molecular genetics
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Molecular Genetics. Chapter 12 Honors Biology Mrs. Stewart, Rm 806. Experiments Showed that DNA is the Genetic Material. In 1928, Frederick Griffith reported studies on a species of bacterium. He studied two varieties of a bacterium, a pathogenic strand and a variant, that was harmless - PowerPoint PPT PresentationTRANSCRIPT
Molecular Genetics
Chapter 12Honors Biology
Mrs. Stewart, Rm 806
Experiments Showed that DNA is the Genetic Material
• In 1928, Frederick Griffith reported studies on a species of bacterium. He studied two varieties of a bacterium, a pathogenic strand and a variant, that was harmless
• A transformation occurred which means that one strain of bacteria was transformed into another one
Griffith’s Experiment
Transformation
Oswald Avery, Colin MacLeod, Maclyn McCarty
Avery, McCarty, and Macleod• Repeated Griffith’s experiment and
used the heat-killed bacteria and made a juice or extract from it
• Added enzymes to the juice that would break down lipids, proteins, and carbohydrates, and RNA
• Transformation occurred in all of these except when tested using DNA
Avery, McCarty, and MacLeod’s Experiment
Bacteriophage• Is a virus that infects a bacterium• Stages of infection
– Attachment– Entry or injection– Replication– Assembly– Lysing of the cell
Lytic Cycle of Viral Infection
Alfred Hershey and Martha Chase
• Were interested in knowing which part of the virus infected the bacterium
• They labeled two batches of viruses with radioactive sulfur-35 and phosphorus-32
• The protein was labeled with S-35 and the DNA core with P-32
• The viruses’ DNA entered the bacteria, and the protein coat remained outside the bacteria
Hershey and Chase’s Experiment
Base Pairing Charts• DNA to DNA
A-TT-AC-GG-C
DNA to RNAA-UT-AC-GG-C
• RNA to RNAA-U U-AC-G G-C
DNA Replication• The process by which DNA duplicates itself• Unzipping occurs when the hydrogen
bonds between the base pairs are broken and the two strands unwind. Each of the separated strands serves as a template for the attachment of complementary bases
• DNA helicase unzips the original strand• DNA polymerase base pairs free
nucleotides to the original strand• DNA ligase ties the strand back together
Replication
Transcription• RNA Polymerase attaches to special
places on the DNA molecule, separates the two strands, and synthesizes a mRNA
• mRNA is complementary to one of the DNA strands
• The base pairing mechanism ensures that mRNA will be a complementary copy of the DNA strand that serves as its template
• RNA Polymerase unwinds and unzips DNA
• Complementary NTP’s (nucleoside triphosphates) add to template
DNA strand from 5’ to 3’• RNA Polymerase begins
transcribing the DNA at a specific point
• RNA strand is identical to the non-coded DNA (and complementary
to the template strand)
Transcription
Translation (Protein Synthesis)• The two subunits of the ribosome bind to a
molecule of mRNA• The initiator codon, AUG, binds to the first
anticodon of tRNA, signaling the beginning of a polypeptide chain
• Soon the anticodon of another tRNA binds to the next mRNA codon
• This tRNA carries the 2nd amino acid that will be placed into the chain of the polypeptide
Translation Continued• A peptide bond (covalent bond)
forms between two amino acids• This polypeptide chain continues to
grow until the ribosome reaches a stop codon of mRNA
• Once here, the new polypeptide and mRNA are released from the ribosome
So proteins are determined by the chain of amino acids that make them up
But how do our protein makers know which amino acids to add?