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A-level Biology Longridge Towers School > Chapter 20 Control of gene Expression > Flashcards

Chapter 20 Control of gene Expression Flashcards

1
Q

When do gene mutations happen?

A

Spontaneously during the S phase of DNA replication.

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2
Q

What is an exon?

A

An exon is the part of a gene that is spliced together to be expressed.

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3
Q

What happens if a mutation occurs in an intron?

A

There will be no change to the final protein.

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4
Q

What happens if a mutation occurs in an exon?

A

This can affect the final protein. The protein may be non-functioning. The impact will depend on the mutation.

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5
Q

What are the 2 main categories of genetic mutations?

A

Single gene mutations.

Chromosome mutations

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6
Q

List the 3 types of single gene mutations.

A

Substitution, insertion and deletion.

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7
Q

What is changed in the DNA sequence when a single gene mutation happens?

A

A single nucleotide.

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8
Q

Describe what happens in a substitution single gene mutation and the impact.

A

One nucleotide gets exchanged for a different nucleotide. The result may be a different amino acid coded for.

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9
Q

Describe what happens in an insertion single gene mutation and the impact.

A

An additional nucleotide gets inserted into the sequence. This may affect the amino acid coded for but also every amino acid that follows. It is called a frameshift mutation.

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10
Q

Describe what happens in a deletion single gene mutation and the impact.

A

A single nucleotide is deleted from the sequence. This may affect the amino acid coded for but also every amino acid that follows. It is called a frameshift mutation.

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11
Q

What is a frameshift mutation?

A

A mutation that affects the ‘reading frame’ of triplets on the DNA so that all codes downstream (following) of the mutation are out by one nucleotide.

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12
Q

Which type of single gene mutations are frameshift mutations?

A

Insertions and deletions are frameshift mutations.

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13
Q

How are chromosome structure mutations different from single gene mutations?

A

Chromosome structure mutations involve multiple genes and alterations to the actual structure of one or more chromosomes. Single gene mutations only affect one gene.

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14
Q

List the 4 types of chromosome structure mutations.

A

Duplication. Deletion. Inversion and translocation.

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15
Q

What are homologous chromosomes?

A

Chromosomes which code for the same genes.

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16
Q

Describe how a translocation takes place.

A

In a translocation a section of one non-homologous chromosome binds to another chromosome.

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17
Q

Why are translocations a problem?

A

If a translocation takes place then homologous chromosomes can no longer pair up as they no longer ‘match’. This results in gametes that are non-viable.

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18
Q

Describe how inversions take place.

A

If a section of a chromosome breaks off then gets repaired after rotating 180 degrees then the genes in the section become inverted.

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19
Q

Why are inversions a problem?

A

Inversions also cause problems with homologous chromosomes pairing up. This results in non-viable gametes.

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20
Q

Describe how chromosome deletions take place.

A

A section of the chromosome breaks off and is lost.

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21
Q

Why are chromosome deletions a problem?

A

Genes are lost.

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22
Q

Describe how duplications can occur.

A

A section of a homologous chromosome gets incorporated resulting in 2 copies of some genes.

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23
Q

What are stem cells?

A

Stem cells are undifferentiated cells capable of differentiating into specialised cells or self-renewing.

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24
Q

Where are embryonic stem cells found?

A

Embryonic stem cells are found in early embryos called blastocysts.

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25
Q

Where are tissue stem cells found?

A

Tissue stem cells are found in all living multicellular organisms.

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26
Q

What does totipotent mean?

A

Totipotent refers to stem cells capable of specialising into any type of cell from that organism as well as extra-embryonic cells like those in the placenta. Embryonic stem cells are totipotent. Totipotent cells occur for a limited time in early mammalian embryos.

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27
Q

What does pluripotent mean?

A

Pluripotent refers to embryonic stem cells that can differentiate into any type of cell found in an embryo but not into extra-embryonic cells. They can be used in treating human disorders.

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28
Q

What does multipotent mean?

A

Multipotent refers to stem cells that can differentiate into multiple (but limited) types of cells. These are sometimes referred to as adult stem cells. They are found throughout the body.

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29
Q

What does unipotent mean?

A

Unipotent cells are adult cells that can only differentiate into other cells of their own lineage. Most cells in animal bodies are unipotent.

30
Q

What does ‘potency’ mean?

A

The potency of a cell refers to its ability to differentiate into more specialised cell types.

31
Q

Why is use of embryonic stem cells for therapies and research controversial?

A

The embryo is not capable of giving consent.

32
Q

What are induced pluripotent stem cells (iPS cells)?

A

iPS cells are pluripotent cells that are produced from adult somatic cells using transcriptional factors. These transcription factors are proteins that cause specific genes to be expressed.

33
Q

What is a potential use of iPS cells?

A

iPS cells will be used to produce organs for transplant without the risk of rejection.

34
Q

How do stem cells become differentiated?

A

As cells specialise certain gens start to be expressed (switched on) while others may be switched off (no longer expressed).

35
Q

What are transcriptional factors?

A

Transcriptional factors are proteins produced in eukaryotes, which travel into the nucleus and control the rate of transcription.

36
Q

How do transcriptional factors work?

A

Transcriptional factors control the transcription of genes by binding to a specific region of DNA called the promoter. These proteins can activate to block the functioning of RNA polymerase.

37
Q

What are repressors?

A

Repressors are transcriptional factors that switch genes off by preventing RNA polymerase from binding.

38
Q

What are inhibitors?

A

Inhibitors are proteins which bind to transcriptional factors stopping them from binding to the promoter.

39
Q

What are activators?

A

Activators are proteins which bind to transcriptional factors allowing them to bind to the promoter.

40
Q

Describe how the hormone oestrogen acts as a transcriptional factor.

A

Oestrogen is a steroid hormone that is hydrophobic. It travels in the blood and diffuses across the cell membrane.

It binds with an oestrogen receptor protein in the cytoplasm to form an oestrogen-oestrogen receptor complex.

The complex travels through a nuclear pore to the nucleus.

The complex binds to an area of the promoter called the hormone response element (HRE). On some genes it acts as an activator and for some a repressor.

41
Q

What are RNA interference (RNAi) molecules?

A

RNAi molecules are small lengths of non-coding RNA. They regulate gene expression by affecting translation instead of transcription. They are double stranded and stop mRNA that has been transcribed from being translated.

42
Q

What are the 2 types of RNAi?

A

Short interfering RNA - in animals only

Micro RNA (miRNA) - in plants and animals

43
Q

What do cells use siRNA for?

A

siRNA degrades unnecessary RNA or the effects of defective genes and protects the cell from viral infection by degrading viral RNA.

44
Q

What is a therapeutic use of siRNA?

A

siRNA can be used in cancer treatment by targeting oncogenes that have been expressed.

45
Q

What do proto-oncogenes do?

A

Proto-oncogenes stimulate cells to start dividing.

46
Q

What do tumour suppressor genes do?

A

Tumour suppressor genes cause cell division to stop once it is no longer needed. The combination of proto-oncogenes and tumour suppressor genes working together keeps cell division in check.

47
Q

What causes cancer?

A

Cancer can be caused by:
Proto-oncogenes remaining switched on.

Tumour suppressor genes not switching on.

48
Q

What are oncogenes?

A

Oncogenes are genes that cause cancer.Proto-oncogenes become oncogenes if they stay switched on.

49
Q

What is p53?

A

P53 is a protein that acts as a tumour suppressor. Mutation of the gene that codes for p53 can result in cancer.

50
Q

Cancer cells are different from normal cells. Give 3 structural features specific to cancer cells.

A

Large nuclei or multiple nuclei.

Irregular shape and size.

Disorganised arrangement of cells.

51
Q

Give 3 other differences between cancer cells and normal cells.

A

Other differences that we can’t see:
They do not produce the proteins needed to function properly.
They have different antigens on their surface membrane.
They do not respond to the usual growth regulation process.

52
Q

What is a tumour?

A

A tumour is a mass of cells growing in an uncontrolled way.

53
Q

Name the 2 different types of tumours?

A

Malignant tumours

Benign tumours

54
Q

Give 5 features of malignant tumours.

A

Cancerous

Fast-growing

Irregular shape

Invade surrounding tissues

May metastasize.

55
Q

What does metastasize mean?

A

Metastasize means that cells can break off and travel around the body in the lymphatic system leading to more cancers elsewhere.

56
Q

Give 4 features of benign tumours.

A

Non-cancerous

Slow-growing

Regular shape

Do not metastasize.

57
Q

How can too much oestrogen lead to cancer?

A

Oestrogen binds to receptors in cells and forms a complex that acts as a transcriptional factor by binding to HREs (hormone response elements) on promoters.

Too much oestrogen can result in genes that stimulate cell division being activated.

58
Q

How does chemotherapy treat cancer?

A

Chemotherapy kills cells, like cancer cells, that are actively dividing.

59
Q

Why does chemotherapy make patients so unwell?

A

The treatment kills all cells that are actively dividing so this includes stem cells in bone marrow, those that line the digestive tract and hair follicles. This results in immune suppression, hair loss and nausea.

60
Q

What are histones and nucleosomes?

A

Histones are proteins that DNA coils around. The DNA gets packaged into units called nucleosomes.

61
Q

What is chromatin?

A

Further coiling of nucleosomes results in chromatin - tightly packed DNA. When this happens we describe the DNA as ‘condensing’.

62
Q

What are histone ‘tags’?

A

Histone tags are chemical groups that can be added or removed from histones. They include acetyl and methyl groups.

63
Q

What is the epigenome?

A

Collectively the histone tags are known as the epigenome.

64
Q

What do histone tags do?

A

Histone tags determine the shape of the histone-DNA complex and help to control the transcription of genes.

65
Q

What is epigenetics?

A

Epigenetics is the study of heritable changes in gene function that have not been caused by changes to the base sequence of DNA.

66
Q

Give features of the epigenome that are different from the genome.

A

Base sequences of DNA are fixed while histone tags can be easily changed.

A base sequence on DNA can only be changed by mutation while histone tags can be changed due to external factors.

Environmental factors that influence the genome can cause specific mutations. Environmental factors can have wide ranging influences on the epigenome.

67
Q

What is methylation?

A

Methylation is the addition of a methyl group to the DNA.

68
Q

What effect does methylation have?

A

Methylation causes nucleosomes to pack tightly together and stops transcription factors from binding so the genes aren’t transcribed.

69
Q

What is acetylation?

A

Acetylation is the addition of acetyl groups to histones.

70
Q

What effect does acetylation have?

A

Acetylation results in loose packing of the histones and allows transcription factors to bind so genes are expressed.

71
Q

Which types of conditions can be treated with drugs which are histone deacetylase inhibitors?

A

Conditions where genes are switched off due to lack of acetylation. These conditions include Prader-Willi Syndrome, Fragile X syndrome and Angelman syndrome.

A-level Biology Longridge Towers School (37 decks)

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