Lecturer: 譚賢明 助理教授 Office: 醫學大樓十樓生科系 B 區 Phone: 5067 Textbook:...
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Transcript of Lecturer: 譚賢明 助理教授 Office: 醫學大樓十樓生科系 B 區 Phone: 5067 Textbook:...
Lecturer: 譚賢明 助理教授Office: 醫學大樓十樓生科系 B 區Phone: 5067Textbook: Stryer’s Biochemistry (6th ed.)
(Chapters 4, 5, 28-31)Lewin’s Cells(Chapters 5 & 6)
分子細胞生物學 Part I
Nucleic acid metabolism: Overview
Ch. 28
Ch. 29,31
Ch. 30
Ch. 4,5
Nucleic acid metabolism: Overview
Genetic information:Genetic information:
1. Duplication: DNA replication
2. Decoding:
DNA RNA proteintranscriptionRNA processing
translation
Nucleoside: base bonded to a sugar(deoxy)adenosine, (deoxy)quanosine, (deoxy)cytidine, (deoxy)uridinethymidine
N-9 (purine) orN-1 (pyrimidine)
C-1’ sugar
Nucleotide: nucleoside joined to one or more phosphateNucleoside 5’-phosphate, or 5’-nucleotide
C-5’ sugarester linkage
Adenosine 5’-triphosphate
Sugars in nucleic acids are linked by phosphodiester bonds(also called the backbone)
Negative charge of the backbone repels nucleophilic species Important for maintaining structure and information
Which is more stable?
DNA & RNA: linear polymer with directionality
(polynucleotide chain)
bases have hydrogen bonddonors and acceptors
Negative charge
DNA: double helix of complementary antiparallel strands
Hydrophobicvan der Waals
Hydrogen bonding(Watson-Crick base pairs)
Hydrophobicvan der Waals
Axial view of DNA: stacked bases
DNA can undergo reversible strand separation
“Denaturation” or “meting” : DNA unwinding1. In vivo: DNA replication and transcription2. In vitro: thermal energy
Factors influencing melting temperature (Tm)1. Base content (G-C vs. A-T)2. Ion concentration3. Agents that destabilize H-bonds
(ex. formamide or urea)4. pH
Denatured random coilsRenatured double stranded by complementarity
(ex. nucleic acid hybridization)
Some DNA molecules are circular and supercoiled
1. Human chromosomes are linear2. DNA molecules from other organisms are “circular”3. Inside cells, DNA has very compact shape4. Superhelix: double helix can itself be twisted or
supercoiled5. “Supercoiling” is biological important because:
* supercoiled DNA is more compact than “relaxed”* supercoiling affect the capacity of double helix to unwind --> interaction between DNA and other molecules
DNA vs. RNA
Difference:1. Hydroxyl group at 2’ position
(RNA is unstable in alkaline solution)2. Uracil instead of thymine
Similarity:1. Polynucleotide2. Double-stranded (ds), single stranded (ss),
linear, circular (RNA is linear ss in vivo)
RNA secondary and tertiary structures
tRNA and rRNA have tertiary structures (some mRNA too, at 3’ ends)
Summary: Molecules of Heredity
1. Nucleic acids2. Double-strand DNA3. Strands annealing vs. separation4. Secondary and tertiary structures:
*supercoils*RNA