6.1.1 Cellular control

Question 1

substitution mutation features

Answer 1

also known as point mutation
one base pair replaces another
same number of amino acids results

Question 2

types of mutation and effects

Answer 2

silent mutations (no effect on protein)
missense mutations (usually has effect on protein)
nonsense mutations (usually had a large effect on protein)

Question 3

silent mutations

Answer 3

change in base pair will still code for same amino acid = same protein = no effect
(most AA coded for by more than one DNA codon)

Question 4

why genetic code is non-overlapping

Answer 4

makes sure genes are read “in-frame” by start and stop codons
no codon codes for more than one amino acid

Question 5

why genetic code is redundant / degenerate

Answer 5

more than one codon codes for the same amino acid

Question 6

missense mutation features

Answer 6

change in base pair causes change in amino acid
= change in primary and tertiary structure of protein
= change in shape and function
e.g. sickle cell anaemia

Question 7

nonsense mutation features

Answer 7

change in base pair causes it to become a stop codon
= early termination of polypeptide chain
= change in shape/function of protein
e.g. cystic fibrosis

Question 8

insertion and deletion mutation features

Answer 8

indel mutations
extra base pairs inserted / some deleted
results in number of base pairs not being in multiples of 3
causes frameshift
alters all subsequent DNA codons
= large change in primary and tertiary structure of protein
= large change in shape and function
if 3 bases are inserted/deleted no frame shift occurs (only 1 less/more amino acid)

Question 9

lac operon in prokaryotes

Answer 9

lacI transcripted and translated to synthesise lacI repressor protein
lacI repressor protein binds to operator region on bacterial DNA, preventing expression of lacZ and lacY genes
when all glucose used up and lactose present
lactose binds to repressor protein
alters its shape and prevents it binding to operator
allows RNA polymerase to bind to promoter region
lacZ and lacY genes undergo transcription
beta-galactosidase and lactose permease are synthesised
thus, lactose induces the enzymes needed to break it down

Question 10

what gene expresses beta-galactosidase

Answer 10

lacZ

Question 11

what gene expresses lactose permease

Answer 11

lacY

Question 12

lactose permease function

Answer 12

embedded into plasma membrane
acts as channel protein for lactose
greater rate of lactose entering the cell

Question 13

beta-galactosidase function

Answer 13

breaks down lactose into glucose and galactose

Question 14

control of gene expression at transcriptional level in eukaryotes method

Answer 14

certain genes only expressed in certain cells
transcription factors (proteins) control which genes are switched on or off
transcription factors bind to specific promoter regions of DNA for gene they control
helps or prevents RNA polymerase from binding and transcribing gene

Question 15

how primary mRNA is spliced method

Answer 15

both intron and exons are transcribed to produce primary mRNA
primary mRNA binds to endonuclease enzyme (forms spliceosome)
primary mRNA spliced by endonuclease enzyme to remove introns
exons join together to produce mature mRNA, leaves cell and translated

Question 16

why introns exist

Answer 16

some primary mRNA spliced in different ways - allows it to code for more than 1 protein

Question 17

do prokaryotes have introns

Answer 17

no

Question 18

control of gene expression at post-transcriptional level method

Answer 18

protein has been made
signalling molecule (first messenger) binds to receptor on cell surface membrane
causes G-protein to activate adenyl cyclase
converts ATP to cAMP (secondary messenger) which activates the protein
can then involve adding functional groups e.g. phosphorylation of many proteins
modified proteins enters nucleus and acts as transcription factor to regulate transcription

Question 19

spliceosome definition

Answer 19

structure formed when primary mRNA binds to endonuclease enzyme

Question 20

regulatory gene definition

Answer 20

codes for repressor protein/transcription factor that switches (structural/another) gene on/off

Question 21

structural gene definiton

Answer 21

codes for protein/polypeptide

Question 22

relationship between regulatory gene and structural gene

Answer 22

regulatory gene controls expression of structural gene

Question 23

homeobox gene definition

Answer 23

homeotic gene containing 180 base-pair sequence that codes for a 60-amino acid sequence called homeodomain sequence (transcription factors)

Question 24

homeotic genes function

Answer 24

control morphogenesis (anatomical development) of organisms

Question 25

homeodomain sequence function

Answer 25

shape specific to part of enhancer region on DNA so it binds to DNA to initiate/stop transcription to switch genes on/off controls development of body plan 60 amino acids long

Question 26

master gene definition

Answer 26

control expression (switch on/off) of many other genes

Question 27

why homeobox genes are highly conserved

Answer 27

found in all plant, animal and fungi species from a common ancestor very similar in all organisms very few mutations in genes as they would largely affect body plans of organisms mutations selected against as they would have killed organisms

Question 28

Hox genes function

Answer 28

homoebox genes found only in animals control formation of anatomical features in correct locations of body plan expressed in embyronic development one by one along anterior-posterior axis causes development of particular body parts in this particular order

Question 29

why different classes of animals develop in similarly as segments

Answer 29

Hox genes similar across different classes of animals | Hox genes switched on in segments, causing development in segments

Question 30

Hox genes between different animals

Answer 30

number and arrangement of Hox genes varies among different animals due to evolution, Hox clusters have duplicated, leading to greater complexity in body structure tetrapods (e.g. humans) have 4 similar Hox genes

Question 31

characteristics scientists want for animals to use in experiments

Answer 31

``` cheap to buy and keep reproduce quickly small large cells readily available ```

Question 32

what information can be learnt from model organisms applied to humans

Answer 32

``` all in same kingdom shared ancestors similar cells shared genes similar embryonic development/ homeobox/Hox genes ```

Question 33

apoptosis definition

Answer 33

programmed cell death

Question 34

necrosis definition

Answer 34

cell death due to trauma/disease

Question 35

apoptosis method

Answer 35

triggered by transcription factors made by Hox genes causing: cytoskeleton broken down by enzymes cell shinks, plasma membrane forms blebs (small protrusions), chromatin condenses DNA breaks up, nuclear envelope breaks down into fragments blebs form vesicles containing organelles vesicles engulfed and digested by phagocytes, preventing damage to other cells by dead cells’ contents

Question 36

controlling apoptosis

Answer 36

genes that regulate cell cycle and apoptosis able to respond to internal and external cell stimuli e.g. stress cell-signalling molecules released (e.g. cytokines, hormones, nitric oxide)

Question 37

how nitric oxide causes apoptosis

Answer 37

makes inner membrane of mitochondria more permeable to hydrogen ions, dissipating proton gradient (reduces ATP production) proteins released into cytoplasm, bind to apoptosis inhibitor proteins, causing apoptosis

Question 38

how mitosis and apoptosis control body development

Answer 38

mitosis causes growth in zygote cells destroyed by apoptosis when cells reach Hayflick limit (divide ~50 times) rate of mitosis and apoptosis should be equal otherwise tumours would form or tissues would degenerate (e.g. Alzheimers) apoptosis vital in body development (e.g. separation of digits, loss of vestigial tail in humans)

Question 39

Hayflick limit

Answer 39

cells should only divide around 50 times

Question 40

why cells are broken down by apoptosis instead of hydrolytic enzymes

Answer 40

hydrolytic enzymes could destroy neighbouring cells