3.8.1 Control of Gene Expression

Question 1

What is a mutation

Answer 1

A change to the sequence of DNA bases or to the amount of DNA in a chromosome

Question 2

What are some causes of DNA mutation

Answer 2

Ionising radiation (alpha particles, x rays, uv rays) chemicals (nicotine and other mutagenic agents)

Question 3

What is a substitution

Answer 3

When one DNA base (eg T) is replaced with another (eg C)

Question 4

Explain how a substitution can be a “silent” mutation

Answer 4

If the mutation changes a codon to a different codon that codes for the same amino acid (due to the degnerate nature of the code) then the mutation will not affect the polypeptide produced

Question 5

Why are insertion or deletion mutations usually quite damaging

Answer 5

They cause a frame shift that means all codons following are affected

Question 6

How can epigenetic changes affect the functioning of the genome?

Answer 6

Methylation of DNA can prevent transcription. Acetylation of histones causes DNA to be loosely associated so allows more transcription

Question 7

What is gene expression controlled by ?

Answer 7

Altering the rate of transcription of genes

Question 8

What are transcription factors ?

Answer 8

Proteins that bind to DNA and activate or deactivate genes increasing or decreasing the rate of transcription. They often bind to promoter regions of the DNA which is a section of DNA just upstream of the gene where RNA polymerase binds

Question 9

Describe how oestrogen can activate transcription

Answer 9

It is a steroid hormone and can diffuse across the phospholipid bilayer. It binds to an oestrogen recetpor inside the cell causing a conformational change that reveals a DNA binding site. The hormone-receptor complex moves to the nucleus and binds to the promoter region of a gene activating transcription

Question 10

What can epigenetic control determine ?

Answer 10

Whether certain genes are expressed, altering the phenotype

Question 11

How does increased methylation of DNA repress a gene?

Answer 11

A methyl group is attached to the DNA coding for a gene(cytosine base). Increased methylation changes the DNA structure so that chromatin packs more tightly making it harder for transcription factors and RNA polymerase to bind. Hence there is reduced transcription

Question 12

How does modification of histones affect gene expression ?

Answer 12

When histones are acetylated, the chromatin is less condensed so transcription proteins can bind to the DNA allowing genes to be transcribed. When acetyl groups are removed, the chromatin is highly condensed so genes in the DNA cannot be transcribed

Question 13

What are histones ?

Answer 13

Proteins that DNA wraps around to form chromatin which makes up chromosomes

Question 14

what is heterochromatin

Answer 14

tightly packaged chromatin associated with silenced genes

Question 15

what is euchromatin

Answer 15

loosely packaged chromating associated with actively transcribed genes

Question 16

How are epigenetic changes to a cells gene expression passed on

Answer 16

When a cell divides and replicates the changes are passed on to the daughter cells

Question 17

What are stem cells ?

Answer 17

unspecialised cells that can develop into other types of cells

Question 18

What is differentiation ?

Answer 18

the process by which a cell becomes specialised

Question 19

What is totipotency ?

Answer 19

the ability of a stem cell to produce all cell types, including all the specialised cells in an organism and extra embryonic cells

Question 20

What is pluripotency ?

Answer 20

the ability of a stem cell to produce all the specialised cells in an organism but not extra embryonic cells because the genes for these cell types have become inactivated

Question 21

Where might you find a multipotent stem cell

Answer 21

In the adult body. For example bone marrow cells are multipotent and can differentiate into many types of blood cell

Question 22

Where are totipotent and unipotent stem cells present ?

Answer 22

In the first few cell divisions of an embryo

Question 23

What is an IPSC?

Answer 23

Induced Pluripotent Stem Cell. An adult cell can be induced to go back to a pluripoten state (this is done by artificially activating a few genes)

Question 24

How do stem cells become specialised ?

Answer 24

different genes in their DNA become activated or inactivated. This may occur through epigenetic mechanisms

Question 25

What are the advantages of patient stem cells over donor stem cells ?

Answer 25

Less risk of infection, no risk of rejection, no need to take immunosuppressant drugs as it is genetically identical to the patients cells

Question 26

Why are there regulatory authorities for human embryo research ?

Answer 26

decide on max age of embryo allowed for research, stopping of cloning, judging what is acceptable by following codes of practice, checking the source of the stem cell is acceptable

Question 27

How can stem cells be used in medicine ?

Answer 27

To replace damaged tissues, to study medicines or organs in vitro

Question 28

What are the potential benefits of stem cell therapies ?

Answer 28

They could save many lives as stem cells can be used to grow organs for people waiting for transplants. They could improve the quality of life for many people

Question 29

Give ethical issues raised by the use embryonic stem cells

Answer 29

Embryos have the right to life as they are a genetically unique individual, cannot consent. Some people have fewer objections to stem cells that have been artificially activated as the cells couldn’t survive past a few days anyway.

Question 30

What is a cancer

Answer 30

A group of cells that divide in an uncontrolled fashion

Question 31

Give features of a benign tumour

Answer 31

Cells generally stick gogether and are surrounded by a capsule. The are relatively normal in appearance and well differentiated. They have localised effects, can often be removed by surgery and rarely reoccur after treatment

Question 32

Give features of a malignant tumour

Answer 32

Cells grow rapidly, are highly mutated and don’t stick together. They form metastases that spread around the body causing secondary tumors. They are treated with chemotherapy and immunotherapy and reoccur more frequently after treatment

Question 33

What is a tumor supressor gene

Answer 33

A gene that normally detects DNA damage or acts to halt progression of the cell cycle

Question 34

How could a tumour supressor gene be inoolved in cancer

Answer 34

If these genes are mutated to becom inactive or are epigenetically silenced (via methylation) then this would cause and increased rate of cell division

Question 35

What is a proto-oncogene

Answer 35

In their normal form proto-oncogenes stimulate cell division but in response to controlled signals

Question 36

What is an oncogene and how are they involved in cancer

Answer 36

Mutated proto-oncogenes that constatntly stimulate cell division. This could be because of mutation or elevated expression because of less methylation of the gene or more acetylation of histone proteins

Question 37

How is oestrogen related to cancer

Answer 37

Oestogen activates transcription factors that may cause increased expression of proto-oncogenes leading to more cell division. Over time it is thought that high lifetime exposure to oestogen may lead to higher relative risk of some cancers

Question 38

What is the Human Genome Project ?

Answer 38

A 13 year long project that identified all of the genes found in human DNA

Question 39

How have scientists used data which is stored in databases from the Human Genome Project?

Answer 39

To identify genes and so proteins that are involved in disease. This information is used to create new drugs that target the identified proteins

Question 40

Answer 40