Genetics 2

Question 1

What are the names of the nucleotides that contain different nitrogenous bases?

Answer 1

Adenosine triphosphate (ATP)

Guanosine triphosphate (GTP)

Cytidine triphosphate (CTP)

Uridine triphosphate (UTP)

Deoxythymidine triphosphate (dTTP)

Question 2

Name the two types of purines and describe how they are formed.

Answer 2

Adenylate (AMP):

1. Inosinate (IMP) + aspartate -> Adenylosuccinate (by adenylosuccinate synthetase, using GTP)
2. Adenylosuccinate -> adenylate/adenosine monophosphate (AMP)

Guanylate (GMP):

1. Inosinate (IMP) -> xanthylate (XMP)
2. Xanthylate + amine group from glutamine -> guanylate/guanosine monophosphate (GMP) (using ATP)

Question 3

How are pyrimidines synthesised?

Answer 3

Carbamoyl phosphate + aspartate + ribose 5-phosphate

Question 4

What is the salvage pathway of purines and pyrimidines?

Answer 4

Adenosine phosphoribosyltransferase catalyses formation of AMP from free adenine and 5-phosphoribosyl-1-pyrophosphate (PRPP).

Hypoxanthine-guanine phosphoribosyltransferase catalyses same reaction with guanine instead of adenine.

Question 5

List the drugs that affect the way nucleotides are biosynthesised.

Answer 5

Azaserine + acivicin

Fluorouracil

Methotrexate

Trimethoprim

Allopurinol

Question 6

Define cytogenetics.

Answer 6

Cytogenetics = using an individual’s karyotype to determine its sex.

Question 7

What is the function of PCR?

Answer 7

Focus on a specific fragment of DNA and copy it billions of times over.

Question 8

How does PCR work?

Answer 8

Primers bind to specific fragments of DNA.

DNA polymerase repeatedly copies that DNA fragment.

Number of DNA copies doubles with each cycle.

Question 9

How is the DNA produced in PCR used?

Answer 9

DNA separated by size using agarose gel electrophoresis.

Ladders (sequences of known sizes) are used as markers.

DNA amplified by PCR can then be sequenced in order to identify genetic mutations.

Question 10

Describe Quantitative Reverse Transcriptase Polymerase Chain Reaction (RT-PCR / RT-qPCR).

Answer 10

Used to determine levels of mRNA in a sample by using reverse transcriptase (converts RNA to DNA).

Resulting DNA amplified by PCR.

Question 11

Describe Quantitative Real Time Polymerase Chain Reaction (qPCR / qRT-PCR).

Answer 11

Uses a fluorescent readout to quantify DNA/mRNA concentration.

Simple method uses SYBR green dye which fluoresces when bound to double-stranded DNA.

Specific probes can be used to label specific DNA strands.

Question 12

What are the two ways in which gene therapy replaces a defective gene with a functional copy?

Answer 12

1. Via vectors (e.g. modified viruses) that can directly enter the target cells in an individual.
2. Via cells from the individual that have had the genes grown in them in the lab.

Question 13

List GMOs and give examples.

Answer 13

GM bacteria - insulin, plaque

GM mice - “knockout”

GM pigs - organ transplant

GM foods - resistance, nutritional value

Question 14

Define ‘clone’.

Answer 14

Clone = a genetically identical copy of an animal.