Download Nitrogenous base Number of strands Sugar DNA RNA Ribose Deoxy

Molecular Biology
Chapter 9
DNA – Deoxyribonucleic Acid

DNA
 stores genetic information
 copied and passed from generation to generation
 Directs the copying of itself  DNA Replication
 Involved in protein production
 Transcription
 Translation
History of DNA – Watson & Crick

Wanted to know if the
genetic material was
protein or DNA.

1953  Deduce exact
structure of DNA


Nucleic Acid
Double Helix

Made of nucleotides
James Watson (left) and Francis Crick
Rosalind Franklin
X-ray images of DNA
DNA Structure

Double Helix is composed of a

Backbone composed of alternating

Sugar



Phosphate
Rungs

Bases





5-C sugar = Deoxyribose
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
Nucleotide = Phosphate + Sugar + Base
© 2013 Pearson Education, Inc.
FIGURE 9.3
(a) Each DNA nucleotide is made up of a sugar, a phosphate group, and a base.
(b) Cytosine and thymine are pyrimidines. Guanine and adenine are purines.
Phosphate
group
Nitrogenous base
Sugar
DNA
nucleotide
DNA
double
helix
Nitrogenous base
(can be A, G, C, or T)
Thymine (T)
Phosphate
group
Sugar
(deoxyribose)
DNA nucleotide
Polynucleotide
Sugar-phosphate
backbone
Hydrogen bond
(b) Atomic model
DNA Replication –
semiconservative replication
Parental (old)
DNA molecule
Daughter
(new) strand
Parental
(old) strand
Daughter DNA
molecules
(double helices)
RNA - Ribonucleic Acid
Structure of RNA:
 Sugar is Ribose
 No T, Uracil (U) instead
 Single stranded (ss)
Figure 10.UN03b
Nitrogenous
base
Sugar
Number of
strands
DNA
RNA
C
G
A
T
C
G
A
U
DeoxyRibose
ribose
2
1
How do DNA and RNA work together?

DNA makes a copy of itself in
the form of RNA


transcription
RNA is used to make
proteins

Translation
* Please note  DNA replication
is a completely separate process
that is NOT related to
transcription and/or translation!
Figure 10.UN05
TRANSCRIPTION
TRANSLATION
Gene
mRNA
DNA
Polypeptide
Types of RNA
1. Messenger RNA (mRNA)
 Carries the message from DNA  directions for making
a protein
Types of RNA con’t.
2. Transfer RNA (tRNA)

Carries and transfers
amino acids to mRNA
Types of RNA con’t.
3. Ribosomal RNA (rRNA)

Mixed with protein to make ribosomes

Two subunits (large & small) used to facilitate translation
Figure 9.19

The protein synthesis machinery includes the large and small subunits of the ribosome,
mRNA, and tRNA. (credit: modification of work by NIGMS, NIH)
Figure 10.UN06
Growing
polypeptide
Amino acid
Large ribosomal
subunit
tRNA
mRNA
Anticodon
Codons
Small ribosomal
subunit
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