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AQA A-Level Biology > Y2: Gene mutations and expressions > Flashcards

Y2: Gene mutations and expressions Flashcards

1
Q

Define degenerate code

A

More than one codon codes for a single amino acid

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2
Q

Define non-overlapping

A

Each base is only read once

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3
Q

Define universal (DNA)

A

The same triplets code for the same amino acids across different species

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4
Q

Define gene mutation

A

Change in base sequence or quantity of bases in DNA

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5
Q

Define chromosome mutation

A

Change in the structure of a whole chromosome or a different total number of chromosomes

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6
Q

Define non-disjunction

A

The chromosomes fail to separate properly during mitosis

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7
Q

Define substitution

A

One or more bases are switched to another

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8
Q

Define deletion

A

One or more bases are removed causing a frame shift and often a truncating protein

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9
Q

Define insertion

A

One or more bases added causing a frame shift and resulting in a longer protein

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10
Q

Define translocation

A

DNA from one chromosome is inserted into another chromosome

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11
Q

Define duplication

A

One or more bases are repeated causing a frame shift

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12
Q

What are the three types of substitution?

what can if affect

A
  1. Nonsense mutations: stop codon is affected, results in a truncated protein
  2. Mis-sense mutations: different amino acid switched, causes a different protein structure
  3. Silent mutations: same amino acid is switched
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13
Q

What are three types of mutations and some examples?

A
  1. Physical: heat/radiation
  2. Chemical- changes base structure: asbestos
  3. Biological: virus, bacteria
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14
Q

Define inversion

A

DNA is separated and flipped around (inverted) so more than one nucleotide is flipped and it becomes a different mRNA molecule

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15
Q

Why do cells differentiate ?

2

A
  1. To conserve energy and resources

2. So they can specialise for a particular purpose

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16
Q

Define self-renewal

A

Potential to divide indefinitely

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17
Q

What are the four types of stem cells?

A
  1. Totipotent
  2. Pluripotent
  3. Multipotent
  4. Unipotent
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18
Q

Where are totipotent stem cells found and what can they form?
2

A

Zygote

Can differentiate into all human cells including the placenta

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19
Q

Where are pluripotent stem cells found and what can they form?
2

A

Embryo

Can differentiate into all adult cells, not placenta

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20
Q

Where are multipotent stem cells found and what can they form?
2

A

Relevant tissue in adults

Can form cells of a particular type eg: bone marrow cells can form any type of blood cell

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21
Q

Where are unipotent stem cells found and what can they form?

2

A

Adults

Can only form one cell type but, unlike normal cells, can self-renew

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22
Q

What are the three stages for induced pluripotency?

A
  1. A differentiated cell is removed from an individual
  2. Proteins are injected (which includes genes and transcriptional factors)
  3. After repeated divisions the cells become undifferentiated so become pluripotent
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23
Q

What is useful about induced pluripotency?

3

A
  1. Could be used to produce transplant tissue or to treat disease
  2. Capable of self-renewal
  3. Does not suffer the ethical drawbacks of embryonic stem cells
24
Q

What are three arguments for using embryonic stem cells?

A
  1. The first few cells from division of fertilised egg have greatest potential to treat human diseases
  2. Embryo at early development is just a ball of identical undifferentiated cells
  3. Can be grown in vitro
  4. Laws prohibit cloning
  5. Wrong to allow human suffering when we can stop it
  6. Embryos are used for other things and thrown away- recycling
25
Q

What are two arguments against using embryonic stem cells?

A
  1. Undermines our respect for human life
  2. People think it could lead to using foetuses and newborn babies for research
  3. Moving towards reproductive cloning
  4. Wrong to use humans as a means to an end
  5. Embryos are human beings
26
Q

What is good about oestrogen?

1

A

It is small and uncharged and lipid soluble so it can enter through the phospholipid bilayer membrane

27
Q

What is a transcriptional factor?

1

A

Protein that regulates transcription activating or repressing the action of RNA polymerase

28
Q

What is the general structure of a transcriptional factor?

2

A

Often have a quaternary structure so are a protein complex with different subunits

Have a DNA binding domain that is complementary to a particular promoter base sequence

29
Q

How does oestrogen regulate gene expression?

7

A
  1. Oestrogen diffuses across phospholipid bilayer membrane and enters cell
  2. Binds to transcriptional factor at receptor site in cytoplasm (activated)
  3. Puts stress on the bonds in the transcriptional factor causing change in tertiary structure
  4. DNA binding domain changes shape to be complementary to the base sequence of the promoter
  5. Transformers factor enters nucleus via nuclear pore
  6. DNA binding domain binds to complementary promote region
  7. Allows RNA polymerase to transcribe gene
    (8. Protein synthesis)
30
Q

Define epigenetics

1

A

Heritable changes in gene expression without altering the sequence of the DNA

31
Q

How are genes switched on?

4

General

A
  1. Want to make DNA less tightly coiled around histone
  2. So transcriptional factor needs to bind
  3. So increased acetylation
  4. And decreased methylation
32
Q

How are genes switched off?

4

General

A
  1. Want to make DNA more tightly coiled around his tone
  2. So no transcriptional factor binding
  3. So decreased acetylation
  4. So increased methylation
33
Q

Describe the process of increased methylation and how it leads to switching off a gene

4

A
  1. Addition of a methyl group to DNA
  2. Attaches to the cytosine base
  3. Prevents binding of transcriptional factors
  4. Attracts Justine deacetylase causing deacetylation
  5. Preventing transcription
34
Q

Describe the process of deacetylation and how it prevents transcription

4

A
  1. Removal of the acetyl group from the histone
  2. Makes the outside of the histone more positively charged
  3. Attracts negative DNA backbone / phosphate group in DNA backbone more attracted to histone
  4. DNA coils more tightly to histone so cannot be transcribed
35
Q

Describe the process of Demethylation and how it allows transcription

4

A
  1. Removal of a methyl group from DNA
  2. Stops the prevention of transcriptional factors binding
  3. Stops attracting histone deacetylase so no deacetylation
  4. So allows transcription
36
Q

Describe the process of acetylation and how it allows transcription

4

A
  1. Addition of acetyl group to histones
  2. Makes outside of the histone more negatively charged
  3. Repels phosphate group in the DNA backbone
  4. DNA unwinds from histone, allows access for transcriptional factors and can be transcribed
37
Q

What enzyme is used in acetylation?

A

AcetylCoA

38
Q

What enzyme is used in deacetylation?

A

Histone deacetylase

39
Q

What form of DNA is formed in acetylation?

How does it appear under a microscope?

A

Euchromatin

Appears lighter as less tightly coiled

40
Q

What form of DNA is formed in deacetylation?

How does it appear under a microscope?

A

Heterochromatin

Appears darker as more tightly coiled so more dense

41
Q

How do epigenetic therapies activate genes?

2

A
  • Inhibit methylation by blocking enzymes that allow it

- Inhibit histone deacetylase so histones stay more negatively charged so DNA is looser and can be transcribed

42
Q

What is siRNA and what is its role?

3

A

A short, double-stranded RNA molecule

Regulates translation.
Prevents gene expression after it has been transcribed.

43
Q

How does siRNA stop translation?

4

A
  1. siRNA becomes associated with an enzyme and is split so it is single stranded
  2. siRNA is complementary to mRNA of a given gene so binds to mRNA sequence
  3. enzyme cuts mRNA into small sections
  4. Renders the mRNA useless as translation cannot occur
44
Q

What is different about the ways benign and malignant tumours grow and spread?

4

Capsule?

A
  • Benign grow slower and are localised (primary tumour)
  • Malignant grow faster and spread (metastasis)
  • Benign are surrounded by capsule of dense disuse so compact and adhesion between cells
  • Malignant are not surrounded by a capsule so they grow into the surrounding tissue, they have no adhesion between cells so spread and form secondary tumours
45
Q

What are the differences between the treatments for benign and malignant tumours and their success rate?
2

A
  • Benign are usually removed by surgery and are less likely to reoccur
  • Malignant are treated by radiotherapy or chemotherapy and are more likely to reoccur
46
Q

What are the differences in the cell differentiation and nuclei in benign vs malignant tumours?
4

A
  • Benign cells are differentiated
  • Malignant cells are undifferentiated
  • Benign cells have normal nuclei
  • Malignant cells have larger and darker nuclei
47
Q

What are proto oncogenes and oncogenes?

Role?
2

A

Proto oncogenes are genes that if mutated become oncogenes and can lead to cancer

Some give signals that cause cell division and control apoptosis

48
Q

What are three results of a mutation of a proto concogene?

A
  1. Substitution/Deletion etc: mutates the protein but is still produced in normal amounts
  2. Duplication: normal protein but it is over expressed
  3. Translocation: proto oncogene is translocated to a new location and is over expressed
49
Q

What are tumour suppressor genes and how do they work?
Role?
2

A

Genes that prevent tumour formation

They slow cell division, repair DNA mistakes and control apoptosis

50
Q

What do normal cells have in terms of cancer genes?

1

A

Balance of proto oncogenes and tumour suppressor genes to regulate cell division

51
Q

What are the two forms of abnormal methylation of tumour suppressor genes?

A

Hypermethylation: increased methylation
Hypomethylation: decreased methylation

52
Q

How does hypermethylation lead to cancer?

A
  1. Hypermethylation occurs in promoter region of tumour suppressor gene
  2. Leads to tumour suppressor gene being inactivated
  3. So transcription of promoter regions of tumour suppressor gene inhibited
  4. Tumour suppressor gene silenced
  5. Inactivation of TSG leads to increased cell division and formation of a tumour
53
Q

How does oestrogen lead to breast cancer?
2

When does your risk increase?
1

A
  1. Oestrogen activates proto oncogene turning it into an oncogene
  2. This causes tumours

Breast tissue produces more oestrogen after menopause so increased risk

54
Q

Whole genome shotgun sequencing: what are primers?

3

A
  • Short pieces of DNA
  • Like promoter region
  • Indicated where DNA polymerase starts
55
Q

Whole genome shotgun sequencing: what are terminator bases?

3

A
  • Stop the action of DNA polymerase
  • Have fluorescent or radioactive labels
  • One different marker for each base
56
Q

Whole genome shotgun sequencing: how does it work?

9

A
  1. Small pieces of DNA inserted into plasmid DNA in bacteria
  2. DNA isolated and put in plate w/ free DNA bases, DNA polymerase, DNA primers, terminator bases
  3. Break H- bonds
  4. Primer bind to plasmid
  5. DNA polymerase binds and adds bases
  6. Eventually terminator base added
  7. Repeated to produce many fragments of different lengths
  8. Gel electrophoresis to separate by length
  9. Read by machine and translated into base sequence
57
Q

How does gel electrophoresis work?

6

A
  1. Capillary tube is lowered into plate/solution
  2. Electrical current applied to gel in capillary tube
  3. Negatively charged DNA travels towards positively charged end of tube
  4. Shorter fragments travel furthest so arranges by size
  5. Laser at the end of capillary tube makes terminator bases light up
  6. Read by machine and translated into base sequence

AQA A-Level Biology (11 decks)

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