Genetics - Central Dogma of Life - Lesson 17 | Don't Memorise

Central Dogma of Life

  • The central dogma describes the flow of genetic information in cells, where DNA is replicated, transcribed to mRNA, and then translated into proteins.

Key Processes

  1. Replication

    • DNA makes copies of itself.

    • Ensures genetic continuity.

    • Replication is semiconservative.

  2. Transcription

    • Definition: Process of synthesizing mRNA from a DNA template.

    • Gene: A segment of DNA that encodes a specific protein.

    • Role of mRNA: Carries the genetic instructions from DNA to the ribosomes.

    • Importance: Essential for protein synthesis; without it, proteins cannot be made.

    • Steps in Transcription:

      • Opening of the DNA double helix.

      • Assembling of transcription enzymes.

      • Gathering of nucleotides to form mRNA.

    • Differences from DNA:

      • mRNA is single-stranded.

      • Thymine (T) is replaced by uracil (U).

Translation

  • Definition: The process where the mRNA code is converted into a protein.

  • Analogy: Similar to translating a language to understand instructions.

  • Process Overview:

    • mRNA translated in the cytoplasm.

    • Ribosomes play a crucial role in translation.

    • Ribosome Structure:

      • Made up of two subunits (small and large).

      • The small subunit binds to the mRNA first, followed by the large subunit.

  • Role of tRNA:

    • Brings amino acids to the ribosome to form the protein chain.

    • Each tRNA has an anticodon that corresponds to the mRNA codon.

Directionality of mRNA

  • 5' and 3' Ends:

    • 5' end has a methyl cap.

    • 3' end has a poly-A tail.

  • Importance of Directionality:

    • Ribosomes recognize and bind to the 5' end for proper translation initiation.

Gene Expression

  • Definition: The combined processes of transcription and translation that convert genes into functional proteins.

  • Eukaryotes vs. Prokaryotes:

    • Eukaryotic cells possess a defined nucleus and undergo complex gene expression processes.

    • Prokaryotic cells lack a membrane-bound nucleus and do not have advanced processes of transcription and translation as seen in eukaryotes.

In summary:

The central dogma describes the flow of genetic information in cells: DNA is replicated, transcribed to mRNA, and then translated into proteins.

Key Processes

  • Replication: DNA makes copies of itself; it is semiconservative, ensuring genetic continuity.

  • Transcription: mRNA is synthesized from a DNA template; essential for protein synthesis. Key steps include opening the DNA, assembling transcription enzymes, and gathering nucleotides. mRNA is single-stranded and replaces thymine (T) with uracil (U).

  • Translation: mRNA code is converted into protein in the cytoplasm, facilitated by ribosomes made of two subunits. tRNA brings amino acids and has anticodons for corresponding mRNA codons. Ribosomes bind to the 5' end of mRNA, marked by a methyl cap and a poly-A tail.

Gene Expression: The processes of transcription and translation convert genes into functional proteins, differing in eukaryotes (with a nucleus) and prokaryotes (without a defined nucleus).