DNA

1
DNA

• Chapter 12

Information and Heredity, The Cellular Basis of
Life
2
Section 12-1 Identifying the Substance of Genes

• Frederick Griffiths Experiments (1920s)
• Bacterial Transformation
• He was studying bacteria that cause pneumonia.
• His experiment led to a discovery of a process a
  called transformation
• - Process in which one strain of bacteria
  changes into another strain.

3
Bacterial Viruses (Bacteriophages) The molecular
cause of transformationWhat role did bacterial
viruses play in identifying the genetic material
?

• Oswald Avery (1940s)
• His goal was to determine what molecule was used
  during transformation.
• By a process of elimination using biological
  enzymes they discovered that D N A was the
  transforming factor.

4
Section 12-1

• The Hershey - Chase Experiment (1950s)
• They did an experiment involving viruses to prove
  the work of both Griffith Avery.
• Viruses are only made of two things
• - protein coat
• - nucleic acid core
• 3 In step 1 of their experiment, they tagged the
  DNA core with radioactive P-32 to see if that was
  the transforming factor. It was the transforming
  factor!!.
• 4. In step 2 of their experiment, they tagged
  the protein coat with radioactive S-35 to see if
  that was the transforming factor. It was not!.

5
Transformation
6
12-1 The Role of DNAWhat is the role of DNA in
heredity

• The DNA that makes up genes can
• 1. Store information in cells.
• 2. Copy this information in cells.
• 3. Transmit this information when cells divide.
• Study the book cell analogy on page 342 of your
  textbook.
• A book can store information, you can copy
  information from this book and the book after
  being copied can be transmitted or given to
  others.

7
Section 12-2 The Structure of DNA

• The Components of DNA The Nucleotide
• A nucleotide is the monomer of a nucleic acid
  such as DNA or RNA.
• It has three components
• - A phosphate group
• - A 5-carbon sugar called deoxyribose
• - A nitrogenous base

8
Nucleotide

• Phosphate / sugar / N base

9
12-2 The Structure of DNA

• Components of DNA The Nucleotide
• There are four different bases in DNA
• - Adenine (A) - Thymine (T)
• - Guanine (G) - Cytosine (C)
• These bases are placed in two groups
• - Purines (double ring) ? A G
• - Pyrimidines (single ring) ? C T
• Chargoffs Rules of Base Pairing
• - A pairs with T - C pairs with G
• - a purine will pair with a pyrimidine

10
12-2 The Structure of DNA

• The Double Helix
• The structure of DNA was discovered through the
  work of three people
• A. Rosalind Franklin (1950s)
• - she used a technique called
• x-ray diffraction to show that DNA has
  two strands that form a helix.

11
12-2 The Structure of DNA

• The Double Helix
• The structure of DNA was discovered through the
  work of three people
• B. James Watson Francis Crick (1953)
• - They expanded on Franklins work by
  building a 3-D model of DNA
• - Their model had a double helix
  structure
• - The helix had a sugar-phosphate
  backbone
• - The bases were in the middle and held
  together by hydrogen bonds.

12
DNA

• There are four levels of folding to produce the
  chromosome structure.
• beads-on-a-string
• 30 nm fiber
• looped domain
• mitotic chromosome

13
DNA
beads-on-a-string DNA is wrapped around histones
forming nucleosomes linked in a row.
14
DNA
30 nm fiber The beads-on-a-string level is coiled
around itself in a solenoid spiral.
15
DNA
looped domain The solenoid spiral loops up and
down to compress itself further.
16
DNA
mitotic chromosome The beads-on-a-string forming
the solenoid spiral forming the looped domain
give rise to the mitotic chromosome.
17
DNA
18
12-3 DNA Replication

• Coping the Code
• Eukaryotic Chromosome Structure

19
Section 12-3 DNA Replication

• What is replication?
• This is the process of making a copy of the
  genome during the S Phase of the cell cycle.
• The steps
• DNA helicase unzips the double helix by
  breaking the H bonds between the bases.
• - Two helicase enzymes work in opposite
  directions form a replication bubble.
• - The site where the helicase is doing the
  unzipping is called a replication fork.

20
Section 12-3 Replication

• The steps
• Within the replication bubble, two DNA polymerase
  work in opposite directions make a
  complementary strand of DNA.
• At the end of replication, there are two exact
  copies of DNA.

21
12-3 Replication in Living Cells

• How does DNA replication differ in
  
  
• prokaryotic cells and eukaryotic cells?
• Prokaryotes or bacteria cells normally have a
  single circular strand of DNA. Replication
  starts from a single point and proceeds in 2
  directions.
• In Eukaryotes or cells with a nucleus,
  replication begins at dozens or even hundreds of
  places and proceeds in both directions.