Control of Gene Expression - Transcription and Cancer

Question 1

what stimulates DNA to start transcription?

Answer 1

transcription factors

Question 2

which genes will transcriptional factors stimulate transcription for?

Answer 2

genes switched on only

Question 3

what can activate transcription factors?

Answer 3

oestrogen

Question 4

how does oestrogen activate transcriptional factors?

Answer 4

diffuses through cell membrane and binds with complementary transcriptional factor in cytoplasm

transcriptional factor changes shape

enters nucleus through a pore

binds with DNA at specific base sequence - stimulates transcription

Question 5

how do transcriptional factors stimulate the transcription of genes?

Answer 5

by binding to a specific base sequence in DNA

Question 6

why can’t transcriptional factors bind to genes that are switched off?

Answer 6

the site on the DNA that binds to the transcriptional factors are not active

Question 7

what determines whether a gene is switched on or off?

Answer 7

association of histones

chromatin

Question 8

how does the association of histones affect whether a gene is turned on or off?

Answer 8

histones affect how tightly the DNA can wind around itself, so determining if the genes are accessible or inaccessible

Question 9

when the association of histones is weak - is the gene switched on or off and why?

Answer 9

the DNA is loosely packed so it is accessible to transcriptional factors and the gene is switched on

Question 10

when the association of histones with DNA is strong - is the gene switched on or off and why?

Answer 10

DNA tightly packed around the histones so is inaccessible to transcriptional factors

gene is switched off

Question 11

what affects the association of histones with DNA?

Answer 11

acetylation of histones

methylation of DNA

Question 12

how does acetylation of histones affect their association with DNA?

Answer 12

it affects the overall charge of the histone - which then affects how associated it is with the DNA sequence

Question 13

what happens when acetyl groups are added to histones?

Answer 13

the histones are less associated with DNA

Question 14

explain how adding acetyl groups to histones can switch on a gene

Answer 14

acetyl group added to histone

histone association with DNA decreases

DNA becomes less tightly wrapped

genes become accessible to transcriptional factors

gene switched on

Question 15

what happens when acetyl groups are removed from histones?

Answer 15

the association of histones with DNA increases

Question 16

explain how deacetylation leads to genes being switched off

Answer 16

acetyl group removed from histone

histone association with DNA increases

DNA becomes more tightly wrapped

genes inaccessible to transcriptional factors

gene switched off

Question 17

what are the ways that methylation can affect whether genes are switched on or off?

Answer 17

affecting binding of transcriptional factors

affects rates of deacetylation of histones

Question 18

during methylation, where is the methyl group added?

Answer 18

to a cytosine base of DNA

Question 19

how does methylation affect the binding of transcriptional factors?

Answer 19

increased methylation prevents binding of transcriptional factors

Question 20

how does methylation affect levels of acetylation of histones?

Answer 20

increased methylation induces deacetylation by attracting histones

Question 21

explain how increased methylation can switch off a gene

Answer 21

increased methylation

deacetylation induced

increased association between DNA and histones

DNA more tightly wrapped

genes innaccesible to transcriptional factors

gene switched off

Question 22

explain how decreased methylation can turn on a gene

Answer 22

decreased methylation

increased acetylation

association between DNA and histone decreases

DNA wrapped less tightly

gene more accessible to transcriptional factors

gene switched on

Question 23

how does chromatin affect whether genes are switched on or off?

Answer 23

different forms of chromatin can affect how tightly wound DNA is

Question 24

what are the types of chromatin that effect whether genes are switched on or off?

Answer 24

heterochromatin

euchromatin

Question 25

what effect does heterochromatin have on DNA?

Answer 25

winds DNA in tightly

Question 26

what effect does euchromatin have on DNA?

Answer 26

packs DNA looser

Question 27

what is the difference between heterochromatin and euchromatin?

Answer 27

heterochromatin is a dense form of chromatin euchromatin lightly packed form

Question 28

what is epigenetics?

Answer 28

where environmental factors cause heritable changes without changing the order of the DNA code

Question 29

what is the epigenome?

Answer 29

the tags on DNA wound around histones

Question 30

what does the epigenome determine?

Answer 30

the shape of DNA

Question 31

what is significant about the epigenome determining the shape of DNA?

Answer 31

the shape keeps inactive genes silenced

Question 32

what is epigenetic silencing?

Answer 32

the epigenome keeping inactive genes silenced

Question 33

what is the epigenome's cellular memory?

Answer 33

the epigenome remembers signals it has received throughout its lifetime

Question 34

what is an example of the epigenome being flexible?

Answer 34

tags can be changed by the environment

Question 35

what environmental factors can affect the epigenome?

Answer 35

diet, stress

Question 36

where does the epigenome receive signals from?

Answer 36

other cells in the body when in the early foetal stage - from mother as well

Question 37

how can epigenetic tags be removed?

Answer 37

by radiation

Question 38

what happens if mRNA is destroyed before translation?

Answer 38

protein synthesis cannot occur

Question 39

what can cause mRNA to be destroyed before translation?

Answer 39

siRNA

Question 40

what is siRNA?

Answer 40

small interfering RNA molecule that stops the translation of mRNA

Question 41

why is siRNA useful?

Answer 41

prevents synthesis of proteins from genes that can cause diseases

Question 42

how is siRNA made?

Answer 42

an enzyme cuts dsRNA into siRNA

Question 43

how does siRNA prevent mRNA from being translated?

Answer 43

siRNA binds with the enzyme used to cut dsRNA into siRNA siRNA and enzyme bind with complementary bases on mRNA enzyme cuts mRNA into sections mRNA can no longer be translated

Question 44

what is dsRNA?

Answer 44

double stranded RNA | (synthesized by humans)

Question 45

what genetic factor causes cancer?

Answer 45

damage to genes that regulate mitosis and cell cycle

Question 46

compare the growth rates of benign and malignant tumours

Answer 46

benign - slow malignant - quick

Question 47

what is the appearance of nuclei in benign tumours?

Answer 47

normal

Question 48

what is the appearance of nuclei in malignant tumours?

Answer 48

larger and darker holding more DNA to divide

Question 49

what is the differentiation of cells in benign tumours?

Answer 49

same differentiation of cells as before the tumour grew

Question 50

what is the differentiation of cells in malignant tumours?

Answer 50

de-differentiated cells

Question 51

do benign tumours spread?

Answer 51

no - due to adhesion molecules keeping the tumour together

Question 52

do malignant tumours spread?

Answer 52

yes as they have no adhesion molecules so spread through bloodstream

Question 53

do benign tumours have a capsule around the tumour?

Answer 53

yes - surrounding the whole tumour

Question 54

what do malignant tumours contain instead of a capuse?

Answer 54

finger-like projections

Question 55

what are the treatments for benign tumours?

Answer 55

surgery

Question 56

what are the treatments for malignant tumours?

Answer 56

chemotherapy, radiotherapy, surgery

Question 57

what genes can cause cancer?

Answer 57

tumour suppressor genes oncogenes

Question 58

what is the role of a proto-oncogene?

Answer 58

to stimulate cell division when growth factors attach to a protein receptor, activating a gene that tells DNA to replicate

Question 59

what happens when a proto-oncogene mutates into an oncogene?

Answer 59

oncogene is permanently activated so always stimulating cell to divide regardless of growth factors receptor protein always activated may also produce more growth factors

Question 60

can oncogenes be inherited?

Answer 60

yes

Question 61

what is the role of tumour supressor genes?

Answer 61

slow down cell division repair DNA mistakes tells cells when to die (apoptosis)

Question 62

what happens to mutated tumour surpressor genes?

Answer 62

become inactivated

Question 63

what is the effect on the cell of mutated tumour supressor genes?

Answer 63

most die some clone to form tumours due to uncontrolled division

Question 64

are tumour supressor genes inherited?

Answer 64

not normally, most acquired by mutation

Question 65

how can hypermethylation lead to cancer?

Answer 65

hypermethylation occurs in specific region of tumour supressor gene tumour surpressor gene inactivated gene switched off

Question 66

how can hypomethylation lead to cancer?

Answer 66

hypomethylation of oncogenes, oncogenes more activated

Question 67

what is the role of oestrogen?

Answer 67

regulates menstrual cycle

Question 68

why is it more common for women to develop breast cancer after menopause?

Answer 68

reduced production of oestrogen in ovaries fat cells in breasts produce more to compensate oestrogen can stimulate tumour growth as it is a transcriptional factor