The Genetic Code and Gene Structure

This page delves into the characteristics of the genetic code and the nature of genes, providing essential information for understanding protein synthesis.

The genetic code has several important features:

1. It includes one 3-base start codon and three different 3-base stop codons.
2. Different codons code for different amino acids.
3. It is non-overlapping, meaning each codon contains only 3 bases.
4. It is degenerate, as most amino acids are coded for by more than one codon.

Example: The amino acid proline is coded by four different codons: CCC, CCU, CCA, and CCG.

Vocabulary: Codon - A sequence of three nucleotide bases in mRNA that codes for a specific amino acid or signals the start or stop of protein synthesis.

Genes are fundamental units of heredity and play a crucial role in protein synthesis:

• A gene is a sequence of bases on one strand of a DNA molecule.
• Each amino acid in a protein is coded by a sequence of three bases (codon), known as the triplet code.

Highlight: The triplet code is a key concept in understanding how genetic information is translated into proteins.

The diagram on this page illustrates the translation process, showing how mRNA codons are read by tRNA anticodons, leading to the assembly of amino acids into a polypeptide chain.

Definition: Anticodon - A sequence of three nucleotides on a tRNA molecule that is complementary to a codon on an mRNA molecule.

Transcription and Translation: The Two Stages of Protein Synthesis

Protein synthesis is a fundamental biological process that occurs in two main stages: transcription and translation. This page provides an overview of both stages and their key components.

Transcription is the first stage of protein synthesis, taking place in the nucleus. During this process:

1. DNA uncoils and hydrogen bonds are broken by DNA helicase.
2. One DNA strand, called the antisense strand, serves as a template for mRNA synthesis.
3. Free nucleotides line up on the template strand and are joined by RNA polymerase.
4. The resulting mRNA molecule moves out of the nucleus through nuclear pores.

Vocabulary: Antisense strand - The DNA strand used as a template for mRNA synthesis during transcription.

Translation is the second stage, occurring at ribosomes in the cytoplasm. This process involves:

1. mRNA attaching to ribosomes on the rough endoplasmic reticulum (RER).
2. tRNA molecules, each carrying a specific amino acid, binding to mRNA codons.
3. Amino acids joining together to form a polypeptide chain.
4. The process repeating until a stop codon is reached.

Highlight: Both mRNA and tRNA play crucial roles in translation, with tRNA acting as the "adaptor" molecule that brings amino acids to the ribosome.

Definition: Polypeptide chain - A long, linear sequence of amino acids joined by peptide bonds, forming the primary structure of a protein.