On DNA: Replication, Transcription, Translation
DNA has 3 main functions to support all forms of life. Replicationis the duplication of DNA parental strand using a semi-conservativemodel. Transcriptionis when DNA is copied into mRNA, which are information carrying intermediates in protein synthesis. Translationis the synthesis of proteins according to instructions given by mRNA templates. Monomers in protein are nucleotidesand DNA/RNA are polymers with poly nucleotides. Each has a base, phosphate, and sugar. Learn to draw and pair AT, CG bases usinghydrogen bonds. In a stick an P model the bottom of the stick is carbon 5, where the phosphate is linked by an ester bond.
When Watson and Crick determined the structure of DNA’s double helix(1953), it was clear how DNA could be precisely copied during cell replication. The double helix has several properties: (1) it has 2 helical polynucleotides that are coiled around a central axis (2) 2 complementary strands are anti-parallel and is copied 5’-> 3’ (3) phosphate sugar backbone is on the outside (hydrophilic), while bases are inside the helix(hydrophobic) (4) bases are 90 degrees to helical axis. There is about 10 bases/turn of the helix. DNA is supercoiled so it can be compact and it will have less interaction with other molecules.
DNA and RNA differ because RNA uses oxygen in the 2’ carbon of its ribose sugar and it uses uracilnotthymine. Absorbance of dsDNA increase when its ssDNA because when it is dsDNA there is 0 absorbance, all the rays pass through it. Once the bases are free in ssDNA than they can absorb the rays.
Understand how DNA polymerase works. It melts the DNA and uses a primer to copy, than you just amplify the crap out of it. Elongation of strand goes from 5’ -> 3’. Retroviruseshas 2 proteins in its arsenal to perform reverse-transcriptase: 1) reverse transcriptase 2) RNA strand.
Steps DNA Replication
(1)Helicase enzyme splits 2 parental strands of DNA
(2)DNA gyrase or topoisomerase prevent recoiling. SSB proteins prevent H-bond reformation.
(3)RNA Primase binds to initiate point 3’-5’ end of parental strand
(4)Elongation occurs in 5’-3’. DNA polymerase creates a leading strand and lagging strand.
(5)DNA pol I reads and removes RNA primases. Okazaki fragments are joined by DNA ligase.
(6) Telomeres are added and DNA replication terminates.
Transcription starts in apromoter region/sitewhereRNA polymerasebinds to. Downstream from the promoter sites are pribnow box (prokaryotes) or TATA box (eukaryotes). Eukaryotes also have enhancer sequences that further promote transcription in promoter sites. Termination occurs in prokaryotes with a hair-pin in the RNA and some modify using a poly A tail. DNA has a termination sequences.
Eukaryotes have splicisomes to make introns into exons. They modify mRNA inside the nucleus before it goes outside to get translated.
Translation uses tRNA, mRNA, and aminoacyl-tRNA synthase to bind tRNA and mRNA together. mRNA is read in codons while tRNA has the anti-codons. There is one start codon, AUG that eukaryotes use. Prokaryotes uses AUG and the shine delgarno sequenceto start translation. There are 3 stop codons UAA, UAG, UGA which are not read, so rRNA just releases the protein after it notices 1 out of those 3 codons.
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