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Nucleotides (1.5), Transcription, Translation - Coggle Diagram
Nucleotides (1.5)
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Protein synthesis
DNA has the code for proteins, and it is confined in the nucleus, it must be transferred to the ribosomes located on the cytoplasm
A gene is a section of DNA that codes for a polypeptide, in eukaryotes genes contain introns + exons,
Post-transcriptional modification, removal of introns, exons spliced together
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Gene is unwound + unzipped by DNA helicase, breaking the H bonds located between the two polynucleotide chains, with one acting as a template for the formation of mRNA
RNA nucleotides align opposite to their complimentary base pairs, RNA polymerase joins the nucleotides together, A pre-mRNA molecule is formed, and leaves the DNA when a seq. is reached
Every 3 bases = 1 codon, and mRNA joins to a ribosome at the "start" codon, and the ribosome can take 2 codons
tRNA in cytoplasm is activated, the correct amino acid is attached to the amino acid binding site, the amino acid is determined by the anticodon, (seq. of 3 bases), requires energy from ATP
tRNA with amino acids collide with codons on mRNA, if the anti-codon + codon are complementary, they will form a codon/anticodon complex, with H bonds.
When two tRNA molecules occupy both ribosome sites, amino acids are brought close enough to form a peptide bond, ribosome moves along the mRNA by one codon.
Ribosome moves along the mRNA by one codon, first tRNA is released from amino acid + ribosome, then returns to cytoplasm for reactivation
Another amino acid is attached until it reaches a "stop" codon, where the polypeptide chain leaves the ribosome to the Golgi body for modification
In the Golgi body, polypeptide can be folded to make a protein, as the golgi body modifies and prepares substances
Triplet code
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Triplet code, as three bases in the code give enough combinations to code for 20 amino acids. 4^2 = 16, 4^3 = 64
Degenerate - Some amino acids = more than one code, Universal - Same in all living things
DNA
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Sugar - Phosphate molecules = condensation reactions, phosphodiester bond
Two strands, antiparallel
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RNA
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rRNA
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Single polynucleotide strand, highly folded = globular structure
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tRNA
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Structure kept using H bond, between pairs
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Bases
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Pyrimidines
Thymine, Uracil, Cytosine
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DNA replication
Conservative
The DNA molecule would be copied from the original, leaving the original DNA molecule as it was and having a new copy.
Dispersive
Sections of the DNA molecule would be copied and spliced together, making each new DNA molecule a mix of original and new DNA.
Semi-conservative
the two polynucleotide chains would part, and new nucleotides attach to each of the chains, leading to each new molecule having one original chain and one new one.
This is how DNA replication works, or its process
DNA helicase breaks H bonds holding polynucleotide chains together, the area where the DNA helicase works is called the "replication fork"
DNA polymerase joins nucleotides to complimentary bases, by catalysing formations of phosphodiester bonds between deoxyribose + phosphate groups.
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Meselson and Stahl
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E.coli grown only with 15N isotopes until, all bases contained 15N, when centrifuged the DNA was near the bottom of the tube, as 15N is heavier
A sample of E.coli was transferred to a new culture medium with 14N, and only replicate once
Sample was withdrawn and centrifuged, DNA was found to be at an intermediate position between 15N and 14N molecules
First generation shows that the replication was not conservative, and each new DNA molecule had half new (14N) and half original (15N) Nucleotides
The E.coli replicated two more times, leading to generations 2 and 3
It cannot be dispersive as bands appear at the "light" and "intermediate" positions if it were to be dispersive, generation 2 / tube C would have more 14N than 155N and the DNA band wold be between the intermediate + light positions
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