M6 CH19: genetics

Question 1

distinguish euchromatin and heterochromatin

Answer 1

chromatin, DNA wrapped around histones
euchromatin: loosely wound DNA, can be transcribed
heterochromatin: tightly wound DNA, can’t be transcribed

Question 2

state the 3 types of transcriptional control

Answer 2

operon: lac operon
chromatin remodelling
transcription factors: cAMP

Question 3

state the 2 types of post transcriptional control

Answer 3

splicing
RNA editing

Question 4

state the 3 types of translational control

Answer 4

binding of inhibitory proteins to mRNA
initiation factors
mRNA degradation

Question 5

state the 3 types of post-translational control

Answer 5

• modification of cAMP
• addition of non protein groups
• modification of primary proteins

Question 6

explain how the lac operon takes place when lactose is present

Answer 6

• lactose binds to repressor protein

Question 7

explain what the difference is between a structural and regulatory gene.

Answer 7

structural gene: codes for a protein
regulatory gene: controls whether the structural gene is expressed or not

Question 8

outline the two types of gene mutations

Answer 8

point mutation:
- the substitution/deletion or insertion of one base into a nucleotide
- only affects one nucleotide

frameshift mutation:
- insertion/deletion of a nucleotide shifts the reading frame of bases, which changes the triplet codes of all the following base orders.

Question 9

state the 3 possible different effects of mutations

Answer 9

no effect
damage
beneficial

Question 10

explain how mutations can have a negative effect on the overall production of proteins
(3)

Answer 10

• some needed proteins may not be synthesised due to frameshift mutation (or point mutation)
• or some non-functional proteins may be synthesised
• these factors may interfere with essential body processes

Question 11

give an example of a mutation that has been proven to be beneficial in humans (2)

Answer 11

• mutation in the cell surface membrane of human cells
• results in HIV not being able to bind and enter the cells

Question 12

outline the 3 umbrella terms for the causes of mutations

Answer 12

physical mutagens
chemical mutagens
biological agents

Question 13

explain what physical mutagens are, give an example and explain how they can cause mutations

Answer 13

cause mutations
e.g. ionizing radiations such as x ray break DNA strands and mutations can occur in the process

Question 14

explain what chemical mutagens are, give an example and explain how they cause mutations

Answer 14

cause mutations
deaminating agents
- chemically altered bases in DNA
- e.g. C converted to U which changes the base sequence, causing different amino acids to be coded for, :. different protein synthesised

Question 15

explain what biological mutagens are, give 3 examples and explain how they cause mutations.

Answer 15

cause mutations
1. alkylating agents
methyl or ethyl groups are attached to bases, resulting in incorrect base pairings
2. base analogs
incorporated into DNA in place of usual base during replication, changing the base sequence
3. viruses
viral DNA may insert itself into a genome, changing the base sequence

Question 16

outline the 4 ways chromosome mutations can take place

Answer 16

1. deletion: section of chromosome breaks off and is lost in cell
2. duplication: sections of chromosome are duplicated
3. translocation: section of chromosome breaks off and joins another homologous chromosome.
4. inversion: section of chromosome breaks off, is reversed and then reattached to chromosome

Question 17

outline why the majority of mutations do not have an influence on an individuals phenotype.

Answer 17

majority of DNA is non coding, mutations are random and so more likely to occur in non coding regions of DNA. mutations in non coding DNA will not impact phenotype
- also, majority of mutations are silent; they do not change any proteins or the activity of proteins so don’t affect phenotype

Question 18

explain how mutations may be beneficial in a changing environment

Answer 18

mutations result in extreme characteristics (v rare)
due to environment changes these extremes prove to be more beneficial than the normal characteristics
directional selection takes place: rare characteristics from mutations are selected for, causing them to increase in frequency as a consequence of natural selection

Question 19

state the name of the enzyme that catalyses the hydrolysis of lactose

Answer 19

b galactosidase (lactase)
hydrolyses lactose into glucose and galactose

Question 20

what are homeobox genes?

Answer 20

• a group of regulatory genes containing a homeobox
• code for transcription factors; T.F and homeodomain bind to DNA and switch genes on/off
• appear in clusters

Question 21

what are hox genes?

Answer 21

• a group of homeobox genes found only in animals
• responsible for the development of body plans; correct body part positioning

Question 22

describe an example of a homeobox gene

Answer 22

pax 6
- when mutated it causes a form of blindness
- found in mice and fruit flies