Chapter 12 DNA - Faribaultmail.faribault.k12.mn.us/~Laura_Childs/S0198C4E2.10/Chapter 12 DNA.pdf12.3 DNA Replication A. Copying the Code 1. Base pairing permits DNA to copy Bases pair

Chapter 12 DNA

12.1 The Substance of Genes

(p. 342-343)

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

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)

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

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

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

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

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)

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)

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)

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