Globular Proteins

Question 1

Why are some proteins referred to as ‘globular’?

Answer 1

Due to their spherical shape, which is induced by their tertiary structures

Question 2

Where would a globular protein’s non-polar, or hydrophobic, amino acids be found?

Answer 2

Buried deep into the hydrophobic interior areas

Question 3

Why are hydrophilic, or polar, amino acids located on the surface?

Answer 3

To allow for dipole-dipole interactions, and to increase solubility

Question 4

What are enzymes?

Answer 4

Biological catalysts

Question 5

True or false: globular proteins serve as messengers.

Answer 5

True

Question 6

What is the oxygen carrier of the blood?

Answer 6

Haemoglobin

Question 7

What is the term given to the red pigment of striated muscle, and what is its function?

Answer 7

Myoglobin; oxygen store, for use during intense muscular activity

Question 8

What type of structure does haemoglobin have?

Answer 8

Tetramer

Question 9

Haemoglobin is an _____-______ protein.

Answer 9

Iron-binding

Question 10

How many polypeptide chains does haemoglobin have?

Answer 10

Four

Question 11

How many alpha chains does haemoglobin have, and how many amino acids are in each alpha chain?

Answer 11

Two alpha chains, and 141 amino acids

Question 12

How many beta chains does haemoglobin have, and how many amino acids are in each alpha chain?

Answer 12

Two beta chains, and 146 amino acids

Question 13

How many molecules of oxygen can haemoglobin bind to?

Answer 13

Four

Question 14

How many amino acids are on the single polypeptide chain of myoglobin, and what type of helical structures do they form?

Answer 14

153 amino acids, and 8-heliced alpha structures

Question 15

What are haem prosthetic groups comprised of?

Answer 15

Non-polypeptides

Question 16

Where are haem prosthetic groups found?

Answer 16

Hydrophobic crevices

Question 17

Myoglobin is concentrated in which types of muscle?

Answer 17

Cardiac and skeletal

Question 18

Describe haem’s physiological properties.

Answer 18

Haem is a ferrous iron-tetrapyrrole with hydrophobic side chains on three sides, and hydrophilic carboxyl group on a fourth side. It has an intense red colour, due to its conjugate bonds; four bonds are to the pyrrole nitrogen atoms, the fifth to the histidine, and the sixth is available for the reversible attachment of oxygen

Question 19

The myoglobin curve is:

Answer 19

Hyperbolic

Question 20

What does the myoglobin curve indicate about myoglobin?

Answer 20

Myoglobin is almost fully saturated at low O2 pressure; therefore, it has a high affinity for O2, and does not release its O2 at the O2 pressure found in capillaries. It only releases its O2 when muscular activity further lowers the tissue O2 pressure. It acts as a reserve store for this purpose. As it becomes saturated at a lower O2 pressure than haemoglobin, it has a higher affinity for O2 than haemoglobin, and so can extract O2 from the blood to replenish its stores

Question 21

The haemoglobin curve is:

Answer 21

Sigmoidal

Question 22

What does the haemoglobin curve indicate about haemoglobin?

Answer 22

Higher O2 concentrations are required to half-saturate haemoglobin than is the case for myoglobin, again demonstrating myoglobin’s stronger affinity for O2. The sigmoidal curve releases most O2 at O2 pressures encountered in the capillaries, but it also means that haemoglobin is still capable of becoming saturated at the oxygen pressure of the lungs

Question 23

Haemoglobin is an __________ protein.

Answer 23

Allosteric

Question 24

True or false: oxygen binding with haemoglobin is cooperative.

Answer 24

True

Question 25

True or false: oxygen binding with myoglobin is cooperative.

Answer 25

False

Question 26

What type of chains are found in foetal haemoglobin (HbF)?

Answer 26

Alpha and gamma

Question 27

True or false: HbF and HbA have vastly different oxygen affinities under similar conditions.

Answer 27

False

Question 28

To which disease does ‘HbS’ refer to?

Answer 28

Sickle-cell anaemia

Question 29

Which shape does the RBC take in HbS?

Answer 29

Crescent

Question 30

Outline the pathophysiology of HbS.

Answer 30

The disease is as a result of exchange of a glutamic acid residue for a valine residue in the beta chain, as a polar residue is being substituted for a hydrophobic residue

Question 31

Where is the sticky, hydrophobic area located in the haemoglobin of a HbS patient?

Answer 31

Exterior of the beta chains. In the corner between helices E and F of the beta chain of the deoxy-HbS, there is a complementary hydrophobic site.
In oxy-HbS, the complementary site is masked, so the formation of the long crescent fibres only occurs in other conditions.

Question 32

True or false: genetics have no bearing on HbS.

Answer 32

False

Question 33

Name two medical complications observed in HbS.

Answer 33

Cardiac failure and thrombosis