Topic 8A - Mutations and Gene Expression

Question 1

Define mutations.

Answer 1

A change to the base sequence of DNA

Question 2

What do mutangenic agents do?

Answer 2

Increase the rate of mutation

Question 3

Describe the types of mutations that can occur (6).

Answer 3

Substitution - one or more bases are swapped for another
Deletion - one or more bases are 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 is moved from one location in the genome to another (this could be within the same chromosome or to a different chromosome)

Question 4

What may happen if any of these mutations occur?

Answer 4

If a mutation occurs in a gene, the sequence of amino acids in the polypeptide it codes for may change, possibly changing the 3D tertiary structure of the protein produced and thereby altering its function.

Question 5

Define genetic disorders.

Answer 5

Inherited disorders caused by abnormal genes or chromosomes.

Question 6

Define hereditary mutations.

Answer 6

A mutation which occurred in a gamete which was then fertilised by another gamete, and passed onto the offspring.

Question 7

Define a frameshift.

Answer 7

A frameshift is when a shift occurs in the DNA code because of a change in the number of bases in the DNA code.

Question 8

Mutations occur __________.

Answer 8

Spontaneously

Question 9

What are some examples of mutagenic agents? (3)

Answer 9

Ultraviolet radiation
Ionising radiation
Carcinogens such as asbestos

Question 10

How can mutagenic agents increase the rate of mutations? (3)

Answer 10

1. Acting as a base
   - Chemicals called base analogs can substitute for a base during DNA replication, changing the base sequence in the new DNA.
2. Altering bases
   
   • Some chemicals can delete or alter bases.
3. Changing the structure of DNA
   - some types of radiation can change the structure of DNA, which causes problems during DNA replication.

Question 11

Define acquired mutations.

Answer 11

Mutations that occur in individual cells after fertilisation.

Question 12

What causes the growth of a tumour?

Answer 12

Uncontrollable cell division caused by acquired or inherited mutations in the genes that control the rate of mitotic cell division

Question 13

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

Answer 13

Tumour suppressor genes

Proto-oncogenes

Question 14

What do functioning tumour suppressor genes do?

Answer 14

They slow cell division by producing proteins that stop cells dividing or cause them to undergo apoptosis.

Question 15

What is apoptosis?

Answer 15

Apoptosis is a type of programmed cell death. It’s where cells that are infected, damaged or have reached the end of their functional life are destroyed.

Question 16

What do mutated tumour suppressor genes do?

Answer 16

The gene becomes inactivated so the protein the gene codes for isn’t synthesised and the cells divide uncontrollably, resulting in a tumour forming.

Question 17

What do functioning proto-oncogenes do?

Answer 17

They stimulate cell division by producing proteins that make cells divide.

Question 18

What do mutated proto-oncogenes do?

Answer 18

The genes can become overactive, stimulating cells to dive uncontrollably resulting in a tumour.

Question 19

Define oncogenes.

Answer 19

A mutated proto-oncogene

Question 20

Malignant tumours are _______. They grow ____ and can _____ and ____ surrounding tissues. Cells can _______ malignant tumours and spread to other parts of the body via the _________________________________.

Answer 20

Cancerous
Rapidly
Invade
Destroy
Break off
Bloodstream and lymphatic system

Question 21

Benign tumours are __________. They usually grow ______ than malignant tumours and are often covered in __________ which _______ cells invading other tissues. Bening tumours are often _______, but they can cause ____________________________________. Some benign tumours can become ________.

Answer 21

Not cancerous
Slower
Fibrous tissue
Prevents
Harmless
Blockages and put pressure on organs
Malignant

Question 22

How do tumour cells differ from normal cells? (6)

Answer 22

• – The nucleus is larger and darker, sometimes there is more than one.
• – They have an irregular shape.
• – They don’t produce all the proteins needed to function correctly.
• – They have different antigens on their surface.
• – They don’t respond to growth regulating processes.
• – They divide by mitosis more often than normal cells.

Question 23

What is methylation?

Answer 23

Adding a methyl group (-CH3) onto something.

Question 24

Methylation of DNA is an important method of regulating ___________ - it can control whether or not a gene is _______ and ________.

Answer 24

Gene expression
Transcribed
Translated

Question 25

What is abnormal methylation?

Answer 25

When methylation occurs too much or too little.

Question 26

Define hypermethylation.

Answer 26

When too much methylation is occurring.

Question 27

Define hypomethylation.

Answer 27

When too little methylation is occurring

Question 28

What happens when tumour suppressor genes are hypermethylated?`

Answer 28

The methyl groups block the genes from being transcribed so the proteins they produce to slow cell division aren’t made. This means cells are able to divide uncontrollably.

Question 29

What happens when proto-oncogenes are hypomethylated?

Answer 29

There are very little methyl groups to stop the genes from being transcribed so there is an increased production of proteins which increases the rate of cell division. This stimulates cells to divide uncontrollably

Question 30

Each woman is exposed to a _______ amount of oestrogen over their lifespan, which may result in early _________ and/or late __________ if you are exposed to an ________ amount. An ________ exposure to oestrogen is also though to increase a woman’s risk of _______________________.

Answer 30

Variable
Menstruation
Menopause
Increased
Increased
Developing breast cancer.

Question 31

Describe and explain the theories linking oestrogen and breast cancer (3).

Answer 31

— Oestrogen can stimulate certain breast cells to divide and replicate. More cell division increases the chances of mutations occurring, and so increases the chance of cells becoming cancerous.

— Oestrogen’s ability to stimulate cell division could mean that if cells do become cancerous, their rapid replication could be further assisted by oestrogen.

— Other research suggests that oestrogen is actually able to introduce mutations directly into the DNA of certain breast cells, again increasing the chances of these cells becoming cancerous.

Question 32

What factors increase a persons chance of getting cancer? (2)

Answer 32

1. Genetic factors: some cancers are linked with specific inherited alleles. If you inherit that allele your more likely to get that type of cancer.
2. Environmental factors: Exposure to radiation, lifestyle choices such as smoking, increased alcohol consumption and a high fat diet have all been linked to and increased chance of developing some cancers.

Question 33

What is gene therapy?

Answer 33

Where faulty alleles in a person’s cells are replaced by working versions of those alleles.

Question 34

What are stem cells?

Answer 34

Stem cells are unspecialised cells that can develop into other types of cells.

Question 35

What are totipotent cells?

Answer 35

Stem cells that can mature into any type of body cell in an organism (including placental cells).

Question 36

What are pluripotent cells?

Answer 36

Stem cells that can specialise into any type of body cell in an organism (excluding placental cells).

Question 37

What are multipotent cells?

Answer 37

Stem cells that are only able to differentiate into a few different types of cells.

Question 38

What are unipotent cells?

Answer 38

Stem cells that can only differentiate into one type of cell.

Question 39

How do stem cells become specialised?

Answer 39

Stem cells all contain the same genes. However during development only some genes and expressed whilst others are turned off. The genes that are expressed get transcribed into mRNA, which is then translated into proteins. These proteins modify the cell - they determine the cell structure and control cell processes (including the expression of more genes, which produced more proteins). Changes to the cell produced by these proteins cause the cell to become specialised.

Question 40

What are cardiomyocytes?

Answer 40

Heart muscle cells that make up a lot of the tissue in our hearts.

Question 41

What do cardiomyocytes do in the heart?

Answer 41

Cardiomyocytes are replaced by new cardiomyocytes if the heart becomes damaged. This is done by a small supply of unipotent stem cells in the heart.

Question 42

What stem cell therapies are in existence? (1)

Answer 42

1. Bone marrow transplants — Bone marrow transplants can be used to replace the faulty bone marrow in patients that produce abnormal blood cells. The new stem cells will then produce healthy red blood cells.

Question 43

What are the sources of stem cells? How are they extracted? (3)

Answer 43

1. Adult stem cells — These are obtained from the body tissues of an adult. They are extracted from the bone marrow via a syringe.
2. Embryonic stem cells — These are obtained from embryos at an early stage of development. Embryos are created via IVF and then extracted.
3. Induced pluripotent stem cells (iPS cells) — These are created by ‘reprogramming’ specialised adult body cells so that they become pluripotent by adding transcription factors that make the adult cells express genes associated with pluripotent stem cells. The adult cells are extracted first and then the transcription factors are introduced via a specially-modified virus.

Question 44

What are the benefits of stem cell therapy? (3)

Answer 44

1. They could save lives — Stem cells could be used to grow organs.
2. They could make stem cells genetically identical to a patient so new tissues wouldn’t be rejected.
3. They could improve the quality of life for many people — replace damaged cells in the eyes to improve a patients vision.

Question 45

What are transcription factors?

Answer 45

Protein molecules which control the transcription of genes.

Question 46

What do transcription factors do in eukaryotes?

Answer 46

They move from the cytoplasm to the nucleus and bind to specific DNA sites called promoters, which are found near the start of their target genes.

Question 47

How do transcription factors control the expression of genes?

Answer 47

They control the rate of transcription

Question 48

What are activators and how do they work?

Answer 48

Activators are transcription factors which stimulate or increase the rate of transcription. They do this by helloing RNA polymerase bind to the start of the target gene and activate transcription.

Question 49

What are repressors and how do they work?

Answer 49

Repressors are transcription factors which inhibit or decrease the rate of transcription. They do this by binding to the start of the target gene, preventing RNA polymerase from binding and therefore stopping transcription.

Question 50

Why are not all cells affected by oestrogen?

Answer 50

Only cells with oestrogen receptors are affected by oestrogen.

Question 51

How are oestrogen-oestrogen receptors complexes formed?

Answer 51

When oestrogen binds to a transcription factor called an oestrogen receptor.

Question 52

What do oestrogen-oestrogen receptors do?

Answer 52

They move from the cytoplasm into the nucleus where they bind to specific DNA sites near the start of the target gene. The complex acts as an activator and helps RNA polymerase bind to the start of the target gene. However, in some genes the complex acts as a repressor and helps prevent transcription from occurring.

Question 53

What is RNAi?

Answer 53

Small lengths of non-coding RNA.

Question 54

What does siRNA do to control gene expression?

Answer 54

Once mRNA has been transcribed, it leaves the nucleus for the cytoplasm. In the cytoplasm, double-stranded siRNA associates with several proteins and unwinds. One of the resulting single strands of siRNA is selected and the other strand is degraded. The single strand of siRNA then bonds to the target mRNA. The base sequence of the siRNA is complementary to the base sequence in the sections of the target mRNA. The proteins associated with siRNA cut the mRNA into fragments - so it can no longer be translated. The fragments then move into a processing body, which contains ‘tools’ to degrade them.

Question 55

What does miRNA do in mammals to control gene expression?

Answer 55

miRNA is processed into a double strand and then two single strands by enzymes in the cytoplasm. One strand associates with proteins and bonds to target mRNA in the cytoplasm. The miRNA-protein complex physically blocks the translation of the target mRNA. The mRNA is then moved into a processing body,!where it can either be stored or degraded. When it’s stored it can be returned and translated at another time.

Question 56

What does miRNA look like when it is first transcribed?

Answer 56

It exists as a long, folded strand that is then processed into a double strand and then into two single strands.

Question 57

What does miRNA do in plants to control gene expression?

Answer 57

miRNA is processed into a double strand and then two single strands by enzymes in the cytoplasm. One strand associates with proteins and bonds to target mRNA in the cytoplasm. The base sequence of the miRNA is complementary to the base sequence in the sections of the target mRNA. The proteins associated with miRNA cut the mRNA into fragments - so it can no longer be translated. The fragments then move into a processing body, which contains ‘tools’ to degrade them.

Question 58

What does siRNA look like when it is first transcribed?

Answer 58

Double-stranded.

Question 59

siRNA is _________ complimentary.
miRNA in plants is _________ complimentary.
miRNA in mammals is _________ complimentary.

Answer 59

Perfectly
Perfectly
Partially