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CH11 - Nucleic Acid Structure, DNA Replication and Chromosome Structure …

- - - - Blood is found to contain living type S bacteria - Transformation
      - Genetic material had been transferred
        
        capsule-secreting trait
        
        was passed on to their offspring
- - - - Discrete unit of genetic material
        
        made of chromatin
        
        millions of base pairs long
        
        DNA compaction
        
        30-nm fiber asymmetric, 3D zigzag of
        nucleosomes
        
        Radial loop domains
        
        DNA wrapping around histones to form
        nucleosomes
        
        Cell division
        
        Euchromatin not as compact
        
        Heterochromatin much more compact
        
        metaphase
    - - Backbone
        
        formed from
        phosphates and sugars
        
        Phosphodiester bond
        
        phosphate group links
        two sugars
      - written as 5’ –TACG – 3’
    - - DNA
        
        Nucleotides composed of
        three components
        
        .
        
        Pentose sugar
        
        Deoxyribose
        
        DNA - Deoxyribonucleic Acid
        
        Nitrogenous base
        Purines ( double ring) – Adenine (A), Guanine (G)
        Pyrimidines (single Ring)– Cytosine (C), Thymine(T)
        
        Phosphate group
      - RNA
        Formed from nucleotides (A, G, C, U)
        
        Nucleotides composed of
        three components:
        
        Pentose sugar
        
        Ribose
        
        RNA - Ribonucleic Acid
        
        Nitrogenous base
        Purines ( double ring) – Adenine (A), Guanine (G)
        Pyrimidines (single Ring)– Cytosine (C), Uracil(U)
        
        Phosphate group
      - Numbering:
        
        Sugar carbon 1' to 5'
        1' Base
        5' Phosphate
      - Base-pairing
        
        Erwin Chargaff analyzed base composition
        of DNA
        
        Chargaff Rule
        adenine (A) = thymine (T)
        cytosine (C) = guanine (G)
        constant width
    - - Semiconservative Model
        
        1 parental strand and 1 newly made daughter strand
      - Conservative Model
        
        1 double helix with both parental strands and the other with 2 new daughter strands
      - Dispersive Model
        
        DNA strands in which segments of new DNA are interspersed
      - Matthew Meselson and Franklin Stahl experiment of models
        
        light form (14N) and heavy form (15N)
        
        parental strands = 15N
        newly made strands = 14N
        
        Semiconservative DNA replication
      - Molecular Mechanism
        of DNA Replication
        
        Origin of replication/ Replication Bubble forms 2 replication forks
        
        Bacteria -single origin
        Eukaryotes -multiple origins
        
        Single origin of replication in bacteria
        
        origin / ending at opposite ends
        
        Multiple origins of replication
        in eukaryotes
        
        steps for DNA replication
        
        DNA helicase to separate strands
        
        Primer is needed to start DNA synthesis which begins in direction of replication fork in leading strand. in the lagging strand the first Okazaki Fragment is made in the opposite direction.
        
        the leading strand elongates and second OF is made.
        
        The leading strand continues to elongate. A third OF is made, 1st & 2nd joined
        
        DNA primase makes RNA primers for synthesis
        
        DNA polymerase III makes DNA from the RNA primers. DNA primase makes second RNA primer for lagging strand
        
        DNA polymerase III elongates in leading strand. in the lagging strand DNA pol III synthesizes DNA. from 2nd primer. DNA pol replaces first primer with DNA.
        
        DNA ligase makes covalent bonds with 1st & 2nd OF. third OF is made ad leading strand elongates.
        
        Bidirectional replication
        
        DNA replication begins outward
        from two replication forks
        
        Terms:
        
        DNA helicase Binds to DNA and travels 5’ to 3’ using ATP to separate strand and move fork ahead
        
        DNA topoisomerase Relieves additional coiling ahead of
        replication fork
        Single-strand binding proteins
        
        Keep parental strands open to act as
        templates
        
        DNA polymerase
        
        Covalently links nucleotides.
        
        Deoxynucleoside triphosphates
        
        Free nucleotides with three phosphate groups.
        
        Breaking covalent bond releasing energy
        
        Functions
        
        5' to3'
        
        Requires a primer
        
        DNA primase makes the primer from RNA
        
        Functions:
        
        Speed
        
        Fidelity
        
        Completeness
        
        genetic changes make specialized enzyme
        
        most species have more than one type
        
        Elcoli - 5 DNA polymerase
        
        3 more items...
        
        Humans - 12 DNA polymerase
        
        3 more items...
        
        Accuracy
        
        Hydrogen bonding AT &GC
        
        Active site of DNA polymerase doesnt from if pairs unmatched
        
        DNA polymerase can proofread mismatched pairs
        
        Telomeres
        Eukaryotes only
        
        at the end of Chromosomes
        
        3' overhang
        
        Telomerase enzyme attaches many copies
        of DNA repeat sequence to the ends of chromosomes
        
        high levels of telomerase in all cancers
        
        DNA polymerase cannot copy the tip of
        the strand with a 3’ end and linear chromosomes would become
        progressively shorter from this
        
        cellular senescence corrects shortening
        
        Steps for Telomere Replication:
        
        Telomerase binds to a
        DNA repeat sequence
        
        Telomerase synthesizes a 6-nucleotide repeat sequence
        
        Telomerase moves 6 nucleotides to the right and begins another repeat
        
        Primase makes an RNA primer near the end of the telomere, and DNA polymerase III synthesizes a complementary strand in the 5′ to 3′ direction The RNA primer is removed.
  - - - Double-stranded helix
        Base-pairing: A with T and G with C
    - - Complementary DNA strands
        5’ -GCGGATTTGG – 3’
        3’ – CGCCTAAACC – 5’
      - Major groove
        
        Proteins bind to affect
        Minor groove
        
        Narrower