paper 2: Gene Expression

Question 1

describe a deletion mutation

Answer 1

one or more DNA bases are removed from the DNA base sequence

Question 2

describe a substitution mutation

Answer 2

when one base is changed for a different base

Question 3

describe an addition mutation

Answer 3

when one or more bases are inserted into a DNA base sequence, causing a frameshift

Question 4

describe an inversion mutation

Answer 4

a group of bases becomes separated from the DNA base sequence and re-join at the same position but in the inverse order

Question 5

describe a translocation mutation

Answer 5

a group of bases become separated from the DNA base sequence on one chromosome and becomes inserted into the DNA sequence of a different chromosome which causes a frameshift

Question 6

describe a duplication mutation

Answer 6

one or more bases are repeated so a frameshift is caused

Question 7

describe the two features in a stem cell

Answer 7

stem cells are undifferentiated and can keep dividing and can differentiate into specialised cells.

Question 8

define the term totipotent stem cells and name at what point in life are they present.

Answer 8

cells which divide and differentiate into any cell type and are present during early life in mammalian embryos

Question 9

define the term pluripotent stem cells nd name at which point in life they are present

Answer 9

cells which divide and differentiate into most cell types and are found later in mammalian embryos

Question 10

define the term multipotent stem cells and name at what point in life they are present

Answer 10

cells which divide and differentiate into a limited number of different cell types and are found in mature mammals

Question 11

define the term unipotent stem cells and name at which point in life are thye present and give an example in humans

Answer 11

cells which divide and differentiate into only one cell type and is found in mature mammals
e.g. cardiomyocytes in the heart muscle

Question 12

explain how stem cell transplants can be used in treatment of diseases.

Answer 12

stem cells are transplanted into the body so they can divide and differentiate to produce healthy cells to replace the damaged cells.

Question 13

describe how leukemia can be treated with stem cells

Answer 13

• bone marrow is used from a close relative to reduce the chance of rejection
• the stem cells continuously divide and differetiate to produce healthy white blood cells, giving a long term treatment

Question 14

describe adult stem cells

Answer 14

from same individual/close relative and are multipotent

Question 15

describe embryonic stem cells

Answer 15

pluripotent

Question 16

what are the advantages of using adult stem cells in medicine

Answer 16

• no ethical issues
• less chnace of rejection (similar/same DNA)

Question 17

what are the disadvantages of using adult stem cells in medicine

Answer 17

• multipotent so can only differentiate into a limited number of cell types
• difficult to isolate

Question 18

what are the advantages of using embryonic stem cells in medicine

Answer 18

• pluripotent so can divide and diferentiate into almost all cell types
• easy to isolate as yoiu use embryos from IVF

Question 19

what are the disadvantages of using embryonic stem cells in medicine

Answer 19

• ethical issues
• high chance of rejection

Question 20

describe what induced pluripotent stem cells are

Answer 20

• normal cells which are removed from a patient and factors are added to make a cell pluripotent
• they can then divide and differentiate into the desired cell type
• specialised cells are transplanted back into the patient

Question 21

what are the advantages of induced pluripotent stem cells

Answer 21

• no ethical issues as using own cells
• can differentiate into almost all cell types
• less chance of rejection

Question 22

explain how transcription factors control transcription

Answer 22

• transcription factors are prtoeins
• in eukaryotes, transcription factrs move from the cytoplasm to the nucleus
• they bind a promoter of a gene
• this stimulates/ inhibits RNA polymerase to transcribe the gene and produce mRNA

Question 23

what are the 2 types of transcription factors and what do they do

Answer 23

• activators: activate transcription by causing RNA polymerase to bind
• inhibitors: inhibit transcription by binding the promoter and preventing RNA polymerase binding

Question 24

describe how oestrogen (or testosterone) acts as a transcription factor

Answer 24

• oestrogen is a lipid so is lipid soluble so crosses the phospholipid bilayer by diffusion
• oestrogen binds to a protein receptor in the cytoplasm
• receptor - oestorogen complex is a transcription factor so binds a promoter
• this stimulates RNA polymerase to transcribe the gene and produce mRNA

Question 25

how can increased oestrogen conc.s lead to an increased risk of breast cancer

Answer 25

- oestrogen can cause breast cells to divide more - more likely that mutations occur when DNA replicates - faster division of cancerious cells will produce tumours more quickly

Question 26

why are all cells not affected by oestorgen

Answer 26

not all cells have a complimentary oestrogen receptor in the cytoplasm

Question 27

describe the steps of RNAi

Answer 27

1. small interfering RNA (siRNA) has a specific complimentary base sequence to the target mRNA 2. the siRNA binds to a protein (RISC) which acts as an enzyme 3. one of the siRNA strands is removed to make it single stranded 4. the siRNA now binds to mRNA molecules by complimentary base pairing 5. the mRNA is destroyed 6. the mRNA can no longer be used in translation and is broken down by enzymes

Question 28

describe the difference between miRNA and siRNA

Answer 28

- miRNA is not fully complimentary and not specific to one mRNA and therefore targets more than one type of mRNA unlike siRNA which can only target one type.

Question 29

how is cancer caused

Answer 29

- mutations in the genes which control mitosis - this leads to uncontrolled xell division formng a mass of cells called a tumour

Question 30

what are the 2 types of tumours

Answer 30

benign and melignant

Question 31

describe a melignant tumour

Answer 31

cells can break off and spread to other parts of the body, forming a tumour elsewhere (metastasis)

Question 32

describe a benign tumour

Answer 32

cells do not spread to other parts of the body ( no metastasis)

Question 33

what is a tumour supressor gene

Answer 33

they produce protiens which inhibit cell division

Question 34

happens when there is a mutation in a tumour supressor gene

Answer 34

- inhibit the formation of proteins which prevents mitosis or makes them non-functional - this leads to uncontrolled cell division

Question 35

what are proto-oncogenes

Answer 35

produce proteins which stimulate cell division

Question 36

what happens when there is a mutation nin a proto-oncogene

Answer 36

- mutations of of proto-oncogenes to oncogenes forms more proteins which cause cell division - leads to uncontrolld cell division

Question 37

define epigenetics

Answer 37

- hertable chnages in gene function - caused by changes in the environment - without changes in the DNA base sequence

Question 38

describe methylation

Answer 38

- methyl groups are added to DNA - transcrition factors cannot bind the promoter - gene is not transcribed

Question 39

describe acetylation of histone proteins

Answer 39

- the addition of histone proteins makes chromatin less eondensed - transcriptions factors can bind the promoter - transcription does occur

Question 40

what would happen if acetyl groups were removed from the histone proteins

Answer 40

- chromatin would become more condensed - transcription factors cannot bind the promoter - transcription does not occur