proteins and enzymes

Question 1

proteins =

Answer 1

polymers made of amino acids

Question 2

dipeptides =

Answer 2

2 amino acids joined tg via a condensation reaction

Question 3

peptide bond =

Answer 3

amine group (NH2) joined to a carboxyl group (COOH) via condensation reaction

Question 4

polypeptides =

Answer 4

many amino acids joined tg via multiple condensation reactions

Question 5

structure of an amino acid

Answer 5

R
|
NH2 — C — COOH
|
H
•variable R group, 20 diff. options
•amine & carboxyl group always present

Question 6

what are the 4 levels of structure a protein can reach? (some may only reach upto the 2nd struc.)

Answer 6

•primary structure
•secondary structure
•tertiary structure
•quaternary structure

Question 7

primary struc.

Answer 7

the seq. of amino acids in a polypeptide chain —> determines struc. & ,therefore, function of protein

Question 8

secondary struc.

Answer 8

the folding of the polypeptide chain into an alpha helix or beta pleated sheet shape —> struc. maintained by H-bond between +vely charged NH2 of one a.a & -vely charged COOH of another

Question 9

tertiary struc.

Answer 9

the folding of the alpha helix into a precise, 3D shape
(not all proteins reach this stage)
–> maintained by:
-disulphide bonds (s-s) –> v. strong
-ionic bonds (formed between R groups) –> weaker than dis. bonds –> easily disrupted by changes in pH
-H bonds –> many but easily broken by the heat

Question 10

quaternary struc.

Answer 10

-large proteins composed of +1 polypeptide chains
-often non-protein groups (prosthetics) are associated with the molecules. eg iron-containing haem in haemoglobin

Question 11

diff. types of proteins

Answer 11

-globular proteins
-fibrous proteins

Question 12

globular proteins

Answer 12

• have globular ball shape
• carry out metabolic functions
• soluble
• eg. enzymes & haemoglobin

Question 13

fibrous proteins

Answer 13

• have little/no tertiary struc.
• form long chains which run parallel to one another –> linked by cross bridges —> makes them stable
• insoluble –>large no. of hydrophobic R groups
• has repetitive a.a seq. –> organised, strong structures –> suitable for structural roles
  > eg. collagen

Question 14

collagen (example of f. protein)

Answer 14

-has quaternary struc. made of 3 p.p chains wound tg. –> each chain linked by cross linkages (bonds between parallel R groups) between amino acids of each chain
-the end of each collagen = staggered
-found in tendons –> minerals can bind to chain, increasing rigidity

Question 15

expl. how a change in the primary struc. of a globular protein may result in a diff. 3D struc.

Answer 15

• seq. of aa’s in primary struc. changes
• diff tertiary struc.
• dis, ionic & H bonds form in diff places

Question 16

test for proteins

Answer 16

• mix protein w biuret reagent
• colour change to purple

Question 17

define ‘hydroxylating’

Answer 17

addition of hydroxyl group

Question 18

what are enyzmes?

Answer 18

-tertiary struc, globular proteins
-act as bio catalysts
-lower activation energy of reaction they catalyse

Question 19

explain how the active site of an enzyme is formed

Answer 19

-determined by primary struc –> specific seq. of aa’s form depressions on surfaces of enzymes –> a.s –> a.s = specific & unique

Question 20

explain how the shape of an enzyme molecule is related to its function

Answer 20

• enzymes have tertiary struc.
• a.s = specific & unique –> complimentary to substrate
• substrate can bind to a.s via temp. bonds, forming enzyme-substrate complex

Question 21

the role of enzymes

Answer 21

• control metabolic pathways –> lower ae’s of reactions
• allow reactions to take place at the relatively low temps. within cells

Question 22

why is the lock & key model no longer used when describing the shape of enzymes?

Answer 22

-no longer used
-limitation = enzymes considered to be rigid structures

Question 23

induced fit model / explain how the a.s of an enzyme causes a high rate of reaction

Answer 23

• active site moulds itself around substrate
• places a strain on bonds maintaining the substrate molecules
• lowers activation energy needed to break these bonds

Question 24

measuring rate of reaction through graph

Answer 24

1) draw tangent
2) calculate gradient of tangent –> gradient = delta Y/delta X
3) include units of gradient

Question 25

factors affecting enzymes

Answer 25

- substrate conc. - temp. - pH - enzyme inhibitors

Question 26

*substrate conc.* | factors affecting enzymes

Answer 26

- low substrate conc = **fewer** sub. molecules for collision --> **less** freq, successful collisions --> less e.s complexes form - high substrate conc = a.s' become **saturated** with substrates --> no more e.s complexes form --> all a.s' **occupied** (addition of enzymes would increase R.O.R --> more a.s' available

Question 27

*temperature* | factors affecting enzymes

Answer 27

- low temp = not enough K.E --> **less** freq, successful collisions between enzyme & sub. molecules --> **decreases** R.O.R - higher temp = increases K.E --> **more** freq, successful collision between enzyme & sub. molecules --> more e.s complexes form --> **increases** R.O.R - temp **above** optimum = **H bonds** maintaining tert. struc. **break** --> a.s changes shape --> enzyme =denatured --> e.s complexes cant form

Question 28

*pH* | factors affecting enzymes

Answer 28

-pH = measure of H+ conc -pH too low/high = interferes with **charges** in amino acids within a.s --> **breaks** bonds holding tertiary struc. in place --> a.s changes shape --> enzyme = denatured

Question 29

competitive inhibitors | factors affecting enzymes

Answer 29

- bind to a.s --> have **similar** shape to substrate - **prevents** e.s complexes - addition of substrate **reduces** effect of inhibitors --> knocks them out of a.s

Question 30

*non-competitive inhibitors* | factors affecting enzymes

Answer 30

- binds to the **allosteric** site --> distorts shape of active site - no e.s complexes form (no matter the substrate conc)

Question 31

describe how amino acids join to form a polypeptide so there is always NH2 at one end & COOH at the other end

Answer 31

1. one amine group joins to one carboxyl group to form a peptide bond 2. in polypep. chain, there is always a **free** amine group at one end & carboxyl group at the other