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Biology A-Level > 7.2 Factors affecting gene expression > Flashcards

7.2 Factors affecting gene expression Flashcards

1
Q

why does cell differentiation take place

A

to form different tissues and organs, and so different cells can go on to produce proteins specific to their cell types

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2
Q

how do scientists measure different degrees of cell differentiation

A

gel electrophoresis

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3
Q

how would a scientists find a known gene out of all the genes present in the DNA of a cell

A
  • they use gene probes, which allow a specific section of DNA and mRNA in a cell to be identified
  • the gene probe finds the unique sequence of nucleotides in DNA that make up the gene by using RNA with a complimentary sequence
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4
Q

describe the process of using gene probes to find a specific sequence of DNA or mRNA

A
  • DNA from the cells under investigation is heated to break hydrogen bonds
  • fluorescently labelled mRNA for the required gene is added (the probe)
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5
Q

what determines the type of cell and its function in the body

A
  • the proteins present in a cell and the quantities of different proteins
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6
Q

what is transcription

A

the process by which the genetic code of DNA is copies into a complimentary strand of RNA before protein synthesis takes place

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7
Q

why is mRNA transcription an effective point to control gene expression

A
  • because a single mRNA strand results in the production of many protein molecules
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8
Q

what is a transcription factor

A

proteins that bind to the DNA in the nucleus and affect the process of transcribing genetic material

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9
Q

what is a promoter sequence and where are they found

A
  • the part of the DNA that the transcription factor binds to
  • usually found just above the point of transcription
  • some of them stimulate DNA transcription, by binding to the promoter sequence, by making transcription start from that point
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10
Q

what is an enhancer sequence, what happens when it is bound to

A
  • a region on the DNA sequence that the transcription factor binds to
  • when they bind here, they regulate the activity of DNA by changing the structure of the chromatin and deciding how open it is to RNA polymerase
  • when its very open, the gene is active and whet it’s closed, it’s not active
  • they can stimulate or prevent the transcription of a gene
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11
Q

what is pre-mRNA, and what are the modifications made to it

A
  • the RNA that’s produced in the nucleus from transcription usually gets modified before it lines up on the ribosomes
  • the introns are removed and sometimes some exons are removed, then they’re rejoined together by spliceosomes
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12
Q

what is RNA splicing

A

when spliceosomes join together the same exons in a variety of ways, so a single gene can produce different versions of functional mRNA that code for different amino acids which in turn produce different polypeptide chains

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13
Q

how is a protein modified

A
  • protein modification can take place after they have been synthesised by being shortened or lengthened by enzymes to give a variety of other proteins
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14
Q

what is epigenetics

A
  • a new area of research in biology
  • studied genetic control by factors other than base sequences on DNA
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15
Q

what are the three intracellular systems that interact to control genes

A
  • DNA methylation
  • histone modification
  • non-coding RNA
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16
Q

what’s a histone

A

a protein that provides structural support for chromatin

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17
Q

what is DNA methylation

A
  • widely used mechanism in epigenetics
  • addition of a methyl (CH3) group to cytosine, SILENCES a gene/ sequence
  • methyl group is added by methyltransferase
  • it can also modify the structure of histones
  • methyl group changes structure of DNA molecule so transcription can’t occur
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18
Q

what is DNA demethylation

A
  • the removal of a methyl group
  • enables the gene to become active so they can be transcribed
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19
Q

what’s the problem with DNA methylation / demethylation

A
  • researchers are finding that its associated with diseases, including a number of human cancers
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20
Q

describe a histone

A
  • positively charged proteins
  • DNA helices wind around histones to form chromatin, which makes up chromosomes
  • the histones determine the structure of chromatin
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21
Q

what is histone acetylation

A
  • an acetyl group (COCH3) is added to one of the lysines in a histone
  • this opens up the structure and activates chromatin, allowing the genes to be transcribed
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22
Q

what is histone methylation

A
  • a methyl group is added to lysine in a histone
  • depending on the position of the lysine, methylation can cause activation or inactivation of the DNA
  • however it is often linked to the silencing of a gene/ chromosome
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23
Q

what does non-coding RNA do

A
  • they affect the transcription of DNA or modify the products of transcription
  • genes or whole chromosomes can be silenced by ncRNAs
24
Q

why does cell differentiation occur and what is it a result of

A
  • it is a result of epigenetic modification to the genetic material of the cell
  • it ensures a wide range of proteins are made within the cell as it differentiates
  • it is a result of DNA methylation or demethylation or histone modification
25
Q

define the following:
1. totipotent cell
2. pluripotent cell
3. multipotent cell

A
  1. undifferentiated cells that can form any of the different cell types
  2. undifferentiated cells that can form most of the different cell types
  3. cells that can form a limited range of the different cell types
26
Q

whats cleavage (hehe)

A
  • first stage of embryonic development
  • forms a small mass of undifferentiated cells forming a hollow sphere (blastocyst)
  • takes place as zygote moves along the oviduct towards the uterus
27
Q

in terms of differentiation, what are the following stages of embryonic cell development:
1. embryonic stem cells
2. blastocyst
3. zygote
4. cells in umbilical cord

A
  1. totipotent
  2. pluripotent
  3. totipotent
  4. pluripotent stem cells
28
Q

describe the process of the early stages of development

A
  • cleavage results in a blastocyst (5-6 days), inner layer is pluripotent, outer layer forms placenta
  • zygote moves along the oviduct towards uterus
  • one large zygote forms a large number of small cells in early embryo (embryonic stem cells)
  • earliest cells in embryo are totipotent
29
Q

how do we use umbilical cord stem cells

A
  • blood drained from umbilical cord and placenta is frozen and is a rich source if pluripotent stem cells
  • used by the child or family members throughout life
  • can’t happen for everyone because they would be too expensive to store
30
Q

describe adult stem cells and what else are they called

A
  • found among normal cells, stay undifferentiated until needed to produce a major cell type in the tissue or organ that they’re held in
  • kept in bone marrow
  • also called somatic stem cells
31
Q

why aren’t adult stem cells used widely

A
  • only a small number of adult stem cells in each tissue
  • difficult to extract and most form a limited range of cells (multipotent)
  • difficult to grow in the laboratory
32
Q

how do undifferentiated cells form different cell types in cell development

A
  • cells are predestined days after conception
  • what they become is linked to their position in the embryo
  • if they’re removed and grown externally, they will still produce the same cell type
  • scientists are still unsure of the mechanism
  • once cells are differentiated, they cannot return back to being undifferentiated
33
Q

describe the evidence for cell determination

A
  • the idea that cell determination occurs irreversible at an early stage was disproved by transplanting tiny patches of tissue from one area of an early embryo to another
  • the cells formed the tissue linked to their new position, not their original position
  • same experiment was completed with a slightly older embryo and scientists saw that cell determination was complete and cells differentiated to form the cells linked to their old position instead
34
Q

how are the changes from embryonic stem cells to stem cells in the blastocyst to fully differentiated somatic cells brought about

A
  • during cell differentiation some parts of the chromosome undergo supercoiling to prevent the genes being transcribed and other areas uncoil to open up and be transcribed.
  • some genes are activated and some are silenced and its the combination of each of these factors that results in the characteristics in mature cells
35
Q

what is an example of epigenetic control in human development

A
  • fetal haemoglobin (2A, 2G) has a stronger affinity to oxygen than adult haemoglobin (2A, 2B)
  • during human development, different versions of globin genes are switched on and off
  • levels of globin chains change through the 40 weeks in pregnancy
  • genes controlling fetal gamma globin are silenced around birth and those for beta globin are activated
36
Q

how are adult stem cells used to make new body parts

A
  • stem cells from the patient are seeded onto framework, which may be collagen based and from or donor or completely synthetic
  • ## stem cells grow to form the required cells and new body part is returned to patient with no risk of rejection
37
Q

what is therapeutic cloning

A
  • an experimental technique that scientists aim to use to produce large quantities of healthy tissue to treat people with Alzheimer’s or type 1 diabetes etc.
38
Q

describe the process pf therapeutic cloning

A
  • produce healthy cloned cells from the patient by removing the nucleus from their normal cell and transfer to a human ovum that has had its nucleus removed
  • newly formed pre-embryo develops and divides to produce embryonic cells with the same genetic information as the patient
  • embryo is used as a source of stem cells
  • stem cells are harvested, embryo is destroyed
  • embryonic stem cells are cultured in a suitable environment so they differentiate into the required tissue
39
Q

what is a problem with therapeutic cloning

A
  • nucleus from the patients normal cells would have to be modified before being added to empty ovum, or the DNA would still carry the genetic mutation causing the disease
40
Q

what are the potential pitfalls of stem cell therapy

A
  • no one is quite sure how genes are switched on and off to form particular types of tissue
  • there are concerns that stem cells could cause the development of cancers in the body
41
Q

what are the advantages of stem cell therapy

A
  • there are no cures for the many conditions that stem cell therapy may solve
  • the ability to produce tailor-made cells to take over the function of damaged cells would revolutionise medicine
42
Q

what drugs to people take after having an organ transplant

A
  • immunosuppressant drugs
43
Q

what’s the big advantage of embryonic stem cell therapy over other stem cell types

A
  • they do not face the risk of rejection
44
Q

how did iPS cells come about

A
  • researchers took adult mouse cells and used genetic engineering techniques to make them pluripotent again
45
Q

are the benefits of of iPS cells

A
  • they overcome ethical objections to using embryonic tissue
  • there is no risk of rejection if cells from an individual are used to make their own stem cells
46
Q

who could benefit from stem cell therapy

A
  • people with Parkinson’s disease
  • those with type 1 diabetes
  • those with damaged nerves, e.g. spine injuries, paralysed
  • those in need for organ transplants
47
Q

how would stem cell therapy help those with Parkinson’s disease

A
  • uncontrollable tremors, body can’t move normally
  • stem cell transplants can replace lost brain cells to restore dopamine production
  • mature fetal cells have been transplanted into brains of adult humans, and produced dopamine for many years
  • very hard to obtain fetal cells
48
Q

How would stem cell therapy help those with type 1 diabetes

A
  • cells stop producing insulin
  • blood glucose concentration is uncontrolled
  • Stem cell therapy can give them working pancreas cells and restore insulin production
  • mouse embryonic stem cells were transplanted into mice with diabetes and it improved control of blood glucose
49
Q

How would stem cell therapy help those with damaged nerves

A
  • damaged nerve cells do not regrow, so those with major injury to their spines may be permanently paralysed
  • embryonic stem cells have been transplanted into mice with damaged spines, and it has improved control of movement and limbs
50
Q

what are the 4 ethical principles

A
  1. respect for autonomy - do not perform procedures on people unless you have their consent
  2. Beneficence - The aim of doing good, give medicine to relieve suffering
  3. Non-maleficence - do no harm
  4. Justice - Treat everyone equally, avoid discrimination
51
Q

for those who are in support of embryonic stem cell use, what do they say about the ethical arguments

A
  • the vast majority of embryos do not make it past the early stages of development to form living babies, so using a small number of early embryos is acceptable
  • once a enough willingly donated embryos are received, it will reduce use of new embryos
  • adult stem cells do not provide a good alternative, they are limited in terms of cell differentiation
52
Q

for those who are against embryonic stem cell use, what do they say about the ethical issues

A
  • it’s wrong it is abuse of human rights
  • religious groups believe its is wrong to use a potential human life
  • it is a potential human so it should have the same human rights as a fully grown adults
53
Q

what is the ethical argument against therapeutic cloning

A
  • they believe it can be taken further with cloned embryos implanted into a uterus as an act of human cloning
54
Q

what are the ethical arguments against use of iPS cells, and what is the biggest issue it faces

A
  • there are no ethical arguments
  • they are more difficult to grow and manipulate than pluripotent embryonic stem cells
55
Q
A

Biology A-Level (25 decks)

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