The Control of Gene Expression

Question 1

what is a mutation?

Answer 1

any change to the base (nucleotide) sequence of DNA

Question 2

how are mutations caused?

Answer 2

by errors during DNA replication

Question 3

how can the rate of mutations be increased?

Answer 3

by mutagenic agents

Question 4

list the types of mutations that can occur

Answer 4

substitution
deletion
addition
duplication
inversion
translocation

Question 5

what is substitution?

Answer 5

one or more bases are swapped for another

Question 6

what is deletion?

Answer 6

one or more based are removed

Question 7

what is addition?

Answer 7

one or more based are added

Question 8

what is duplication?

Answer 8

one or more bases are repeated

Question 8

what is inversion?

Answer 8

a sequence of bases is reversed

Question 9

what is translocation?

Answer 9

a sequence of bases is moved from one location in the genome to another. this could be the movement within the same chromosome or movement to a different chromosome.

Question 10

what is the result of a mutation in a polypeptide?

Answer 10

a mutation in a polypeptide that makes up an enzyme may change the shape of the enzyme’s active site. this may stop substrates from being able to bind to the active site, leaving the enzyme unable to catalyse the reaction.

Question 11

why don’t all mutations affect the order of amino acids?

Answer 11

the degenerate nature of the genetic code means that some amino acids are coded for by more than one DNA triplet. this means not all types of mutations will always result in a change to the amino acid sequence of the polypeptide.

Question 12

what mutations do change the amino acid sequence of a polypeptide and why?

Answer 12

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

Question 13

what are some examples of mutagenic agents?

Answer 13

ultraviolet radiation, ionising radiation, some chemicals and some viruses.

Question 14

what are the ways that mutagenic agents are able to increase the rate of mutations?

Answer 14

acting as a base — chemicals called base analogs can substitute for a base during DNA replication, changing the base sequence in the new DNA.
altering bases — some chemicals can delete or alter bases.
changing the structure of DNA — some types of radiation can change the structure of DNA, which causes problems during DNA replication.

Question 15

what are stem cells?

Answer 15

stem cells are unspecialised cells that can develop into other types of cell.
stem cells divide to become new cells, which then become specialised.
all multicellular organisms have some form of stem cell.

Question 16

where are stem cells found?

Answer 16

stem cells are found in the embryo and in some adult tissues.

Question 17

what are totipotent cells?

Answer 17

these are stem cells that can mature/develop into any type of body cell in an organism.
they are only present in mammals in the first few cell divisions of an embryo.

Question 18

what are multipotent stem cells?

Answer 18

stem cells present in adult mammals. these are able to differentiate into a few different types of cell.

Question 19

what are unipotent stem cells?

Answer 19

stem cells present in adult mammals. these can only differentiate into one type of cell.