proteins

Question 1

how are dipeptides formed?

Answer 1

when two amino acids join by a condensation reaction = peptide bond.water released

Question 2

how are polypeptides formed?

Answer 2

by the condensation of many amino acids

Question 3

whats the primary structure of a protein?

Answer 3

the sequence of the amino acids in the polypeptide chain- the polymer

Question 4

whats the secondary structure of a protein?

Answer 4

hydrogen bonds between amino acids cause folding of amino acid sequence into alpha helix or b pleated sheets

Question 5

whats the tertiary structure of a protein?

Answer 5

the further folding of the secondary structure.
more bonds can form between diff parts of the polypeptide chain. more ionic /hydrogen bonds. 2 cysteine = disulphide bridges

Question 6

whats the quaternary structure of a protein?

Answer 6

a protein made of more than one polypeptide chain. 3 d shape. e.g. haemoglobin, isulin, collagen

Question 7

what are proteins made of

Answer 7

amino acids joined together = dipeptide
several amino acids = polypeptide

Question 8

what is the formula of an amino acid

Answer 8

carboxylic acid (COOH)
amine at the other end (NH2)
R group - varies

Question 9

what are some protein functions

Answer 9

1. enzymes: catalyse reactions, spherical, soluble, vital for digestion of larger mols to smaller mols.
2. antibodies: immune response, in blood, 4 chains (light and heavy)
3. transport proteins: membranes

Question 10

explain how enzymes fold

Answer 10

fold in specific ways to create active sites
e.g. amylase breaks down polysaccharide starch into maltose

Question 11

describe structural proteins

Answer 11

• physically strong, structure to organs
• e.g. keratin(hair/nails) and collagen (3 polypeptide chains. connective tissue)

Question 12

test for proteins

Answer 12

1.biuret test
2. solution needs to be alkaline so add sodium hydroxide
3. add copper sulphate
4. present = blue-purple

Question 13

what is an enzyme

Answer 13

proteins that speed up rate of chemical reactions - biological catalysts.
catalyse metabolic reactions e.g. resp or digestion

Question 14

enzymes may contain one or more active sites.. what do they do?

Answer 14

as = part of enzyme where substrate will bind
substrate = mols enzyme interacts with.
active site is highly specific due to its tertiary structure

Question 15

describe activation energy

Answer 15

in order for chemical reaction to occur a certain amount of energy is required = activation energy (often heat)

Question 16

what do enzymes do to the activation energy

Answer 16

lower activation energy required for a reaction to proceed = occur at lower temps

Question 17

what actually lowers the activation energy

Answer 17

binding of the substrate to active site of an enzyme (enzyme-substrate complex)

Question 19

what are the 2 reasons for the lowering of the activation energy?

Answer 19

1. if substrate mols need to be joined together their proximity in an e-s complex reduces repulsion that may be. helps substrate bond easily.
2. if enzyme is catalysing breakdown of a single mol into smaller mols, the e-s complex puts strain on bonds in the substrate = break down easily

Question 20

whats the lock and key model

Answer 20

• theory of how enzymes work
• shape of the substrate (key) fits perfectly in the active site (lock).
• perfectly complimentary to one another.
• Emil Fischer 1894

Question 21

whats the induced fit model

Answer 21

• enzyme and substrate are not perfectly complimentary to one another
• substrate induces change in shape of active site to create a perfect fit
• Daniel Koshland 1950s

Question 22

enzyme properties

Answer 22

• specific tertiary structure = very specific usually only catalyse one reaction. e.g. maltase
• enzyme and substrate must be complimentary to one another - if not, no E-S complex
• if tertiary structure changed, active site shape will change = no E-S complex = denatured = not functional.

Question 23

how can you measure enzyme activity

Answer 23

how fast product is made
how fast substrate is broken down

Question 24

how does temp affect ezymes

Answer 24

• temp inc rate of enzyme activity
• due to inc kinetic energy present
• more collisions etween enzyme and substrate mols
• inc likelihood of successful collisions
• successful collisions= ES complexes

Question 25

what happens when the temp is to high?

Answer 25

- make bonds inside enzyme vibrate - after certain temp, bonds break (rupturing of bonds = change in shape active site, active site and substrate no longer comp so e-s cannot form) - denatured - no longer functional

Question 26

whats theoptimum temp

Answer 26

in humans, 37c

Question 27

how does pH impact enzymes

Answer 27

- H+ and OH- ions can disrupt bonds in the active site. - ionic and hydrogen bonds break - affects tertiary structure - E-s complexes cant form

Question 28

how does substrate conc affect enzymes

Answer 28

- higher sub conc = fast rate of reaction - bc higher chance of collisions, more active sites likely to be occupied - eventually all active sites **saturated** - any further inc in sub= no difference to rate - referred to as Vmax of reaction (maximum rate)

Question 29

how does enzyme conc affect enzymes

Answer 29

- more enzymes available = more active sites - inc liklihood of collisions between.... - if substrate is limited, there may be more active sites than subsrate - any inc in active sites is **superfluous** as already enough as to dead w available subs.

Question 30

how can enzymes be inhibited?

Answer 30

inhibition can be competitive or non-competitive

Question 31

explain competitive inhibition

Answer 31

- comp inhibitors have **similar shape** to **substrate** - compete w substrate for enzyme active sites - comp inhibitor binds, it **blocks** active site preventing substrate from binding - **slows** rate of reaction

Question 32

explain non-competitive inhibition

Answer 32

- non-comp inhibitors bind to **allosteric site**, have diff shape to substrate - site on enzyme away from active site - inhibitor binds to allos site, change in shape of active site induced - sub mols no longer comp - slows down reaction

Question 33

how can you measure the rate of a reaction

Answer 33

1. set up several boiling tubes w same vol and conc of H2O2 (keep pH constant w buffer) 2. put each tube into water bath at diff temps, e.g.... 3. add same conc and vol of catalase into each tube 4. record how much O2 is given off in first min

Question 34

explain enzyme controlled reaction of amyalse

Answer 34

1. breaks down starch to maltose 2. starch goes blue/black when iodine added 3. amylase added to spotting tile ( as starch broken down, iodine oes orange) 4. it will break down starch slowly at low temps, quickly at optimum, high stop bc denatured