3.1.4 proteins

Question 1

what are the monomers of proteins?

Answer 1

amino acids

Question 2

what does the structure of an amino acid contain ?

Answer 2

amine group ( NH3)
carboxyl group (COOH)
R group (variable group)

Question 3

what bond is formed from the condensation reaction between 2 amino acids?

Answer 3

peptide bond

Question 4

how are dipeptides formed?

Answer 4

the condensation of two amino acids

Question 5

how are polypeptides formed?

Answer 5

by the condensation of many amino acids

Question 6

define primary structure of a protein

Answer 6

sequence of a chain of amino acids

Question 7

define secondary structure of a protein

Answer 7

occurs when the sequence of amino acids are linked by hydrogen bonds and pleated sheets

Question 8

define tertiary structure of a protein

Answer 8

occurs when certain attractions are present between alpha helices and pleated sheets

Question 9

define quaternary structure of proteins

Answer 9

a protein consisting of more than one amino acid
may also contain a prosthetic group

Question 10

how are disulphide bridges formed?

Answer 10

the amino acid cysteine contains sulfur atoms which can form disulphide bridges which are strong covalent bonds

Question 11

how are ionic bonds formed?

Answer 11

formed between carboxyl and amine groups not involved in peptide bonds, or between oppositely charged R groups of amino acids

Question 12

outline the biuret test

Answer 12

treat the sample with sodium or potassium hydroxide to make it alkaline
add a few drops of copper sulfate to the sample
a colour change from blue to lilac/ purple indicates the presence of a protein

Question 13

outline the induced fit model of enzyme action

Answer 13

enzymes active site changes shape slightly to fit around the substrate
active site moulds around the substrate putting a strain on certain bonds in the substrate
this lowers the activation energy needed to break bonds
active site and substrate are not complementary

Question 14

what factors affect enzyme activity?

Answer 14

temperature
PH
substrate conc.
enzyme conc.
inhibitors

Question 15

explain the effect of temperature on enzyme activity

Answer 15

as temperature increases the kinetic energy of the enzyme and the substrate increases
this means there are more collisions between the active site of the enzyme and the substrate
this means there are more enzyme substrate complexes formed and more product

Question 16

define PH

Answer 16

a measure of the concentration of hydrogen ions in a solution

Question 17

how do you calculate PH?

Answer 17

-log[H+]

Question 18

explain the effect of changing substrate concentration on enzyme activity

Answer 18

more substrate molecules bind to active sites and so more enzyme substrate complexes form
more product produced
once all active sites are in use the enzyme is saturated

Question 19

explain the effect of changing enzyme concentration on the enzyme activity

Answer 19

more enzyme active sites are available to bind to substrates meaning more enzyme substrate complexes formed and more product is released

Question 20

what is a competitive inhibitor?

Answer 20

a substance that binds at the active site of an enzyme

Question 21

what is a non-competitive inhibitor?

Answer 21

a substance that binds to the allostearic site of an enzyme

Question 22

what does optimum temperature mean for enzymes?

Answer 22

the temperature the enzymes work best at