第二十章核苷、核苷酸和核酸
Nucleosides,Nucleotides,
and Nucleic Acids
核酸中的碱基(Base in Nucleic Acids)
DNA——Deoxyribonucleic acid
RNA——Ribonucleic acid
Nucleic acid
base
O
O
PO
O
O
O-
base
O
O
PO
O
O-
base
O
O
PO
O
O
O-
base
O
O
PO
O
O-
OH
OH
RNA DNA
β-glycosidic bond β-glycosidic bond
ribose 2-deoxy-ribose
核酸中的碱基(Base in Nucleic Acids)
Nucleoside = base + sugar
Nucleotide = base + sugar + phosphate
Nucleic acid = polynucleotide
Nucleotide sequence = Base sequence
The bases in DNA and RNA
N
N
N
H
N
NH
2
NH
N
N
H
N
O
NH
2
Adenine(A)
Guanine(G)
Purine
N
N
H
NH
2
O
NH
N
H
O
O
NH
N
H
O
O
Cytosine(C) Thymine(T) Uracil(U)
Pyrimidine
(in DNA) (in RNA)
核酸中的碱基(Base in Nucleic Acids)
Why DNA contains T instead of U?
N
N
H
NH
2
O
Cytosine(C)
NH
N
H
O
O
Uracil(U)
NH
N
H
NH
O
tautomerization
H
2
O
NH
N
H
O
O
Thymine(T)
Base pairing in DNA,A = T,G ≡ T —— double helix
N
N
O
O
N
N
N
N
N
N
N
O
N
N
N
N
H
H
NH
H
sugar
sugar
H
H
O
NH
H
sugar
sugar
thymine adenine cytosine guanine
核酸中的碱基(Base in Nucleic Acids)
思考题：嘌呤和嘧啶都存在互变异构的变化，请尝试写出它们各自的互变异构结构，并回答这种互变异构对于碱基配对将产生什么影响？pH
改变对于碱基的配对有无影响，为什么？
N
N
O
O
N
N
N
N
N
N
N
O
N
N
N
N
H
H
NH
H
sugar
sugar
H
H
O
NH
H
sugar
sugar
thymine adenine cytosine guanine
ATP
N
N
N
N
NH
2
OPO
O
O
P
O
O
O
~
P
O
O
O
~
O
OH
OH
The structure of ATP
ATP —能量转换中间体
ATP —大大移动平衡反应
? ATP可使与之相偶联的平衡反应向生成物方向的速率提高10
8
倍，
ΔG
= +16.7 kJ·mol-1
A B
PiADPBOHATPA
eq
2
++→?++
K
ΔG
=16.7+（-30.5）= -13.8 kJ·mol-1
ATP —磷酸化剂
O
OH
OH
HO
OH
OH
+ATP
O
OH
OH
HO
O
OH
P
O
O
O
+ ADP
DNA的双螺旋结构
DNA的双螺旋结构
DNA
Replication
下周二下午2：30在F515举行专题报告会，
欢迎有兴趣同学参加下周一讲述药物设计基本原理和杂环化合物合成（也属考试内容）
6月7日举行期末考试具体时间和地点请留心网上通知