武汉大学《基因的分子生物学》Section C

•Molecular Biology Course
C2 Chemical and Physical Properties of Nucleic Acids
1. Stability of Nucleic Acids 2. Effect of Acid & applications 3. Effect of alkali & applications 4. Chemical denaturation 5. Viscosity & applications 6. Buorant density & application
Nucleotides
A nucleotide is a nucleoside with one or more phosphate groups bound covalently to the 3’-, 5’, or ( in ribonucleotides only) the 2’-position. In the case of 5’-position, up to three phosphates may be attached. Phosphate ester bonds
•Molecular Biology Course
C1 Nucleic Acid Structure (DNA & RNA):
basesnucleosides nucleotide phosphodiester bonds primary sequence structure, modified nucleic acids
Conformational variability of RNA is important for the much more diverse roles of RNA in the cell, when compared to DNA.
Structure and Function correspondence of protein and nucleic acids
NUCLEOTIDES
Adenosine 5’-triphosphate (ATP) Deoxyadenosine 5’-triphosphate (dATP) Guanosine 5’-triphosphate (GTP)
Guanine (G) Guanosine
Deoxyguanosine
Deoxy-guanosine 5’-triphosphate (dGTP)
• Sugar-phosphate backbones (negatively charged): outside • Planner bases (stack one above the other): inside
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3’
5’
C. Properties of nucleic acids
7 561 8 9 4 3 2
Thymine (T) is a 5-methyluracil (U)
C. Properties of nucleic acids C1 Nucleic Acid Structure (DNA & RNA):
Nucleosides
The bases are covalently attached to the 1’ position of a pentose sugar ring, to form a nucleoside
Protein
Nucleic Acids
Fibrous protein Globular protein Structural •Enzymes, proteins •antibodies, •receptors etc
Helical DNA Genetic information maintenance
Deoxynucleotides (containing deoxyribose)
Ribonucleotides (containing ribose)
C. Properties of nucleic acids BASES Adenine (A) NUCLEOSIDES
Adenosine Deoxyadenosine
4 32 1
A:T
G:C
Base pairing
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C. Properties of nucleic acids
•Helical turn:
10 base pairs/turn 34 Ao/turn
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C. Properties of nucleic acids
C1 Nucleic Acid Structure : RNA structure 1. Single stranded nucleic acid 2. Secondary structure are formed some time 3. Globular tertiary structure are important for many functional RNAs, such as tRNA, rRNA and ribozyme RNA
Forces for secondary and tertiary structure: intramolecular hydrogen bonding and base stacking.
tRNA
Ribozyme RNA
Secondary structure
Tertiary structure
C. Properties of nucleic acids
Chemical properties
Physical properties
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C. Properties of nucleic acids
Stability of Nucleic Acids
1. Hydrogen bonding
• • Does not normally contribute the stability of nucleic acids or protein Contributes to specific structures of these macromolecules. For example, a-helix, b-sheet, DNA double helix, RNA secondary structure
supercoiling & energy, topoisomer & topoisomerase
C. Properties of nucleic acids C1 Nucleic Acid Structure (DNA & RNA):
Bases
Bicyclic Purines:
Monocyclic pyrimidine:
•Molecular Biology Course
SECTION C Properties of Nucleic Acids
The Race for the Double Helix (1994)
The diffraction pattern from the DNA optical transform slide shows the central cross pattern indicative of the helical arrangement of the strands of DNA. It also shows a missing 4th layer line which is the result of the two strands of the double helix being offset by 3/8 of a period. The strongly diffracting phosphorus atoms create the diamonds. The satelites above and below the cross are attributed to the base pairs.
attached phosphate groups 3’ end: free hydroxyl (-OH) group
Phosphodiester bond
C. Properties of nucleic acids
C1 Nucleic Acid Structure : DNA double helix
Globular RNA
•Ribozymes •Transfer RNA (tRNA) •Signal recognition etc.
C. Properties of nucleic acids
C1 Nucleic Acid Structure : Modified Nucleic Acids
Modifications correspond to numbers of specific roles. We will discuss them in some related topics. For example, methylation of A and C to can avoid restriction digestion of endogenous DNA sequence (Topic G3).
•Watson and Crick , 1953 •The genetic material of all organisms except for some
viruses
•The foundation of the molecular biology
C. Properties of nucleic acids
•Two separate strands Antiparellel (5’3’ direction) Complementary (sequence) Base pairing: hydrogen bonding that holds two strands together