Gene expression

Question 1

What is a gene mutation

Answer 1

A change in the base sequence of DNA

Question 2

What is a mutagenic agent

Answer 2

A factor that increases the rate of mutation

Question 3

How can a gene mutation lead to production of a non functional enzyme/protein

Answer 3

Changes sequence of base triplets so codons on MRNA
Changes sequence of amino acids
Changes position of all bonds
Changes tertiary structure
Enzymes specific - active site changes, substrate cannot bind

Question 4

Different gene mutations

Answer 4

Substitution - base is replaced
Addition - base is added
Deletion - base is lost
Duplication - base is repeated
Inversion - a sequence of bases detaches and rejoins in the same position in the reverse order
Transolcation - sequence of bases detach and inserted in a different location within the same chromosome

Question 5

Explain why not all gene mutations affect order of amino acids

Answer 5

Some substitutions only change 1 triplet code
Genetic code is degenerate
Some mutations occur in introns which don’t code for AA so are removed through splicing

Question 6

Explain why a change in amino acid sequence is not always harmful

Answer 6

May not change tertiary structure
May give a selective advantage

Question 7

What is a frameshift

Answer 7

Mutation changes the number of nucleotides by a number not divisible by 3
Shifts the way genetic code is read

Question 8

How can mutations lead to production of shorter polypeptides

Answer 8

Deletion or translation

Question 9

What are stem ce;;s

Answer 9

Unspecialised cells capable of dividing by mitosis and differentiating into other cells

Question 10

Totipotent cells

Answer 10

Occur in embryos
Can divide and diffrentiate into any type of body cell

Question 11

Pluripotent cells

Answer 11

Found in embryos
Can divide and diffrentiate into most types of cells

Question 12

Multipotent cells

Answer 12

Found in mature mammals
Can divide and diffrentiate into limited cell type

Question 13

Unipotent cells

Answer 13

Only one cell type

Question 14

How can stem cells be used to treat human disorders

Answer 14

Translated into patients to divide in unlimited numbers
Then diffrentiate into required healthy cells

Question 18

What are transcription factors

Answer 18

Proteins which regulate the transcription of target genes by binding to a specific DNA base sequence on a promoter region

Question 19

How can transcription be regulated using TF

Answer 19

Move from cytoplasm to nucleus
Bind to DNA at specific base sequence on promoter gene
inhibits or promotes transcription by allowing DNA polymerase to bind

Question 20

How does oestrogen affect transcription

Answer 20

Diffuses into the cell and oestrogen binds to its receptor (an inactive TF)
This changes the shape of the inactive TF forming an active TF
This diffuses into the nucleus and binds to a specific DNA base sequence on the promoter region
This stimulates transcription of target gene forming MRNA by helping RNA polymerase bind

Question 21

Explain why oestrogen only affects target cells

Answer 21

Other cells don’t have oestrogen receptors

Question 22

What is epigenetic

Answer 22

Heritable changes in gene function without changing the base sequence
Caused by environmental factors

Question 23

What is the epigenetic control in inhibiting transcription

Answer 23

increased methylation
Decreased acetylation

Question 24

What is the epigenetic control in allowing transcription

Answer 24

Decreased methylation
Increased acetylation

Question 25

How can methylation inhibit transcription

Answer 25

Increased methylation DNA wrapped more tightly around histones Preventing TF and DNA polymerase binding

Question 26

How can acetylation inhibit transcription

Answer 26

Decreased acetylation of histones increases positive charge of histones So histones bind to DNA as it is more negatively charged more tightly preventing TF and DNA polymerase binding

Question 27

Explain the relevance of epigenetics on disease development and treatment

Answer 27

Environmental factors (eg. diet, stress, toxins) can lead to epigenetic changes ● These can stimulate / inhibit expression of certain genes that can lead to disease development ○ Increased methylation of DNA OR decreased acetylation of histones inhibits transcription ○ Decreased methylation of DNA OR increased acetylation of histones stimulates transcription ● Diagnostic tests can be developed that detect these epigenetic changes before symptoms present ● Drugs can be developed to reverse these epigenetic changes

Question 28

What is RNA interference

Answer 28

Inhibition of translation of MRNA produced from target genes by RNA molecules This inhibits expression of a target gene

Question 29

Describe the regulation of translation by RNA interference

Answer 29

SIRNA bind to a protein It is synthesised as double stranded RNA Single stranded SIRNA binds to target MRNA on complementary base sequence Leads to hydrolysis of MRNA into fragments Preventing transaltion

Question 30

How to tumours form

Answer 30

Mutations in DNA can lead to uncontrolled cell division Mass of abnormal cells - tumour

Question 32

Function of tumour suppressor genes

Answer 32

They code for proteins that slow the cell cycle or cause apoptosis for tumour cells

Question 33

Explain the role of tumour suppressor genes in the development of tumours

Answer 33

A mutation in DNA base sequence can lead to the production of a non functional protein by changed AA sequence Decreased acetylation of increased methylation prevents: - Production of protein - Polymerase and Tf binding so inhibits transcription -Leads to uncontrolled cell division

Question 34

Function of proto Onco genes

Answer 34

Stimulate cell division

Question 35

Role of oncogenes in development of tumours

Answer 35

Mutation in DNA leads to overproduction of a protein Decreased methylation or increased acetylation increases production of protein Stimulates RNA polymerase to bind Stimulates transcription Uncontrolled cell division