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Biology 🧬 > control of gene expression > Flashcards

control of gene expression Flashcards

1
Q

substitution

A

one or more bases swapped for another

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2
Q

deletion

A

one or more bases removed

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3
Q

addition

A

one or more bases added

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4
Q

duplication

A

one or more bases repeated

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5
Q

inversion

A

a sequence of bases is reversed

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6
Q

translocation

A

sequence of bases moved from one location in genome to another
(could be within same or different chromosomes)

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7
Q

when do gene mutations occur?

A

spontaneously during DNA replication

mutagenic agents increase the rate of mutation

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8
Q

effects of mutations

A

different amino acid sequence made in polypeptide

change in sequence may change tertiary structure of protein
could stop it functioning

eg if its an enzyme, active site won’t be complementary shape to substrate

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9
Q

what does degenerate mean? and its impact on mutations

A

some amino acids coded for by more than one DNA triplet

means not all mutations change amino acid sequence

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10
Q

what is a frame shift?

A

happens due to mutations
- often addition, duplication and deletions
happens as they change the number of bases in a DNA code

changes nature of all base triplets that follow, code read in a different way
- affects amino acid sequence

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11
Q

examples of mutagenic agents

A

UV radiation
ionising radiation
chemicals

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12
Q

how can mutagenic agents increase rate or mutations? (3)

A

act as a base
- substitute for a base
- causes substitution mutations
- changes base sequence

alter a base
- can delete or alter bases
- changes sequence

changing DNA structure
- causes issues in replication
- increases likelihood of mutations

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13
Q

causes of cancer

A

when mutations happen in genes that control cell division
- tumour supressor genes
- proto-oncogenes

causes uncontrolled cell growth
results in tumour
- mass of abnormal cells which invade and destroy surrounding tissue

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14
Q

malignant tumours

A

cancers
- grow rapidly
- invade and destroy surrounding tissue
- cells can break off and spread in bloodstream

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15
Q

benign tumours

A

not cancerous
- grow slower
- covered in fibrous tissues, stops invading
- often harmless, can become malignant

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16
Q

what do tumour cells look like?

A
  • irregular shape
  • larger and darker nucleus
  • different antigens
  • divide more frequently (don’t respond to regulating processes)
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17
Q

role of tumour suppressor genes

A

working normally:
- slow cell division
- produce proteins to stop cell division or to make cells self destruct

can be inactivated by a mutation:
- doesn’t produce protein to slow division
- stimulates cells divide uncontrollably = tumour

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18
Q

role of proto-oncogenes

A

working normally:
- stimulate cell division
- produces proteins to make cell divide

effect can be increased due to mutation:
- gene becomes overactive
- stimulates cells to divide uncontrollably = tumour

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19
Q

what are oncogenes?

A

Mutated proto oncogene
caused by hypomethylation

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20
Q

what is methylation?

A

adding a methyl group

methylation of DNA controls weather or not the DNA is transcribed and translated

abnormal methylation is when it happens to much or too little
- hypomethylation
- hypermethylation

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21
Q

how can abnormal methylation cause tumours?

A
  • hypermethylation of tumour - suppressor genes
  • gene isn’t transcribed
  • protein to slow division not made
  • divide uncontrollably = tumour
  • hypomethlyation of proto-oncogenes
  • act as oncogenes
  • increases amount of proteins that stimulate cell division
  • divide uncontrollably = tumour
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22
Q

how does oestrogen cause cancer?

A

increased exposure over long periods of time - increased risk of breast cancer

  1. can stimulate certain breast cells to divide
    more cell division taking place increases chance of mutations and cells becoming cancerous
  2. the ability to stimulate division mean any cancerous cells would be able to divide even faster
    tumour form more quickly
  3. may be able to introduce mutations directly in DNA causing mutations
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23
Q

2 types of risk factors

A

something that increases someones chance of developing cancer

genetic - linked to specific inherited alleles - if inherited, more at risk

environmental - exposure to radiation, smoking, increased alcohol and fat diet increase risk

24
Q

how can understanding roles of the genes be used in prevention?

A

if a specific mutation causing cancer is known, it can be screened for

knowing this risk can allow for prevention
- screened more often
- lifestyle choices
increased recovery when found early

knowing genes can also mean better tests for cancers
- easier and more accurate diagnosis

25
Q

how can understanding roles of the genes be used in treatment and cures?

A

treatments are different for different mutations
- allows for more specific treatments to be made
- more effective in targeting it
- more treatment (eg higher doses) can be used for more aggressive cancers caused by different mutations

gene therapy - replace faulty genes with working ones
knowing which gene cause the cancers can also them be to changed

26
Q

what are stem cells?

A

unspecialised cells that can differentiate into other types of cell

27
Q

what are totipotent cells?

A

stem cells that can divide and produce any type of body cell

only translate part of their DNA, allowing them to become specialised

only present in mammals in first few divisions of embryo
- then become pluripotent

28
Q

what are pluripotent cells?

A

found in embryos

can specialise into any cell but ones that make up placenta

29
Q

multipotent stem cells

A

found in adult mammals

able to differentiate into few types of cell
eg red and white blood cells from bone marrow

30
Q

unipotent stem cells

A

only differentiate into one type of cell

found in adult mammals

31
Q

how to stem cells become specialised?

A

only transcribe and translate part of their DNA

all contain same genes
due to conditions, some genes are expressed and other switched off

mRNA only transcribed from specific genes so only specific proteins made in translation
proteins modify cell eg structure
= specialised

32
Q

unipotent cells in the heart

A

cardiomyocytes - heart muscle cells

thought that heart cells couldn’t be regenerated (issue if damaged)

now thought there is small supply of unipotent stem cells in heart
- specials to replace damaged cells

33
Q

use of pluripotent stem cells in treating disorders

A

as they can specialise into any type of cell, can be used to replace damaged cells

  • bone marrow contains stem cells that can specialise into any blood cell
  • bone marrow transplants are used to replace faulty bone marrow in patents with abnormal blood cells
  • cells in transplant divide and specialise into healthy blood cells

eg leukaemia

34
Q

sources of stem cells

A

adult stem cells - body tissues of adult
eg bone marrow
obtained in simple operation
but not as flexible - multipotent (a few types)

embryonic stem cells - embryos in early stages of development
created in lab using in vitro fertilisation (outside of womb)
stem cells remove and embryo destroyed
pluripotent - any number of any cell

iPS cells

35
Q

what are iPS cells?

A

induced pluripotent stem cells

created in a lab
reprogramming specialised adult body cells to become pluripotent

  • made to express transcription factors associated with pluripotent cells
  • cause there body cells to express genes associated with the stem cells

will be useful in medicine and ethical (see benefits of stem cells)

36
Q

how are iPS cells made?

A

made to express transcription factors to make them express genes associated with pluripotent stem cells

  • infect with specific modified virus
  • virus has genes coding for transcription factors in its DNA
  • when it infects, genes passed on to adult cells DNA, cell produces transcription factors
37
Q

benefits of stem cell treatments

A

save many lives
eg those waiting for transplants, new organs made from stem cells to reduce waiting

improve quality of life
replace damaged cells eg blindness

iPS cells are from adult stem cells - more ethical
but can still specialise into any cell

iPS made from patients cells - genetically identical
less chance of rejection

38
Q

issues of using stem cells treatments

A

ethical issues of using embryonic stem cells
- results in destruction of embryo, could become fetus
- less objection to those from egg cells that haven’t been fertilised, wouldn’t become fetus

should use adult stem cells - doesn’t destroy embryo
but can’t specialise into any cell

39
Q

why do cells have different functions?

A

cells in an organism all have the same genes

but structure and function varies as not all genes are expressed (transcribed and translated)
different genes expressed = different proteins made, determine structure and processes

40
Q

what are transcription factors?

A

proteins that control whether or not genes are transcribed
bind to promotor reigons upstream of gene

41
Q

how do transcription factors work?

A

control expression by controlling rate of transcription

  • in eukaryotes, move from cytoplasm to the nucleus
  • bind to specific DNA sites near start of target gene (the gene they citron the expression of)

activators - stimulate or increase rate of transcription
help RNA polymerase bind to start of target gene (promoter) and activate transcription

repressors - inhibit or decrease rate of transcription
bind to start of target gene (promoter) to prevent RNA polymerase from binding

42
Q

how does oestrogen initiate transcription?

A

oestrogen is a steroid hormone
affects transcription

oestrogen binds to a transcription factor called an oestrogen receptor
- forms an oestrogen - oestrogen receptor complex

complex moves from cytoplasm to nucleus

binds to specific DNA site near start of target gene (promoter)

complex can act as an activator
helps RNA polymerase bind
initiates transcription

or repressor (blocks RNA polymerase)

43
Q

what is RNA interference? (RNAi)

A

where small, double stranded RNA molecules (non-coding) stop mRNA from target genes being translated into proteins

also affects gene expression (inhibits)

done by siRNA (small interfering)
or miRNA (micro)

44
Q

how is siRNA made?

A

DNA transcribed and replication = Double stranded RNA
Broken up by enzymes into double stranded siRNA
DICER, hydrolyses

Hydrogen bonds broken
Joined to enzyme (eg RISC)
Creates siRNA

45
Q

how does siRNA work in mammals? (miRNA in plants)

A

DNA transcribed and replicated
= double stranded RNA
broken up by enzymes into pieces
(eg DICER)
hydrogen bonds broken
= single stranded siRNA

associates with enzyme
(eg RISC)

siRNA then binds to target mRNA
- base sequence of siRNA complementary to base sequence of target mRNA

Enzyme with siRNA, cut the mRNA into fragments
- can’t be translated

fragments move to processing body where they are degraded

46
Q

how does miRNA work?

A

miRNA not always complementary to target mRNA
- is less specific than siRNA, can target more than one mRNA molecule

miRNA associates with enzymes and binds to target mRNA in cytoplasm

miRNA - protein complex blocks the translation of target mRNA

mRNA then moved into processing body and stored or degraded
(stored to be translated later)

47
Q

what is epigenetic control? (+ how it works)

A

determines whether or not a gene is expressed (transcribed and translated)

works by attachment or removal of chemical groups - epigenetic marks
to or from DNA or histones

don’t later base sequence
change how easy it is for enzymes need for transcription to interact and transcribe DNA

can occur in responses to changes in the environment

48
Q

types of epigenetic changes (2)

A

increased methylation
decreased acetylation

= genes not expressed

49
Q

inheritance of epigenetic marks

A

organisms inherit DNA base sequence from parents

some epigenetic marks are passed on to offspring (most removed)

means expression of some gene in offspring affected by environmental changes that impacted their parents

50
Q

how does increased methylation inhibit transcription?

A

methyl group (epigenetic mark) is attached to the DNA coding for a gene

attaches at a CpG site
(where cytosine and guanine are joined by a phosphodiester bond)

increased methylation changes the DNA structure
transcriptional machinery can’t interact (eg enzymes)
gene isn’t transcribed (not expressed)

51
Q

how does decreased acetylation inhibit transcription?

A

DNA wraps around histones to make chromatin
can be highly or less condensed due to presence of acetyl groups (epigenetic marks)

histones can be acetylated - add acetyl group
- makes chromatin less condensed
- DNA more accessible to machinery
- can be transcribed

acetyl groups can be removed from histones
- chromatin highly condensed
- genes in DNA less accessible, machinery can reach it
- not transcribed

histone deacetylase (HDAC) responsible for removing acetyl group

52
Q

how does epigenetics lead to development of disease?

A

methylation controls which genes are expressed
abnormal methylation of certain genes can result in cancers:

hypermethylation of tumour suppressor genes
hypomethylation of proto-oncogenes

controls which genes are expressed, lead to uncontrolled cell growth

53
Q

how can drugs treat epigenetic changes?

A

epigenetic changes are reversible
drugs designed to counteract epigenetic changes

increased methylation = gene switched off
drugs can stop DNA methylation so gene still expressed

decrease acetylation = gene switched off
drugs can inhibit histone deacetylase (which remove the acetyl group) so genes remain acetylated, can be expressed

but drugs must be specific as epigenetic changes can happen naturally, must target right cells

54
Q

Pre transcriptional control

A

Transcription factors
Increased or decrease transcription

55
Q

Post transcriptional control

A

RNA interference
Stop translation

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