genetics of living systems

Question 1

4 ways genes are regulated

Answer 1

• Transcriptional - genes turned on and off
• post transcriptional -mRNA can be modified which regulates translation of certain proteins
• translational - can be stopped or started
• post translational - proteins can be modified after translation in other organelles

Question 2

TRANSCRIPTIONAL CONTROL

- 3 different methods

Answer 2

• Chromatin remodelling
• Histone modification
• trancription factors (lac operon in bacteria)

Question 3

Chromatin remodelling

what is heterochromatin?

Answer 3

HETEROCHROMIN
—> TIGHTLY wound DNA

—>causes chromatin to be visible during cell division

—> no transcription as RNA polymerase cant access genes

—> ensures NO PROTEIN SYNTHESIS DURING DIVISION

Question 4

Chromatin remodelling

What is euchromatin?

Answer 4

EUchromatin
—> loosely wound DNA
—> can be freely transcribed

Question 5

Chromatin remodelling

why is it used?

Answer 5

ensures protein synthesis only occurs during interphase

—> as it is time + energy consuming

Question 6

Histone modification

Answer 6

histones can be modified to increase/decrease degree of DNA packing

histones are positively charged, DNA is negatively charged

Question 7

how to cause DNA to coil less tighly

Answer 7

ACETYLATION- addition if acetyl group

PHOSPHORYLATION- addition of phosphate group

—> these reduce +ve charge on histones
—> increased repulsion

=> allows certain genes to be transcripted

Question 8

how to cause DNA to be bound more tightly

Answer 8

METHYLATION- addition if methyl group

—>makes histones more hydrophobic
—>DNA coils more tighly
—> prevents transcription

Question 9

what is epigenetics?

Answer 9

external control of gene expression by modificstion of DNA

Question 10

LAC OPERON

type of genes in lac operon

Answer 10

structural genes

Question 11

LAC OPERON

genes in lac operon

Answer 11

lacZ - gene codes for enzyme that breaks down lactose

lacY - gene codes for channel protein to allow lactose into bacterium

lacA - idgaf

Question 12

LAC OPERON

why do bacteria need operons?

Answer 12

-more common in prokaryotes as they are more simple/small structure

=> efficient way of saving resources bc if gene products arent needed, all of genes involved in production can be turned off

Question 13

LAC OPERON

what gene codes for the repressor?

Answer 13

regulatory gene —> lacI

Question 14

repressor gene function

Answer 14

codes for repressor protein( transcription factor)

which binds to the OPERATOR

RNA POLYMERASE cant carry out
transcription

Question 15

LAC OPERON

when lactose is present

Answer 15

• lactose binds to repressor protein which inactivates it
• repressor cant bind to operator anylonger
• RNA polymerase can bind to PROMOTER and carry out transcription
• three structural genes are synthesised

Question 16

role if Cyclic AMP (cAMP)

Answer 16

RNA polymerase carrys out transcription slowly
needs to be increased to prod right amount of proteins

—> cAMP binds to cAMP receptor protein (CRP)
- activates CRP

which increases transcription rate

Question 17

role of cAMP

when glucose is low

Answer 17

high lvls of cAMP produced

• more cAMP - CRP compexes
• more freq transcription

Question 18

POST TRANSCRIPTIONAL CONTROL

splicing

Answer 18

after transcription pre mRNA is made
=> cap added to 5’ end
=> poly adenine tail added to 3’ end
HELPS KEEP mRNA STABLE

SPLICING CAN TAKE PLACE
to make multiple different proteins from one gene
—>introns ( non coding parts) cut off and removed
—> exons (coding parts)joined together

Question 19

POST TRANSCRIPTIONAL CONTROL

RNA editing

Answer 19

change nucleotide base
SAME CHANGES AS MUTATION
- addition
-deletion
- substitution

Question 20

TRANSLATIONAL CONTROL

3 methods

Answer 20

mRNA degradation

-more resistant molecule the longer it will last

Question 21

POST TRANSLATIONAL CONTROL

Answer 21

modifications to proteins

Question 22

Mutation

Answer 22

change in sequence of bases in dna

Question 23

types of mutations

Answer 23

substitution

deletion

insertion

Question 24

mutations

substitution?

Answer 24

single nucleotide changes in a codon
=>change in codon
=> may cause change in primary structurr
=> degenerate nature of DNA means codon could still code for the same amino acid

Question 25

insertion mutation

Answer 25

addition if a nucleotide in a codon

Question 26

deletion mutation

Answer 26

nucleotide is removed from codon

Question 27

cause of insertion or deletion mutation?

Answer 27

causes a FRAMESHIFT MUTATION

DNA is read in codons and is non overlapping

insertion/deletion moves the reading frame

=> so each successive codon will now be different and code for different amino acids

Question 28

when does insertion/deletion not cause frameshift mutation

Answer 28

when multiples of 3 of nucleotides are added/ deleted

multiples of three correspond to full codons
reading frame wont change

only extra/less amino acids will be added

Question 29

causes of mutations

Answer 29

spontaneous mutation

mutagens - physical/chemical/biological

depurination/depyramidation - abscence of a base can lead to insertion of incorrect base im DNA replication

Free radicals(oxidising agents)- cam affect structure of nucleotides /can interfere with base pairing

Question 30

physical mutagens

Answer 30

ionising radiations eg x-rays

=> break one/both DNA strands

Question 31

chemical mutagens

Answer 31

deaminating agents

• chemically alters bases in DNA

eg converting cytosine to uracil changing base sequence

Question 32

Biological mutagens

Answer 32

ALKYLATING AGENTS
—> methyl/ethyl groups attached to bases
—> results in incorrect base pairing

BASE ANALOGS
—> similar structure to bases
—> incorporates in usual place of base during replication
—> change base sequence

VIRUSES
—> viral DNA may insert itself into genome, changing base sequence

Question 33

Effects of mutations

Answer 33

silent

nonsense

missense

Question 34

silent mutations

Answer 34

when substitution of a nucleotide changes codon

but due to degenerative nature of DNA

the new codon codes for the same amino acid
=> so overall function if the protein isnt changed

Question 35

nonsense mutations

Answer 35

codon become a STOP codon instead of coding for an amino acid

• creates proteins that are too short so non functional
• usually have negative effects on phenotypes

Question 36

Missense mutations

Answer 36

when a new amino acid is incorporated into protein

due to frame shift mutation from deletion/insertion if codons

Question 37

conservative missense mutations

Answer 37

when the new amino acid has similar properties to the original

effect of mutation is less severe

Question 38

non-conservative missense mutations

Answer 38

new amino acid has different properties than original

dis functional protein

Question 39

beneficail mutations

Answer 39

ability to digest lactose

able to drink milk as an adult
=>helps prevent osteoporosis
=>prevent starving during famines

Question 40

chromosome mutations

Answer 40

deletion- section of chromosome is broken off

duplication- sections on chromosome duplicated

Translocation- sections of one chromosome breaks off and joins non-homologous chromosome

Inversion- section of chromosome is reversed

Question 41

Homeobox genes

Answer 41

codes for a part of a protein the HOMEODOMAIN which binds to DNA and switches genes on and off

IS A TRANSCRIPTION FACTOR

Question 42

how long is a homeobox?

Answer 42

180 base pairs long

so codes for 60 amino acids

Question 43

how conserved is the homeobox

Answer 43

HIGHLY conserved in plants, aninmals and fungi

Question 44

Hox genes

Answer 44

group of homeobox genes only present in ANIMALS

Question 45

what are Hox genes for

Answer 45

they are responsible for correct positioning of body parts

Question 46

how are Hox genes found ?

Answer 46

found in gene clusters

mammals have 4 clusters on different chromosomes

Question 47

how many hox genes do humans have

Answer 47

at least 39