Regulation of transcription + translation

Question 1

What are transcriptional factors?

Answer 1

Proteins that bind to different base sequences of DNA so initiate transcription of genes

Question 2

How do transcriptional factors work?

Answer 2

• For transcription to begin, the gene is switched on by transcriptional factors that move from the cytoplasm into the nucleus
• Each transcriptional factor has a site that binds to a specific base sequence of the DNA in the nucleus
• When it binds it causes this region of DNA to begin the process of transcription
• mRNA is produced + the info it carries is translated into a polypeptide
  -When a gene is not being expressed, the site on the transcriptional factor that binds to DNA is not active
• As the site on the transcriptional factor binding to DNA is inactive, it can’t cause transcription + polypeptide synthesis

Question 3

How does oestrogen initiate transcription?

Answer 3

Oestrogen is a steroid hormone that can initiate transcription
- Oestrogen is lipid soluble so can diffuse through cell surface membrane
- It binds to a receptor site on a transcriptional factor
- When it binds, it changes the shape of the DNA binding site on the transcriptional factor + this makes it complimentary to DNA so it can bind to it (its activated)
- Activated transcriptional factor can enter nucleus through nuclear pore + can bind to specific base sequence on DNA
- This stimulates transcription of the gene

Question 4

What is epigenetics?

Answer 4

Gene expression (protein synthesis) is controlled by epigenetics
- The heritable change in gene function, without changes to the base sequence of DNA
These changes are causes by changes to the environment + can inhibit transcription

Question 5

What is the epigenome?

Answer 5

Factors such as diet, stress + toxins can add chemical tags to the DNA + a single layer of chemical tags on DNA is called the epigenome, which impacts the shape of the DNA histone complex + whether the DNA is tightly wound so won’t be expressed or unwound so it will be expressed
If the DNA is tightly wound, then transcriptional factors can’t bind so the epigenome can inhibit transcription

Question 6

Methylation of DNA

Answer 6

• Increased methylation of DNA inhibits transcription
• When methyl groups are added to DNA, they attach to the cytosine base
• This prevents transcriptional factors from binding + attracts proteins that condense the DNA histone complex
• Methylation prevents a section of DNA from being transcribed

Question 7

Acetylation of histone proteins

Answer 7

• Decreased acetylation of associated histone proteins on DNA inhibits transcription
• If acetyl groups are removed from DNA then the histones become more positive + are attracted more to the phosphate group on DNA
• This makes the DNA + histones more strongly associated + hard for the transcription factors to bind

Question 8

Describe the relevance of epigentics on the development + treatment of disease, especially cancer

Answer 8

Tumour suppressor genes: produce proteins to slow down cell division + to cause cell death if DNA copying errors are detected
If a mutation results in the tumour suppressor gene not producing proteins to carry out this function, the cell division could continue, + mutated cells could not be identified + destroyed
Abnormal methylation- links to the control of transcription- methylation can cause a gene to turn on or off
- Tumour suppressor genes could become hypermethylated, meaning an increased number of methyl groups attached to it resulting in the gene being inactivated + becomes turned off
- Opposite could occur in oncogenes as they may be hypomethylated, reducing the number of methyl groups attached resulting gin the gene being permanently switched on

Question 9

Describe the role of RNA interference (RNAi)

Answer 9

In eukaryotes + some prokaryotes, translation of mRNA produced from target genes can be inhibited by RNAi
This is when an mRNA molecule that has already been transcribed gets destroyed before its translated to create a polypeptide chain
This is done by small interfering RNA (siRNA

Question 10

Describe the process of RNA interference

Answer 10

• An enzyme can cut large double-stranded RNA into siRNA
• One strand of siRNA combines with another enzyme
• siRNA-enzyme complex with bind via complementary base pairing to another mRNA molecule
• Once bound the enzyme will cut up the mRNA into smaller sections so it can’t be translated into a polypeptide + the gene has not been expressed