Gene Expression (Unit 8.2)

Question 1

What are stem cells

Answer 1

Undifferentiated cells capable of diving by mitosis to replace themselves indefinitely and differentiating into other types of specialised cells

Question 2

How do stem cells become specialised during development

Answer 2

Stimuli leads to activation of some genes
So mRNA is transcribed only from these genes and then translated into proteins
These proteins modify cells permanently and determine cell structure/function

Question 3

What are totipotent cells

Answer 3

Occur for a limited time in early mammalian embryos
Can divide and differentiate into any type of body cell

Question 4

How do stem cells become specialised during development

Answer 4

Stimuli leads to activation of some genes
So mRNA is transcribed only from these genes and then translated into proteins
These proteins modify cells permanently and determine cell structure/function

Question 5

What are pluripotent cells

Answer 5

Found in mammalian embryos
Can divide and differentiate into most cell types

Question 6

What are multipotent cells

Answer 6

Found in mature mammals
Can divide and differentiate into any type limited number of cells

Question 7

Example of multipotent cells

Answer 7

Multipotent cells in bone marrow can divide and differentiate into different types of blood cell

Question 8

What are unipotent cells

Answer 8

Found in mature mammals
Can divide and differentiate into just one cell type

Question 9

Example of unipotent cells

Answer 9

Unipotent cells in heart can divide and differentiate into cardiomyocytes

Question 10

How can stem cells be used in the treatment of human disorders

Answer 10

Transplanted into patient to divide in unlimited numbers
Then differentiate into required healthy cells (replace damaged cells)

Question 11

Examples of stem cells treating human disorders

Answer 11

Type 1 diabetes- create healthy islet cells that produce insulin
Blood cancers/sickle cells disease- destroy patients bone marrow, transplant stem cells from healthy person to divide and differentiate into healthy cells

Question 12

What does iPS cells stand for

Answer 12

Induced pluripotent stem cells

Question 13

How are iPS cells produced

Answer 13

Obtain adult somatic cells from patient
Add specific protein transcription factors associated with pluripotency to cells so they express genes associated with pluripotency
Culture cells to allow them to divide by mitosis
Once made can divide and differentiate into healthy cells to be transplanted into same patient

Question 14

Positives for the use of stem cells

Answer 14

Can divide and differentiate into healthy cells so can save lives and improve quality of life
Embryos are left over from IVF so otherwise would be destroyed
iPS are unlikely to be rejected by immune system as they are made with patients own cells
iPS made without destruction of embryo and adult can give consent

Question 15

Negatives for the use of stem cells

Answer 15

Ethical issues with embryonic stem cells as requires destruction of embryo and potential life (embryo can’t give consent)
Immune system can reject cells
Cells could divide out of control, leading to the formation of tumours

Question 16

What are transcription factors

Answer 16

Proteins which regulate (stimulate/inhibit) transcription of specific target genes in eukaryotes by binding to a specific DNA base sequence on a promoter region

Question 17

How can transcription be regulated using transcription factors

Answer 17

Transcription factors move from the cytoplasm to the nucleus
Then bind to DNA at a specific DNA base sequence on a promoter region
This stimulates/inhibits transcription of target genes by helping or preventing RNA polymerase binding

Question 18

What is oestrogen

Answer 18

A lipid soluble steroid hormone

Question 19

How does oestrogen affect transcription

Answer 19

Oestrogen is a lipid soluble hormone, so diffuses into cell across the phospholipid bilayer
In cytoplasm oestrogen binds to its receptors on an inactive transcription factor forming an oestrogen- receptor complex
This changes the shape of the inactive transcription factors forming an active transcription factor
The complex diffuses from cytoplasm into the nucleus
This then binds to a specific DNA base sequence on teh promoter region of a target gene
Stimulating transcription of target genes forming mRNA by helping RNA polymerase to bind

Question 20

Why does oestrogen only affect target cells

Answer 20

Because other cells do not have oestrogen receptors

Question 21

What is epigenetics

Answer 21

Heritable changes in gene function without changes to DNA base sequence. Caused by changes in the environment

Question 22

What is the epigenome

Answer 22

All chemical modification of DNA and histone proteins e.g methyl groups and acetyl groups

Question 23

How is transcription inhibited through epigenetics

Answer 23

Increase methylation of DNA
Decreased acetylation of histones

Question 24

How is transcription allowed through epigenetics

Answer 24

Decreased methylation of DNA
Increased acetylation of histones

Question 25

How do methylation and acetylation inhibit transcription

Answer 25

Increased methylation of DNA- methyl groups added to cytosine bases in DNA so nucleosomes pack more tightly together preventing transcription factors and RNA polymerase binding to promoter Decreased acetylation of histones- increase positive charge of histones so histones bind to DNA more tightly preventing transcription factors and RNA polymerase binding to promoter

Question 26

How can the translation of mRNA be inhibited in eukaryotes and some prokaryotes

Answer 26

By RNA interference (RNAi)

Question 27

How does RNAi inhibit translation of mRNA

Answer 27

By RNA molecules e.g siRNA, miRNA

Question 28

How is translation by RNA interference regulated

Answer 28

sirRNA or miRNA binds to a protein forming a RISC Single stranded miRNA/siRNA with RISC binds to target mRNA with a complementary base sequence Leads to hydrolysis of mRNA into fragments (prevents ribosome binding) Prevents translation of target mRNA into protein

Question 29

How are epigenetics relevant on disease development and treatment

Answer 29

Environmental factors e.g diet, stress and toxins- can stimulate/inhibit expression of genes (methylation/acetylation) Diagnostic tests developed to detect epigenetics changes before symptoms Drugs developed to reverse epigenetic changes

Question 30

How do tumours form

Answer 30

Mutations in DNA/genes controlling mitosis can lead to uncontrolled cell division A tumour forms if this results in mass of abnormal cells

Question 31

Main characteristics of benign tumours

Answer 31

Non cancerous Grow slowly Cells have normal, regular nuclei Do not spread by metastasis Removed by surgery but rarely return

Question 32

Main characteristics of malignant tumour

Answer 32

Cancerous Grow faster Cells have irregular, larger, darker nuclei Spread by metastasis Removed by surgery combined with chemotherapy but often return

Question 33

What do tumour suppressor genes code for

Answer 33

Code for proteins that inhibit cell cycle or cause self destruction of potential tumour cells

Question 34

What is the role of tumour suppressor genes in the development of tumours

Answer 34

Mutation leads to production of non functional protein (alters tertiary structure) Increased DNA methylation or decreased histone acetylation- prevents production of a protein (prevents RNA polymerase binding, inhibiting transcription) Both lead to uncontrolled cell division

Question 35

What do proto-oncogenes code for

Answer 35

Code for proteins that stimulate cell division

Question 36

What is the role of oncogenes in the development of tumours

Answer 36

Mutation leads to overproduction of protein or permanently activated protein Decreased DNA methylation or increased histone acetylation increases production of protein (helps RNA polymerase to bind, stimulating transcription) Both lead to uncontrolled cell division

Question 37

Why do tumours require mutations in both alleles of a tumour suppressor gene but only one allele of an oncogene

Answer 37

One functional allele of a tumour suppressor gene can produce enough protein to slow the cell cycle- cell division is controlled One mutated oncogene allele can produce enough protein to lead to uncontrolled cell division

Question 38

What can drugs do to prevent uncontrolled cell divison

Answer 38

Reverse epigenetic changes

Question 39

How do drugs change oncogenes to inhibit transcription

Answer 39

Increased DNA methylation or decreasing histone acetylation

Question 40

How do drugs change tumour suppressor genes to stimulate transcription

Answer 40

Decreased DNA methylation or increased histone acetylation

Question 41

What is the role of increasing oestrogen concentrations in the development of some breast cancers

Answer 41

Some breast cancer cells have oestrogen receptors which are inactive transcription factors If concentration of oestrogen increases, more oestrogen binds to receptors so more oestrogen-receptor complexes form which are active transcription factors These bind to promoter region Increasing transcription, increasing rate of cell division

Question 42

How do drugs that have a similar structure to oestrogen help treat oestrogen-receptor breast cancers

Answer 42

Drugs bind to oestrogen receptors, preventing binding of oestrogen So no transcription factors bind to promoter regions of genes that stimulate the cell cycle