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a-level biology > 6.1.1 Cellular Control > Flashcards

6.1.1 Cellular Control Flashcards

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1
Q

mutation

A

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

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2
Q

gene mutations

A

chnage to base sequence of DNA in 1 gene

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3
Q

chromosome mutations

A

change to the structure/ number of chromosomes

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4
Q

where do most mutations occur

A

somatic body cells - not inherited
associated with mitosis

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5
Q

mutations in meiosis

A

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

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6
Q

mutagens

A

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

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7
Q

physical mutagens

A

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

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8
Q

chemical mutagens

A

deaminating agents
e.g. convert cytosine to uracil

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9
Q

biological agents (mutagens)

A

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

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10
Q

two main classes of gene mutations

A

point mutations - substitution
insertion or deletion mutations - INDEL

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11
Q

point mutations - substitution

A

1 base or nucleotide change

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12
Q

INDEL mutations

A

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

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13
Q

three types of point mutations

A

silent mutations
missense mutations
nonsense mutations

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14
Q

silent mutations

A

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

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15
Q

missense mutations

A

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

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16
Q

sickle cell anaemia

A

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

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17
Q

nonsense mutations

A

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

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18
Q

Duchenne muscular dystrophy

A

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

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19
Q

insertion and deletion - INDEL mutations

A

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

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20
Q

thalassaemia

A

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

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21
Q

neutral effects of mutations

A

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

22
Q

examples of neutral effects of mutations

A

ability to enjoy coriander
smell honeysuckle
presence of ear lobes

23
Q

beneficial effect of mutations
example

A

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

24
Q

harmful effects of mutations
examples

A

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

25
Q

chromosome mutations

A

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

26
Q

duplication in chromosome structure

A

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

27
Q

deletion in chromosome structure

A

absence of certain genes
could be fatal

28
Q

inversion and translocation in chromosome structure

A

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

29
Q

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

A

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

30
Q

operons

A

a cluster of genes controlled by a single promoter region

31
Q

regulation of gene expression in prokaryotes

A

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

32
Q

the lac operon

A

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

33
Q

enzymes that are produced in the absence of glucose

A

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

34
Q

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

A

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

35
Q

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

A

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

36
Q

epigenetics

A

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

37
Q

regulation of gene expression in eukaryotes

A

chromatin remodelling
histone modification

38
Q

chromatin remodelling

A

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

39
Q

2 forms of chromatin

A

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

40
Q

histone modification

A

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

41
Q

transcription factors

A

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

42
Q

functions of transcription factors in eukaryotic cells

A

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

43
Q

introns

A

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

44
Q

exons

A

coding regions of DNA
encode proteins & amino acids

45
Q

post-transcriptional gene regulation

A

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)

46
Q

post-translational gene regulation

A

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

47
Q

formation of cAMP

A

ATP + adenyl cyclase = pyrophosphate + cAMP

48
Q

homeotic genes

A

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

49
Q

homeobox sequences

A

a stretch of 180 DNA base pairs (excluding introns)

50
Q

homeodomain

A

act as transcription factors - activate or repress certain genes

51
Q

mutations in homeobox genes

A

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

a-level biology (26 decks)

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