Proteins

Question 1

how many AA exist from which proteins can be made?

Answer 1

20 AA
different proteins have these AA joined together in different order.

Question 2

draw the common structure of AA

Answer 2

• Alpha carbon in center(chiral center)
• Varible R group(side chain)
• coo- (acidic group)
• NH3+ amine (basic group)

Question 3

what is the difference in 20 naturally occuring AA?

Answer 3

different side chains (R group)
different side chains give AA different properties and shapes

Question 4

what are types of side chains you can have?
give examples of AA

Answer 4

1. negatively charged- acidic asparic acid, glutamic acid
2. positively charged- Basic lysine, histidine
3. polar side chains- uncharged as they cancel
4. non polar - alanine, glycine, valine

Question 5

AA are optically active,
what does this mean and which forms of aa usually exists?

Answer 5

AA have 2 enantiomers as a result of different arrangement od atoms around alpha carbon
L isomer or D but only L isomer is found in amino acids

Question 6

How do 2 AA join together?

Answer 6

• Condensation reaction
• water is removed from amine group of one AA and carboxyl group of another
• after water is removed product is called AA residue

Question 7

what is the special property of peptide bond?
what does this property mean to proteins

Answer 7

peptide bond is planar
Restricted rotation around peptide(amide) bond so atoms around C-N cant move however other atoms can move and twist
this restricted rotation makes proteins rigid

Question 8

meaning of oligopeptide

Answer 8

short chains of AA residues

Question 9

are peptide bonds in cis or trans orientatin?

Answer 9

trans
ketone and nh groups are on different sides of peptide bond

Question 10

which way is the sequence of polypeptide chain written?

Answer 10

start with n terminus on left
end with c terminus

Question 11

what is the 1 structure of AA

Answer 11

• sequence of AA residues in the polypeptide chain from n terminus to c terminus
• determined by DNA
• MOST basic level

Question 12

2nd level

Answer 12

polypeptide chain folds into a-helix or B-sheet
folding is due to H bonds

Question 13

tertiary structure

Answer 13

bending and twisting of 2 structure into a more compact, 3D shape(ionic, H and disulfide bonds)

Question 14

quaternary structure

Answer 14

some proteins are made of more than 1 polypeptide chain joined to prosthetic group

Question 15

what does prosthetic group mean

Answer 15

cofactor that binds to protein or enzyme
iron in Hb(metals fe2+ or Cu2+)

Question 16

How is a-helix formed?

Answer 16

a-helix is right handed helix as it coils in clockwise direction
there are 36 AA residues per turn
theres a skeleton with side chains that extend out
the structure of helix is stabilised by H bonds
co group of one AA is H bonded to NH group of another AA 4 residues down the chain

Question 17

B sheet structure of it

Answer 17

sheet like structure
parts of the polypeptide chain form H bonds with other chains so cross linked together
H bonding stabilises the structure
Parallel B sheet- Adjacent chains run in same direction
antiparallel B sheet- adjacent chains run in opposite directions

Question 18

tertiary structure

Answer 18

3 structure determines the 3d shape of protein mol

Question 19

methods used to find out shape of proteins

Answer 19

X ray crysalography

Question 20

different shapes of proteins you can have + GIVE examples

Answer 20

globular- myoglobin, haemoglobin, insulin, enzymes, transporters
Fibrous- have structural role in cells provide strength and support (collagen, elastin, keratin)
some proteins form fillaments or tubes-
actin+ microtubules

Question 21

Quaternary structure of proteins

Answer 21

different polypeptide chains join together and associate with prosthetic groups
Hb

Question 22

how many polypeptide chains make up Hb what are these subunits called and how many o2 can it carry
what prosthetic group is attached to it

Answer 22

Hb is made of 4 polypeptide chains: 2 alpha globin and 2B globin
each of these chains contain a haem group (contains iron) each iron can carry an o2 mol

Question 23

thalasemia and sickle cell anaemia

Question 24

Types of bonds involved in protein foldiong

Answer 24

covalent bond- disulfide b/w sulfate groups of AA
Ionic bond-AA side chains are +ve and -ve so form ionic bon ds with each other
H bond- B/W h+N/O/F very electronegative atoms (bind substrate to enzyme)
VDW- B/W atoms as e- can move
Hydrophobic interactions- side chains of AA with aromatics are non polar, interactions of these side chains and aqueous environment

Question 25

how proteins fold into hydrophobic core

Answer 25

in aqueous environment non polar side chains arrange themselves middle of core and polar side chains face outside the core towards aqueous environment

Question 26

what causes protein denaturation?
what happens to a protein when its denatured?
can it be renatured?

Answer 26

Denaturation is caused by Heat, detergening agents(acid, high conc alkali), organic solvent or mechanical force
brings about conformational change to shape of protein so protein can no longer function
its sometimes possible to renature a protein if detergent is removed under right conditions

Question 27

mutation of proteins can have detrimental effect, name some diseases associated with protein mutations

Answer 27

• cystic fibrosis
• phenylketunoria
• sickle cell anaemia
• ## beta thalassemia

Question 28

what is beta thalassemia

Answer 28

recessive genetic disorder causes b-globin deficiency so reduced or no b globin is produced
hb is a protein molecule made of 4 globin chains each bonded to a haem group(a-globin, b-globin, delta and gamma) these can be present in any combination.
symptoms: shortness of breath, fatigue

Question 29

sickel cell disease