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Protein Synthesis and Cellular Respiration: Key Concepts for Anatomy & Physiology

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Protein Synthesis

Overview of Protein Synthesis

Protein synthesis is the process by which cells build proteins based on genetic instructions encoded in DNA. This process is fundamental to cell structure and function.

  • Central Dogma: Describes the flow of genetic information: DNA → RNA → Protein.

  • DNA: Contains instructions for protein synthesis, organized into genes.

  • Transcription: DNA is copied into messenger RNA (mRNA).

  • Translation: mRNA is decoded by ribosomes to build proteins.

  • Codons: Triplets of nucleotides in mRNA that specify amino acids.

Example: The DNA sequence TAC GGA CCA GCA codes for the mRNA sequence AUG CCU GGU CGU, which is then translated into a specific sequence of amino acids.

Genetic Code

The genetic code is a set of rules by which information encoded in mRNA is translated into proteins. Each codon (three-base sequence) corresponds to a specific amino acid or a stop signal.

  • Start Codon: AUG (codes for methionine; initiates translation)

  • Stop Codons: UAG, UGA, UAA (signal termination of translation)

  • mRNA vs. DNA: mRNA contains uracil (U); DNA contains thymine (T).

Codon

Amino Acid

AUG

Methionine (Start)

UAG, UGA, UAA

Stop

UUU, UUC

Phenylalanine

Additional info: Table includes all 64 codons for 20 amino acids.

Transcription

Transcription is the process by which a segment of DNA is copied into mRNA by the enzyme RNA polymerase.

  • Initiation: RNA polymerase binds to DNA and separates the strands.

  • Elongation: RNA polymerase adds complementary RNA nucleotides to the growing mRNA strand.

  • Termination: Transcription ends when RNA polymerase reaches a termination signal.

Exons: Coding regions of DNA that are expressed. Introns: Non-coding regions that are removed during mRNA processing.

Region

Function

Exon

Codes for protein

Intron

Removed during splicing

Spliceosomes: Protein complexes that remove introns from pre-mRNA.

Translation

Translation is the process by which ribosomes synthesize proteins using the sequence of codons in mRNA.

  • Initiation: Ribosome assembles at the start codon (AUG) on mRNA.

  • Elongation: tRNA molecules bring amino acids to the ribosome, matching their anticodon to the mRNA codon. Peptide bonds form between amino acids.

  • Termination: When a stop codon is reached, the ribosome releases the completed polypeptide.

tRNA: Transfer RNA picks up specific amino acids and brings them to the ribosome.

Ribosome: Composed of small and large subunits; coordinates the interaction of mRNA and tRNA.

Sequence of Events in Translation

  • Initiation: Ribosome binds to mRNA at the start codon.

  • Elongation: tRNA brings amino acids; peptide bonds form; ribosome moves along mRNA.

  • Termination: Ribosome reaches stop codon; polypeptide is released.

Cellular Respiration

Overview of Cellular Respiration

Cellular respiration is the process by which cells convert biochemical energy from nutrients into ATP, the energy currency of the cell. It involves a series of metabolic pathways.

  • ATP: Adenosine triphosphate, the main energy carrier in cells.

  • Anabolic Reactions: Build larger molecules from smaller ones.

  • Catabolic Reactions: Break down larger molecules into smaller ones.

Carbohydrate Metabolism and ATP Synthesis

Glucose metabolism is a major source of ATP production in cells. The overall reaction for aerobic respiration is:

  • Equation:

  • Three Stages: Glycolysis, Citric Acid Cycle (Krebs Cycle), Electron Transport Chain

Glycolysis

Glycolysis is the first step in glucose metabolism, occurring in the cytoplasm. It breaks down one glucose molecule into two pyruvate molecules, producing ATP and NADH.

  • Phases: Energy investment, cleavage, energy payoff

  • Net Yield: 2 ATP, 2 NADH per glucose

Citric Acid Cycle (Krebs Cycle)

The citric acid cycle occurs in the mitochondria and completes the oxidation of glucose derivatives, generating NADH and FADH2 for the electron transport chain.

  • Electron Acceptors: NAD+, FAD

  • Net Yield: 6 NADH, 2 FADH2, 2 ATP per glucose

Electron Transport Chain and Oxidative Phosphorylation

The electron transport chain (ETC) is a series of protein complexes in the inner mitochondrial membrane that transfer electrons from NADH and FADH2 to oxygen, producing ATP.

  • Oxidative Phosphorylation: ATP is synthesized as electrons move through the ETC and create a proton gradient.

  • Chemiosmosis: Protons flow back into the mitochondrial matrix through ATP synthase, driving ATP production.

  • Produces: Most of the cell's ATP (about 28 per glucose)

Summary: From DNA to Protein

Genetic information flows from DNA to RNA to protein, with each step involving specific enzymes and regulatory mechanisms. Cellular respiration provides the energy required for these processes.

  • Complementary Base Pairing: Ensures accurate transfer of genetic information during transcription and translation.

  • ATP: Required for synthesis and function of proteins.

Additional info: These notes expand on the original slides by providing definitions, explanations, and context for each process, ensuring a self-contained study guide for Anatomy & Physiology students.

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