t8 gene expression

Question 1

definition of gene mutation

Answer 1

change in the DNA base sequence

Question 2

definition of epigenome

Answer 2

all of the chemical modifications to histone proteins and DNA in an organism

Question 3

definition of epigenetics

Answer 3

inheritable changes in gene function, without changes to DNA base sequence

Question 4

what is a transcription factor

Answer 4

protein that initiates the transcription of genes by binding to specific base sequences on DNA (promoter region) and allowing RNA polymerase to bind

Question 5

what is a mutagenic agent + examples

Answer 5

factor that increases the rate of mutations
eg. UV light, X-rays, asbestos, alpha and beta particles

Question 6

6 types of mutation (brief)

Answer 6

1. addition
2. deletion
3. substitution
4. duplication
5. translocation
6. inversion

Question 7

what is an addition mutation

Answer 7

-an extra nucleotide (with a new base) is inserted into the DNA base sequence, causing a frame shift to the RIGHT
-can dramatically change the amino acid sequence produced, affecting the tertiary structure of the polypeptide, potentially leading to a non-functional protein
-however, if 3 bases are inserted, frame shift wont occur

Question 8

what is a deletion mutation

Answer 8

-nucleotide (and its base) is randomly deleted from the DNA base sequence, causing a frame shift to the LEFT
-can dramatically change the amino acid sequence, affecting the tertiary structure, potentially leading to a non-functional protein

Question 9

what is a substitution mutation

Answer 9

-a base in the DNA sequence is randomly swapped for a different base
-only affects the amino acid for the triplet in which the mutation occurs (no frame shift)
-can cause silent mutation (no change to amino acid sequence as genetic code is degenerate), missense mutation (alters single amino acid) or nonsense mutation (causes premature stop codon)

Question 10

what is a duplication mutation

Answer 10

-a whole gene or section of a gene is repeated, so 2 copies of the same gene/section appear on the same chromosome
-produces frame shift to the RIGHT

Question 11

what is an inversion mutation

Answer 11

-a group of bases become separated from the DNA sequence and then rejoin in the same position, but in the reverse order
-affects multiple amino acids, affecting the tertiary structure, so potentially leading to a non-functional protein
-usually occur during crossing-over in meiosis

Question 12

what is a translocation mutation

Answer 12

-a group of bases becomes separated from the DNA and rejoins on a separate gene or to the same chromosome in a different location
-the cut gene is now non-functional as it has a section missing, and the gene that has gained the translocated section is likely to be non-functional.

Question 13

benefit of mutation

Answer 13

-produce the genetic diversity necessary for natural selection and speciation

Question 14

costs of mutations

Answer 14

-almost always harmful and produce an organism less suited to its environment
-mutations in body cells lead to disruptions of regular cellular activity eg. mutations in cell division processes can lead to cancer
-cause hereditary mutations when they occur in gametes

Question 15

what is a stem cell

Answer 15

-unspecialised cells that can divide by mitosis an unlimited number of times
-can make copies of themselves, or develop into specialised cells by differentiation

Question 16

what is cell differentiation

Answer 16

-process by which a cell develops into a specialised cell suited for its role by producing different proteins

Question 17

what are totipotent stem cells

Answer 17

-can divide and produce any type of body cell INCLUDING new embryonic cells and placental cells
-initially unspecialised, but specialise during embryonic development
-exist for a limited time in early embryos

Question 18

what are pluripotent stem cells

Answer 18

-can divide and produce any type of body cell EXCEPT placental cells
-can divide an unlimited number of times and keep replacing themselves, allowing them to be used in treating human cells (iPS cells)

Question 19

what are multipotent adult stem cells

Answer 19

-can differentiate into a limited range of cell types, and are used to produce new cells for the processes of growth, cell replacement and tissue repair
-found in the bone marrow - these can only differentiate into blood cells (rbcs, phagocytes and lymphocytes)

Question 20

what are unipotent stem cells

Answer 20

-adult cells that can only differentiate into a single type of cell in their own lineage
-eg. cardiomyocytes - unipotent type of stem cell found in the cardiac muscle that is important after damage through heart attack or age

Question 21

what are induced pluripotent stem cells (iPS cell)

Answer 21

-produced from adult somatic (body) cells using transcription factors
-transcription factors cause specific genes to be expressed which revert cell back to its pluripotent state
-could be used to generate transplants without the risk of immune rejection

Question 22

2 types of transcription factors + explanation

Answer 22

1. activators - stimulate/increase rate of transcription by helping RNA polymerase bind to the promoter region
2. repressors - inhibit/decrease the rate of transcription by binding to the promoter region and blocking RNA polymerase from binding

Question 23

how does oestrogen affect transcription

Answer 23

1. diffuses through phospholipid CS membrane (as it is lipid-based due to being a steroid hormone)
2. binds to transcription factor in the cytoplasm, forming oestrogen-oestrogen receptor complex, changing the shape of the transcription factor and making it complementary to the DNA
3. complex enters the nucleus through nuclear pore and binds to promoter region on DNA
4. RNA polymerase can then attach to the DNA, initiating transcription

Question 24

how are changes to the epigenome made

Answer 24

-changed in environment eg. toxins from smoking, stress, exercise and diet

Question 25

2 types of epigenetic tags (brief)

Answer 25

1. increased methylation of DNA
2. decreased acetylation of histones

Question 26

effect of increased methylation of DNA

Answer 26

-addition of methyl groups to DNA causes DNA to coil tightly, preventing transcription factors from binding, preventing transcription

Question 27

effect of decreased acetylation of histones

Answer 27

when acetyl groups are removed from histones, the DNA coils tightly, preventing transcription factors from binding, preventing transcription

Question 28

cancer treatments - what do drugs that reverse epigenetic changes do

Answer 28

1. removal of methyl groups from DNA of tumour suppressor genes will enable them to be expressed, regulating the cell cycle and stopping tumour development
2. removal of acetyl groups from histones attached to oncogenes causes the DNA to wrap more tightly, silencing these genes (turns them back into proto-oncogenes). this causes cell death (apoptosis)

Question 29

how does small interfering RNA (siRNA) regulate transcription

Answer 29

1. an enzyme cuts large, double stranded molecules of RNA into smaller sections called siRNA
2. one of the 2 strands combines with another enzyme, and the siRNA molecule guides the enzyme to an mRNA molecule via complementary base pairing
3. once in position, the enzyme cuts the mRNA into smaller sections, so the mRNA is no longer capable of being translated into a polypeptide. this means the gene has not been expressed

Question 30

properties of benign tumours

Answer 30

-grow very slowly
-are contained and dont metastasise
-often specialised
-can usually be removed through surgery alone
-rarely reoccur after treatment

Question 31

properties of malignant tumours

Answer 31

-grow rapidly
-are uncontained and can metastasise
-often unspecialised
-removal involves surgery and chemo/radiotherapy
-can reoccur after treatment

Question 32

how can oestrogen cause breast cancer

Answer 32

-increased oestrogen concentrations in fatty tissue of the breast in post-menopausal women can be linked to breast cancer as oestrogen binds to transcription factors, activating the genes promoting cell division, leading to tumour formation.

Question 33

risk factors for cancer

Answer 33

1. genetic risks
2. environmental risks - alcohol, radiation exposure, smoking, lack of exercise and high-fat diet linked to obesity