GENETICS OF LIVING SYSTEMS OCR Biology A Level

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  • Created by: Davina1st
  • Created on: 10-10-21 19:06
What is a mutation?
A change in the base/nucleotide sequence of the DNA which can result in a new allele occurring.
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What are the three main types of mutation?
Substitution, deletion and insertion
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What is a substitution mutation?
Where one (or more) base is swapped for another. E.g. ATTGCT becomes ATAGCT
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What is a point mutation?
When a substitution mutation involves just one nucleotide alteration
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What are the three types of point mutations? describe
Silent - altered base sequence still codes for the same amino acid, missense - subsituted base codes for a different amino acid and the final protein cannot function properly, nonsense - when the triplet code changes to a stop codon.
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What is a deletion mutation?
Where one (or more) nucleotides are removed from the DNA sequence e.g. ATGCCT to ATG^CT
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What is an insertion mutation?
Where one (or more) nucleotides are added to the DNA sequence. e.g. ATGCCT to ATG A CCT
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What is a frameshift mutation?
Where that one/or more mutation(s) alters every triplet codon from the point of mutation onwards.
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What are the consequences of a mutation?
Sequence of amino acids altered = change in primary protein structure = chnage in folding of secondary and tertiary structures = changed final 3d shape and function. Enzymes, hormones, antibodies, haemoglobin affected.
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When is a mutation neutral?
It occurs in non-coding introns, the altered triplet code codes for the same amino acid (silent), chemically similar amino acid which makes no difference, the altered amino acid is not crucial in the shape of the protein.
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When is a mutation beneficial?
Has advantageous effects that increase the chance of survival, e.g. antibiotic resistant bacteria. The ability to digest lactose in humans.
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When is a mutation harmful?
It has a disadvantageous affect on an organism which decreases its chance of survival. e.g. cystic fibrosis.
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Give an example of a physical mutagen and its effect on DNA
Ionising radiation, like X-rays and UV lights. Can break the DNA (of one/both strands) and may mutate as it repairs.
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Give an example of a biological mutagen and its effect on DNA
Viruses, they insert their genetic material into the hosts DNA altering the sequence, alkylating agents - meth/ethyl groups added to bases=incorrect pairing, base analogs - changes base sequence.
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Give an example of a chemical mutagen and its effect on DNA
Deaminating agents - alter the bio-chemical structure/base sequence of DNA.
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What is a translocation mutation?
A section of one chromosome breaks off and joins another non-homologous chromosome.
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What is an inversion mutation?
A section of a chromosome breaks off, is reversed, and then joins back onto the chromosome.
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What are the four ways in which genes can be regulated?
Transcriptional, post-transcriptional, translational and post-translational.
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What are the two types of transcriptional control?
Altering chromatin structure and histone modification
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How does chromatin remodelling act as transcriptional control?
When DNA is tightly wrapped around histones (heterochromatin) transcription cannot occur. During interphase when DNA is wrapped loosely around histones (euchromatin), RNA can access DNA to make mRNA. Ensures proteins made at the correct stage.
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How does histone modification act as transcriptional control?
Addition of a acetyl/phosphate reduces positive charge on histones so negative DNA wraps loosely allowing transcription to occur. Addition of a methyl group =more hydrophobic histones so DNA coils tightly=prevention of trnascription.
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Describe the process of post transcriptional control of gene expression
During transcription, introns and exons are copied into mRNA forming primary mRNA transcripts. Introns are removed by splicing (as they do not code for amino acids). The mature mRNA then leaves the nucleus. Cap and tail added so mRNA doesn't degrade
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Exons can join back together in any order, true or false?
True
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Describe the process of translational control
Inhibitory proteins - these bind to mRNA and stop attaching to the ribosomes so inhibit translation, initiation factors - help the binding of mRNA to ribosomes, so promote translation and protein synthesis.
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How does post translational control work?
Final modifications of the proteins made, addition of non-protein groups (carbo/lipid), folding and shortening of a protein into its final shape, activation of proteins by cAMP
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What are protein kinases/ what are their role?
Enzymes that catalyse the addition of phosphate groups to proteins=changed tertiary structure, many enzymes are activated by phosphorylation so are important regulators of cell activity. Activated by cAMP.
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What is cAMP?
Cyclic AMP - common activator molecule. Result in the change of 3d shape of a protein e.g. active site of an enzyme enabling it to its function.
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What is an operon?
A set of genes transcribed under the control of an operator gene. Segment of DNA containing adjacent genes including structural, operator and regulatory genes. Functional unit of transcription and genetic regulation.
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What is the lac operon system in prokaryotes?
An operon which regulates the genes needed to utilise lactose in E.coli.
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What is apoptosis?
Programmed cell death
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What does conserved mean in evolutionary terms?
Has remained in all descendant species throughout evolutionary history.
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What is a homeobox sequence?
Sequence of 180 base pairs (excluding introns) found within genes that are involved in regulating patterns of anatomical development in animas, fungi and plants.
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What is morphogenesis?
The regulation of the pattern of anatomical development.
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What is a protein made from a homeobox gene called?
Homeodomain
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What are hox genes?
one group of homeobox genes that are only present in animals, responsible for the correct positioning of body parts
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Hox genes are found singularly on chromosomes, true or false?
False - mammals have 4 clusters of hox genes on different chromosomes, the order in which they appear is the order in which they are expressed.
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How do homeobox genes determine body plan in organisms?
Some determine the polarity of the embryo (head and tail ends), the polarity of each segment, which structures develop from each segment e.g. arms, legs, wings etc.
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What are somites/what are their role?
Directed by hox genes to develop a particular way in individual vertebrae.
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What is diploblastic and triploblastic?
Diploblastic - 2 primary tissue layers and triploblastic - three primary tissue layers.
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Describe the three types of symmetry
Radial - seen in diploblastic animals like jellyfish, no left or right sides only top and bottom, bilateral - both left and right sides and a head and tail, asymmetry - no lies of symmetry (sponges)
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Why are homeobox genes highly conserved?
They are crucial to the survival of organism, mutations will have been eliminated by natural selection as they cannot survive with a different body plan.
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Apoptosis is not involved in the metamorphosis of some species, true or false?
False - it is involved in metamorphosis like when a caterpillar changes to a butterfly/tadpoles to a frog.
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Describe the sequence of events of apoptosis
Enzymes break down cytoskeleton, cytoplasm becomes dense and tightly packed with organelles, CSM changes and protrusions (blebs) form. Chromatin condenses, nuclear envelope breaks DNA breaks fragments. Cell into vesicles and ingested phagocytic cells
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How are homeobox genes and apoptosis linked?
Homeobox genes code for protein transcription factors, these then activate the genes needed for apoptosis coding for enzymes needs programmed cell death.
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What is the link between apoptosis and mitosis?
Rate of cells dying by apoptosis should equal rate of cells produced by mitosis.
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Give examples of internal stimuli that can affect apoptosis.
DNA damage, hormones, cytokines (cell signals) from the immune system.
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Give examples of external stimuli that can affect apoptosis
Infections of pathogens, changes in temperature, changes in light intensity (relating to seasonal changes), and stress.
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What is a substitution mutation?

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Card 4

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What is a point mutation?

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Card 5

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What are the three types of point mutations? describe

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