DNA structure and function Flashcards
What are nucleotides?
Monomers of nucleic acids
8 common varieties
Made from: nitrogenous base, sugar and at least one phosphate group
Either purine or pyrimidine
What are the purines and pyrimidines?
Purines - two rings (larger)
Adenine and Guanine
Pyrimidines - one ring (smaller)
Cytosine, Thymine and Uracil
All use a pentose sugar
What are some properties of the nucleotide bases?
Planar
Aromatic rings
Sp2 hybridised C
Polar functional groups around the edges of the rings
What are some properties of the nucleotide sugars?
Based on the pentose – ribose (RNA) or 2’-deoxyribose (DNA)
Not flat
Not an aromatic ring
Sp3 hybridised C
Polar functional groups around and in the ring
What are the bases, nucelosides (without PO4-) and the nucelotides of A, G, C, U and T?
Adenine - Adenosine - Adenylic acid Guanine - Guanosine - Guanylic acid Cytosine - Cytidine - Cytidylic acid Uracil - Uridine - Uridylic acid Thymine - Deoxythymidine - Deoxythymidylic acid
What is the most well known nucleotide?
ATP - adenosine triphosphate
Contains: adenine, ribose and 3 phosphate groups
Used as an energy carrier/tranfer agent
What are nucleic acids?
Polymers of nucleotides
The phosphates bridge the 3’ and 5’ positions of niehgbouring ribose units
The phosphates of these polynucleotides are acidic, so at physiological pH, nucleic acids are polyanions
Describe the bond between nucleotides?
The linkage between nucleotides are phosphodiester bonds
The phosphate is esterified to two ribose units
What is the 5’ end and the 3’ end?
5’ end - the terminal residue whose C5′ is not linked to another nucleotide
3’ end - the terminal residue whose C3′ is not linked to another nucleotide
Nucleic acids are written left to right - 5’ end to 3’ end
What is Chargaff’s rule?
Chargaff’s rule 1:1 ratio of A=T and G=C, with each having the same amount (meaning same amount of A as T)
What is the structure of DNA?
A double helix of antiparallel strands of polynucleotides - forms right handed helices
Complementary base pairs (the basis of inheritance) joined by hydrogen bonds
The bases occupy the core and the sugar-phosphate chains run along the perihpery to minmise repulsion between charged PO4- groups
The surface contains two grooves of unequal widths:
Major and minor
What can purines and pyrimidines assume?
They can assume different tautomeric forms
Tautomerisation - the ability of the nucleotide bases to form differing chemical forms with the same chemical formula = isomers
What does tautomerisation affect?
Which form is dominant affects H bond donor/acceptors
This would allow variant base pairing = mutation destroying the genetic material
However, equilibria is strongly leaning towards the keto form = not a problem
What different formations can DNA adopt?
B-DNA - Right handed helix, wide major groove, narrow minor groove and pitch 34 A
A-DNA - Right handed helix, narrow major groove, wide minor groove and pitch 34 A
Forms when dehydrating B-DNA
Z-DNA - Left handed helix, flat major groove, narrow minor groove and pitch 44 A
Hypothetical structure but should exist in vivo
B-DNA is the most common form
Describe B-DNA structural features?
Two antiparallel polynucleotide strands in a right handed manner
Planes of nucleotide bases perpendicular to the helix axis - only edges of the base pairs are exposed to solvent
Each base pair has approximately the same width = near perfect symmetry
Ideal B-DNA has 10 base pairs per turn and pitch (rise per turn) of 34 A
