Download Nutritional biochemistry

Nutritional biochemistry (CHS262)
Definition
It is the science deals with the study of the chemical structure of the
living cells and its biochemical reaction pathways, also it deals with the
study of the chemical and physical nature of nutritive substances, its
biological functions and metabolic pathways.
Amino acid
It is the building unit of protein and enter in the structure of hormones,
porphorines, vitamins, DNA( purines, and pyrimidine).
How to obtain a. a?
1. by analysis of proteins.
2. Chemically synthetics.
Number of a.a in nature: 20 a. a .found in proteins.
Chemical structure of a. a:
They compose carbon atom connected to 4 groups
1. Carboxylic group (-COOH).
2. Amino group (-NH2).
3. Hydrogen group.
4. Side chain (R) differ from a. a to another
H
|
R- C --COOH
│
NH2
Classification ;
According to the polarity of the side chain in water pH7.
1.Non polar and hydrophobic(poorly soluble in water):
e.g. alanine-phenylalanine-leucine-isoleucine-proline-tryptophane-valinemethionine.
Structure of alanine (Ala)
CH3-CH-COOH
│
NH2
2.Non polar and hydrophilic(soluble in water because it has the
ability to form hydrogen bonds with water):
e.g. serine-threonine-cysteine-tyrosine-glycine-asparagine-glutamine
Structure of glycine (gly)
H-CH-COOH
│
NH2
3. Basic a. a. and positive charged-R side chain:
e.g. histidine-argnine-lysine.
Structure of lysine(lys):
CH2-CH2-CH2-CH2-CH-COOH
│
│
NH2
NH2
4. Acidic a. a. and negative charge-R side chain:
e.g. aspartic acid-glutamic acid.
Structure of aspartic acid (Asp):
CH2-CH-COOH
│
COOH
│
NH2
►►►►►►►►►►►►►►►►►►►►►►►►►►►►►
►
Miscellaneous group: rare in protein.
1. Hydroxyl proline found collagen protein.
2. Methyllysine found in myosin (protein of muscle).
:
►►►►►►►►►►►►►►►►►►►►►►►►►►►►►
►
Non proteineous group:
1. Ornthine→ derive from argnine, it is an intermediate product in urea
formation cycle.
2. Creatine→ derives from glycine, converted to phosphocreatine (store
energy inside the body).
3. Hydroxytryptophan→derived from tryptophan and found CNS.
Other classification (nutritionally)
Essential aa;
I.M for the growth and health and cannot synthetics by the body so must
be available in our diet. leucine- isoleucine – histidine –lysine -threoninemethionine – valine -phenylalanine-tryptophan.
Non essential a.a.:
They can be synthesized by the body from carbohydrates, lipids and other
a.a.
They include Glycine Alanine-Serine-Cysteine-tyrosine-Aspartic acid
and Glutamic acid
Peptide;
Amino acids are joined through peptide bonds, where the COOH of an a.a
join to NH2
Of another a.a and form dipeptide ,tripeptide, tetrapeptide, polypeptide
and protein
molecules.
R-CH-COOH +H2N-CH-COOH→R-CH-CO-NH-CH-COOH+H2O
│
│
NH2
R
│
NH2
│
R
Protein:
Definition
Proteins are the most fundamental and the major structural and functional
component of living cells.
Composition: C, H, O and nitrogen (16%).
Amino acids are the structural units or the fundamental chemical building
blocks of proteins. A.a are a family of molecules that are made up of C,
H, O and nitrogen. It is the nitrogen that’s sets proteins apart from other
nutrients and gives protein unique function of building and repairing
tissues.
H
|
NH2 _C _CooH Amino acid
|
R
The R group distinguishes the 20 different a.a from each other.
Protein:
Are very large molecules and sometimes composed of several hundred
amino acids.
Protein differs in:
Number of a.a.
Sequence of a.a.
Shape of protein molecule (globular & fibrous)
The function of protein is related to a.a sequence and shape of the
molecule.
Sickle cell anemia is an example of a protein (hemoglobin) that has one
a.a out of place (due to replacement of glutamic acid by valine).
Classification:
1. On the basis of their function;
a. Enzyme: Is biocatalyst, they
greatly enhance the rate of specific
chemical reaction that would otherwise occur v.slowly.
e.g.lactase-phosphatase-hydrogenase-ribonuclease.
They are up to1500 enzyme
b.Structural protein: are long fibrous molecules
e.g collagen protein(enter in C.T
keratin (enter in formation of nail ,hair, feather &skin.
Elastin (enter in formation of wall of blood vessels).
c. Transport protein: carries materials from 1 part of the body to another
through circulation.
e.g
 Albumin: serves as a transport medium for bilirubin, calcium, fatty
acid and some drugs.
 Hemoglobin: serves as a transport medium for oxygen.
 Lipoprotein; serves as transport medium for fat and found in blood.
d.Hormones: several hormones are protein in nature.
e.g
Insulin secreted from pancrease control the level of sugar and its
deficiency result in diabetes mellitus.
 Growth hormone secreted from pituitary gland and controls
process of growth.
 Parathyroid hormone secreted from parathyroid gland and controls
the level of calcium and phosphorous.
e- Defense protein: are formed in response to the presence of foreign
substance in the body.
f- Storage protein: store nutritive substance.
e.g.
Casein in milk –ova albumin in egg.
g- Contractile protein: protein involved in contraction and relaxation of
skeletal muscles.
e.g
Actin and myosin.
g-Protein for maintains of osmotic pressure and pH:
e.g Albumin.
2-Classification on the basis of structure.
a-simple protein:
they consist of a.a only & not join to any other compound.
They are classified according to their shape into:
 Fibrous protein: has long , extended, sheet like shape , high
mechanical strength, low solubility and digestability e.g collagenelastin-keratin.
 Globular protein:
They are v.soluble –coiled-& easy to be denaturized.
e.g.
albumin in egg &serum.
Globulins in plasma.
Enzymes- prolamin in semen of some fish- histone & protamins in the
nucleus of any cell- casein in milk-gliadin in corn.
b-conjugated proteins:
This protein is conjugated with non proteinous group.
a-Nucleoprotein:
They are formed of simple protein+nucleic acid.
simple proteins (histone &protamine)
They are found also in semen.
b-Phosphoprotein:
They are formed of simple protein conjugated with phosphoric acid
with ester bond.
e.g casein of milk.
c-Glycoprotein:
They are formed of simple protein +carbohydrates.
They are found in saliva.
d-Chromoprotein:
They are formed of protein+coloured substance.
e.g.hemoglobulin and cytochrome.
e-Lipoprotein:
They are formed of protein and lipid.
They are found in serum, brain and nervous system.
f-Metalloprotein:
They are formed of protein + non organic substance e.g.Mg,Ca.
e.g. enzymes.
3-Derived protein:
they are protein in nature but have some difference in its
character.
e.g. proteoses and peptone.
3-Nutritional classification:
a- Complete protein: these proteins contain all the essential a.a in
amount needed by the body as in animal products, meat, milk,
cheese and eggs.
b- Incomplete protein: proteins lacking of 1 or more essential
a.a.Found in plant products
e.g. . Grains, peas, seeds and nuts.
LEVEL OF SERUM PROTEIN IN HEALTHY YOUNG AND
MIDDLE AGE ADULT IS
6-8g/100ml.
In states of dehydration total protein increases to approximates 1015%, the rise being reflected in all protein fractions.
Hypoproteinemia: decreases in total protein level occur in patients
with severe burn, extensive bleeding and open wound.
FOOD SOURCES
Milk , milk product, meat poultry, fish and eggs are good sources
of animal proteins.
Vegetables are poor sources of proteins. Legumes are also a good
source of proteins.
Denaturation of proteins:
Denaturation is a change in chemical structure as a result of
which the function of protein is lost or altered. Factors that can
cause denaturation include heat, change in pH, vigorous
shaking...etc.
Functions of proteins:
1- Growth and replacement: syntheses and replacement of old
tissue is an important function of proteins. It requires
constant supply of essential and non essential a. a.
2- Immunity: protects the body from invasion of bacteria.
Specific shaped protein produced by WBC to inactivate
antigen i.e. a role in developing resistance of the body
against diseases.
3- Fluid balance: Protein helps to maintain level of fluid
between cells and tissues of the body...
4- Sodium and potassium balance: Na+ and K+ ions are very
important for the normal functioning of many cells. Na ions
are concentrated outside the cells (extra cellular) and K ions
are concentrated inside the cells (intracellular). Protein
maintains their concentration outside and inside the cells.
5- Buffer action: Proteins help in maintaining the normal pH of
the blood (7.3-7.4). It is because they are able to combine
with acidosis and alkalosis.
6- Energy value: source of energy (4Kcal/g), but at the expense
other functions of proteins.
Relationship between nitrogen and protein:
The level of protein in substance can be estimated by
measuring the amount of nitrogen present in it.
The conversion factor is 6.25
Amount of nitrogen x6.25= amount of protein
Sources of Nitrogen in the body:
1. Protein nitrogen.
2. Non-protein nitrogen (free amino acid, peptides, urea,
creatinine, creatine, ammonia etc...)
Nitrogen balance: It is a technique for determining the adult
protein needs. The technique measures protein intake (nitrogen
consumed) and nitrogen excreted through feces, skin and
perspiration.
Positive nitrogen balance: When more nitrogen is ingested than
excreted, e.g. in growing children, pregnant women, person
recovering from illness, persons diet changed from low to high
protein. They need to synthesize new tissues to replace the
damage one.
Negative nitrogen balance: When more nitrogen is excreted
than ingested, e.g. person in surgery or accident, suffering from
starvation , immobilized, bed ridden, diet changed from changed
from high to low protein.
Nitrogen equilibrium: amount of nitrogen consumed is equal to
amount of Nitrogen excreted e.g. mostly healthy person (21-40
years old).
Evaluation of protein quality: The quality of proteins are
determined by their amino acid contents, biological value and
protein efficiency ratio (PER).
1. Amino acid content: the number of essential amino acid
present in a protein. A protein that contains all the essential
amino acids in exactly the right amounts is more completely
utilized in the body than the one that contains some of the
essential a. a in too small amounts.
2. Biological
value (BV): it is measures the absorb nitrogen
that is retained for the growth or maintenance and not
excreted through feces, urine, or skin.
Quantity of nitrogen retained by the body x100
BV=………………………………………………………………
Quantity of nitrogen absorbed from the dietary protein
A BV of 70 is minimum for a protein that contributes to the tissue
growth, assuming that an adequate number of calories are also
ingested.
3. Protein efficiency ratio (PER): it measures the growth of rats
in relation to the amount of protein eaten.
Weight gain by the animals
PER=………………………………………………….
Protein intake by the animals
Proteins of high biological value: animal proteins e.g. eggs, milk,
meat, poultry.
Proteins of low biological value: plant proteins.
Digestion of protein:
Digestion of protein begins in the stomach . stomach secretes HCL
that denaturates the protein , unfolding it and making the a.a more
accessible to the action of the enzymes.
Glands in the stomach lining secretes the pro enzyme pepsinogen,
an inactive precursor of the enzyme pepsin.
Pepsin
Protein……………………..polypeptides+peptides ofvarious lengths
HCl
From the stomach, polypeptide and peptides of various lengths
enter the small intestine (i.e duodenum) where most protein
digestion takes place.
Both pancrease and the small intestie make digestive proenzymes.
Pancrease make trypsinogen and chymotrysinogen which are
secreted into small intestine in response to the presence of
protein. These prozymogens are converted to active forms in the
small intestines the active protease break polypeptides into smaller
peptides. Only a small percentage of proteins are completely
digested to individual a.a. most proteins at this point are dipeptide,
tripeptide and still larger polypeptides.
Inside the intestinal cells the final stage of protein digestion take
place.
Here
dipeptides,
tripeptides
and
polypeptides
completely broken to a.a
Absorbtion of proteins. A.a are absorbed by the ileum
and jejunum.
are
Metabolism: cells absorb a.a from the blood to synthesize proteins,
which is controlled by DNA in the nucleus.
Amino acids are catabolized primarily in liver by deamination
reaction.
-Amino group is removed --- the N2 is converted to ammonia then
urea
-The rest of a. a -----oxidized to release energy
Or converted to fat and stored in adipose tissue
Protein energy malnutrition( PEM):
Malnutrition is caused by deficiency of protein, energy or both in
the diet.
PEM is a condition that results from a long term inadequate intake
of energy and protein, that can lead to wasting of body tissue and
increased susceptibility to infection.
Marasmus
A type of PEM that results from the deficiency of both proteins and
calories. It usually occurs in infants (6-18 months of age ) , when
mother breast milk provides insufficient protein and calories due to
mal nutrition in the mother . Marasmus may be characterized by:
1- Marked muscle wasting.
2- Loss of subcutaneous fat.
3- Old man face
4- Growth failure.
5- Loose stool in some children
6- Edema is minimal or absent
7- Hyperammonia (excess of ammonia in the blood).
8- Diarrhea is common
9- Hypophosphatemia (deficiency of phosphate in the blood).
Kwashiorkor
A type of PEM that results from a decrease protein intake. This
results in the older child when the next baby is born. The older
baby is weaned from nutritious breast milk and placed on a
watered – down version of family diet. In areas of poverty, this
diet is often low protein, or the protein is not absorbed easily
It is characterized by:
1- Edema(result from decrease protein synthesis )
2- Growth failure
3- Muscle wasting.
4- Hepatomegaly
5- Change in the hair and skin
6- Hypoalbuminemia (low level of albumen in the blood)
7- Moon face
8- Misery
9- Diarrhea
10-
Susceptibility to common childhood infection
In adult, it occurs in hospitalized patients who are under acute
stress from illness and surgery and be supported with 5%
dextrose solution. Some common symptoms are easily
pluckable hairs edema and delayed wound healing.
Water
Life can be sustained without food for a longer time than without water.
In human the water content varies between 45-65% of the total body
weight, it depends on the age, sex and gross body weight About 55% of
water is localized inside the cells and about 45% is extracellular fluid
(ECF). ECF consists of interstitial fluid, lymph, plasma and transcellular
fluid such as urine, cerebrospinal fluids and fluids found in salivary
glands, liver and pancreas.
Function of water:
1- Major constituent of body fluids (blood, lymph, urine etc…).
2- Universal medium of all chemical reactions in the body.
3- Aids in digestion, absorption, transport and excretion of substances
in human body.
4- It aids in controlling body temperature.
5- Acts as lubricant.
Properties of water
1- Water is a polar molecule
2O H+
│
OH3- Forms hydrogen bonds.
4- It has high boiling point.
5- At 37○C it is very stable
6- Being universal solvent, it is capable of dissolving polar, inorganic
and large organic molecules.
Water balance in healthy adult
Water intake
water loss
Water intake is between 800urine 800-1000
1100ml
Water in food is between 600feces 200ml
900
Metabolic water 200ml
vapour 600-1000ml
…………………………………………………………………………
1600-2200ml
1600-2200ml
Minerals
Mineral are inorganic substances that play important role in a variety of
metabolic reaction as cofactor. They form one of the essential
components of the diet. In animals and humans minerals constitute
approximately4% of the body weight. They are essentially divided into
two major groups.
Macrominerals: Are those that are required in large amounts. They
constitutes about 99.7% of all the essential minerals of the body. It
includes calcium, magnesium, phosphorus, sodium, potassium, chlorine,
sulphur. Ca, P, Mg represents 80% of total mineral content. They are
mainly concentrated in bones.
Microminerals: Are those that are required in very small quantities in
the diet. It constitutes about 0.3% of all the essential minerals of the body.
They include iron, Fluorine, Zinc, Selenium, Manganese, Iodine, Copper,
Molybdenum,Chromium, cobalt.
Functions
1. Provide strength to organic endoskeleton(ca, p, Mg deposit in bones)
2. Principal electrolytes (Na,K,cl) for ionic and osmotic balance and
electrical gradient
3- Provide structure to protein (Sulphur)
4- Function with certain enzymes.
Mineral Antagonist;
Many substances including some essential elements are antagonistic to
each other during absorption from gastrointestinal tract. Example high
iron (leads to iron deficiency).
Fibers, phytic acids some drugs may also reduce mineral absorption.
Vit C, citric acid, lactose, fructose, glucose, histidine, lysine, valine—
faciltates mineral absorption and called as facilitators.
Lack of dietary adequacy of essential elements results in classical disease
conditions.
Anemias (Cu, Fe), Rickets (Ca), Goiter(I).
Carbohydrates
The carbohydrates are a group of organic compound, the
"Carbon hydrates", whose carbons are extensively hydrated.
They are defined as polyhydroxy aldhydes or ketones. Dietary
carbohydrates provide 48% of the caloric need. Carbohydrates
are synthesized by plants and which are the form in which plants
store their own supplies of fuel. The main functions of CHO in
the body are to provide energy.
Each gram gives about 4 Kcal of energy to the body. They are
quick source of energy. Carbohydrates occur in several forms in
the plants. They are classified as:
Monosaccharides (single molecule, like glucose).
Disaccharides (pairs, two glucose units linked together)
Polysaccharides (a chain of monosaccharides ).
Monosaccharides: they are grouped according to the number of
carbon atoms per molecule.
Triose (contain three carbons, such as glyceraldehydes)
Pentose (contain five carbons, such as ribose, ribulose)
Hexose (contain six carbons, such as glucose, fructose).
Nutritionally important CHO are hexoses (glucose, fructose,
galactose), amongst these the most important is D – Glucose.
D - Glucose is common ly referred to as blood glucose or blood
sugar. All the hexose contain six carbon, 12 hydrogen and six
oxygen (C6H12O6 ) . They differ from one another only in the
way in which hydrogen and oxygen atoms are arranged around
the carbon chain. They may exist either in aldose (aldehyde)
form (glucose ) or in ketose (ketone) form (fructose).
Hexoses and other monosaccharides are present both in cyclic
and open chain forms
O
||
C-H
│
H - C- O H
│
HO- C -H
│
H - C -OH
│
H - C -OH
│
H - C -OH
│
H
D-glucose
O
││
C
H
│
C
OH
│
HO
C
H
C
H
│
HO
│
C
OH
│
C
OH
│
H
D-Galactose
C H2
OH
│
C= O
│
Ho
C
H
│
C
OH
│
C
OH
│
C
OH
│
H
D-fructose
Open chain structure
Pyranose
Furanose
----------------------------------------
----------------------
Cyclic structure
Disaccharides: Every disaccharide is composed of two
monosaccharides units, either same or different. They accounts
for 35% of dietary carbohydrates.
Synthesis
C12H22O11+ H2O
2 C6H12O6
Hydrolysis
Nutritionally important disaccharides are lactose, sucrose and
Maltose.
Hydrolysis
Lactose…………………………………………→ Galactose + Glucose
(milk sugar)
lactase enzyme
β(1-4) glycosidic bond
Lactose is a major dietary carbohydrate of infants. It is the only natural
source of galactose
Sucrose: A major dietary CHO, providing about 20-30% of total dietary
calories
Hydrolysis
Sucrose…………………………………………→ Glucose + fructose
(table sugar)
sucrase enzyme
α(1-2) glycosidic bond
Maltose: present in germinating cereals. It is not found naturally to any
great extent in the diet, found as a hydrolysis product of starch.
Hydrolysis
Maltose…………………………………………→ Glucose + Glucose
Maltase enzyme
α(1-4) glycosidic bond
Lactose
Maltose
Sucrose
Polysaccharides: These CHO are much more complex as compared to
mono and disaccharides'. The three homopolysaccharides of glucose
comprise the major dietary CHO are starch, glycogen and cellulose.
All of them are synthesized from glucose.
Starch: It provides largest proportion of dietary calories.
Starch is made from glucose by plants as principal energy store of cereal
grains (wheat) , potato (vegetable) etc.
Starch contain two types of glucose-glucose bonding which are called as
glucosidic linkages. α (1-4) bond forms extended straight chain
molecule, α(1-6) bond provides branching and termination. Starch is
made up of two types of molecules. They are amylose and amylopectin.
Amylose: it is a linear chain polymer of glucose which contains only α(14) bond.
Amylopectin ;it is a branched polymer of glucose which contains both
α(1-4) bond and α(1-6) bonds.
Digestive enzyme specific for α(1-4) bond and α(1-6) linkages are present
in mouth and small intestine. These enzymes rapidly degrade starch
polymer.
α –amylase enzyme produced by salivary glands and pancreas randomly
hydrolyzes the α (1-4) linkages of the polysaccharide. it cannot,
hydrolyzes α(1-6) bonds. After this hydrolysis the remaining glucose
polymer skeleton is called as limit dextrin. A debranching enzyme amylo1,6-glucosidase hydrolyzes the α(1-6) linkages.
Glycogen: Also called as animal starch. It is the energy stored
polysaccharide in animals and human. Glycogen is structurally very
similar to starch, containing both α (1-4) bond and α(1-6) bonds linking
glucose units .Glycogen is highly branched molecule, containing higher
amount of α(1-6)bond as compared to starch. The larger amount of
branching provides rapid hydrolysis of glycogen to provide energy for
muscular work.
Most of the glycogen is stored in the muscles then in the liver ( a total of
about 360g).A very small amount is present in brain. Glycogens maintain
blood glucose level and supply energy for muscular work. After a big
meal of carbohydrate the store of glycogen in animal body increases. On
the other hands, after a hard spells of muscular work, the stored supplies
of glycogen may become almost exhausted.
Cellulose : Structural polysaccharide of plants. It contain repeated units
of glucose which are linked together by β(1-4) glycosidic bonds. It is
entirely a straight chain glucose polymer. Equal quantities of starch and
cellulose have same caloric value. But calories with cellulose are not
available to humans, because they do not posses β(1-4) glycosidase (β
amylase)and consequently glucose cannot be released from it . Rumens
(cattle, sheep) derive calories from cellulose because of the presence β1-4
glycosidase enzyme produce by microflora of the rumen.
Dietary fibers : Cellulose, hemicelluloses and pectins which are
component of the skins of fruits, coverings of seeds and structure part of
edible plants are usually reffered to as"fibers '. the human body does not
have the enzymes capable of breaking these substances and so fibers are
not digested in the body .
Dietary fibers have no nutritional importance but they are physiologically
very important .
1-the water holding capacity of fibers is very high.
2-They help in elimination of intestinal waste.
3- they stimulate the peristaltic (rhythmic) movements of the
gastrointestinal tract by adding bulk to the intestinal contents.
4-They reduce constipation(low incidence of colon cancer
6- They reduced blood cholesterol level.
Lactose intolerance
Many healthy person, both children and adult have the inability to
digest lactose, the sugar found in milk . The defect,either inherited or
acquired, results from a deficiency of enzyme lactase, which is necessary
to convert lactose into glucose and galactose for its absorption
The undigested lactose in the intestinal tract produce gastrointestinal tract
disturbance (abdominal pain , diarrhea , crams , gas formation ).
Milk to which the enzyme lactase is added and fermented dairy products(
yogurt, cottage cheese, in which lactose has been changed to lactic acid
by the action of microorganisms) may be used by lactose intolerant
person without adverse.
Bifidus factor :
Lactose accunts for about 25% of the total dietry CHO. The amount of
lactose in human and cow milk is about 6.8 and 4.8 per 100 ml
respectively. Due to the high amount of lactose in mothers milk, not all of
it can be digested. A part of it is left and fermented in the small intestine
to lactic acid . lactic acid increase the acidity in the lower intestinal tract.
This promote the growth of microorganism, lactobacillus bifidus is
believed to be very beneficial to young infants in preventing the growth
of other undesirable bacteria that causes intestinal disturbances . thus
bifidus factor is found primarily in the intestines of breast fed infants.
.
Amylose
Amylopectin
Cellulose