Download DNA Structure

Mrs. Stewart
Biology I Honors
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 Acids
 Macromolecules containing :
 Carbon
 Hydrogen
 Oxygen
 Nitrogen
 Phosphorus
 Function: Store and transmit
genetic/hereditary information
Two types of Nucleic
Acids
DNA
RNA
DNA Stands for:
Deoxyribonucleic Acid
DNA Structure
 DNA 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 group
2. sugar
3. Nitrogenous base
Nucleotides
Phosphate
Nitrogenous
Base
Pentose
Sugar
DNA sugar
 The 5 carbon sugar for DNA is Deoxyribose
 That is where the name (Deoxyribo)nucleic
acid comes from
Nucleotides
 The 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
Adenine
C
Cytosine
T
Thymine
G
Guanine
Purines
A
Adenine
G
Guanine
Pyrimidines
T
Thymine
C
Cytosine
Chargaff’s rule
 Erwin 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% Adenine
 15% Thymine
 35% Cytosine
 35% 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 Structure
 Because of this complementary base pairing,
the order of the bases in one strand
determines the order of the bases in the other
strand.
A
T
C
G
T
A
C
G
A
T
G
C
T
A
Practice:
 Complete the complementary DNA strand for the
following sequence:
GTAACTCCT
CATAGAGGA
CTCCTAA AC
GAGGATTTG
TAGAATGCC
ATCTTACGG
DNA Structure
 To 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.
AGG-CTC-AAG-TCC-TAG
TCC-GAG-TTC-AGG-ATC
DNA Structure
 A 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.
DNA
Gene
Trait
Protein
Your Task
 Draw a flow chart to
show how to get from:
DNA
Replication
Mrs. Stewart
Biology I Honors
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 replication
 Create complementary DNA strands to
simulate replication
DNA Double Helix
 Made of 2 strands of nucleotides
 These strands are joined together with
the pairing of the Nitrogen bases
 (A, T, C, G)
 The bases are joined by Hydrogen bonds
Think – Pair - Share
 Look 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 DNA
 Refers to the orientation of the
carbon atoms on the
deoxyribose
 Strands run in opposite
directions
 One strand is “upside down”
Think – pair - share
 Why does DNA need to replicate itself?
DNA Replication
 DNA makes an exact copy of itself
 Occurs during the S stage of interphase
Semi-conservative
 Each 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
Helicase
 Enzyme 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 Polymerase
Uses “free-floating” nucleotides in
the nucleus to build the
complementary strand of DNA
5‘ to 3‘ direction
 The 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
 Animation of replication #1
 Animation of replication #2