8. Control of Gene Expression (incomplete)

Question 1

what is a gene mutation?

Answer 1

a change to the base sequence of DNA

Question 2

when are gene mutations most likely to occur

Answer 2

during DNA replication

Question 3

do gene mutations occur spontaneously?

Answer 3

yes

Question 4

what is a mutagenic agent?

Answer 4

a substance that increases the rate of mutation

Question 5

what are two different types of mutagenic agent?

Answer 5

• high energy and ionising radiation (eg gamma rays, UV and X rays)
• carcinogens eg chemicals in tobacco smoke

Question 6

what are the 6 types of mutation that can occur?

Answer 6

• substitution
• deletion
• addition
• duplication
• inversion
• translocation

Question 7

what is an addition mutation?

Answer 7

when one or more bases are added to the base sequence

eg. AGGTTAC becomes AGGTTACA

Question 8

what is the impact of an addition mutation on the base sequence?

Answer 8

all the subsequent codons are affected, resulting in a frame shift

Question 9

what is a deletion mutation?

Answer 9

when one or more bases are removed from the base sequence
eg. AGGTTA becomes AGGTT

Question 10

what is the impact of a deletion mutation on the base sequence?

Answer 10

causes a frame shift, a change to all the subsequent triplets

Question 11

what is the impact of a substitution mutation on the base sequence?

Answer 11

only one codon will change (the codon where the substitution occurred)

Question 12

what is a substitution mutation?

Answer 12

when one or more bases are swapped with eachother

eg. AGGTTAC becomes AGGTTAG

Question 13

what can mutations result in?

Answer 13

a different amino acid sequence in the encoded polypeptide

Question 14

what is an inversion mutation?

Answer 14

when a section of bases detach from the DNA sequence, and reattach at the same position but in the reverse order

eg. AGGTTAC becomes AGGATTC

Question 15

what is the impact of an inversion mutation on the base sequence?

Answer 15

new amino acids may be coded for in the affected region

Question 16

what is a translocation mutation?

Answer 16

when a section of bases detaches from the DNA sequence on one chromosome and attaches onto a different chromosome

Question 17

what are the impacts of a translocation mutation?

Answer 17

can change the resulting phenotype

Question 18

what can mutations result in?

Answer 18

a different amino acid sequence in the encoded polypeptide

Question 19

what can a different amino acid sequence in the encoded polypeptide do to the tertiary structure of a protein?

Answer 19

• the hydrogen, ionic and disulphide bonds between R groups will form in different places, causing the tertiary structure to fold differently, forming a different 3D shape and thus a non-functioning protein (or non complimentary enzyme due to change in active site shape, so no EZ complexes can form)

Question 20

why might a mutation not always affect the order of amino acids?

Answer 20

• due to the degenerate nature of the genetic code (more than one triplet of bases codes for the same amino acid), some mutations may still code for the same amino acid (eg. substitutions), so there will be no overall effect on the encoded polypeptide.

Question 21

what types of mutation will almost always cause a change to the amino acid sequence of a polypeptide? why?

Answer 21

additions, duplications and deletions
- because these mutations change the number of bases in the DNA code. this causes a frame shift in all of the triplets of bases that follow, so that each subsequent triplet is read in a different way.

Question 22

what are stem cells?

Answer 22

stem cells are unspecialised cells that continually divide/differentiate to become any type of cell (specialised)

Question 23

what is differentiation?

Answer 23

the process by which cells become specialised

Question 24

what are the four different types of stem cell?

Answer 24

totipotent
multipotent
pluripotent
unipotent

Question 25

which type of stem cell can divide to produce any type of body cell?

Answer 25

totipotent stem cells

Question 26

what do totipotent stem cells do during development?

Answer 26

translate only part of their dna, leading to specialisation.

Question 27

• for how long do totipotent stem cells occur?
• during this time, where do they occur?

Answer 27

• a limited time
• early mammalian embryos (hence why they are sometimes called embryonic stem cells)

Question 28

where are pluripotent stem cells found?

Answer 28

in embryos

Question 29

where are multipotent and unipotent stem cells found?

Answer 29

in mature mammals

Question 30

what can pluripotent stem cells do?

Answer 30

divide in unlimited numbers and develop into most types of body cell (cannot divide into placenta cells)
- can be used to treat human disorders

Question 31

what can multipotent stem cells do?

Answer 31

divide to produce a limited number of different cell types

Question 32

what are the issues and benefits of using pluripotent stem cells to in treatments?

Answer 32

• sometimes the treatment doesnt work
• the stem cells may continually divide to create tumours
• ethical debates g. whether it is right to make a therapeutic clone of yourself in an embryo to get the stem cells, and then destroy the embryo.
• stem cells can be used to grow organs that can save lives
• bone marrow cells already being used to treat leukemia

Question 33

what can unipotent stem cells do?

Answer 33

can only differentiate into one type of cell, such as cardiomyocytes (heart muscle cells)
- cannot regenerate

Question 34

what can be used to overcome the ethical issues of using embryonic stem cells? how are they produced?

Answer 34

• induced pluripotent stem cells (iPS)
• can be produced by taking somatic (normal) adult specialised cells and infecting them with a modified virus with genes coding for transcription factors so that the cells become pluripotent. the transcription factors will then attach to the promoter region of DNA and stimulate RNA polymerase to stimulate transcription