SCI10 Q3 protein synthesis

Proteins

  • Definition: Proteins are composed of amino acids linked together by peptide bonds.

Roles and Functions of Proteins

  • Channels in membranes: Control the movement of molecules in and out of the cell.

  • Structural molecules: For example, proteins form hair or muscle in animals.

  • Hormones: Regulate the activity of cells.

  • Antibodies: Function in the immune system to combat pathogens.

  • Enzymes: Serve as catalysts in biochemical reactions.

Protein Synthesis

  • Genetic Codes: Found in DNA or RNA, consisting of nucleotide bases that code for amino acids.

  • Triplet Structure: Nucleotide bases are usually arranged in triplets to encode for specific amino acids.

DNA vs. RNA

  • Structure:

    • DNA: Double-stranded helix.

    • RNA: Single-stranded.

  • Components:

    • DNA: Sugar deoxyribose, phosphate, and nucleotide bases (A, T, C, G).

    • RNA: Sugar ribose, phosphate, and nucleotide bases (A, U, C, G).

  • Functions:

    • DNA: Stores genetic information.

    • RNA: Functions in protein synthesis, transcribing and translating genetic information.

Stages of Protein Synthesis

  1. Transcription:

    • Occurs in the nucleus.

    • DNA unzips with the help of RNA polymerase.

    • mRNA is synthesized by copying the DNA template.

    • mRNA exits the nucleus to the cytoplasm.

  2. Translation:

    • mRNA is translated into a polypeptide chain that forms proteins.

    • Involves ribosomes, tRNA, and mRNA codons.

    • Important Codons:

      • Start Codon: AUG (initiates translation).

      • Stop Codons: UAG, UGA, UAA (terminate translation).

Types of RNA

  • Messenger RNA (mRNA): Transcribes DNA into RNA.

  • Ribosomal RNA (rRNA): Binds mRNA and tRNA to facilitate translation.

  • Transfer RNA (tRNA): Translates mRNA codons into the corresponding amino acids.

Detailed Translation Process

  • Initiation: Ribosome assembles around the mRNA, reading the start codon AUG.

  • Elongation: The ribosome moves along mRNA, adding amino acids linked by peptide bonds to form a growing polypeptide chain.

  • Termination: Stops when a stop codon is read, releasing the completed polypeptide.

Summary of Key Points

  • Proteins are essential for cellular structure and function.

  • Protein Synthesis occurs in two main stages: transcription in the nucleus and translation in the cytoplasm.

  • mRNA codons dictate the sequence of amino acids, forming proteins essential for biological processes.