Proteins

Question 1

Amino acids

Answer 1

A molecule made from an amine group (NH2), a carboxyl group (COOH), an R group (which can be many different molecules, e.g. a H atom) and a central carbon atom attached to a H atom

Question 2

Proteins

Answer 2

Proteins are polymers of amino acids joined by peptide formed between the carboxyl group of one amino acid and the amine group of another. Peptide bonds are formed by condensation reactions

Question 3

Primary protein structure

Answer 3

The linear sequence of amino acids in a polypeptide; the sequence determines the location and type of chemical bonds between R bonds, which in turn determine the folding of the polypeptide

Question 4

Secondary protein structure

Answer 4

An ɑ-helix (spiralled shape) or a ß-pleated sheet held together by hydrogen bonds

Question 5

Tertiary structure

Answer 5

The 3D folding of the secondary structure which form globular proteins

Question 6

Globular proteins

Answer 6

Proteins held together by (very strong) disulphide bonds, (weak) hydrogen bonds and ionic bonds (broken by changes in pH) between R groups of non-adjacent amino acids. Globular proteins contain an active site with a specific shape formed by chemical bonds, and include enzymes, antibodies and hormones. Hydrophobic interactions (on the inside of the protein) and hydrophilic interactions (on the outside of the protein) between the R groups also determine the shape, and allow the protein to be soluble

Question 7

Fibrous proteins

Answer 7

Straight, unfolded chains with little tertiary structure, these structural proteins are found in connective tissue and tendons, and in hair and nails as keratin

Question 8

Quarternary structure

Answer 8

The 3D arrangement of more than one tertiary polypeptide (e.g. haemoglobin)

Question 9

Substrate concentration

Answer 9

The maximum rate of reaction (Vmax) is limited by the number (concentration) of enzymes

Question 10

Enzyme concentration

Answer 10

Vmax is limited by the concentration of substrate

Question 11

pH

Answer 11

Different enzymes have different optimal pH levels

Question 12

Temperature

Answer 12

With a low temperature, the enzyme and substrate have a low kinetic energy, so fewer collisions lead to few enzyme-substrate complexes and a lower rate of reaction. With a high temperature, the bonds holding an active site in its shape break and the the shape changes, leading to fewer enzyme-substrate complexes and a low rate of reaction

Question 13

Competitive inhibition

Answer 13

The inhibitor fits into the active site and prevents the substrate from reacting to create a product

Question 14

Non-competitive inhibition

Answer 14

A molecule binds to a protein and changes the shape of the active site; this is a type of reversible inhibition

Question 15

Enzymes

Answer 15

Enzymes are biological catalysts that reduce the activation energy of chemical reactions. They are produced by cells and speed up the rate of chemical reactions. They have an optimum temperature of 40˚C. The body stays at 37˚C in order to provide a buffer against further temperature increases. They have a 3D, globular structure, determined by the sequence of amino acids in their primary structure. Because they have a high number of polar amino acids, they are soluble in water

Question 16

Activation energy

Answer 16

Activation energy is the energy needed for a chemical reaction to occur by breaking, forming or weakening chemical bonds

Question 17

Active site

Answer 17

Part of the enzyme’s structure is known as the active site. It has a very specific shape, which can only bind to certain substrate molecules with a complementary shape. The shape and position of the active site is determined by the position of amino acids within the molecule

Question 18

Induced fit theory

Answer 18

The active site of the enzyme moulds itself around a substrate, forming an enzyme-substrate complex. The R groups of the amino acids lower the activation energy, inducing a chemical reaction. When the product is formed it no longer binds to the active site, so it is released