gene expression

Question 1

define genome (1)

Answer 1

all the DNA in an organism/ entire set of genes of a cell or organism

Question 2

define proteome (1)

Answer 2

the entire range of proteins that an organism is able to produce

Question 3

why do antibodies bind to transcription factors? (2)

Answer 3

• antibody and transcription factors have specific tertiary structures
• complementary

Question 4

name and describe the roles of 2 enzymes used to insert DNA fragments into plasmids. (2)

Answer 4

DNA ligase- joins DNA to plasmid

restriction enzyme- cuts plasmid

Question 5

suggest 2 features of the structure of different proteins that enable them to be separated by gel electropheresis (2)

Answer 5

• different R groups
• charge

Question 6

describe how alterations to tumour suppressor genes can lead to development of tumours. (3)

Answer 6

• increased methylation of tumour suppressor gene
• mutation in tumour suppressor gene
• amino acid sequence altered
• results in uncontrollable cell division

Question 7

describe how STRs could be removed from a sample of DNA (2)

Answer 7

• restriction endonucleases
• cut DNA at specific base sequences
  OR
  at recognition sites

Question 8

explain the importance of knowing the base sequences in PCR (2)

Answer 8

• for primers
• to produce a complementary base sequence

Question 9

give 2 features of STRs that enable them to be separated by gel electropheresis (2)

Answer 9

• number of nucleotides
• (Negative) charge

Question 10

give 2 reasons why bacteria are able to use human DNA to make human proteins (2)

Answer 10

• genetic code is universal
• mechanism of transcription/ translation is universal

Question 11

suggest and explain 1 reason why bacteria may not be able to make every human protein (1)

Answer 11

• cannot splice so cannot remove introns

Question 12

explain the purpose of a marker gene (1)

Answer 12

• shows the gene has been taken up

Question 13

scientists used a radioactively labelled DNA probe to show that cells contained SUT1 gene.

describe how they would do this (4)

Answer 13

• extract DNA and add restriction endonucleases
• separate fragments using gel electropheresis
• treat DNA to form single strands
• probe binds to base pair with the SUT1 gene
• use autoradiography to show bound probe

Question 14

when SUT1 gene is transcribed, sense SUT1 mRNA is made. the scientists genetically modified plants by inserting an extra gene, producing antisense SUT1 mRNA.

type A- genetically modified
type B- not genetically modified

suggest how production of antisense SUT1 mRNA in type A would reduce expression of the SUT1 gene. (4)

Answer 14

• antisense mRNA is complementary to sense mRNA
• antisense mRNA binds to sense mRNA
• ribosomes would not be able to bind
• less translation of mRNA/ less production of SUT1

Question 15

explain which 2 types of mutation make up a translocation mutation (2)

Answer 15

addition mutation because bases are added to 1 chromosome
deletion mutation because bases are removed from 1 chromosome

Question 16

explain why the effects of a single additional base may have: (3)
A) considerable effect on polypeptide
B) little effect on polypeptide

Answer 16

A) changes all subsequent codons
frame shift to right
if inserted early then most codons will be changed and more AAs are changed

B) if inserted at the end of sequence then few codons are changed, few AAs differ

Question 17

a mutation causes 3 bases to duplicate. explain how effects of this differ if the duplicated bases are consecutive rather than in 3 separate locations (3)

Answer 17

consecutive: adds an AA;
subsequent codons are unaffected

separate: frame shift to right; changes the AAs

Question 18

suggest 2 reasons why the addition of a single base into a DNA sequence may not alter the AA sequence (2)

Answer 18

1. genetic code is degenerate
2. frame shift may not alter some codons as replacement bases could be same as original ones.

Question 19

explain what is meant by totipotent cells (1)

Answer 19

can differentiate into any type of cell

Question 20

distinguish between: (4)
- totipotent
- pluripotent
- multipotent
- unipotent

Answer 20

1. differentiates into any cell, in zygote
2. differentiates into all cells but placenta, in embryo & fetus
3. differentiates into limited no of cells, in umbilical cord & some adult tissues
4. differentiates into only 1 type of cell, found in adult tissue e.g. skin

Question 21

all cells posess the same genes yet a skin cell can produce keratin but not myosin, whilst a muscle cell produces myosin but not keratin.
explain why (2)

Answer 21

• not all genes are expressed
• in skin, genetic code for keratin is translated into keratin protein, myosin genetic code is not translated.

Question 22

suggest why skin cells can divide by being unipotent when cells of other organs cannot (1)

Answer 22

skin cells are on outside of body- are subject to damage and need replacing frequently

Question 23

what is the role of a transcription factor (1)

Answer 23

stimulates transcription of a gene

Question 24

describe how oestrogen stimulates expression of a gene (5)

Answer 24

1. diffuses through phospholipid portion of CSM into cytoplasm
2. binds to receptor protein of TF
3. changes shape of DNA binding site of TF- can now bind to DNA
4. TF enter nucleus via nuclear pore
5. TF binds to DNA
6. stimulates transcription of the gene

Question 25

explain what is meant by epigenetics (2)

Answer 25

- process by which environmental factors cause heritable changes in gene function - without changing the base sequence of DNA

Question 26

name 2 mechanisms by which changes in the environment can inhibit transcription (2)

Answer 26

- increased DNA methylation - decreased histone acetylation

Question 27

suggest how siRNA could be used to: (2) A) identify roles of genes in a biological pathway B) prevent certain diseases

Answer 27

A) siRNA that blocks a gene can be added to cells. observe effects and determines role of blocked gene. B) siRNA can block the gene causing the disease

Question 28

the enzyme histone deactlyase removes acetyl groups. suggest effect of this on: (4) A) arrangement of chromatin B) transcription

Answer 28

A) removes acetyl groups so histone is more positive; stronger attraction to negative phosphate; chromatin more condensed B) TFs cant bind due to condensed chromatin; transcription ceases

Question 29

describe a process by which oestrogen may cause breast cancer in post-menopausal women

Answer 29

- fat cells make more oestrogens - these release inhibitor molecule that prevents transcription - causes proto oncogenes to develop into oncogenes - increases rate of cell division--> tumour

Question 30

explain why activation of a proto-oncogene can cause development of tumour while it requires deactivation of a tumour suppressor gene to do so

Answer 30

- increases rate of cell division - their activation produces a tumour - TSGs decrease cell division so their deactivation produces tumours

Question 31

suggest 2 reasons why surgical removal of a benign tumour is usually sufficient (2)

Answer 31

have adhesion molecules so keeps tumour compact and easy to remove in 1 go.

Question 32

suggest why surgical removal of malignant tumour requires follow up chemotherapy (1)

Answer 32

spreads to other body parts

Question 33

HDAC removes acetyl groups from histones. phenylbutryic acid is an inhibitor of HDAC. suggest how phenylbutyric acid may be used to treat cancer.

Answer 33

HDAC makes chromatin more condensed and inaccessible to TFs; transcription stops; inhibitor starts transcription again and expresses genes which repair DNA;

Question 34

explain why determining the proteome of simple organisms is easier than complex ones like humans (2)

Answer 34

- not ass with histones - only 1 circular plasmid - no introns

Question 35

explain how knowledge of proteome of a pathogen helps control the disease it causes

Answer 35

identify proteins that act as antigen on pathogens surface; create vaccine;