T1: Proteins

Question 1

how to draw protein

Answer 1

C in centre
H2N and COOH side branches
R group and hydrogen top and bottom

H2N amine group
COOH carboxyl group
R variable side chain

Question 2

describe the overall structure of a protein

Answer 2

polymer of amino acids joined by peptide bonds formed by condensation

Question 3

dipeptide

Answer 3

2 amino acids

Question 4

polypeptide

Answer 4

3+ amino acids

Question 5

peptide bond formation

Answer 5

OH removed from COOH
H removed from H2N
final peptide bond is C-N

Question 6

primary structure of a protein

Answer 6

the sequence of amino acids in the polypeptide chain

linked by peptide bonds

determined by bases in DNA could change due to mutations

Question 7

secondary structure of protein

Answer 7

folding of the polypeptide chain due to hydrogen bonding

forms alpha helices or beta pleated sheets
H bonds provide stability

Question 8

tertiary structure of a protein

Answer 8

3D folding of the polypeptide chain due to hydrogen bonding and ionic and disulfide bonds

Question 9

quaternary structure of protein

Answer 9

2 or more polypeptide chains held together by hydrogen, ionic and disulfide bonds

Question 10

protein examples

Answer 10

a proteins shape determines its function

enzymes, antibodies, transport proteins, structural proteins

Question 11

enzyme shape and functions

Answer 11

spherical and soluble so have roles in metabolism + larger protein synthesis

Question 12

antibody shape and function

Answer 12

2 light and 2 heavy polypeptide chains with a variable region

found in blood and involved in the immune response

Question 13

transport protein shape and function

Answer 13

transport molecules and ions across membranes e:g channel proteins

Question 14

structural proteins shape and function

Answer 14

long polypeptide chains with cross links between them
e:g keratin (hair + nails) and collagen (tissue)

Question 15

what is an enzyme?

Answer 15

a protein and a biological catalyst that lowers the activation energy of a reaction

Question 16

describe the induced fit model of enzyme action (3)

Answer 16

before the reaction the active site is not complementary to the substrate

the shape of the active site changes as the substrate binds
distorting the bonds in substrate leading to reaction

Question 17

why do enzymes have a specific active site?

Answer 17

the 3D shape of the enzyme depends on the tertiary structure of the protein which depends on the primary structure (order of amino acids)

Question 18

how do enzymes and substrates work generally?

Answer 18

if enzyme is hydrolysing the substrate then fitting into the active site puts strain on the bonds so the substrate breaks easily

if the substrate is joining then the enzyme holds the molecules close reducing repulsion

Question 19

how to measure the rate of an enzyme controlled reaction?

Answer 19

how fast the product is made (product-time graph)

how fast the substrate is hydrolysed (substrate conc and enzyme activity)

Question 20

what are the 5 factors affecting enzyme activity?

Answer 20

temperature
pH
substrate concentration
enzyme concentration
inhibitors

Question 21

how does temperate affect the rate of an enzyme controlled reaction?

Answer 21

more heat = more KE so a higher number of ESC’s formed

different enzymes have diff optimum temps, above which they denature stopping reaction

Question 22

how does pH affect the rate of enzyme controlled reaction?

Answer 22

alters H bonds and ionic bonds holding the active site’s 3D shape

if too high or low the enzyme is denatured and the active site changes shape

Question 23

how does substrate concentration affect the rate of an enzyme controlled reaction?

Answer 23

more substrate molecules = more collisions so more ESC’s formed

when all active sites are full, enzyme concentration becomes the limiting factor

Question 24

how does enzyme concentration affect the rate of an enzyme controlled reaction?

Answer 24

more active sites are available so more ESC’s formed

increases rate until a saturation point where active sites are permanently occupied

Question 25

define enzyme inhibitor

Answer 25

molecules that bind to the enzyme that they inhibit
can be competitive or non-competitive

Question 26

how do competitive inhibitors work

Answer 26

they compete with the substrate molecules to bind to the active site, they block substrate so no reaction occurs

these can be overcome by using higher concentration of substrate

Question 27

how do non competitive inhibitors work

Answer 27

bind to the enzyme (but not at the active site) and causes changes that alter the shape of the active site

these can resist a change in concentration of substrate because they don’t bind directly