6.1.1 Cellular Control

Question 1

mutation

Answer 1

a random/spontaneous change to the sequence of bases in DNA
gene mutations, chromasome mutations

Question 2

gene mutations

Answer 2

chnage to base sequence of DNA in 1 gene

Question 3

chromosome mutations

Answer 3

change to the structure/ number of chromosomes

Question 4

where do most mutations occur

Answer 4

somatic body cells - not inherited
associated with mitosis

Question 5

mutations in meiosis

Answer 5

these mutations can be inherited
chances are low as there is a huge number of sperm cells released at once

Question 6

mutagens

Answer 6

increase the chance of a mutation occuring
physical, chemical, biological agents

Question 7

physical mutagens

Answer 7

ionising radiation
e.g. UV, gamma, x-rays

Question 8

chemical mutagens

Answer 8

deaminating agents
e.g. convert cytosine to uracil

Question 9

biological agents (mutagens)

Answer 9

e.g. viruses
e.g. agents that change structure of chemical bases

Question 10

two main classes of gene mutations

Answer 10

point mutations - substitution
insertion or deletion mutations - INDEL

Question 11

point mutations - substitution

Answer 11

1 base or nucleotide change

Question 12

INDEL mutations

Answer 12

cause a FRAMESHIFT
1 or more mucleotides are added/deleted - sequence of amino acids may be different from point of mutation onwards

Question 13

three types of point mutations

Answer 13

silent mutations
missense mutations
nonsense mutations

Question 14

silent mutations

Answer 14

has no effect on the primary or secondary/tertiary structure of the protein
DNA is degenerate - reduces the effect of point mutation

Question 15

missense mutations

Answer 15

a change in the base triplet sequence that leads to a change in the amino acid sequence in the protein

Question 16

sickle cell anaemia

Answer 16

caused by a missense mutation and causes crystallisation of haemoglobin which causes red blood cells to become sickled
decreases SA:Volume

Question 17

nonsense mutations

Answer 17

a point mutation may alter a base triplet so that it becomes a STOP codon/triplet
results in a truncated/shortened amino acid with no function - protein will be degraded

Question 18

Duchenne muscular dystrophy

Answer 18

caused by nonsense mutation - protein ** dystrophin** is not produced
muscle cells waste away

Question 19

insertion and deletion - INDEL mutations

Answer 19

if bases are added or removed NOT in a multiple of 3, the reading frame for RNA polymerase shifts - DNA is non-overlapping

Question 20

thalassaemia

Answer 20

haemoglobin disorder: due to frameshifts as a result of deletions
Hb cannot sequester Fe3+ ions… must be removed by metal chelation therapy

Question 21

neutral effects of mutations

Answer 21

if mutation is in non-coding region
if mutation is silent
if mutation causes change to protein structure and a different characteristic but it is not advantageous or disadvantageous

Question 22

examples of neutral effects of mutations

Answer 22

ability to enjoy coriander
smell honeysuckle
presence of ear lobes

Question 23

beneficial effect of mutations
example

Answer 23

the ability to digest lactose
allows organism to break lactose down into glucose + galactose to be used as respiratory substrates

Question 24

harmful effects of mutations
examples

Answer 24

phenylketonuria: caused by substitution mutation in a gene encoding an enzyme involved in phenylalanine conversion
if Phe allowed to build up = brain damage

Duchenne muscular dystrophy: defective gene encoding dystrophin protein
muscles waste away

Question 25

chromosome mutations

Answer 25

changes in chromosome structure: duplication, deletion, inversion, translocation can be caused by mutagens + normally occur during meiosis - often lead to developmental abnormalities

Question 26

duplication in chromosome structure

Answer 26

could lead to over-expression of certain genes could affect metabolism

Question 27

deletion in chromosome structure

Answer 27

absence of certain genes could be fatal

Question 28

inversion and translocation in chromosome structure

Answer 28

all genes are still present but may inhibit or disable the expression of other genes around them

Question 29

explain how the degenerate nature of the genetic code reduces the effect of point mutations

Answer 29

there are multiple codons which code for the same amino acid = some mutations do not affect the primary structure of the protein

Question 30

operons

Answer 30

a cluster of genes controlled by a single promoter region

Question 31

regulation of gene expression in prokaryotes

Answer 31

bacteria have one circular chromosome genes controlling related functions are located together to form operons

Question 32

the lac operon

Answer 32

E.coli normally metabolises glucose as the most efficient respiratory substrate but when glucose is absent and lactose is present = lactose induces production of 2 enzymes consist of a length of 6000 base pairs

Question 33

enzymes that are produced in the absence of glucose

Answer 33

**lactose permease** - lac Y gene that encodes channel proteins specific to lactose - these get inserted into bacterial plasma memb. **beta-galactosidase** - lac Z breaks glycosidic bond between glucose and b-galactose = glucose + b-galactose can then be used as respiratory substrate

Question 34

when the lac operon is switched off (at high glucose concentrations)

Answer 34

repressor protein is constantly produced active repressor binds to operator region = prevents RNA polymerase from binding to the promoter region

Question 35

when the lac operon is switched on (in the absence of glucose)

Answer 35

lactose (inducer molecule) binds to repressor protein & changes its shape repressor removed & RNA polymerase binds to promoter region = initiates transcription of lac Z/lac Y genes genes then translated, folded & modified to become active enzymes

Question 36

epigenetics

Answer 36

the control of gene expression through the modification of DNA structure & histone structure

Question 37

regulation of gene expression in eukaryotes

Answer 37

chromatin remodelling histone modification

Question 38

chromatin remodelling

Answer 38

heterochromatin = tightly wound around histones RNA polymerase is unable to bind to promoter region and cause gene expression

Question 39

2 forms of chromatin

Answer 39

euchromatin: loosely wound around histones (cells in interphase) heterochromatin: tightly wound around histones (cells in mitosis/meiosis)

Question 40

histone modification

Answer 40

**acetylation:** reduces positive charge on histones causing DNA to coil less tightly around histones **methylation:** histones become more hydrophobic so they bind more tightly to each other, causing DNA to wrap more tightly around histones

Question 41

transcription factors

Answer 41

**proteins** act within nucleus to control which genes in a cell are on/off they **slide along part of a DNA molecule** seeking out the correct/specific promoter region - either activate/prevent transcription of the gene (aids/inhibits attachment of RNA polymerase to DNA) involved in **regulating** cell cycle checkpoints, protein synthesis

Question 42

functions of transcription factors in eukaryotic cells

Answer 42

aids/inhibits attachment of RNA polymerase to DNA regulates cell cycle checkpoints regulates protein synthesis regulates cell division regulates gene expression

Question 43

introns

Answer 43

non-coding regions of DNA do not encode proteins do not encode amino acids

Question 44

exons

Answer 44

coding regions of DNA encode proteins & amino acids

Question 45

post-transcriptional gene regulation

Answer 45

**modifies pre-mRNA to make it fit for purpose (mature mRNA)** removal of introns via splicing exons joined together by a ligase enzyme cap and tail added to mature mRNA to prevent degradation in cytoplasm (stabilises mRNA)

Question 46

post-translational gene regulation

Answer 46

involves **activation** of proteins by cyclic AMP - 2nd chemical messenger 1. binding of signal molecule to specific receptor on plasma memb. activates G-protein 2. adenylyl cyclase is activated 3. ATP converted into cAMP 4. cAMP activates protein kinase = activates proteins - phosphorylates them

Question 47

formation of cAMP

Answer 47

ATP + adenyl cyclase = pyrophosphate + cAMP

Question 48

homeotic genes

Answer 48

a large ancient group of genes involved in controlling development of body plan - ensures body parts develop in the correct positions

Question 49

homeobox sequences

Answer 49

a stretch of 180 DNA base pairs (excluding introns)

Question 50

homeodomain

Answer 50

act as transcription factors - activate or repress certain genes

Question 51

mutations in homeobox genes

Answer 51

lead to organisms that are not viable lead to an organism born with deformities which would quickly eliminate it by natural selection