proteins and enzymes Flashcards
proteins =
polymers made of amino acids
dipeptides =
2 amino acids joined tg via a condensation reaction
peptide bond =
amine group (NH2) joined to a carboxyl group (COOH) via condensation reaction
polypeptides =
many amino acids joined tg via multiple condensation reactions
structure of an amino acid
R
|
NH2 — C — COOH
|
H
•variable R group, 20 diff. options
•amine & carboxyl group always present
what are the 4 levels of structure a protein can reach? (some may only reach upto the 2nd struc.)
•primary structure
•secondary structure
•tertiary structure
•quaternary structure
primary struc.
the seq. of amino acids in a polypeptide chain —> determines struc. & ,therefore, function of protein
secondary struc.
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
tertiary struc.
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
quaternary struc.
-large proteins composed of +1 polypeptide chains
-often non-protein groups (prosthetics) are associated with the molecules. eg iron-containing haem in haemoglobin
diff. types of proteins
-globular proteins
-fibrous proteins
globular proteins
- have globular ball shape
- carry out metabolic functions
- soluble
- eg. enzymes & haemoglobin
fibrous proteins
- 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
collagen (example of f. protein)
-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
expl. how a change in the primary struc. of a globular protein may result in a diff. 3D struc.
- seq. of aa’s in primary struc. changes
- diff tertiary struc.
- dis, ionic & H bonds form in diff places
test for proteins
- mix protein w biuret reagent
- colour change to purple
define ‘hydroxylating’
addition of hydroxyl group
what are enyzmes?
-tertiary struc, globular proteins
-act as bio catalysts
-lower activation energy of reaction they catalyse
explain how the active site of an enzyme is formed
-determined by primary struc –> specific seq. of aa’s form depressions on surfaces of enzymes –> a.s –> a.s = specific & unique
explain how the shape of an enzyme molecule is related to its function
- enzymes have tertiary struc.
- a.s = specific & unique –> complimentary to substrate
- substrate can bind to a.s via temp. bonds, forming enzyme-substrate complex
the role of enzymes
- control metabolic pathways –> lower ae’s of reactions
- allow reactions to take place at the relatively low temps. within cells
why is the lock & key model no longer used when describing the shape of enzymes?
-no longer used
-limitation = enzymes considered to be rigid structures
induced fit model / explain how the a.s of an enzyme causes a high rate of reaction
- active site moulds itself around substrate
- places a strain on bonds maintaining the substrate molecules
- lowers activation energy needed to break these bonds
measuring rate of reaction through graph
1) draw tangent
2) calculate gradient of tangent –> gradient = delta Y/delta X
3) include units of gradient
factors affecting enzymes
- substrate conc.
- temp.
- pH
- enzyme inhibitors
substrate conc.
factors affecting enzymes
- 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
temperature
factors affecting enzymes
- 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
pH
factors affecting enzymes
-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
competitive inhibitors
factors affecting enzymes
- 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
non-competitive inhibitors
factors affecting enzymes
- binds to the allosteric site –> distorts shape of active site
- no e.s complexes form (no matter the substrate conc)
describe how amino acids join to form a polypeptide so there is always NH2 at one end & COOH at the other end
- one amine group joins to one carboxyl group to form a peptide bond
- in polypep. chain, there is always a free amine group at one end & carboxyl group at the other
