Biology 135A: Gene Expression Overview

Gene Expression Overview

• Biology 135A, Gene Expression (Ch. 17)
• Course Instructor: Rajab
• The process of turning genetic information into functional gene products (proteins)
• Involves two major steps: transcription and translation

Outline of Gene Expression

• Discovery of genes and the genetic code
• Transcription
• RNA modification
• Translation

Introduction to Transcription and Translation

• DNA → RNA → Protein
• Transcription occurs in the nucleus, generating messenger RNA (mRNA)
• mRNA moves to the cytoplasm for translation
• Translation takes place on ribosomes in the cytoplasm, producing polypeptides

The Genetic Code

• Triplet code: 64 codons
• Template and non-template (coding) DNA strands
• mRNA is synthesized and translated in the 5' → 3' direction

Genetic Code Characteristics

• 61 codons for amino acids
• 3 stop codons
• Degenerate code: multiple codons can code for the same amino acid
• Universal code: the same mRNA codons specify the same amino acids in all organisms

Eukaryotic RNA Processing

• Capping and tailing: protection and initiation
• Export from the nucleus
• Splicing: removal of introns, linking exons together
• Spliceosome and spliceosome components for splicing process

Alternative Splicing

• One gene can code for multiple proteins, depending on which exons are included in the final mRNA

Translation-Overview

• Major players: mRNA, tRNA, amino acids, aminoacyl tRNA synthetases, ribosomes, polypeptide
• mRNA is decoded to produce polypeptide chains

tRNA Structure and Function

• Single-stranded
• Acceptor stem for amino acid attachment
• Anticodon for complementary base pairing with mRNA

Aminoacyl-tRNA Synthetases

• Enzymes that attach amino acids to their corresponding tRNA molecules

Ribosomes Structure and Function

• Small and large subunits
• P, A, E sites for tRNA binding and polypeptide synthesis

Translation Initiation

• Initiator tRNA, mRNA binding site, small ribosomal subunit, large ribosomal subunit, start codon

Translation Elongation

• Codon recognition, peptide bond formation, translocation
• mRNA moves in the 5' to 3' direction

Translation Termination

• Stop codons (UAG, UAA, or UGA), release factor
• Polypeptide released from the ribosome

Protein Folding and Targeting

• Proteins fold as they are made
• Signal peptide targets proteins to specific locations
• Signal recognition particle (SRP) recognizes specific signal sequence and halts protein synthesis until the protein reaches the ER
• Translocation complex into the endoplasmic reticulum (ER)
• Polypeptides folded into correct conformation
• Protein destination decided by signal peptide
• Ribosomes either free or bound to ER

Polyribosomes

• Multiple ribosomes translate the same mRNA simultaneously

Coupled Transcription/Translation in Bacteria

• Simultaneous transcription and translation in bacteria occurs in the cytoplasm.
• The ribosomes attach to the mRNA as it is being transcribed.

COVID mRNA Vaccines

• mRNA vaccines contain instructions to make a viral protein
• Cells produce the protein, prompting an immune response
• No exposure to the whole virus, so no symptoms

Explore the essential processes of gene expression in this quiz based on Biology 135A, Chapter 17. Delve into transcription, translation, and the genetic code, and understand how genetic information is transformed into proteins. Test your knowledge on the principles governing these vital biological processes.