20 - Gene Expression

Question 1

mutation

Answer 1

change in amount or structure of the DNA of an organism

Question 2

point mutations

Answer 2

change only one nucleotide at a particular locus

eg. substitution, addition, deletion

Question 3

duplication

Answer 3

one or more bases are repeated, causes frame shift to right

Question 4

inversion

Answer 4

a group of bases become separated from the DNA sequence and rejoins in the reverse order

Question 5

translocation

Answer 5

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

Question 6

mutagens

Answer 6

environmental factors that increase rate of mutation

Question 7

cons of mutation:

Answer 7

are often harmful
can produce organisms less suited to environment
can lead to problems in cellular activities

Question 8

benefit of mutation

Answer 8

provide genetic variation required for natural selection and speciation

Question 9

embryonic stem cells

Answer 9

undifferentiated and totipotent

can divide and produce any type of body cell

Question 10

totipotent cells

Answer 10

only occur in a limited time in early mammalian embryos

Question 11

pluripotent cells

Answer 11

found in embryos
can divide in unlimited numbers
can be used in treating human diseases

Question 12

unipotent cells

Answer 12

found in mature mammals
can only differentiate into a single type of cell
derived from multipotent cells

Question 13

multipotent cells

Answer 13

found in mature mammals and can differentiate into a limited number of specialised cells

Question 14

stem cells found in animals (after early development):

Answer 14

inner lining of small intestine
skin
bone marrow (form blood cells)

Question 15

expression of genes in differentiated cells

Answer 15

some genes are permanently expressed, some genes are never expressed, some are only expressed when necessary

Question 16

induced pluripotent cells iPS

Answer 16

genetically altered in labs to acquire characteristics of embryonic stem cells
cells are induced to express genes that were previously switched off
produced from unipotent cells or adult somatic cells using appropriate protein transcription factors

Question 17

controlling the expression of a gene

Answer 17

1. transcriptional factors turn on the gene to allow transcription to begin
2. each transcription factor binds to a specific base sequence of DNA
3. the region it binds to begins transcription
4. mRNA is produced and goes on to be translated into a polypeptide

Question 18

promoter region

Answer 18

specific region of DNA which the transcriptional factor binds to

Question 19

oestrogens role in activating genes

Answer 19

binds to the transcriptional factor and causes its DNA binding site to change shape
transcriptional factor is then able to bind to promoter region of DNA, stimulating transcription

Question 20

epigenetics

Answer 20

heritable changes in gene function, without changes to base sequence of DNA
DNA code is fixed, however epigenome is flexible

Question 21

epigenome

Answer 21

the chemical tags which determine the shape of the DNA-histone complex (aka chromatin)
these tags can respond to environmental changes

Question 22

weak association between DNA and histones

Answer 22

chromatin is less condensed

therefore more accessible by transcription factors

Question 23

strong association between DNA and histones

Answer 23

chromatin more condensed
therefore less accessible by transcription factors
(production of mRNA by transcription cannot be initiated in these areas, so gene switched off)

Question 24

acetylation

Answer 24

process by which an acetyl group is transferred to a histone (usually donated by acetyl coA)

decreased acetylation increases the positive charge on the histone
increased attraction between histone and phosphate groups of DNA
stronger association between DNA and histone so chromatin more condensed

Question 25

methylation

Answer 25

addition of a methyl group to the cytosine bases of DNA

inhibits transcription of genes by:

1. preventing the binding of transcriptional factors to DNA
2. attracting proteins which condense the chromatin by inducing deacetylation

Question 26

epigenetic therapies

Answer 26

use drugs to inhibit enzymes involved in histone acetylation or DNA methylation
must be targeted specifically at cancer cells
if the drugs affect normal cells they would activate gene transcription, making them cancerous

Question 27

inhibiting the translation of mRNA

Answer 27

enzyme cuts large double stranded RNA molecules into smaller sections called small interfering RNA (siRNA)
one of the siRNA strands combines with an enzyme
the siRNA molecule guides the enzyme to an mRNA molecule
it pairs with the complementary bases on the mRNA strand and the enzyme cuts the mRNA into small sections
the mRNA can no longer be translated into a polypeptide

Question 28

tumours and cancer

Answer 28

not all tumours are cancerous
cancerous tumours are malignant
non-cancerous tumours are benign

Question 29

benign tumours

Answer 29

can grow to a large size
grow very slowly
cell nucleus has relatively normal appearance
cells often well differentiated
tend to have localised effect on body
cells produce adhesion molecules that make them stick together and so they remain within the tissue from which they arise

Question 30

malignant tumours

Answer 30

can grow to a large size
grow rapidly
cell nucleus is often larger and appears darker due to abundance of DNA
cells become de-differentiated
often have systematic (whole body) effects
do not produce adhesion molecules and so tend to spread to other regions (metastasis producing sceondary tumours)

Question 31

proto-oncogenes

Answer 31

stimulate a cell to divide when growth factors attach to a protein on its cells surface membrane

Question 32

oncogenes

Answer 32

they are mutations of proto-oncogenes

an oncogene can be permanently activated:

1. receptor protein on the membrane can be permanently activated, so that cell division occurs without the presence of growth factors
2. oncogene may code for a growth factor which is then produced in excessive amounts, stimulating excessive cell division

Question 33

tumour suppressor genes

Answer 33

maintain the rate of cell division, repair mistakes in DNA and cause apoptosis (programmed cell death)

Question 34

effect of mutated tumour suppressor gene

Answer 34

it is inactivated
as a result stops inhibiting cell division
cells are able to grow out of control

Question 35

hypermethylation of tumour suppressor genes

Answer 35

1. hypermethylation occurs in promoter region of a tumour suppressor gene
2. transcription of promote regions of tumour suppressor gene is inhibited
3. the tumour suppressor gene becomes inactivated
4. its inactivation leads to increased cell division and formation of a tumour

Question 36

hypomethylation

Answer 36

reduced methylation

can occur in oncogenes, where it leads to their activation and therefore the formation of tumours

Question 37

oestrogen and breast cancer

Answer 37

increased oestrogen concentrations after menopause are though to cause breast cancer

oestrogen acts on a gene that controls cell division and growth, activating it
continued cell division may produce a tumour

oestrogen causes proto-oncogenes in breast tissue to develop into oncogenes