12 - reactions of biological compounds

Proteins

proteins are organic biopolymers that have many important in living things.

Biopolymers are synthesized from very large numbers of small monomers (amino acids for proteins), made in living organisms.

Condensation reactions

Condensation Polymerization is a form of a step-growth polymerization where smaller bifunctional monomers (compounds with two reactive end-groups) react to produce polymers while releasing by-products such as water or methanol molecule. The by-products are normally referred to as condensate.

• Common condensation polymers include polyesters, polyamides such as nylon, polyacetals, and proteins.

• Proteins, carbohydrates and lipids are formed via condensation

bifunctional monomers (how)

For condensation polymerization to occur, the monomers must contain reactive functional groups on either end. they must be different of either monomer.

This happens in two ways:

1. the moments have two different functional grounds at each end. the polymer formed from these are called homopolymers.

2. two kinds of monomers each have two of the same functional groups that are different from each other. polymer made from these are called heteropolymers/copolymers.

by-products of condensation

water is the by-product in the reactions to form most large molecules.

other small molecules, including ammonia, hydrogen chloride and methanol are sometimes a by-product.

general structure & formula of amino acid

includes a amino functional group -NH2, a carboxyl functional group -COOH and a hydrogen atom -H. All of these are attached to a central carbon C. There is also a sidechain/R-group, which distinguishes each amino acid from another.

formula for 2-amino acids: H2N-CH(R)-COOH.

R groups (side chain) properties

• may be polar or non-polar in different amino acids

• can behave as acids/proton donors or bases/proton acceptors

forming proteins

large protein molecules are formed by many reactions between amino acids. these are completed in a highly organized way to ensure that the correct amino acid order is present in the protein.

initially a reaction between two amino acids → form a dipeptide

dipeptide reacts with more amino acids → form a polypeptide

polypeptide continues to react with additional amino acids → form full protein

(all of these reactions are condensation reactions, and a molecule of water is produced each time the chain grows)

forming dipeptides

dipeptides are formed when a condensation reaction occurs between the carboxyl functional group of one amino acid and the amine functional group of a second amino acid (an amide/peptide link is formed)

each time a pair of different amino acids react in this way, there are two possible product molecules depending on which ends of each molecule react together

forming polypeptides

polymers formed by further reactions between the amino acids, where they form long chains.

organisms make their dipeptides, polypeptides and larger proteins in ribosomes. this is in a step known as translation where genetic instructions are used to make proteins with a specific amino acid sequence.

a polypeptide constructed from more than 50 amino acids is usually called a protein

carbohydrates

Made from the elements carbon, hydrogen and oxygen. range in size from small molecules to very large polymers.

(includes starch and glycogen and cellulose and glucose)

monosaccharides

Monosaccharides are the smallest carbohydrates.

Includes glucose, fructose and galactose. These all have the same molecular formula C6H12O6 (they are isomers)

The structures of these look very similar, however, the position of the -OH groups are different, and these slight variations lead to significant differences in their functions.

As they all contain a number of polar hydroxyl (OH) groups, they can form hydrogen bonds with water, meaning monosaccharides are highly soluble in water.

glucose

formed in the cells of green plants through the process of photosynthesis (takes place in the presence of light)

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

photosynthesis is an endothermic reaction, where the sun’s energy is transformed into chemical potential energy in glucose. living organisms use glucose as a source of energy.

found in all living things.

animals cannot perform photosynthesis, so they need to consume plants or animals to meet their energy needs

disaccharides

disaccharides are carbohydrates formed from the reaction between two monosaccharide molecules, where a condensation reaction occurs between the hydroxyl functional groups on neighbouring molecules. a water molecule is formed as a by-product.

(two monosaccharides are joined by an oxygen atom. the bond is called a glycosidic link.)

examples include maltose, sucrose etc.

polysaccharides

reactions between monosaccharides can continue to produce a polymer (polysaccharide), which can contain thousands of mono units.

they are generally insoluble in water.

three most important polysaccharides are starch, cellulose and glycogen. they are all polymers of the same monomer, glucose.

starch

plants are able to produce a polymerize glucose molecules to form starch,

the polymerisation is a condensation reaction, forming glycosidic links between each glucose molecule. this produces water molecules a a by-product.

plants use starch for storage of energy, and when this energy is required, the plant can break down the starch back into glucose and utilize the glucose as an energy source.

a second form of starch, known as amylopectin, can form if some of the glucose molecules undergo condensation reactions between hydroxyl groups at different positions around the glucose rings

glycogen

also formed from polymerisation of glucose, and is highly branched.

animals use glycogen for energy storage, and is formed from excess glucose and stored in the liver or muscle tissues. if energy is needed, the glycogen can be broken down to glucose, which can then be used in cellular respiration.

lipids

lipids are fats and oils, and are a major energy source in our diets. fats are used by animals to store chemical energy.

fats are solids at room temp and oils are liquids at room temp.

triglycerides

large non-polar molecules that make up fats and oils.

as they are non-polar, they are unable to form hydrogen bonds with water. hence, fats are insoluble in water and oils are immiscible (cannot mix) with water.