Proteins

Question 1

Primary structures

Answer 1

AA sequence
Condensation reaction
/
Creates resonance structure 
(Partial charge-short bond N C)
=
Very restricted movement in backbone 

Creates sheets.

Question 2

What is Tm

Answer 2

50% of the protein has been unfolded

= melting point for this protein

Question 3

Non covalent forces allow proteins to refold after denaturants are removed?

Answer 3

Hydrophobic interactions

H bonding

S-S bonding (otherwise would be random, needs to fold first)

Question 4

Collagen

Answer 4

Fibrous protein
Alpha chain with repeating tripeptide
3 chains twist in right handed helical
Glycine allows really tight turns =strength

Glycine-proline-alanine
+4 hydroxy proline

Made outside cell!!!

Question 5

How many covalent bonds seperate adjacent AA in peptide backbone?

Answer 5

3

Alpha carbon
CO
NH
Then next alpha carbon

Question 6

What accounts for partial double bond characters of Peptide bond?

Answer 6

Coo- = negative chargr

NH -= positive charge

Question 7

Conjugated protein

Answer 7

Has other groups not just AA

Myoglobulin has a prosthetic group = porfryn ring covalently bound

Is Fe2+ as the 3+ won’t pick up oxygen. It is therefore buried deep in the globular protein so it doesn’t react and becomes 3+

Question 8

Myoglobuli

Answer 8

Single peptide chain (153)
8 alpha helices
*single heme molecule is burried deep in protein surrounded by hydrophobic AA

Question 9

Haem structure

Answer 9

4 poly peptide chain
2æ chains
2b chains

R state = relaxed

T state = tense

Fe2+= needs 6 bonds.

• histadine
• oxygen
• 4 in porphyrin ring

F helix is really close to prphyrin ring which has histidine

Question 10

Heam binding oxygen in R and T state

Answer 10

Transition due to histadine

Lung PH 7                   Tissue pH 6
Above pKa                   At pKa
Deprotonated             50% Protonated
-ve                                 +ve
                                       Repel fe+
Pick up oxygen           Give up Oxygen

R state = relaxed and oxygen affinity
Subunits further apart, less interaction so able to bind oxygen

T state= tense state closer, more interactions so affinity for oxygen drops

Question 11

Co-operative binding of o2

Answer 11

When 1 subunit is oxygenated causes a conformational change and three other subunits increase affinity for 02

Sigmoid curve.

Changes from T - R

Question 12

Different affinity for oxygen
Heam
Myoglobin

Answer 12

Due to quaertinary structure

Heam = tissue 64% because conformational change alters oxygen binding

Myo= only on Heam and doesn’t change so always good at binding o2
94%