Mrs. StewartBiology I Honors
DNAStructur
e
STANDARDS:CLE 3210.4.1 Investigate how
genetic information is encoded in nucleic acids.
CLE 3210.4.2 Describe the relationships among genes, chromosomes, proteins, and hereditary traits.
OBJECTIVES: (today, I will…)Evaluate the structure of nucleic
acids Determine how genetic information is
“coded” in nucleic acids Create complementary DNA strands
using Chargaff’s rule
Nucleic AcidsMacromolecules containing :
Carbon HydrogenOxygenNitrogenPhosphorus
Function: Store and transmit genetic/hereditary information
Two types of Nucleic Acids
DNARNA
DNA Stands for:
Deoxyribonucleic Acid
DNA StructureDNA is made up of two strands that are
arranged into a twisted, ladder-like structure called a Double Helix.
A strand of DNA is made up of millions of tiny subunits called Nucleotides.
Each nucleotide consists of 3 parts:1. Phosphate group2. sugar3. Nitrogenous base
Nucleotides
Phosphate
Pentose
Sugar
Nitrogenous
Base
DNA sugarThe 5 carbon sugar for DNA is
Deoxyribose
That is where the name (Deoxyribo)nucleic acid comes from
NucleotidesThe phosphate and sugar form the
backbone of the DNA molecule, whereas the bases form the “rungs”.
There are four types of nitrogenous bases.
4 different Nitrogen bases
A
AdenineT
Thymine
G
GuanineC
Cytosine
Purines
A
Adenine
G
Guanine
Pyrimidines
T
Thymine
C
Cytosine
Chargaff’s ruleErwin Chargaff observed that the
percentage of adenine equals the percentage of thymine, and the percentage of cytosine equals the percentage of guanine.
Example: in one strand of DNA the following amounts may be found:15% Adenine15% Thymine35% Cytosine35% Guanine
Complementary base pairing:Each base will only bond with one
other specific base. (Chargaff’s rule)
Adenine (A)Thymine (T)
Cytosine (C)Guanine (G)
Form a base pair.
Form a base pair.
DNA StructureBecause of this complementary base
pairing, the order of the bases in one strand determines the order of the bases in the other strand.
G
G
A
T
T
A
A
C
T
G
C
A
T
C
Practice:Complete the complementary DNA strand for
the following sequence:
G T A A C T C C TC A T A G A G G A
C T C C T A A A CG A G G A T T T G
T A G A A T G C CA T C T T A C G G
DNA StructureTo crack the genetic code found in
DNA we need to look at the sequence of bases.
The bases are arranged in triplets (sets of 3) called codons.
A G G - C T C - A A G - T C C - T A GT C C - G A G - T T C - A G G - A T C
DNA StructureA gene is a section of DNA that codes for a
protein.
Each unique gene has a unique sequence of bases.
This unique sequence of bases will code for the production of a unique protein.
It is these proteins and combination of proteins that give us a unique phenotype.
Protein
DNA
Gene
Trait
Your TaskDraw a flow chart to
show how to get from:
Mrs. StewartBiology I Honors
DNA Replicati
on
STANDARDS:CLE 3210.4.1 Investigate how
genetic information is encoded in nucleic acids.
CLE 3210.4.2 Describe the relationships among genes, chromosomes, proteins, and hereditary traits.
OBJECTIVES: (today, I will…)Evaluate the structure of DNA and
the need for replicationCreate complementary DNA strands
to simulate replication
DNA Double HelixMade of 2 strands of nucleotidesThese strands are joined together with the pairing of the Nitrogen bases(A, T, C, G)
The bases are joined by Hydrogen bonds
Think – Pair - ShareLook at the picture and try to figure
out what “antiparallel” means.
Did you notice that the strands of DNA run in “opposite directions”?
5’ and 3’ ends of DNARefers to the orientation
of the carbon atoms on the deoxyribose
Strands run in opposite directions
One strand is “upside down”
Think – pair - shareWhy does DNA need to replicate
itself?
DNA ReplicationDNA makes an exact copy of itselfOccurs during the S stage of
interphase
Semi-conservativeEach strand of the double
helix will serve as a template for the new strands that will form
End result is two complete DNA double helixes – each containing one strand from the original molecule and one newly made complementary strand
HelicaseEnzyme that “unzips” the
DNA double helix by breaking the Hydrogen bonds between the bases to separate the strands in preparation for replication
Creates a “replication fork”
DNA PolymeraseUses “free-floating” nucleotides in the nucleus to build the complementary strand of DNA
5‘ to 3‘ directionThe new DNA strands need to form in
the 5 prime to 3 prime direction.
Leading strand: forms continuously because it is forming in the 5’ to 3’ direction
Lagging strand: forms in short segments called Okazaki fragments, so that it can also form in the 5’ to 3’ direction
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