Chapter 20- Gene expression Flashcards by bella ewings

Gene mutation

any change to one or more nucleotide bases or any rearrangement of the bases

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Substitution

A nucleotide is replaced by another nucleotide that has a different base

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Three consequences of base substitution

Stop codon formed- polypeptide production prematurely stopped. Different protein produced
Codon for a different amino acid formed- structure of polypeptide would differ by a single AA. Protein differs in shape
Different codon formed which produces same AA- no consequence. Occurs as genetic code is degenerate

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Deletion

Loss of nucleotide base from a DNA sequence

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Consequences of deletion

Frame shift to the left. Gene read in different triplets. Different AAs coded for. Different polypeptide coded for. Non-functional protein produced

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Addition of bases and consequence

Extra base becomes inserted into the sequence.Frame shift to the right. left. Gene read in different triplets. Different AAs coded for. Different polypeptide coded for. Non-functional protein produced. If three extra bases added then no frame shift.

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Duplication of bases

One or more bases repeated. Frame shift to the right. left. Gene read in different triplets. Different AAs coded for. Different polypeptide coded for. Non-functional protein produced

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Inversion of bases

Bases become separated from the DNA sequence and rejoin at the same position but in the inverse order.Different AAs coded for. Different polypeptide coded for. Non-functional protein produced

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Translocation of bases

A group of bases becomes separated from the DNA sequence on one chromosome and becomes inserted into the DNA sequence of another chromosome.

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Causes of mutations

High energy ionising radiation- eg X-rays and uv light. Disrupt DNA structure
Chemicals- eg nitrogen dioxide- directly alter the structure of DNA or interfere with transcription

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Totipotent stem cells

Cells found in the early embryo and can differentiate into any type of cell

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Pluripotent stem cells

Found in embryos and can differentiate into almost any type of cell

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Multipotent stem cells

Found in adults and can differentiate into a limited number of cells

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Unipotent stem cells

Can only differentiate into a single type of cell

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How are induced pluripotent stem cells produced

Unipotent cells are genetically altered to make them acquire the characteristics of embryonic stem cells by turning on genes.

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Uses of embryonic stem cells

Regrow tissues
Heart muscle cells to treat heart damage
Beta cells in pancreas to treat type 1 diabetes

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How do transcriptional factors work?

Each transcriptional factor has a site that binds to a specific base on the DNA sequence (complementary)
Binding causes this region of DNA to begin transcription
-mRNA is produced and info translated into polypeptide
When a gene is not being expressed the site on the transcriptional factor is not active

How does oestrogen stimulate the expression of a gene

Lipid soluble so diffuses into cytoplasm through phospholipid bilayer
Binds to receptor molecule on transcriptional factor (COMPLEMENTARY SHAPE)
Binding causes the DNA binding site on the transcriptional factor to change shape which can now bind to DNA
Binding of transcriptional factor to DNA stimulates transcription of the gene

Epigenetics

the process by which heritable changes in gene function are caused by environmental factors.

Epigenome

Chemical tags that mark the DNA

What is the purpose of the epigenome?

-Keeps genes that are inactive in a tightly packed environment ensuring that they cannot be read
-Unwraps active genes so that the DNA is exposed and can easily be transcribed

How does condensation of the DNA-histone complex inhibit transcription?

-Association of DNA with histones is strong
-DNA is not accessible to transcription factors
-Production of mRNA cannot be initiated

What is acetylation?

process whereby an acetyl group is transferred to a molecule

What happens when there is decreased acetylation?

-Increased positive charge on histones so increased attraction to phosphate groups on DNA (stronger association)
-DNA not accessible to transcription factors
-Transcription factors cannot initiate mRNA production

What is methylation?

Process whereby a methyl group is transferred to a molecule

How does increased methylation inhibit the transcription of genes?

-prevents transcriptional factors from binding to DNA -attracting proteins that condense the DNA-histone complex making the DNA inaccessible to transcription factors

How does siRNA work

siRNA is a type of RNAi that is complementary to the mRNA sequence it inhibits. siRNA targets a specific sequence of mRNA. After siRNA has bound to mRNA, the mRNA is broken down into smaller fragments. The fragments of mRNA are degraded.

Contrast malignant and benign tumours

Benign- grow very slowly, cell nucleus has relatively normal appearance, tumours are surrounded by a capsule so remain a compact structure Malignant- grow rapidly, cell nucleus is larger and darker, tumours are not surrounded by a capsule so can spread to surrounding tissue

What is a tumour

uncontrollable cell divison

What is cancer

a result of mutations in genes that regulate mitosis

How do tumours develop

- gene mutation in either the tumour suppressor gene or oncogenes -abnormal methylation of a tsg or oncogenes -increased oestrogen concentration

How does an proto-oncogene mutation result in the development of a tumour

-Mutate to become oncogenes -cause the proteins that stimulate mitosis to be permanently activated

What are tumour suppressor genes

produce proteins involved in slowing down cell divison and to cause cell death if dna replicating errors are detected

How would a mutation in tsg cause a tumour to develop

If proteins are not produced then cell division would continue and mutated cells would not be identified and destroyed

How does increased methylation lead to the development of a tumour

tumour suppressor genes could become hypermethylated. TSG inactivated and switched off. Leads to increased cell divison

How does decreased methylation of oncogenes lead to the development of a tumour

Hypomethylated. Leads to gene being permntelt switched on. Increased cell division

How does increased oestrogen concentration lead to the development of a tumour

Oestrogen can bind to and activate a gene that initiates transcription and if this is a photo-oncogene it becomes permanentely switched on

Why is breast cancer more likely to occur after the menopause

Ovaries usually produce oestrogen but after the menopause oestrogen is produced by fat cells in breast tissues

What is the genome

the entire genetic material of an organism

what does DNA sequencing mean

working out the DNA base sequence for all the DNA in a cell

How can the proteome of a prokaryotic organism be determined

Genome can be directly used as prokaryotic organisms dont contain introns

Why can we not use the genome to determine the proteome in eukaryotic organisms

Contain introns and regulatory genes in their DNA