Section 8 - Unit 20: Gene Expression Flashcards
Oestrogen is a hormone that affects transcription. It forms a complex with a receptor in the cytoplasm of target cells. Explain how an activated oestrogen receptor affects the target cell (2 marks)
- Receptor / transcription factor binds to promoter which stimulates RNA
polymerase - Transcribes gene / increase transcription
Oestrogen only affects target cells. Explain why oestrogen does not affect other cells in the body (1 mark)
- Other cells do not have the oestrogen receptors
Give two characteristic features of stem cells (2 marks)
- Will keep dividing
- Undifferentiated
Explain how the methylation of tumour suppressor genes can lead to cancer (3 marks)
- Methylation prevents transcription of gene
- Protein not produced that prevents cell division
- No control of mitosis
Describe how altered DNA may lead to cancer (6 marks)
- (DNA altered by) mutation
- (mutation) changes base sequence
- of gene controlling cell growth / oncogene / that monitors cell division
- of tumour suppressor gene
- change protein structure / non-functional protein / protein not formed
- (tumour suppressor genes) produce proteins that inhibit cell division
- mitosis
- uncontrolled / rapid / abnormal (cell division)
- malignant tumour
Explain how examining mRNA enables scientists to discover whether cancer is present (3 marks)
- mRNA base sequence has changed
- gene / DNA structure is different / has mutated
- cancer gene active / tumour suppressor gene inactive
What are totipotent cells, where are they found and how are they totipotent? (3)
- Can divide and produce any type of body cell
- During development only part of DNA is translated so cell eventually becomes specialised
- Found in the very early stages of embryos
Pluripotent cells - what are they and what are they used for (2)
- Can divide in unlimited numbers into almost any type
- Used in treating human disorders however, they can sometimes divide rapidly to form tumours
Multipotent and unipotent cells - what are they and where are they found (2)
- Found in mature mammals
- Divide to form a limited number of different cell types
Induced pluripotent cells (2)
- Produced from adult somatic cells
- Made into pluripotent cells by switching off transcription factors which make the cell specialised
Define epigenetics (2)
- Heritable changes in gene function
- Without changes to the base sequence of DNA
State two changes which inhibit transcription (2)
- Increased methylation of DNA
- Decreased acetylation of associated histones
Explain how increased methylation of DNA inhibits transcription (3 marks)
- Methyl groups (+ve charge) bind to DNA (-ve charge)
- Causing chromatin to be more condensed
- So transcription factors cannot bind to the DNA
Explain how decreased acetylation inhibits transcription (4 marks)
- Acetyl groups (-ve charge) are removed from histones, increasing the +ve charge on the histones
- This increases attraction to phosphate groups on DNA
- Causing chromatin to be more condensed
- So transcription factors cannot bind to the DNA
Explain why stem cells are effective in replacing faulty blood cells (3 marks)
- Healthy blood cells produced
- Not faulty cells
- Stem cells divide and replicate
Explain how an inhibitor of DNA methyltransferase (an enzyme which adds methyl to cytosine bases on tumour suppressor genes) stop tumour formation (3 marks
- Decreased methylation
- DNA histone complex less tightly wound
- So tumour suppressor genes transcribed
- And mitosis controlled
The mRNA for a gene is called the sense strand. An antisense strand is added and the transcription of this gene is stopped. Explain how (4 marks)
- Antisense mRNA is complementary to sense mRNA
- Antisense mRNA would bind to sense mRNA
- Ribosomes can’t bind
- So less translation of mRNA
Explain how cells become specialised [3 marks]
- Only some of the genes are expressed
- So only part of the DNA is translated into proteins
- The proteins translated are the ones required to carry out the special function
Define self-renewal [1 mark]
- The process in which stem cells make copies of themselves through mitosis
Explain how hormones stimulating transcription work [5 marks]
- They are lipid soluble so can diffuse through the phospholipid bilayer
- In the cytoplasm, they bind to a complementary receptor protein
- This changes the tertiary structure of the protein, causing it to become activated as a transcription factor
- This can now enter the nucleus through the nuclear pores and bind to the promoter region of DNA
- Stimulating RNA polymerase to carry out transcription
What is the epigenome [1 mark]
- Set of chemical modifications to the DNA and DNA-associated proteins in the cell, which alter gene expression, and are heritable
State two factors which cause genetic variation [2 marks]
- Crossing over
- Random fertilisation
