how do we know dna is the genetic material?
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How do we know DNA is the genetic material?. Griffith and later Avery 2 strains of pneumonia causing bacteria: rough and smooth TRANSFORMATION. How do we know DNA is the genetic material?. Hershey and Chase Bacteria and bacteriophages (viruses) Radioactive sulfur and phosphorus. - PowerPoint PPT PresentationTRANSCRIPT
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How do we know DNA is the genetic material?
• Griffith and later Avery• 2 strains of pneumonia causing bacteria:
rough and smooth• TRANSFORMATION
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How do we know DNA is the genetic material?
• Hershey and Chase• Bacteria and bacteriophages (viruses)• Radioactive sulfur and phosphorus
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How do we know the structure of DNA?
• Chargaff’s rules – BASE-PAIRING RULES
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How do we know the structure of DNA?
• Franklin• X-ray shows shape is two twisted strands
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How do we know the structure of DNA?
• Watson and Crick• Build model of DOUBLE HELIX• Where are the bases?• Where are the sugars?• Where are the phosphates?
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Structure of DNA• Polymer of nucleotides (monomer)• Nucleotide – sugar + phosphate + base– Sugar – deoxyribose– Bases – purines – 2 rings – adenine and guanine pyrimidines – 1 ring – cytosine and thymine
• Base-pairing rules – purine to pyrimidine! A bonds to T G bonds to C
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Structure of DNA• Double helix– Double – 2 strands– Helix – a spiral
• Looks somewhat like a twisted ladder– Sides of ladder – sugar and phosphate– Steps of ladder – nitrogenous bases
• Nucleotides are held to each other by covalent bonds
• Bases are held together by hydrogen bonds
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DNA REPLICATION• Precedes cell division: mitosis, meiosis, binary
fission– Occurs during interphase
• Replication – DNA copies DNA• CAN YOU SEQUENCE THE STEPS?• CAN YOU WRITE THE STEPS?• EACH NEW DNA MOLECULE CONSISTS OF ONE
OLD STRAND AND ONE NEW STRAND
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PROTEIN SYNTHESIS• How does cell use DNA code to build protein?• 2 processes: TRANSCRIPTION and TRANSLATION
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PROTEIN SYNTHESIS• Requires the help of many enzymes and RNA• RNA– Single stranded– Sugar : ribose– Nitrogenous bases: adenine, guanine, cytosine, URACIL – What are the base pairing rules?
• 3 types involved in protein synthesis1. Messenger RNA – mRNA2. Ribosomal RNA – rRNA3. Transfer RNA - tRNA
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TRANSCRIPTION• Occurs in nucleus of eukaryotes – Where does it
occur in prokaryotes?• DNA is copied by messenger RNA• How does mRNA know where to begin copying?• Can you sequence the steps?• Can you write the steps?
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TRANSLATION• Occurs in cytoplasm at the ribosome• messenger RNA is read (decoded) by the ribosome;
transfer RNA supplies the amino acids to build the protein (polypeptide)
• How does the ribosome know where the beginning and end of the message are?
• Can you sequence the steps?• Can you write the steps?• Do you know the base pairing rules?• Can you use a codon chart to determine the order of
the amino acids?
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MUTATION• What is a mutation?• What is the difference between a point mutation
and a chromosome mutation?• Can you recognize and explain the effects of the
following point mutations?– Substitution– Frame shift (due to additon or deletion of a base)
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MUTATION• Can you recognize and explain the effects of the
following chromosome mutations?– Deletion– Inversion– Translocation– Duplication
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What is the significance of mutations?• Neutral• Disrupt cell function• Source of genetic variation – source of NEW
genetic information• Exploited by human beings to improve or
develop new plants and animals.– polyploidy
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Chromosome Structure
• Can you distinguish between chromatin and chromosome? When is each seen in the cell?
• What are histones and nucleosomes?• How are prokaryotic chromosomes different
from eukaryotic chromosomes?• What are genes? Where are they located?
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Editing of mRNA
• In eukaryotes the mRNA copy of DNA must be edited before it leaves the nucleus?
• Why?• What is removed from the mRNA? Introns or
Exons?
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What do genes code for? What do these molecules do in cells?