Fats contain saturated fatty acids.
 Oils contain at least one double bond in their fatty acids and are thus unsaturated.
 Most oils contain several double bond and are thus said to be polyunsaturated.
 Fats are solid triglycerides at room T
 ex: butter, lard, tallow
 Oils are liquid triglycerides at room T
 ex: castor oil, olive oil, linseed oil
 Generally, polyunsaturated oils are thought to be better for health than fats, as they reduce the
risk of heart disease.
 A diet high in saturated fats can produce high levels of cholesterol in the body which can
lead to the blocking of arteries.
 The melting point of fats and oils (generally speaking) is directly related to the degree of
saturation in their fatty acid tails.
 The more unsaturated the fatty acid (the more double bonds it has), the lower its melting
point.
 The regular tetrahedral arrangement of saturated fatty acids means that they can pack
together closely. Thus, the van der Waal’s forces holding fatty acid molecules
together are stronger, since the surface area between them is greater.
 Saturated carbons in the fatty acids have 109.5 bond angles. The double bonds in
unsaturated fatty acids have 120 bond angles. As the bonds change from 109.5 to
120 at the double bonds in unsaturated fatty acids, it produces a kink in the chain.
The fatty acids are unable to pack as closely together, so the van der Waal’s
forces between molecules become weaker, which results in lower melting points.
 Compare stearic acid and linoleic acid, which make up the triglycerides on the
previous page. Both contain the same number of carbon atoms, and have very
37

similar molecular masses. However, stearic acid has a melting point of 69.6C, while
linoleic acid melts at –5C, since linoleic acid contains two double bonds.
This packing arrangement is similar in the fatty acid tails of fats and helps explain
why unsaturated fats (oils) have lower melting points.
saturated fatty acids
lauric acid
myristic acid
palmitic acid
stearic acid
unsaturated fatty acids
oleic acid
linoleic acid
# of C atoms
# of C=C bonds
melting point (C)
12
14
16
18
0
0
0
0
44.2
54.1
62.7
69.6
18
18
1
2
10.5
-5.0
Determining the Number C=C Bonds in an Unsaturated Fat
 Unsaturated fats can undergo addition reactions.
 Certain reactants (H2, I2, etc.) will react at the double bond, adding to it, resulting in two
saturated carbons.
 Margarine is made by the hydrogenation of vegetable oils, so that it is a solid at room T.
 This process is similar to the hydrogenation of 1-pentene shown below:
CH3CH2CH2CH=CH2 + H2
Ni
CH3CH2CH2CH2CH3 (CH3CH2CH2CH-CH2)
H
 Iodine can also add to a double bond, similar to the way hydrogen adds to double bonds.
H
38
 The addition of iodine to unsaturated fats can be used to determine the number of C=C
double bonds since one mole of iodine will react quantitatively with one mole of double
bonds. (i.e. – The number of double bonds broken is exactly equal to the number of
iodine molecules used up. Thus, the number C=C double bonds can be determined from
moles of I2 which add to one mole of fat.)
 Iodine in coloured. As the iodine is added to the unsaturated fat, the purple colour of
the iodine will disappear as the addition reaction takes place.
 Often fats are described by their iodine number, which is the number of grams of
iodine that add to 100g of fat (or # of moles of iodine that add per mole of fat).
Hydrolysis of Fats to Form Soap
 Saponification is the process of making soap.
 The process of saponification is one of the oldest chemical processes known, dating back
over two thousand years. Its purpose has been to make soap for cleaning.
 Fats and oils are the starting points for making soaps in saponification.
 Fats and oils can be saponified using an aqueous base solution:
O
CH2OC(CH2)7CH=CH(CH2)7CH3
O
CHOC(CH2)7CH=CH(CH2)7CH3 + 3 NaOH
O
CH2OC(CH2)7CH=CH(CH2)7CH3
CH2OH
+
CHOH + 3 CH3(CH2)7CH=CH(CH2)7COO Na
CH2OH
 The sodium and potassium salts of the fatty acids are soaps. If you look at the contents
label on a bar of soap, you probably will see listed sodium tallowate, sodium cocoate, and
even sodium palm kernelate. This means that the mixtures of triglycerides from tallow
(hard fat from animals), coconut oil, and palm kernel oil have been saponified to give the
sodium salts of the fatty acids derived from these fats and oils.
 The cleaning action of soaps is determined by their general structure:
39
 At one end of the molecule we find an ionic portion (-COO-). This ionic portion is
attracted strongly to water molecules, and is called hydrophilic (water-loving).
 The rest of the molecule is composed of a hydrocarbon fragment which does not dissolve
in water and is referred to as hydrophobic (water-hating).
 In aqueous solution these molecules with the large hydrocarbon portion do not dissolve
as individual particles, but form clusters, called micelles. These micelles are composed
of 50 - 150 soap molecules, arranged so that they form a sphere, with the hydrocarbon
portions directed to the interior of the sphere, and the hydrophilic polar end directed
outwards where they can interact with water molecules.
 Diagram of a few soap molecules forming a micelle in water:
Polar (ionic) part of molecule
directed outwards to interact with water.
 Greasy dirt is difficult to wash away with only water, because the dirt does not dissolve
in water. With soap present, the greasy dirt is attracted to the hydrocarbon portion of the
micelles. Thus it is removed from the material being washed, and is taken into the
interior of the soap micelles. The micelles remain dispersed in water, and carry away the
dirt with them.
 Soaps are much less effective at washing in hard water, which contains magnesium
(Mg2+) and calcium (Ca2+) ions. These positive ions react with the anionic portion of the
soap to form a precipitate. (They form insoluble calcium or magnesium salts of the fatty
acids.) This precipitate appears as a deposit on clothes, scum on the water, or a ring
around the bathtub.
 Detergents are synthetic molecules (such as alkyl benzene sulfonates) which have
polar and non-polar portions, like soaps, but are not deposited by calcium or
magnesium ions. Their calcium and magnesium salts are water soluble.
40

Soaps, however, do have the advantage that they are readily biodegradable, whereas
synthetic detergents (particularly those containing branched alkyl chains) cause more
pollution.
Major Functions of Fats
 We should consider three major functions of fats in the body:
(1) energy sources; (2) insulation; (3) cell membranes
(1) Energy sources - fats or oils major function is to store energy
Advantages of Carbohydrates
Advantages of Lipids
1. Carbohydrates are more easily digested
than lipids, so the energy stored by carbohydrates can be released more rapidly.
1. Fats store about twice as much energy per
gram as the same amount of carbohydrate.
Thus stores of lipid are lighter than stores
of carbohydrate that contain the same
amount of energy.
2. Plants, being sedentary, can store their
energy in the form of starches
2. Animals, being mobile, store much of their
long term energy reserves as fats in
adipose cells which swell and shrink as
fat is deposited and withdrawn from storage.
3. Carbohydrates are soluble in water and so
are easier to transport to and from storage
(remember that blood transports glucose to
blood cells as needed).
3. Lipids are insoluble in water and so do not
cause problems with osmosis in cells.
(2) heat insulation – some animals have a layer of fat under the skin (adipose, or fatty tissue) to
provide thermal insulation and protection to parts of the body
41
(3) cell membranes – fats form part of the cell membrane as well (think phospholipids)
V.
Vitamins
 Vitamins are organic molecules required in the diet in amounts that are quite small compared
with the relatively large quantities of essential amino acids and fatty acids animals need.
 Tiny amounts of vitamins may suffice, from about 0.01 to 100 mg per day, depending on
the vitamin.
 So far, 13 vitamins essential to humans have been identified.
 Apart from vitamin D, the body cannot synthesize its own vitamins, and cannot
function correctly without them. Thus, the body must obtain these vitamins from
food.
 Vitamin deficiencies can cause severe problems and diseases.
Fat Soluble vs. Water Soluble Vitamins
 Vitamins can be classified as fat soluble or water soluble.
 The structure of fat soluble vitamins is characterized by long non-polar hydrocarbon
chains or rings.
 Fat soluble vitamins include vitamins A, D, E, F and K.
 They can accumulate in the fatty tissues of the body.
 In some cases, an excess of fat soluble vitamins can be as serious as a deficiency.
42
 The molecules of water soluble vitamins, such as vitamin C and the eight B-group
vitamins, contain hydrogen attached directly to highly electronegative oxygen or nitrogen
atoms that can hydrogen bond with water molecules.
 They do not accumulate in the body so a regular intake is required.
43
vitamin C
 Prolonged cooking destroys most vitamins.
 Most vitamins are unstable at higher temperatures, and so will be affected by prolonged
cooking.
 When boiling vegetables, it is better to use small amounts of water and use the stock in
gravy or soups to avoid loss of water soluble vitamins.
 Vitamins containing C=C double bonds and –OH groups are readily oxidized and
keeping food refrigerated slows down this process.
Vitamin Structures
 Vitamin A (retinol)
 Vitamin A is found in cod liver oil, green vegetables, carrots and fruit.
44

Carrots also indirectly provide a good source, as they contain -carotene, which the
body converts to vitamin A.
 Although it does contain one –OH group, vitamin A is fat soluble, due to the long, nonpolar hydrocarbon chain.
 Unlike most other vitamins, vitamin A is not readily broken down by cooking.
 Vitamin A is an aid to night vision.
 In the body, vitamin A (retinol) is oxidized to retinal.



Retinal combines with the protein opsin to form rhodopsin. Rhodopsin is a lightsensitive material in the rods of the retina. Rhodopsin helps convert light signals into
electrical signals that can travel along the optic nerve to the brain.
A deficiency in vitamin A leads to night blindness.
A serious deficiency can lead to xeropthalmia, a chronic form of conjunctivitis,
which is the commonest form of blindness in the Third World.
 Vitamin D (calciferol)
 Vitamin D is also fat soluble.
 It is found in fish liver oils and in egg yolk.
45

It can be formed on the surface of the skin through the action of ultraviolet light in
sunlight on 7-dehydrocholesterol.
ultraviolet light
Vitamin D is involved in the uptake of
calcium and phosphate ions from the blood
into the body and especially in the formation
of bone structure.
 A deficiency of vitamin D leads to bone softening and malformation – a condition known
as rickets.
 Vitamin D can be destroyed through oxidation by some of the bleaching agents used in
the manufacture of purified flour.
7-Dehydrocholesterol
Vitamin D
46
 Vitamin C (ascorbic acid)
 Vitamin C is found in fresh fruit and vegetables.
 Due to the large number of polar –OH groups, it is soluble in water, and therefore is not
retained for long by the body.
vitamin C
collagen
 Vitamin C is broken down by cooking, so raw vegetables provide a better source than
boiled vegetables.
 The various roles played by vitamin C are not fully understood.
 Claims that it is effective in preventing both the common cold and cancer appear to
be unfounded.
 It does aid the healing of wounds and helps to prevent bacterial infections.
 It is involved in the biosynthesis of the protein collagen, found in connective tissue,
such as cartilage, ligaments, and tendons.
 The most famous disease associated with a lack of vitamin C is scorbutus (‘scurvy’).
 The symptoms are swollen legs, rotten gums, and bloody lesions.
 It was a common disease in sailors, who spent long periods without fresh food, until
the cause was recognized.
 Vitamin C is easily oxidized. It can help to preserve food by being more readily oxidized
than the food it is preserving.
47
VI. Hormones
 Hormones are chemicals produced in glands and transported to the site of action by the blood
stream.
 These glands are controlled by the pituitary gland, which is itself regulated by the
hypothalamus.
 Hormones act as chemical messengers and perform a variety of different functions.
 Examples of specific hormones include adrenaline, thyroxine, insulin, and the sex hormones.
(1) Adrenaline
 Adrenaline (epinephrine) is produced in the adrenal glands – 2 small organs located above
the kidneys.
 It is a stimulant closely related to the amphetamine drugs.
 Adrenaline is released in times of excitement, initiating several physiological responses:
 a rapid dilation of the pupils and airways
 an increase in the heartbeat and rate of release of sugar into the bloodstream
 Adrenaline is sometimes known as the ‘fight or flight’ hormone.
adrenaline
amphetamine
3,4-methylenedioxymethamphetamine
(MDMA or Ecstasy)
48
(2) Thyroxine
 Thyroxine is produced in the thyroid gland located in the neck.
 It is unusual in that it contains iodine.
 A lack of iodine in the diet can cause the thyroid gland to swell to produce the
condition known as goiter.
 Thyroxine regulates the body’s metabolism.
 Low levels of thyroxine cause hypothyroidism, characterized by lethargy as well as
sensitivity to cold and a dry skin.
 An overactive thyroid can cause the opposite effect. This is known as
hyperthyroidism, with symptoms of anxiety, weight loss, intolerance to heat, and
protruding eyes.
49
(3) Insulin
 Insulin is a protein containing 51 amino acid residues.
 It is formed in the pancreas – an organ located in the back of the abdomen – and regulates
blood sugar levels.
 In diabetics, the levels of insulin are low or absent, and glucose is not transferred
sufficiently from the bloodstream to the tissues.
 This is known as hyperglycemia and results in thirst, weight loss, lethargy, coma, and
circulatory problems.
 Long term sufferers of diabetes can suffer blindness, kidney failure, and need limbs
amputated due to poor circulation.
 It is treated by reducing sugar intake and taking daily insulin injections.
 Too much insulin can cause hypoglycemia, where blood sugar level falls, resulting in
dizziness and fainting.

Proinsulin serves as the precursor molecule (major storage form) of insulin within
pancreatic beta-cells. When blood glucose levels are high, proteolytic enzymes split
proinsulin into two molecules: physiologically active insulin (51 amino acids), and an
inactive connecting peptide called C-peptide (31 amino acids).
50
(4) Sex Hormones
 The sex hormones are all steroids.
 Steroids are lipids with carbon skeletons having four fused rings and various functional
groups attached.
 Steroids include cholesterol and other hormones such as the sex hormones
 Cholesterol is the precursor from which all other steroids are made except for retinoic
acid.
 Cholesterol is formed in the liver, and is found in all tissues (as a common
component of animal cell membranes), the blood, brain, and spinal cord.
cholesterol
progesterone
testosterone
Cholesterol in Cell Membrane
(binds to and immobilizes phospholipids; makes
membranes less fluid and stronger)
51
 The male sex hormones are produced in the testes and comprise mainly testosterone and
androsterone.
 These hormones are anabolic – encouraging tissue, muscle, and bone growth – and
also androgenic – conferring the male sexual characteristics.
male sex hormones
 The female sex hormones are structurally very similar with just small changes in the
functional groups attached to the steroid framework.
 They are produced in the ovaries from puberty until menopause.
 The two main female sex hormones are estradiol and progesterone.
 They are responsible for sexual development and for the menstrual and reproductive
cycles in women.
female sex hormones
52
Oral Contraceptives
The Menstrual Cycle
 At the beginning of the menstrual cycle, the pituitary gland releases follicle stimulating
hormone (FSH). FSH travels to the ovaries causing the release of estradiol, which prepares
for the release of the ovum or egg and the buildup of the uterine wall.
 After about two weeks, a feedback system stops the release of FSH and triggers the release of
the luteinizing hormone (LH). This travels to the ovaries and releases progesterone. The
progesterone causes the egg to be transported to the uterus as well as continuing to build up
the uterine wall.
 If the egg is fertilized, it embeds itself into the uterine wall and hormone levels rise
dramatically. Otherwise, hormone levels fall and menstruation begins.
Oral Contraceptives
 The most common ‘pill’ contains a mixture of estradiol and progesterone and mimics
pregnancy by intentionally keeping the hormones at high levels so that no more eggs are
released.
 It is usual to take the pill for 21 days and then a placebo for 7 days so that a mild period
will result, but without the risk that the hormone levels will fall and allow the unexpected
release of an egg.
 Estradiol and progesterone may also be give to post-menopausal women as hormone
replacement therapy (HRT) partly to prevent brittle bone disease (osteoporosis).
Steroid Use and Abuse
 The anabolic steroids have similar structures to testosterone and build up muscle.
 They may be given to someone recuperating form a serious illness to build up muscles
weakened by inactivity.
 Some athletes have abused these drugs as they can enhance athletic performance.
 Competitors are given random urine tests to detect these and other banned
substances.