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Gene expression Flashcards

(53 cards)

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1
Q

What is a gene mutation?

A

A random change in the DNA base sequence

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2
Q

When do gene mutations occur?

A

During DNA replication, in the interphase (S phase) part of the cell cycle.

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3
Q

What is a mutagenic agent?

A

Factors that damage DNA and increase the rate of mutation.

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4
Q

Why are deletion mutations more likely to produce a non-functional protein?

A

Because the removal of one base pair changes every triplet code after the point of deletion, causing a frameshift so a completely different protein is made.

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5
Q

Why are substitution mutations less likely to produce a non-functional protein?

A

Because the genetic code is degenerate, so the new triplet may code for the same amino acid, resulting in the same protein being produced.

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6
Q

What is a substitution mutation?

A

When one or more bases are swapped for another.

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7
Q

What is an addition mutation?

A

When one or more bases are added.

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8
Q

What is a deletion mutation?

A

When one or more bases are removed.

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9
Q

What is an inversion mutation?

A

When one or more bases are reversed.

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10
Q

What is a duplication mutation?

A

When one or more bases is repeated.

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11
Q

What is a translocation mutation?

A

When a sequence of bases is moved from one location to another (either on same chromosome or onto another).

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12
Q

What are the 3 mutations that produce a non-functional protein?

A

-Deletion
-Addition
-Duplication

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13
Q

What are stem cells?

A

Undifferentiated cells that divide by mitosis to produce more stem cells that mature to become adapted for a specific function.

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14
Q

What changes does cell differentiation involve?

A

Changes to the cell shape, cell contents, or numbers of organelles. These are permanent changes.

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15
Q

How do stem cells replace themselves?

A

They divide by mitosis.

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16
Q

What happens to genes during cell differentiation?

A

Some genes are switched on and expressed , whereas others are switched off and not expressed. The expressed genes are transcribed in mRNA, which is then translated into proteins. These proteins modify the cell so that it becomes specialised for specific functions.

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17
Q

What are totipotent stem cells?

A

Embryonic stem cells that can produce any type of body cell and only occur for a limited amount of time (in the first few divisions). After this, it becomes pluripotent.

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18
Q

What are pluripotent stem cells?

A

Embryonic cells present after the first few divisions that can produce any type of body cell EXCEPT cells that make up the placenta.

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19
Q

What are multi-potent stem cells?

A

Stem cells found in mature mammals which produce a limited number of different cell types. Their role is to replace cells that have been damaged or died.

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20
Q

What are unipotent stem cells?

A

Stem cells found in mature mammals which produce only one type of cell.

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21
Q

What does stem cell therapy involve?

A

It involves injecting stem cells into a patient, which then divide and differentiate to replace damaged tissue by illness or injury.

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22
Q

What are the advantages and disadvantages of using pluripotent stem cells from embryos?

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A

Pros:
-They can divide for unlimited time
-They can differentiate into all types of body cell

Cons:
-They can be unethical as they involve destroying human embryos that have the potential to develop into a human being

23
Q

What are the advantages and disadvantages of using multi-potent stem cells from adults?

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A

Pros:
-No ethical issues
-No risk of rejection if taken from own body

Cons:
-Hard to find
-Can cause discomfort to extract
-Can only differentiate into a limited range of cells

24
Q

What are the advantages and disadvantages of using induced pluripotent stem cells (iPS)?

Study These Flashcards
A

Pros:
-Can differentiate into any type of cell
-No risk of rejection
-No ethical issues

Cons:
-At early development
-Can cause gene mutation, as the transcription factor genes can insert anywhere in the stem cell’s DNA
-Can cause cancer if they insert into a tumour suppressor gene

25
What are induced pluripotent stem cells (iPS cells) and how are they created?
They are multi-potent stem cells that have been genetically reprogrammed to become undifferentiated, pluripotent stem cells. They are created by infecting multi-potent cells with a genetically modified virus that contains human genes that code for transcription factors, which “switch on” genes so that the cell becomes pluripotent.
26
What are transcription factors?
Proteins that stimulate or prevent transcription
27
When is a gene “expressed”?
When it is transcribed and translated to produce a protein
28
What are the 3 things gene expression is controlled by?
-Transcription factors -Epigenetics -RNA interference
29
What are epigenetics?
Attaching or removing chemical groups to/from DNA or histone proteins to stimulate or prevent transcription
30
What is RNA interference?
Using siRNA to prevent mRNA from being translated (gene silencing)
31
Describe the process involving transcription factors?
-Before transcription, RNA polymerase binds to the promoter region on DNA, upstream from the start of the gene. -Transcription factors move from the cytoplasm into the nucleus via nuclear pores. -If it is an activator, it will bind to the promoter region and help RNA polymerase to to bind to the promoter to stimulate the transcription of the gene. -If it is a repressor, it will bind to the promoter region and block the binding site for RNA polymerase so it cannot bind, preventing transcription.
32
How can oestrogen stimulate transcription?
Certain cells contain transcription factors called oestrogen receptors in their cytoplasm. Oestrogen binds as it’s complementary, forming a transcription factor complex. The binding changes the shape so that now it can bind to DNA. This complex then travels from the cytoplasm to the nucleus, binding to the promoter region of certain genes. The complex acts as an activator, helping RNA polymerase to bind to the promoter to transcribe a gene.
33
What is the epigenome?
The layer of chemical tags on DNA and histone proteins
34
How can genes be switched off? (ADMISOG)
-Increased methylation of DNA -Decreased acetylation of histones
35
Describe the process of increased DNA methylation
-Methylation is the addition of a methyl group to cytosine bases in DNA. -This changes the structure of DNA, so it’s harder for RNA polymerase to bind, so it cannot be transcribed.
36
Describe the process of decreased histone acetylation?
-Acetylation is the addition of an acetyl group to histone proteins. -This causes DNA to become less condensed and easier to transcribe, as it’s easier for RNA polymerase to bind. - The removal of an acetyl group makes DNA more condensed and therefore harder to transcribe as it’s harder for RNA polymerase to bind.
37
Why is epigenetic control important?
-Most epigenetic markers are removed between generations because the cells of a zygote need to be totipotent, however some epigenetic changes escape this process and are passed on to offspring, so the epigenetic changes can be inherited (such as smoking etc). -Epigenetic changes are reversible though however, because they alter DNA structure, not DNA base sequence. -Drugs are being developed to treat inherited diseases caused by unwanted epigenetic changes. The aim is to use them to “switch on” genes that are wrongly switched off by epigenetic markers and vice versa.
38
Describe how siRNA silences genes
-In the cytoplasm, siRNA binds to a protein called RISC to form a complex. -RISC breaks the double stranded siRNA into its separate strands. One strand remains attached to RISC, the other is discarded. -The remaining siRNA strand binds to a specific mRNA molecule in the cytoplasm that has a complementary sequence. Therefore one type of siRNA binds to only one sort of mRNA. -This binding causes the RISC protein to cut the mRNA molecule in two. -Enzymes then cut the mRNA into pieces so it can’t be translated.
39
What can RNA interference be used for?
-Genetically modifying crops by silencing undesirable genes -Treating cancer by preventing translation of oncogenes to stop them from making proteins that lead to uncontrolled cell division -Treating genetic disease by preventing translation of genes that code for harmful proteins -Antiviral therapies
40
Describe what is meant by malignant tumour
A tumour that: -causes cancer -grows rapidly -invades and destroys surrounding tissues -can break off into cells and migrate to other parts of the body in blood or lymph to set up secondary tumours (metastasis)
41
Describe what is meant by a benign tumour?
A tumour that: -does not cause cancer -does not invade other tissues -grows slowly -does not undergo metastasis
42
What harmful things could a benign tumour lead to?
- Blockages -Pressure on surrounding organs -Damages to the organs they are found in
43
What is a tumour?
A mass of abnormal, undifferentiated cells produced by uncontrolled cell division
44
What is the role of proto-oncogenes and tumour-suppressor genes?
To control the cell cycle and ensure it stops and starts when it should. Proto-oncogenes stimulate cell division, tumour-suppressors inhibit cell division.
45
What happens when there is a mutation in proto-oncogenes?
Mutated proto-oncogenes are called oncogenes and these over produce the regulatory protein so that cell division occurs too rapidly and uncontrollably
46
What happens when there is a mutation in tumour-suppressor genes?
A non-functional regulatory protein will be produced, so cell division won’t be inhibited, so cell division will occur too rapidly and uncontrollably.
47
Describe abnormal methylation that causes cancer
-Increased methylation of DNA prevents transcription and this is called hypermethylation, which occurs in the promoter region of tumour suppressor genes. -This causes the protein that prevents cell division to not be produced. -Therefore no control of cell division
48
How does hypomethylation lead to cancer?
-This is reduced methylation in oncogenes, so it leads to their activation and the formation of tumours.
49
How can increased exposure to oestrogen increase the risk of cancer?
-Oestrogen binds to oestrogen receptors (transcription factors) inside breast cancer cells to form a transcription factor complex which activates genes involved in cell division. -It stimulates rapid division of breast cells by increasing the risk of mutations in proto-oncogenes/tumour suppressor genes, creating tumour cells. -It then stimulates rapid division of the tumour cells, so the tumour grows quickly.
50
How can we reduce the risk of cancer from genetic factors?
-Regular genetic screening identifies people with the mutated allele. -Preventative surgery can remove tumours
51
How can we reduce the risk of cancer from environmental factors?
-Don’t smoke -Avoid exposure to UV radiation, as it is a mutagen.
52
What are the ways that chemotherapy slows division of cancer cells?
-Preventing DNA replication (inhibits DNA polymerase) -Preventing mitosis (interferes with spindle formation in metaphase by preventing spindle contraction during anaphase) -Damaging DNA (using radiation or drugs to damage the cell so much it destroys itself) -Reversing epigenetic changes (by preventing DNA methylation or keeping tumour suppressor genes acetylated)
53
What are 2 targeted cancer treatments?
-Gene therapy (placing working alleles of mutated tumour suppressor genes into cells) -Blocking growth factor receptors, which stimulate cancer to divide. Either chemotherapy drugs are complementary to the receptor, so block the binding of them, or monoclonal antibodies are produced which have a specific binding site complementary to the growth factor or receptor, so binding can’t occur either

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