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The Structure and Function of DNA Chapter 10
Lecture Objectives 1. DNA & RNA: Structure & Function 2. Transcription & Translation
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DNA – Deoxyribonucleic Acid
stores genetic information copied and passed from generation to generation Directs the copying of itself DNA Replication Involved in protein production Transcription Translation
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History of DNA – Watson & Crick
Wanted to know if the genetic material was protein or DNA. 1953 Discovered exact structure of DNA Nucleic Acid Double Helix Made of nucleotides James Watson (left) and Francis Crick
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Rosalind Franklin X-ray images of DNA Figure 10.3
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DNA Structure Double Helix is composed of… Sugar phosphate backbone
5-C sugar = Deoxyribose Phosphate group Nitrogenous bases “rungs” Adenine (A) – larger double ring structure Thymine (T) – smaller single ring structure Guanine (G) – larger double ring structure Cytosine (C) – smaller single ring structure Nucleotide (monomer) = Phosphate + Sugar + Base *See chapter 3 notes for refresher on DNA/RNA structure
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RNA Structure RNA is a single-stranded molecule (most of the time)
RNA contains a ribose sugar (vs. deoxyribose) – has hydroxyl group Hydroxyl groups make RNA less stable than DNA because it is more prone to hydrolysis. The complementary base to adenine in DNA is thymine, whereas in RNA, it is uracil (U).
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Why Uracil in RNA? Energetically less expensive to produce
In DNA, uracil is readily produced by chemical degradation of cytosine Having thymine as the normal base makes detection and repair of such incipient mutations more efficient.
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DNA structure Figure 10.1 Phosphate group Nitrogenous base
Sugar Nitrogenous base (can be A, G, C, or T) DNA nucleotide Thymine (T) DNA double helix Phosphate group Sugar (deoxyribose) DNA nucleotide Polynucleotide Sugar-phosphate backbone Figure 10.1
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Hydrogen bond (b) Atomic model Figure 10.5
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DNA Replication = semiconservative replication
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Two daughter DNA molecules
Figure 10.7 Origin of replication Origin of replication Parental strands Origin of replication Parental strand Daughter strand Bubble Two daughter DNA molecules
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Gene 1 Gene 2 DNA molecule Gene 3 DNA strand TRANSCRIPTION RNA Codon
Figure 10.9 Gene 1 Gene 2 DNA molecule Gene 3 DNA strand TRANSCRIPTION RNA Codon TRANSLATION Polypeptide Amino acid
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1 2 3 RNA polymerase DNA of gene Promoter DNA Initiation Terminator
Figure 10.12 RNA polymerase DNA of gene Promoter DNA 1 Initiation Terminator DNA RNA 2 Elongation RNA nucleotides RNA polymerase 3 Termination Growing RNA Newly made RNA Completed RNA Direction of transcription Template strand of DNA RNA polymerase (a) A close-up view of transcription (b) Transcription of a gene
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Addition of cap and tail Cap RNA transcript with cap and tail
Figure 10.13 Intron Exon Exon DNA Intron Exon Transcription Addition of cap and tail Cap RNA transcript with cap and tail Introns removed Tail Exons spliced together mRNA Coding sequence Nucleus Cytoplasm
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Amino acid attachment site
Figure 10.14 Amino acid attachment site Hydrogen bond RNA polynucleotide chain Anticodon tRNA (simplified representation) tRNA polynucleotide (ribbon model)
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(a) A simplified diagram of a ribosome
Figure 10.15 Next amino acid to be added to polypeptide tRNA binding sites Growing polypeptide P site A site tRNA Large subunit mRNA binding site mRNA Ribosome Small subunit Codons (a) A simplified diagram of a ribosome (b) The “players” of translation
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Met Large ribosomal subunit Initiator tRNA A site P site mRNA
Figure 10.17 Met Large ribosomal subunit Initiator tRNA A site P site mRNA 1 2 Start codon Small ribosomal subunit
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1 ELONGATION 2 3 Amino acid Polypeptide
Figure 10.18 Amino acid Polypeptide tRNA P site Anticodon mRNA A site Codons 1 Codon recognition ELONGATION New peptide bond mRNA movement 2 Peptide bond formation 3 Translocation
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Discussion – small groups
What are the differences between DNA replication, transcription and translation? What is semiconservative replication? Write the complementary base pairs for replicating this segment of DNA AGTCCG Transcribe this section of DNA to RNA ATGCAT Knowing how mutations can be harmful, why is beneficial for multiple codons to code for the same amino acid?
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Helpful review videos DNA synthesis
These vids go into a little more detail than we did in class but are still good for reviewing! Transcription/Translation
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