Biology Catalyst
Wednesday, 5/28/14
1. Go to class website http://aofscience.weebly.com. Scroll
down to CATALYSTS and answer the question. Press
submit when you are done. (Don’t have a computer?
Use your phone or a catalyst sheet.)
QUESTIONS:
1. WACKY WEDNESDAY! Write a fun, DNA-related joke.
2. Why is it important for DNA to be replicated carefully?
Period 3 Biology Agenda 5/28/14
• Catalyst
• Announcements*
– HW: Watch DNA Transcription Video Tutorial
Online
• DNA Replication Discussion
• DNA Structure and Replication Practice
• DNA Structure and Replication Quiz
Molecular Genetics Overview
1.
2.
3.
4.
5.
6.
7.
DNA Structure ✔
DNA Replication
DNA Transcription
Types of RNA
Protein Translation
Mutations
Genetic Engineering
+
Objectives
We will be able to
1. Explain how DNA is replicated.

THE CENTRAL DOGMA OF MOLECULAR
BIOLOGY
DNA Replication
2007-2008
End goal of DNA Replication
• Create identical strands of
DNA as the original DNA
• This means that each DNA
molecule after replication
has one original strand and
one new strand.
DNA Replication Animation
• https://www.youtube.com/watch?v=27TxKoF
U2Nw#t=322
DNA Nucleotides
DNA is made up of
nucleotides that contain:
1. Phosphate group
2. Deoxyribose molecule
3. Nitrogen-containing
base
DNA Nucleotide Bases
There are 4 nucleotide bases:
- Adenine (A)
- Guanine (G)
- Cytosine (C)
- Thymine (T)
Chargaff’s Rule
• Percentage of [A] is
almost exactly the
same as [T]
• Percentage of [G] is
almost exactly the
same as [C]
• A=T, C=G
Chargaff’s Practice!
• ACATGGACCCTTTTAAAA
TGTACCTGGGAAAATTTT
Watson and Crick
1953 article in Nature
Double helix structure of DNA
“It has not escaped our notice that the specific pairing we have postulated
immediately suggests a possible copying mechanism for the genetic material.”
Watson & Crick
Directionality of DNA
• You need to
number the
carbons!
nucleotide
PO4
N base
– it matters!
5 CH2
O
This will be
IMPORTANT!!
4
1
ribose
3
OH
2
Copying DNA
• Replication of DNA
– Base pairing lets each
strand act as a template
for a new strand
– new strand is 1/2 parent
template &
1/2 new DNA
• Semi-conservative
copy process
Let’s meet
the team…
DNA Replication
• Large team of enzymes coordinates replication
Steps of DNA Replication
1. DNA unzips/unwinds
2. DNA polymerase attaches
3. Two new complementary strands of DNA are
formed
Replication: 1st step – Unzipping DNA
– Enzyme: DNA Helicase
• unwinds part of the DNA helix so that the code can be
read.
DNA Unzips
In order for DNA to replicate
or copy itself, it has to
unwind to create two strands
that can serve as copies.
Replication: 2nd step – Reading the bases
1. Primase adds primer (short sequences of RNA
nucleotides) to 5’ end FIRST. (DNA polymerase can
only add to existing nucleotides.)
2. DNA Polymerase attaches to one side of the DNA
strand and “reads” the bases.
Replication: 3rd step – Build a new strand
 Build daughter DNA strand

DNA
Polymerase III
Enzyme: DNA Polymerase
adds complementary
bases to the old strand of
DNA
3. New complementary strands of DNA
are formed
DNA polymerase continues to
add on base pairs along the
original DNA strand to create
two new DNA molecules that
are nearly perfectly identical to
each other!
Replication fork
3’
5’
5’
3’
5’
3’
5’
3’
direction of replication
DNA polymerases
• DNA polymerase III
– 1000 bases/second!
– main DNA builder
Thomas Kornberg
??
• DNA polymerase I
– 20 bases/second
– editing, repair & primer removal
DNA polymerase III
enzyme
Arthur Kornberg
1959
Editing & proofreading DNA
• 1000 bases/second =
lots of typos!
• DNA polymerase I
– proofreads & corrects typos
– repairs mismatched bases
– removes abnormal bases
• repairs damage
throughout life
– reduces error rate from
1 in 10,000 to
1 in 100 million bases
Fast & accurate!
• It takes E. coli <1 hour to copy
5 million base pairs in its single
chromosome
– divide to form 2 identical daughter cells
• Human cell copies its 6 billion bases &
divide into daughter cells in only few hours
– remarkably accurate
– only ~1 error per 100 million bases
– ~30 errors per cell cycle
What does it really look like?
1
2
3
4
2007-2008
DNA Replication Animation
• https://www.youtube.com/watch?v=27TxKoF
U2Nw#t=322
DNA Replication
DNA Replication
DNA Replication Classwork
• Use the next 15 minutes to answer the
questions on DNA Replication.