Proteins

Question 1

What are the features of a peptide bond?

Answer 1

shorter than a normal single bond, rigid, planar, prevents free rotation and always in trans configuration

Question 2

Is a peptide bond charged?

Answer 2

No but it is polar

Question 3

Define a secondary structure

Answer 3

The regular arrangement of amino acids help together with hydrogen bonds

Question 4

What are the features of an alpha helix?

Answer 4

tightly packed, coiled, side chains extend outwards, hydrogen bonds parallel to spiral, each turn contains 3.6 amino acids and a 0.54nm pitch.

Question 5

Define tertiary structure

Answer 5

The folding of domains and the final arrangement of domains in the polypeptide

Question 6

What is the only amino acid that doesn’t display stereoisomerism?

Answer 6

Glycine

Question 7

What are the 2 types of spatial arrangement that an amino acid can take and which one is the only form naturally found?

Answer 7

2 arrangements: L-form and D-form

L-form is the only form found naturally

Question 8

Define isoelectric point

Answer 8

The pH at which a protein has no overall net charge

Question 9

What features do acidic proteins have?

Answer 9

contain many negatively charged amino acids and have a low pI

Question 10

What features do basic proteins have?

Answer 10

contain many positively charged amino acids and have a high pI

Question 11

Define homomeric proteins

Answer 11

When the polypeptide chains in the quaternary structure are identical

Question 12

Define heteromeric proteins

Answer 12

When the polypeptide chains in the quaternary structure are different

Question 13

Define denaturation

Answer 13

Loss of protein structure sufficient to cause the loss of function

Question 14

Which amino acid does not contain a carboxyl group?

Answer 14

Proline

Question 15

What value is physiological pH?

Answer 15

pH = 7.4

Question 16

What is sickle cell anaemia?

Answer 16

A disease of the RBCs resulting from the substitution of glutamate for valine in the beta subunit of haemoglobin. (A->T)

Question 17

What is albumin?

Answer 17

A blood protein that functions as a transporter for a variety of molecules

Question 18

If a Ka value is higher what does this mean?

Answer 18

The larger the Ka value, the stronger the acid because most of the acid will dissociate.

Question 19

What is the Henderson-Hasselbach equation?

Answer 19

pH = pKa + log([A-]/[HA])

Question 20

How do you make a buffer?

Answer 20

By mixing a weak acid with its conjugate base

Question 21

If pH>pK the molecule is…

Answer 21

Deprotonated

Question 22

If the isoelectric point is greater than 7 then what kind of protein is it?

Answer 22

Basic protein

Question 23

If the isoelectric point is less than 7 then what kind of protein is it?

Answer 23

Acidic protein

Question 24

If the pH>pI then the molecule is…

Answer 24

Deprotonated

Question 25

What is a amphipathic molecule?

Answer 25

One that has both polar and non-polar regions

Question 26

What are some of the roles of proteins?

Answer 26

catalysts (enzymes), structural support, transporters, machines (contraction and motion), immune protection, receptors, ion channels and ligands in cell signalling

Question 27

Why are some R-groups positively charged?

Answer 27

Due to their high pKa value, they have acted as bases and accepted a proton.

Question 28

Why are some R-groups negatively charged?

Answer 28

Due to their low pKa values, they have acted as acids and donated a proton

Question 29

What are conjugated proteins?

Answer 29

Proteins that contain covalently linked chemical components in addition to amino acids.

Question 30

Why can't we transport oxygen directly in the blood?

Answer 30

Oxygen isn't very polar so does not dissolve in the aqueous environment of the blood.

Question 31

What are the features of myoglobin?

Answer 31

contains 1 haem group in the centre, comprised of 153 amino acids, compact and 75% alpha helical

Question 32

What are the features of haemoglobin?

Answer 32

comprised of 4 polypeptide chains, each chain contains a haem group and undergoes a structural change on binding oxygen

Question 33

What is the difference between the T state and R state of haemoglobin?

Answer 33

The T state has a low affinity for oxygen as this is before any oxygen has bound. The R state has a high affinity for oxygen as an oxygen molecule has bound and changed the structure so that the haem groups are more exposed and therefore can bind to oxygen more easily.

Question 34

What is the role of 2,3-bisphosphoglycerate?

Answer 34

This is a by product of glycolysis that causes the affinity of haemoglobin for oxygen to decrease. 1 BPG binds per tetramer and acts as a regulator by promoting oxygen release in the tissues.

Question 35

Define thalassaemias

Answer 35

A group of genetic disorders where there is an imbalance between the number of alpha and beta chains in haemoglobin.

Question 36

How many common amino acids are there?

Answer 36

20 common amino acids

Question 37

Define transition state

Answer 37

A high energy intermediate that lies between the reactants and products

Question 38

How does an increase in temperature increase the rate of reaction?

Answer 38

It increases the vibrational energy of the reactants. This increases the amount of molecules with the activation energy so more successful collisions will occur.