proteins and enzymes

Question 1

What is the COOH group of an amino acid

Answer 1

carboxyl group

Question 2

what is the R group of an amino acid

Answer 2

side group

Question 3

what is the NH2 of an amino acid

Answer 3

amine group

Question 4

how many amino acids are there in all organisms

Answer 4

there are 20 and they all differ in their side {R] group

Question 5

what are polypeptide

Answer 5

formed by the condensation of many amino acids and a water molecule is released and a peptide bondis formed

Question 6

what are dipeptides

Answer 6

formed by the condensation of 2 amino acids

Question 7

describe a primary structure of a protein

Answer 7

sequence of amino acids in the polypeptide chain joined by peptide bonds

Question 8

describe a secondary structure of a protein

Answer 8

sequence of amino acids have hydrogen bonds in the chain and holds it and makes it coil into an alpha helix or a beta pleated sheet

Question 9

describe a tertiary structure of a protein

Answer 9

coiled chain of amino acid forming a 3D shape due to interaction between R groups hold by ionic, hydrogen bonds and disulfide bridges

Question 10

describe a quaternary structure of protein

Answer 10

a protein held by more than one polypeptide chain that determines 3D shape e.g haemoglobin

Question 11

test for proteins

Answer 11

biuret reagent
1. add sodium hydroxide
2. add copper sulfate solution
3. positive=colour change blue to purple

Question 12

what are enzymes

Answer 12

biological catalysts that speed up a chemical reaction without being used upand they do this by loweing the activation energy

Question 13

Explain the specificity of enzymes

Answer 13

● Specific tertiary structure determines shape of active site
○ Dependent on sequence of amino acids (primary structure)
● Active site is complementary to a specific substrate
● Only this substrate can bind to active site, inducing fit and forming an enzyme-substrate complex

Question 14

Describe how models of enzyme action have changed over time

Answer 14

● Initially lock and key model (now outdated)
○ Active site a fixed shape, complementary to one substrate
● Now induced-fit model

Question 15

what happens when a enzyme binds to the substrate

Answer 15

enzyme substrate complexes are formed

Question 16

what is the acceptable model of enzyme action

Answer 16

induced fit model

Question 17

describe the induced fit model

Answer 17

1. Substrate binds to active site not completely complementary to
   active site of enzyme
2. Causing active site to change shape slightly so it is complementary to substrate
3. So enzyme-substrate complex forms
4. Causing bonds in substrate to bend / distort, lowering activation energy

Question 18

describe the lock and key theory

Answer 18

shape of enzyme active site is complementary to substrate exactly-lowers activation energy
enzyme substrate complex is formed

Question 19

what are the factors that affect enzymes

Answer 19

temperature
PH
substrate concentration
enzyme concentration
competitive/non competitive inhibitors

Question 20

how does temperature affect enzymes

Answer 20

● As temp. increases up to optimum, rate of reaction increases
○ More kinetic energy
○ So more Enzyme substrate complexes form
● As temp. increases above optimum, rate of reaction decreases
○ Enzymes denature - tertiary structure and active site change shape
○ As hydrogen / ionic bonds break
○ So active site no longer complementary
○ So fewer enzyme Substrate complexes f

Question 21

how does PH affect enzymes

Answer 21

if PH is too high or low it will interfere with the charges of the amino acids

rate of reaction decreases
○ Enzymes denature - tertiary structure and active site change shape
○ As hydrogen / ionic bonds break
○ So active site no longer complementary
○ So fewer E-S complexes form

Question 22

how does enzyme concentration affect enzymes

Answer 22

more enzymes mean more active sites so more enzyme substrate complexes form. rate of reaction increases until substrate concentration becomes the limiting factor[not enough substrates]

Question 23

how does substrate concentration affect enzymes

Answer 23

more substrates mean more enzyme substrate complexes form which increase rate of reaction
when all substrates are complementary enzyme concentration becomes the limiting factor

Question 24

how does a competitive inhibitor affect enzymes

Answer 24

● As concentration of competitive inhibitor increases, rate of reaction decreases
○ Competes for / binds to / blocks active site
○ So substrates can’t bind
○ So fewer enzyme-substrate complexes form
● Increasing substrate concentration reduces effect of inhibitors

Question 25

how does a non competitive inhibitor affect enzymes

Answer 25

● As concentration of non-competitive inhibitor increases, rate of reaction decreases
○ Binds to allosteric site
○ Changes enzyme tertiary structure / active site shape
○ So active site no longer complementary to substrate
○ So substrates can’t bind
○ So fewer enzyme-substrate complexes form

Question 26

what are globular proteins

Answer 26

theyre spherical and compact it is involved in many metabolic reactions e.g enzyme/haemoglobin

Question 27

describe the method of chromatography

Answer 27

• put a spot of a solution of mixture on a pencil line
  -place paper in solvent
• allow solvent to rise up paper
• amino acids move at diff distances based on solubility to paper
  -use UV light to see spot
  -calculate RF and match to data base

Question 28

how do u calculate RF

Answer 28

distance of spot/ distance of solvent

Question 29

Define amino acids

Answer 29

The monomers from which proteins are made

Question 30

Explain the role of hydrogen,ionic bonds and disulphide bridges in the structure of proteins

Answer 30

Hydrogen and ionic bonds form attractions between the negative and positive charges on different parts of the molecule
Disulphide bridges form the 3D structure