gene expression Flashcards
define genome (1)
all the DNA in an organism/ entire set of genes of a cell or organism
define proteome (1)
the entire range of proteins that an organism is able to produce
why do antibodies bind to transcription factors? (2)
- antibody and transcription factors have specific tertiary structures
- complementary
name and describe the roles of 2 enzymes used to insert DNA fragments into plasmids. (2)
DNA ligase- joins DNA to plasmid
restriction enzyme- cuts plasmid
suggest 2 features of the structure of different proteins that enable them to be separated by gel electropheresis (2)
- different R groups
- charge
describe how alterations to tumour suppressor genes can lead to development of tumours. (3)
- increased methylation of tumour suppressor gene
- mutation in tumour suppressor gene
- amino acid sequence altered
- results in uncontrollable cell division
describe how STRs could be removed from a sample of DNA (2)
- restriction endonucleases
- cut DNA at specific base sequences
OR
at recognition sites
explain the importance of knowing the base sequences in PCR (2)
- for primers
- to produce a complementary base sequence
give 2 features of STRs that enable them to be separated by gel electropheresis (2)
- number of nucleotides
- (Negative) charge
give 2 reasons why bacteria are able to use human DNA to make human proteins (2)
- genetic code is universal
- mechanism of transcription/ translation is universal
suggest and explain 1 reason why bacteria may not be able to make every human protein (1)
- cannot splice so cannot remove introns
explain the purpose of a marker gene (1)
- shows the gene has been taken up
scientists used a radioactively labelled DNA probe to show that cells contained SUT1 gene.
describe how they would do this (4)
- 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
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)
- 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
explain which 2 types of mutation make up a translocation mutation (2)
addition mutation because bases are added to 1 chromosome
deletion mutation because bases are removed from 1 chromosome
explain why the effects of a single additional base may have: (3)
A) considerable effect on polypeptide
B) little effect on polypeptide
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
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)
consecutive: adds an AA;
subsequent codons are unaffected
separate: frame shift to right; changes the AAs
suggest 2 reasons why the addition of a single base into a DNA sequence may not alter the AA sequence (2)
- genetic code is degenerate
- frame shift may not alter some codons as replacement bases could be same as original ones.
explain what is meant by totipotent cells (1)
can differentiate into any type of cell
distinguish between: (4)
- totipotent
- pluripotent
- multipotent
- unipotent
- differentiates into any cell, in zygote
- differentiates into all cells but placenta, in embryo & fetus
- differentiates into limited no of cells, in umbilical cord & some adult tissues
- differentiates into only 1 type of cell, found in adult tissue e.g. skin
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)
- not all genes are expressed
- in skin, genetic code for keratin is translated into keratin protein, myosin genetic code is not translated.
suggest why skin cells can divide by being unipotent when cells of other organs cannot (1)
skin cells are on outside of body- are subject to damage and need replacing frequently
what is the role of a transcription factor (1)
stimulates transcription of a gene
describe how oestrogen stimulates expression of a gene (5)
- diffuses through phospholipid portion of CSM into cytoplasm
- binds to receptor protein of TF
- changes shape of DNA binding site of TF- can now bind to DNA
- TF enter nucleus via nuclear pore
- TF binds to DNA
- stimulates transcription of the gene
explain what is meant by epigenetics (2)
- process by which environmental factors cause heritable changes in gene function
- without changing the base sequence of DNA
name 2 mechanisms by which changes in the environment can inhibit transcription (2)
- increased DNA methylation
- decreased histone acetylation
suggest how siRNA could be used to: (2)
A) identify roles of genes in a biological pathway
B) prevent certain diseases
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
the enzyme histone deactlyase removes acetyl groups. suggest effect of this on: (4)
A) arrangement of chromatin
B) transcription
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
describe a process by which oestrogen may cause breast cancer in post-menopausal women
- 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
explain why activation of a proto-oncogene can cause development of tumour while it requires deactivation of a tumour suppressor gene to do so
- increases rate of cell division
- their activation produces a tumour
- TSGs decrease cell division so their deactivation produces tumours
suggest 2 reasons why surgical removal of a benign tumour is usually sufficient (2)
have adhesion molecules so keeps tumour compact and easy to remove in 1 go.
suggest why surgical removal of malignant tumour requires follow up chemotherapy (1)
spreads to other body parts
HDAC removes acetyl groups from histones. phenylbutryic acid is an inhibitor of HDAC.
suggest how phenylbutyric acid may be used to treat cancer.
HDAC makes chromatin more condensed and inaccessible to TFs;
transcription stops;
inhibitor starts transcription again and expresses genes which repair DNA;
explain why determining the proteome of simple organisms is easier than complex ones like humans (2)
- not ass with histones
- only 1 circular plasmid
- no introns
explain how knowledge of proteome of a pathogen helps control the disease it causes
identify proteins that act as antigen on pathogens surface;
create vaccine;
