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Biology AOS 1 - Coggle Diagram
Biology AOS 1
Manipulation of DNA
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CRISPR-Cas9 = edit DNA
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gRNA sequence is created to be a 20 base sequence that is complementary to the target sequence of DNA
Cas9 recognises a PAM sequence and uses the guide RNA to identify the corresponding DNA sequence within the host cell's genome and cleave both strands
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The cell detects and repairs the broken strand of DNA and in doing so integrates the changes into genomic DNA
Previously only endonuclease restriction sites could be used to cut the DNA but now we can make gRNA to be complementary to any segment of DNA
Deletion of a base = causes a frameshift mutation that results in a silent gene and therefore no protein is produced
Insertion of a base = Cas 9 makes a cut at the insertion site and a health gene can be inserted either from another organism or just another healthy gene from the organism
Occurs naturally in bacteria in defence to viruses where the Cas 9 cuts the foreign DNA to prevent it from continuing to take over the cell
PCR = amplify DNA
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Denaturation = at 94 degrees for 1 minute the hydrogen bonds between DNA strands break and the strands separated
Annealing = at 55 degrees for two minutes the primers are added which bind to the target DNA sequences through complementary base pairing on their target single strand piece of DNA
Extension = at 72 degrees for 1 minute Taq polymerase uses the primers as a starting point and extend the primers, synthesising the new strands of DNA by adding nucleotides
Process is repeated, which doubles the DNA each time
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Gene regulation
Prokaryotic trp operon
collection of 5 structural genes which encode for the enzymes involved in the synthesis of tryptophan (A,B,C,D,E)
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operon = group of linked structural genes with a common promoter and operator that is transcribed as a single unit
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leader region = upstream region in some genes that contain attenuators, contains a double trp codon so where trp levels are high the ribosome will quickly translate this region whereas if trp levels are low the ribosome will be slower to translate so will pause waiting for trp
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Protein structure
proteins are a polypeptide chain formed in translation made up of amino acids that is further folded to allow function
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secondary structure - three different folding can occur in the amino acids which depends on the R groups of the amino acids - alpha helix, beta-pleated sheets + random coiling
tertiary structure = total irregular 3D folding held together by ionic or hydrogen bonds to form a complex shape, this shape is critical for the function of the protein - involves hydrogen bonds, covalent disulfide cross links + interactions between R groups
quaternary structure = two or more polypeptide chains interact to form a protein eg. globular proteins eg. haemoglobin or fibrous proteins eg. collagen
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Nucleic acids
DNA
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adenine, thymine, guanine, cytosine
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RNA
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adenine, uracil, guanine, cytosine
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Gene expression
transcription
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RNA polymerase binds to the promoter (upstream on the template strand), DNA unwinds and RNA polymerase reads DNA strand in a 3' to 5' direction
Complementary nucleotides are brought into place to form an RNA chain, adding to the 3' end of the mRNA strand
RNA polymerase moves past the coding region and into the downstream of the gene where transcription stop and pre-mRNA is released
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translation
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mRNA is read by the ribosome in codons, translation begins at the start codon (AUG)
Amino acids are brought to the ribosome by tRNA where tRNA has a complementary anti-codon to the codon of the mRNA strand which codes for a particular amino acid
Ribosome moves along the mRNA, joining amino acids to the growing polypeptide chain by peptide bonds until the stop codon is reached (UAA, UAG or UGA)
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