Genetics- Chapter 14 Translation and Proteins

Chapter 14: Translation and Proteins

Learning Objectives

• Translation Basics

  • Understand how mRNA is translated by ribosomes and tRNAs.

  • Explore the steps involved in mRNA translation.

• Structure and Function of the Ribosome

  • Investigate the structure of bacterial and eukaryotic ribosomes.

• Insights from Metabolic Studies

  • Examine how studies on inborn errors of metabolism provide insights into protein function in heredity.

• Gene-Protein Relationships

  • Discuss how Neurospora studies led to the One-Gene: One-Enzyme hypothesis.

• Genetic Variability and Protein Structure

  • Explore how variations in protein structure contribute to biological diversity.

• Posttranslational Modifications

  • Understand how posttranslational modifications affect protein functionality.

• Roles of Proteins

  • Discover the various functions of proteins within biological systems.

14.1 Translation of mRNA Depends on Ribosomes and Transfer RNAs

• Translation

  • Biological process that polymerizes amino acids into polypeptide chains.

  • Requires: amino acids, mRNA, ribosomes, and tRNA.

• Transfer RNA (tRNA)

  • Adapts genetic information from mRNA to corresponding amino acids.

  • Each tRNA has an anticodon complementary to mRNA codons.

• Ribosomes

  • Composed of ribosomal RNA (rRNA) and ribosomal proteins.

  • Prokaryotic ribosomes: 70S; Eukaryotic ribosomes: 80S.

14.2 Steps of Translation

• Initiation

  • Involves mRNA, ribosomal subunits, initiator tRNA, GTP, and initiation factors.

  • Forms the initiation complex with tRNA binding to the start codon (AUG).

• Elongation

  • Ribosomes scan mRNA, adding amino acids to the polypeptide chain.

  • Catalyzed by elongation factors like EF-Tu and EF-G.

• Termination

  • Signaled by stop codons (UAG, UAA, UGA).

  • Release factors stimulate polypeptide release from tRNA.

• Polyribosomes

  • Multiple ribosomes translating one mRNA simultaneously.

14.4 Translation Is More Complex in Eukaryotes

• Eukaryotic translation involves more factors for initiation, elongation, and termination than in bacteria.

• mRNA processing involves a 5' cap and poly-A tail for stability.

• The Kozak sequence enhances translation efficiency.

14.8 Variation in Protein Structure Provides the Basis of Biological Diversity

• Proteins vs. Polypeptides

  • Polypeptides are amino acid chains; proteins are folded polypeptides.

• Amino Acid Classification

  • Amino acids categorized as nonpolar, polar, positively/negatively charged based on R groups.

• Peptide Bonds

  • Formed via dehydration reaction between amino acids; dipeptides consist of two amino acids.

• Protein Structures

  • Levels of structures: Primary (amino acid sequence), Secondary (alpha helices and beta sheets), Tertiary (3D conformation), Quaternary (multiple polypeptide chains).

14.9 Posttranslational Modification Alters the Final Protein Product

• Posttranslational modifications crucial to functional capabilities of proteins, including:

  • Modifications of N-terminus amino acids,

  • Trimming polypeptides and complexing with metals.

14.10 Proteins Perform Many Diverse Roles

• Proteins, as the most diverse macromolecules, perform crucial functions:

  • Transport Proteins: Hemoglobin and myoglobin for oxygen transport.

  • Structural Proteins: Collagen, keratin for tissue structure.

  • Contractile Proteins: Actin and myosin in muscle.

  • Enzymatic Proteins: Catalyze biochemical reactions, essential for metabolism.