Genetics and Gene Expression Overview

Overview of Genetics

• Genetics is the study of nucleic acids that control hereditary characteristics.

• The two important nucleic acids are:

  • Deoxyribonucleic Acid (DNA): Contains the genetic instructions.

  • Ribonucleic Acid (RNA): Involved in protein synthesis.

• Gene Expression: The process by which information from a gene is used to synthesize proteins that influence inherited traits.

Structure of a Cell and Nucleus

• DNA is located in the nucleus of the cell.

• Genes on DNA contain instructions for making RNA and proteins which determine inherited traits.

• Ribosomes (mainly on the Rough Endoplasmic Reticulum) are responsible for protein synthesis in the cytoplasm.

Transcription Process

• Transcription: The process of copying a gene from DNA into RNA.

  • The DNA does not leave the nucleus.

  • The RNA copy (transcript) leaves the nucleus to be translated into protein.

• RNA polymerase is the enzyme involved in transcription, facilitating complementary base pairing:

  • A pairs with U (in RNA) instead of T (in DNA).

• Steps of Transcription:

  1. Unwind DNA to expose the gene.

  2. Use one strand as a template for RNA production.

  3. Match RNA nucleotides to the exposed DNA bases, forming an RNA strand.

  4. Release the RNA molecule from DNA once finished, allowing DNA strands to reconnect.

Types of RNA Produced

1. Messenger RNA (mRNA): Carries instructions for protein synthesis to ribosomes.

2. Ribosomal RNA (rRNA): Combines with proteins to form ribosomes.

3. Transfer RNA (tRNA): Transports specific amino acids to ribosomes during translation.

mRNA Processing

• In immature mRNA, regions called exons (coding) and introns (non-coding) exist.

• During processing, introns are removed, and exons are spliced together to form mature mRNA that exits the nucleus for translation.

Translation Process

• Translation: The process by which ribosomes synthesize proteins based on the sequence of codons in mRNA.

• Occurs in three stages:

  1. Initiation: Assembly of ribosomal subunits, mRNA, and the first tRNA carrying the first amino acid.

  2. Elongation: Sequential addition of amino acids to the growing polypeptide chain. Guided by tRNA matching codons.

  3. Termination: Release of newly formed protein when a stop codon is reached.

• Genetic Code: The relationship between DNA, mRNA codons, and the corresponding amino acids.

• Codons are sequences of three mRNA nucleotides that signify specific amino acids during protein synthesis.

Codon Examples and Genetic Code

• Start Codon: AUG (methionine).

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

• The genetic code is considered redundant since multiple codons can correspond to the same amino acid due to the use of only 20 amino acids.

Key Relationships in Gene Expression

• DNA sequence → mRNA codons → Amino acids to build proteins.

• A mixture of codons can lead to the production of various proteins from a single gene due to alternative splicing during mRNA processing.

Conclusion and Upcoming Tasks

• Understanding both transcription and translation is crucial for grasping how genetic information is expressed in traits.

• As an exercise, given a DNA sequence, transcribe it to mRNA and then translate that mRNA into the corresponding amino acid sequence.