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Biology > 8) Control of gene expression > Flashcards

8) Control of gene expression Flashcards

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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
Q

How does epigenetic control determine whether a gene is switched on or off?

A
  • 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
Q

In epigenetics, what are the 2 ways that the inhibition of transcription can occur?

A
  • Increased methylation of DNA

- Decreased acetylation of associated histones

27
Q

How increased methylation of DNA inhibits transcription:

A
  • 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
Q

How decreased acetylation of associated histones inhibits transcription:

A
  • 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
Q

Epigenetics in the development + treatment of disease

A
  • 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
Q

RNA interference (RNAi) definition

A

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
Q

RNA interference (RNAi) definition

A

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
Q

Characteristics of benign tumours:

A
  • 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
Q

Characteristics of malignant tumours

A
  • 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
Q

What are the 2 genes that control cell division?

A

Proto-oncogenes

Tumour suppressor genes

35
Q

Role of proto-oncogenes in the development of tumours:

A
  • 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
Q

Role of tumour suppressor genes in the development of tumours

A
  • 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
Q

The role of abnormal methylation of oncogenes and tumour suppressor genes in the development of tumours:

A

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
Q

Role of increased oestrogen concentrations in the development of some breast cancers:

A
  • 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
Q

Using oncogenes and tumour suppressor genes to prevent, treat + cure cancer:

A
  • Treatment is different for different mutations
  • Drugs can bind to a specific protein + suppress cell division
  • Radiotherapy, Gene therapy
40
Q

Genome definition

A

The entire set of DNA, including the genes, of an organism

41
Q

Proteome definition

A

All the proteins produced in a given type of cell or organism, at a given time, under specific conditions by the genome

42
Q

Summary of process of gene sequencing:

A
  • 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
Q

Translating the genome of simpler organisms:

A
  • 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
Q

Translating the genome of more complex organisms:

A
  • 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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