cellular control

Question 1

mutations

Answer 1

a random change in the nucleotide base sequence within the DNA molecule

Question 2

what is a mutagen?

Answer 2

something that increases the rate of spontaneous mutations

Question 3

physical mutagens

Answer 3

-ionising radiation
-breaking DNA strand

Question 4

chemical mutagens

Answer 4

-deaminating agents
-alter bases in DNA

Question 5

biological agents

Answer 5

-alkylating agents
methyl/ethyl groups attached to bases - leads to the incorrect
pairing of bases during replication

-base analogs
incorporated into DNA instead of the usual base during replication
changes base sequence

-viruses
viral DNA inserts itself into a genome changing the base sequence

Question 6

substitution mutations

Answer 6

one base pair is replaced for another
usually leads to a single different amino acid being inserted during translation

Question 7

deletion mutations

Answer 7

base pair is lost from the DNA sequence causing a ‘frame shift’
results in every codon being ‘down stream’ being different

Question 8

insertion/addition mutations

Answer 8

extra base pair is inserted into the DNA sequence causing frame shift
results in every codon being ‘down stream’ being different

Question 9

substitution mutations

Answer 9

1. MIS SENSE
   one nucleotide base substituted with another
   means one amino acid in the sequence is wrong
2. NONSENSE
   one base is substituted with another
   causes stop codon to be created
3. SILENT
   substitution occurs where no effect on the amino acid
   due to degenerate nature of the code

Question 10

deletions and insertions

Answer 10

one base in a gene changes then the protein/enzyme may be non-functional

deletion mutation of a nucleotide base can cause a frame shift as the code will now read one base to the right for every codon

Question 11

effects of mutations

Answer 11

NO EFFECT
no change in phenotype as normally functioning protein is made
- degenerate nature of the genetic code (some AA have more than one codon)
- AA is replaced with a similar AA
- AA is in part of a polypeptide that does effect folding/function (e.g. active site of an enzyme)

DAMAGING
proteins are made that are non-functional or not synthesised at all

BENEFICIAL
a protein is made that has new and useful characteristics
this is what drives evolution by natural selection

Question 12

advantageous mutation

Answer 12

ability to ingest lactose after stop suckling
can prevent osteoporosis

Question 13

mutation that can be inherited

Answer 13

cystic fibrosis
70% caused by deletion of 3 bases for a protein
means 1 AA out of 1480 is missing (1479)

sickle cell anaemia
point mutation on codon 6
causing valine AA to be placed instead of glutamic acid
causes sickling of red blood cells

Question 14

mutations with neutral effects

Answer 14

silent mutations do not change protein structure (degenerate)
mutation may occur n noncoding region
gene is changed into a different allele with no dis/advantages
e.g. ability to smell honey suckle flowers

Question 15

chromosome mutation

Answer 15

affects whole chromosome/multiple
can be caused by mutagens

DELETION section of chromosome breaks off and lost
DUPLICATION section on chromosome duplicated
TRANSLOACTION section of one chromosome breaks off and joins another
INVERSION section of a chromosome breaks off, is reversed and joins back onto the chromosome

Question 16

control of gene expression

Answer 16

-housekeeping gene
genes that code for enzymes needed for reactions in metabolic
pathways
needed constantly

-protein based hormones
for growth and development
only required by certain cells at certain times
coded for by tissue specific genes

-gene regulation
genes need to be turned on/off as the rate of proteins synthesis
changes for demand

Question 17

transcriptional genes

Answer 17

genes can be turned on/off

Question 18

post-transcriptional genes

Answer 18

mRNA can be modified which regulates translation and types of proteins needed

Question 19

translational genes

Answer 19

translation stopped or started

Question 20

post-translational genes

Answer 20

proteins modified after synthesis which changes their functions

Question 21

an operon

Answer 21

group of genes that are under the control of the same regulatory mechanism and are expressed at the same time

more common in prokaryotes

efficient way of saving resources
certain gene products are not needed
all the genes involved in their production can be switched off

Question 22

lac operon

Answer 22

1. E Coli usually uses glucose as a respiratory substrate to make ATP
2. E Coli can use lactose as a respiratory substrate to make ATP
3. If placed in lactose it can quickly make 3 proteins to aid in using
   lactose
4. Lactose permease - which transports lactose into the cell
   Beta galactosidase - enzyme that hydrolyses lactose into glucose
   and galactose
   Transacetylase

Question 23

regulatory gene

Answer 23

NOT part of operon but codes for a repressor protein which regulates transcription of ZY gene
Makes a repressor protein/transcription factor
Product of this gene switches another gene on/off

Question 24

operator (O)

Answer 24

can switch structural gene on/off
do not code for polypeptides

Question 25

promoter (P)

Answer 25

RNA polymerase binds here for transcription of ZY do not code for polypeptides

Question 26

structural genes

Answer 26

- Makes enzymes/polypeptide/protein - Expression of the structural gene is controlled by the regulatory gene - DNA that can be transcribed to make one long piece of mRNA that can be translated into Lac Z - Beta galactosidase Lac Y - Lactose permease Lac A - Transacetylase

Question 27

how lac operon functions when NO LACTOSE

Answer 27

1. RNA transcribes regulatory gene 2. Translation of mRNA by ribosome to form repressor protein 3. This binds to O but it covers P so RNA polymerase cant do transcription 4. No mRNA formed No translation No enzymes made

Question 28

how lac operon functions when LACTOSE PRESENT

Answer 28

1. RNA transcribes regulatory gene 2. Translation of mRNA by ribosome to form repressor protein 3. This binds to O but it covers P so RNA polymerase cant do transcription 4. Lactose acts as an inducer molecule binds to other side of repressor protein 5. Causes it to change shape and leave O 6. RNA polymerase can now attach to promoter region Transcription of ZYA genes 7. mRNA translated to form Lac Z - Beta galactosidase Lac Y - Lactose permease Lac A - Transacetylase

Question 29

function of repressor protein

Answer 29

bind to operator blocks promoter prevents RNA polymerase from transcribing structural genes ZYA

Question 30

advantages of this lac operon system

Answer 30

enzymes made by E Coli when lactose available for respiration no enzymes produced if no lactose no resources wasted making unnecessary enzymes