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AQA A Level Biology 2018 > Mutations and Gene Expression > Flashcards

Mutations and Gene Expression Flashcards

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1
Q

Types of mutations:

A 
Substitution
Deletion
Addition
Duplication
Inversión
Translocation
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2
Q

What is a mutation?

A

Change to the base sequence of DNA - caused by errors during DNA replication.

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3
Q

Some mutations can cause…

A

Genetic disorders - inherited disorders caused by abnormal genes or chromosomes.

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4
Q

What are hereditary mutations?

A

If a gamete has a genetic disorder or cancel and then it is fertilised, passed on to offspring.

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5
Q

Why do additions, duplications and deletions almost always cause a change in the amino acid sequence?

A

Because these change the number of bases in the DNA code - causes a frameshift so the triplet code is read in a different way.

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6
Q

How can mutagenic agents increase the rate of mutation?

A
  • chemicals called base analogs can substitution a base, changing base sequence.
  • chemicals can delete or alter bases.
  • changing the structure of DNA which causes problems during DNA replication.
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7
Q

Mutations that occur after fertilisation…

A

Acquired mutations

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8
Q

What happens if mutations occur in genes that control the rate of cell division?

A

Causes uncontrolled cell division - resulting in a tumour (mass of abnormal cells)

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9
Q

Two genes which control cell division:

A
  • tumour suppressor genes

- proto-oncogenes

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10
Q

How can tumour suppressor genes be affected?

A

If a mutation occurs in the DNA sequence, they can be inactivated.

This means the proteins they make can to be produced so cells divide uncontrollably.

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11
Q

What do Tumour suppressor genes do?

A

They slow cell division by producing proteins that stop cells dividing or cause them to self destruct.

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12
Q

What do proto-oncogenes do?

A

They stimulate cell division by producing proteins that make cells divide.

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13
Q

How can proto-oncogenes be affected?

A

If a mutation occurs in the DNA sequence and in it, gene can become overactive so cells divide uncontrollably.

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14
Q

What is a muted proto-oncogene called?

A

Oncogene

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15
Q

Malignant tumours

A

Cancers - grow rapidly and destroy surrounding tissues, can break off and spread to other parts via bloodstream or lymphatic system.

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16
Q

Benign tumours

A

Not cancerous - grow slower and are covered in fibrous tissue that stops cells invading other tissues, harmless but can cause blockages and put pressure on organs.

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17
Q

How do tumour cells differ from normal cells? (4)

A
  • irregular shape
  • nucleus is larger and darker
  • different antigens
  • divide by mitosis more frequently
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18
Q

What is methylation?

Why is it important?

A

Adding a CH3 group onto something - this is important for regulating gene expression, can control whether or not a gene is transcribed.

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19
Q

What happens when methylation is happening normally?

A

It plays a key role in many processes

But when it happens too much or too little, it becomes a problem.

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20
Q

Hypermethylation

A

When methylation happens too much

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21
Q

Hypomethylation

A

When methylation happens too little

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22
Q

What happens when tumour suppressor genes are hypermethylated?

A

The genes are not transcribed, proteins to slow cell division not made - cells grow uncontrollably.

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23
Q

What happens when proto-oncogenes are hypomethylated?

A

They act as oncogenes - increasing the production of proteins that encourage cell division - cell divides uncontrollably leading to tumour.

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24
Q

Increased exposure to oestrogen…

A

Increases a woman’s risk of developing breast cancer.

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25
Q

How does oestrogen contribute to the development of breast cancer? (3)

A
  • oestrogen stimulate some breast cells to divide and replicate - more divisions increases mutations so more chance of cancerous cells.
  • stimulating division means if cells do become cancerous, their rapid replication forms tumours.
  • other research shows it may be able to introduce mutations directly to breast cells.
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26
Q

Genetic factors of cancer

A

Some cancers are linked to specific alleles - if you inherit it, more likely to get it

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27
Q

Environmental factors of cancer

A

Radiation
Smoking
Alcohol
High fat diet

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28
Q

Mastectomy

A

Removal of one or both beasts

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29
Q

Gene therapy

A

Where faulty alleles in a persons cells are replaced by working versions of the alleles

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30
Q

Stem cells are..

A

Unspecialised cells that can developed into any other cells.

31
Q

Stem cells found

A

Embryo

And some adult tissues

32
Q

Totipotent stem cells

A

Only present in mammals in the first few cell divisions of an embryo

33
Q

Multipotent stem cells

A

Able to differentiate into a few diff types of cells

34
Q

Unipotent stem cells

A

Can only differentiate into one type of cell

35
Q

How do stem cells become specialised?

A
  • stem cells all contain same genes but not all of them are expressed = some are expressed, some switched off
  • mRNa only transcribed from specific genes so the mRNa gets translated into proteins - they modify the cell and cause it to be specialised.
36
Q

Red blood cells production from a stem cell

A

Produces a new cell in which the genes for Haemoglobin production is expressed, removing nucleus is expressed.

37
Q

Cardiomyocytes

A

Heart muscle cells that make up a lot of the tissue in our hearts

38
Q

For ages everyone thought…

A

That we weren’t able to regenerate our heart cells - this is a problem if heart attack occurs etc

39
Q

Some scientists now think that…

A

Old or damaged cardiomyocytes can be replaced by new cardiomyocytes derived from a small supply of unipotent stem cells in the heart.

40
Q

Bone marrow contains

A

Stem cells that can become specialised to form any type of blood cell.

41
Q

Bone marrow transplants can be used to…

A

Replace the faulty bone marrow in patients that produce abnormal blood cells - stem cells in the transplanted can divide and specialise to produce healthy blood cells.

42
Q

Bone marrow transplants have already treated…

A

Leukaemia

Lymphoma

SCID

43
Q

What is SCID
Severe combined immunodeficiency

Treatment:

A

Genetic disorder that affects the immune system - people with it have defective white blood cells so they can’t fight against infections.

Bone marrow transplant can be used to produce white blood cells - immune system functions

44
Q

Stem cells can be used to treat: (3)

A
  • spinal cord injuries to replace nerve tissue
  • bladder conditions, can grow whole bladders
  • organ transplants, organs can be grown from stem cells
45
Q

2 advantages of stem cells:

A
  • can save many lives

- improve quality of life for many

46
Q

3 sources of stem cells:

A
  • adult bone marrow
  • embryo
  • induced pluripotent stem cells
47
Q

Adult stem cells

A

Bone marrow

Simple operation, little risk

But can only specialise into limites range of cells

48
Q

Embryonic stem cells

A

Embryos via IVF

Stem cells removed and embryo destroyed

Can divide into all types of body cells

49
Q

Induced pluripotent stem cells

IPS

A

Reprogrammes specialised adult body cells to become pluripotent

Made to express transcription factors usually associated with stem cells, causing the body cells to express genes assosciated with pluripotency.

50
Q

How can transcription factors be introduced to the adult cells?

A

Infecting then with a specially modified virus - this virus has the genes coding for the transcription factors within its DNA

When virus infects adult cells the genes are passed into the adult cell’s DNA so the cell is able to produce the transcription factors

51
Q

Ethical issues with embryonic stem cells (2)

A
  • embryo right to life, destruction of embryos raises controversy
  • believe they should use adult cells instead but they’re only multipotent
52
Q

Why do all cells have the same genes but have different structures and functions?

A

Because different genes are expressed

53
Q

The transcription of genes is controlled by…

A

Protein molecules called transcription factors

54
Q

How do transcription factors work in eukaryotes:

A
  • they move to nucleus from cytoplasm and bind to speeding DNA sites near the start of their target genes
  • control expression by controlling rate of transcription
55
Q

Activators

A

Transcription factors which work to stimulate or increase the rate of transcription

By helping RNA polymerase bind to the start of the target gene and activate transcription

56
Q

Represora

A

Transcription factors which inhibit or decrease the rate of transcription

By binding to the start of the target gene and preventing RNA polymerase from binding, stopping transcription.

57
Q

How can oestrogen affect the expression of genes:

A
  • can bind to a transcription factors called oestrogen receptors forming an oestrogen-oestrogen receptor complex
  • this complex moves from the cytoplasm into the nucleus where it binds to specific dna sites next to target gene
  • acts as an activator for transcription
58
Q

Oestrogen is a …

A

Steroid hormone

59
Q

Gene expression is also effected by…

A

RNA interference

RNAi

60
Q

RNAi is where…

A

Small, double stranded RNA molecules stop mRNA from target genes being translated into proteins.

61
Q

Molecules involved in RNAi:

A

sIRNA

miRNA

62
Q

How does sIRNA and miRNA work in plants? (3)

A
  • when mRNA is transcribed, leaves the nucleus and double stranded sIRNA assosciates with several proteins and unwinds - a single strand then binds to target mRNA (complentary)
  • proteins associated with the sIRNA cut the mRNA into fragments so it can no longer be translated
  • the fragments then move into a processing body which contains tools to degrade them
63
Q

How does miRNA work in mammals?

A
  • in mammals, the miRNA isn’t usually fully complementary to the target mRNS - less specific so targets more than one mRNA.
  • assosciatts witn proteins and binds to target MRNA.
  • mRNA- protein complex physically blocks the translation of target mRNA
  • the mRNA is moved into a processing body where it can be either stores or degraded.
64
Q

Epidemic control can determine…

A

Whether a gene is switched on or off

65
Q

How does epigenetic control work?

A

Through the attachment or removal or chemical groups - epigenetic marks

66
Q

What do epigenetic marks do?

A

Don’t alter the base sequence of DNA - they alter how easy it is for the enzymes and other proteins needed for transcription to interact with and transcribe the DNA.

67
Q

Can epigenetic changes be inherited by offspring?

A

The marks are usually removed but some escape and are passed to offspring - causes he expression of some genes in the offspring can be affected by environmental changes that affected their parents.

68
Q

One method of epigenetic control:

A
  • when a methyl group is attached to the DNA coding for a gene
  • the group always attached at a CpG side, increased methylation changes the DNA structure so that the transcriptional machinery can’t interact with the gene - gene not expressed.
69
Q

What is the CpG site?

A

Where a cytosine and guanine base are next to eachother in the DNA.

70
Q

Histones

A

Proteins that DNA wraps around to form chromatin which makes up chromosomes

Chromatin can be highly condensed or not - it affects the accessibility of the DNA

71
Q

Decreased acetylation effect: (3)

A
  • Histones can be epigenetically modified by addition or removal of acetylene groups
  • when they are acetylated, chromatin is less condensed means that the transcription machinery can not access DNA
  • when acetyl groups are removed from the Histones, the chromatin becomes highly condensed and genes in the DNA can’t be transcribed because the transcriptional machinery can’t access them.
72
Q

Histone deacteylase:

A

Enzymes are responsible for removing the acetyl groups

73
Q

Twin studies can help us to…

A

Determine the influences on phenotype from the environment

74
Q

How can drugs be able to treat diseases caused by epigenetic changes: (2)

A

HDAC inhibit drugs can work by inhibtating the activity of histone de acetyl ase enzymes which are respinsible for removing the acetyl groups from Histones.

Drugs that stop DNA methylation can sometimes be used to treat diseases caused because of increased methylation.

AQA A Level Biology 2018 (17 decks)

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