Download Chapter 13: Carbohydrates

Biochemistry
 Biochemistry is the study of the chemistry of living
organisms
 Much of biochemistry deals with the large, complex
molecules necessary for life as we know it
 However, most of these complex molecules are actually
made of smaller, simpler units – they are biopolymers
 There are four main classes of biopolymers – lipids,
proteins, carbohydrates, and nucleic acids
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Tro: Chemistry: A Molecular Approach, 2/e
Lipids
 Lipids are a family of compounds that are generally
insoluble in water (ie. Non-polar).
 Classes of Lipids:
 Waxes = fatty acid and long chain alcohol (ester)
 Fats & Oils = glycerol + three fatty acids
 Phospholipids = glycerol + 2 fatty acids + phosphate + an
amino alcohol
 Sphingolipids = fatty acid + sphingosine + phosphate + an
amino alcohol
 Glycolipids = fatty acid + glycerol or sphingosine + one
monosaccharide.
 Steroids = a fused ring structure of three cyclohexanes and
one cyclopentane.
Fatty Acids
 Long chain carboxylic acids.
 12 – 18 Carbon’s are the most common.
 Stearic acid is most often found in animal fat.
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2COOH
And it can also be represented like this:
O
C
OH
Fatty Acids
 Can be saturated – all C-C single bonds.
 Can be mono-unsaturated – one C-C double bond.
 Ex) Oleic Acid found in olives and corn.
 CH3(CH2)7CH=CH(CH2)7COOH
 Can be poly-unsaturated – more than one C-C double
bond.
 Ex) Linoleic Acid found in soybeans and sunflowers.
 CH3(CH2)4CH=CHCH2CH=CH(CH2)4COOH
 In the Unsaturated acids, the cis isomer is usually
found.
Physical Properties of Fats and Oils
 The repeating zigzag shape of saturated fatty acids found in fats
allows them to fit close together leading to strong attractions. As
a result, a fat is solid at room temperature.
 The unsaturated fatty acids found in oils do not stack together
because of the double bonds. As a result, an oil is a liquid at
room temperature.
Fats and Oils
 Fats and oils are the most common lipids.
 Often called triglycerides because they are a
tri-ester of glycerol and three fatty acids.
 Tristearin consists of three stearic acid
molecules reacting with glycerol.
Reaction to Produce a Fat or Oil
+ 3 H2O
Steroids and Cholesterol
 Steroids are any compounds
containing the steroid nucleus
(Pictured at right).
 Cholesterol is the most
important and abundant steroid
in the body.
 You cannot exist without this
substance!
 The sex hormones and the
adrenocortical hormones depend
on cholesterol for their synthesis.
Cholesterol and Hormones
H3C
CH 3
CH 3
CH 3
Cholesterol,
Estrogen, and
Testosterone
CH 3
HO
CH 3
CH 3
OH
CH 3
HO
O
OH
Carbohydrates
 Simple Sugars have the formula Cn(H2O)n and
were once thought to be “hydrates” of Carbon.
 The Carbon cycle.
___________
 6CO2 + 6H2O + energy  C6H12O6 + 6O2
_____________
Types of Carbohydrates
 Monosaccharides – do not hydrolyze into
smaller units.
 Disaccharides – consist of two mono units
joined together – these will hydrolyze.
 Polysaccharides – consist of many mono units
and are sometimes called “complex
carbohydrates.”
Monosaccharides
 Have between three and eight C atoms.
 Number of C’s determines whether it is a triose (3),




tetrose (4), pentose (5), hexose (6), etc.
All have at least two –OH groups and the term
polyhydroxy- is sometimes used.
Will also have either an aldehyde or ketone group.
Aldehyde = aldose and ketone = ketose.
Molecules are written with the C backbone in a vertical
direction.
Monosaccharides
 Ketose or Aldose?
 How many chiral carbons?
CH 2OH
C
H
C
O
OH
CH 2OH
Monosaccharides and Chirality
 Large monosaccharides have several chiral C’s.
 If the lowest chiral C has the OH group on the
left, then it is called the L isomer. If it is on the
right, then it is called the D isomer.
 Hint: C’s with double to the O are not chiral
and the -CH2OH groups are also not chiral.
Glucose
 How many chiral carbons?
 Is this the D or L isomer?
 Note: D-glucose is oxidized in
the body to produce energy
and L-glucose cannot be
oxidized.
H
O
C
H
C
OH
HO
C
H
H
C
OH
H
C
OH
CH 2OH
Cyclic Structure
 In solution, glucose and other mono-
saccharides become cyclic.
Disaccharides
 Composed of two mono units.
 Some common ones are:
 Sucrose = Glucose + Fructose
 Lactose (Milk sugar) = glucose + galactose
 Maltose = glucose + glucose
 In the presence of water and an acid catalyst,
these linked molecules will split apart back
into their mono units.
Sucrose
Polysaccharides
 This is essentially a polymer of glucose units
(usually).
 Plant Starch exists in two forms: Amylose and
Amylopectin.
 Amylose is a long,continuous chain of glucose molecules.
Typically has 250 – 4000 units.
 Amylopectin is a branched chain of glucose molecules.
Branches are about every 25 units.
Polysaccharides
 Animal Starch is also called ___________. This is

essentially a branched chain as well.
 Branches are about every 10 – 15 units.
____________, found in cell walls of plants and animals,
is also a long chain of glucose units much like amylose.
Polysaccharides
 The linkage between each unit in cellulose is
different (b linkage) and is resistant to
hydrolysis.
 Human’s do not possess the enzymes to break
this material down for energy as some animals
do.
 We often refer to this material in our diet as
“fiber.”
Amino Acids and Proteins
The Amino Acids
 Are the building blocks of all




proteins.
Twenty different versions of
these.
All contain the carb. acid and
amine functional groups.
Center C is called the alpha
Carbon and it is chiral (except
in Glycine)
Abbreviated by three letter
designations.
R
O
H
N
C
C
OH
H
H
Amino Acids
 The R groups can be non-polar, polar, acidic, or basic.
Alanine
Serine
Non-polar R group
Acidic R Group
The Peptide Bond
 Amino acids link together by the reaction of a
carboxylic acid on one with the amine of
another.
 The linkage between the two is called a
peptide bond.
Peptide Formation
 Reaction to form peptide bond between any two
amino acids is a condensation type:
Primary Structure
 Chains of 3 – 50 amino acids are called polypeptides.
 When more than 50 amino acids are joined, we usually
call it a protein.
 The specific sequence of amino acids in a protein is
called the primary structure.
 Our DNA codes for only a limited number of specific
sequences for making proteins.
 Approximately 100,000 different proteins found in
humans.
Secondary Structure
 This refers to how the amino acids along the
polypeptide are arranged in space.
 The three most common types are:
 Alpha Helix - which is a corkscrew shape of the chain that
results from Hydrogen bonding between every fourth amino
acid. All of the R groups then are pointed outward.
 Beta-Pleated Sheet – rows of amino acids are held flat with
HB keeping them rigid.
 Triple Helix – is three peptide chains woven together like a
braid. HB is also a powerful force that holds this together.
Alpha Helix & Beta-Pleated Sheet
Tertiary Structure
 This is the overall 3D shape of the protein.
 The types and interactions of the R groups are
important in this area.
 Globular proteins, like hemoglobin and insulin, have a very
compact and round shape. The non-polar R groups point
inward and the polar R groups point outward and this makes
these proteins soluble in water.
 Fibrous proteins, like keratin (hair, skin), consist of long,
thin, fibrous shapes. Cross-linking is an important aspect
and determines whether you have curly or straight hair.
Tertiary Structure
Overview of Protein Structures
Albumin
Lysozyme
Nucleic Acids
 Basic structure is a polymer of four different bases.
 Each nucleotide consists of three parts: a sugar, a base,
and a phosphate group.
Nucleotide Structure
 Each nucleotide has three parts –
a cyclic pentose, a phosphate
group, and an organic aromatic
base
 The pentoses are the central
backbone of the nucleotide
 The pentose is attached to the
organic base at C1 and to the
phosphate group at C5
 The phosphate groups then link
to each other to form a polymer
DNA and RNA
 Deoxyribonucleic Acid is found primarily in the nucleus of
the cell.
 Ribonucleic Acid is found throughout the cell.
 The sugar molecule Ribose differs by a single oxygen atom.
Bases
 In DNA, the four cyclic bases are Adenine, Guanine, Cytosine,
and Thymine. In RNA, Thymine is replaced by Uracil.
Base Pairing in DNA
Base Pairing in DNA
 The bases in nucleic acids are complementary – they
precisely pair with another base.
 Adenine pairs with Thymine via two hydrogen bonds
 Guanine pairs with Cytosine via three hydrogen bonds
Linking Nucleotides
Linking Nucleotides
Genetic Structure
 Each sequence of three nucleotides is called a codon
 A codon codes for one amino acid
 AGT = Serine
 ACC = Threonine
 This is universal for all living things!
DNA Double Helix
DNA Double Helix
 Base pairing generates the helical
structure
 In DNA, the complementary bases
hold strands together by H-bonding
 allow replication of strand
DNA Replication
Protein Synthesis
 Transcription → translation
 In nucleus, DNA strand at gene separates and a
complementary copy of the gene is made in RNA
 messenger RNA = mRNA
 The mRNA travels into the cytoplasm where it links with
a ribosome
 At the ribosome, each codon on the RNA codes for a
single amino acid, and these are joined together to form
the polypeptide chain
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Protein Synthesis
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