Proteins

Question 1

Polypeptide

Answer 1

Amino acids are the monomers that Join together to form polymers

Question 2

Structure of amino acids

Answer 2

Each amino acid has a central carbon atom
Amino group on its lift - NH2
Carboxylate group on its right COOH ( double bonded oxygen)
H below
And R above

Question 3

R group

Answer 3

Determines how the amino acid interacts and bonds with other amino acids in the polypeptide

Question 4

Essential amino acids

Answer 4

20 different types of amino acids that are common in all organisms but only 10 of these are essential

Question 5

Peptide bond

Answer 5

When two amino acids react together, a bond forms between the carboxyl group of one amino acid and the amine group of a second amino acid

Question 6

Transport proteins

Answer 6

Channel proteins transport molecules across the cell membrane that are too large to diffuse freely or molecules that carry a charge

Question 7

Enzymes

Answer 7

Biological catalysts which increase the rate of a reaction without being used up in the reaction

Question 8

Antibodies

Answer 8

Made up of polypeptide chains and are used in the immune response
They are diverse proteins as every antibody has a different sequence of amino acids

Question 9

Structural proteins

Answer 9

Long, strong polypeptide chains which are connected by cross-links that hold the chains parallel to each other

Question 10

The biuret test

Answer 10

Add sample to distilled water and biuret solution and shake then leave upright for 5 mins
The biuret test changes colour from blue to violet when proteins are present

Question 11

Primary structure

Answer 11

Sequence of amino acids which is determined by the gene encoding the protein
A change in the nucleotide sequence of the gene’s coding region may lead to a different amino acid being added to the growing polypeptide chain

Question 12

Secondary structure

Answer 12

Primary polypeptide chain folds to form a secondary structure where amino acids can form hydrogen bonds which causes he protein to fold e.g alpha helix or a beta pleated sheet
The 2º structure is stable since although individual hydrogen bonds are weak, there are many bonds throughout the molecule

Question 13

Tertiary structure

Answer 13

Secondary polypeptide folds further to form a tertiary, three dimensional polypeptide chain
Interactions between r groups creates the complex 3D tertiary structure of a protein
There are many weak and strong interactions that hold the final 3D shape of the protein - ionic, hydrogen and disulphides bridges

Question 14

Quaternary structure

Answer 14

Multiple 3D polypeptides can come together to form a complex e.g collagen, insulin ( globular shape) , haemoglobin ( 4 polypeptide )

Question 15

Biological catalyst

Answer 15

substance that speeds up a chemical reaction without being used up itself

Question 16

Activation energy

Answer 16

specific amount of energy needed for a reaction to start , enzymes lower the activation energy by binding to reactant molecules and allowing chemical bond-breaking and bond-forming processes to happen more easily

Question 17

The lock and key model

Answer 17

Originally used to explain enzyme action

Which proposes that the enzyme and substrate fit together perfectly

Question 18

The induced fit model

Answer 18

Suggests that there is a more dynamic interaction between enzyme and substrate
As an enzyme and substrate come together, their interaction causes a small shift in the enzyme’s structure which means that the enzyme and substrate can bind to form an enzyme-substrate complex and catalyse a reaction

Question 19

PH and enzymes

Answer 19

Changing the pH changes the number of hydroxide ions and hydrogen ions surrounding the enzyme which interact with the charges on the enzymes amino acids affecting hydrogen bonding and ionic bonding so resulting in changes to the tertiary structure

Question 20

Temperature and enzymes

Answer 20

Increasing the temperature will increase the kinetic energy of the molecules which increases the chance of a collision between the enzyme and substrate and so more collisions are likely in a set period of time
Increasing the temperature by 10ºc will approx double the rate of reaction

Question 21

Enzyme concentration

Answer 21

Increasing the concentration of enzyme in a solution means there are more enzyme molecules available to catalyse the substrate in a given amount of time

Question 22

Substrate concentration

Answer 22

Increasing the conc. of the substrate increases the numbers of substrate molecules that can form ES complexes at any one time which increases the initial rate of reaction but when all the enzyme molecules are engaged in ES complexes the rate cannot increase any further

Question 23

Competitive inhibitors

Answer 23

Competitive inhibitors are similar in shape to the usual substrate and affect the active site directly, blocking access for the formation of ES complexes, increasing the substrate concentration can compensate for the effects of a competitive inhibitor as there is no permanent damage to the shape of the active site

Question 24

Non-competitive inhibitors

Answer 24

Affect another part of the enzyme molecule causing a change to the shape of the active site which is no longer complementary to the substrate molecules