Download Carbohydrates

Biomolecules
•
•
•
•
Carbohydrates .
Proteins .
Lipids .
Nucleic Acids .
Carbohydrates
• Carbohydrates are made of carbon,
hydrogen, and oxygen atoms, always in a
ratio of 1:2:1.
• Carbohydrates are the key source of energy
used by living things.
• The building blocks of carbohydrates are
monosaccharides (sugars) such as glucose
and fructose.
• Formed by photosynthesis in plants
Types of Carbohydrates
• – Monosaccharide (1 sugar)
• – Disaccharide (2 sugars linked in a chain)
• – Oligosaccharides ( less than 10 sugars in a
chain ).
• – Polysaccharide (large No of sugars linked in
a chain)
Function of Carbohydrates
1- The major source of energy used by living
organisms .
2- Forming structural components in the cell ,
eg. Cell wall of plant cell and in cell
memberanes
• Polysaccharides are used by many organisms as
building materials. For example, in plants
cellulose form the cell wall .
Oligomeric or polymeric carbohydrates are often
covalently bound to lipids or proteins.eg.the
glycolipids and glycoproteins in cell membranes .
Glycoproteins also occur in the blood as plasma
proteins .
Cell membrane
Monosaccharides
• Two most common
– Glucose
• Primary storage form of
energy in human body
– Fructose
• Main sugar found in most
plants
• Others types consumed
– Galactose (from mammalian
milk)
* The Two types of monosaccharides are Aldoses and
Ketoses
-The backbones of common monosaccharide molecules are
unbranched carbon chains in which all the carbon atoms
are linked by single bonds.
- In the open-chain form, one of the carbon atoms is
double-bonded to an oxygen atom to form a carbonyl
group; each of the other carbon atoms has a hydroxyl
group.
- If the carbonyl group is at an end of the carbon chain (that
is, in an aldehyde group) the monosaccharide is an aldose;
- If the carbonyl group is at any other position (in a ketone
group) the monosaccharide is a ketose.
- The simplest monosaccharides are the two three-carbon
trioses: glyceraldehyde, an aldotriose, and dihydroxyacetone, a
ketotriose .
-Monosaccharides with four, five, six, and seven carbon
atoms in their backbones are called, respectively,
tetroses, pentoses, hexoses, and heptoses.
- There are aldoses and ketoses of each of these chain lengths .
- The hexoses, which include the aldohexose D-glucose and the
ketohexose D-fructose are the most common monosaccharides
in nature.
- The aldopentoses D-ribose and 2-deoxy-D-ribose are
components of nucleotides and nucleic acids ( DNA and RNA )
Reaction between the aldehyde group at C-1 and the
hydroxyl group at C-5 forms a hemiacetal linkage,
producing either of two stereoisomers the α and β
anomers, which differ only in the stereochemistry around
the hemiacetal carbon.
Disaccharides
Two monosaccharides bind together
How do two monosaccharides combine to make
a disaccharide ?
- By dehydration reaction and
formation of O-Glucosidic bond .
Polysaccharides
Polysaccharides are long chains of monosaccharides
linked together .
Polysaccharides
- Most carbohydrates found in nature occur as
polysaccharides, polymers of medium to high
molecular weight.
- Polysaccharides differ from each other in the
1-identity of their recurring monosaccharide units .
2- in the length of their chains .
3- in the types of bonds linking the units .
4- and in the degree of branching.
Two types :
Homopolysaccharides contain only a single type of
monomer.
Heteropolysaccharides contain two or more different
kinds of monomer ..-
■ Polysaccharides serve as stored fuel and as structural
components of cell walls and extracellular matrix.
■ The homopolysaccharides starch and glycogen
are stored fuels in plant, animal, and bacterial
cells. They consist of D-glucose .
■ The homopolysaccharides cellulose, chitin, and dextran
serve structural roles. Cellulose, composed of ( β 1-4)-linked Dglucose residues, lends strength and rigidity to plant
cell walls. Chitin, a polymer of ( β 1-4)-linkedNacetylglucosamine , strengthens the exoskeletons of
arthropods.
Two types of bonds ; ( α 1-4) and ( α 1-6 )linked D-glucose
residues
( β 1-4)-linked D-glucose residues
Starch
Starch contains two types of glucose polymer, amylose
and amylopectin.
Amylose consists of long, unbranched chains of D-glucose
residues connected by ( α1-4) linkages. Such chains vary in
molecular weight from a few thousand to more than a
million.
Amylopectin also has a high molecular weight (up
to 100 million) but unlike amylose is highly branched
The glycosidic linkages joining successive glucose
residues in amylopectin chains are ( α 1-4); the branch
points (occurring every 24 to 30 residues) are ( α 1-6)
linkages.
b-amylopectin
Proteins
- Proteins are the most abundant biological
macromolecules .
- Occurring in all cells and all parts of cell.
Proteins occur in great variety; thousands of different
kinds, ranging in size from relatively small peptides to
huge polymers with molecular weights in the
millions
- proteins have enormous diversity of biological
function
Proteins functions
• Most abundant and functionally diverse group of molecules
• Indispensable for life :
• Have several diverse functions:
- Catalytic functions [enzymes]
- Receptor [insulin receptor]
- Structural function [collagen]
- Transport [haemoglobin, myoglobin]
- Protective functions [immunoglobulins]
- Hemostasis [clotting factors]
- Hormonal functions [insulin, glucagon, GH]
- Control of gene expression [transcription factors]
- DNA packing [histones]
- Act as buffers
Proteins
* Amino acids
are the building blocks of proteins.
* There are 20 different amino acids that
make up human proteins.
* A peptide bond forms between amino acids
by dehydration reaction.
* sequence is genetically determined
• The amino acid sequence is encoded
in DNA
• Protein shape is determined by the
amino acid sequence
Proteins
■ The 20 amino acids commonly found as
residues in proteins contain an -carboxyl
group, an -amino group, and a distinctive R
group substituted on the -carbon atom.
General structure of an amino acid
Levels of Protein Structure
Four Levels of Protein
Structure
- All proteins have their
own specific primary
structure [a.a sequence],
determined by their
Genes .
- Different proteins have
different extent of
secondary structure.
Some have none.
- All intracellular proteins
have a tertairy structure
- Proteins made of more
than one subunit
[polypeptide] have
quarternary structure