13.7 Mutations, Gene Expression and Cancer

Question 1

What are the 3 types of genetic code?

Answer 1

Universal, non-overlapping and degenerate

Question 2

Define universal code

Answer 2

The same 3 bases on mRNA (codon)/DNA (triplet) code for the same amino acid in all organisms.

Question 3

Define non-overlapping code

Answer 3

The ribosome reads each base only once in the codons/triplets- the first three bases are read first, followed by the second three, the third three and so on.

Question 4

Define degenerate code

Answer 4

More than one triplet/codon codes for an amino acid

Question 5

3 bases on DNA

Answer 5

Triplet

Question 6

3 bases on mRNA

Answer 6

Codon

Question 7

3 bases on tRNA

Answer 7

Anticodon

Question 8

Define mutation

Answer 8

A mutation is a change to the DNA base sequence.

Question 9

Define gene mutation

Answer 9

AKA single-point mutation.
Change to a single base in DNA base sequence of a gene.
Occurs randomly and happen spontaneously.

Question 10

What may a mutation lead to?

Answer 10

Change in primary stucture of polypeptides, altering secondary structure, altering tertiary structure, making protein non-functional

Question 11

Types of gene mutation

Answer 11

Addition, substitution, deletion

Question 12

What is a silent mutation?

Answer 12

One where the mutation does not change the amino acid coded for so will have no effect on the polypeptide chain.

Question 13

What is a frame shift?

Answer 13

When one full DNA nucleotide is gained or lost through addition or deletion mutations, this results in an altercation of base triplets from the mutation onwards. The reading frame will have been shifted either left or right.

Question 14

Effect of timing of addition or deletion mutation

Answer 14

The earlier addition or deletion occurs, the more triplets that could be affected and so more AAs altered.

Question 15

Define chromosome non-disjunction

Answer 15

Where daughter cells are produced containing too many chromosomes.
Pair of homologous chromosomes may fail to separate during metaphase 1 OR sister chromatids may fail to separate in metaphase 2.

Question 16

Types of chromosomal mutations

Answer 16

Inversion, duplication, translocation

Question 17

What is an inversion mutation?

Answer 17

When a segment of bases or a chromosome is reversed end to end.

Question 18

What is a duplication mutation?

Answer 18

A doubling of part of a chromosome, an entire chromosome, or even the whole genome.

Question 19

What is a translocation mutation?

Answer 19

When groups of base pairs relocate from one area of the genome to another. This usually is between non-homologous chromosomes.

Question 20

Examples of mutagenic agents

Answer 20

1. High energy ionising radiation (e.g. X rays, gamma rays, alpha and beta particles, ultra violet)
2. DNA reactive chemicals (e.g. benzene, bromine, hydrogen peroxide)
3. Biological agents (e.g. some viruses and bacteria)

Question 21

What is a totipotent cell?

Answer 21

Can divide (by mitosis) and produce any type of body cell.
Only translate part of their DNA to produce specific proteins, leading to cell specialisation
Found in zygote and early embryo (up to 8 cell stage)

Question 22

What does gene expression require?

Answer 22

Transcription and translation

Question 23

What is a pluripotent cell?

Answer 23

Can divide by mitosis but also begin to differentiate into the majority of specialised cells that make up tissues in the fetus.
Only translate part of their DNA.
Found in embryo and fetal stem cells.

Question 24

What is a multipotent cell?

Answer 24

Retain the ability to differentiate into some different cell types.
Found in mature mammals (in tissues).
e.g. cells in the bone marrow that differentiate into RBC and WBC

Question 25

What is a unipotent cell?

Answer 25

Capable of giving rise to only one cell type. Found in mature mammals e.g. cells in the heart differentiate into cardiomyocytes.

Question 26

What are multipotent and unipotent stem cells vital for?

Answer 26

Growth and repair of damaged tissues.

Question 27

How are stem cells used in medical research?

Answer 27

- Produce tissues for skin grafts. - Research into producing organs for transplant. - Research into how cells become specialised. - Research into cancer and other serious diseases. - Use of stem cells to cure diseases like Parkisons

Question 28

What is a danger when using stem cells?

Answer 28

May divide out of control, leading to a tumour.

Question 29

Ethical concerns when using stem cells

Answer 29

People consider that: - It isnt right to use stem cells from embryos as embryos have human status from the moment of conception. - Embryos could be potential human beings, but at early stages it is not a true human being and the removal of cells from spare embryos for medicine has benefits. - Embryos have no moral rights whatsoever. - Animals must be used in experiments before stem cells can be trialled on humans

Question 30

What is a promoter region?

Answer 30

One or more base sequences found upstream of a gene that control expression of the gene.

Question 31

What is a transcription factor?

Answer 31

Proteins that, when activated, bind to promoter region of a gene to stimulate RNA polymerase to begin transcription of the target gene.

Question 32

Describe the mechanism by which a signal protein causes the synthesis of mRNA.

Answer 32

* signal protein {binds to / joins to / interacts with / activates} * receptor on surface membrane; * messenger molecule moves from cytoplasm and enters nucleus; * {produces / activates} transcription factor; * binds to promoter region; * RNA polymerase transcribes target gene;

Question 33

Explain how oestrogen enables RNA polymerase to transcribe its target gene.

Answer 33

* Oestrogen (lipid soluble hormone) diffuses through the cell membrane through the phospholipid bilayer; * attaches to complementary ERα receptor; * ERα receptor changes tertiary structure/shape; * ERα receptor leaves protein complex which inhibited it’s action; * oestrogen receptor binds to promoter region; * enables RNA polymerase to transcribe target gene.

Question 34

Why does RNA interference occur?

Answer 34

-Protein synthesis uses large amounts of ATP -Overproduction of a specific protein is a waste of valuable ATP -If a cell has synthesised enough of a specific protein

Question 35

Two types of interfering RNA

Answer 35

microRNA (miRNA) small interfering RNA (siRNA)

Question 36

How does interfering RNA work?

Answer 36

- miRNA or siRNA binds to protein in the cytoplasm to form a RISC complex (RNA-induced silencing complex) - miRNA/ siRNA has a complementary base sequence to part of a specific mRNA molecule. - RISC inhibits gene expression by binding to complementary mRNA, causing either: 1. mRNA to be hydrolysed by an enzyme- RNA hydrolase. 2. Inhibition of initiation of ribosomal translation so ribosome cant attach to mRNA

Question 37

What are epigenetics?

Answer 37

Involves inheritable changes in gene expression without changes to DNA base sequences.

Question 38

How do inheritable changes (epigenetics) inhibit translation?

Answer 38

Increased methylation of DNA Decreased acetylation of histones

Question 39

Explain the process of methylation of DNA

Answer 39

Methyl group attached to CG bases on the promoter region upstream of the gene. Catalysed by methyltransferase enzyme.

Question 40

Explain the process of acetylation of histones.

Answer 40

Acetyl groups attached to tails of histone molecules. Results in them becoming loosely packed, less condensed. Promoter region exposed so transcription factors can bind, so RNA polymerase can bind so target gene can be transcribed.

Question 41

What is a malignant tumour?

Answer 41

Fast growing, non-capsulated, do metastasise (spread)

Question 42

What is a benign tumour?

Answer 42

Slow growing, capsulated, do not metastasise (spread)

Question 43

What do proto-onco genes do?

Answer 43

Stimulate cell division

Question 44

What do tumour suppressor genes do?

Answer 44

Inhibit cell division

Question 45

Explain how the methylation of tumour suppressor genes can lead to cancer.

Answer 45

* Methylation prevents transcription of gene; * Protein not produced that prevents cell division / causes cell death / apoptosis; * No control of mitosis.

Question 46

Describe how alterations to tumour suppressor genes can lead to the development of tumours.

Answer 46

* (Increased) methylation (of tumour suppressor genes); * Mutation (in tumour suppressor genes); * Tumour suppressor genes are not transcribed/expressed * OR * Amino acid sequence/primary/ tertiary structure altered; * (Results in) rapid/uncontrollable cell division;

Question 47

Describe how altered DNA may lead to cancer.

Answer 47

* (DNA altered by) mutation; * (mutation) changes base sequence; * of gene controlling cell growth / oncogene / that monitors cell division; * of tumour suppressor gene; * change protein structure / non-functional protein / protein not formed; * (tumour suppressor genes) produce proteins that inhibit cell division; * mitosis; * uncontrolled / rapid / abnormal (cell division); * malignant tumour;