Protein Synthesis

Overview of Protein Synthesis

• The process by which cells create proteins based on genetic information stored in DNA.

DNA

• Definition: DNA contains genes, sequences of nucleotide bases.

• Function: Genes code for polypeptides (proteins) that build cells and perform cellular functions.

• Composition of Proteins:

  • Made up of hundreds of amino acids linked together.

  • There are 20 types of amino acids, some of which are essential (cannot be synthesized by the body).

  • Infinite combinations lead to polypeptide chains that can be hundreds or thousands of monomers long.

Amino Acid Structure

• Components: Each amino acid contains:

  • Amine group (NH3)

  • Carboxyl group

Protein Synthesis Initiation

• Challenge: DNA is located in the nucleus while proteins are synthesized in the cytoplasm.

• Solution: RNA (Ribonucleic Acid) serves as the messenger between DNA and ribosomes.

Ribonucleic Acids (RNA)

• Function of RNA: Carries messages from DNA in the nucleus to ribosomes in the cytoplasm.

• Roles:

  • DNA is referred to as the Master Plan.

  • RNA acts as the Blueprint of this plan.

Differences between RNA and DNA

• Sugar Content:

  • RNA contains ribose.

  • DNA contains deoxyribose.

• Nucleotide Bases:

  • RNA contains uracil (U) instead of thymine (T), which is found in DNA.

• Structure:

  • RNA is typically single-stranded.

  • DNA is double-stranded.

Types of RNA

• Messenger RNA (mRNA): Copies DNA’s code and carries genetic information to ribosomes.

• Ribosomal RNA (rRNA): Along with proteins, it comprises ribosomes.

• Transfer RNA (tRNA): Transports amino acids to ribosomes for protein synthesis.

Steps of Protein Synthesis

• Two Main Steps:

  1. Transcription: The process where genetic information from DNA is copied into mRNA.

     • Occurs in the nucleus.

     • mRNA replaces thymine with uracil in its complementary strand.

  2. Translation: The mRNA associates with rRNA at the ribosome, forming a chain of amino acids to synthesize proteins.

     • mRNA is read in segments of three bases known as codons.

     • Each codon pairs with a complementary tRNA’s anticodon to add specific amino acids, creating a polypeptide chain.

The Central Dogma of Molecular Biology

• Definition: The flow of genetic information from DNA to RNA to proteins.

• Summary of Events:

  1. DNA in the nucleus serves as a template.

  2. mRNA is processed and then exits the nucleus.

  3. mRNA associates with ribosomes in the cytoplasm to initiate translation.

  4. tRNA brings specific amino acids based on mRNA codons and the corresponding anticodons.

  5. A peptide chain is formed, ultimately folding into functional proteins.

Codon Chart Reference

• Function: Used to determine which amino acids correspond to specific codons.

• Example:

  • UUC codes for Phenylalanine (Phe/F).

  • AUG is the start codon, coding for Methionine (Met/M).

  • Various combinations lead to specific amino acids essential for building proteins and ultimately determining organism characteristics.