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DNA is anti-parallel
• Two strands run parallel to each other but with opposite alignments (directions)
• McGraw-Hill DNA
• Why is being anti-parallel 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:
NA RAALAAATAAN ALAYDARA (enzyme review)
Question:Question:When and where does When and where does DNA Replication DNA Replication take take
place?place?
Synthesis Phase (S phase)Synthesis Phase (S phase)
• S phase in interphase of the cell cycle.
• Nucleus of eukaryotes
Mitosis-prophase-metaphase-anaphase-telophase
G1 G2
Sphase
interphase
DNA replication takesDNA replication takesplace in the S phase.place in the S phase.
Topoisomerase
Topo som r s Youtu Ai e a e be n AAa d (1:45)
• Topoisomerase Animation (2:16)
Enzyme HelicaseEnzyme Helicase: separatesseparates (breaking H-
bonds) double helix at the replication fork
DNA-RNA-Protein (see ani)
YAU TUAA NA r pl t onD e ica i (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).
DNA replication is initiated at many points in eukaryotic chromosomes.
• Called Replication Bubbles
• They will eventually all meet to form whole
replicated strand
Origins of Replication• sites along the DNA molecule where
enzymes start the DNA replication - then proceeds in both directions to form “bubbles”
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
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: DNAEnzyme: DNA LigaseLigasea linking enzyme joins the strands
Example: joining two Okazaki Example: joining two Okazaki fragments together.fragments together.
Lagging Strand
Okazaki Fragment 2Okazaki Fragment 2
DNA ligaseDNA ligase
Okazaki Fragment 1Okazaki Fragment 1
5’
5’
3’
3’
DNA LIGASEis the enzyme that joins the Okazaki fragments (sugar -
phosphate backbone) with covalent bonds
NA RAALAAATAAN (D
looA or lf igs Aa e
2:00
SUMMARYDNA 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
• McGraw Hill Replication Fork animation
DNA Replication Easy Version (3:11)
• DNA Replication Youtube (7:48)
• Good CLICK and REVIEW
DNA Replication ActivityWork in Lab Groups
• Card stock papers are original DNA strands
• Colored paper are new DNA strands
• MAKE OWN ENZYMES-construction paper
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 5DNA 5’’--GCGTATGGCGTATG--33’’
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'