Gene Expression

Question 1

Define mutation

Answer 1

Any change to the base (nucleotide) sequence of DNA

Question 2

When do mutations occur?

Answer 2

During errors in DNA replication

Question 3

How can the rate of mutation be affected?

Answer 3

Mutagenic agents

Question 4

What are the 6 types of mutations?

Answer 4

Substitution, deletion, addition, inversion, duplication and translocation

Question 5

Define substitution

Answer 5

One or more bases is swapped for another

Question 6

Define deletion

Answer 6

One or more bases are removed

Question 7

Define addition

Answer 7

One or more bases are added

Question 8

Define duplication

Answer 8

One or more bases are repeated

Question 9

Define inversion

Answer 9

A sequence of bases is reversed (ATGCCT now ACCGTT)

Question 10

Define translocation

Answer 10

A sequence of bases is moved from one location in the genome to another.

Question 11

What is a hereditary mutation?

Answer 11

When a gamete containing a mutation for a genetic disorder is fertilised, the mutations will be present in the new foetus.

Question 12

Why do mutations not always have an effect?

Answer 12

Due to the degenerate nature of the genetic code - meaning some AA are coded for by more than one triplet.

Question 13

Give examples of mutagenic agents.

Answer 13

• high ionising radiation; e.g. short wave radiation such as X-rays
• chemicals; e.g. nitrogen dioxide may directly alter the structure of DNA

Question 14

What are acquired mutations?

Answer 14

Mutations that occur in individual cells after fertilisation

Question 15

What happens if an acquired mutations occurs in a gene that controls cell division?

Answer 15

Can cause uncontrolled cell growth

Question 16

Which two genes cause cell division?

Answer 16

Tumour suppressor genes and proto-oncogenes

Question 17

Outline how mutations in tumour suppressor genes cause cancer.

Answer 17

When functioning normally, tumour suppressor genes slow cell division by producing proteins that stop cells dividing or cause them to self destruct (apoptosis).

If a mutation occurs, the protein for this isn’t produced. So the cells divide uncontrollably, resulting in a tumour.

Question 18

Outline how mutations in photo-oncogenes cause cancer.

Answer 18

When functioning normally, PO genes stimulate cell division (by producing proteins that make the cell divide).

If a mutation occurs, the gene can become overactive. This stimulates the cells to divide uncontrollably and cause a tumour.

Question 19

Difference between malignant or benign tumours?

Answer 19

Malignant spread throughout the body and grow rapidly. They are cancers.

Benign tumours are localised and grow slowly. They are not cancerous.

Question 20

In what way are tumour cells different to normal cells?

Answer 20

• irregular shape
• different antigens on their surface
• divide (by mitosis) more frequently
• nucleus is darker and larger

Question 21

Outline hypermethylation.

Answer 21

When tumour suppressor genes are hypermethylated, there genes aren’t transcribed - so the proteins they produce (to slow cell division) aren’t made.
This means that cells are available to divide uncontrollably by mitosis.

Question 22

Outline hypomethlation

Answer 22

Hypomethylation of protons-oncogenes cause ten to act as oncogenes - increasing the production of proteins that encourage cell division.
This stimulates the cell to divide uncontrollably, which causes the formation of tumours.

Question 23

Outline how increased oestrogen may contribute to breast cancer.

Answer 23

• oestrogen can stimulate certain breast cells to divide and replicate, so with more cell divisions taking place, this naturally increases the chance of mutations occurring, and so increases the chance of cells becoming cancerous.
• the ability to stimulate division could also mean that if cells do become cancerous, their rapid replication could be further assisted by oestrogen helping tumours to form quickly.

Question 24

Outline genetic factors involved in the risk of cancer.

Answer 24

Some cancers are linked with specific inherited alleles. Therefore if you inherit said allele, you’re more likely to get that type of cancer.

Question 25

Outline environmental factors involved in the risk of cancer.

Answer 25

Exposure to radiation, lifestyle choices e.g. smoking, increased alcohol consumption and a high fat diet have all been linked to an increased chance of developing some cancers.

Question 26

How can understanding a specific mutation in a cancer related gene help to treat cancer?

Answer 26

If a specific causing mutations is known, then it's possible to screen for the mutation in a person's DNA (e.g. BRCA1 tumour suppressor gene). Preventative steps can then be taken e.g. mastectomy.

Question 27

At what stage of development can totipotent cells be found in mammals?

Answer 27

In the first few cell divisions of an embryo.

Question 28

Describe the difference between pluripotent and multipoint stem cells.

Answer 28

Pluripotent cells are made after totipotent cells. They can specialise into any cell, but lose the ability to become cells that make up the placenta. Multipotent cells are only able to differentiate into a few types of cells - e.g. RBC and WBC made from multipoint cells found in bone marrow.

Question 29

How do stem cells become specialised?

Answer 29

1. mRNA is only transcribed from specific genes. 2. The mRNA from these genes is then translated into proteins. 3. These proteins modify the cell (they determine the cell structure and control cell processes (inc the expression of more genes which produces more proteins)). 4. These changes to the cell produced cause the cell to become specialised. These changes are difficult to reverse, so stays specialised.

Question 30

Name 2 conditions stem cell treatment could be used to treat?

Answer 30

Heart disease; stem cells used to replace damaged heart tissue. Organ transplant; organs grown from stem cells to provide new organs for people on organ donor waiting lists.

Question 31

One difference between adult and embryonic stem cells

Answer 31

Adult cell - obtained from body tissue of adult cell. Also can only specialise into a limited range of cells (they're multipotent) Embryonic cell - obtained from embryos at an early stage of development. Also can divide into all types of body cells (they're pluripotent)

Question 32

What do transcription factors do?

Answer 32

Control the transcription of target genes

Question 33

What is the basic principle of transcription?

Answer 33

DNA into mRNA , using RNA polymerase

Question 34

If all cells in and organism carry the same DNA, why is the structure and function different?

Answer 34

Because not all the genes in the cell are expressed (transcribed and used to make a protein). Because different genes are expressed, different proteins are made and these proteins modify the cell; they determine the cell structure and cell processes.

Question 35

What kind of molecule is a TF?

Answer 35

Protein

Question 36

Outline the basic way that Bfs work.

Answer 36

1. In eukaryotes, TFs move from the cytoplasm to the nucleus. 2. In the nucleus, they bind to specific DNA sites near the start of their target genes.

Question 37

What are activators?

Answer 37

A TF that stimulates / increases the rate of transcription.

Question 38

What are repressors?

Answer 38

Bfs that inhibit / decrease the rate of transcription.

Question 39

Outline how oestrogen can initiate the transcription of target genes.

Answer 39

1. Oestrogen binds to a TF, forming an oestrogen-oestrogen receptor complex. 2. The complex moves from cytoplasm into nucleus where it binds to specific DNA sites near the start of the target gene. 3. The complex can act as an activator of transcription (e.g. helping RNA polymerase bind to the start of the target gene).

Question 40

Outline how siRNA can inhibit the translation of mRNA

Answer 40

1. Once mRNA has been transcribed, it leaves the nucleus to the cytoplasm. 2. In the cytoplasm, double stranded siRNA associates with several proteins and unwinds. A single strand then binds to target mRNA (complementary base sequences). 3. The proteins associated with the siRNA cut the mRNA into fragments; so it can no longer be translated. The fragments then move into a processing body where they're degraded.

Question 41

Outline how miRNA can inhibit translation.

Answer 41

1. Associates with proteins and binds to target mRNA in the cytoplasm. 2. The miRNA-protein complex physically blocks the translation of the target mRNA. 3. The mRNA is then moved into a processing body, where it's degraded or stored.

Question 42

Why is miRNA stored?

Answer 42

So it can be returned and translated at another time.

Question 43

Difference between siRNA and miRNA?

Answer 43

The base sequence of siRNA is complementary to the base sequence in the sections of the target mRNA, but isn't fully complementary in miRNA, so is less specific. Also, siRNA cuts the mRNA into fragments, whereas the miRNA-protein complex physically blocks the translation of the target mRNA.

Question 44

Outline increased methylation.

Answer 44

The addition of a methyl group (CH3) to a molecule, at a CpG site (where C and G are next to each other). Inhibits transcription in two ways: - prevents the binding of TFs to the DNA. - attracts proteins that condense the DNA-histone complex(by inducing deacetlyation of histone), making the DNA inaccessible to TFs.

Question 45

Outline how decreased acetylation of histones can switch off genes.

Answer 45

1. When histones are acetylated, the chromatin is less condensed, meaning the TF can access the DNA, so is transcribed. 2. When acetyl groups are removed from the histones, the chromatin becomes highly condensed and the genes in the DNA can't be transcribed because the transcriptional machinery can't physically access them.

Question 46

Which type of molecule are responsible for removing acetyl groups?

Answer 46

Histone deacetylase (HDAC) - enzymes.

Question 47

Give a characteristic that varies due to both environmental and genetic factors.

Answer 47

Overeating: environmental: increased availability of food in developed countries. genetic: food consumption increases dopamine in the brain, so once enough had been released, people would stop eating.

Question 48

Define epigenetic.

Answer 48

Heritable changes in gene function, without changes to the base sequence.