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Biology > 8) Control of gene expression > Flashcards

8) Control of gene expression Flashcards

1
Q

Gene mutation definition

A

Any change to the base sequence if DNA

Arise during DNA replication

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2
Q

Mutagenic agents:

A

Increase the rate of mutation by:

  • Acting as a base- causes a substitution mutation
  • Altering bases- some chemicals delete or alter bases
  • Changing the structure of DNA
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3
Q

6 types of gene mutation

A

Addition, Deletion, Substitution, Inversion, Duplication, Translocation of bases

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4
Q

Addition mutation:

A
  • One or more bases are added
  • Frame shift to right
  • Gene now read in the wrong 3 base groups and the coded information is altered
  • Most triplets will be different + the amino acids they code for
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5
Q

Deletion mutation:

A
  • One or more bases are removed

- Frame shift left

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6
Q

Substitution mutation:

A
  • Nucleotide in a section of a DNA molecule is replaced by another nucleotide
  • Due to degenerate nature of genetic code- new triplet may still code for the same amino acid so mutation will have no effect on polypeptide produced
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7
Q

Inversion mutation:

A

A sequence of bases is reversed

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8
Q

Duplication mutation:

A
  • One or more bases are repeated

- Produces a frame shift to the right

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9
Q

Translocation of bases mutation:

A
  • Sequence of bases is moved from one location in the genome to another
  • Often- significant effects on gene expression
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10
Q

Effect of gene mutation on encoded polypeptide

A
  • Mutation = different order of DNA bases
  • = different amino acid sequence
  • Changes final 3D shape of protein
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11
Q

Stem cells definition

A

Unspecialised cells that can develop into other types of cell- retain ability to differentiate.

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12
Q

Totipotent cells definition

A

Stem cells that can divide + develop into any type of body cell in an organism + are only present in mammals in the first few cell divisions of an embryo

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13
Q

How totipotent cells become specialised:

A

1) Stem cells all contain same genes- during development, not all of them are transcribed + translated
2) Some genes expressed, some switched off
3) mRNA only transcribed from specific genes- translated into proteins
4) These proteins modify the cell

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14
Q

Types of stem cells found in more mature mammals:

A

Pluripotent, Multipotent, Unipotent

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15
Q

Pluripotent stem cells:

A
  • After first few cell divisions of an embryo- embryonic stem cells become pluripotent
  • Can still specialise into any cell in body, but lose ability to become the cells that make up the placenta
  • Divide in unlimited numbers + can be used in treating human disorders
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16
Q

Multipotent stem cells:

A
  • Adult mammals

- Differentiate into a few different types of cell

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17
Q

Unipotent Stem cells:

A
  • Adult mammals
  • Can only differentiate into 1 type of cell
  • Eg Cardiomyocytes- heart muscle cells. Damaged cardiomyocytes can be replaced by new cardiomyocytes derived from a small supply of unipotent cells
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18
Q

Induced Pluripotent stem cells (IPS):

A
  • Type of pluripotent cell that is produced from unipotent stem cells
  • Unipotent cells are genetically altered in a lab to make them acquire the characteristics of embryonic stem cells which are a type of pluripotent cell
  • Process- inducing genes and transcriptional factors within the cell to express themselves
19
Q

Use of stem cells in treating human disorders:

A
  • Embryonic stem cells created by IVF- ethical issues due to destruction of embryos
  • Some believe should only use adult stem cells (no destruction)- but can’t develop into all the specialised cell types
  • Induced pluripotent stem cells (IPS) could solve this problem- have potential to be as flexible as embryonic stem cells + are obtained from adult tissue
  • Save lives + improve QOL
  • Eg pluripotent cells used to re-grow tissues that have been damaged
20
Q

Transcriptional factors definition

A

Molecules that control the transcription of genes

21
Q

Process of gene expression by transcriptional factors:

A

1) In eukaryotes, transcriptional factors move from the cytoplasm to the nucleus
2) Here, they bind to a specific base sequence on the DNA in the nucleus near the start of their target genes
3) Causes this region of DNA to begin process of transcription
4) mRNA produced + info translated into a polypeptide
5) When gene not expressed, site on the transcriptional factor that binds to DNA is not active- DNA not transcribed + no polypeptide synthesis occurs

(Some transcriptional factors act as repressors- decrease rate of transcription by preventing RNA polymerase from binding to the start of the target gene)

22
Q

Oestrogen definition

A

Steroid hormone that can affect transcription

(As well as transcriptional factors, the expression of a gene can be affected by other molecules in the cell- eg oestrogen)

23
Q

Role of oestrogen in initiating transcription:

A

1) Binds to transcriptional factor (oestrogen receptor)
2) Forms an oestrogen-oestrogen receptor complex
3) Binding changes the shape of the DNA binding site on the transcriptional factor- can now bind to DNA
4) Complex moves from cytoplasm into nucleus- binds to specific DNA site near start of target gene
5) Complex acts as an activator of transcription- helps RNA polymerase bind to the start of the target gene

24
Q

Epigenetics definition

A

Process where environmental factors cause heritable changes in gene function without changing the base sequence of DNA

25
How does epigenetic control determine whether a gene is switched on or off?
- DNA wrapped around proteins called histones - Both DNA + histones are covered in chemicals called the epigenome - Attachment or removal of epigenetic marks to or from DNA or histones alter how easy it is for the enzymes needed for transcription to transcribe the DNA
26
In epigenetics, what are the 2 ways that the inhibition of transcription can occur?
- Increased methylation of DNA | - Decreased acetylation of associated histones
27
How increased methylation of DNA inhibits transcription:
- Methyl group (an epigenetic mark) attaches to the DNA coding for a gene - Increased methylation changes the DNA structure by attracting proteins that condense the DNA-histone complex- makes DNA inaccessible to transcriptional factors - Gene not expressed
28
How decreased acetylation of associated histones inhibits transcription:
- When acetyl groups are removed from histones- chromatin becomes highly condensed - Genes in the DNA can't be transcribed as transcriptional enzymes can't access them
29
Epigenetics in the development + treatment of disease
- Epigenetic changes can be responsible for certain diseases - Increased methylation or decreased acetylation results in the inactivation of a normally active gene----- disease - Epigenetic treatments can be used to counteract these changes - Treatments use drugs to inhibit enzymes that cause methylation of DNA/ decreased acetylation
30
RNA interference (RNAi) definition
Where small, double-stranded RNA molecules stop mRNA from target genes being translated into proteins Molecule involved in RNAi is called small interfering RNA (siRNA)
31
RNA interference (RNAi) definition
1) Enzyme cuts large double stranded molecules of RNA into smaller sections called small interfering RNA (siRNA) 2) 1 of the 2 siRNA strands combine with an enzyme 3) siRNA molecule guides the enzyme to a mRNA molecule by pairing up its bases with the complementary on a section of mRNA molecule 4) Enzyme cuts mRNA into smaller sections 5) mRNA no longer capable of being translated into a polypeptide - gene not expressed
32
Characteristics of benign tumours:
- Grow slowly - Cells produce adhesion molecules that make them stick together + so they remain within the tissue from which they arise - Surrounded by capsule - Cells well differentiated - Cell nucleus- normal appearance - Localised effects on body + less life-threatening
33
Characteristics of malignant tumours
- Grow fast - Cells do not produce adhesion molecules + so can spread to other regions of the body, forming secondary tumours - Not surrounded by capsule- so can grow finger like projections into surrounding tissue - Cells become un-differentiated - Cell nucleus- larger + darker due to abundance of DNA - Systemic (whole body) effects + life threatening
34
What are the 2 genes that control cell division?
Proto-oncogenes Tumour suppressor genes
35
Role of proto-oncogenes in the development of tumours:
- When functioning normally- proto-oncogenes STIMULATE cell division by producing proteins that make cells divide - If mutation in proto-oncogene- gene becomes OVERACTIVE- acts as an oncogene - Oncogene- increase production of proteins that encourage cell division + they cause cells to grow out of control-------- tumour
36
Role of tumour suppressor genes in the development of tumours
- When functioning normally- tumour suppressor genes slows cell division by producing proteins that cause cells to self destruct or stop cells dividing - Mutation in gene- protein isn't produced (gene UNDERACTIVE) - Causes cells to divide uncontrollably------ tumour
37
The role of abnormal methylation of oncogenes and tumour suppressor genes in the development of tumours:
HYPOMETHYLATION of proto-oncogenes - Decreased methylation = proto-oncogenes act as oncogenes - Oncogenes increase the production of proteins that encourage cell division- stimulates divisions out of control------- tumour HYPERMETHYLATION of TUMOUR SUPPRESSOR GENES - Methyl groups added to promoter region of tumour suppressor gene - Gene not transcribed- proteins produced to slow cell division not made- divide out of control -------- tumour
38
Role of increased oestrogen concentrations in the development of some breast cancers:
- Increased concentrations- stimulate certain breast cells to divide - Oestrogen releases inhibitor molecule that prevents transcription- causes proto-oncogenes of breast tissue to develop into oncogenes - Oncogenes increase rate of division----- tumour
39
Using oncogenes and tumour suppressor genes to prevent, treat + cure cancer:
- Treatment is different for different mutations - Drugs can bind to a specific protein + suppress cell division - Radiotherapy, Gene therapy
40
Genome definition
The entire set of DNA, including the genes, of an organism
41
Proteome definition
All the proteins produced in a given type of cell or organism, at a given time, under specific conditions by the genome
42
Summary of process of gene sequencing:
- Methods only work on fragments of DNA - DNA needs to be split up into smaller pieces first - Smaller pieces sequenced (bases read) and then put back in order to give the sequence of the whole gene Sequencing methods- continuously updated. Past- labour intensive + expensive. Now- automated + cost-effective
43
Translating the genome of simpler organisms:
- Easier - Don't have much non-coding DNA + have less DNA - Means- relatively easy to determine their proteome from the DNA sequence of their genome - Useful- can help identify protein antigens on the surface of microbes- lead to development of vaccines
44
Translating the genome of more complex organisms:
- Harder - Contain large sections of non-coding DNA - Contain regulatory genes- (determine when the genes that code for a particular protein should be switched on or off) - Makes it more difficult to translate the genome into proteome- hard to find the parts of DNA that code for proteins among the non-coding and regulatory DNA

Biology (7 decks)

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