Test 114  (Genetics)

1. The polymerase chain reaction: 

a. produces multiple copies of DNA

b. requires oligonucleotide primers

c. has a high specificity but low sensitivity

d. requires the use of heat 

e. can be used to detect RNA virus

Answera.T  b.T  c.F  d.T  e.T
PCR is highly sensitive and therefore it is essential that the specimen contains no contaminant. Contaminant with even a single copy of DNA may be detectable. It can be used to detect RNA using reverse transcriptase.
 

2. With regard to mitochondrial DNA:

a. it is double-stranded

b. it mutates 10 times more frequently than nuclear DNA

c. each mitochondrion contains about 100 DNA 
    molecules

d. it has no introns

e. Leber's congenital amaurosis is caused by defective 
    mitochondrial DNA

Answera.T   b.T   c.F  d.T  e.FMitochondrial DNA has no introns and repair mechanisms. Therefore, a mutation can easily cause a disturbance of the DNA sequence. 
Each mitochondrion contains about 2 to 10 DNA molecules.
Leber's optic neuropathy and not Leber's congenital amaurosis is caused by defective mitochondrial DNA.

 
3. The following are true about nuclear DNAs:

a. about 50% of the nuclear DNA codes for proteins

b. they are tightly wrapped around histones to form 
    nucleoprotein complex

c. introns interrupt the coding sequence

d. exons are removed during splicing

e. the base pairings are bound together by hydrogen 
    bonds

Answera.F   b.T  c.T  d.F  e.T
Only 3% of nuclear DNA codes for protein. Introns which interrupts the DNA sequence are removed during splicing.
.

4. The HLA B27 molecule:

a. is class II major histocompatibility antigen

b. is expressed mainly in antigen presenting cells

c. occurs in 8% of the general population

d. occurs in 90% of patients with ankylosing spondylitis 

e. is commoner in patients with Yersinia arthritis

Answera.F  b.F  c.T  d.T  e.T
HLA B27 molecule is class I HLA or major histocompatibility antigens. Class II HLA antigens are found in antigen presenting cells.

5. The following are true about mRNA:

a. only 1% of the cellular RNA is mRNA

b. human mRNA is monocistronic

c. introns are not transcribed into mRNA

d. mutation of the DNA sequence invariably gives rise to 
    a change in the amino acid sequence of the resulting 
    protein

e. RNA polymerase II gives rise to protein encoding 
    mRNA

Answera.T   b.T  c.F  d.F  e.T
Human mRNA is monocistronic meaning each mRNA codes for one protein. Introns are transcribed and then spliced out of the RNA before mRNA leaves the nucleus. The same amino acid may be encoded by multiple codons. As a result, mutation of DNA sequence does not always give rise to change in the amino acid sequence.

 
 

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