Test 24 (Biochemistry)

1. Amyloidosis:

a. the protein stained with Lugol's iodine

b. the deposition is extracellular

c. has a polymorphous structure

d. AL type is seen in 15% of patients with multiple myeloma.

e. causes death mainly through cardiac failure

answera.T   b.T   c.F   d.T   e.F
Amyloid proteins stained dark brown with Lugol's iodine and this gives a useful macroscopic indication of  the presence of amyloidosis.
The protein has a beta-pleated sheet structure
The main cause of death in amyloidosis is through renal failure.

2. Proto-oncogenes:

a. are only found in malignant tissues

b. are retroviruses capable of causing tumours

c. inactivates oncogenes

d. regulates cell growth and differentiation

e. causes neurofibroma

answera.F   b.F   c.F   d.T   e.T
Proto-oncogene are normal genes which have central roles in the signal-transduction pathways that control cell growth and differentiation. 
Oncogenes were originally identified as genes carried by cancer causing viruses and they are the mutated form of proto-oncogenes. It is now known that oncogenes can arise from gene substitution or translocation not just through virus.
 

3. The following are true about G proteins:

a. they are first messengers

b. when activated, the alpha subunit exchange GDP for GTP

c. they are transmembrane signal receptor molecules

d. vibrio cholerae secrets an exotoxin which makes G-proteins resistant to 
     inactivation

e. the activities of G-proteins are reduced in pseudohypoparathyroidism.

answera.F   b.T   c.F   d.T   e.T
G-prtoeins are membrane bound receptors which are the binding sites for an external stimulus or first messenger (for example, hormones, light or neurotransmitters). They interact with second messenger pathways which are responsible for a change in the state of the cell, for example, a growth factor binding to a cell surface receptor leads to initiation of mitosis. 
The coupling of the first and second messengers via G-proteins is an ubiquitous mechanism in human cells. G-proteins are composed of three subunits (alpha, beta and gamma).
When a ligand binds to its receptors, the a subunit releases GDP and binds GTP which gives it an active conformation allowing it to interact with a second messenger system for example cyclic-GMP.
In cholera, exotoxins produced by the bacteria make the G-proteins resistant to inactivation which leads to fluid and electrolyte loss.
In pseudohypoparathyrodism, the activities of the G-proteins are reduced and as a result there is a reduced response to parathyroid hormone, T3 and gonadotrophins.

4. True statements about p53 include:

a. a protein coded by a tumour suppressor gene

b. it suppresses mitosis

c. it is important regulators of apoptosis

d. its presence in the serum indicate colonic cancer

e. it is defective in Li-Fraumeni syndrome

answera.T   b.T   c.T   d.F   e.T
p53 is a protein coded by a tumour suppressor gene.
It encodes a transcription factor which downregulate the cell cycle by preventing the cell from entering mitosis.
It is also a central regulator of apoptosis.
It is the most commonly mutated gene in tumours such as breast and colon. It is the primary defect in Li-Fraumeni syndrome (a familial cancer syndrome involving the development of multiple solid organ tumours).
 

5. Gout:

a. is characterized by hyperuricaemia.

b. is diagnosed by hyperuricaemia

c. causes scleritis

d. patient with gout should avoid eating offal

e. typically affects the first metatarsophalangeal joint.

answera.T   b.F   c.T   d.T   e.T
While hyperuricaemia is important for the development of gout. A high hyperuricaemia is not diagnostic of gout as hyperuricaemia can exists without gout. A definite diagnosis depends on the finding of uric acid crystal within the affected joint by needle aspiration.
Deposit of uric acid in the sclera can give rise to scleritis.
Uric acid results from the breakdown of nucleic acid and offal (ie. liver, kidney and heart) is a rich source of such material.

 

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