What is central dogma? From DNA to Protein

1
What is central dogma?From DNA to Protein

• All proteins consist of polypeptide chains
• A linear sequence of amino acids
• Each chain corresponds to the nucleotide base
  sequence of a gene

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What is the first step?

• 1. Transcription Enzymes uses base sequence of
  a gene as template to make strand of RNA
• Two DNA strands unwind in a specific region
• RNA polymerase assembles strand of RNA
• Covalently bonds RNA nucleotides (adenine,
  guanine, cytosine, uracil) according to
  nucleotide sequence of exposed gene

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What is the second step?

• 2. Translation
• Information in the RNA strand is decoded
  (translated) into a sequence of amino acids

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Prokaryotes and eukaryotes

• In prokaryotic cells (no nucleus)
• Transcription and translation occur in cytoplasm
• In eukaryotic cells
• Genes are transcribed in the nucleus
• Resulting mRNA is translated in the cytoplasm

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Three types of RNA

• Messenger RNA (mRNA)
• Carries protein-building codes from DNA to
  ribosomes
• Ribosomal RNA (rRNA)
• Forms ribosomes (where polypeptide chains are
  assembled)
• Transfer RNA (tRNA)
• Delivers amino acids to ribosomes

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RNA and DNA compared

• DNA
• exists as double-stranded molecules
• hereditary information
• double helix
• contains deoxoyribose sugar
• RNA
• Disposable copies of hereditary information and
  some are catalytic
• exists as a single stand.
• contains ribose instead of deoxyribose
• contains uracil in place of thymine

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RNA Modification Alternative Splicing

• Before mRNA leaves the nucleus
• Introns are removed
• Some exons are removed along with introns
  remaining exons are spliced together in different
  combinations
• Poly-A tail is added to 3 end of new mRNA

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What is the genetic code?

• Messenger RNA (mRNA) carries DNAs
  protein-building information to ribosomes for
  translation
• mRNAs genetic message is written in codons
• Sets of three nucleotides along mRNA strand

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Codons

• Codons specify different amino acids
• A few codon signals stop translation
• Sixty-four codons constitute a highly conserved
  genetic code