Honors Biology Notes Name:_____________________DNA and Replication

This page’s Word bank:

phosphate C sugar Nitrogen bases

Nitrogen base

Deoxyribonucleic acid

A

nucleotides deoxyribose G phosphate T hydrogen chromosome

Chargaff’s Rule

A must pair with T

G must pair with C

The bases form weak HYDROGEN bonds

DNA Structure

A coiled DNA is called a CHROMOSOME

Sides made of a sugar called DEOXYRIBOSE bonded to a PHOSPHATE group by phosphodiester bonds.

Center made of NITROGEN BASES bonded together by weak ______HYDROGEN________________bonds

DNA stands for DEOXYRIBONUCLEIC ACID

Made up of subunits called NUCLEOTIDES Nucleotides made of 3 parts:

1.PHOSPHATE 2. DEOXYRIBOSE SUGAR 3. NITROGEN BASE

Pentose Sugar:

Carbons are numbered clockwise 1’ to 5’

Memory trick!Apples on TreesCars in Garages

Honors Biology Notes Name:_____________________This page’s Word bank:

purines 2 2 replicated Anti- parallel3 pyrimidines pyrimidines S interphase

Antiparallel Strands

• One strand of DNA runs directionally from 5’ to 3’ (sugars)

• The other strand is ANTIPARALEL in direction going 3’ to 5’ (sugars)

Nitrogenous Bases

Double ring PURINE

Adenine (A)Guanine (G)

Single ring PYRIMIDINE

Thymine (T)Cytosine (C)

Base pairing

Purines only pair with PYRIMIDINES

3 hydrogen bonds required to bond Guanine & Cytosine

2 hydrogen bonds are required to bond Adenine & Thymine

Review Question? If there is 30% Adenine in a DNA sample, how much Cytosine is present?

ADENINE + THYMINE = 30% + 30% = 60%

ALL BASES IN DNA = 100%

(ADENINE + THYMINE) + (CYTOSINE + GUANINE) = 100%

60% + (CYTOSINE + GUANINE)= 100%

(CYTOSINE + GUANINE) = 40%

CYTOSINE= 20%

GUANINE = 20%

20% cytosine

DNA Replication

Memory Trick!

“Y” are you single?

T or C

Honors Biology Notes Name:_____________________Replication Facts

DNA has to be REPLICATED before a cell divides

DNA is copied during the S phase of interphase

New cells will need 2 DNA strands

S phase is during INTERPHASE of the cell cycle

Inside the NUCLEUS of eukaryotes

This page’s Word bank:

polymerase helicase

new break identical

Base-

pairs

nucleus 5’ complementary

old Hydrogen bonds

Semi-conservativ

e

2 2 Semi-conservativ

e

nucleotides

Replication fork

Anti-paralle

l

DNA Replication (the making of more DNA)

Process allows for 2 cells (new cells) to have one IDENTICAL copy of COMPLEMENTARY/PARENTAL DNA

in their nucleus.

DNA replication is SEMI CONSERVATIVE: The new “twisted-ladder” of DNA is made of a OLD strand & an

NEW strand.

DNA replication occurs in NUCLEUS

1: DNA separates, hydrogen bonds BREAK because they are weak bonds.

2: Original DNA acts as template; Free NUCLEOTIDES bind to their BASE PAIRS (COMPLEMENTARY)

3: Strands are proof read. 2 new strands are made – SEMI CONSERVATIVE because parent strand in “conserved”.

DNA POLYMERASE adds the new nucleotides

DNA Replication (cont.) Begins at Origins of Replication

Two strands open forming REPLICATION FORK (Y-shaped region)

New strands grow at the forks

Honors Biology Notes Name:_____________________DNA Synthesis Step One:

HYDROGEN bonds are broken by the enzyme, HELICASE

Step Two:

DNA POLYMERASE adds free nucleotides to both strands.

DNA polymerase can only add nucleotides to the 5’ end of the DNA

This causes the NEW strand to be built in a ANTIPARALELL direction

This page’s Word bank:

Ligase,

okazaki lagging lagging discontinuous

leading proofread

ligase

The LEADING Strand is synthesized as a single strand from the point of origin toward the opening replication fork

The LAGGING Strand is synthesized discontinuously against overall direction of replication

This strand is made in DISCONTINUOUS short segments It is replicated from the replication fork toward the origin

OKAZAKI Fragments - series of short segments on The LAGGING strand

The enzyme LIGASE joins the Okazaki fragments together to make one strand

Step 3: New DNA strands are PROOFREAD and mistakes are repaired

DNA polymerase initially makes about 1 in 10,000 base pairing errors

Enzymes proofread and correct these mistakes

The new error rate for DNA that has been proofread is 1 in 1 billion base pairing errors

DNA Damage & Repair

MEMORY TRICK Helicase = Helicopter

Honors Biology Notes Name:_____________________• Chemicals & ultraviolet radiation damage the DNA in our body cells

• Cells must continuously repair DAMAGED DNA

• Excision repair occurs when any of over 50 repair enzymes remove damaged parts of DNA

• DNA polymerase and DNA ligase replace and bond the new nucleotides together

This page’s Word bank:

Old Template

new

Semiconservative Model of Replication

• Idea presented by Watson & Crick

• The two strands of the parental molecule separate, and each acts as a TEMPLATE for a new complementary strand

• New DNA consists of 1 PARENTAL (original) and 1 NEW strand of DNA

Review Question: What would be the complementary DNA strand for the following DNA sequence?

DNA 5’-CGTATG-3’

3’ – GCATAC – 5’

Honors Biology Notes Name:_____________________

List the function for the following enzymes.

• Helicase: OPENS THE DNA HELIX

• DNA polymerase: ELONGATES/ADDS NEW NUCLEOTIDES TO A GROWING DNA STRAND

• Ligase: CONNECTS/GLUES THE OKAZAKI FRAGMENTS IN THE LAGGING STRAND TOGETHER

DNA Correctly Copied

••

POLYMERASE

LIGASE

LAGGING STRAND

POLYMERASE

REPLICATION FORK

TEMPLATE STRANDS

LEADING STRAND

OKAZAKI

FRAGMENTS

5’’

3’

WORD BANK

Template Strands

Replication Fork

DNA polymerase

Okazaki Fragments

Leading Strand

Lagging Strand

DNA Ligase

5’

3’

SOME WORDS MAY BE USED TWICE

A T

G C

C C

T A

A T

T A

A T

A T

G C

C C

T A

A T

T A

A T

A T

G C

C C

T A

A T

T A

A T

Honors Biology Notes Name:_____________________•••

Original original original new new original