Objectives
• Describe the chemical composition and general
structure of carbohydrates.
• Describe three classes of carbohydrates, how they
are synthesized, specific examples of each (name,
empirical and structural formulas) and their
functions.
• Describe the chemical composition and structures
of lipids
• Describe the formation of a triglyceride
• Describe the 4 levels of protein structure.
• Describe the major functions of proteins.
Carbohydrates
• A carbohydrate is a large biological molecule
consisting only of carbon (C), hydrogen (H),
and oxygen (O), which are combined as (,,
where n is 3 or more.
• The general empirical formula for a
carbohydrate is CH2O.
If a carbohydrate has 5 carbons atoms, what
would be its empirical formula?
C5H10O5
Functions of Carbohydrates
•
Provide energy source: A fuel source when catabolized during
cellular respiration. Energy is stored in the chemical bonds
within the molecule and released during cellular respiration.
Usually simple sugars.
• Provide energy storage: Plants store energy in a complex
carbohydrate form called starch (amylose). Animals store
energy in a complex carbohydrate in their muscle tissue and
liver in the called glycogen.
• Structural Building Material: Plants build their cell walls of a
complex carbohydrate material called cellulose. Animals such
as arthropods build their exoskeletons of a complex
carbohydrate called chitin. Chitin is also found in the cell
walls of Fungi.
Classes of Carbohydrates
• There are three major classes of carbohydrates:
1. Monosaccharides (simple sugars) These are the
monomers or building blocks for all other classes of
carbohydrates. Examples: glucose, fructose, galactose, and
ribose.
2. Disaccharides are produced by joining two simple
sugars by dehydration synthesis forming a covalent bond
between them. Examples: sucrose (table sugar), maltose,
lactose
3. Polysaccharides (complex carbohydrates) are produced by
joining many monosaccharides together by many dehydration
synthesis reactions forming a polymer molecule. Examples:
amylose, glycogen, cellulose, and chitin
Monosaccharides (Simple sugars)
• They may exist in a linear molecule or in ring forms.
• They are classified according to the number of
carbon atoms in their molecule.
5 carbons are called pentoses ex. Ribose
6 carbons are called hexoses ex. Glucose
• MONOSACCHARIDES ARE THE BUILDING BLOCKS
FOR ALL OTHER CARBOHYDRATES!
Monosaccharide Isomers
H
H
H—C—OH
H—C—OH
O
C
H
O
H
H
C
C
H
C
C
OH
OH
OH
H
C
C
H
OH
H
OH C
C
H
OH
α- GLUCOSE
OH
FRUCTOSE
What is the empirical formula for these molecules?
H—C—OH
H
C6H12O6
Disaccharide Formation and Structure
• Disaccharides are formed when two monosaccharides
are joined by dehydration synthesis reaction.
Disaccharide Formation and Structure
CH2OH
H
CH2OH
O
H
H
CH2OH
O
H
H
CH2OH
O
H
H
O
H
H20
+
O
OH
OH
α- GLUCOSE
HO
α- GLUCOSE
OH
OH
OH
MALTOSE
Polysaccharide Structure and Formation
• Polysaccharides are chains of monosaccharides that
have been joined by many dehydration synthesis
reactions.
• The function of the polysaccharide depends on what
type of isomer of glucose the polysaccharide is made.
This determines how the glucose molecules bond
together (linkage) and whether they can be used for
energy storage or structural molecules.
Polysaccharide Structure
(a)  and  glucose
ring structures
4
1
4
 Glucose
 Glucose
1 4
(b) Starch: 1–4 linkage of  glucose monomers
1
1 4
(c) Cellulose: 1–4 linkage of  glucose monomers
INTRODUCTION
Lipids are heterogeneous group of water
insoluble (hydrophobic) organic molecules.
They are fats, oils, steroids and waxes.
Insoluble in water, but soluble in non-polar
solvents such as ether, chloroform.
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BIOLOGICAL IMPORTANCE OF LIPIDS
Important dietary constituents.
Have high energy value.
Fats stored in adipose tissue, serve as thermal
insulator.
With proteins and carbohydrates, they form
important cellular constituents (lipoproteins,
glycolipids).
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CLASSIFICATION OF LIPIDS
Classified into simple, complex and derived
lipids
1.SIMPLE LIPIDS: Esters of fatty acids (FA) with
various glycerol
a. Fats: esters of FA with glycerol
b. Waxes: esters of FA with higher
molecular weight alcohols
2. COMPLEX LIPIDS: Esters of FA containing groups
in addition to an alcohol and a FA
a. Phospholipids: Esters of FA with
alcohol and phosphoric acid.
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CLASSIFICATION CONTD…..
3. DERIVED LIPIDS: These include FA, glycerol,
steroids, some alcohols, fatty aldehydes and ketone
bodies.
 Acylglycerols (glycerides), cholesterol &
cholesterol esters are termed neutral lipids
because, they are uncharged.
16
Lipid structure (Triglyceride)
•
A triglyceride is composed
of an alcohol called
glycerol covalently bonded
to three fatty acid
molecules by dehydration
synthesis reactions. This
process forms three ester
groups between the alcohol
and one with each fatty acid
chain.
Figure 5.10b
Ester linkage
(b) Fat molecule (triacylglycerol)
Introduction
Proteins are polymers of amino acids linked covalently
through peptide bonds.
Proteins are large molecules and can be split into smaller units
by hydrolysis-amino acids.
Proteins: Classification
Depending upon their solubility and physical properties ,
proteins are divided into three classes.
1- Simple proteins: Simple proteins are those which
contain only amino acids. e.g. albumin and globulin
2- Conjugated proteins: Conjugated proteins are
those which contain a non amino acid component in
addition to the amino acids.
e.g. lipoprotein , phosphoproteins etc.
3- Derived proteins: Derived from simple proteins
(denaturation) e.g. peptones.
Properties of Proteins
• Molecular weights range from 10000-several hundred
thousand
•Generally proteins are soluble in water, except the
membrane proteins which are hydrophobic
•Absorption maxima in the ultraviolet region
•Proteins are charged molecules, but the charge
depend on the pH of the buffer.
•Move under an electric field and can be separated by
electrophoresis
Functions of Proteins
1. Proteins build new tissues of the body.
2. They maintain and replace damaged tissues.
3. They carry out regulating activities as
enzymes and hormones.
4. They are protective as antibodies.
5. They help in other activities such as
movement of skeletal muscles, transport of
oxygen, pigmentation of skin etc.
Four Levels of Protein Structure
• The primary structure of a protein is its unique
sequence of amino acids
• Secondary structure, found in most proteins, consists
of coils and folds in the polypeptide chain
• Tertiary structure is determined by interactions
among various side chains (R groups)
• Quaternary structure results when a protein consists
of multiple polypeptide chains
4 Levels of Protein Structure