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A2 Biology > Topic 8: The Control Of Gene Expression > Flashcards

Topic 8: The Control Of Gene Expression Flashcards

1
Q

3.8.1 Changes of base sequence in DNA alters structure of proteins

What is a mutation?

A
  • A change in the base sequence of DNA
  • Often arise spontaneously during DNA replication
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2
Q

What are some forms of mutation?

A
  • Addition
  • Deletion
  • Substitution
  • Inversion
  • Duplication
  • Translocation of bases
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3
Q

What are addition and deletion mutations?

A
  • Where one or more nucleotides (bases) are either inserted or deleted from the DNA sequence
  • This type of mutation alters the sequence of nucleotides after the insertion/deletion point known as a frameshift
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4
Q

What is a substitution mutation?

A
  • Where one nucleotide (base) in the DNA sequence is replaced by another
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5
Q

What is a duplication mutation?

A
  • Where one or more nucleotides (bases) duplicate and repeat and therefore produces a frameshift
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6
Q

What is an inversion mutation?

A
  • Where a group of nucleotides (bases) become seperated from the DNA sequence then rejoin in the reverse order i.e. they have flipped
  • This therefore affects the amino acid that is produced
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7
Q

What is a translocation mutation?

A
  • Where a group of nucleotides (bases) become seperated from the DNA sequence and are then inserted into the DNA of a different chromosome
  • This can often lead to significant effects on the phenotype
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8
Q

Which mutations are most likely to have a significant impact and why?

A
  • Insertion, deletion, duplication, translocation
  • Because they produce a frameshift which means the entire amino acid sequence will be produced different
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9
Q

Which mutations are less likely to have a significant impact and why?

A
  • Substitution, Inversion
  • Because they only alter one or very few triplets the amino acid sequence might not be affected due to the degenerate nature of the genetic code
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10
Q

Is a mutation resulting in a change to the amino acid sequence always harmful and why?

A
  • No, it may be neutral if the resulting change in protein has no effect on the organism
  • Also may be beneficial, which is the basis for evolution and natural selection
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11
Q

How is the mutation rate increased?

A
  • by mutagenic agents
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12
Q

What is a mutagenic agent? Give examples of this

A
  • factors that increase the rate of gene mutation
  • chemical mutagens such as alcohol and benzene
  • Ionising radiation such as UV and X-Ray
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13
Q

3.8.2.1 Most of a cells DNA is not translated

What is a stem cell?

3.8.2 Gene expression is controlled by a number of features

A
  • Undifferentiated cells that can divide indefinitely and turn into other specific cell types
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14
Q

Name and define the four types of stem cells?

A
  • Totipotent- can develop into any cell type which can include the placenta and embryo
  • Pluripotent- can develop into any cell type but EXCLUDING the placenta and embryo
  • Multipotent- can only develop into a few different types of cell
  • Unipotent- these cells can only differentiaate into one type of cell
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15
Q

What happens to totipotent cells during embryonic development?

A
  • Certain parts of the DNA are selectively translated so that only some genes are “switched on” in order to differentiate the cell into a specific type and to form the tissues that make up the foetus
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16
Q

Give a unique feature of pluripotent cells and then the use of this feature

A
  • They can divide in unlimited numbers and therefore can be used to repair and replace damaged tissues
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17
Q

What is a unipotent cell? Give an example

A
  • A cell that can only develop into one type of cell
  • This happens at the end of specialisation when the cell can only propogate its own type
  • An example is cardiomyocytes (heart cells)
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18
Q

Which types of stem cells are found in embryos?

A
  • Totipotent and Pluripotent
  • Multipotent and unipotent cells only found in mature mammals
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19
Q

Give some uses of stem cells

A
  • Medical therapies-e.g. bone marrow transplants, treating blood disorders
  • Drug testing-on artificially grown tissues
  • Research-e.g. on **formation of organs and embryos
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20
Q

How are induced ploripotent stem cells produced?

A
  • From mature, fully specialised (somatic) cells
  • The cell regains capacity to differentiate through the use of proteins, in particular transcription factors
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21
Q

3.8.2.2 Regulation of transcription and translation

What is a transcription factor?

3.8.2 Gene expression is controlled by a number of features

A
  • A protein that controls the transcription of genes so that only certain parts of the DNA are expressed
  • they bind to a specific site on DNA to begin the process of transcription
  • e.g. in order to allow the cell to specialise
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22
Q

How do transcription factors work?

A
  • move from the cytoplasm into nucleus
  • bind to promoter region upstream of target gene
  • makes it easier or more difficult for RNA polymerase to bind to gene, this increases or decreases the rate of transcription
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23
Q

Give an example of a hormone that affects transcription and explains how it works

A
  • Steroid hormone oestrogen diffuses through cell membrane
  • Forms hormone-receptor complex with ER a receptor in the cytolasm
  • Complex enters the nucleus and acts as a transcription factor to facilitate the binding of RNA polymerase
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24
Q

What is the role of oestrogen in controlling transcription?

A
  1. The lipid soluble nature of oestrogen means that it can freely diffuse across the cell
    membrane     where it binds to a receptor molecule on a transcription factor
  2. The binding alters the shape of the DNA binding site on the transcription factor and makes it able to bind to the DNA
  3. The transcription factor therefore enters the nucleus via the nuclear pore where it binds to DNA
    This stimulates the transcription of the gene that makes up the DNA
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25
Q

What is small interfering RNA?

A
  • also called silencing RNA is used for short term switching off of genes
  • siRNA binds to a complementary sequence of mRNA
  • mRNA is usually single stranded and the cell therefore detects the double stranded form on mRNA and views it as abnormal
  • Therefore the mRNA is broken down by enzymes preventing translation
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26
Q

What is meant by epigenetics?

A
  • A heritable change in the gene function WITHOUT change to the base sequence of DNA
  • shows that environmental factors can make changes to the function of genes which can be inherited
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27
Q

How does increased methylation of DNA affect gene transcription?

A
  • Involves addition of CH3 group to cytosine bases which are next to guanine
  • prevents transcription factors from binding
  • therefore gene transcription is supressed
28
Q

How does decreased acetylation of histones affect gene transcription?

A
  • positvely charged histones bind to negatively charged DNA
  • decreasing acetylation increases positive charge of histones
  • binding becomes too tight and prevents transcription factors from accessing the DNA
  • so transcription is supressed
29
Q

How might epigenetic changes affect humans?

A
  • They can cause disease either by activating a genes function (such as in cancer) or by supressing it
30
Q

Give an application of epigenetics

A
  • Treatment of various diseases
  • Development of ways to reverse epigenetic changes
31
Q

Describe the process of RNA interference including the organisms in which it occurs

A
  • RNA molecules act to inhibit gene expression usually by destroying mRNA so that it cannot be translated
  • occurs in eukaryotes and some prokaryotes
32
Q

3.8.2.3 Gene expression and cancer

Give some characteristics of benign tumours

3.8.2 Gene expression is controlled by a number of features

A
  • slow growth
  • defined by a clear boundary due to cell adhesion molecules
  • Cells retain function and normal shape
  • dont spread easily
  • easy to treat
33
Q

Give some characteristics of malignant tumours

A
  • rapid and uncontrollable growth
  • III defined boundary
  • Cells DO NOT retain function and they often die
  • spreads quickly and easily
  • difficult to treat
34
Q

Describe the role of tumour-suppressive genes

A
  • code for proteins that control cell division in particular stopping the cell cycle when damaged is detected
  • they are also involved in programming apoptosis i.e. self destruction of the cell
35
Q

Explain how tumour-supressing genes can be involved in developing cancer

A

A mutation in the gene could code for a nonfunctional protein

  • Increased methylation or decreased acetylation could prevent transcription
  • cells will divide uncontrollably resulting in a tumour
36
Q

Describe the role of proto-oncogenes

A
  • control cell division in particular they code for proteins that stimulate cell division
37
Q

Explain how proto-oncogenes can be involved in developing cancer

A
  • mutation in the gene could turn it into a permanently activated oncogene
  • Decreased methylation or increased acetylation can cause excess transcription
  • results in uncontrolled cell division and the formation of a tumour
38
Q

Explain how abnormal methylation of genes cause cancer

A
  • Hyper-methylation of tumour-suppressor genes or oncogenes can impair their funtion and cause the cell to divide uncontrollably
39
Q

Explain how oestrogen can be involved in developing breast cancer

A
  • oestrogen is an activator of RNA polymerase
  • therefore in areas with a high concentration of oestrogen such as adipose tissue in the breasts, cell division can become uncontrolled
40
Q

3.8.3 Using genome projects

What is the genome?

A
  • the complete set of genetic information contained in the cells of an organism
41
Q

What is genome sequencing?

A
  • Identifying the DNA base sequence of an individual
  • This allows us to determine the amino acid sequence of the polypeptides coded for by that DNA
42
Q

What is the proteome?

A
  • the complete set of proteins that can be produced by a cell
43
Q

Can we directly translate the genome into the proteome?

A
  • in simple organism YES
  • in complex organisms due to the presence of non-coding DNA and regulatory genes, it is much harder to obtain the proteome
44
Q

Give an application of sequencing the proteome in single organisms

A
  • identifying potential antigens for use in vaccine production
45
Q

Give some applications of genome sequencing

A
  • comparing genomes between species to determine evolutionary relationships
  • genetic matching
  • **personalised medicine
  • synthetic biology
46
Q

How have sequencing methods changed over time?

A
  • was a manual process
  • now it has become automated
  • a reaction mixture is created and after the process is complete a machine reads the base sequence
47
Q

3.8.4.1 Recombinant DNA technology

What is meant by recombinant DNA technology?

3.8.4 Gene tech allows the study/alteration of gene function

A
  • the transfer of DNA fragments from one organism or species to another
48
Q

Why does recombinant DNA technology work?

A
  • because the genetic code is universal and therefore transcription and translation occur by the same mechanism and result in the same amino acid sequence across organisms
49
Q

Summarise the process of using reverse transcriptase to produce DNA fragments

A
  • mRNA complementary to the target gene is used as a template
  • it is mixed with free nucleotides which match up to their base pairs and reverse transcriptase which forms the sugar phosphate backbone to **create cDNA (complementary DNA)
50
Q

Summarise the process of using enzymes to produce DNA fragments

A
  • restriction endonucleases cut DNA at specific sequences
  • different REs will ALWAYS cut at the SAME sequence
  • therefore using particular REs allow you to cut out a certain gene of interest
51
Q

In which two ways can we amplify DNA fragments

A
  • in vitro/ polymerase chain reaction
  • In vitro/ using host cells
52
Q

Describe the reaction mixture in the first stage of PCR

A
  • contains the DNA fragment to be amplified,
  • primers that are complementary to the start of the fragment
  • free nucleotides to match up to exposed bases
  • DNA polymerase to create new DNA
53
Q

Summarise the process of amplifying DNA fragments using PCR

A
  1. Heated to break apart the DNA strands
  2. Cooled which allows primers to bind
  3. Heated again to activate DNA polymerase and allow free nucleotides to join
  4. New DNA acts as a template for next cycle
54
Q

Summarise the process of inserting a DNA fragment into a vector

A
  • A plasmid used as the vector and is cut using the same restriction enzymes as DNA so that the ends are complementary
  • DNA ligase joins fragment and plasmid together
55
Q

Summarise the process of inserting a vector into a host cell

A
  • known as cell transformation
  • the host cells are mixed with vectors in an ice-cold solution, then heat shocked to encourage cells to take up the vectors
  • Cells can then be grown and the DNA fragment will be cloned
56
Q

Summarise the process of identifying transformed cells

A
  • marker genes e.g coding for fluoroescence can also be insterted into vectors along with DNA
  • when cells begin to grow, UV light can be used to identify which cells have taken up the vector and which havent
57
Q

3.8.4.2 Differences in DNA between individuals of the same species..

How can DNA probes be used to locate specific alleles?

3.8.4 Gene tech allows the study/alteration of gene function

A
  • probe designed so that its sequence is complementary to the allele you want to find
  • they are labelled, amplified using PCR then added to a sample of single stranded DNA
  • The probe will bind if the allele is present
58
Q

Give some applications of DNA probes

A
  • To screen someones DNA for a particular heritable health condition
  • To identify a gene for use in genetic engineering
  • To predict how someone will respond to a drug
59
Q

What is the purpose of hybridisation?

A
  • to measure degree of difference between two strands of DNA
  • can be used to compare someones DNA to a certain gene to see if the have it
60
Q

Summarise the process of DNA hybridation

A
  • one DNA strand is labelled and mixed with an unlabelled comparison strand
  • the more similar the strands the more strongly they will bind and more energy will be required to break the strands apart
61
Q

What are the benefits of genetic profiling?

A
  • can identify heritable diseseases very early therefore begin to **treat them before symptoms develop, reducing impact on individual
  • treatment can also be personalised to make it more effective
62
Q

What is genetic fingerprinting?

A
  • technique used to compare two DNA samples and determine whether they came from the same individual
63
Q

How does genetic fingerprinting work?

A
  • every organisms genomes contains non-coding regions called variable number tandem repeats (VNTRs)
  • the probability of two individuals having the same VNTRs is very low so we can compare these areas to see if two DNA samples came from the same person
64
Q

Summarise the process of genetic fingerprinting analysis

A
  • DNA sample is obtained
  • VNTRS cut out using restriction enzymes
  • They are then labelled and cloned using PCR
  • fragments are separated using gel electrophoresis
  • banding patterns of each sample can then be compared
65
Q

How does gel electrophoresis work?

A
  • DNA fragments are placed at one end of a slab of gel
  • An electric current is applied causing the DNA fragments to move towards the other end of the gel
  • Shorter fragments travel further
  • The pattern of bands created is unique to every individual
66
Q

Give applications of genetic fingerprinting

A
  • Forensics- e.g. to identify victims or suspects
  • Medical diagnosis- e.g. to identify type of haemoglobin produced by an individual to diagnose sickle cell anaemia
  • Animal and plant breeding- e.g. breed out harmful alleles and ensure pedigree

A2 Biology (4 decks)

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