2. proteins and enzymes fact test

Question 1

what are the structural roles of proteins

Answer 1

it’s the main component of body tissues like muscle, skin and hair

Question 1

what are proteins also known as

Answer 1

polypeptides

Question 2

what are the catalytic roles of proteins

Answer 2

all enzymes are proteins, catalysing many biochemical reactions

Question 3

what are the signalling roles of proteins

Answer 3

many hormones and receptors are proteins

Question 4

what are the immunological roles of proteins

Answer 4

all antibodies are proteins

Question 5

what are the monomers from which proteins are made called

Answer 5

amino acids

Question 6

what does the general structure of an amino acid consist of

Answer 6

central carbon
hydrogen
R group (variable)
amino group
carboxyl group

Question 7

what is a polypeptide

Answer 7

long chain of amino acids joined together by peptide bonds

Question 8

what is the name of the bond which joins amino acids together

Answer 8

peptide bond

Question 9

what is the order of amino acids determined by

Answer 9

the order of bases in the gene that code for the polypeptide

Question 10

what does peptide bond formation involve

Answer 10

removal of water in a condensation reaction

Question 11

how is a dipeptide formed

Answer 11

by a condensation reaction between 2 peptides (amino acids)

Question 12

what is the primary structure of a protein

Answer 12

sequence of amino acids

Question 13

what is the secondary protein structure

Answer 13

local folding of the polypeptide chain into alpha helixes or beta pleated sheets (caused by hydrogen bonding)

Question 14

what is the tertiary protein structure

Answer 14

3D folding pattern of a protein due to side chain (R group) interactions

are usually globular

Question 15

what is the quaternary protein structure

Answer 15

protein consisting of more than one amino acid chain

Question 16

what are bonds in a protein dependent on

Answer 16

interaction between R groups

Question 17

what are disulfide bonds / bridges and which structure are they present in

Answer 17

a strong S=S double bond formed between sulfur atoms
present in tertiary structure

Question 18

what are ionic bonds and which structure are they present in

Answer 18

some R groups carry a positive or negative charge so an ionic bond can form between 2 oppositely charged R groups
present in tertiary structure

Question 19

which structure are hydrogen bonds present in

Answer 19

secondary and tertiary

Question 20

what other bond is present in the tertiary structure but is not on the spec

Answer 20

hydrophobic/hydrophilic interactions

Question 21

what does the biuret test for

Answer 21

the presence of peptide bonds

Question 22

how do you carry out the biuret test

Answer 22

ensure sample is in solution
add biuret reagent
stays blue if no peptide bonds present
turns purple if peptide bonds are present

Question 23

what are enzymes and what are they used for

Answer 23

they are biological catalysts meaning they are used in metabolic reactions to increase the rate of reaction

it lowers activation energy of the reaction it catalyses

Question 24

what is the active site and what does it do

Answer 24

the small part of an enzyme which is involved in catalysis, it may consist of just a few amino acids

Question 25

what do amino acids which aren't part of the active site do

Answer 25

maintain the precise tertiary structure of the enzyme and active site

Question 26

what is an enzyme-substrate complex and how is it formed

Answer 26

substrate binds to the active site of an enzyme forming and enzyme-substrate complex

Question 27

what is the lock and key model

Answer 27

substrate will only fit active site of one particular enzyme the shape of the substrate is complementary to that of the active site and it fits exactly

Question 28

what is the induced fit model

Answer 28

- shape of enzyme and active site are not complementary - enzyme is flexible and can mold around substrate - enzyme changes shape slightly to fit the profile of the substrate (like a glove fitting a hand) - as it changes shape, it puts pressure on the substrate molecule - this distorts a particular bond in the substrate molecule and lowers the activation energy needed to break the bond

Question 29

why is the induced fit model better than the lock and key model

Answer 29

it is a better explanation as it explains how other molecules can affect enzyme activity and how activation energy is lowered

Question 30

how do you calculate pH

Answer 30

-log10 [H+]

Question 31

what does the graph of the effect of temperature on enzyme activity look like

Answer 31

as temperature increases, rate of reaction increases gradually the rate peaks at (give value) above the optimum, the rate decreases steeply to 0

Question 32

explain why the graph of the effect of temperature on enzyme activity looks the way it does

Answer 32

- at low temperatures, enzyme and substrate have less kinetic energy so there are few successful collisions between substrate and active site meaning fewer enzyme-substrate complexes (ESC) formed and less product produced - as temperature increases, enzyme and substrate gain kinetic energy, increasing number of collisions between substrate and active site, more ESC formed and increasing rate of reaction - peak indicates optimum temperature - beyond optimum temperature, hydrogen bonds maintaining the tertiary structure of the enzyme are broken, this changes shape of active site, denaturing the enzyme, meaning fewer/no ESC formed, reducing rate of reaction

Question 33

what does the graph of the effect of pH on enzyme activity look like

Answer 33

rate peaks at particular pH above or below this pH, rate steeply decreases

Question 34

explain why the graph of the effect of pH on enzyme activity looks the way it does

Answer 34

- peak represents optimum pH - changing the pH changes the concentration of H+ ions - change in pH can affect changes in the active site meaning substrate can no longer bind to active site to form ESC - a larger change in pH can cause ionic and hydrogen bonds in tertiary structure of enzymes to break. this can cause the tertiary structure to change, leading to a change in shape of the active site, meaning fewer/no ESC can form

Question 35

what does the graph of the effect of substrate concentration on enzyme activity look like

Answer 35

as substrate concentration increases, rate of reaction increases until it reaches a plateau no further increase in substrate concentration increases the rate

Question 36

explain why the graph of the effect of substrate concentration on enzyme activity looks the way it does

Answer 36

- at a low concentration, not all active sites are occupied by substrates therefore fewer ESC formed - when the graph levels off, all active sites are occupied and enzyme is working at maximum rate - beyond this point, enzyme concentration is limiting factor

Question 37

what does the graph of the effect of enzyme concentration on enzyme activity look like

Answer 37

as enzyme concentration increases, rate of reaction increases until it reaches a plateau no further increase in enzyme concentration increases the rate

Question 38

explain why the graph of the effect of enzyme concentration on enzyme activity looks the way it does

Answer 38

- at low enzyme concentration, there is excess substrate and the umber of available active sites (enzyme concentration) is limiting the rate - when graph levels off, all substrates are bound to active sites - beyond this point, enzyme molecules are in excess and the concentration of substrate is limiting the rate

Question 39

what are competitive inhibitors and what do they do

Answer 39

have a similar shape to substrate but not the same occupies active site so fewer ESC form inhibition can be overcome by increasing substrate concentration substrate and competitor compete for active site of the enzyme

Question 40

what are non-competitive enzymes and what do they do

Answer 40

permanently binds to the enzyme at a site away from the active site called the allosteric site this causes active site to change shape preventing ESC from forming inhibition cannot be overcome by increasing substrate concentration

Question 41

what is end product inhibition

Answer 41

- allows control over metabolic pathways, so we don't get too much or too little of a substance in cells - enzymes are part of a pathway, where the product of one enzyme is the substrate for the next - the end product can act as an inhibitor of an enzyme earlier on in the pathway - too much product leads to more inhibition which means product level decreases - too little product leads to less inhibition which means product level increases