notes ch12 dna
TRANSCRIPT
Chapter 12: DNA
DNA has 3 functions: Storing information Copying information Transmitting information
12.1 The Role of DNA
DNA – deoxyribonucleic acid Nucleotides – monomers that make up
a DNA molecule 3 parts:
5 Carbon sugar (deoxyribose) Phosphate group Nitrogenous base
Adenine (A) Guanine (G) Cytosine (C) Thymine (T)
12.2 The Structure of DNA
Edwin Chargaff (1949)Chargaff’s Rule
[A]=[T][C]=[G]
Solving the Structure of DNA
Adenine
Thymine
Guanine
Cytosine
35%
45%
Rosiland Franklin used X-ray diffraction to visualize DNA structure (1952).
Watson and Crick were the first to model DNA as a double helix in 1953.
All the previous discoveries show us the structure of DNA and how DNA can function as a carrier of genetic information.
Characteristics of the double helix model: Antiparallel strands Hydrogen Bonding Base Pairing
The Double Helix Model
Antiparallel StrandsRun in opposite directionsBase PairingBases are held together by hydrogen bonds.Base PairingA bonds with T, and C bonds with G
Complimentary base pairs
hydrogen bond covalent bond
If the sequence of bases on one strand of a DNA molecule is TCGAACTGA, the sequence on the other (complimentary) strand is:
Practice Base Pairing
Why does DNA replicate?(Hint: Think back to Mitosis) DNA is replicated in the S phase of the cell
cycle, before the cell divides.
12.3 DNA Replication
Step 1 The DNA double helix
unwinds DNA helicase
(enzyme). breaks the H bonds
between the bases. The areas where the
double helix separates are called replication forks.
Copying the Code
Step 2 DNA polymerase (enzyme)
moves along each DNA strand adding complimentary bases according to the base pairing rules.
DNA polymerase also proofreads the DNA molecule to reduce errors.
Step 3 The process continues
until all of the DNA has been copied.
DNA polymerase detaches.
This process produces two DNA molecules each composed of one new and one original strand.
Both DNA molecules produced are identical to each other.
DNA replication takes place at many points on a eukaryotic chromosome. Allows replication to happen more quickly.