Regulation of Gene Expression

Question 1

What are stem cells?

Answer 1

• undifferentiated cells that can continually divide by mitosis + become specialised

Question 2

What is cell differentiation?

Answer 2

• process in which stem cells become specialised

Question 3

What is cell specialisation?

Answer 3

• process in which stem cells develop specific structures to help carry out their functions

Question 4

Where do stem cells originate from?

Answer 4

• pluripotent stem cells: embroys, up to 16 days after fertilisation
• multipotent stem cells: umbilical cord blood, placenta + mature body tissue of adults (e.g. in bone marrow)

Question 5

What are the diff. types of stem cells?

Answer 5

• totipotent
• pluripotent
• multipotent
• unipotent

Question 6

What are totipotent stem cells?

Answer 6

• cells that can divide + produce any type of body cell
• during dev, they translate only part of their DNA, resulting in cell specialisation, in which they’re no longer totipotent
• occur only for a limited time in early mammalian embryos

Question 7

What are pluripotent stem cells?

Answer 7

• cells that can differentiate into any cell type found in embryo, but not extra-embryonic cells
• found in embryo
• can divide in unlimited NO°s
• can be used in treating human disorders

Question 8

What are multipotent stem cells?

Answer 8

• cells that can divide + differentiate to form a limited NO° of diff cell types
• found in mature mammals (e.g. in bone marrow)

Question 9

What are unipotent stem cells?

Answer 9

• adult cells that can divide to form a limited NO° of diff cell types, + can only differentiate into 1 type of cell
• e.g. formation of cardiomyocytes

Question 10

Evaluate use of stem cells in treating human disorders.

Answer 10

• can be used to regrow damaged cells in humans (e.g. replace burns skin cells or β cells for type 1 diabetes)
• however, sometimes treatment doesn’t work or stem cells continually divide to create tumours
• also debate on ethicality of making a therapeutic clone of urself, to make an embryo for stem cells, to cure a disease + then destroy embryo

Question 11

What are induced pluripotent stem cells (iPS)?

Answer 11

• pluripotent stem cells produced from adult somatic cells, using appropriate protein transcription factors

Question 12

How are iPS cells created?

Answer 12

• in a lab, by returning any adult unipotent body cell, to a state of pluripotency, by switching genes, that were switched off to make a cell specialised, back on, using appropriate protein transcription factors

Question 13

Why could iPS cells be used to treat human disorders instead of embryonic stem cells?

Answer 13

• bc overcome some ethical issues w using embryonic stem cells, such as they don’t cause destruction of an embryo, + adult can give permission
• bc have shown a self-renewal property, in which they can divide indefinitely to give limitless supplies

Question 14

How is transcription controlled in eukaryotes?

Answer 14

• transcription of target genes is stimulated or inhibited when specific transcriptional factors move from cytoplasm into nucleus
• this can turn genes on/off, meaning only certain proteins are produced in a particular cell, enabling it to become specialised

Question 15

What are transcriptional factors?

Answer 15

• proteins that bind to specific DNA base sequences, to initiate transcription of genes
• once bound, transcription begins, creating an mRNA molecule for that gene, which is then translated in cytoplasm to create protein
• w/o binding of a transcriptional factor, gene is inactive, so protein isn’t made

Question 16

Explain how oestrogen affects gene transcription.

Answer 16

• oestrogen (lipid soluble, steroid hormone) initiates transcription by binding to a receptor site on transcriptional factor
• this causes transcriptional factor to undergo a conformational change, so it’s complementary to DNA, meaning it can bind w DNA to initiate transcription of a gene

Question 17

What is epigenetics?

Answer 17

• heritable changes in gene function, w/o changing DNA base sequence, to control gene expression in eukaryotes
• caused by changes in envi (smoking/diet/stress/exercise) + can inhibit transcription

Question 18

What is the epigenome?

Answer 18

• a single layer of chemical tags on DNA, which impacts shape of DNA-histone complex
• determines if DNA is tightly wound, so transcription factors can’t bind, inhibiting transcription, + so won’t be expressed, or unwound, so will be expressed

Question 19

How can epigenetic factors inhibit transcription?

Answer 19

• by inc. methylation of DNA
• by dec. acetylation of associated histones

Question 20

Explain how inc methylation of DNA inhibits transcription.

Answer 20

• when methyl groups are added to DNA, they attach to cytosine bases
• this prevents transcriptional factors from binding + attracts proteins that condense DNA-histone complex, preventing a section of DNA from being transcribed

Question 21

Explain how dec. acetylation of associated histones inhibits transcription.

Answer 21

• when acetyl groups are removed from DNA, histones become more positive + are attracted more to phosphate group on DNA
• this makes DNA + histones more strongly associated + hard for transcription factors to bind