BIOL110s05-24 - BIOL 110: Principles of Biology Spring 2005...

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Unformatted text preview: BIOL 110: Principles of Biology Spring 2005 Lecture 24, W 3/30/05 http://www.smccd.net/accounts/staplesn/biol110/ • ONLINE Quizzes (bi-weekly) from now on! – Link TO QUIZZES: – (Cañada College I.D. for login and password) (Cañ http://smcwebtest.smccd.net/accounts/staplesn/index.tpx http://smcwebtest.smccd.net/accounts/staplesn/index.tpx – Time-limited (so study well first!); Time– ~ 30 minutes to complete; once only. – You must take Quiz 4 by TONIGHT!! • Midterm 2 back Fri. • Journal Reports #1 Due this week!! REVIEW: • Ch. 9: DNA Structure & Function – What is the Hereditary Material – What is the Structure of DNA? TODAY: • Ch. 9: DNA Structure & Function – How is DNA copied/replicated? – How are organisms Cloned? • Ch. 10: From DNA to Proteins – How does Genotype become Phenotype? • “Gene Expression” = transcription, translation Expression” 1 Watson-Crick Model 1. DNA consists of two two nucleotide strands 2. Strands run in opposite opposite directions 3. Strands are held together by hydrogen bonds between hydrogen bases 4. A binds with T (2 H-bonds) and C with G (3 H-bonds) 5. Molecule is a double helix double • A=T • G≡C IV. DNA Structure Helps Explain How it Duplicates • DNA is two nucleotide strands held together by hydrogen bonds • Hydrogen bonds between two strands are easily broken (few at a time) • Each single strand then serves as template template for new strand 2 DNA Replication: “SemiConservative” • Each parent strand remains intact • Every DNA molecule is half “old” and half “new” • Enzyme: “DNA Polymerase” Polymerase new old old new Base Pairing During Replication • Each old strand serves as the template for template complementary new strand complementary – A pairs only with T • T pairs only with A – G pairs only with C • C pairs only with G 3 V. Cloning • Making a genetically identical copy of an individual • Researchers have been creating clones for decades • These clones were created by embryo splitting – (Tetra the monkey clone) Dolly: Cloned from an Adult Cell • Showed that differentiated cells could be used to create clones • Sheep udder cell was combined with enucleated egg cell • Dolly is genetically identical to the sheep that donated the udder cell 4 Micropipette about to penetrate unfertilized sheep egg to remove nucleus Figure 9.9(1) Page 144 Egg has been emptied of its nucleus, which holds DNA DNA/Nucleus from donor cell is about to enter the enucleated egg. A spark will stimulate cell divisions. Goodbye, Dolly • • • • • First mammal to be cloned from an adult cell Nuclear transfer technique DNA in adult cell is “reset” Many clones have abnormalities Dolly had an early onset of arthritis, died of an infectious disease – 1997-2003 5 From DNA to Proteins Chapter 10 *** Steps from DNA to Proteins Same two steps produce ALL proteins: 1) DNA is transcribed to form RNA transcribed – Occurs in the nucleus – RNA moves into cytoplasm 2) RNA is translated to form polypeptide translated chains, which fold to form proteins Central Dogma of Molecular Genetics transcription DNA RNA translation Protein 6 I. Three Classes of RNAs • Messenger RNA – Carries protein-building instruction • Ribosomal RNA – Major component of ribosomes • Transfer RNA – Delivers amino acids to ribosomes A Nucleotide Subunit of RNA RNA (vs. DNA): 1. Uracil, not Thymine (AUGC) 2. Ribose sugar 3. 2’ hydroxyl (oxygen) present 4. Chemically unstable (labile) 5. Usually single-stranded single6. Complex folding upon itself (internal hydrogen bonds) uracil (base) phosphate group sugar (ribose) 7 Base Pairing During Transcription • A new RNA strand can be put together on a DNA region according to base-pairing rules • As in DNA, C pairs with G • Uracil (U) pairs with adenine (A) Transcription & DNA Replication • Like DNA replication: – Nucleotides added in 5’ to 3’ direction • (Phosphate at 5’ end; new nucleotides added on at 3’ 5’ 3’ hydroxyl end) • Unlike DNA replication: – Only small stretch of DNA is template – RNA polymerase catalyzes nucleotide addition – Product is a single strand of RNA 8 Promoter • A base sequence in the DNA that signals the start of a gene – The “docking site” for RNA Polymerase RNA – Shows enzyme where to go, and where to start transcription. • For transcription to occur, RNA polymerase must first bind to a promoter Gene Transcription Gene transcribed DNA winds up again DNA to be transcribed unwinds mRNA transcript RNA polymerase • Only a short stretch of DNA template open at a time. 9 Adding Nucleotides 5’ growing RNA transcript 3’ 3’ direction of transcription 5’ G C A C C A A T A A C C A T A base sequence of gene region C G U G G U U A mRNA U U G G U A U II. Genetic Code 1. Set of 64 base triplets triplets 2. Codons – Nucleotide bases read in blocks of three – 3-nucleotide “words” = code for a specific specific amino acid! 3. 61 specify amino acids – 1 = START translation (AUG = methionine) START (AUG 4. 3 STOP translation STOP 10 tRNA Structure • “Reads” mRNA nucleotide sequence • Brings in the right amino acid for each 3-nucleotide “word” (CODON) • Ribosome takes the amino acid from the tRNA, and transfers it to the growing polypeptide chain • Voila!!!..... Protein!!! codon in mRNA anticodon in tRNA amino acid tRNA molecule’s attachment site for amino acid OH Ribosomes tunnel small ribosomal subunit large ribosomal subunit intact ribosome The Protein Manufacturing Machines!! • Read the mRNA message • TRANSLATE the nucleotide words (codons) into the language (codons) of amino acids Polypeptide produced!! Polypeptide 11 TRANSCRIPTION Unwinding of gene regions of a DNA molecule Overview Pre mRNA Transcript Processing mRNA rRNA protein subunits ribosomal subunits tRNA Mature mRNA transcripts mature tRNA TRANSLATION Convergence of RNAs Cytoplasmic pools of amino acids, tRNAs, and ribosomal subunits Synthesis of a polypetide chain at binding sites for mRNA and tRNA on the surface of an intact ribosome FINAL PROTEIN Destined for use in cell or for transport III. Mutations: Hereditable changes in DNA sequence A. Effect of Base-Pair Substitution original base triplet in a DNA strand a base substitution within the triplet (red) As DNA is replicated, proofreading enzymes detect the mistake and make a substitution for it: POSSIBLE OUTCOMES: OR One DNA molecule carries the original, unmutated sequence The other DNA molecule carries a gene mutation Change amino acid, or put in early STOP? 12 ...
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