Transcript Ch_6
Environmental Biology for Engineers and Scientists D.A. Vaccari, P.F. Strom, and J.E. Alleman © John Wiley & Sons, 2005 Chapter 6 - Genetics Figure 6-1. Crossbreeding between two pea plants homozygous for seed shape. True-breeding (homozygous) parent generation F1 generation (all heterozygous) Round seeds Wrinkled seeds (RR) (rr) All round seeds (Rr) Self-fertilization F2 generation Round seeds Round seeds Round seeds Wrinkled seeds (RR) (Rr) (Rr) (rr) Figure 6-3. Cell processes involving genetic material DNA Transcription Replication mRNA DNA DNA Translation Polypeptide Figure 6-4. Schematic of DNA replication. Replication bubble 3’ 5’ Replication fork RNA Primers 3’ 5’ Figure 6-5. (a) Transcription and (b) translation. In transcription, messenger RNA is formed from the DNA template at the chromosome. The mRNA is subsequently is transported to the cytoplasm where it encounters ribosomes and participates in translation. In translation, mRNA is used as a template to produce polypeptides. The numbered arrows indicate the approximate sequence of events. Unzipped DNA double helix AC C A C T A G G A T C C T G T x x G (a) x x x x A T G x x x x T A C C x x x G x x x x x x x x x x x x x x x C UA G G A U C C U G U x TG G T G A T C C T A G G A C A x C A C C A mRNA A U G C G Polypeptide Met tRNA Met Arg Pro (b) Arg Gly 1 Leu Leu 3 Ser Pro Gly 2 3 3 A U G C G A C C A C U A G G A U C C mRNA Ribosome C G A C C A C U A G G A U C C U GU Transcription Messenger RNA is formed from the DNA template. It subsequently is transported to the cytoplasm where it encounters ribosomes and participates in translation. Unzipped DNA double helix AC C A C T A G G A T C C T G T x x G x x x x x x x A T x T A G C C x x G C x UA G G A U C C U G U TG G T G A T C C T A G G A C A x C A C C A U G C G A mRNA x x x x x x x x x x x x x x x x Translation The numbered arrows show the approximate sequence of events in protein synthesis. Polypeptide tRNA Met Arg Met 1 Arg Pro Gly Ser Pro Leu Leu Gly 2 3 3 3 A U G C G A C C A C U A G G A U C C mRNA Ribosome C G A C C A C U A G G A U C C U G U Figure 6-6. Structure of the transfer RNA molecule. [Schaum's Biology] Figure 6-7. Types of point mutations. The sequence is read from left to right, with location of mutations and altered amino acids marked by underscores. Shown are the sequence for the DNA strand that is being expressed, its complementary DNA strand, the messenger RNA formed from the sequence, and the resulting amino acid sequence. NORMAL SEQUENCE Compl-DNA ATG TCC TGT CCA TGG GGA CGA DNA TAC AGG ACA GGT ACC CCT GCT mRNA AUG UCC UGU CCA UGG GGA CGA Amino acid Met Ser Cys Pro Trp Gly Arg BASE-PAIR SUBSTITUTION Compl-DNA ATG TCC TAT CCA TGG GGA CGA DNA TAC AGG ATA GGT ACC CCT GCT mRNA AUG UCC UAU CCA UGG GGA CGA Amino acid Met Ser Tyr Pro Trp Gly Arg BASE-PAIR INSERTION Compl-DNA ATG TCC TGG TCC ATG GGG ACG A DNA TAC AGG ACC AGG TAC CCC TGC T mRNA AUG UCC UGG UCC AUG GGG ACG A Amino acid Met Ser Trp Ser Met Gly Thr BASE-PAIR DELETION Compl-DNA ATG TCC TT_C CAT GGG GAC GA DNA TAC AGG AA_G GTA CCC CTG CT mRNA AUG UCC UU_C CAU GGG GAC GA Amino acid Met Ser Phe His Gly Asp Figure 6-8. Development of DNA probes complementary to part of a gene for a short amino acid sequence. Methionine has only one possible codon, but histidine has two and glycine has four. Thus there are eight possible oligonucleotide combinations for this sequence of amino acids. A mixture of all eight is prepared and the one that is complementary to the gene will selectively bind to it. [Based on Klug] Amino Acid ... met his gly ... Eight candidate oligonucleotides ... AUG CAU GGA ... ... AUG CAU GGT ... ... AUG CAU GGC ... ... AUG CAU GGG ... ... AUG CAC GGA ... ... AUG CAC GGT ... ... AUG CAC GGC ... ... AUG CAC GGG ... Selected oligonucleotide ... AUG CAC GGA ... Complementary gene ... TAC GTG CCT ... Figure 6-9. Phylogenetic tree for some primates. [Based on Klug] The numbers inside the graph show the estimated number of million years ago that the two lines diverged. DT50H 8 7 6 4 5 3 2 0 1 Chimpanzee (Pan troglodytes) 3.3 Pigmy Chimpanzee (Pan paniscus) 8.4 Human (Homo sapiens) 10.7 17 Gorilla (G. gorilla) Orangutan (Pongo pygmaeus) 24 Common Gibbon (Hylobates lar) 10.2 36 Siamang (H. syndactylus) Old World Monkeys (Cercopithecidae) 30 20 Millions of years ago 10 0 Figure 6-10. Types of life cycles in sexual reproduction. [From Raven]