Mutations

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Gene mutations: substitution

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Code may not be altered due to degenerate nature of the genetic code.
But new codon may code for a new amino acid

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Gene mutations: deletion

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Example of framework shift, codons no longer read in 'regular' threes due to absence of one or more bases

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Gene mutations: insertion

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Example of framework shift, codons cannot be read due to addition of one of more bases

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Effects of mutations: beneficial

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Altered phenotype is useful for the organism e.g sickle cell makes sufferers immune to malaria

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Effects of mutations: harmful/damaging

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Phenotype alteration means protein synthesis can no longer occur, meaning a failure to produce certain proteins

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Effects of mutations: neutral

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A silent point mutation, phenotype is not altered and the protein carries out its normal function

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Examples of a physical mutagen

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Radiation e.g X-rays

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Examples of a chemical mutagen

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Deaminating agents and free radicals

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Examples of a biological mutagen

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Viruses e.g meningitis and alkylating agents

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Silent mutations

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The protein and subsequent phenotype remains unchanged

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Nonsense mutations

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A stop codon is formed in the middle of the strand, stopping it from being read correctly

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Missense mutations

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Incorrect amino acid is incorporated into the primary structure of a protein, changing or inhibiting it's function (sickle cell)

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Example of a TRANSCRIPTIONAL LEVEL control mechanism

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Lac Operon in E.Coli

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Explanation of a TRANSCRIPTIONAL LEVEL control mechanism

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Lactose binds to the repressor protein, causing it to change its structure. It's no longer complimentary and moves away from the operator. RNA polymerase is no longer blocked and so binds to the promotor and moves down the lac genes, coding for proteins that breakdown and use lactose

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What happens when there is no lactose?

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The operator is inhibited by the repression protein which has a complimentary shape. This prevents RNA polymerase reading the lac genes

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TRANSCRIPTIONAL gene regulation: Chromatin remodelling

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Two types: Euchromatin is loosely bound to DNA and so allows it to be transcribed to mRNA
Heterochromatin is tightly wound to DNA and prevents transcription to mRNA

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TRANSCRIPTIONAL gene regulation: Histone modification

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DNA is - and histones are +.Therefore DNA winds around the histones.
Acetylation and phosphorylation= weak winding
Methylation= tight winding, preventing trasncription

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TRANSCRIPTIONAL gene regulation: CAMP

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CRP binds to it to increase the transcription rate of RNA polymerase in the lac operon reaction

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POST-TRANSCRIPTIONAL gene regulation: RNA processing

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Introns are removed by SPLICING
'5 cap and 3' tail added to the pre-mRNA to delay degradation and help in binding to ribosomes for synthesis

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POST-TRANSCRIPTIONAL gene regulation: RNA editing

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Insertion, deletion and substitution are examples used to increase the range of proteins that can be created from a single RNA strand

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TRANSLATIONAL gene regulation: Protein kinases

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Used to catalyse the addition of phosphate groups to proteins and change their tertiary structure and function(s)

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TRANSLATIONAL gene regulation: mRNA degradation

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mRNA molecules that are more resistant last longer in the cytoplasm and allow for more synthesis. Inhibitory proteins prevent mRNA binding to ribosomes, decreasing synthesis

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POST-TRANSLATIONAL gene regulation: Modifications

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Addition of non-protein groups such as lipids, carbohydrates and phosphates.
Proteins fold/shorten and amino acids and modified

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What makes pre-mRNA into mRNA during transcription?

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The removal of introns from the molecule, leaving only exons

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Apoptosis

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Programmed cell death

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What are the first stages of apoptosis?

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Protein filaments and microtubules (cytoskeleton) breakdown and is digested by enzymes.
Plasma surface membrane changes and 'blebs' form (bulges on the surface membrane)

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What are the final stages of apoptosis?

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The cell breaks into membrane bound fragments that are removed by phagocytosis, this prevents harmful substances being released into the surrounding tissues

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Apoptosis of programmed cell death is
If is does not occur....

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A controlled process, failure of programmed cell death can lead to the formation of (malignant) tumours

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Homeobox gene

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A regulatory gene 60 amino acids long (180 base pairs).
It acts as an 'on' and 'off' switch for DNA, telling it when to activate genes.
They're highly conserved regions within Hox Genes

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What controls body plans?

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Proteins known as hox genes

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What do hox genes control? What's their mechanism of action?

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They control development and code for a homeodomain- a part of a protein that binds to specific parts of DNA.

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What is the role of a homeodomain?

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Allows genes to become transcription factors by binding to the star codon of a developmental gene and activating or repressing transcription

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How is apoptosis regulated?

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Internal stimuli such as DNA damage during the cell cycle.
External stimuli such as stress of malnutrition

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Hox genes are only found in

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Animals

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Homeobox genes are only found in

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Animals, fungi and plants

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What is the role of mitosis in gene expression and regulation

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It's responsible for proliferation and cell division to increase cell numbers and promote growth