Unformatted text preview: From mutation to evolution: How does it all fit together?
Genes sequences of DNA DNA double helix of base pairs Guanine-Cytosine (C-G) Guanine(C Adenine-Thymine (A-T) Adenine(A- DNA Replication and Repair
A cell replicates its DNA before dividing Enzymes unwind the double helix DNA polymerases assemble complementary DNA strands on templates from free nucleotides DNA ligase seals gaps in new DNA strands ONE GENE ONE PROTEIN HYPOTHESIS Each gene codes for one protein (enzyme, structural, immunoglobulin, hormone) Information from genes transcribed into proteins via transcription and translation Alteration of base pair sequence in DNA can result in the production of different proteins Two double-stranded DNA molecules doubleresult One strand of each is new Semiconservative DNA Replication Replication Errors
DNA repair mechanisms fix DNA damaged by chemicals or radiation Proofreading by DNA polymerases corrects most base-pairing errors baseUncorrected errors are mutations Proteins All proteins consist of polypeptide chains A linear sequence of amino acids Each chain corresponds to the nucleotide base sequence of a gene 1 The Path From Genes to Proteins: Transcription
Transcription Enzymes use the base sequence of a gene as a template to make a strand of RNA transfer of information from DNA to RNA via base pair coding inside nucleus messenger RNA (mRNA) carries information to cytoplasm The Path From Genes to Proteins: Translation
Translation Information in the RNA strand is decoded (translated) into a sequence of amino acids
p transfer of information from RNA into proteins via codons of three bases per amino acid (20 amino acids) transfer RNA (tRNA) interprets mRNA and synthesizes proteins from amino acids Transcription: DNA to RNA Three Types of RNA
Messenger RNA (mRNA) Carries protein-building codes from DNA to proteinribosomes Two DNA strands unwind in a specific region Ribosomal RNA (rRNA) Rib l ( RNA) RNA polymerase assembles a strand of RNA Covalently bonds RNA nucleotides (adenine, (adenine, guanine, cytosine, uracil) according to the nucleotide uracil) sequence of the exposed gene Forms ribosomes (where polypeptide chains are assembled) Transfer RNA (tRNA) Delivers amino acids to ribosomes 2 The Genetic Code Codons Messenger RNA (mRNA) carries DNA's proteinprotein-building information to ribosomes for translation mRNA's genetic message is written in codons Sets of three nucleotides along mRNA strand Codons specify different amino acids A few codon signals stop translation SixtySixty-four codons constitute a highly conserved genetic code Genetic Code: RNA Triplets From DNA to Polypeptide 3 tRNA and rRNA Function in Translation
Transfer RNA (tRNA) Anticodon binds to mRNA codon Also binds amino acid specified by codon rRNA
Ribosomal RNA (rRNA) and proteins make up the two subunits of ribosomes Different tRNAs carry different amino acids tRNAs deliver free amino acids to ribosomes during protein synthesis Three Stages of Translation
mRNAmRNA-transcript information directs synthesis of a polypeptide chain during translation Translation proceeds in three stages Initiation Elongation Termination Initiation Elongation Elongation 4 Elongation Termination Mutated Genes and Their Protein Products
Mutations are permanent, small-scale smallchanges in the base sequence of a gene Common mutations include insertions, base-p deletions, deletions, and base-pair substitutions Mutations in genes may result in changes in protein structure, protein function, or both The changes may lead to variation in traits among individuals Mutations
Chromosome breakage can result in mutations during repair or meiosis Deletion chromosome fragment lost during cell division missing certain genes Duplication fragment becomes attached as an extra segment to chromosome Inversion chromosomal fragment reattaches to the original chromosome but in the reverse orientation Gene Mutations Translocation chromosomal fragment joins a nonhomologous chromosome. 5 Deletions and duplications can occur during meiosis affect offspring Duplications and translocations are typically harmful result in cell or embryo death Mutations during mitosis can affect g , g, individual organisms, e.g., cancer Mutagens factors that cause mutations Radiation Chemicals Viruses Metabolic activation, e.g., alcohol From DNA to protein
Essence of gene expression is in protein synthesis Proteomics the study protein production by entire genes or genomes Forms the basis for natural selection e.g., substitution of valine for glutamic acid at amino acid position 6 in hemoglobin results in expression of sickle cell disease How do mutations fit into evolution?
Small, non-lethal mutations in gametes noncan affect gene frequency in a population If these mutations increase fitness of individuals with that mutation then mutation, frequency of the gene in the population increases Microevolution has occurred How does this fit into evolution?
Homeotic genes Are master control genes Regulate many other genes Help direct embryonic development in many organisms Mutations in homeotic genes may result in large differences in organism structure Fly chromosome Mouse chromosomes Homeoboxes Are sequences of nucleotides common in many organisms Can turn groups of genes on and off during development Fruit fly embryo (10 hours) Mouse embryo (12 days) Adult fruit fly Adult mouse 6 ...
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