DNA REPLICATION
Animation gone Crazy
• DNA Replicates and Replicates
DNA is anti-parallel
• Two strands run
parallel to each other
but with opposite
alignments
(directions)
• McGraw-Hill DNA
• Why is being antiparallel an advantage
to the DNA
molecule?
DNA REPLICATION
• Semi-conservative =
each one of the
parent DNA strands
is passed to the
daugher DNA + one
new strand for each
• Semi-conservative
DNA (30 secs)
SNEAK PREVIEW:
DNA REPLICATION
PLAYERS (enzyme
review)
Question:
When and where does DNA Replication take
place?
Synthesis Phase (S phase)
• S phase in interphase of the cell cycle.
• Nucleus of eukaryotes
S
phase
DNA replication takes
place in the S phase.
G1
interphase
Mitosis
-prophase
-metaphase
-anaphase
-telophase
G2
Fill out DNA Replication
Enzymes CHART
• Lots of enzymes are
needed to start each step
Enzyme Topoisomerase
also called DNA gyrase
• Unwinds double helix
Enzyme
DNA
Enzyme
Topoisomerase
• Topoisomerase Youtube I and II (1:45)
• Topoisomerase Animation (2:16)
Enzyme Helicase:
separates (breaking Hbonds) double helix at the
replication fork
DNA-RNA-Protein (see ani)
YOU TUBE DNA replication (1:05)
Helicase
DNA Helicase
• The enzyme is unwinding the chain and
breaking the H-bonds between the
complementary base pairs (A-T, G-C).
Enzyme:
Primase
Helicase Primase
Helicase
= the enzyme
that makes RNA
nucleotides
into a primer
RNA Primer
• Nucleotides for the starting point
for DNA replication
• Short strands of RNA
DNA replication is initiated at many
points in eukaryotic chromosomes.
• Called Replication Bubbles
• They will eventually all meet to form whole
replicated strand
DNA Replication Bubble: DNA
duplicates in both directions
EM of DNA replication
Origins of Replication
• sites along the DNA molecule where
enzymes start the DNA replication - then
proceeds in both directions to form
“bubbles”
Replication Forks
Y-shaped regions of replicating DNA
molecules where new strands are
growing.
SSB’s
single strand binding proteins
• Stabilize the DNA strands as they
are being replicated
• Prevents rejoining of DNA strands
DNA Polymerases
• DNA Polymerase I
• Cuts off RNA primers and fills in with
DNA (between Okazaki fragments) –
lagging strand
• Can proofread
• DNA Polymerase III
• Elongates the strand by adding DNA
nucleotides on leading strand
• Also proofreads and corrects the
DNA strand
Anti-parallel strand builds in
the opposite direction (but
always in 5’ to 3’ direction)
Leading Strand Lagging Strand
• Template strand of
DNA
• Continuous addition
of nitrogenous bases
• in 5’ to 3’ direction
• McGraw-Hill Replication Fork
• Other DNA strand
• Forms short strands
of Okazaki fragments
(that will be joined
later)
• in the 5’ to 3’ direction
•
DNA Replication You Tube (1:35)
• OKAZAKI FRAGMENTS
• The short strands of newly made DNA
fragments on the lagging strand are called
Okazaki fragments after the Japanese
Biochemist Reiji Okazaki.
•
Enzyme: DNA Ligase
a linking enzyme joins the strands
Example: joining two Okazaki
fragments together.
DNA ligase
5’
3’
Okazaki Fragment 1
Lagging Strand
Okazaki Fragment 2
3’
5’
DNA LIGASE
is the enzyme that
joins the Okazaki
fragments (sugar phosphate backbone)
with covalent bonds
DNA REPLICATION
(look for ligase) 2:00
SUMMARY
DNA Replication (5:45) –
shows all the enzymes
• Summary Youtube of DNA replication (4:11)
• Good explanation of the 5’ to 3’ strands
and leading and lagging strands
Includes all your friendly
enzymes
• DNA Replication (3:56) Great animation
How Fast?
• Prokaryotic DNA polymerase can work
at about 1000 bases per second.
• Eukaryotic DNA polymerase can work at
about 50 bases per second.
Animation: DNA Replication
• DNA makes DNA
• *DNA with enzymes cartoons
All Together Now
• McGraw Hill Replication Fork animation
DNA Replication Easy Version (3:11)
• DNA Replication Youtube (7:48)
• Good CLICK and REVIEW
What if there is a mistake?
Typically
about one in
a billion
nucleotides
is incorrectly
paired
DNA Replication Activity
Work in Lab Groups
• Card stock papers
are original DNA
strands
• Colored paper are
new DNA strands
• MAKE OWN
ENZYMESconstruction paper
Proofreading
Initial base-pairing errors
are usually corrected by
DNA polymerase I.
Telomeres
• At the ends of each
chromosome is a
protective cap
called a telomere.
• Each time a cell
divides, the
telomeres are
snipped shorter,
Telomerase
• enzyme which adds DNA
sequence repeats
("TTAGGG" in all
vertebrates) to the 3' end of
DNA strands (an overhang)
• McGraw Hill Telomeres
Animation
Telomeres Added to ends of
chromosomes
Rutgers Telomere Animation
QUIZ
• Activity (choose your enzymes and
proteins)
MOVIE
• Media Showcase (cool animation)
• Replication Overview Movie
Question:
• What would be the complementary DNA
strand for the following DNA
sequence?
DNA 5’-GCGTATG-3’
Answer:
DNA 5’-GCGTATG-3’
DNA 3’-CGCATAC-5’
QUESTION
• In this diagram of the process of DNA
replication at a replication fork, the strand
labeled B is the:
• A template strand
• B lagging strand
• C leading strand
• D Okazaki fragment
• E RNA primer
QUESTION
• In this diagram of the process of DNA
replication at a replication fork, the newly
synthesized DNA strand labeled C is the:
A coding strand
• B parental DNA
• C leading strand
• D lagging strand
ANSWER
• C lagging strand
• The lagging strand is the newly
synthesized DNA where addition of
nucleotides is on the end opposite or
away from the replication fork.
QUESTION
• In this diagram of the process of DNA
replication at a replication fork, the black
boxes labeled D and E are:
• A RNA primers
• B DNA template strands
• C Okazaki fragments
• D DNA polymerase
• E Newly synthesized DNA strand
ANSWER
• A. RNA primers
• The initiation of replication always
starts with a short RNA piece.
The DNA replicating enzymes will
only add nucleotides to the 3' end
of DNA.
QUESTION
• For the DNA strand 5'-TACGATCATAT-3'
the correct complementary DNA strand is:
A 3'-TACGATCATAT-5
• 'B 3'-ATGCTAGTATA-5‘
• C 3'-AUGCUAGUAUA-5‘
• D 3'-GCATATACGCG-5‘
• E 3'-TATACTAGCAT-5'
ANSWER
• B 3'-ATGCTAGTATA-5'