By hsieh and chua central dogma of molecular biology
“The central dogma of molecular biology deals withthe detailed residue-by-residue transfer of sequentialinformation. It states that such information cannot betransferred back from protein to either protein ornucleic acid.” Francis Crick, 1958
1. InitiationHelicase unwinds DNAforming a “replication fork”Multiple replication forksalong a DNA molecule createreplication bubbles
2 Elongation---Adding New NucleotidesRNA Primase adds a complimentary RNA primer to each template strand as astarting point for replicationDNA Polymerase reads the template strand (3’ to 5’) and adds newcomplimentary nucleotides (5’ to 3’)DNA synthesized in the direction of the replication fork is called the leadingstrand
the antiparallel nature of DNA, replication occurs in two directionsAn RNA primer is laid down on the other strand, and new nucleotidesare added 5’ to 3’ moving away from the replication fork. This is thelagging strand and the segment of DNA produced is called an Okazakifragment
The DNA unwinds some more and the leading strand isextended by DNA polymerase adding more DNAnucleotides. Thus, the leading strand is synthesizedcontinuously.
DNA polymerase adds new DNA . This produces thesecond Okazaki fragment. Thus, the lagging strand issynthesized discontinuously
3 TerminationA different type of DNA polymerase removes the RNAprimer and replaces it with DNA
The genome of any organism contains all the informationfor making that organism. The information is encoded invarious types of genes that are transcribed into 4 types ofRNA: mRNA - Messenger RNA: Encodes amino acid sequence of a polypeptide tRNA - Transfer RNA: Brings amino acids to ribosomes during translation rRNA - Ribosomal RNA: With ribosomal proteins, makes up the ribosomes, the organelles that translate the mRNA snRNA - Small nuclear RNA: With proteins, forms complexes that are used in RNA processing in eukaryotes
Messenger RNA carries the actual code that specifies theamino acid sequence in a polypeptideMaking mRNA starts with a protein encoding gene on atemplate strand of DNA
1. InitiationRNA Polymerase binds to a promoter which is a region ofbases that signals the beginning of a geneRNA Polymerase is bound to the TATA box of the promoter bytranscription factorsThe double helix unwinds and is ready to be transcribed
2 . ElongationRNA Polymerase moves along the protein encodinggene adding new RNA nucleotides in the 5’ to 3’direction and complimentary to the DNA templateWorks at up to 60 nucleotides/second
3 Termination RNA Polymerase reaches the terminator region of the protein encoding gene All the enzymes and factors are released
If 3 RNA bases codefor 1 aminoacid, RNA couldcode for 43 = 64amino acids. Morethan enough codingcapacity for 20amino acidsCode is redundantfor most aminoacids
Messenger RNA (mRNA) 1.Synthesized in Transcription 2.Composed of Codons 3. Codons are 3-base sequences of mRNA
Transfer RNA (tRNA)3 base anitcodon pairswith the mRNA codon
A Codon OHHO P O N NH2 Adenine O N CH2O N N O H HO P O O N O CH2O NH N N NH2 Guanine O H NH2 HO P O O N N Arginine CH2O N N OH H Adenine
Amino Acids There are 20 amino acids, each with a basic structure Amino acids are held together by peptide bonds • Therefore, there is a total of 64 codons with mRNA, 61specify a particular amino acid.
1 Initiation 5’ G-cap of mRNA binds to ribosome • Besides selecting the amino acid Start codon AUG and methionine, the codon AUG also anticodon with serves as the “initiator” codon, Methionine bind a P site which starts the synthesis of a protein A site is open and ready to receive new tRNAs
2 Elongation --- Adding New Amino Acids 1.Codon recognition 2.Peptide bond formation 3.Translocation
3 Termination 1.A stop codon is reached UAA,UAG,UGA All parts release
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