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Nucleotides and Nucleic Acids - Coggle Diagram
Nucleotides and Nucleic Acids
Functions of Nucleotides and Nucleic Acids
Nucleic acids are polymers of nucleotides used for
storage of genetic info (DNA)
transmission of genetic info (mRNA)
protein synthesis (tRNA and rRNA)
processing of genetic information (ribozymes)
Nucleotides are also used in the monomer form for cellular functions
energy for metabolism (ATP)
enzyme cofactors (NAD+)
signal transduction (cAMP)
Nucleotides and Nucleosides
Nucleotide
nitrogeneous base
pyrimidine or purine
planar structures
Absorb UV light around 250–270 nm
Thymine is found only in DNA.
Uracil is found only in RNA.
Cytosine, adenine, and guanine are found in both DNA and RNA.
All are good H-bond donors and acceptors
Neutral molecules at pH 7
pentose
phosphate
Negatively charged at neutral pH)
attached to 5’ position
attached to other positions for specialized function
Nucleoside
nitrogeneous base
pentose
Nomenclature
Deoxyribonucleotides
Ribonucleotides
β−N-Glycosidic Bond
In nucleotides, the pentose ring is attached to the nitrogenous base via a N-glycosidic bond.
The bond is formed
N1 in pyrimidines
N9 in purines
quite stable toward hydrolysis, especially in pyrimidines
catalyzed by acid
syn conformation
anti conformation
found in normal B-DNA
Tautomerism of Nitrogenous Bases
UV Absorption of Nucleobases
decay rapidly
effective photoprotection of genetic material
Nucleic acids不會發螢光 所以可用UV吸收光測得濃度
Minor Nucleosides
in DNA
5-Methylcytosine
found in eukaryotes and bacteria
N6-Methyladenosine
common in bacteria but not found in eukaryotes
Epigenetic marker
prokaryotes
mark own DNA so that cells can degrade foreign DNA
eukaryotes
mark which genes should be active
Modification is done after DNA synthesis.
in RNA
Inosine
in tRNA
provides richer genetic code
Pseudouridine
in tRNA and rRNA.
common in eukaryotes but found also in eubacteria
made from uridine after RNA synthesis
stabilize the structure of tRNA
help in folding of rRNA
Polynucleotides
Covalent bonds are formed via phosphodiester linkages
negatively charged backbone
DNA backbone is fairly stable
Hydrolysis accelerated by enzymes (DNAse)
RNA backbone is unstable
In water
RNA lasts for a few years
In cells
mRNA is degraded in a few hours
Linear polymers
Directionality
5’ to 3’
Hydrolysis of RNA
RNA在鹼性的狀態下不穩定
Hydrolysis is catalyzed by enzymes (RNase).
RNase enzymes are abundant around us.
S-RNase
prevents inbreeding in plants
RNase P
是一種核酶(由 RNA 製成的酶)處理 tRNA 前體
Dicer
is an enzyme that cleaves double-stranded RNA into oligonucleotides.
protection from viral genomes
RNA interference technology
Hydrogen-Bonding Interactions
A pairs with T
2 H bond
C pairs with G
3H bond
Purine pairs with pyrimidine.
Watson-Crick Model of B-DNA
Other Forms of DNA
Complementarity of DNA Strands
Two chains differ in sequence
sequence is read from 5’ to 3’
Two chains are complementary.
Two chains run antiparallel.
Replication of Genetic Code
Strand separation
2.Each strand serves as a template for the synthesis of a new strand.
Synthesis is catalyzed by enzymes known as DNA polymerases
A newly made DNA molecule has one daughter strand and one parent strand.
Messenger RNA
使用 DNA 模板合成，通常以單鏈形式出現
Contains ribose instead of deoxyribose
Contains uracil instead of thymine
One mRNA may code for more than one protein
Together with transfer RNA (tRNA), transfers genetic
information from DNA to proteins
回文序列可以形成髮夾和十字形
Complex Structures Are Stabilized by Non-Watson- Crick Base-Pair Interactions
DNA Denaturation
Genetic code remains intact.
Hydrogen bonds are broken
UV absorbance increases
induced by high temperature, or change in pH
reversible
annealing
DNA 變性通常通過 260 nm 的紫外分光光度法監測。
The reversible thermal denaturation and annealing form the basis for the polymerase chain reaction.
Factors Affecting DNA Denaturation
Tm depends on base composition.
High CG increases Tm
Tm depends on DNA length
Longer DNA has higher Tm
It is important for short DNA
Tm depends on pH and ionic strength
High salt increases Tm
Molecular Mechanisms of Spontaneous Mutagenesis
Deamination
very slow reactions
large number of residues
100 C → U events/day in a mammalian cell.
Depurination
N-glycosidic bond is hydrolyzed
10,000 purines lost/day in a mammalian cell
氧化和化學誘變的分子機制
Oxidative
Oxidative damage
hydroxylation of guanine
mitochondrial DNA is most susceptible
Chemical
Chemical alkylation
methylation of guanine
Cells have mechanisms to correct most of these modifications.
可用來傷害癌細胞
輻射誘變的分子機制
紫外光誘導嘧啶二聚化
skin cancers
Ionizing radiation (x rays and γ rays) causes ring opening and strand breaking.
difficult to fix
Other Functions of Nucleotides
Energy Source
Coenzymes
Regulatory Molecules
