Download DNA Structure Notes (12.1)

DNA Structure (12.1)
State Standards
2A. Distinguish between DNA and RNA.
2B. Explain the role of DNA in storing and
transmitting cellular information.
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Chapter 12 Molecular Genetics
12.1 DNA: The Genetic Material
Genetics
 Genetics is the branch of biology that studies
heredity, the passing of traits (characteristics)
from parents to offspring.
 This passing of
traits involves the 2
nucleic acids,
DNA & RNA.
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Chapter 12 Molecular Genetics
12.1 DNA: The Genetic Material
Nucleic Acid Structure
 Nucleotides are the building blocks of DNA &
RNA
 Nucleotides consist of a five-carbon sugar, a
phosphate group, and a nitrogen-containing base
Chapter 12 Molecular Genetics
12.1 DNA: The Genetic Material
DNA Structure
 The sugar found in
DNA is called
deoxyribose.
Chapter 12 Molecular Genetics
12.1 DNA: The Genetic Material
DNA Structure
Cont’d
 The double helix
shape of DNA is
often compared to a
twisted ladder.
 The ladder is made
of 2 very long chains
of nucleotides.
Chapter 12 Molecular Genetics
12.1 DNA: The Genetic Material
DNA Structure Cont’d
 The rails of the ladder
are represented by the
alternating
deoxyribose and
phosphate.
 The pairs of bases
(cytosine–guanine or
thymine–adenine)
form the steps or
rungs.
Chapter 12 Molecular Genetics
12.1 DNA: The Genetic Material
Base Pairing
 The bases in a nucleic
acid always pair up in
the same way.
 This is called
Chargaff’s rule.
Chapter 12 Molecular Genetics
12.1 DNA: The Genetic Material
Base Pairing Cont’d
Adenine always pairs with
Thymine.
Guanine always pairs with
Cytosine.
The 2 sides of the ladder
are held together by
hydrogen bonds.
Chapter 12 Molecular Genetics
12.1 DNA: The Genetic Material
The DNA Language
•DNA carries information in a
triplet code.
•Each sequence of 3
nucleotides codes for a
certain amino acid or for the
beginning or end of a
sequence.
•The genetic code is unique
for each organism.
Chapter 12 Molecular Genetics
12.1 DNA: The Genetic Material
Chromosome Structure
 DNA coils around histones to form nucleosomes,
which coil to form chromatin fibers.
 The chromatin fibers supercoil to form
chromosomes that are visible during cell division.
Chapter 12 Molecular Genetics
12.1 Formative
Questions
What is the base-pairing rule for purines
and pyrimidines in the DNA molecule?
0%
B
A
0%
A
B
C
D
0%
0%
D
1.
2.
3.
4.
C
A. A—G and C—T
B. A—T and C—G
C. C—A and G—T
D. C—U and A—G
Chapter 12 Molecular Genetics
12.1 Formative
Questions
What are chromosomes composed of?
0%
0%
C
A
B
C
D
B
A
0%
1.
2.
3.
4.
0%
D
A.chromatin and histones
B. DNA and protein
C. DNA and lipids
D. protein and centromeres
Chapter 12 Molecular Genetics
Chapter Assessment
Questions
Look at the following
figure. Identify the
proteins that DNA
first coils around.
0%
B
A
0%
A
B
C
D
0%
0%
D
1.
2.
3.
4.
C
A. chromatin fibers
B. chromosomes
C. histones
D. nucleosome
#14.
Use the analogy of a
staircase or a railroad
track to describe the
structure of DNA.