Download DNA Replication

DNA: Structure and Replication
Slide # 2
Two Types of Nucleic Acids
Nucleic Acids: carry the genetic instructions
for all life
Nucleic
Acid
Stands for
Type of
Sugar
DNA
Deoxyribonucleic deoxyribose
acid
RNA
Ribonucleic acid
ribose
# of
Function
strands
2
“double
helix”
Stores
genetic
material
1 single Transfers
genetic
material
Slide # 3
Discovery of Nucleic
Acid
1.1869: Friedrich Miescher
discovered nuclein
– Noticed that nuclein had
a lot of phosphate
2. He found nuclein in every
type of cell he studied.
Miescher’s lab
Slide # 4
Griffith’s Experiment
1. 1928: Frederick Griffith
a. Showed that bacteria
could be transformed
b. transformation: process
in which bacteria can
take up the genes of
another bacteria and
express those genes
Slide # 5
Avery’s Experiment
Avery
continued
Griffith’s
experiment!
Avery showed that DNA is the transforming agent!
Slide # 6
Hershey and Chase Experiment
1. 1952: Hershey & Chase
used radioactive
markers on viruses
a. showed that virus
only injects nucleic
acid into bacteria
b. bacteria take up
nucleic acid and can
express the new genes
c. demonstrated that DNA
is the genetic material
of the cell
Slide # 7
Components of DNA
DNA is made up small, repeating units
(monomers) called nucleotides.
Nucleotide has 3 parts:
1. A phosphate group
2. A sugar (deoxyribose)
3. Nitrogen base (4 different
bases)
– Adenine “A”
– Thymine “T”
– Cytosine “C”
– Guanine “G”
Adenine Guanine Cytosine Thymine
Phosphate
group
Go to
Section:
Deoxyribose
Slide # 8
Chargaff: Discovered Ratios of
Nitrogen Bases
1. 1940’s: Erwin Chargaff discovered
that the % of base “A” was almost
equal to the % of base “T” & the
percent of base “C” was nearly
equal to the % of base “G”– didn’t
know why
2. Also discovered that composition of
DNA (% of A, T, C, & G) varies from
species to species
3. Both discoveries gave support that
DNA carries the genetic code!
Chargaff
Slide # 9
Percentage of Bases in Four Organisms
Go to
Section:
Source of DNA
A
T
G
C
Streptococcus
29.8
31.6
20.5
18.0
Yeast
31.3
32.9
18.7
17.1
Herring
27.8
27.5
22.2
22.6
Human
30.9
29.4
19.9
19.8
Slide # 10
Rosalind Franklin: The Famous Picture Taker
1.1952: Rosalind Franklin:
an expert in x-ray
crystallography.
2.She took the x-ray picture
of DNA -- shows DNA is a
double helix.
3.1958: Franklin died (37
years old)
James Watson & Francis Crick: Puzzle Solvers
Slide # 11
1. 1953: Discovered the structure of DNA
2. Described DNA as a double helix (twisted
ladder)
a. Sides of ladder are made up of sugar &
phosphate groups
b. Steps of ladder are made up of nitrogen
base pairs (A-T & C-G)
-- Applied Chargaff’s rules
c. Base pairs (steps) are held together by
weak hydrogen bonds
d. Sequence (order) of nitrogen bases
determines the genetic instructions /
“genetic code” of organism.
James Watson
Francis Crick
Slide # 12
Knowing the Structure Tells how DNA Replicates
1.DNA Replication: makes 2
identical DNA strands by
copying the original model
2.Each new strand contains
one old (parent) strand & one
new (daughter) strand
3.DNA replication occurs
during cell division – inside
the nucleus
Parent strand: gray
Daughter strand: red
Slide # 13
Steps in DNA Replication
1. DNA unwinds (DNA Helicase)
2. DNA polymerase breaks hydrogen bonds
that hold nitrogen bases together
3. DNA ligase hydrogen bond new nitrogen
bases onto DNA parent strand
• Chargaff’s rules applied: A-T & C-G
• Nucleotides added in 5’ to 3’ direction
4. Sugar-phosphate groups bond to
nitrogen bases to complete daughter
strand
5. Result: 2 identical DNA strands each
contains 1 parent strand & 1 daughter
strand
Slide # 14
Steps in DNA Replication
Daughter
strand
Parent
strand
Strands are antiparallel
Slide # 15
When Does Replication Occur?
1. The cell replicates (makes a copy) its DNA
right before cell division.
2. When two new cells are produced in cell
division, each new cell needs its own copy of
the DNA (identical copy!)
3. After DNA replication, the cell will divide in half
(cell division) and give each new cell a copy of
the DNA