Control of Gene Expression

Question 1

Define Mutation

Answer 1

Mutations are any change to the nucleotide base. They can be caused by errors during DNA replication.

Question 2

State and Define the 6 types of mutation.

Answer 2

Substitution- One or more bases are swapped for another
Deletion- One or more bases is removed
Addition- One or more bases are added
Duplication- One or more bases are repeated
Inversion- A sequence of bases is reversed
Translocation- A sequence of bases us moved from one location to the genome of another.

Question 3

Why can mutations lead to problems?

Answer 3

The order of DNA bases in a gene determines the sequence of amino acids in a particular polypeptide, if a mutation occurs, the sequence of amino acids could change subsequently change the tertiary structure of a protein changing its function.

Question 4

Why can mutations have no negative outcomes?

Answer 4

Not all mutations cause a change in the protein. The degenerate nature of all genetic code means some amino acids are coded by more than one DNA triplet.

Question 5

What is a frameshift?

Answer 5

Frameshift- When the mutation causes a change in the number of bases so the triplet code is read in another way.

Question 6

What is a mutagenic agent and give examples?

Answer 6

Physical or chemical agents that increase the rate of mutations
Examples include UV and ionization radiation as well as some chemicals and viruses.

Question 7

What are the three ways mutagenic agents could increase the rate of mutations?

Answer 7

Act as a Base- Substituted for a base during replication

Altering Bases- Some chemicals delete or alter bases

Changing DNA structure- Some types of radiation can change the structure of DNA causing replication problems

Question 8

How do tumours form and how do they become cancerous?

Answer 8

When mutations occur in genes that control the rate of cell replication, it can cause uncontrolled cell division forming a tumour.

Tumours that invade and destroy tissues are called cancers.

Question 9

State and define the two types of tumours.

Answer 9

Malignant Tumour- These are cancerous. They usually grow rapidly and invade all tissues. Cells can break off and spread to other parts of the body in the bloodstream.

Benign Tumour- Not cancerous, they usually grow slower than malignant tumours and are covered in fibrous tissues that stops cells invading. They are usually harmless but can cause blockages and preassure.

Question 10

What are the two types of genes that control cell division?

Answer 10

• Tumour Suppressor Genes
• Proto-oncogenes

Question 11

Talk about Tumour Suppressor Genes and how they can cause a tumour.

Answer 11

When functioning normally, these slow cell division by producing proteins that stop dividing or cause them to self- destruct.

If a mutation happens in this gene, the gene will be inactivated and the protein it codes for isn’t produced so the cell divides uncontrollably

Question 12

Talk about Proto-Oncogenes and how they can cause a tumour.

Answer 12

When functioning normally, they stimulate cell division by producing proteins.

If mutation happens, the gene can become overreactive which stimulates the cells to divide uncontrollably.

Question 13

What are Oncogenes?

Answer 13

these are formed from mutated proto-oncogenes and result are permanently switched on resulting in cell division that is uncontrolled.

It does this by permanently activating a cell surface receptor or coding for a growth factor.

Question 14

What is Methylation and why is it important in gene expression?

Answer 14

Methylation is the addition of methyl onto something. Methylation of DNA is an important method of regulating gene expression as it can control whether or not a gene is transcribed and translated.
- at CpG site, with no change to DNA base sequence
- chromatin more tightly packed (heterochromatin)
- harder for RNA polymerase to bind

Question 15

Talk about abnormal methylation of tumour suppressor genes.

Answer 15

HYPERMETHYLATION- too much
Genes are not transcribed so the proteins they produce to slow cell division aren’t made. This means. that cells are able to divide uncontrollably causing tumours

HYPOMETHYLATION- too little
The hypomethylation of Proto-Oncogenes causes them to act as oncogenes, increasing the production of the proteins that encourage cell division, which could lead to tumours

Question 16

Talk about the role of Oestrogen in Brest Cancer.

Answer 16

Some women may be exposed to more oestrogen than others due to starting menstruation earlier, or the menopause later, which could overextended period of time increase the risk of breast cancer.

This could be due to oestrogen stimulating certain breast cells to divide and replicate or some research suggests that oestrogen is able to introduce mutations directly into the DNA of certain breast cells.

Question 17

What are the two categories of risk factors for cancer?

Answer 17

Genetic Factors- Cancer can be linked with specific inherited alleles If you inherit that allele, you’re more likely to get that type of cancer

Environmental Factors- Exposure to radiation lifestyle choices such as smoking, increased alcohol consumption, and a high fat diet have all been linked to an increased chance of developing some cancers

Question 18

What is a stem cell?

Answer 18

Stem cells are undifferentiated cells which can keep dividing to give rise to other types of cells

Question 19

State and define each type of stem cell.

Answer 19

Totipotent- cells in the embryo which can form any type of cells in the body and embryonic cells
Pluripotent- can form any cell in the body but not embryonic cells. They are also found in early embryos and can help replace damaged tissues.
Multipotent- can differentiate into other cells but are limited i.e. bone marrow
Unipotent- can only differentiate into one type of cell

Question 20

What are induced pluripotent stem cells?

Answer 20

Pluripotent stem cells created from unipotent stem cells.

Question 21

Give an example of a stem cell therapy.

Answer 21

Bone Marrow Transplant:
Bone marrow transplants can be used to replace the faulty bone marrow in patients that produce abnormal blood cells. The stem cells in the transplanted bone marrow divide and specialise to produce healthy blood cells. This has been used successfully to treat some genetic disorders such as sickle cell anemia.

Question 22

How are stem cells obtained?

Answer 22

Adult Stem Cells- Obtained from the body tissues of an adult and the bone marrow

Embryonic Stem Cells- IVF, When an egg cell is fertilised by sperm outside the body. in early stages of development, stem cells are removed and the rest of the embryo is destroyed.

Question 23

Talk about ethical considerations of Stem Cells?

Answer 23

Some people believe that at the moment of fertilisation, an individual is formed that has the right to live so they believe it’s wrong to destroy the embryos

While other people believe that because stem cells are obtained from egg cells that haven’t been fertilised by sperm, but have been artificially activated to start dividing, that they can be used.

As adults are able to consent to stem cell removal. And it results in little injury and no death. People believe we should only use adult stem cells

However, because adult stem cells aren’t as flexible as embryonic stem cells, they have less use in scientific research

Question 24

What are transcription factors and how do they work?

Answer 24

These are proteins that bind to specific sites on a DNA sequence, determining transcription

They bind to promotor regions near the start of the gene allowing them to control the rate of transcription and subsequently the level of gene expression.

Question 25

What are the two types of transcription factor?

Answer 25

Activators, which increase the rate of transcription, helping RNA polymerase binds to the promoter and start transcription

Represses, which reduce the rate of transcription by blocking the binding of RNA polymerase.

Question 26

Talk about oestrogen in the regulation of transcription and translation

Answer 26

The Hormone oestrogen has the ability to alter transcription through altering Transcription factors:
1. As oestrogen is lipid soluble, it can freely diffuse across the membrane and bind to a receptor molecule on a transcription factor

2. The finding alters the shape of theDNA binding site on the transcription factor, making it able to bind to the DNA
3. The transcription factor therefore enters the nucleus via the nuclear pore, where it binds to DNA. This stimulates the transcription of the gene that makes up the DNA

Question 27

What are the two types of RNA repressors?

Answer 27

Small Interfering RNA (siRNA)- Fully complementary to target, meaning they can only bind to a specific mRNA sequence

MicroRNA (miRNA)- Partially complementary to target, meaning it combined to different parts.

Question 28

Talk about siRNA in the control of transcription and translation.

Answer 28

It is used for short term switching off of genes. The siRNA binds to a complementary sequence of mRNA, As mRNA is usually single stranded. The cell therefore detects the double strand on mRNA and views it as abnormal. This causes the mRNA to be broken down by Enzymes preventing translation

Question 29

Talk about miRNA in the control of transcription and translation.

Answer 29

miRNA is first processed into two single strands. One strand associates with proteins and binds to target mRNA Which essentially blocks the translation of the target mRNA.

Question 30

What is Epigenetics?

Answer 30

The study of heritable changes to the phenotype that don’t involve changes to base sequences. This means it doesn’t involve mutations

Question 31

What is an epigenome?

Answer 31

The chemical compounds and proteins that can attach to DNA and histones, affecting how genes are expressed.

Question 32

What are the mechanisms of epigenetic control?

Answer 32

• DNA methylation
• Acetylation of Histones

Question 33

Talk about DNA methylation in epigenetic control.

Answer 33

A methyl group is added to the DNA sequence at a CpG site inhibiting the transcription by physically blocking it or attracting proteins that condensed chromatin making it more tightly packed
This prevents transcription factors and RNA polymerase from binding to the promoter region silencing the gene

Question 34

Talk about Acetylation of histones in epigenetic control

Answer 34

When histones are acetylated, the chromatin is less condensed. This means that the transcriptional machinery can access the DNA allowing genes to be transcribed.

When Acetyl groups are removed from the Histones, the chromatin becomes highly condensed, and genes in the DNA can’t be transcribed because transcription factors can’t physically access them.

Question 35

Talk about epigenetics and cancer

Answer 35

Epigenetics can increase the risk of developing cancer increase. methylation of tumour suppressor genes reduce their expression, which can lead to cancerous tumours.

Question 36

Heterochromatin

Answer 36

tightly packed, harder for transcriptional enzymes to access DNA so gene is switched off
(DNA methylation)

Question 37

Euchromatin

Answer 37

loosely packed, easier for transcriptional enzymes to access DNA so gene is switched on
(acetylation)