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DNA- Replication
Chapter 9, Section 2 & 3
Regular Biology
Objectives
Describe structure of DNA
 Explain importance of DNA
 Understand why living things need to
make copies of DNA
 Describe how copies of DNA are made
 Explain what happens if a mutation occurs
in replication

Structure of DNA
Deoxyribose Nucleic Acid


Double helix
Made of 2 strands
of nucleotides
1.
2.
3.
Phosphate
Sugar (deoxyribose)
Nitrogen Base




Adenine (“A”)
Thymine (“T”)
Cytosine (“C”)
Guanine (“G”)
Nucleotide
About DNA


Sugar & Phosphate
make up the sides
In the middle of DNA



Adenine pairs with
Thymine (A-T)
Cytosine pairs with
Guanine (C-G)
Practice:
TATGGAGAGTC
ATACCTCTCAG
Complementary base pairs
More Practice
1. GTATTCAGGA
CATAAGTCCT
2. TAACAGA
ATTGTCT
3. GATTACA
CTAATGT
Names to Know, pg 196

Chargaff- (1949) A
pairs with T. G pairs
with C

Mrs. Franklin- (1952)
X-ray pictures of DNA

Watson & Crick(1953) DNA is double
helix
Prokaryote DNA is:




Prokaryote DNA is
circular
Has 2 replication
forks
Replication occurs in
opposite directions
around the circle until
they meet
Can replicate in 1
hour or less
Eukaryote DNA is:






Eukaryote DNA is double stranded
Compacted in chromosomes
Each chromosome can have
about 100 replication forks
Each “new” DNA strand is about
100,000 nucleotides long.
The DNA in your body would
wrap around the Earth about 1.5 times!
Takes about 8 hours to replicate
human chromosomes in Interphase
Prokaryote vs Eukaryote
Make a Venn Diagram
Prokaryote vs Eukaryote DNA
ReplicationMaking more DNA
Where?

What?
Happens in the nucleus
• Occurs during Interphase
• S (synthesis) phase
• Occurs whenever is needed
When?
Replication- Making more DNA
Why?

Important for Mitosis and Meiosis
Mitosis- new cells for growth & repair
 Meiosis- new cells for sperm & egg


Important for making more copies
of a protein, enzyme, etc
Replication- making more DNA
1.
2.
Two strands separate, forming replication
fork
DNA polymerase (an enzyme) brings
bases to make “new” strands

3.
4.
500/sec in bacteria, 50/sec in humans….WOW!
Half of DNA strand is “old” and half is
“new”
Result: two strands of DNA form that are
identical to the original molecule
But what if there’s a mistake?

Types of Mutations

Frameshift- (the new part of DNA shifts to be
longer or shorter than it should be)
 Deletion

Correct base is deleted
 Insertion


Incorrect Base is added
Point mutation (base pair substitution)
 Wrong
base pair is stuck in the place of another
Build-in Mutation Reducers

Replication has “proof-readers” to help
reduce errors



DNA polymerase
Chaperone proteins
These proteins and enzymes reduce
errors to about 1 error for every 1 billion
nucleotides.
But what if a mutation DOES
happen?
DNA
(Genes)
RNA
Protein
(Enzyme)
Discussion!
Genetic TechnologyTerms to Know
Genetic engineering Recombinant DNA- DNA made from 2 or
more organisms
 Vector- What gets the gene into the cell


Usually a virus, yeast, or plasmid
Plasmid- circular bits of DNA
 Restriction enzymes- proteins which cut
the DNA at specific points

New Technology

Human Genome Project- mapping entire human genome
sequence. Finished in 2003.

Cloning- process used to creating identical copy of
organism

Polymerase Chain Reaction (PCR)- process that makes
more DNA

DNA Fingerprinting- use gel electrophoresis to separate
DNA of different lengths
Genetic Engineering Information

Gel Electrophoresis



Uses electric charges
within gel
DNA is negative, thus
travels to positive end
Separates molecules
by size
http://learn.genetics.utah.edu/units/biotech/
More New Technology
Genetically Modified Foods- genetically
selecting certain traits for crop
improvement
 Transgenic Animals- Animals that have
other DNA in their cell. Used to make
proteins, medicine, etc.
 Gene Therapy- insert genes into organism
to help stop or prevent disease

Remember…
“There is no gene for
Human Spirit!”