Download NOTES: 12.2 – 12.3 – DNA Structure

NOTES: 12.2 – 12.3 – DNA Structure & Replication
12.2 - DNA Structure
● it was known that DNA was made up of nucleotides joined into long strands by
covalent bonds…but HOW were they connected…what was the structure?
●Made up of
.
● Each nucleotide composed of 3 parts:
-
(
)
• Adenine (
)
• Guanine (
)
• Thymine (
)
• Cytosine (
)
Chargaff’s Rules
Source of DNA
Streptococcus
Yeast
Herring
Human
Percentage of Bases in Four Organisms
A
T
G
29.8
31.6
20.5
31.3
32.9
18.7
27.8
27.5
22.2
30.9
29.4
19.9
C
18.0
17.1
22.6
19.8
What do these data suggest to you?
●
●
What DNA Looks Like:
● Rosalind Franklin: used X-Ray diffraction patterns to discover that DNA strands
● Watson & Crick: while trying to build a 3-D model of DNA, Watson was shown Franklin’s photograph
and measurements and within weeks, he and Crick figured out the structure of DNA
(“twisted ladder”)
DNA Structure =
● Backbone:
&
of each nucleotide
● “Steps of Ladder:”
● Any base sequence is possible!
What’s holding the strands together?
●
!!!
● Hydrogen Bonds form between
base pairs as well as between
base pairs
12.3: DNA REPLICATION
The Review
● Prokaryotic cells do
-DNA molecules are located in the cytoplasm
-Usually a circular DNA molecule and it is referred to as the cells chromosome
● Eukaryotic cells
-Can have 1000x more DNA than prokaryotic cells
-DNA is located in the form of a number of chromosomes
-# of chromosomes varies widely from species to species
DNA molecules are long…how does DNA fit in the nucleus?
● It forms
!
● DNA coils around proteins called
and then this chromatin supercoils around
itself until
form
DNA Replication
● before a cell divides, it must
its DNA so that all cells have a copy of the genetic
instructions
● this process involves A LOT of
!
●each half of the DNA double helix can serve as a "
" for the replication of
another DNA double helix molecule
-The strands are said to be
DNA REPLICATION: THE PROCESS
1) an enzyme
(separates the 2 DNA strands) by breaking the
bonds between base pairs
2) a
is inserted to
each side of the DNA strand with the help of
3) The sugar-phosphate groups are
to the growing DNA chain (
4) an enzyme (
will "
“
“)
)
" the order of bases & make corrections