From Genes to Proteins Biology 2121 Chapter 3
Nucleic Acids Nucleicacids: • Deoxyribonucleic acid (DNA) • Ribonucleic acid (RNA) Monomers: ‘Nucleotide’ • 5-carbon sugar (ribose or deoxyribose) • Phosphate group • Nitrogen base (cytosine, guanine, thymine, cytosine)
DNA Phosphorus • Sugar-Phosphate backbone Nitrogen base pairs with the complementary base Double Helix Basepairingrules: • G pairs with C • T with A
RNA Samestructureexcept: • 5-carbon sugar is ribose • Uracil replaces thymine • Singlestranded, not double stranded Types • mRNA (messenger) • rRNA (ribosomal) • tRNA (transfer)
DNA and Genes Segments of DNA contain genes Genes • information to code for the production of polypeptides • on the surface of the ribosome.
DNA Replication Before a proteins can be built: • DNA must undergo replication • Helicase separates the strands of DNA • DNApolymerase assembles the nucleotides Occurs during Interphase • S-Phase Replicate this strand of DNA • AAGCCGTTA • Animation
Transcription Information from DNA must be transported to the ribosomes DNAunwinds and is copied by RNA • mRNA mRNA moves out of the nucleus (pores) and attaches to the ribosomes Transcribe this stretch of DNA • AAA TGC • Animation • Animation II
mRNA Editing Pre-mRNA will lose non-coding sequences called introns • ‘junk DNA’ Information codes for polypeptide (protein) • Exon
Translation Aminoacids • assembled on the surface of a ribosome Aminoacids • tRNA binds an amino acid • In cytoplasm tRNA bonds with sequences in the mRNA • codons • anticodon on tRNA bonds with codon on mRNA
Translation The codon sequences of mRNA may be translated into amino acids using the genetic code Always read from the mRNA! Translate: • AUG CAC GUU GGU • Animation
Polyribosomes A single stand of mRNA can produce hundreds of the same polypeptide in a short period of time.