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Nucleotides and nucleic acid - Coggle Diagram
Nucleotides and nucleic acid
Nucleic acids
What: polymers of nucleotides
Functions
Storage of genetic info(DNA)
transmission of genetic info (mRNA)
processing of genetic information (ribozymes)
protein synthesis (tRNA and rRNA)
RNA
Hydrolysis
unstable under alkaline conditions(Base)
catalyzed by enzymes (RNase)
S-RNase in plants prevents inbreeding.
RNase P is a ribozyme (enzyme made of RNA) that
processes tRNA precursors.
Dicer(切丁酶): cleaves double-stranded RNA into oligonucleotides.
protection from viral genome
RNA interference technology
mRNA
One mRNA may code for more than one protein
synthesized using DNA template and generally occurs as a single strand
Palindromic(回文) Sequences Can Form Hairpins and Cruciforms
DNA
Forms of DNA
A form
B forms(common one)
Z form
Complementarity of DNA Strands
suggests a possible copying mechanism for the genetic material
Replication
Denaturation
Induced by high temperature/ change in pH
Reversible:annealing
monitored by UV spectrophotometry at 260 nm
Factors Affecting DNA Denaturation
Base composition (C&G Tm higher )
DNA length
pH and ionic strength
Denaturation of Large DNA Molecules Is Not Iniform(from A&T多的地方開始）
Each strand serves as a template
DNA polymerases
Nucleotides
Functions
energy for metabolism (ATP)
enzyme cofactors (NAD+)
signal transduction (cAMP)
Comprise
Nitrogenous base
Pyrimidine
Cytosine
Thymine (DNA but也有少少變異在RNA show up)
Uracil(RNA)
N1連接pentose
Purine
Adenine
Guanine
N9 connect to pentose
Characteristics
Nitrogen-containing heteroaromatic molecules
Planar or almost planar structures
Absorb UV light (effective photoprotection of genetic material)
Connection : N-glycosidic bond
Free rotation
Syn 0度 向內
anti 180度 向外(found in normal B-DNA)
Bond cleavage is catalyzed by acid
Prototropic Tautomers(互變異構物)：H+ switch
Lactation-lactim (heterocycles)Sth. similar to Uracil
Base pair
A&T C&G(Watson-Crick base pairs)
Purine pairs with pyrimidine.
Pentose
DNA: β-2’-deoxy-d-ribofuranose(去氧)
RNA: β-d-ribofuranose
Different puckered conformations of the sugar ring are possible.
Phosphate
Phosphate group
Negatively charged at natural pH
Typically attached to 5’ position(5號C)
Two leaving group (beta&gamma)
Attached to other positions for specialized function
Nucleoside(without phosphate)
IN DNA
Modification is done after DNA synthesis
5-Methylcytosine:eukaryotes & bacteria
N6-Methyladenosine:bacteria
mark own DNA so that cells can degrade foreign DNA
(prokaryotes)
mark which genes should be active (eukaryotes)
In RNA
Inosine
Sth. like pyrimidine
Provide richer genetic code
Where:tRNA(wobble position)
Pseudouridine
more common in eukaryotes but found also in
eubacteria
Where:tRNA &rRNA
Made from uridine
Stabilize the structure of tRNA
Help in folding of rRNA
5號C接ribose(uridine:N1)
Other functions
Energy source ex. ATP
Coenzyme
Regulatory molecules ex. cAMP
Polynucleotide
phosphodiester linkages(covalent bond) negatively charged backbone
Hydrolysis accelerated by enzymes (DNAse)
no branching or cross-links
We read the sequence from 5’ to 3’
Molecular Mechanisms of Mutagenesis
Deamination(spontaneous)
Slow
Large number of residues
Depurination(spontaneous)
N-glycosidic bond is hydrolyzed
Fast
Oxidative damage
hydroxylation of guanine
mitochondrial DNA is most susceptible
Cells have mechanisms to correct most of these modifications.
Chemical Mutagenesis
Chemical alkylation
methylation of guanine
Cells have mechanisms to correct most of these modifications.
Radiation-Induced Mutagenesis
UV light :skin cancer
induces dimerization of pyrimidine
Ionizing radiation :(x rays and γ rays)
ring opening
strand breaking
Difficult to fix
Some can modification
Accumulation of mutations is linked to aging and carcinogenesis