Lecture Notes: Transcription and Translation

Overview

• This lecture is the fourth on Chapter 4, focusing on transcription and translation.
• Previously covered DNA replication in labs and a video by the Amoeba Sisters.

Key Concepts

DNA Overview

• Location & Structure:
  • DNA is located in the nucleus, composed of nucleotides.
  • Each nucleotide consists of a deoxyribose sugar, phosphate, and one of four nitrogenous bases (adenine, cytosine, guanine, thymine).
  • DNA is double-stranded, forming a twisted ladder structure with complementary base pairs connected by hydrogen bonds.
  • Humans have 46 DNA molecules (23 pairs), organized into chromatin (non-dividing state) or chromosomes (dividing state).
• Function:
  • DNA contains genes, segments coding for proteins.
  • Genes influence phenotype by coding proteins that affect cellular function.

Transcription Overview

• Purpose:
  • Converts DNA to mRNA inside the nucleus for protein synthesis.
• Process:
  • Initiation: RNA polymerase binds to DNA at the promoter region, unwinding the DNA.
  • Elongation: Free ribonucleotides pair with the DNA template strand; RNA polymerase catalyzes the formation of mRNA.
  • Termination: RNA polymerase reaches the terminal region, releasing the mRNA.
• Pre-mRNA Modifications:
  • Splicing: Removal of introns, keeping exons which code for proteins.
  • Addition of a 5' cap and poly-A tail.

Translation Overview

• Purpose:
  • Converts mRNA to protein in the cytoplasm using ribosomes.
• Components Needed:
  • Ribosomes, mRNA, tRNA, and amino acids.
• Process:
  • Initiation: Formation of a complex between mRNA and ribosomal subunits; initiation tRNA binds at the start codon (AUG).
  • Elongation: tRNAs bring amino acids to match codons on mRNA; peptide bonds form between amino acids, elongating the protein chain.
  • Termination: A stop codon on mRNA signals the end of translation; the newly formed protein is released.

RNA Types

• mRNA (Messenger RNA): Carries genetic information from DNA to ribosomes.
• tRNA (Transfer RNA): Matches mRNA codons with the correct amino acids during protein synthesis.
• rRNA (Ribosomal RNA): Component of ribosomes, catalyzing protein assembly.

Additional Concepts

• Relation of DNA to Proteins and Body Function:
  • DNA indirectly influences metabolic changes and functions through protein synthesis.
  • Proteins created from DNA instructions can become enzymes, hormones, or structural components.

Recommendations

• Further Study:
  • Watch the Crash Course Ed Puzzle video for a deeper understanding of transcription and translation.