Gene Expression

Question 1

What are the three possible consequences of substitution of bases?

Answer 1

• The formation of a stop codon, cutting off the amino acid sequence prematurely,
• The formation of a new codon and a singe different amino acid,
• The formation of a new codon that codes for the same amino acid so there is no change.

Question 2

What happens when a base is deleted?

Answer 2

Causes a frame shift left so most triplets will be incorrect.

Question 3

Name 6 gene mutations.

Answer 3

• Substitution,
• Deletion,
• Addition,
• Duplication of bases,
• Inversion of bases,
• Translocation of bases.

Question 4

What happens when a base is added?

Answer 4

Causes a frame shift right, so most triplets will be incorrect.

Question 5

What is duplication of bases and what happens?

Answer 5

One or more bases are repeated, produces a frame shift right.

Question 6

What is inversion of bases?

Answer 6

A group of bases becomes separated the rejoin at the same position in the inverse order.

Question 7

What is translocation of bases?

Answer 7

A group of bases become separated from the DNA sequence on one chromosome and become inserted into the DNA sequence of a different chromosome.

Question 8

Name 2 mutagenic agents.

Answer 8

High energy ionising radiations and chemicals.

Question 9

What is a totipotent cell?

Answer 9

Has the ability to give rise to all types of cells, such as fertilised eggs.

Question 10

What is the name for cells which can differentiate into other types of cell?

Answer 10

Stem cells.

Question 11

Name 4 types of stem cell.

Answer 11

1. Embryonic stem cells,
2. Umbilical cord blood stem cells,
3. Placental stem cells,
4. Adult stem cells.

Question 12

What is a pluripotent stem cell and give two examples?

Answer 12

Can differentiate into almost any type of cell. Eg. embryonic stem cells and fetal stem cells.

Question 13

What is a multipotent stem cell and where are they found?

Answer 13

Can differentiate into a limited number of specialised cells. Found in adults.

Question 14

What is a unipotent stem cell and where are they made?

Answer 14

Can only differentiate into one type of cell, they are made in adult tissue.

Question 15

What is an iPS cell?

Answer 15

Body cells (unipotent cells) which have been genetically altered to give them characteristics of embryonic stem cells which are pluripotent.

Question 16

Describe the effect of oestrogen on gene transcription.

Answer 16

Oestrogen diffuses into cells (is lipid-soluble) and then binds with a complementary transcriptional factor, this changes the shape of the transcriptional factors DNA binding site so it can bind to DNA. This enters nucleus binding to base sequence and initiating transcription.

Question 17

What is the epigenome?

Answer 17

Chemical tags on DNA which are influenced by the environment.

Question 18

What is chromatin?

Answer 18

The DNA histone complex

Question 19

What affect does adding an acetyl group have on DNA and transcription?

Answer 19

Decreases the attraction of phosphates on DNA and histones so the DNA is less tightly wound and the promoter regions that transcription factors bind to are available. There for mRNA can be produced - the gene is switched on.

Question 20

What affect does adding a methyl group have on DNA and transcription?

Answer 20

The methyl group is added to cytosine and can prevent the binding of transcriptional factors to the promoter region or can attract proteins they condense the DNA-histone complex making the DNA inaccessible.

Question 21

How can methylation cause cancers?

Answer 21

If the promoter region of genes which produce proteins that prevent mutations or prevent uncontrolled cell growth are highly methylated.

Question 22

How can RNA interfere with gene expression?

Answer 22

By breaking down mRNA before it can be translocated.

Question 23

How is siRNA produced?

Answer 23

An enzyme cuts large double-stranded molecules of RNA into smaller sections which then combines with an enzyme.

Question 24

How does the siRNA break down mRNA?

Answer 24

The siRNA guides the enzyme it is attached to to mRNA by pairing up its bases with the complementary ones on the single stranded mRNA. The enzyme then cuts the mRNA into smaller sections.

Question 25

What are cancerous and non-cancerous tumours called?

Answer 25

Malignant and benign.

Question 26

What is an oncogene?

Answer 26

A mutation of a proto-oncogene. These stimulate cells to divide. The mutation can cause it to remain switched on if

• the receptor protein on the cell surface membrane is permanently activated,
• the oncogene codes for a growth factor than stimulates division.

Question 27

Give 3 forms of tumour suppressor genes

Answer 27

TP53
BRCA1
BRCA2

Question 28

What is the p53 protein involved in?

Answer 28

apoptosis

Question 29

What is bioinformatics?

Answer 29

The science of collecting and analysing complex biological data such as genetic codes.

Question 30

What is whole genome shotgun sequencing?

Answer 30

The DNA is cut into many small, easily sequenced sections, then computer algorithms align overlapping segments to assemble the entire genome.

Question 31

Why is determining the proteome of prokaryotic cells easy?

Answer 31

There is only one circular piece of DNA that is not associated with histones.
There are no introns which are typical of eukaryotes.