DNA REPLICATION

PP 282 - 290

PRACTICE QUESTIONS

PG 290, #3, 7, 8, 10

DNA REPLICATION

• Semiconservative•

EXAMPLE PROBLEM

• If the following DNA is replicated, what would the daughter molecules look like. Label the strands.

3’

3’5’

5’A T A C C G A C T G A T G G C A CT A T G G C T G A C T A C C G T G

DNA REPLICATION OVERVIEW

• A large protein enzyme complex: • opens • uses the old strand to create a • finishes

DNA REPLICATION OVERVIEW

• DNA Replication Overview 1:40 to 2:50

DNA REPLICATION

• 3 STEPS:• • •

REPLICATION INITIATION

• Origin of replication (ori)• Ori’s are a

• The enzyme, helicase, • What does it do?

REPLICATION INITIATION

• The single-stranded regions of DNA want to ___________

• ___________________________bind to the strands and keep them open

SSBPs

REPLICATION INITIATION

• The open region of the DNA is called the _____________• This is where the

copying will take place

REPLICATION INITIATION

• As the helicase moves along unwinding the DNA, ________ develops ahead of replication fork• Think twirling a rubber

band• The enzyme __________

alleviates the tension

tension

REPLICATION INITIATION

• Prokaryotic organisms generally have:• • • Replication:

ori

chromosome

REPLICATION INITIATION

• Eukaryotic organisms generally have:• • • Replication occurs

oriorichromosome

NOTE: NEW STEP!!!! ELONGATION

REPLICATION ELONGATION

• Replication Elongation

REPLICATION ELONGATION OVERVIEW• Taking the single stranded pieces of DNA and using

them as a template to create a new strand

• Strand is created by adding the complementary nucleotides to one end of the new DNA strand, one after another

REPLICATION ELONGATION

• DNA Polymerase• The main enzyme that catalyzes the

addition of nucleotides to the end of a DNA strand

• Discovered in 1959 by Arthur Kornberg• A discovery so monumental that he wins

the Nobel prize the same year

REPLICATION ELONGATION

• Interesting to note:• While Arthur Kornberg did discover the first DNA

polymerase, his was not the major one used in DNA replication

• That was discovered by his son, Tom Kornberg, in 1970

• Not to be outdone, his other son, Roger Kornberg, uses a novel method to get the crystal structure of another enzyme, RNA polymerase, which wins him the Nobel prize in 2006

REPLICATION ELONGATION

• DNA polymerase • Prokaryotes: DNA polymerase I, II, III, IV & V• Eukaryotes: over 15 different types

• The enzyme only catalyzes the addition of nucleotides to • Therefore new strands grow in a __________direction• AND the template strand is read from _________

STEPS TO ELONGATION

1. Primase:

5’3’

5’ 3’

STEPS TO ELONGATION2. DNA polymerase III:

3. The appropriate nucleoside triphosphate:

4. A pyrophosphate group (PPi) is:

A AT

TTP P P

REPLICATION ELONGATION

REPLICATION ELONGATION

• This process is occurring in the replication fork following the helicase• Both ssDNAs need to be copied

• How are they different?

• What problem does this cause?

LEADING STRAND SYNTHESIS

5’

5’

3’

3’

helicase

SSBPs

gyrase

primase

5’

3’

DNA polymerase III

LAGGING STRAND SYNTHESIS

Okazaki fragment

5’

3’

5’

3’

5’

3’

helicasegyrase

REPLICATION ELONGATION

• Leading strand is replicated continuously• Lagging strand is replicated discontinuously

• DNA Replication Overview 1:40 to 2:50

FINISHING ELONGATION

All the Okazaki fragments must finally be connected.

DNA polymerase I – • occurs in the _______ direction

• DNA ligase – • Okazaki fragments are

3. REPLICATION TERMINATION

Telomeres

TTAGGG

TELOMERES

TELOMERASE

• Explain what happens to the telomere during each round of replication, why this is important and why some cells have a mechanism to repair this while others do not…

TELOMERASE

• Telomeres and aging?

TELOMERASE

• Telomerase: