Chapter 12: DNA
12.1 The Role of DNA
• DNA has 3 functions:
– Storing information
– Copying information
– Transmitting information
12.2 The Structure of DNA
• DNA – deoxyribonucleic acid
• Nucleotides – monomers that make
up a DNA molecule
– 3 parts:
• ...
Solving the Structure of DNA
Edwin Chargaff (1949)
Chargaff’s Rule
[A]=[T]
[C]=[G]
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.
The Double Helix Model
• All the previous discoveries show us the
structure of DNA and how DNA can
function as a carrier o...
Antiparallel Strands
Run in opposite
directions
Base Pairing
Bases are held together
by hydrogen bonds.
Base Pairing
A bon...
Practice Base Pairing
• If the sequence of bases on one strand of a
DNA molecule is TCGAACTGA, the sequence
on the other (...
12.3 DNA Replication
• Why does DNA replicate?
(Hint: Think back to Mitosis)
– DNA is replicated in the S phase of the cel...
Copying the Code
• Step 1
– The DNA double
helix unwinds
• DNA helicase
(enzyme).
– breaks the H bonds
between the bases.
...
• Step 2
– DNA polymerase
(enzyme) moves along
each DNA strand adding
complimentary bases
according to the base
pairing ru...
• 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 ...
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Notes ch12 DNA

  1. 1. Chapter 12: DNA
  2. 2. 12.1 The Role of DNA • DNA has 3 functions: – Storing information – Copying information – Transmitting information
  3. 3. 12.2 The Structure 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)
  4. 4. Solving the Structure of DNA Edwin Chargaff (1949) Chargaff’s Rule [A]=[T] [C]=[G] Adenine Thymine Guanine Cytosine 35% 45%
  5. 5. • Rosiland Franklin used X-ray diffraction to visualize DNA structure (1952).
  6. 6. • Watson and Crick were the first to model DNA as a double helix in 1953.
  7. 7. The Double Helix Model • 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
  8. 8. Antiparallel Strands Run in opposite directions Base Pairing Bases are held together by hydrogen bonds. Base Pairing A bonds with T, and C bonds with G Complimentary base pairs hydrogen bond covalent bond
  9. 9. Practice Base Pairing • If the sequence of bases on one strand of a DNA molecule is TCGAACTGA, the sequence on the other (complimentary) strand is:
  10. 10. 12.3 DNA Replication • Why does DNA replicate? (Hint: Think back to Mitosis) – DNA is replicated in the S phase of the cell cycle, before the cell divides.
  11. 11. Copying the Code • 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.
  12. 12. • 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.
  13. 13. • Step 3 – The process continues until all of the DNA has been copied. – DNA polymerase detaches.
  14. 14. • 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.

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