a level biology > Cellular Control > Flashcards

Cellular Control Flashcards

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1
Q

Mutation

A
  • a random spontaneous change
  • in the base/nucleotide sequence of the DNA
  • can result in a new allele occurring
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2
Q

Types of mutation

A
  • substitution
  • deletion
  • insertion
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3
Q

Substitution mutation

A
  • 1 or more bases is swapped for another
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4
Q

Example of substitution mutation

A
  • ATGCCC into ATTCCT
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5
Q

Point mutation

A
  • if a substitution involves just 1 nucleotide alteration
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6
Q

types of point mutation -

A
  • silent
  • missense
  • nonsense
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7
Q

silent mutation

A
  • when the altered base sequence still codes for the same amino acid
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8
Q

example of a silent mutation

A
  • if TTA changes to TTG
  • they both still code for Leucine
  • so there are no consequences for the final proteins made
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9
Q

Missense mutation

A
  • when the substituted base codes for a different amino acid in the primary protein structure
  • as a result the final protein structure is altered in some way
  • may or may not have an effect on its function
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10
Q

Nonsense mutation

A
  • when the base sequence is altered in such a way that the triplet code changes from an amino acid to a stop codon
  • resulting in a shorter protein which will not function properly
  • will probably be broken down in the cell
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11
Q

effects of a substitution mutation

A
  • only alter 1 base in the sequence
  • this could have no effect = altered triplet code could still code for same amino acid
  • at most only 1 amino acid in the sequence would be altered
  • it would then depend on how crucial that 1 amino acid is to the final shape and structure of the protein
  • sometimes the final protein will function as normal
  • sometimes it will not
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12
Q

deletion mutation

A
  • where 1 or more nucleotides are removed from the DNA sequence
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13
Q

example of a deletion mutation

A
  • ATGCCT
  • becomes ATG^CT
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14
Q

insertion mutation

A
  • where 1 or more nucleotides are added to the DNA sequence
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15
Q

example of an insertion mutation

A
  • ATGCCT
  • becomes ATG A CCT
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16
Q

frameshift mutation

A
  • both insertions and deletions would alter the whole triplet code
  • from the point of mutation onwards
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17
Q

frameshift mutation - effects

A
  • expected to alter most of the amino acid coded for
  • it would more than likely mean that the final protein would not function
  • due to having a completely different shape to normal
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18
Q

consequences of mutations

A
  • sequence of bases in the DNA that codes for the sequence of amino acids in the primary protein structure
  • this determines how the protein twists and folds to form its secondary and tertiary structures
  • this then determines its final 3D shape and its function
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19
Q

example of consequences of mutations

A
  • if the final protein needs a very precise 3D shape to function
  • a mutation could result in the final shape of the protein being different
  • it may no longer function properly
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20
Q

how can mutations cause new alleles to appear in population

A
  • mutations cause new versions of genes to appear
  • when we look at the effect of all these different mutations of an organism
  • some are neutral, some are beneficial, some are harmful
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21
Q

when does a neutral mutation occur

A
  • it occurs in the non coding sections of DNA (introns)
  • it results in an altered triplet code but it still codes for the same amino acid
  • altered triplet code results in a different amino acid in the sequence but it is so chemically similar to the original amino acid that it makes no difference to how the final protein works
  • it codes for a completely different amino acid in the sequence but this amino acid is not crucial for how the final protein works
  • it may result in a different final protein but this does not affect the survival chances of the organism
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22
Q

neutral mutation

A
  • neither harmful nor beneficial to the organism
  • they do not increase or decrease the chances of survival
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23
Q

when is a mutation beneficial

A
  • it has advantageous effects on the organism
  • increases chances of survival
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24
Q

example of a beneficial mutation in bacteria

A
  • some have mutations to resist the effects of antibiotics
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25
example of a beneficial mutation in humans
- some humans can digest lactose due to a mutation
26
explain the mutation which allows humans to digest lactose
- most mammals become lactose intolerant after they cease to suckle - the ability to digest lactose is found primarily in European countries who are likely to farm cattle - appears to have risen spontaneously in more than 1 areas
27
lactose
- sugar present in milk
28
what are the benefits of being able to drink milk and process lactose as an adult
- prevents diseases - e.g osteoprosis - prevented individuals from starving during famines
29
how are beneficial mutations linked to natural selection
- help drive evolution
30
when is a mutation harmful
- has a disadvantageous effect on an organism - reduces its chances of survival
31
example of a harmful mutation
Cystic Fibrosis
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Cystic Fibrosis
- caused by deletion of 3 bases in a gene which codes for a membrane transport protein in the cells of airways - it causes excessive mucus production - reduced lung function - reduced life expectancy
33
when can mutations be beneficial or harmful in different circumstances
- blue eyes - skin tone
34
when are blue eyes useful
- means less pigmentation through iris - more light can get through to the retina at the back of the eye - better vision - useful in parts of the world with lower light intensity
35
when are blue eyes not useful
- where light intensity is very high - can cause cataracts - in these regions it is better to have brown eyes - more pigmentation in iris - so more light is absorbed before reaching retina - reducing risk of damage
36
when is darker skin more useful
- more melanin - protects against sunburn and skin cancer - useful in regions where there is high light intensity
37
when is paler skin more advantageous
- in regions of lower light intensity - where there is a lower risk of skin cancer - allows enough sunlight to penetrate in order to make vitamin D
38
how are mutations caused
- spontaneously - rate of mutation is increased by mutagens
39
mutagens
- chemical physical and biological agents - which actually cause mutations
40
example of physical mutation
- ionising radiations - e.g x-rays
41
effect of physical mutation on DNA = ionising radiation
- break 1 or both DNA strands - some breaks can be repaired - but mutations can occur in the process
42
examples of biological mutations
- alkylating agents - base analogs - viruses
43
how do alkylating agents effect DNA
- methyl or ethyl groups are attached to bases - causing incorrect pairing of bases in replication
44
base analogs - biological mutation - effects
- incorporating DNA in place of usual base during replication - changing the base sequence
45
viruses - biological mutation - effects
- viral DNA may insert itself into a genome - changing the base sequence
46
effect on the DNA from deaminating agents
- chemically alter bases in DNA - e.g converting cytosine to uracil in DNA - changing base sequence
47
chromosome mutations
- affect the whole chromosomes - or a number of chromosomes within a cell
48
what are chromosome mutations caused by
- mutagens - normally occurs during meiosis
49
what do changes in chromosome structure include due to chromosome mutation
- deletion - duplication - translocation - inversion
50
deletion - chromosome mutation
- section of chromosome breaks off - is lost within the cell
51
duplication - chromosome mutation
- sections get duplicated on a chromosome
52
translocation - chromosome mutation
- section of 1 chromosome breaks off - joins another non-homologous chromosome structure
53
inversion - chromosome mutation
- section of chromosome breaks off - is reversed - joins back onto the chromosome
54
housekeeping genes
- genes which code for enzymes that are necessary for reactions present in the metabolic pathway
55
protein based hormones
- needed for growth and development of of an organism/enzymes - only needed for certain cells at certain times - to carry out a short lived response
56
what codes for protein based hromones
- tissue specific genes
57
where is the entire genome of an organism found
- in every prokaryotic cell - in the nucleus of every eukaryotic cell (which has a nucleus)
58
why are the expression of genes and rate of synthesis of protein products regulated
- some genes are not required by every cell
59
how are genes regulated
- turned off an on - rate of product synthesis increased or decreased - depending on demand
60
how is gene regulation useful to bacteria
- it allows bacteria to respond to changes in environment - expressing genes when only products are needed - prevents resources being wasted
61
why is gene regulation more complex in eukaryotic cells than prokaryotic
- as they have to respond to both changes in the external and internal environment - it is needed for cells to specialise and work in a coordinated way
62
what are the levels of gene regulation
- transcriptional - post transcriptional - translational - post translational
63
transcriptional gene regulation
- genes can be turned off and on
64
post transcriptional gene regulation
- mRNA can be modified which regulates translation - and types of proteins that are produced
65
translational gene regulation
- translation can be stopped and started
66
post translational gene regulation
- proteins can be modified after synthesis - which changes their functions
67
what mechanisms affect transcriptional control of genes
- chromatin remodelling - histone modification - Lac operon - role of cyclic AMP
68
chromatin remodelling - DNA structure
- long molecule - wound around histones (proteins) - to allow it to be packaged into the nucleus of a cell - chromatin = resulting DNA complex
69
heterochromatin
- tightly wound DNA - causing chromosomes to be visible during cell division
70
eurochromatin
- loosely wound DNA - present in interphase
71
why isn't transcription of genes possible when DNA is tightly wound
- RNA polymerase cannot access the genes
72
transcription - loosely wound DNA
- possible
73
when does protein synthesis occur
- during interphase
74
protein synthesis - purpose
- ensures proteins needed for cell division are synthesised in time - prevents complex and high energy consuming processes of protein synthesis to occur during cell division
75
why does DNA coil around histones
- histones are + charged - DNA is - charged - histones can be modified to increase or decrease degree of packing
76
acetylation / phosphorylation
- reduces + charge on histones - making them more - - causing DNA to coil less tightly - allowing transcription
77
methylation
- makes histones more hydrophobic - so histones bind more tightly to each other - so DNA coils more tightly - preventing transcription
78
epigenetics
- to describe the control of gene expression - by modification of DNA
79
operons
- a group of genes that are under the control of the same regulatory mechanism - are expressed at the same time
80
why are operons more common in prokaryotes
- smaller and simpler genome
81
benefits of operons
- efficient way of saving resources - if certain gene products are not needed - all of the genes involved in their production are switched off
82
lac operon
- group of 3 genes - lacZ lacY lacA - involved in metabolism of lactose
83
lacZ lacY lacA
- structural genes - code for 3 enzymes - transcribed onto a single long molecule of of mRNA
84
lacI
- regulatory gene - located near to the operon - codes for a repressor protein - preventing transcription of structural genes in the absence of lactose
85
glucose is better to metabolise and is the preferred respiratory substrate - what may happen if glucose is in short supply
- lactose can be used as a respiratory substrate - different enzymes are needed to metabolise lactose
86
down regulation
- repressor protein constantly produced - binds to operator (close to structural genes) - preventing RNA polymerase binding to DNA and therefore transcription
87
promoter
- section of DNA that is the binding site for RNA polymerase
88
when lactose is present - what happens to repressor proteins
- lactose binds to repressor proteins - causing it to change shape - so it no longer binds to operator - RNA polymerase can bind to promoter - 3 structural genes are transcribed - enzymes synthesised
89
role of cyclic AMP
- binding of RNA polymerase results in a slow rate of transcription - this needs to be increased to produce the needed quantity of enzymes to metabolise lactose efficiently - achieved by binding CAMP
90
when is binding cyclic AMP only possible
- when CRP is bound to CAMP
91
what will happen to levels of CAMP when glucose is transported into the cell
- decreases levels of CAMP - reducing transcription of genes needed to metabolise lactose - as glucose is the preferred substrate of e-coli and other bacteria
92
post transcriptional control - stages
- RNA processing - RNA editing
93
product of transcription
- pre-mRNA
94
what happens to pre-mRNA
- it is modified forming mature mRNA - so it can then bind to a ribosome - and code for the synthesis of the required protein
95
what happens to pre-mRNA - RNA processing
- a cap is added to the 5' end - a tail is added to the 3' end - helping to stabilise mRNA - delay degradation in the cytoplasm - the cap also aids binding of mRNA to ribosomes
96
cap
modified nucleotide
97
tail
long chain of adenine nucleotides
98
splicing - RNA processing
- also occurs post translational control - RNA is cut at specific points - removing introns - exons are joined together
99
introns
non coding DNA
100
exons
coding DNA
101
RNA editing
- nucleotide sequence - of some mRNA molecules can be changed - through base addition/deletion/substitution - same effect as point mutations - resulting in synthesis of different proteins - these may have different functions - increasing range of proteins produced from a single mRNA molecule/gene
102
why do genes need to be switched on and off at appropriate times in different cells
- correct proteins to be made at different stages of development - proteins activated at right time
103
what happens once mRNA is mature
- leaves nucleus - ready for translation
104
importance of adding cap and tail to mRNA
- stabilises mRNA - prevents degradation in cytoplasm
105
what is mature mRNA known as
functional mRNA
106
what enzymes are used in splicing
spliceosomes
107
spliceosomes
- can join same exons in a variety of ways - so 1 gene can produce different versions of functional mRNA - different arrangements=different phenotypes /proteins/polypeptides
108
why does 1 gene code for many polypeptides
- depends on order exons are joined in
109
Translational control - what mechanisms regulate protein synthesis
- degradation of mRNA - binding of inhibitory proteins to mRNA - activation of initiation factots
110
degradation of mRNA -
- the more resistant the molecule the longer it will last in the cytoplasm - so a greater quantity of protein is made - all mRNA eventually needs to break down in the cytoplasm
111
binding of inhibitory proteins
- to mRNA prevents it binding to ribosomes and synthesis of proteins
112
activation of initiation factors
- aid the binding of mRNA to ribosomes - promoting translation and protein synthesis
113
protein kinases
- catalyse the addition of phosphate groups to proteins - addition of phosphate group changes tertiary structure and function of protein - many enzymes are activated by phosphorylation - so protein kinases are important regulators of cell activity - often activated by secondary messenger CAMP
114
post translational control
- involves the final modifications to the proteins
115
what does post translational control include
- addition of non-protein groups - folding and shortening of protein into its final shape - activation of proteins by cAMP - modifying of amino acids and the formation of bonds
116
cyclic AMP - impact
- change 3D shape of protein - which could activate active site of an enzyme. enabling its function
117
body plans
- living organisms come in all shapes and sizes - it is the same small group of genes that control the growth and development of these different living forms
118
morphogenesis
- the regulation of the pattern of anatomical development
119
homeobox gene sequences
- regulatory genes which control body plan - each sequence is a stretch of DNA 180 base pairs long - each homeobox codes for a sequence of 60 amino acids in a protein
120
Homeodomain
- a sequence of 60 amino acids in a protein - highly conserved in all animals/fungi/plants
121
homeodomain proteins - uses
- binds to DNA - switches other genes on/off (promotes or inhibits transcription) - determine the body plan of multicellular organisms
122
transcription factors
promotes or inhibits transcription
123
hox genes
- type of homeobox genes only found in animals - responsible for correct positioning of body parts
124
how are hox genes arranged
- found in clusters on particular chromosomes ~ hox clusters
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how are hox genes arranged in mammals
- 4 clusters on different chromosomes - the order in which they appear on the chromosome is the order in which they are expressed
126
when are homeobox genes activated
- different genes expressed at different stages of embryo development
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how to homeobox genes determine body plan
- determine polarity of the embryo - determine the polarity of each segment of the organism - determine which structures develop from each segment (e.g arms, legs) - switch different genes on & off in different cells = determines cell identity - expressed in set order during development
128
how are body plans represented
- cross sections through the organism - showing fundamental arrangement of tissue layers
129
animals are segmented - how do these segments work over time
- specialised to perform different functions - hox genes in the head control development of mouthparts
130
somites
- individual vertebrae and associated structures have all developed from these - directed by hox genes to develop in a particular way depending on their position in a sequence
131
the body shape of most animals shows symmetry; what are the types of symmetry
- radial symmetry - bilateral symmetry - asymmetry
132
radial symmetry
- seen in dipoblastic animals like jellyfish - have no left or right sides - only a top and a bottom
133
bilateral symmetry
- seen in most animals - organisms have both left and right sides and a head and tail - rather than just a top or bottom
134
asymmetry
- e.g sponges - no lines of symmetry
135
homeobox genes - evolution
- changed very little - as they are so crucial to the body plans of an organism
136
what would happen if homeobox genes mutated
- organisms would no longer be viable and would struggle to survive - natural selection has eliminated most organisms with mutated homeobox genes
137
homeobox genes - development of organisms
- many miotic divisions from zygote to adult - these are controlled by homeobox genes - ensuring each new daughter cells contains the full genome and is the clone of a parent cell - in cell differentiation when cells in different part of the body specialise certain genes are switched on and others are switched off
138
example of homeobox genes going wrong - 2 headed calf
- mutation in regulatory hox genes - calf has 2 heads but 1 brain - so heads react simultaneously
139
retinoic acid
- derivative of vitamin A - activates homeobox genes necessary for development of skeleton and CNS in vertebrates - it is a morphogen and controls pattern of tissue development
140
retinoic acid - birth defects
- if too much is taken in by a women during the first month of pregnancy - it can interfere with expression of these genes - causing birth defects, e.g brain deformities
141
thalidomide effect on body plan
- taken by many pregnant women - affected behaviour of 1+ homeobox genes at particular stage of embryonic development - fetus arms and legs may not develop properly
142
apoptosis
- programmed cell death - some cells break down as a part of normal development of an organism
143
what is apoptosis involved in
- development of different parts of an organism before and after birth - metamorphosis, e.g caterpillars to butterflies
144
sequence of events in apoptosis
- enzymes break down cell cytoskeleton - cytoplasm becomes dense with tightly packed organelles - cell surface membrane changes and small protrusions called blebs form - chromatin condenses - nuclear envelope breaks and DNA breaks into fragments - cell breaks into vesicles that are ingested by phagocytic cells - whole process happens quickly
145
why does the cell break into vesicles that are ingested by phagocytic cells in apoptosis
- cell debris does not damage other cells /tissues
146
how is apoptosis linked to homeobox genes
- homeobox genes code for transcription factors - these activate genes needed for apoptosis - e.g coding for enzymes needed for programmed cell death
147
example of apoptosis in humans
- development of hands and feet in embryo - apoptosis causes skin between fingers and toes to break down - morphogenetic apoptosis
148
why is it important for a balance between apoptosis and mitosis in development of body plans in embryos
- so correct body plan develops - some cells are produced, some die (should be equal) - genes which control the 2 processes are switched on and off at appropriate times of development
149
what can not enough apoptosis lead to
- formation of tumours
150
what can too much apoptosis lead to
cell loss and degeneration
151
what plays a crucial role in maintaining the right balance of apoptosis
cell signalling
152
control of apoptosis
- genes involved in regulating mitosis and apoptosis can be affected in both internal and external stimuli
153
internal stimuli that can affect apoptosis
- DNA damage - hormones - cytokines from immune system
154
external stimuli that can affect apoptosis
- infections by pathogens - changes in temperature - changes in light intensity
155
other things that can affect apoptosis
- stress - disrupts homeostatic balance within the body
156
when do factors affecting apoptosis take effect
growth and development of organisms
157
morphogenesis
- causes an organism to form its shape
158
necrosis
- occurs when cells are exposed to normal conditions - pathological process - disintegration of membrane - passive, unregulated process
159
how many hox genes do humans have
- 39 - hox genes are thought to have risen from 1 ancient homeobox gene by duplication and accumulated mutations over time
160
how are body plans represented
- cross sections through the organism - showing fundamental arrangement of tissue layers
161
most animals are segmented - how are these segments specialised
- to perform different functions - e.g hox genes in head control mouthparts
162
why do hox genes control somites
- so somites develop in a particular way - depending on their position in a sequence
163
role of mitosis
- increase number of cells leading to growth
164
role of apoptosis
- removing unwanted cells and tissues
165
what can cells undergoing mitosis do
- release chemical signals - that stimulate mitosis and cell proliferation - leading to remodelling of tissues
166
stress
homeostatic balance within the organism is upse
167
why is the cell cycle controlled by genes
- ensure new cells are only made when needed for growth and repair - to preserve energy and prevent tumour formation
168
tumour suppressor gene
- responsible for making proteins - that stop the cell cycle from continuing
169
proto-oncogenes
- responsible for producing proteins - that initiate the cell cycle
170
direct consequence of genetic code being degenerate
- it is possible a mutation could leave the primary structure of protein unchanged
171
explain why some gene mutations do not effect function of protein
- may still leave secondary & tertiary structure unchanged - silent mutation = unchanged structure - mutation may change part of tertiary structure where the protein doesn't function
a level biology
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