DNA ReplicationIn Eukaryotes and Prokaryotes

BOCA

• What are the nucleotide bases for DNA?

• Which bases bond together?

DNA replication involves making _____ from DNA.

1. Protein2. DNA3. RNA4. rRNA

The Replication Process

– Before a cell divides, it duplicates its DNA in a copying process called replication.

– This process ensures that each resulting cell has the same complete set of DNA molecules.

Ultimately the information in DNA is used to make:

1. Proteins2. Lipids3. Carbohydrates

How is DNA Copied

How do you make exact copies?Each strand of the double helix of DNA serves as a template, or model, for the new strand

What does the structure of DNA tell you about how to copy it?

How is DNA Copied

Semi-Conservative

DNA ReplicationEukaryotes

Begins at many origins

Strands must separate and unwindHelicase, Topoisomerases, and SSB

proteins

Add PrimerPrimase

Chromosome Structure

Eukaryotic chromosome structure

DNA (linear molecule)

Histone proteins

Chromosome Structure

Prokaryotic chromosome structure

DNA (Circular Molecule)

The Role Of Enzymes– The principal enzyme involved in DNA replication is

called DNA polymerase.

– DNA polymerase is an enzyme that joins individual nucleotides to produce a new strand of DNA.

– DNA polymerase also “proofreads” each new DNA strand, ensuring that each molecule is a perfect copy of the original.

DNA Replication

ReplicationDNA polymerase

Fuse sectionsDNA ligase

DNA Replication

Strands separate and unwind(Helicase)

Add Primer (Primase)

Replication (DNA polymerase)

Fuse sections/fragments (DNA ligase)

New sections built 5’-3’ and anti-parallel

Telomeres

– The tips of chromosomes are known as telomeres.

– The ends of DNA molecules, located at the telomeres, are particularly difficult to copy.

– Over time, DNA may actually be lost from telomeres each time a chromosome is replicated.

– An enzyme called telomerase compensates for this problem by adding short, repeated DNA sequences to telomeres, lengthening the chromosomes slightly and making it less likely that important gene sequences will be lost from the telomeres during replication.

“Leading Strand” DNA synthesis would occur in locations?

1. I and II2. I and III3. I and IV4. II and III5. II and IV

Origin

I

II

III

IV

3’

20

How does DNA replication differ in prokaryotic cells and eukaryotic cells?

• Replication in most prokaryotic cells starts from a single point and proceeds in two directions until the entire chromosome is copied.

• In eukaryotic cells, replication may begin at dozens or even hundreds of places on the DNA molecule, proceeding in both directions until each chromosome is completely copied.

1. Why is replication necessary?

2. When does replication occur?

3. Describe how replication works.

4. Use the complementary rule to create the complementary strand:

A---?G---?C---?T---?A---?G---?A---?G---?C---?A---?G---?T---?

Replication Quiz

1. Why is replication necessary?So both new cells will have the correct DNA2. When does replication occur?During interphase (S phase).3. Describe how replication

works.Enzymes unzip DNA and

complementary nucleotides join each original strand.

4. Use the complementary rule to create the complementary

strand:

A---TG---CC---GT---AA---TG---CA---TG---CC---GA---TG---CT---A

Replication Quiz