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Ch 10 Structure of Genetic Material Inheritance • To be heritable • The genetic material must be able to copy itself. • The genetic material must be able to direct the expression of an organisms phenotype. • The genetic material must generate variation in some manner. DNA & RNA Sugar-phosphate backbone Phosphate group A C Nitrogenous base A Sugar DNA nucleotide Thymine (T) C Nitrogenous base (A, G, C, or T) Phosphate group O H3C C O T T O P O CH2 O– G G C H C N N C O C H H C H C C H O H Sugar (deoxyribose) T T DNA nucleotide DNA polynucleotide H O DNA H O H3C H C C C N N C H H H O N C C C N H H N C H O H H Thymine (T) N C N C C N C N H O N C H H H Twist N C C C N N C Guanine (G) Purines Pyrimidines C H Adenine (A) Cytosine (C) N H N H H Base Pairing RNA Key Hydrogen atom Carbon atom Nitrogen atom Oxygen atom Phosphorus atom DNA Replication • Semi conservative model Unwinding the Helix Replication Replication Replication Replication The genetic code Transcription RNA nucleotides RNA polymerase T C C A A U C C A T A G G T Direction of transcription Figure 10.9A Newly made RNA A T T A Template Strand of DNA Transcription • Initiation • Elongation • Termination Introns Exon Intron Exon Intron Exon DNA Transcription Addition of cap and tail Cap RNA transcript with cap and tail Introns removed Tail Exons spliced together mRNA Coding sequence Nucleus Cytoplasm Figure 10.10 Proteins synthesized at ribosomes tRNA-binding sites Large subunit Next amino acid to be added to polypeptide Growing polypeptide tRNA mRNAbinding site mRNA Small subunit Codons Figure 10.12B, C Initiation Codon Start of genetic message End Figure 10.13A mRNA mRNA, a specific tRNA, and the ribosome subunits assemble during initiation Met Met Large ribosomal subunit Initiator tRNA P site U A C A U G U A C AUG Start codon 1 mRNA Figure 10.13B A site Small ribosomal subunit 2 Elongation So what is all of the noncoding “junk” in the genome? • Now that the complete sequence of the human genome is available we know what makes up most of the 98.5% that does not code for proteins, rRNAs, or tRNAs Exons (regions of genes coding for protein, rRNA, tRNA) (1.5%) Repetitive DNA that includes transposable elements and related sequences (44%) Figure 19.14 Serial repeats Alu elements (10%) Simple sequence DNA (3%) Repetitive DNA unrelated to transposable elements (about 15%) Introns and regulatory sequences (24%) Unique noncoding DNA (15%) Large-segment duplications (5-6%) Inhibitory RNA Bacteria • Bacteria replicate DNA and use binary fission to reproduce – How to they produce new gene combinations? Bacteria DNA enters cell • Transformation Fragment of DNA from another bacterial cell Bacterial chromosome (DNA) • Transduction Phage Fragment of DNA from another bacterial cell (former phage host) Bacteria Mating bridge • Conjugation Sex pili Donor cell (“male”) Recipient cell (“female”) Mutations – Changes in the DNA base sequence – Substituting, inserting, or deleting nucleotides alters a gene with varying effects on the organism The similarity in the amino acid sequences of the various globin proteins supports this model of gene duplication and mutation Table 19.1 Evolution of Genes with Novel Functions • The copies of some duplicated genes have diverged so much during evolutionary time that the functions of their encoded proteins are now substantially different • A particular exon within a gene could be duplicated on one chromosome and deleted from the homologous chromosome In exon shuffling errors in meiotic recombination lead to the occasional mixing and matching of different exons either within a gene or between two nonallelic genes EGF EGF EGF EGF Epidermal growth factor gene with multiple EGF exons (green) F F F Fibronectin gene with multiple “finger” exons (orange) F Exon shuffling F Exon duplication EGF K Plasminogen gene with a “kfingle” exon (blue) Figure 19.20 Portions of ancestral genes Exon shuffling TPA gene as it exists today K K