Protein Production

Overview of Protein Production

  • The process of protein production follows the Central Dogma of Molecular Biology which involves DNA, RNA, and proteins.

  • Major organelles involved in protein production include:

    • Nucleus: site of transcription where DNA is used to create mRNA.

    • Ribosomes: responsible for translation, synthesizing proteins from mRNA.

    • Rough Endoplasmic Reticulum (rER): provides a site for protein synthesis and initial processing.

    • Golgi Apparatus: final processing, sorting, and packaging of proteins.

    • Cytoskeleton: aids in the transport of vesicles containing proteins.

Fates of Proteins After Production

  • Proteins have two main fates post-production:

    1. Execute functions within the cell.

    2. Be secreted outside the cell or incorporated into the cell membrane.

Differences Between Transcription and Translation

  • Transcription (Tc): occurs in the nucleus where DNA is transcribed into mRNA.

  • Translation (TL): occurs at the ribosome where mRNA is translated into a polypeptide chain (protein).

Monomers Involved

  • Monomers of Biological Macromolecules:

    • DNA and RNA: nucleic acids (nucleotide monomers).

    • Proteins: composed of about 20 different amino acids.

Why mRNA is Made

  • mRNA is synthesized to carry genetic information from DNA to the ribosomes because:

    • DNA cannot leave the nucleus without risking damage or alteration.

    • mRNA serves as a temporary blueprint for protein synthesis.

Protein Secretion

  • The term protein secretion refers to the process where proteins are transported out of the cell to serve various functions in different locations.

Characteristics of Proteins

  • Proteins make up 40% of the body's dry weight.

  • Different types of proteins and their functions:

    • Contractile Proteins: e.g., actin and myosin.

    • Structural Proteins: e.g., collagen found in skin and bones.

    • Signaling Proteins: e.g., hormones.

    • Defense Proteins: e.g., antibodies that protect the immune system.

Overview of Transcription and Translation Steps

  1. Transcription:

    • Occurs in the nucleus to produce pre-mRNA.

    • Pre-mRNA undergoes processing to remove introns and add a 5' cap and poly-A tail.

  2. Translation:

    • Processed mRNA exits the nucleus via nuclear pore complexes to reach the cytoplasm.

    • mRNA binds to the small subunit of ribosomes.

    • Translation occurs on the rough ER:

      • The nascent protein enters the lumen of the rough ER.

      • Post-translational modifications take place.

    • Proteins are loaded into vesicles and transported to the Golgi Apparatus.

  3. Golgi Processing:

    • Proteins arrive at the cis face, undergo additional modification, and are sorted.

    • Modified proteins are packaged into vesicles and released from the trans face of the Golgi for transport to their final destination.

Summary of Transport and Modification

  • Proteins destined for lysosomes or secretion undergo specialized processing.

  • The transport of vesicles along the cytoskeleton ensures proteins reach their required locations.

  • Throughout the process, the integrity of DNA is maintained, preventing permanent damage, and ensuring efficient protein production.