Cell Growth and Reproduction, and Protein Synthesis

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Cell Growth and Reproduction, and Protein
Synthesis
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Cell Growth and Reproduction

• Cell Life Cycle
• Interphase
• G1, S, G2
• DNA replication
• Mitosis
• Prophase, Metaphase, Anaphase, Telophase
• Cytokinesis

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Protein Synthesis

• Role of RNA
• mRNA, tRNA, rRNA
• Transcription
• Making mRNA complement
• Editing mRNA
• Translation

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DNA Synthesis
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General Information

• One gene-one polypeptide hypothesis
• Bridge
• RNA
• DNA ? RNA ? Protein
• Transcription
• Synthesis of RNA under direction of DNA
• Translation
• Actual synthesis of a polypeptide

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DNA vs. RNA

• DNA
• Sugar is deoxyribose
• Nitrogenous bases
• A, G, C, and T

• RNA
• Sugar is ribose
• Nitrogenous bases
• A, G, C, and U
• 3 types
• mRNA
• rRNA
• tRNA

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Transcription (Overview)

• Info is copied from DNA to RNA
• Copy protein building instruction
• mRNA
• Occurs in nucleus
• mRNA then leaves nuclear envelope

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Translation (Overview)

• Occurs in cytoplasm
• On ribosomes
• Translation of mRNA into amino acid sequence

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Triplet Code

• Gene ? Protein based on triplet code
• Need mRNA first
• 3 nucleotide bases code for a single amino acid
• Called a codon
• Must be read correctly
• Ordering called the reading frame

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Transcription

• RNA polymerase
• Three steps
• Polymerase binding and initiation
• Elongation
• Termination

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Polymerase Binding and Initiation

• Promoters
• Initiation site for transcription
• Transcription factors
• Aids polymerase in finding promoter region
• Polymerase
• Separates two DNA strands

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Elongation of RNA strand

• Polymerase separates double helix
• Exposes DNA for transcription
• Transcription simultaneous

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Termination of Transcription

• Termination site on DNA
• RNA strand released
• AATAAA site in eukaryotes
• mRNA editing
• Introns must be removed
• spliceosomes

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Translation

• tRNA
• Transfers amino acids to a ribosome
• Contains the anticodon
• Builds polypeptide codon by codon
• Occurs on ribosomes
• Contains rRNA
• P site, A site, E site (not shown in the
  following pictures)

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Translation

• Three stages
• Chain initiation
• Chain elongation
• Chain termination
• Energy required for initiation and elongation
  (GTP)

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Initiation

• mRNA, tRNA, and ribosomes come together
• GTP required to form initiation complex
• tRNA goes from A site to P site
• A site ready for next tRNA

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Elongation

• Amino acids added one by one
• Three step cycle
• Codon recognition
• Peptide bond formation
• Translocation

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Termination

• Termination codon
• UAA, UAG, UGA
• Release factor in A site
• Bond broken
• Between tRNA in P site and last amino acid of
  polypeptide chain
• Polypeptide and tRNA free

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Functional Protein

• Polypeptide coils and folds
• 3-D structure forms
• Some posttranslational modifications may be
  required

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