Structure of deoxyribose

1
Structure of deoxyribose

• The carbons are numbered 1 to 5
• The phosphate is linked to the sugar between the
  3 and 5 carbons
• Sugar phosphate backbone

2
5 and 3 ends of DNA

• The 5 end has the free phosphate (P)
• The 3 end is the free OH end
• The strands are anti-parallel

3
Direction of replication

• DNA replication proceeds 5 ? 3
• A free 3 end is needed to add another nucleotide

4
DNA Replication

• 1. The molecule unzips to expose free ends. One
  is the 3 end the other is the 5 end
• 2. DNA synthesis can now begin
• 3. Synthesis on the free 3 end is CONTINUOUS,
  this is called the LEADING STRAND
• 4. Synthesis on the free 5 end is DISCONTINUOUS,
  this is the LAGGING STRAND
• 5. The enzyme that is responsible for DNA
  synthesis on BOTH strands is DNA polymerase BUT
  this enzyme requires a free 3 end at which it
  can add new bases!

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DNA Replication(continued)

• 6. Synthesis of the lagging strand is in short
  segments of DNA, about 1000 bases
• 7. These short segments are called OKAZAKI
  FRAGMENTS
• 8. The enzyme DNA ligase seals the gaps between
  these fragments to produce a gaps free
  discontinuous strand

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(No Transcript)
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Directions of replication
8
RNA compared to DNA
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Types of RNA

• 1. Messenger RNA (mRNA)
• 2. Ribosomal RNA (rRNA)
• 3. Transfer RNA (tRNA)

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Transcription

• 1. This is the process of making a copy of a gene
  (sequence of DNA that codes for a protein or
  functional product)
• 2. The enzyme responsible for this process is RNA
  POLYMERASE
• 3. Copies the gene is a 5 ? 3 direction
• 4. Gene transcription begins at a site called the
  PROMOTER and ends at another site called the
  TERMINATOR

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Transcription(making mRNA)
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Example of transcription and translation

• 3 TACAGAGTACGAACT 5 (antisense) this is copied
• 5 ATGTCTCATGCTTGA 3 (sense)
• ? ? ?
• 5 AUGUCUCAUGCUUGA 3 mRNA (gene copy)
• 3 bases codon amino acid
• Met-ser-his-ala-stop Protein
• 3strand of DNA is the TEMPLATE or ANTISENSE
  strand THE STRAND THAT IS COPIED!
• 5 strand of DNA is the INFORMATIONAL or SENSE
  strand

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Transcription
(s
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Another example of transcription

• 3 GGGGGGGGGGGGGGG 5 anti-sense
• 5 CCCCCCCCCCCCCCC 3 sense
• ?Transcription
  (anti-sense)
• 5 CCCCCCCCCCCCCCC 3
• ?Translation
• Pro-pro-pro-pro-pro-pro-
• Remember-copy the 3 strand and by the rules of
• base paring you get the sense strand sequence!

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Genetic code
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Protein Synthesis(Translation)
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Translation
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Translation
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Translation
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Translation
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Transfer RNA
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Exons and Introns

• 1. These are terms unique to eukaryotic cells
• 2. EXONS are information regions in DNA that must
  be expressed
• 3. INTRONS are non-coding regions in DNA that are
  not expressed

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RNA processing in eukaryotic cells
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Control of Gene Expression

• 1. Control is at the level of TRANSCRIPTION
• 2. Genes that are NOT needed are NOT expressed,
  i.e., the gene is not transcribed
• 3. Many genes are always expressed because the
  cell always needs the gene product
• 4. Such genes are CONSTITUTIVE

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Genetic Control

• 1. REPRESSION inhibition of gene expression
• 2. INDUCTION switching on gene expression

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Model of Inducible Gene System

• Lactose operon
• OPERON is defined as a set of operator and
  promoter sites and the genes that they control
• Described in E. coli by Francois Jacob and
  Jacques Monod
• Genetic ON/OFF switch

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Operon
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Off and On of the lac operon
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Tryptophan operon(repressible operon)
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Mutations

• Change in the base sequence of DNA
• May or may not have an effect on the organism
• The potential magnitude of the change depends on
  the gene affected

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BASE SUBSTITUTION

• TACTTCAAACCGATT
• AUGAAGUUUGGCUAA
• Met-lys-phe-gly-stop

• TACTTCAAATCGATT
• AUGAAGUUUAGCUAA
• Met-lys-phe-ser-stop
• MISSENSE MUTATION

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BASE SUBSTITUTION

• TACTTCAAACCGATT
• AUGAAGUUUGGCUAA
• Met-lys-phe-gly-stop

• TACATCAAACCGATT
• AUGUAGUUUGGCUAA
• Met-STOP
• NONSENSE MUTATION

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BASE DELETION

• TACTTCAAACCGATT
• AUGAAGUUUGGCUAA
• Met-lys-phe-gly-stop

• TACTTCAACCGATT
• AUGAAGUUGGCUAA.
• Met-lys-leu-ala.
• FRAMESHIFT MUTATION

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Bacterial SEX!!!

• 1. Transformation
• 2. Conjugation
• 3. Transduction

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Transformation(Griffith 1928)
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Transformation
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Conjugation

• Cell to cell contact required
• Plasmid exchange through the sex pilus
• Plasmid is called the F factor

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Conjugation
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Hfr cell
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Hfr x F- cell
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Transduction