Lecture 11 Objectives genomics Define genetics genome chromosome gene genetic code genotype phenotype and Genetics The study of what genes are how they carry information how information is expressed and how genes are replicated Chromosome carries hereditary information in the form of genes Genome All of the genetic material in a cell Gene A segment of DNA that encodes a functional product usually a protein Genetic code sequence of nucleotides in DNA or RNA that determines the specific amino acid sequence in the synthesis of proteins It is the biochemical basis of heredity and nearly universal in all organisms Genotype The genes of an organism Phenotype Expression of the genes Genomics The molecular study of genomes Describe how DNA serves as genetic information Segments that carry genetic information genes ACGU in messenger RNA consists of two long polymers nucleotides with backbones sugars and phosphate joined by ester bonds Strands run in opposite directions anti o bridge the four letter genetic code parallel Attached to sugar are bases It is the sequence of these four bases along the backbone that encodes information This information is read using the genetic code specifies the sequence of the amino acids within proteins Code is read by copying stretches of DNA into the related nucleic acid RNA in a process called transcription mRNA Within cells DNA is organized into long structures called chromosomes During cell division these chromosomes are duplicated in the process of DNA replication Describe functions of mRNA rRNA and tRNA mRNA mRNA is transcribed from a DNA template and carries coding information to the sites of protein synthesis the ribosomes is translated in codons three nucleotides Translation of mRNA begins at the start codon AUG Translation ends at a stop codon UAA UAG UGA rRNA Ribosomal RNA provides a mechanism for decoding mRNA into amino acids and interacts with tRNAs during translation by providing peptidyl transferase activity The tRNAs bring the necessary amino acids corresponding to the appropriate mRNA codon tRNA used in biology twith the twenty letter code of amino acids in proteins One end of the tRNA carries the genetic code in a three nucleotide sequence called the anticodon The anticodon forms three base pairs with a codon in mRNA during protein biosynthesis Describe DNA replication RNA transcription and protein translation DNA replication It is a semi conservative it would produce two copies that each contained one of the original strands and one new strand of DNA Its copied via DNA polymerase in the 5 3 direction initiated by a RNA primer Leading strand is continuous and lagging strand is discontinuous RNA primers are removed and Okazaki fragments are joined by a DNA polymerase and DNA ligase Okazaki fragments are short molecules of single stranded DNA that are formed on the lagging strand during DNA replication 1 Enzymes unwind at parental double helix 2 Proteins stabilize the unwound parental DNA 3 The leading strand is synthesized continuously by DNA polymerase 4 Lagging strand is synthesizes discontinuously RNA polymerase synthesizes a short RNA primer which is then extended by DNA polymerase 5 DNA polymerase digest RNA primer and replaces it with DNA 6 DNA ligase joins the discontinuous fragments of lagging strand synthesis of complementary strand of RNA from DNA template A RNA transcription strand of mRNA is synthesized using specific gene as template RNA polymerase binds to DNA at promoter 1 strand serves as template for RNA synthesis for given gene Polymerase assembles free nucleotides into new chain using complementary base pairs RNA moves along DNA and continues until RNA polymerase reaches terminator RNA polymerase and new mRNA are released from DNA Protein translation mRNA begins at the start codon AUG Translation ends at a stop codon UAA UAG UGA mRNA is translated in codons three nucleotides Translation of 1 Components needed to be translated come together 2 On ribosome tRNA carrying 1st amino acid is paired w the START CODON on the mRNA tRNA carrying 2nd amino acid approaches 3 P site where the 1st tRNA sits on ribosome Next to it is called the A site where the 2nd codon of mRNA pairs w a tRNA carrying the 2nd Amino Acid 4 1st amino acid joins 2nd by peptide bond First tRNA is released 5 Ribosome moves along mRNA until 2nd tRNA is in P site 6 Ribosome continues to move along mRNA and new amino acids are added to polypeptide 7 Ribosome reaches STOP codon polypeptide is released 8 Finally last tRNA is released ribosome comes apart Released polypeptide forms new protein Explain the regulation of gene expression in bacteria by operon Operon is a functioning unit of genomic DNA containing a cluster of genes under the control of a single regulatory signal or promoter Promoter sequence provides a site for RNA polymerase to bind and initiate transcription Close to the promoter lies a section of DNA called an operator The operon may also contain regulatory genes repressor gene Control can be positive activator protein or negative repressor protein Positive control an activator protein stimulates transcription by binding to DNA Negative control binding of a repressor to the operator to prevent transcription Classify mutations by type and describe how mutations are prevented and repaired Base substitution point mutation Change in one base Mutations may be neutral beneficial or harmful Missense mutation Change in one base Nonsense mutation Results in a nonsense codon Nucleotide excision repairs mutations Frameshift mutation Insertion or deletion of one or more nucleotide pairs Define mutagen Mutagen agent that causes mutations Describe the purpose of and outline the procedure for the Ames test Ames test is a biological assay to assess the mutagenic potential of chemical compounds A positive test indicates that the chemical is mutagenic and therefore may act as a carcinogen Differentiate between horizontal and vertical gene transfer Describe plasmids and transposons Conjugative plasmid Carries genes for sex pili and transfer of the plasmid Plasmids Dissimilation plasmids Encode enzymes for catabolism of unusual compounds R factors Encode antibiotic resistance Transposons Segments of DNA that can move from one region of DNA to another Contain insertion sequences for cutting and resealing DNA transposase Complex transposons carry other genes Lecture 12 Objectives Define taxonomy scientific name and the three domain system Taxonomy The science of
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