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 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 D-glucose residues, lends strength and rigidity to plant cell walls. Chitin, a polymer of ( β 1-4)-linkedN-acetylglucosamine , 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 * There are 20 different amino acids that * 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

General structure of an amino acid 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