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