chapter 12 dna - faribaultmail.faribault.k12.mn.us/~laura_childs/s0198c4e2.10/chapter 12 dna.pdf12.3...
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Chapter 12 DNA
12.1 The Substance of Genes
(p. 342-343)
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A. Role of DNA (hereditary molecule)
1. Storing Information
Genes written into DNA control development of each trait (ex: eye color gene)
2. Copying Info
Every gene must be copied b4 division
3. Transmitting Info
Genes made of DNA are sorted and passed on w/cell division/each generation
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Section 12.2 A. Structure of DNA
1. Nucleic Acids (NA) and Nucleotides
Acidic macromolecules
Nucleotides are the building blocks (subunits) of DNA
Deoxyribose (5C sugar)
Phosphate group
Nitrogenous base (molecule w/Nitrogen)
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2. Nitrogenous Bases & Covalent Bonds
Contain nitrogen
4 bases: Adenine/Guanine (2 rings) and Cytosine/Thymine (1 ring); A; G; C; T
Form covalent bonds between sugar-phosphate
Bases absorb UV light=tells amt of DNA in cell
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B. Structure of DNA 1. Chargaff’s Rule: Amt of (A)=(T) Amt of (G)=(C) 2. Franklin’s X-rays diffraction X-rayed purified, stretched DNA 2 twisted strands w/ N-bases in middle 3. Watson and Crick: used Franklin’s work to build 3D-model of DNA
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C. Double Helix Model
1. Backbone: sugar/phosphate
2. Rungs: N-base
3. Antiparallel strands: “mirror”
opposite strand arrangement
4. Hydrogen Bonding: weak
center bond between
N-bases (permits replication)
5. Base pairing=Chargaff’s Rule
A H-bonds w/T; G H-bonds w/C
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12.3 DNA Replication
A. Copying the Code
1. Base pairing permits DNA to copy
Bases pair w/only 1 other base
on opposite strand
Complementary strands (mirror
images) contain info to
reconstruct other strand
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2. The Replication Process & Enzymes Replication: DNA copied during S phase of Interphase
Old strand “template” for 2 new complementary strands
Enzymes help:
1. Helicase unzips
2. DNA Polymerase adds complementary
N-bases (also “proofreads” so no mistakes)
Old: TACGTT/New: ATGCAA
2 identical DNA molecules (1/2 old:1/2 new)
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3. Telomeres
Repeated DNA code at tips of chromosome
Telomerase builds telomere tip and prevents gene damage or loss during replication
Switched off in adulthood
Cancers can activate (w/rapid division)
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B. Replication in Living Cells
1. Prokaryotic DNA Replication
Regulatory proteins initiate S phase
Single start point proceeding in two directions
2 attached identical chromosomes (split w/division)
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2. Eukaryotic DNA Replication
1000 x’s more DNA than prokaryotes
Chromosomes made of chromatin=DNA coiled around histones
Multiple start points
Proteins check for damage (not foolproof-change may alter gene)
Copied chromosomes remains attached until Anaphase