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A-level Biology > Unit 3.8 - the control of gene expression > Flashcards

Unit 3.8 - the control of gene expression Flashcards

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1
Q

what are stem cells?

A

cells that retain the ability to differentiate into other cells

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2
Q

what are embryonic stem cells?

A

they come from embryos in the early stages of development. they can differentiate into any type of cell in the intial stages of development

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3
Q

what are umbilical cord blood stem cells?

A

they are derived from umbilical cord blood and are similar to adult stem cells

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4
Q

what are placental stem cells?

A

they are found in the placenta and develop into specific types of cells

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5
Q

what are adult stem cells?

A

they are found in the body tissues of the fetus through to the adult. they are specific to a particular tissue or organ within which they produce the cells to maintain and repair tissues

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6
Q

what are totipotent stem cells?

A

they are found in the early embryo and can differentiate into any type of cell. a zygyte is totipotent.

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7
Q

what are pluripotent stem cells?

A

they are found in embryos and can differentiate into almost any type of cell

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8
Q

what are multipotent stem cells?

A

they are found in adults and can differentiate into a limited number of specialised cells.

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9
Q

what are unipotent stem cells?

A

they can only differentiate into a single type of cell. they are derived from multipotent stem cells and are made in adult tissue

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10
Q

what are mutagenic agents?

A
  1. high energy ionising radiation can disrupt the structure of DNA which causes problems during DNA replication
  2. chemicals such as nitrogen dioxide may directly alter the sequence of DNA by altering or deleting bases or can interfere directly with transcription
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11
Q

how are adult and embryonic stem cells used?

A

adult - they are obtained from the body tissues of an adult eg bone marrow. they can only specialise into a limited range of cells (multipotent)
embryonic - they are obtained from embryos at an early stage where they are created in a lab using IVF, stem cells are removed from them after 4-5 days where they can divide an unlimited number of times

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12
Q

what are induced pluripotent cells (iPS)?

A

they’re a type of pluripotent cell that are produced from unipotent stem cells which can almost be any type of cell. these body cells are genetically altered in a lab to make them acquire characteristics of embryonic stem cells. these cells are capable of self renewal which means they can potentially divide indefinitely so they could replace embryonic stem cells in treatments and overcome ethical issues

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13
Q

how do you make iPS?

A
  • it involves inducing genes and transcriptional factors, within the cell to express themselves. basically to turn on genes that were otherwise turned off. the iPS cells are similar to embryonic stem cells in form and functions.
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14
Q

what are cardiomyocytes?

A

they are heart muscle cells that make up a lot of the tissue in our hearts, recent research has shown that our hearts do have some regenerative capability. some think that old cardiomyocytes can be replaced by new ones derived from a small supply of unipotent stem cells in the heart.

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15
Q

what do people believe about cardiomyocyte process?

A
  1. some believe that its a slow process and that its possible that some cardiomyocytes are never replaced throughout a person’s entire lifetime
  2. other believe that its occurring more quickly, so that every cardiomyocyte in the heart is replaced several times in a lifetime
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16
Q

what are transcriptional factors?

A

the transcription of genes is controlled by protein molecules called transcriptional factors

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17
Q

describe how transcription occurs using transcriptional factors?

A
  1. for transcription to begin the gene is switched on by the factors that move from the cytoplasm into the nucleus
  2. each transcriptional factor has a site that binds ti a specific base sequence of the DNA in the nucleus
  3. when it binds, it causes this region of DNA to begin transcription
  4. mRNA is produced and the info it carries is then translated into a polypeptide
  5. when a gene is not being expressed ie switched off, the site on the transcription factor that binds to the DNA isnt active
  6. as the site on the transcriptional factor binding to the DNA is inactive it cannot cause transcription and polypeptide synthesis
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18
Q

how does oestrogen switch on a gene and start transcription by combining with a receptor site on the transcriptional factor?

A
  1. oestrogen is a lipid-soluble molecule and therefore diffuses easily through the phospholipid portion of the cell-surface membrane
  2. once inside the cytoplasm of a cell, oestrogen binds with a site on a receptor molecule of the transcriptional factor. the shape of this site and the shape of the oestrogen molecule are complementary
  3. by binding with the site, the oestrogen changes the shape of the DNA binding site on the transcriptional factor, which can now bind to DNA -its activated
  4. the transcriptional factor can now enter the nucleus through a nuclear pore and bind to specific bases sequences on dna
  5. the combination of the transcriptional with dna stimulates transcription of the gene that makes up the portion of dna
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19
Q

what are epigenetics?

A

its when environmental factors can cause heritable changes in gene function without changing the base sequence of DNA, it works by attachment or removal of chemical groups to or from DNA or histone proteins

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20
Q

what are tags?

A

both dna and histones are both covered in chemicals called tags. these chemical tags form a second layer called the epigenome, which determines the shape of the DNA- histone complex

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21
Q

why are epigenomes flexible?

A

the chemical tags respond to environmental changes eg diet and stress which can cause the tags to adjust the wrapping and unwrapping of the dna and so switches genes on and off.

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22
Q

what is the epigenome of a cell?

A

it is the accumulation of the signals it has received during its lifetime and acts like a celular memory. environmental factors cause the epigenome to activate or inhibit specific set of genes via signal which stimulates the proteins to carry its message inside the cell where it is passed by a series of other proteins into the nucleus.

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23
Q

what happens after the environmental signal has passed into the nucleus?

A

the message passes to a specific protein which can be attached to a specific sequence of bases on the dna. once attached the protein can change the acetylation of histones leading to the activation or inhibitions of a gene, or it can change the methlyation of dna by attracting enzymes that can add or remove methyl groups

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24
Q

what is the association of dna with histones like?

A

it is weak as the dna-histone complex is less condensed, in this condition the dna is accessible by transcription factors, which can initiate the production of mRNA, which switches the gene on

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25
Q

what happens when the assocation of dna and histones is stronger?

A

the complex is more condensed and in this condtiion the dna isnt accessible by transcription factors, whuch cannot interfere initiate production of mRNA so the gene is switched off.
- condensation of the dna-histone complex therefore inhibits transcription. it can be brought about by decreased acetylation of the histones or by methylation of dna

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26
Q

what is deacetylation?

A
  • Deacetylation is the reverse reaction where an acetyl group is removed from a molecule, this is increases the positive charges on histones and therefore increases their attraction to the phosphate groups of DNA.
  • the association between DNA and histones is stronger as the chromatin becomes highly condensed and so the DNA isn’t accessible to the transcription factor. the transcription factors cannot initiate mRNA production from DNA so the DNA is switched off
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27
Q

what is methylation?

A

it is the addition of a methyl group to a molecule. the group is added to the cytosine bases of DNA. it inhibits the transcription of genes by either preventing the binding of transcriptional factors to the DNA or attracts proteins that condense the DNA-histone complex by inducing deacetylation of the histones, making the DNA inaccessible to transcription factors

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28
Q

what happens to most epigenetic tags?

A

they are removed between generations but a few escape this process and pass unchanged from parent to offspring

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29
Q

what are epigenetic changes responsible?

A

for certain diseases, altering any of the epigenetic processes can cause abnormal activation or silencing of genes. they can cause an increase in the incidence of mutations

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30
Q

what is epigenetic therapy?

A

they use drugs to inhibit certain enzymes involved in either histone acetylation of dna methylation. it must be specifically targeted to cancer cells. if the drugs were to affect normal cells they could activate gene transcription and make them cancerous.

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31
Q

how is epigenetic therapy used in diagnostic tests?

A

it helps detect the early stages of diseases. these tests can identify the level of dna methylation and histone acetylation at an early stage of disease

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32
Q

how is siRNA involved inbreaking down mRNA down before its coded info can be translated into a polypeptide?

A
  1. an enzyme cuts large double-stranded molecules of RNA into smaller sections small interfering RNA (siRNA)
  2. one of the two siRNA strands combines with an enzyme
  3. the siRNA molecule guides the enzyme to a messenger RNA molecule by pairing up its bases with the complementary ones on a section of the mRNA molecule
  4. once in position, the enzyme cuts the mRNA into smaller sections
  5. the mRNA is no longer capable of being translated into a polypeptide
  6. this means that the gene has not been expressed it has been blocked
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33
Q

what is substitution?

A

where a nucleotide in a section of DNA molecule is replaced by another molecule that has a different bases

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34
Q

what are the first 2 consequences of dna substitution?

A
  1. the formation of one of the three stop codons that mark the end of a polypeptide chains. as a result the production of the chain coded for by the section of dna would be stopped prematurely. the final protein would almost be different and perform a different function
  2. the formation of a codon for a different amino acid, means that the structure of the polypeptide produced would differ in a single amino acid. the protein of which this polypeptide is made, a part may differ in shape but not function
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35
Q

what is the third consequence of dna substitution?

A

3, the formation of a different codon but one that produces a codon for the same amino acid as before, this because the genetic code is degenerate and so the mutation therefore has no effect on the polypeptide produced

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36
Q

what happens when a base is deleted?

A

it creates a frame shift as the reading frame that contains each three letters for the code has been shifted to the left by one letter. the gene is now read in the wrong three-base groups and the coded info is altered. the polypeptides will be different and lead to the production of a non-functional protein that could alter the phenotype

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37
Q

what are the other types of mutation?

A
  1. addition - an extra base also causes a frame shift and the whole sequence of triplets become altered
  2. duplication - one or more of bases are repeated, this produces a frame shift to the right
  3. inversion - a group of bases become separated from the dna sequence and region at the same position but in the inverse order
  4. translocation - a group of bases become separated from the dna sequence on one chromosome and become inserted into the dna sequence of a different chromosome
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38
Q

what are the types of tumours?

A
  • malignant tumours are cancerous that can grow to large size but at a faster rate
  • benign tumours are non cancerous that can also grow to a large size but at a slower rate
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39
Q

what are cancer cells derived from?

A

they are derived from a single mutant cell, the initial mutation causes uncontrolled mitosis in the cell. Later, a further mutation in one of the descendant cells leads to other changes that cause subsequent cells to be different from normal cells in growth and appearance

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40
Q

what are oncogenes?

A

they are mutations of protoncogenes which stimulate a cell to divide when growth factors attach to a protein receptor on its cell surface membrane. this then activates the genes that cause DNA to replicate and the cell to divide.

41
Q

what happens when a proto-oncogene mutates into a oncogene that becomes permanently activated (switched on)?

A

1- the receptor protein on the cell membrane can be permanently activated, so that cell division is switched on even in the absence of growth factors
2- the oncogene may code for a growth factor that is then produced in excessive amounts, again stimulating excessive cell division

42
Q

whats the result of a permanently activated oncogene?

A

the result is that cells divide too rapidly and out of control and a tumour or cancer develops. a few cancers are caused by inherited mutations of proto-oncogenes that cause the oncogene to be activated but most cancer causing mutations involving oncogenes are acquired not inherited

43
Q

what is a tumour suppressor gene?

A

they slow down cell division, repair mistakes in DNA, they tell cells when to die in a process called apoptosis. they have the opposite role from proto-oncogenes.
- a normal TSG mainatins normal rates of cell division and so prevents formation of tumours

44
Q

what happens when a normal tumour suppressor gene becomes mutated?

A

it stops inhibiting cell division and cell grow out of control. the mutated cells that are formed are usually structurally and functionally different from normal cells. while most of these die, those that survive can make clones of themselves and form tumours

45
Q

what is an important difference between TSG and oncogenes?

A

oncogenes cause cancer as a result of the activation of proto-oncogenes, whilst TSG cause cancer when they are inactivated

46
Q

what is abnormal DNA methylation?

A

its common in the development of a variety of tumours. the most common one is hypermethylation (increased methylation)

47
Q

how does hypermethylation occur?

A
  1. hypermethylation occurs in a specific region, the promoter region of tumour suppressor genes
  2. this leads to the tumour suppressor gene being activated
  3. as a result, transcription of the promoter regions of tumour suppressor gene is inhibited
  4. the tumour suppressor gene is therefore silenced (switched off)
  5. as the tumour suppressor gene normally slows down the rate of cell division, its inactivation leads to increased cell division and the formation of a tumour
48
Q

where does hypermethylation occur?

A

in a TSG known as BRCA1 and leads to the development of breast cancer. another form of abnormal methylation is hypomethlation (reduced methylation), this occurs in oncogenes where it leads to their activation and forms tumours

49
Q

what is oestrogen?

A

it plays a role in regulating the menstrual cycle in women. it is known that after the menopause, a woman’s risk of developing breast cancer increases.

50
Q

how does oestrogen cause cancer?

A
  • this is thought to be due to increased oestrogen concentrations as the fat cells of breasts tend to produce more oestrogen after menopause
  • these locally produced oestrogens appear to trigger breast cancer in postmenopausal women
51
Q

what happens when the locally produced oestrogens trigger a tumour ie cancer?

A
  • once a tumour has developed, it further increases oestrogen concentration which therefore leads to increased development of the tumour. it also appears that white blood cells that are drawn to the tumour oestrogen production, this leads to greater development of the tumour also
  • if the gene that oestrogen acts on is one that controls cell division and growth, then it will be activated and its continued division could produce a tumour
52
Q

what have improvements in technology allowed us to do? what is bioinformatics?

A

they allowed us to separate the genomes of a variety of organisms.
- bioinformatics is the science of collecting and analysing complex biological data, it uses computers to read, store and organise biological data at a much faster rate

53
Q

what is whole-genome sequencing (WGS)?

A

WGS determines the complete DNA base sequence of an organism. this involves researchers cutting the DNA into many small, easily sequenced sections and then uses algorithms to align overlapping segments the entire genome.

54
Q

when is protein only produced?

A

its only produced when a gene is switched on and genes are not switched on all the time. all the proteins are produced in a given type of cell (cellular proteome) or organism (complete proteome), at a given time, under specified conditions

55
Q

why is it easy to determine the proteome of prokaryotic organisms?

A

the vast majority of prokaryotes have one circular piece of DNA that isn’t associated with histones, and also there are non-coding portions of DNA which are typical of eukaryotic cells
- this knowledge can be used eg those that act as antigens can be used in vaccines against diseases caused by these pathogens

56
Q

what is the problem of determining the genome and proteome of complex organisms?

A

translating knowledge of the genome into the proteome as the genome contains many non-coding genes as well as others that have a role in regulating other genes

57
Q

what is recombinant DNA?

A

its the DNA of two different organisms that have been combined, the resulting organism is known as a transgenic or genetically modified organism (GMO)

58
Q

why does combining the DNA of two different organisms work?

A

the DNA is universal and can be used by all living organisms. this explains why the coded information on the transferred DNA can be interpreted. with proteins its the same also, as a result the transferred DNA can be transcribed and translated within the cells of the recipient organism

59
Q

what is the process of making proteins using dna technology of gene transfer and cloning?

A
  1. isolation of DNA fragments that have the gene for the desired protein
  2. insertion of DNA fragment into vector
  3. transformation where the dna is transferred into suitable host cells
  4. identification of the host cells that have successfully taken up the gene using gene markers
  5. growth/cloning of the population of host cells
60
Q

describe the general conversion of mRNA to cDNA using reverse transcriptase? A

A
  1. most cells contain only two copies of each gene, making it difficult to obtain a DNA fragment containing the target gene, they also contain mRNA
  2. extract the mRNA for this cell that provides the code for this protein, the mRNA acts as a template on which a single-stranded complementary copy of DNA (cDNA) is formed using reverse transcriptase
  3. DNA polymerase is used to place complimentary nucleotides in the correct order using cDNA as a template
61
Q

describe the conversion of mRNA to cDNA using reverse transcriptase in insulin?

A
  1. a cell that readily produces the protein is selected eg B cells of the islets of langerhans
  2. these cells have large amounts of relevant mRNA, which is therefore more easily extracted
  3. reverse transcriptase is then used to make DNA from RNA known as complementary cDNA because its made up of the nucleotides that are complementary to the mRNA
  4. to make the other strand of DNA, the enzyme DNA polymerase is used to build up the complementary nucleotides on the cDNA template. this double strand of DNA is the needed gene
62
Q

what are restriction endonuclease enzymes?

A

they are used by bacteria to defend themselves by cutting up viral DNA. each type of endonuclease cuts a DNA double strand at a specific sequence of bases called a recognition sequence

63
Q

where does the endonuclease cut? B

A
  • sometimes this happens between two opposite base pairs, which leaves two straight edges known as blunt ends
  • others cut in a staggered way which leaves an uneven cut in which each strand of the DNA has exposed bases called sticky ends
64
Q

what is a palindrome?

A
  • the four unpaired bases at each end from left to right, they are two sequences that are opposites of one another, they are palindrome
  • the recognition sequence is referred to as a 6 bp palindrome sequence which is a typical way to produce sticky ends
65
Q

describe the gene machine process? C

A
  1. the desired sequence of nucleotide bases of a gene is determined from the desired protein in which the amino acid sequence is also determined
  2. the desired sequence of nucleotide bases for the gene is fed into a machine
  3. the sequence is checked for biosafety and biosecurity to ensure it meets standards
  4. oglionucleotides are made where the computer designs a series of small, overlapping single strands of nucleotides which can be assembled into the desired gene
  5. each of the oglionucleotides are assembled by adding a nucleotide at a time, they’re joined together to make a gene using the polymerase chain reaction
  6. the chain reaction also constructs the complementary strand of nucleotides to make the required double standed gene and is coped numerous times
  7. using sticky ends, the gene can be inserted into a bacterial plasmid which acts as a vector for the gene allowing it to be stored, cloned or transferred to another organism
  8. the genes are checked using standard sequencing techniques and those with errors are rejected
66
Q

what is in vivo gene cloning?

A

it is the transferring the fragments to a host cell using a vector

67
Q

what are recognition sites? (vivo gene cloning)

A

the sequences of DNA that are cut by restriction endonucleases are called recognition sites. if its cut in a staggered fashion, the cut ends of the DNA double strand are left with a single strand which is a few nucleotide-bases long. the nucleotides on the single strand at once side of the cut are complementary to those on the other side
- this means that the single stranded end of one fragment is complementary to the other single stranded end, therefore once the complementary bases of two sticky ends have paired up, an enzyme called DNA ligase is used to bind the the two sections of DNA

68
Q

how do you prepare the DNA fragment? (vivo gene cloning)

A
  • it involves the addition of extra lengths of DNA. for the transcription of any gene to happen, the enzyme that synthesises mRNA (RNA polymerase) is a region of DNA, known as a promoter. the nucleotide bases of the promoter attach both RNA polymerase and transcription factors and begins transcription
69
Q

what is the terminator region? (vivo gene cloning)

A

as a region of DNA binds RNA polymerase and begins transcription of a gene, another region releases RNA polymerase and ends transcription. the terminator region

70
Q

what is the DNA fragment inserted into after it has been cut and the promoter and terminator regions are added? (vivo gene cloning)

A

it is inserted into a carrying unit known as a vector, which is used to transport the DNA into the host cell
- plasmids are used as they contain genes for antibiotic resistance and restriction endonucleases are used at one of these antibiotic-resistance genes to break the plasmid loop. the endonuclease used is the same one as the one that cut out the DNA fragment, which ensures the sticky ends of the opened up plasmid are complementary to the sticky ends of the DNA fragment

71
Q

what happens when DNA fragments are mixed with opened up plasmids? (vivo gene cloning)

A

they may become incorporated into them. the join is made permanent using the enzyme DNA ligase, these plasmids now have recombinant DNA

72
Q

what is transformation?

A
  • once the DNA has been incorporated into at least some of the plasmids, they must be introduced into bacterial cells in transformation and involves the plasmids and bacterial cells being mixed together in a medium containing calcium ions
  • the calcium ions along with changes in temperature make the bacterial membrane permeable, allowing the plasmids to pass through the cytoplasm
73
Q

why wont all bacterial cells possess the DNA fragments with the desired gene for the desired protein? (vivo gene cloning)

A
  • only a few cells take up the plasmids when the two are mixed together
  • some plasmids will have closed up again without incorporating the DNA fragment
74
Q

how do we find out which bacterial cells have taken up the plasmids? (vivo gene cloning)

A
  • using antibiotic resistance, which is unaffected by the introduction of the gene
    1- all the bacterial cells are grown on a medium that contains the antibiotic ampicillin
    2- bacterial cells that have taken up the plasmids will have acquired the gene for ampicillin resistance
    3- these bacterial cells are able to break down the ampicillin and survive
    4- the bacterial cells that have not taken up the plamsids will not be resistant to ampicillin and therefore die
75
Q

how do we find out whether a gene has been taken up by bacterial cells? (vivo gene cloning)

A

marker genes are used, they all include using a second, separate gene on the plasmid

76
Q

how does an antibiotic resistant marker work?

A
  • it identifies those cells with plasmids that have taken up the new gene, a technique called replica plating is used. the process uses the other antibiotic-resistant gene in the plasmid, the gene that was cut in order to incorporate the required gene
  • the bacteria that have taken up the required gene will no longer be resistant to the antibiotic tetracycline and so can be identified by growing them on a culture using tetrracycline
77
Q

what is the problem with the treatment using tetracycline?

A

it will destroy the very cells that contain the required gene. however by using replica plating its possible to identify living colonies of bacteria containing the required gene

78
Q

how does a fluorescent marker work?

A
  • the desired gene in question produces fluorescent protein (GFP) produced by jellyfish. any bacterial cell that has taken up the plasmid with the gene that is to be cloned will not be able to produce GFP. bacterial cells that havent taken up the gene will continue to produce GFP and to fluoresce.
  • as the bacterial cells with the desired genes are not killed, there’s no need for replica plating and results can be obtained by looking under a microscope which is faster
79
Q

how do enzyme markers work?

A
  • lactase will turn a particular colourless substrate blue, the required gene is transplanted into the gene that makes lactase. If a plasmid with the required gene is present in a bacterial cell, the colonies grown from it won’t produce lactase.
  • when these bacterial cells are grown on the colourless substrate they will be unable to change its colour. where the gene hasn’t been taken up the bacteria, they wont turn the substrate blue, these bacteria can be discounted
80
Q

what is in vitro gene cloning?

A

the polymerase chain reaction (PCR) is a method of copying fragments of DNA. the process is both automated and making it both rapid and efficient

81
Q

what does in vitro gene cloning require?

A

1- the dna fragment to be copied
2- DNA polymerase which is capable of joining nucleotides together in a strand
3- primers are short sequences of nucleotides that have a set of bases complementary to those at one end of each strand of the two DNA fragments
4- nucleotides
5- thermocycler a computer controlled machine that varies temperature precisely

82
Q

what are the first two stage of the DNA polymerase chain reaction? (in vitro gene cloning)

A 
1 Separation of DNA strand: the DNA fragments, primers and DNA polymerase are places in a vessel in the thermocycler. the temperature is increased to 95C causing the two strands of the fragments to separate due to the breaking of hydrogen bonds 
2 Addition (annealing) of the primers: mixture is cooled to 55C, causing the primers to join (anneal) to their complementary bases at the end of the DNA fragment. the primers provide the starting sequences for DNA polymerase to begin DNA copying as DNA polymerase can only attach nucleotides to the end of exisitng chain
- primers prevent the two separate strands from rejoining
83
Q

what is stage 3 of the DNA polymerase reaction? (in vitro gene cloning)

A

3 Synthesis of DNA: temperature increased to 72C. this is the optimum temperature for the DNA polymerase to add complementary nucleotides along each of the separated DNA strands. it begins at the primer on both strands and adds nucleotides in sequence until the end of the chain

84
Q

what happens when the two strands are complete? (in vitro gene cloning)

A

the process is repeated by subjecting them to the temperature cycle again to make more and more copies of DNA. allows billions to be made in a few hours

85
Q

what are the advantages of in vitro cloning?

A
  • it is very rapid, many copies can be made in a short amount of time. useful for crime scenes
  • doesn’t require living cells, bacteria doesn’t need to be cultured only a base sequence is needed
86
Q

what are the advantages of in vivo cloning?

A
  • useful where we wish to introduce a gene into another organism eg bacteria can be used to deliver into another organism
  • involves almost no risk of contamination, the gene that has been cut by the same restriction endonuclease can match the sticky ends of the opened-up plasmid
  • it is very accurate, although mutations can arise, new technology has made it less likely and rare
  • cuts out specific genes - the culturing of transformed bacteria produces many copies of a specific gene
87
Q

what is a DNA probe?

A

its a short, single-stranded length of DNA that has some sort of label attached that makes it easily available

  • radioactively labelled probes: which are made up of nucleotides with isotope 32P. the probe is identified using an x-ray film that is exposed by radioactivity
  • fluorescently labelled probes: which emit light under certain conditions for instance when the probe has bound to the target DNA sequence
88
Q

how are DNA probes used to identify particular alleles of genes?

A
  1. a DNA probe is made that has base sequences that are complementary to the part of the base sequence of DNA that makes up the allele of the gene we want to find
  2. the diuble stranded DNA that is being tested is treated to separate its two strands
  3. the separated DNA strands are mixed with the probe, which binds to the complementary base sequences on one of the strands -> DNA hybridisation
  4. the site at which the probe binds can be identified by the radioactivity or fluorescence that the probe emits
89
Q

how do we find out the base sequence of the particular allele that we trying to locate? (before making the probe)

A

DNA hybridisation takes place when a section of DNA or RNA is combined with a single-stranded section of DNA which has complementary bases. Before hybridisation, the two strands of the DNA molecule must be separated. this is achieved by heating the DNA until the strands separate into to two
- when cooled, the bases on each strand anneal with each other to reform the original double strand

90
Q

Using DNA probes and DNA hybridisation how can we locate a specific allele?

A

1- the sequence of nucleotides on the mutated allele is determined by DNA sequencing. genetic libraries now store the sequences of many common genes
2- fragment of DNA with complementary bases to the mutant allele of the gene is produced
3- DNA probe is formed by fluorescently labelling the DNA probe
4- PCR techniques are used to make many copies of the DNA probe
5- Probe is added to single-stranded DNA fragments from the person being screened
6- if the donor has the mutant allele, one of the probe is likely to bind to it as the base sequences are complementary to the probe and bind
7- these fragments will now be labelled with the probe and can be distinguished from the rest of the fragmetns
8- if complementary fragments are present, the DNA probe will be taken up and the dye will fluoresce. this is detected by a special microscope

91
Q

how can genetic screening be used?

A
  1. screen individuals who may carry a mutant allele, as it can determine the probablities of a couple of having offspring with a disorder
  2. possible to fix 100s of different DNA probes by adding a sample of DNA to an array, any complementary DNA sequences in the donor DNA will bind to more than one probes. makes it possible to trst for many disorders
  3. detection of oncogenes, it a mutated gene is detected by screening it can help make people who are at a greater risk of cancer make more informed decisions
92
Q

what is personalised medicine?

A

genetic screening allows doctors to provide advice and healthcare based on an individuals genotype. some people’s genes can mean that a particular drug may be more or less effective in treating a condition. this saves money by not overprescribing the drug

93
Q

what is genetic counselling?

A

its a form of social work, where advice and information are given that enable people make personal decisions. you can research the family history of an inherited disease and to advise parents on the likelihood of it arising in their children.

94
Q

what is genetic fingerprinting?

A

it is used to compare the DNA from all organisms, it is based on the fact that the DNA of every individual is unique.
- DNA bases which are non-coding are known as variable number tandem repeats (VNTRs). for every individual the number and length of VNTRs has a unique pattern

95
Q

what is gel electrophoresis?

A

it is used to separate the DNA fragments according to their size. (smaller fragments move further than the larger ones)

96
Q

how does gel electrophoresis work?

A
  • DNA fragments are placed onto an agar gel and voltage is applied
  • the resistance of the gel means that the larger the fragments, the slower they move. if the DNA fragments are labelled, eg with radioactive DNA probes their final position in the gel can be determined by placing a sheet of x-ray film over the agar gel.
  • the radioactivity from each DNA fragment exposes the film and shows where the fragments are situated on the gel
97
Q

Describe genetic fingerprinting?

A

1, Extraction: Dna is extracted from the sample

  1. Digestion: restriction endonuclease cut the DNA into the fragments
  2. Separation: DNA fragments are separated by electrophoresis to nylon membrane
  3. Hybridisation: DNA probes are used to bind to VNTRs which have complementary base sequences
  4. Development: X-ray film is placed over the nylon membrane. the film is exposed by the radiation from the radioactive probes and a series of bars are revealed where the radioactive DNA probes have attached
98
Q

what happens when there appears to be a match in genetic fingerprinting?

A

the pattern of bars of each fingerprint is passed through an automated scanning machine, which calculates length of the DNA fragments from the band. it uses data by measuring the distances travelled during the electrophoresis by known lengths of DNA. the closer the match between the two patterns, the greater the probability they’re the same person

99
Q

what are the uses of genetic fingerprinting?

A

1 Forensic science - comparing the banding pattern of DNA found at a crime scene to the DNA of the suspects. this calculates the probability of a suspect being at the scene. However it isnt always correct, DNA may have been left on another occasion, DNA may belong to a close relative
2 Genetic relationships - patterns can be used to determine whether individuals are genetically related
3 Disease diagnosis - disorders can be diagnosed by looking at banding patterns
4 Plant and animal breeding - during breeding programmes, fingerprints of organisms can be used to ensure that diversity is maintained. Also can be used to determine whether a organism has a desirable allele. if it does, it will be used in the breeding programme to increase the numbers of this allele

A-level Biology (8 decks)

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