You can tell people apart by their
fingerprints because everyone’s are a little
bit different…
DNA is like a fingerprint because everyone’s is a little different!
DNA stands for:
D: Deoxyribose
N: Nucleic
A: Acid
DNA is too
small to see,
but under a
microscope it
looks like a
twisted up
ladder!
Every living thing has DNA. That means
that you have something in common with a
zebra, a tree, a mushroom and a beetle!!!!
DNA is packed tightly in the cell
Learning Target: Describe the structure of a
DNA molecule
chromosome
DNA double
helix
Supercoils
histones
DNA is made up of steps and rails like a ladder.
This is a rail/side
This is a step/rung
Green can only go with Red
Purple can only go with Yellow
DNA Structure:
organic polymer made up of repeating nucleotides
Nucleotide
H bonds
Sugar-phosphate
backbone
Nitrogen Bases
A
T
C
G
Building blocks of DNA:
Nucleotides
The sugar = Deoxyribose
Shape = pentose
The phosphate
The nitrogenous bases
Purines
The nitrogenous bases
Pyrimidines
How are the pyrimidines different from the
purines?
Purines =(2 Carbon rings) Pyrimidines = (1 Carbon ring)
A
G
C
T
Four different Nucleotides
BASIC
STRUCTURE
DNA is a polymer formed by base
pairing: Base pairing rule
PRACTICE BASE PAIRING
__________________________________
A G T C C G T T A G T
T C A G G C A A T C A
The Double Helix
A.The overall shape of DNA is described as a
double helix (a twisted ladder).
B.What forces holds the two strands together?
Hydrogen
bonds
Covalent Bonds
Who Discovered the DNA Structure?
• Watson and Crick – 1953
• Model was a rope ladder
that had been given a twist
= double helix
http://www.immediart.com/catalog/images/big_images/SPL_E_H400040-Watson_and_Crick_with_their_DNA_model-SPL.jpg
Where have we seen DNA being
replicated?
Cell cycle
MITOSIS
AND
MEIOSIS
DNA Replication
• 1. DNA “unzips”
– Enzymes (helicases) break H bonds b/w nitrogen bases
– Forming a replication fork (where the 2 strands
separate)
• 2. Free DNA nucleotides pair up along the nitrogen
bases
– DNA polymerases (enzymes) make sure that the bases
pair correctly
• 3. Bonds form
– Covalent bonds form b/w sugars and phosphates
– Hydrogen bonds form b/w nitrogen bases for both
molecules
DNA Replication
• Result: 2 new exact copies of original
DNA molecule/ happens b/4 mitosis
• See page 316 in book and animations
DNA Replication
• ANIMATION
• ANIMATION DETAILED
How are DNA and RNA similar?
• DNA is composed of nucleotides and RNA
is composed of nucleotides
How are DNA and RNA different?
How are DNA and RNA
different?
• DNA…
– Nucleotides = deoxyribose sugar
– Double helix structure
– Stays inside nucleus
• RNA…
–
–
–
–
Nuleotides = ribose sugar
Single-strand structure
Located both inside and outside of nucleus
Uracil instead of thymine (U instead of T)
Enzymes involved in DNA
replication
• Helicase – opens the double helix to allow
for replication
• DNA polymerase – reads the original DNA
strand and lays down complementary bases
• Ligase - glues the newly formed DNA
together
DNA replication practice
• You are DNA polymerase. Helicase has opened
the DNA strand – read each side and produce the
complementary copies.
__________________________________
AGGTAACCGGTTACGATTAT
TCCATTGGCCAATGCTAATA
AGGTAACCGGTTACGATTAT
TCCATTGGCCAATGCTAATA
PRACTICE BASE PAIRING
RULES AGAIN
__________________________________
A G T C C G T T A G T
T C A G G C A A T C A
Protein Synthesis= transcription and
translation
• DNA contains all the information for your
traits – the genes
• These genes are blueprints and need to
remain safe – kept inside the nucleus
• Copies can be made though – a messenger