Protein Synthesis LT and Study Guide-KEY

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Study Guide: Protein Synthesis Testable Targets

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1. DNA vs. RNA

  • Differences in Structure and Function:

    • Sugar in Backbone:

      • DNA: deoxyribose

      • RNA: ribose

    • Nitrogen Bases:

      • DNA: Adenine, Thymine, Cytosine, Guanine

      • RNA: Adenine, Uracil, Cytosine, Guanine

    • Strandedness:

      • DNA: Double-stranded

      • RNA: Single-stranded

    • Function:

      • DNA: Master molecule of cellular functioning

      • RNA: Involved in protein production

    • Types of RNA: mRNA, tRNA, rRNA

2. DNA Transcription Process

  • Definition: Transcription means to copy.

  • Location:

    • Eukaryotes: Nucleus

    • Prokaryotes: Cytoplasm

  • Step-by-Step Process:

    1. Initiation: RNA polymerase binds to the promoter region, DNA unwinds to expose bases.

    2. Elongation: RNA polymerase reads DNA and builds mRNA with complementary bases.

    3. Termination: Occurs when RNA polymerase encounters a stop sequence; mRNA detaches from DNA.

  • RNA Polymerase: Enzyme making RNA transcript from DNA template; it moves 3’ to 5’ along the DNA strand.

3. Role of mRNA in Transcription

  • mRNA serves as a mobile copy of one side of the DNA, which travels to ribosomes where translation occurs.

  • Base Pair Matching:

    • DNA: A, T, G, C

    • RNA: U, A, C, G

  • Promoter: DNA region where RNA Polymerase initiates transcription (includes the TATA box).

4. Introns and Exons (HONORS ONLY)

  • Introns: Non-coding segments spliced out of primary transcripts.

  • Exons: Coding segments that remain in the final mRNA.

  • Alternative Splicing: Different arrangements of exons allow one gene to produce multiple proteins.

  • 5’ Cap & Poly-A Tail: Added to mRNA for protection and stability before translation.

5. Purpose of Transcription

  • MRNA acts as the messenger, carrying DNA’s message to ribosomes for protein synthesis.

6. RNA Translation Process

  • Definition: Translation is the process of decoding the mRNA into an amino acid sequence.

  • Location:

    • Eukaryotes: Ribosomes (cytoplasm or Rough ER)

    • Prokaryotes: Ribosomes in the cytoplasm

  • Step-by-Step Process:

    1. mRNA codons read by tRNAs with anticodons, each carrying corresponding amino acids.

    2. tRNAs bind at A site, P site, and exit through E site, forming peptide bonds between amino acids.

    3. Process continues until a stop codon is reached (UAA, UAG, UGA).

7. Codons and Amino Acids

  • Codon: Sequence of three nitrogen bases on mRNA; determines amino acid sequence.

  • Start Codon: Signals start of translation (AUG).

  • Stop Codons: Signal end of translation (UAA, UAG, UGA).

  • Anticodon: Complementary sequence found on tRNA, paring with mRNA codons.

8. Mutations

  • Definition: Changes in normal DNA sequences.

  • Types:

    • Induced Mutations: Caused by environmental factors.

    • Spontaneous Mutations: Occur randomly without known cause.

  • Point vs. Frameshift Mutations:

    • Point: Change in a single base; often a substitution.

    • Frameshift: Insertion or deletion of a base, affecting all downstream codons.

9. Effects of Mutations

  • Mutations can have positive, negative, or neutral effects based on their impact on the protein structure and function.

  • Example of Beneficial Mutation: Lactose tolerance in humans allows for better nutrition from milk.

10. Silent Mutations

  • Definition: Mutations that do not change the amino acid sequence due to redundancy in the genetic code.

11. Importance of Codon Chart

  • Different codon sequences can code for the same amino acid, aiding in understanding mutation effects.