Download Nucleotides and Nucleic Acids

Chapter 8.2: Nucleic Acid
Structure
CHEM 7784
Biochemistry
Professor Bensley
CHAPTER 8.2
Nucleic Acid Structure
Today’s Objectives – (To learn and understand the)
– Structure of double stranded DNA
– Structures of ribonucleic acids
Central Dogma of Biology
Nucleotides and Nucleosides
• Nucleobase =
Nitrogeneous base
• Nucleoside =
Nitrogeneous base + Pentose
• Nucleotide =
Nitrogeneous base + Pentose +
Phosphate
Covalent Structure of DNA (1868-1935)
OH
HO
P
O
• Friedrich Miescher
isolates “nuclein” from
cell nuclei
O
Thymine
C5H7O
O
HO
P
O
O
Structure of DNA:
Adenine
C5H7O
1929
• Hydrolysis of nuclein:
O
(Levene and London)
– phosphate
– pentose
– and a nucleobase
OH
HO P O
H
H
O
H
H
Thymine
H
OH
CH2O
• Chemical analysis:
P O
O
H
Structure of DNA:
1935
(Levene and Tipson)
H
O
H
H
Adenine
H
OH
CH2O P O
O
O
– phosphodiester linkages
– pentose is ribofuranoside
Road to the Double Helix
• Franklin and Wilkins:
–“Cross” means helix
–“Diamonds” mean that
the phosphate-sugar
backbone is outside
– Calculated helical
parameters
• Watson and Crick:
– Missing layer means
alternating pattern
(major & minor groove)
– Hydrogen bonding:
A pairs with T
G pairs with C
Double helix fits the data!
Watson, Crick, and Wilkins shared 1962
Nobel Prize
Franklin died in 1958
Watson-Crick Model of B-DNA
Structure of DNA
Double Helix
• Right handed
helix
• Rise = 0.33
nm/nucleotide
• Pitch = 3.4 nm /
turn
• 10.4 nucleotides
per turn
• Two groves –
major and minor
Complementarity of DNA strands
• Two chains differ in
sequence (sequence is
read from 5’ to 3’)
• Two chains are
complementary
• Two chains run
antiparallel
View down the Double Helix
Hydrophobic
Interior with base
pair stacking
Sugar-phosphate
backbone
Replication of Genetic Code
• Strand separation occurs first
• Each strand serves as a template for the
synthesis of a new strand
• Synthesis is catalyzed by enzymes known as
DNA polymerases
• Newly made DNA molecule has one daughter
strand and one parent strand.
“It has not escaped our notice that the specific pairing
we have postulated immediately suggests a possible
copying mechanism for the genetic material”
Watson and Crick, in their Nature paper,1953
DNA
Secondary
Structure
Palindromic Sequences can form Hairpins
and Cruciforms
Ribonucleic Acid (RNA)
• Ribosomal RNA (rRNA) – integral part of
ribosomes (very abundant)
• Transfer RNA (tRNA) – carries activated
amino acids to ribosomes.
• Messenger RNA (mRNA) – endcodes
sequences of amino acids in proteins.
• Catalytic RNA (Ribozymes) – catalzye
cleavage of specific RNA species.
Messenger RNA:
Code Carrier for the Sequence of Proteins
• Is synthesized using DNA template
• Contains ribose instead of deoxyribose
• Contains uracil instead of thymine
• One mRNA may code for more than one protein
Transfer RNA: Matching Amino Acids
with the mRNA Code
tRNA molecules have quite complex structures,
this is an actively studied field