基因體學研究在藥學上之應用
Nucleic Acid Structure
DNA Structure
nitrogenous bases
– A, T, G, C
pentose sugar
– deoxyribose
usually a double helix, composed of two
complementary strands
– base pairing rules
A with T
G with C
nucleoside = nitrogenous base
+ pentose sugar
phosphodiester bond
two polynucleotide
chains are antiparallel
RNA Structure
nitrogenous bases
– A, G, C, U (instead of T)
pentose sugar
– ribose
usually consists of single strand
– can coil back on itself
forms hair-shaped structures with
complementary base pairing and helical
organization
base pairing rules
– A with U
– G with C
Types of RNA
three types
– ribosomal RNA (rRNA)
– transfer RNA (tRNA)
– messenger RNA (mRNA)
differ from each other in function, site of
synthesis in eucaryotic cells, and
structure
The Central Dogma
Pattern of DNA Synthesis
semiconservative
– each parental
strand is conserved
– two parental
strands separate
and serve as
templates for
synthesis of new
strands
transcription
recognition site for ribosome
synthesis continues
until terminator
reached
E. coli ribosome
site where amino
acid is attached
complementary to
codon in mRNA
Aminoacyl-tRNA
amino acid
 rest of tRNA
initiation
codon
transpeptidation reaction
Pharmacogenomics
• prolonged muscle relaxation after
Suxamethonium v.s. inherited deficiency
of plasma cholinesterase
Hemolysis after antimalarial therapy v.s.
inherited level of erythrocyte glucose 6phosphate dehydrogenase
• peripheral neutropathy of isoniazid
v.s. inherited differences in acetylation
of isoniazid
• Pharmacogenetics
define the more narrow spectrum of inherited
differences in the drug metabolism and
disposition
• Genes are considered to be polymorphic when
variant alleles exist stably in the population
- Gene Polymorphism
• Gene locus
A specific place on a chromosome where
a gene is located
• Allele
One of the different forms of a gene
that can exist at a single locus
• Allele frequency
The proportion of all alleles of that gene
in the population that are of this specific
type
P
AA
Gametes
aa
X
a
A
Zygote
Locus
Aa
½A
½a
½A
¼ AA
¼ Aa
½a
¼ Aa
¼ aa
• Multiple allelle
A, B, C, D…. Etc.
Genetic variation at the galactosemia locus
• gene encodes galactose-1-phosphate uridyltransferase (GALT)
• recessive mutation results in inability to metabolize galactose
• causes mental retardation and death
• some protection afforded by complete removal of milk from the diet
• variant alleles exist in addition to several galactosemia (g) alleles
• spectrum of enzymatic activities indicates that “normal” individuals
do not all have the same enzymatic activity levels
Genotype
Frequency
G/G
G/D
G/LA
G/g
D/D
D/LA
LA/LA
D/g
LA/g
g/g
87.4%
7.5
3.7
0.9
0.16
0.16
0.04
0.04
0.02
0.0025
Enzyme
Activity
100
75
120
50
50
95
140
25
70
<5
Phenotype
Normal
Normal
Normal
Normal
Normal
Normal
Normal
Borderline
Normal
Galactosemia
Relative number of individuals
Population distribution of “normal” GALT activities
G/G
G/g
G/LA
G/D
g/g
0
20
40
60
80
100
120
1 40
Relative GALT enzyme activity
160
CLASSIFICATION
Phase I (Functionalization): Phase II (Conjugation):
Oxidation
Cytochrome P450(CYP)
Alcohol Dehydrogenase(ADH)
Monoamine Oxidase
Reduction
Cytochrome P450
Hydrolysis
Esterases
Amidases
Glucuronosyltransferases(GT)
N-Acetyltransferases(NAT)
Sulfotransferases (ST)
Methyltransferases (MT)
Glutathione Transferases(GST)
Amino Acid Transferases
• Single nucleotide polymorphism
- Common variations among DNA of individuals
Nature Biotechnology May 2000
Volume 18 Number 5 pp 505 - 508
The use of single-nucleotide Polymorphism
maps in pharmacogenomics
Jeanette J. McCarthy1 & Rolf Hilfiker2
1. Millennium Predictive Medicine, Inc., Cambridge, MA 02139.
2. Solvias AG, Basel, Switzerland.
• Metabolic polymorphism
• Polymorphism of target proteins (e.g.
receptors)
• Transporter polymorphism
Genetic Polymorphisms in Drug Metabolism and Disposition
• Pharmacogenomics
Refer to the entire spectrum of genes that
determine the drug behavior and sensitivity