Introduction to Organic and
Biochemistry
(CHE 124)
Reading Assignment
General, Organic, and Biological Chemistry: An Integrated Approach
3rd. Ed. Ramond
Chapter 13
Nucleic Acids
Central Dogma of Molecular
Biology
Replication
DNA
Transcription
 RNA
Translation
 Protein
mRNA. tRNA, rRNA, snRNA
Nucleus
– Replication - DNA directed DNA synthesis
– Transcription - DNA directed RNA synthesis
· Processing of mRNA capping, polyadenylation, splicing
• Cytoplasm
– Translation - RNA directed Protein synthesis
Nucleic Acids
• Nucleic Acid - linear, non-branched polymer of
nucleotides
Classes of Nucleic Acids
– RNA = ribonucleic acid
– DNA = 2' deoxyribonucleic acid
Functions of Nucleic Acids
Building blocks of DNA and RNA
– DNA = Genetic material
– RNA = Adapter molecule between DNA and protein
Transport chemical energy within the cell
– ATP
Signal molecule
 cyclic AMP
Nucleotide
• Nucleotide contains:
–Pentose sugar
–Nitrogenous base
–Phosphate
–One or more
Adenosine Triphosphate (ATP)
Nucleotide
• phosphate group
Pyrimidine Bases
Pyrimidine
Thymine
(T)
5-methyl-2,4-dioxypyrimidine
Cytosine
(C )
4-amino-2-oxypyrimidine
Uracil
(U)
2,4-dioxypyrimidine
DNA ONLY
DNA and RNA
RNA ONLY
Purine Bases
Purine
Adenine
(A)
6 – aminopurine
Guanine
(G)
2- amino-6-oxypurine
DNA and RNA
DNA and RNA
Sugar Phosphate Backbone
• Nucleotides connected by 3’ to 5’ phosphodiester
bond
– Imparts uniform negative charge to DNA / RNA
• Negative charge repels nucleophilic species (e.g. hydroxyl) thus
the phosphodiester bond resists hydrolytic attack.
• Separation by agarose gel electrophoresis
– Creates 3’ and 5’ end (directionality)
Bases are attached to sugar by Beta
Glycosidic linkage
• N-9 of purine and N-1 of pyrimidine
Nucleotide
Nucleoside = sugar + nitrogenous base,
Nucleotide = sugar + nitrogenous base + phosphate.
Adenosine
(A nucleoside)
Adenosine monophosphate
(A nucleotide)
Watson and Crick
(Complementary) Base Pairing
G C
A T
Nucleotide content determines
melting point of DNA.
DNA is Organized into Genes
• Gene
–discrete, functional unit of DNA
–when expressed, (transcribed) yields a
functional product
• rRNA, tRNA, snRNA
• mRNA - translated into a polypeptide
sequence.
–Open reading frame - long stretch of
nucleotides that can encode polypeptide
due to absence of stop codons.
Double Helix
• B form
– Diameter of helix = 20.0 Å (2.00
nm)
– 10.4 base pairs / turn; 34 Å (3.4 nm)
– 1 base pair 3.4 Å (0.34 nm)
• Note
–
–
–
–
–
Complementary base pairing
Major grove
Minor grove
Antiparallel
Hydrogen bonding between
complementary base pairs.
Chromatosomes Pack to Form
Chromatin Fibers
Histones H1, H2A, H2B, H3, H4
Histones contain (>20%) arg and lys ---basic amino acids
Karyotype
• Photograph of
chromosomes from
a single organism
• Arranged by size
(largest to smallest)
• Homo sapiens
– 46 chromosomes
– 23 pairs
• 3 billion base pairs
(hapliod)
• 25,000 genes
Types of RNA
• Types of RNA
–
–
–
–
–
Ribosomal RNA (rRNA)– part of the ribosome
Transfer RNA (tRNA) Messenger RNA (mRNA)– sequence translated into protein sequence.
Small nuclear RNA (snRNA) – involved in splicing (spliceosome)
Micro RNA (mi RNA) – small RNA complementary to mRNA that
inhibits translation of the mRNA
– Small interfering RNA (siRNA) – small RNA that binds to mRNA
causing destruction of mRNA
RNA molecules are complementary
to the DNA template.
• mRNA is complementary to template strand
• mRNA is identical (except for U to T changes) to
the coding strand.