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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