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 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.

Fill out DNA Replication Enzymes CHART

• Lots of enzymes are needed to start each step

Enzyme Topoisomerasealso called DNA gyrase

• Unwinds double helix

Enzyme

DNA

Enzyme

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).

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: 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

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 ActivityWork in Lab Groups

• Card stock papers are original DNA strands

• Colored paper are new DNA strands

• MAKE OWN ENZYMES-construction 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 5DNA 5’’--GCGTATGGCGTATG--33’’

Answer:Answer:

DNA 5DNA 5’’--GCGTATGGCGTATG--33’’

DNA 3DNA 3’’--CGCATACCGCATAC--55’’

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'