Protein%20Synthesis:%20An%20Overview

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Protein Synthesis An Overview

• SBI 4UI 5.2

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Where is the DNA?

• Cytoplasm?
• Nucleus?
• Outside the cell?

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Central Dogma

• DNA is too important to leave the nucleus
• Plus, there are only 2 copies of DNA in a somatic
  cell
• Plus, ribosomes often need to make large amounts
  of protein
• Plus, DNA would then have to reenter the nucleus
• What to do?

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Central Dogma

• Messenger RNA (mRNA)
• DNA is transcribed into mRNA
• mRNA can travel to ribosomes to translate into
  polypeptide chains
• This process in known as the central dogma of
  molecular genetics

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Transcription

• DNA ? mRNA
• Transcription is like making a carbon copy

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Translation

• Ribosomes
• mRNA ? amino acid sequences
• Translation is like translating

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Ribonucleic Acid
DNA RNA
Carries genetic information Carries genetic information
Deoxyribose sugar Ribose sugar
Adenine pairs with thymine Adenine pairs with uracil
Double stranded Single stranded
Resides in nucleus Resides in nucleus and cytoplasm
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Messenger RNA

• Varies in length
• Intermediary between DNA and ribosomes
• Like a blueprint for protein production
• Contains codons

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Transfer RNA

• Delivery system of amino acids to ribosomes as
  they make proteins
• Very short (70-90 base pairs)
• Contains anticodons

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Ribosomal RNA

• Central component of the ribosome
• Protein manufacturing machinery
• Varies in length

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Transcription

• Initiation
• RNA polymerase binds to the promoter
• Elongation
• Begins adding ribonucleotides ? mRNA
• Termination
• Stop signal ends transcription and mRNA is
  released

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Translation

• Initiation
• Ribosome recognizes a sequence on mRNA and binds
  to it
• Ribosome moves along mRNA 3 nucleotides at a time
  (3 nucleotides 1 amino acid)
• Elongation
• tRNA delivers appropriate amino acid
• Termination
• 3 base nucleotide codes as stop signal and
  polypeptide is released

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Genetic Code

• 20 amino acids, but only 4 bases
• Triplet(3) of nucleotides codon
• 43 64 possible combinations
• Start codon signals initiation
• Stop codon signals termination

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To Do

• Section 5.2
• Understanding Concepts 1-11