Methionine and cysteine.

DNA and RNA are polymers of monomers called nucleotides, each of which is composed of a nitrogen base, a pentose sugar and a phosphate. A purine or a pyrimidine and a ribose or deoxyribose sugar is called nucleoside.

Anabolic (building up of organic molecules). Synthesis of proteins from amino acids and synthesis of polysaccharides from simple sugars are examples of anabolic reactions.

(NH₂), an acidic carboxylic group (COOH) and a hydrogen atom (H) and side chain or variable R group. The amino acid is both an acid and a base is called amphoteric.

Chitin is a homopolysaccharide with amino acids added to form mucopolysaccharide. The basic unit is a nitrogen-containing glucose derivative known as N-acetyl glucosamine. It forms the exoskeleton of insects and other arthropods. It is also present in the cell walls of fungi.

Monosaccharides are relatively small molecules constituting single sugar unit. Glucose has a chemical formula of C₆H₁₂O₆' It is a six carbon molecule and hence is called as hexose.

1. It is a RNA which translates the code from mRNA and transfers amino acids to the ribosome to build proteins.
2. It is highly folded into an elaborate 3D structure and comprises about 15% of total RNA

rRNA (ribosomal RNA): Single-stranded, metabolically stable, makeup the two subunits of ribosomes. It constitutes 80% of the total RNA. It is a polymer with varied length from 120 - 3000 nucleotides and gives ribosomes their shape. Genes for rRNA are highly conserved and employed for phylogenetic studies.

They modify enzyme activity by causing a reversible change in the structure of the enzyme active site. This, in turn, affects the ability of the substrate to bind to the enzyme. Such compounds are called Allosteric inhibitors. ego The enzyme hexokinase which catalysis glucose to glucose-6 phosphate in glycolysis is inhibited by glucose 6 phosphate. This is an example for feedback allosteric inhibitor.

Triglycerides are composed of single molecule of glycerol bound to 3 fatty acids. These include fats and oils. Fatty acids are long chain hydrocarbons with a carboxyl group at one end which binds to one of the hydroxyl groups of glycerol, thus forming an ester bond. Fatty acids are structural unit of lipids and are carboxylic acid of long chain hydrocarbons. The hydrocarbon can vary in length from 4 - 24 carbons and the fat may be saturated or unsaturated. In saturated fatty acids the hydrocarbon chain is single bonded.
eg. Palmitic acid, Stearic acid and in unsaturated fatty acids.
eg. Oleic acid, linoleic acid) the hydrocarbon chain is double bonded (one/two/three). In general solid fats are saturated and oils are unsaturated, in which most are globules.

Aldoses and ketoses are reducing sugars. This means that, when heated with an alkaline solution of copper (II) sulphate (a blue solution called Benedict's solution), the aldehyde or ketone group reduces Cu²⁺ ions to Cu⁺  ions forming brick red precipitate of copper (I) oxide. In the process, the aldehyde or ketone group is oxidised to a carboxyl group (- COOH). This reaction is used as test for reducing sugar and is known as Benedict's test. The results of Benedict's test depends on concentration of the sugar. If there is no reducing sugar it remains blue.
(i) Sucrose is not a reducing sugar.
(ii) The greater the concentration of reducing sugar, the more is the precipitate formed and greater is the colour change.

(i) These are made of hundreds of monosaccharide units. Polysaccharides also called "Glycans".
(ii) Long chain of branched or unbranched monosaccharides are held together by glycosidic bonds.
(iii) Polysaccharide is an example of giant molecule, a macromolecule and consists of only one type of monomer.
(iv) Polysaccharides are insoluble in water and are sweetless. Cellulose is an example built from repeated units of glucose monomer.
(v) Depending on the function, polysaccharides are of two types: Storage Polysaccharide and structural Polysaccharide.

1. Prokaryotic mRNA (Polycistronic) carry coding sequences for many polypeptides.
2. Eukaryotic mRNA (Monocistronic) contains information for only one polypeptide.

Ribonucleic acid (RNA): Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA is single stranded and is unstable when compared to DNA.

Types of RNA:
1. mRNA (messenger RNA) - Single stranded, carries a copy of instructions for assembling amino acids into proteins. It is very unstable and comprises 5% of total RNA polymer. Prokaryotic mRNA (Polycistronic) carry coding sequences for many polypeptides. Eukaryotic mRNA (Monocistronic) contains information for only one polypeptide.
2. tRNA (transfer RNA) - Translates the code from mRNA and transfers amino acids to the ribosome to build proteins. It is highly folded into an elaborate 3D structure and comprises about 15% of total RNA. It is also called as soluble RNA.
3. rRNA (ribosomal RNA) - Single stranded, metabolically stable, make up the two subunits of ribosomes. It constitutes 80% of the total RNA. It is a polymer with varied length from 120 - 3000 nucleotides and gives ribosomes their shape. Genes for rRNA are highly conserved and employed for phylogenetic studies.

Hydrogen Bond:
1. It is formed between some hydrogen atoms of oxygen and nitrogen in a polypeptide chain. The hydrogen atoms have a small positive charge and oxygen and nitrogen have small negative charge. Opposite charges attract to form hydrogen bonds.
2. Though these bonds are weak, large number of them maintains the molecule in 3D shape.
Ionic Bond:
1. It is formed between any charged groups that are not joined together by peptide bond. It is stronger than hydrogen bond and can be broken by changes in pH and temperature.
Disulfide Bond:
1. Some amino acids like cysteine and methionine have sulphur.
2. These form disulphide bridge between sulphur atoms and amino acids.
Hydrophobic Bond:
1. This bond helps some protein to maintain structure.
2. When globular proteins are in solution, their hydrophobic groups point inwards away from water.