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Flashcards in Proteins Deck (55)
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1

Binding of oxygen to myoglobin saturation curve =

Hyperbolic

2

Haemoglobin -

= oxygen carrier protein in RBCs

- contains prosthetic group = Heam group with Fe

3

O2 binding to Hb …

Sigmoidal curve

4

Pathway of communication of Hb…

O2 binds to Fe2+
Pulls Histidine side chains towards ring
Breaks interactions at subunit interface allowing re,active rotation of subunits

5

Oxygenation of Hb…

Moves Fe2+ into centre of porphyrin ring

6

O2 binding to Hb affected by…

H+
CO2
BPG
=all favour deoxy form
= these effectors promote O2 release in tissues

7

Effect of PH on O2 binding Hb…

Ph decrease = H+ releases O2

8

Effects of CO2 on Hb…

Generates H+
Bind directly to Hb amine groups

9

2,3-bisphosphoglycerate…

Reduces affinity of Hb for O2

10

Foetal haemoglobin -

- Binds 2,3-bisphosphoglycerate less tightly than adult haemoglobin
- binds O2 more tightly than adult haemoglobin
- oxygen can pass from mothers blood to foetus

11

Sickle cell anaemia -

- disease caused by defective Hb
- caused by mutation in beta chain
- leads to loss of solubility and precipitation in RBCs

12

Evidence for mechanism of ribonuclease:

1) ph dependence of reaction
2) use of small molecule inhibitor, e.g. iodoacetate
3) use of a non-hydrolysable substrate analog
4) site directed mutagenesis

13

Collagen -

Provides tensile strength in skin, bones, teeth, cartilage

3 polypeptides

14

Insufficient vitamin C…

Proline not converted to hydroxyproline = no cross links = weak collagen = scurvy

15

Oestrogen receptor -

Regulates response to oestrogen

Soluble protein, nuclear hormone receptor

Needs 2 key domains; ligand binding domain + DNA binding domain

16

Myoglobin -

Oxygen storing molecule in muscle
Contains haem prosthetic group containing Fe
Histidine involved in O2 binding

17

Prosthetic group =

Compound permanently associated with a protein that contributes to the proteins function

18

O2 binding to myoglobin:
Fractional saturation =

Binding sites occupied / total binding sites

19

Enzymes =

Proteins which catalyse biological reactions

Specific
Unchanging after reaction
Speed up reactions
Cannot alter reaction equilibrium

Effected by thermodynamics and kinetics

20

Michaelis-Menton equation:

V = Vmax[S] / Km+[positive]


V = rate
[S] = conc of substrate
Vmax= max rate of reaction
Km = Michaelis constant

21

Km =

The substrate concentration at which the reaction proceeds at half the maximum rate (Vmax)

= the substrate concentration at which half of enzyme molecules have substrate bound to their active site

22

Lineweaver-burk plot …

A plot of 1/v against 1/[s] will give a straight line :

y = m x + c

1/v = Km/Vmax x 1/[s] + 1/Vmax



Gradient = Km/Vmax

Y intercept = 1/Vmax

X intercept = -1/Km

23

The lower the Km…

The higher the affinity for the substrate

24

Turnover number (Kcat) =

A measure of the conversion of substrate to product under optimum conditions

25

Enzyme efficiency =

Ratio of Kcat : Km

26

Active site =

Region of enzyme where reaction occurs

27

Specificity =

Complementary between enzymes and substrate

Lock + key theory
Induced fit theory

28

Irreversible enzyme inhibitors :

Bind tightly by covalent bonds

29

Reversible enzyme inhibitors :

Non covalent

Competitive = binds at active site

Non competitive = binds at allosteric site

30

Competing inhibitor =

Binds at active site

Vmax is unaffected
Km is increased