8.2: Gene expression

Question 1

What are stem cells

Answer 1

undiffentiated cells that continuously divide

Question 2

What are the five types of stem cells

Answer 2

totipotent
pluripotent
multipotent
unipotent
induced pluripotent stem cells (iPS)

Question 3

What are totipotent stem cells

Answer 3

can differentiate into any type of cell

Question 4

What are pluripotent stem cells

Answer 4

can differentiate into any type of cell except placental cells

Question 5

What are multipotent stem cells and give an example in bone marrow

Answer 5

can differentiate into a limited number of specialised cells, found in adult tissue which usually produce the same type of cell. Bone marrow produces any type of blood cell

Question 6

What are unipotent stem cells and give an example related to cardiac

Answer 6

can only differentiate into a single type of cells. Cardiomyocyte (cardiac muscle cell)

Question 7

What are induced pluripotent stem cells

Answer 7

a type of pluripotent stem cell that is produced from unipotent stem cells. These cells are genetically altered in a lab by “switching on” the genes and transcriptional factors that were “switched off” to make them specialised.

Question 8

What is common about somatic cells

Answer 8

all somatic cells are genetically identical

Question 9

What happens when cells differentiate and how does this happen

Answer 9

cells differentiate - become specialised to perform specific functions
this is due to different genes either being expressed or silenced

Question 10

What are 3 ways gene expression can be controlled by

Answer 10

1- Regulating transcription
2- Regulating translation
3- Epigenetics

Question 11

What region of a gene regulates expression

Answer 11

Promoter region

Question 12

What are transcription factors

Answer 12

proteins that bind to the promoter region of a gene which allows RNA polymerase to bind to the gene and initiate transcription. These can be activated/inhibited by other molecules

Question 13

Explain the process of a transcription factor binding to a gene

Answer 13

Oestrogen (lipid soluble) diffuses across the phospholipid bilayer and attaches to the receptor site on the transcription factor (TF), this causes the TF to change shape (change in tertiary structure), the DNA binding site on the TF is now complementary in shape to the DNA sequence on the promoter region TF IS NOW ACTIVATED. TF moves into the nucleus through the nuclear pores and attaches to the promoter region. This allows RNA polymerase to attach to the gene and initiate transcription -> gene is expressed

Question 14

What would happen if a transcription factor were to not bind to its gene

Answer 14

without the binding of a TF, the gene is inactive and so the protein won’t be made (as transcription cannot occur)

Question 15

Explain the process of the regulation of translation

Answer 15

mRNA is copied to make double stranded RNA (dsRNA), the dsRNA is then cut by an enzyme to make several molecules of small interfering RNA (siRNA). An enzyme joins to the siRNA and converts it to single stranded siRNA, this guides the enzyme to a (complementary) target sequence on the mRNA molecule (that is in excess), the two join by complementary base pairing, the enzyme hydrolyses phosphodiester bonds in the mRNA (cuts up the mRNA, therefore mRNA cannot attach to ribosome, cannot translate entire sequence) and so translation cannot occur

Question 16

What is oestrogen

Answer 16

a steroid hormone that initiates transcription

Question 17

What is epigenetics/what does it involve

Answer 17

epigenetics involves heritable changes in gene function, without changes to the base sequence of DNA, these changes are caused by changes in the environment by increase/decrease of methylation of the DNA/acetylation of associated histones

Question 18

With relation to epigenetics, what are the two factors that causes genes to be silenced/switched off

Answer 18

methylation of DNA
deacetylation of histones

Question 19

With relation to epigenetics, what are the two factors that causes genes to be expressed/switched on

Answer 19

demethylation of DNA
acetylation of histones

Question 20

Explain how methyl groups affect genes

Answer 20

Methyl groups attach to the cytosine base in DNA, preventing the transcription factor from binding. As the methyl group is slightly positive, it attracts proteins that condense the DNA-histone complex, and so there is no space for the transcription factor to bind onto. Preventing this section of DNA from being transcribed and so causing genes to be silenced/switched off

Question 21

Explain how acetyl groups affect genes

Answer 21

When acetyl groups are removed, the histones become more positive and so more attracted to the negative phosphate group on DNA, therefore DNA and histones are more strongly associated, leads to increased coiling, and so no space for the transcription factor to bind onto. Preventing this section of DNA from being transcribed and so causing genes to be silenced/switched off

Question 22

what is the name for chromatin when it is more condensed

Answer 22

heterochromatin

Question 23

what is heterochromatin

Answer 23

chromatin when it is more condensed

Question 24

what is the name for chromatin when it is less condensed

Answer 24

euchromatin

Question 25

what is euchromatin

Answer 25

chromatin when it is less condensed

Question 26

Describe the difference between an individual's DNA base sequence and an individual's epigenome

Answer 26

an individual's DNA base sequence is fixed, natural selection is responsible for changing allele frequencies. An individual's epigenome is flexible, chemical tags (methyl, acetyl) respond to environmental changes such as diet and stress etc

Question 27

What two genes are involved in the control of the cell cycle

Answer 27

proto-oncogenes and tumour suppressor genes

Question 28

Describe the function of proto-oncogenes

Answer 28

they code for proteins that promote the progression of the cell cycle: - initiate DNA replication - stimulate cell division & differentiation - inhibit apoptosis (cell death)

Question 29

Describe the function of tumour suppressor genes

Answer 29

they code for proteins that inhibit the progression of the cell cycle: - bind to transcription factors inhibiting them - inhibit DNA replication - inhibit cell division - stimulate apoptosis (cell death)

Question 30

How is a tumour formed

Answer 30

from the uncontrolled cell division of mutated cells

Question 31

What are the two types of tumour

Answer 31

benign and malignant

Question 32

What are the differences between benign and malignant tumours

Answer 32

Benign grow in one place, don't spread, grow slowly, are surrounded by a capsule, and are non-cancerous Malignant have cells which can break off and spread around the body (metastasis), grow rapidly, are not surrounded by a capsule, and are cancerous - spread to other tissues forming secondary tumours

Question 33

what are the differences in surgery between benign and malignant tumours

Answer 33

benign - surgery malignant - surgery, chemotherapy/radiotherapy

Question 34

What two gene mutations leads to tumour development

Answer 34

mutation in the proto-oncogene and/or tumour suppressor gene

Question 35

What do proto-oncogenes mutate into and explain what happens and how

Answer 35

When proto-oncogenes mutate into oncogenes they are permanently activated, this results in increased production of the proteins that stimulate DNA replication & cell division. This may be caused by demethylation of the promoter region of these genes (hypomethylation)

Question 36

What do tumour suppressor genes mutate into and explain what happens and how

Answer 36

the mutation of tumour suppressor genes leads to their inactivation/silencing. This results in decreased production of the proteins that inhibit cell division and promote apoptosis (and so mutated cells are not identified and destroyed). This can be caused by methylation of the promoter region of these genes (hypermethylation)

Question 37

Explain how oestrogen-dependent breast tumours develop

Answer 37

At menopause, oestrogen production ceases from ovaries and begins from breast tissue. Excess oestrogen can cause over-expression of proto-oncogenes in breast tissue, and so there is increased cell division, therefore increased number of breast tissue cells, and so increased oestrogen production hence positive feedback mechanism. Increased probability that mutations will occur within these cells. Once a tumour develops within the breast tissue, a positive feedback mechanism leads to the growth of the tumour.

Question 38

Explain the process by which a positive feedback mechanism leads to the growth of an oestrogen dependent breast tumour

Answer 38

Oestrogen binds to transcription factors called ERa. ERa transcription factor regulates expression of the gene that codes for the ERa transcription factor, therefore ERa directly regulates the expression of its own gene, and so resulting in a positive feedback loop.

Question 39

What are 4 treatments for oestrogen dependent breast cancer

Answer 39

1- Enzyme inhibition 2- Inhibit the ERa transcription factor 3- siRNAs 4- monoclonal antibodies

Question 40

Explain how enzyme inhibition is a treatment for oestrogen dependent breast cancer

Answer 40

synthesis of oestrogen is catalysed by an enzymes, drugs are used to inhibit this enzyme and so prevent synthesis of oestrogen

Question 41

Explain how inhibiting the ERa transcription factor is a treatment for oestrogen dependent breast cancer

Answer 41

Tamoxifen has a similar shape to oestrogen, and permanently binds to the ERa transcription factor in tumour cells, and so oestrogen cannot bind reducing the production of regulatory proteins in the cell cycle and so inhibiting growth of the tumour

Question 42

Explain how the use of siRNAs is a treatment for oestrogen dependent breast cancer

Answer 42

Drugs that use siRNAs prevent the translation of oncogenes, and so prevents production of proteins such as growth factors, growth factor receptors, regulatory proteins. This could also be used to treat non-oestrogen dependent breast cancers

Question 43

Explain how monoclonal antibodies is a treatment for oestrogen dependent breast cancer

Answer 43

Herceptin binds to the growth factor receptor on the cell surface membrane of breast tumour cells, preventing the growth factor from binding and so prevents expression of oncogenes