Regulation of Transcription and Translation

Question 1

What is a transcription Factor ?

Where does it bind ?

Answer 1

protein that moves from the cytoplasm to DNA in the nucleus. It binds to a specific gene at the promoter region on the DNA, allowing RNA polymerase to bind and stimulate transcription, to form mRNA

Question 2

What does it mean if a gene is switched off ?

Answer 2

the promotor region is blocked
transcription factor cannot bind to the DNA
transcription is prevented, therefore the gene is not expressed

Question 3

Why can Oestrogen diffuse directly through the phospholipid bilayer ?

Answer 3

its small and lipid-soluble

Question 4

Explain how Oestrogen initiates transcription

Answer 4

Oestrogen diffuses through the phospholipid bilayer into the cell as its lipid soluble
Once in the cytoplasm oestrogen binds to the receptor molecule of the transcription factor (Oestrogen and the receptor site are complimentary in shape to each other )
This causes a change in shape of the receptor on the transcriptional factor
When this happens it causes an inhibitor molecule to be released from the DNA binding site
The transcriptional factor then enters the nucleus
This then binds to the promoter region of the desired gene
Transcription begins through the stimulation and binding of RNA polymerase

Question 5

Suggest how Oestrogen could cause breast cancer to develop

Answer 5

activates genes by releasing inhibitor
transcription can then occur
if the gene affected controls cell division then it would be activated
cause proto-oncogenes to be mutated to oncogenes
could lead to uncontrolled cell division

Question 6

What is the definition of Epigenetics ?

Answer 6

Epigenetics is heritable changes in gene function without changes to the base sequence of DNA

Question 7

What is the definition of the Epigenome ?

Answer 7

The layer of chemical tags that cover the DNA and histones.

This will determine the shape of the DNA and histone complex

Question 8

What type of factors cause changes in gene function without mutating the DNA ?

Answer 8

Environmental factors such as alcohol, diet, stress, toxins, exercise, smoking

Question 9

Describe how DNA is arranged

Answer 9

DNA has a double helix shape
DNA associates with/ wraps around histone proteins
Packaged and condensed into chromosomes

Question 10

What is Epigenetic silencing ?

Answer 10

inactive genes are tightly packed and therefore do not get expressed

Question 11

Explain how genes can be ‘switched on’

Answer 11

They have a weak association with histones
Therefore the DNA is less condensed.
Promoter region accessible to transcription factor
Transcription can occur.
mRNA is formed.

Question 12

Explain how genes can be ‘switched off’

Answer 12

They have a strong association with histones
Therefore the DNA is more condensed
Promoter region is not accessible to transcription factor
Transcription cannot occur
mRNA is not formed

Question 13

What effect does increased methylation have on gene expression ?

Answer 13

causes gene to not be expressed

Question 14

How does increased methylation prevent gene expression ?

Answer 14

Causes DNA histone complex to become more condensed
promoter region is not accessible to transcription factors
Therefore Transcription cannot occur
mRNA is not formed
This results in the specific protein not being produced

Question 15

What effect does decreased methylation have on gene expression ?

Answer 15

causes gene to be expressed

Question 16

How does decreased methylation allow genes to be expressed ?

Answer 16

causes DNA histone complex to become less condensed
promoter region is accessible to transcription factors
Therefore transcription can occur
mRNA is formed

Question 17

What happens during DNA methylation?
What is the enzyme involved ?

Answer 17

During DNA methylation, a methyl group is added to carbon atom 5 of a cytosine base
Catalysed by Methyltransferase

Question 18

What are the two changes in the genes environment that inhibit transcription ?

Answer 18

decreased acetylation of histones
increased methylation of DNA

Question 19

What is Acetylation ?

Answer 19

Acetylation is the process where an acetyl group is transferred to a molecule

Question 20

What affect does decreased acetylation have on gene expression ?

Answer 20

causes genes to not be expressed

Question 21

How does decreased acetylation prevent gene expression ?

Answer 21

Decreased acetylation increases the positive charges on histones and increases their attraction to phosphate groups resulting in more stronger attraction and therefore a more condensed DNA histone complex
This means promoter region is inaccessible to transcription factors
Transcription does not occur
mRNA is not formed

Question 22

What effect does increased acetylation have on gene expression ?

Answer 22

causes genes to be expressed

Question 23

how does increased acetylation cause genes to be expressed ?

Answer 23

causes DNA histone complex to become less condensed
Promoter region is accessible to transcription factors
transcription can occur
mRNA is formed.

Question 24

Some colorectal cancer patients were found to have less DNA methylation than expected. Would this lead to more or less gene expression? How could this lead to cancer ?

Answer 24

More gene expression
More genes switched on
Less DNA methylation means DNA histone complex will be less condensed.
Promotor region is accessible to transcription factors
Transcription can occur
Oncogenes switched on

Question 25

In some normal cells there is no methylation in the promoter region, in some cancer cells this is methylated. What would the result of increased methylation be, can you think of a gene this could happen in to cause Cancer ?

Answer 25

DNA histone complex becomes more condensed
less binding of transcription factors to DNA
more genes turned off
This would affect Tumour Suppressor gene.
Less regulation of cell cycle

Question 26

How else can Gene expression be controlled?

Answer 26

by breaking down mRNA prior to translation

Question 27

Explain the process of how translation can be controlled by Small interfering RNA

Answer 27

An enzyme cuts large double stranded molecules of RNA (produced under laboratory conditions) into smaller sections of siRNA
one of the SiRNA strands combines with an enzyme (strand which is complimentary to the mRNA) to form a RISC
the SiRNA guides the enzyme to the mRNA by pairing up its bases with the complimentary base sequence on the mRNA
The enzyme then cuts the mRNA into smaller sections so it cannot be translated so the gene is not expressed as there is no polypeptide.

Question 28

What are the advantages of using siRNA ?

Answer 28

Used to identify the role of specific genes,
If siRNA with a known effect on a specific gene is deliberately added the effects of the absence of that gene can be observed

Question 29

RNA interference enables a cell to what ?

Answer 29

prevent the expression of a gene

Question 30

what is RNAi ?

Answer 30

small lengths of non coding RNA . they regulate gene expression by affecting translation.

Question 31

what are the two different types of RNAi ?

Answer 31

short interfering RNA (siRNA)
micro RNA (miRNA)- in plants and animals

Question 32

What is the function of RNAi ?

Answer 32

enables cells to prevent the expression of a gene

Question 33

How does RNAi cause a gene to be silenced ?

Answer 33

as a result of RNA interference, mRNA molecules produced by transcription of a gene can no longer be translated.
Even though the gene is switched on, the protein it encodes for is not produced.

Question 34

what are the two things that can happen to mRNA as a result of RNAi ?

Answer 34

mRNA is hydrolysed by an enzyme- RNA hydrolase
ribosomes are prevented from attaching to the mRNA
These mean that mRNA can no longer be translated

Question 35

Describe and explain how the expression of a target gene is affected by siRNA

Answer 35

has complimentary base sequence to the mRNA transcribed from the target gene
mRNA can no longer be translated
because mRNA has been hydrolysed into pieces