Dr Kramer

Question 1

What is a Gene?

Answer 1

A unit of heredity which is transferred from a parent to offspring and is held to determine some characteristic of the offspring.

Question 2

What is a Chromosome?

Answer 2

The arrangement/mapping of genes (Chromosomes are vital during meiosis as they allow for crossing over of genetic information)

Question 3

How do differences arise?

Answer 3

Mutation - The generator

Meiosis - The manipulator

Question 4

What does a typical eukaryotic gene include and how is it processed to produce a polypeptide?

Answer 4

Gene is made up of exons (coding regions) and introns (non-coding regions). The gene is transcribed by RNA polymerase to mRNA which is then processed and spliced (methylation of the 5’ end and polyadenylation of the 3’ end). Ribosomes and tRNAs are then used to translate the mature RNA into a polypeptide.

Question 5

How are genes expressed?

Answer 5

Top strand = coding + non-transcribed

Bottom strand = non-coding, template + transcribed

Question 6

In which direction is DNA read during transcription?

Answer 6

3’ to 5’

Question 7

In which direction is mRNA synthesised?

Answer 7

5’ to 3’

Question 8

In which direction is mRNA read during translation?

Answer 8

3’ to 5’

Question 9

In which direction is a polypeptide synthesised?

Answer 9

N to C

Question 10

What is the triplet reading frame and what are the different types?

Answer 10

The grouping of three successive bases in a sequence of DNA that constitutes the codons for the amino acids encoded by the DNA. 3 different frames Frame 1 (0), Frame 2 (+1) and Frame 3 (-1). Reading frame with the longest sequence before a stop codon is used.

Question 11

What is the genetic code?

Answer 11

Triplet code = 64 possible codons. 61 codons code for amino acids with 1 (AUG) = methionine (start codon). 3 codons (UAG, UAA and UGA) do not code for amino acids but are used as stop codons.

Question 12

Is the genetic code universal?

Answer 12

YES

Question 13

What does the linear structure of codons determine?

Answer 13

The linear structure of amino acids.

Question 14

What proteins subunits are found in haemoglobin?

Answer 14

α = 141 amino acid residues (Chromosome 16)
β = 146 amino acid residues (Chromosome 11)

Question 15

What is a definition of a gene?

Answer 15

A gene produces a functional unit. Can be a sequence of amino acids in a polypeptide or a sequence of nucleotides in an untranslated RNA (ribosomal or RNA)

Question 16

What is a mutation?

Answer 16

A heritable alteration in a gene or chromosome (a change in the sequence of nucleotides/bases). Also the process that produces alleles.

Question 17

What is a single nucleotide change?

Answer 17

Base substitution and or base additions or deletions.

Question 18

What is a large scale change?

Answer 18

Chromosome rearrangements and transposable elements

Question 19

What kind of mutations cause changes in gene product?

Answer 19

Transition - changes to the same type of base (purine to purine or pyrimidine to pyrimidine).
Transversion - changes to a different base type (purine to pyrimidine).

Question 20

What symptoms are seen in those with sickle cell anaemia?

Answer 20

Susceptibility to infection, weakness, impaired growth and anaemia in oxygen supply is limited.

Question 21

What mutation causes sickle cell anaemia?

Answer 21

Mutation occurs in codon 7 on chromosome 11. (Base substitution mutation)

Question 22

Do all mutations have an effect?

Answer 22

No because of the redundant nature of the genetic code so more than one codon codes for the amino acid.

Question 23

What kind of mutations cause changes to the amount of gene product produced?

Answer 23

Mutations which affect translation and transcription (tend to not be in the gene). May alter promoter activity, alter the site of initiation, prevent splicing of mRNA and reduce the stability of mRNA produced (less chance of being transcribed).

Question 24

What kind of mutations cause changes to polypeptide length?

Answer 24

Deletions and additions (Hb Lyon has 2 less amino acids in the β chain)
Chain termination- Change a sense to a stop codon.
Frameshift - single base addition or deletion may move the reading frame and stop codons now code for amino acids. (Seen in α-wayne where a deletion has occured so chain is 139 amino acids long). Deletion = frameshit (-1) Addition = frameshift (+1)

Question 25

What types of chromosomal mutations are there?

Answer 25

Deletion, Addition/insertion, Inversion, Translocation.

Question 26

How do transposable elements cause mutation?

Answer 26

A transposable element can be randomly inserted into a gene causing the gene to be deactivated.

Question 27

What is a transposable element?

Answer 27

A sequence of DNA, smaller than a gene, which is able to move and be inserted into parts of the genome.

Question 28

How may transposable elements be used in the food industry?

Answer 28

Birdseye use transposable elements to produce sweet peas as they inactivate the gene responsible for producing a ‘starch-branching enzyme resulting in the accumulation of sugars.