The control of gene expression

Question 1

Definition of gene expression.

Answer 1

The process of converting geentic information into functional proteins.

Question 2

Definition of differentiation.

Answer 2

Process by which cells become specialised for a particular function.

Question 3

Definition of stem cell.

Answer 3

Cells that have the ability to differentiate into specilaised cells (potency). Have the ability to replicate themselves indefinitely- self renewal.

Question 4

Definition of totipotent stem cells.

Answer 4

Can differentiate into any type of cell.

Question 5

Definition of pluripotent stem cells.

Answer 5

Can differentiate into most types of cells.

Question 6

Definition of multipotent stem cells.

Answer 6

Can differentiate into a limited number of cells.

Question 7

Definition of unipotent stem cells.

Answer 7

Can differentiate into a single type of cell.

Question 8

What type of stem cell are embryonic stem cells?

Answer 8

From embryos up to 16 cell stage, they are totipotent. 16 cell stage to blastocyst are pluripotent.

Question 9

What type of stem cells are umbilical stem cells?

Answer 9

From umbilical cord to blood are mulitpotent.

Question 10

What type of stem cell are placental stem cells?

Answer 10

Found in the placenta and develop into specific types of cells- multipotent.

Question 11

What type of stem cell are adult stem cells?

Answer 11

Found in tissues of foetus and adult. Specific to a particular tissue and maintain / repair that tissue. Can be multipotent or unipotent.

Question 12

What are IPS cells?

Answer 12

Induced Pluripotent Cells.

Question 13

IPS cells involve reverting a unipotent stem cell, what does this involve?

Answer 13

Inducing genes and trasncription factors. Turns genes on that were otherwise switched off.

Question 14

What does IPS cells being able to induce genes and transcription factors prove about adult stem cells?

Answer 14

Adult stem cells retain the same genetic information that was present in the embryo.

Question 15

What is a key feature of the IPS cells that is important for medical research and treatment?

Answer 15

Capable of self-renewal.

Question 16

List some of the ethical objections to use of embryonic stem cells (3 points).

Answer 16

1. Undermines respect for human life.
2. Could lead to use of foetuses for reasearch.
3. Could lead to reproductive cloning.

Question 17

List some the arguments for using embryonic stem cells (3 points).

Answer 17

1. Ball of cells don’t represent humans.
2. Laws already in place to provide enough protection.
3. Shouldn’t allow continuous suffering of human if can be treated.

Question 18

Describe transcription (5 points).

Answer 18

1. DNA helicase breaks the hydrogen bonds.
2. One strand acts as a template.
3. Free RNA nucleotides form complementary base pairs: adenine-uracil, cytosine-guanine.
4. RNA polymerase joins nucleotides togetehr forming phosphodiester bonds.
5. Introns are removed from pre-mRNA via splicing to form mRNA.

Question 19

Defintion of transcription factor.

Answer 19

A protein or molecules that moves from the cytoplasm to the DNA and binds toa specific base sequence of the DNA molecule.

Question 20

Definition of promotor.

Answer 20

DNA sequence before gene allowing RNA polymerase to bind to initiate transcription.

Question 21

Describe how a hormone / estrogen effects transcription (5 points).

Answer 21

1. Oestrogen binds to the receptor as complemtary in shape.
2. Shape of the DNA binding site changes.
3. Easier for RNA polymerase to bind to the promotor.
4. Binds to the promotor on the DNA.
5. Transcription occurs.

Question 22

Definition of epigenetics.

Answer 22

Environmental factors can cause heritable changes in gene function without changing the base sequence of DNA.

Question 23

What is the epigenome?

Answer 23

The layer formed by the chemical tags attached to the DNA and histones.

Question 24

Describe how addition of methyl groups to DNA causes genes to be switched off / not expressed (4 points).

Answer 24

1. DNA more tightly packed.
2. Harder for genes to be transcribed.
3. Transcription factors cannot bind to the promtor.
4. Genes switched off / not expressed.

Question 25

Describe how addition of acetyl groups to histones causes genes to be switched on / expressed (4 points).

Answer 25

1. DNA more loosely packed. 2. Genes can be transcribed more easily. 3. Transcription factors can bind to the promotor. 4. Genes switched on / expressed.

Question 26

Describe translation (6 points).

Answer 26

1. mRNA attaches to a ribosome. 2. Each amino acid is joined together by a peptide bond. 3. Ribosome moves to start codon. 4. tRNA brings amino acid. 5. Anticodon to codon. 6. Ribosome moves along to next codon.

Question 27

Describe how RNA interfernce (RNAi) can be used to block gene expression by preventing translation of mRNA into a polypeptide chain (4 points).

Answer 27

1. Double sranded RNA. Large double stranded RNA molecule are cut into smaller sectionscalled small interfering RNA (siRNA) by an enzyme. siRNA poduced around 21 nucleotides long. 2. Guid strand and enzyme. One of the two siRNA strands- guide strand, combines with an enzyme. 3. Bind to mRNA. The siRNA guid strand guides the enzyme to the mRNA and siRNA guid strand pairs with the complementary bases on mRNA strand. 4. mRNA is broken down.The enzyme cute the mRNA into smaller sections so it can no longer be translated.

Question 28

Describe the stages of mitosis (5 points).

Answer 28

1. Prophase- chromosomes appear due to supercoiling around histones. 2 chromtids held by centromere. 2. Metaphase- Chromosomes line up along the equator, centrioles produce spindle fibres. 3. Anaphase- Spindle fibres contract pulling chromatids apart to polar ends of the cell. 4. Telophase- chromosomes uncoil and become invisible again. 5. Cytokinesis- cytoplasm splits forming two daughter cells.

Question 29

Definition of cancer.

Answer 29

Disease caused by damage to genes that regulate mitosis and the cell cycle leading to uncontrolled mitosis. Forms abnormal mass of cells called a tumour.

Question 30

Definition of a benign tumour.

Answer 30

(Non-cancerous) Grows slowly and does not spread. Mitosis occurs at the centre of the tumour.

Question 31

Definition of malignant tumour.

Answer 31

(Cancerous) Grows quickly and spreads. Mitosis occurs at the edges of the tumour.

Question 32

Definition of metastasis.

Answer 32

Movement of cells around the bodt.

Question 33

Describe proto-oncogenes (4 points).

Answer 33

1. Codes for proteins that stimulate cell division. 2. Maintains normal tissues. 3. Not permanently switched on. 4. Needs a growth factor to be turned on.

Question 34

What are the effects of a mutation occurring in the proto-oncogenes? (4 points).

Answer 34

1. Permanently switched on. 2. Production of proteins increase. 3. Leads to cells dividing out of control. 4. Tumour formation.

Question 35

Describe the tumour supressor gene (4 points).

Answer 35

1. Produces proteins which inhibits cell division. 2. Repairs mistakes in DNA. 3. Stimulates apoptosis (cell death). 4. Can inhibit prot-oncogenes and stop cell division. `

Question 36

Describe the effect of a mutation that occurs in the tumour supressor gene (4 points).

Answer 36

1. Protein is not produced. 2. Cell division not inhibited, so uncontrolled cell division. 3. Malignant tumour formed. 4. The faster the rate, the faster the tumour will grow.

Question 37

Describe abnormal methylation of the tumour suppressor gene (6 points).

Answer 37

1. Hypermethylation. 2. Adds methyl group to promotor of TSG. 3. DNA more tightly packed. 4. Prevents transcription factors binding, so proteins not produced. 5. TSG not activated. 6. Uncontrolled cell division and tumour formation.

Question 38

Describe the link between oestrogen and breast cancer (5 points).

Answer 38

1. Fat cells in the breast produce high levels of oestrogen after the menopause, which can trigger breast cancer. 2. Oestrogen binds to the receptors of transcription factors, activating it. 3. Transcription occurs, gene is switched on. 4. If this genecontrols cell division, then uncontrolled cell division could occur. 5. For example: Proto-oncogenes become oncogenes.