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A LEVEL BIO (y13) > 8A - Mutations and Gene Expression > Flashcards

8A - Mutations and Gene Expression Flashcards

1
Q

what is a gene mutation?

A

a change in the base sequence of DNA molecule that may result in an altered polypeptide

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2
Q

mutations occur…

A

continuously and spontaneously

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3
Q

when do errors in DNA often occur?

A

errors in the DNA often occur during DNA replication

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4
Q

what can mutations do?

A

-DNA base sequences determine the sequence of amino acids that make up a protein
-mutations in a gene can sometimes lead to a change in the polypeptide that the gene codes for

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5
Q

do most mutations alter the polypeptide formed?

A

no, they may only alter it slightly so that its structure or function is not changed (as the genetic code is degenerate)

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6
Q

types of mutation:

A

-insertion, deletion or substitution of a nucleotide
-inversion, duplication or translocation of a section of a gene

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7
Q

what is an insertion mutation ?

A

when a nucleotide (with a new base) is randomly inserted into the DNA

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8
Q

effects of an insertion mutation:

A

-it changes the amino acid that would have been coded for by the original base triplet, as it creates a new, different triplet of bases
-an insertion mutation also has a knock-on effect by changing the triplets (groups of three bases) further on in the DNA sequence
(frameshift mutation)

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9
Q

negative effects of an insertion mutation:

A

it may dramatically change the amino acid sequence produced from this gene and therefore the ability of the polypeptide to function

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10
Q

what is a deletion mutation?

A

when a nucleotide (and therefore its base) is randomly deleted from the DNA sequence

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11
Q

effects of a deletion mutation:

A

-changes the amino acid that would have been coded for
-has a knock-on effect by changing the groups of three bases further on in the DNA sequence (frameshift)

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12
Q

negative effects of a deletion mutation:

A

this may dramatically change the amino acid sequence produced from this gene and therefore the ability of the polypeptide to function

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13
Q

what is a substitution mutation?

A

when a base in the DNA sequence is randomly swapped for a different base is

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14
Q

effects of a substitution mutation:

A

it will only change the amino acid for the triplet (group of three bases) in which the mutation occurs; it will not have a knock-on effect

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15
Q

forms of substitution mutations:

A

-silent mutations
-missense mutations
-nonsense mutations

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16
Q

what is a silent substitution mutation?

A

the mutation does not alter the amino acid sequence of the polypeptide (this is because certain codons may code for the same amino acid as the genetic code is degenerate)

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17
Q

what is a missense substitution mutation?

A

amino acid in the polypeptide chain
(eg: sickle cell anemia)

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18
Q

what is a nonsense substitution mutation?

A

the mutation creates a premature stop codon (signal for the cell to stop translation of the mRNA molecule into an amino acid sequence) → the polypeptide chain produced is incomplete → the final protein structure and function is affected

(cystic fibrosis is an example of a disease caused by a nonsense mutation, although this is not always the only cause)

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19
Q

what is a gene inversion mutation?

A

-it usually occurs during crossing-over in meiosis
-the DNA of a single gene is cut in two places
-the cut portion is inverted 180° then rejoined to the same place within the gene

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20
Q

what is the effect of a gene inversion mutation?

A

-a large section of the gene is ‘backwards’ and therefore multiple amino acids are affected
-inversion mutations frequently result in a non-functional protein
-in some cases, an entirely different protein is produced

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21
Q

why are gene inversion mutations harmful?

A

the original gene can no longer be expressed from that chromosome

(if the other chromosome in the pair carries a working gene the effect of the mutation may be lessened)

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22
Q

what is a gene duplication mutation?

A

a whole gene or section of a gene is duplicated so that two copies of the gene/section appear on the same chromosome
(the original version of the gene remains intact and therefore the mutation is not harmful )

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23
Q

effects of a gene duplication mutation:

A

overtime, the second copy can undergo mutations which enable it to develop new functions
Duplication mutations are an important source of evolutionary change

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24
Q

what is a translocation gene mutation?

A

-a gene is cut in two places
-the section of the gene that is cut off attaches to a separate gene
-

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25
what is the effect of a translocation gene mutation?
-the cut gene is now non-functional due to having a section missing -the gene that has gained the translocated section is likely to also be non-functional If a section of a pro
26
examples of harmful gene translocation mutations:
1) if a section of a proto-oncogene is translocated onto a gene controlling cell division, it could boost expression and lead to tumours 2) similarly, if a section of a tumour suppressor gene is translocated and the result is a faulty tumour suppressor gene, this could lead to the cell continuing replication when it contains faulty DNA
27
EXAMINER TIP → silent mutation
A silent mutation is a change in the nucleotide sequence that results in the same amino acid sequence.This is possible because some amino acids can be coded for by up to four different triplet codon sequences.Silent mutations are often a change in the 2nd or 3rd base in the codon, rather than the first.For example, valine is coded for by four different triplet codon sequences (GUU, GUC, GUA and GUG) – therefore, as long as the first two nucleotides in the codon are guanine and uracil the amino acid valine will be inserted into the polypeptide.
28
what does the genetic code being degenerate mean?
more than one triplet code codes for the same amino acid
29
define a frameshift
some gene mutations change all base triplets downstream from (after) the mutation
30
what causes mutations?
exposure to mutagenic agents
31
examples of mutagenic agents:
-UV rays -X rays -high energy ionising radiation (alpha, beta or gamma radiation) -benzopyrene from tobacco smoke -asbestos
32
how can a mutation affect the ability of a protein to perform its function?
-if the shape of the active site on an enzyme changes, the substrate may no longer be able to bind to the active site -a structural protein (like collagen) may lose its strength if its shape changes
33
the effect of gene mutations on phenotype:
-proteins affect the phenotype of an organism via specific cellular mechanisms -if a mutation causes a major alteration in a polypeptide then cellular mechanisms could be affected, which may impact the phenotype of the organism
34
example of a mutation affecting phenotype:
-a mutation in the TYR gene in humans affects the structure of an enzyme that is needed for the production of the pigment melanin -the phenotype of the human is affected by the lack of melanin Individuals with the mutation have albinism; very pale skin and hair
35
what is a mutagen?
a factors which increases the rate of mutation
36
what are carcinogens?
agents that may cause cancer
37
mutagens and cancers:
many mutagens are also categorised as carcinogens if they lead to the development of cancerous cells, however, this is not true of all mutagens there are also carcinogens which are not mutagens, they work by increasing cell division but do not actually cause changes in the DNA
38
what is a stem cell?
a cell that can divide (by mitosis) an unlimited number of times
39
what can each new cell produced by a stem cell do?
ach new cell that is produced when a stem cell divides has the potential to remain a stem cell or to develop into a specialised cell through differentiation
40
what is differentiation?
the process whereby stem cells become more specialized cell types
41
what is potency?
the ability of stem cells to differentiate into more specialised cell types
42
what are the four types of potency?
-totipotency -pluripotency -multipotency -unipotency
43
what can a totipotent stem cell divide into?
-totipotent cells can divide and produce any type of body cell -also referred to as embryonic stem cells
44
where do totipotent stem cells exist?
for a limited time in early mammalian embryo and in extra-embryonic cells (the cells that make up the placenta)
45
zygotes
-the zygote formed when a sperm cell fertilises an egg cell is totipotent -the embryonic cells up to the 16-cell stage (morula) of human embryo development are also totipotent
46
the development of totipotent cells:
1) initially, the totipotent cells in the embryo are unspecialised 2) during development, totipotent cells begin to translate only a specific part of their DNA, which results in cell specialisation 3) these specialised cells then form tissues and are no longer classed as totipotent 4) there are no totipotent cells present in the later stages of development as cells lose their ability to differentiate into any cell type
47
what are pluripotent stem cells?
embryonic stem cells that can differentiate into any cell type found in an embryo but are not able to differentiate into extra-embryonic cells
48
function of pluripotent stem cells:
-can divide in unlimited numbers and keep replacing themselves -can be used in treating human disorders
49
what are iPS cells?
induced pluripotent stem cells
50
how can iPS cells be produced?
-from adult somatic cells using appropriate protein transcription factors -transcription factors cause specific genes to be expressed which dedifferentiate a cell back to its pluripotent state
51
what can iPS cells be used for?
each individual can have their own pluripotent stem cell line produced from their body's cells and these could potentially be used to generate transplants without the risk of immune rejection
52
what happens as organs and tissues develop?
cells become more and more specialised
53
why must cells develop and specialise?
to fulfil particular roles → adult cells gradually lose their ability to divide until eventually, they are no longer able to divide
54
what are multipotent stem cells?
-adult stem cells that remain to produce new cells for the essential processes of growth, cell replacement and tissue repair -adult stem cells can divide (by mitosis) an unlimited number of times, they are only able to produce a limited range of cell types
55
examples of where multipotent stem cells are found?
bone marrow are multipotent adult stem cells – they can only differentiate into blood cells (red blood cells, monocytes, neutrophils and lymphocytes)
56
where can stem cells be found?
throughout the body (eg. in the bone marrow, skin, gut, heart and brain)
57
what is tem cell therapy?
the introduction of adult stem cells into damaged tissue to treat diseases (eg. leukemia) and injuries
58
what are unipotent cells?
adult cells that can only differentiate into their own lineage
59
examples of unipotent cells:
heart muscle cells (cardiomyocytes) can generate new cardiomyocytes through the cell cycle to build and replace heart muscle
60
what are most cells in animal bodies?
unipotent
61
EXAM TIP:
Don’t forget, while still classed as stem cells (as they can divide any number of times), only a limited range of specialised cells can be formed from adult stem cells as they have already partially differentiated. For example, stem cells in bone marrow can only produce cells that differentiate into the different types of blood cells.
62
why are stem cells useful?
due to their ability to differentiate into multiple cell types, stem cells have huge potential in… -therapeutic treatment of disease -producing transplants
63
which potencies can embryonic stem cells be?
one of two potencies: -totipotent (if taken in the first 3-4 days after fertilisation) -pluripotent (if taken on day 5)
64
where are embryos used for embryonic research taken from?
-they are specifically donated for this purpose -they are fertilised in vitro
65
how can adult stem cells be used?
in stem cell therapy (being researched)
66
what is stem cell therapy?
the introduction of adult stem cells into damaged tissue to treat diseases and injuries
67
is the use of adult or embryonic stem cells less controversial?
the use of adult stem cells is less controversial than embryonic stem cells because the donor is able to give permission
68
multipotent cells & matches:
if multipotent stem cells are being donated from one person to another they need to be a close match in terms of blood type and other body antigens as there is a chance that the cells used are rejected by the patient's immune system
69
what are iPS cells?
cells that have been developed by scientists using an adult's somatic cells that are unipotent (fully differentiated)
70
what are somatic cells?
any cell in the body that is not a gamete (sperm or egg) cell
71
how are iPS cells produced?
-as all somatic cells contain the same genetic material scientists are able to use specific transcription factors to target the genes that control pluripotency -scientists 'switch on' these genes that are usually silenced in differentiated cells which allows them to revert back to pluripotent cells
72
what can iPS cells be used for?
to produce any type of cell required for repair/treatment of the body
73
benefits of iPS cells:
iPS cells could be used instead of embryonic cells, this would avoid the ethical issues associated with using embryonic stem cells
74
issues with iPS cells:
-the technique is not verified yet as during research iPS cells have caused tumour formation -this is thought to be because some of the genes switched on will control the cell cycle and its regulation, which if uncontrolled will lead to tumour formation
75
overall benefits of using stem cells:
-great potential to treat a wide-variety of diseases like diabetes paralysis -organs developed from a patient's own stem cells reduces the risk of organ rejection and the need to wait for an organ donation -adult stem cells are already used successfully in a variety of treatments
76
issues of using stem cells:
-stem cells cultured in the lab could become infected with a virus which could be transmitted to the patient -there is a risk of cultured stem cells accumulating mutations that can lead to them developing into cancer cells -low numbers of stem cell donors
77
social issues of stem cells:
-embryonic stem cells can be collected before birth (from amniotic fluid) or after birth (umbilical cord blood) and stored by a clinic - but this can be expensive and isn't an option for everyone -a lack of peer-reviewed clinical evidence of the success of stem cell treatments -educating the public sufficiently about what stem cells can and cannot be used for
78
ethical issues of stem cells:
-stem cells may be sourced from unused embryos produced in IVF treatment - is it right to use them? -is it right to create embryos through therapeutic cloning and then destroy them? -should an embryo be treated as a person with human rights?
79
how is gene expression controlled in eukaryotes?
with transcription factors
80
what is a transcription factor?
a protein that controls the transcription of genes by binding to a specific region of DNA
81
what do transcription factors ensure?
that genes are being expressed in the correct cells, at the correct time and to the right level
82
the structure of a gene:
upstream - refers to the DNA before the start of the coding region the promoter - a section of DNA upstream of the coding region that is the binding site for proteins that control the expression of the gene
83
which proteins bind to the promoter region?
-transcription factors -RNA polymerase
84
which direction is DNA transcribed and translated in?
while DNA is translated in the 3' to 5' direction, it is transcribed in the 5' to 3' direction to produce messenger RNA (mRNA)
85
how to transcription factors work?
-they enter the nucleus from the cytoplasm through nuclear pores -transcription factors are activated through a signalling pathway that usually starts from outside the cell
86
what do transcription factors do when they bind?
either initiate or inhibit the transcription of the gene from taking place
87
what to transcription factors interact with?
transcription factors interact with RNA polymerase, either by… → assisting RNA polymerase binding to the gene (to stimulate expression of the gene) → by preventing it from binding (to inhibit gene expression)
88
what does the presence of a transcription factor do?
either increase or decrease the rate of transcription of a gene
89
what does oestrogen do in animals?
works as a transcription factor that activates the transcription of many genes
90
what is oestrogen?
a steroid hormone found in mammals
91
what are steroid hormones?
small, hydrophobic, lipid-based hormones that can diffuse through the cell membrane and can pass directly into the nucleus through nuclear pores
92
some roles of oestrogen:
oestrogen is involved in controlling the female fertility cycle & stimulating sperm production in males (up to 100 different genes are controlled by oestrogen)
93
steps of the oestrogen stimulation pathway:
1) oestrogen diffuses through the cell surface membrane into the cytoplasm 2) oestrogen diffuses through a nuclear pore into the nucleus 3) within the nucleus, oestrogen attaches to an ERα oestrogen receptor that is held within a protein complex 4) this causes the ERα oestrogen receptor to undergo a conformational change 5) the new shape of the ERα oestrogen receptor allows it to detach from the protein complex and diffuse towards the gene to be expressed 6) the ERα oestrogen receptor binds to a cofactor which enables it to bind to the promoter region of the gene 7) this stimulates RNA polymerase binding and gene transcription
94

A LEVEL BIO (y13) (10 decks)

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