Integrated SequencePhysics Chemistry Organic Biology

Web Resources

University of Saskatchewan - Similarities and Differences Between DNA and RNA
Basic table covering structural similarities and differences between DNA and RNA.



  click if a link is broken



Special points of emphasis

Intermolecular Forces

Nucleic Acids

Gene Expression

Nucleic acids are polymers of nucleotides in which the 5' oxygen of one nucleotide is linked to the 3' oxygen of another by means of a phosphate ester linkage, called a phosphodiester bond. DNA differs from RNA in that DNA lacks a hydroxyl group on the number two carbon of ribose.

The Watson and Crick model of DNA structure proposed the double helix in which adenine and thymine form a base pair connected by two hydrogen bonds while guanine and cytosine form a base pair with three hydrogen bonds. Base pairing allows DNA to serve as the template for its own replication as well as to serve as the template for protein biosynthesis. Base pairing allows for the complementary relationship of gene sequence with protein sequence (a triplet of adjacent nucleotides being a codon, standing for a single amino acid) mediated by mRNA and tRNA (although the relationship between the sequence of codons in DNA and the ultimate amino acid sequence in proteins can be complex, especially in eukaryotes, where the primary RNA transcript generally undergoes processing prior to translation on the ribosomes).




Intermolecular Forces

Chemical Thermodynamics and the Equilibrium State

Nucleic Acids

Gene Expression

The Molecular Biology Laboratory

Because the unwinding of the double helix occurs abruptly at a certain temperature, the process is referred to as 'melting'. The higher the GC percentage, the higher the melting temperature. The melting temperature can be lowered by the addition of urea or formamide.

Urea and formamide are the two most common agents which accomplish chemical denaturation. These substances act to disrupt the hydrogen bonding between the nitrogen bases. Usually some combination of formamide, urea, and heat is employed, for example, in sample preparation for denaturing electrophoresis of DNA, an important separation technique for analysis or purification in the molecular biology laboratory.




Chemical Thermodynamics and the Equilibrium State

Reactions of Carboxylic Acids and Derivatives

Reactions of Organic Phosphorus Compounds

Nucleic Acids

Gene Expression

The chain elongation reactions catalyzed by DNA or RNA polymerases are nucleophilic addition-elimination reactions similar to the acyl substitution reactions among carboxylic acid derivatives but occurring here upon the innermost phosphate group of a deoxyribonucleoside triphosphate instead of a carbonyl group. Picture deoxyribonucleoside triphosphate in your mind. The nucloephile is the 3' -OH terminus of the primer. Thermodynamically, the synthesis is driven forward by the hydrolysis of pyrophosphate.

The other major announced change with the new 2007 MCAT, aside from the somewhat shorter, computerized format, will be an increased emphasis on genetics and molecular biology. A major part of the challenge in preparing will be to work on your vocabulary and comprehension skills for passages in this area. In the above passage, were you comfortable reading 'deoxyribonucleoside triphosphate' or even more importantly, '-OH terminus of the primer'?




Proteins

Nucleic Acids

Gene Expression

Read for comprehension: DNA structure is dynamic. Evidence suggests the possibility that variations in structural properties depending on base sequence such as the rotation angle between residues and base roll might serve as conformational targets for proteins. Of the three forms, A-DNA. B-DNA (Watson-Crick form) and Z-DNA, B-DNA is by far the most commonly seen in the biological context. The B-DNA helix has a major and minor groove, an important structural feature for DNA-protein interactions.







The WikiPremed MCAT Course is a free comprehensive course in the undergraduate level general sciences. Undergraduate level physics, chemistry, organic chemistry and biology are presented by this course as a unified whole within a spiraling curriculum.

Please read our policies on privacy and shipping & returns.  Contact Us.
MCAT is a registered trademark of the Association of American Medical Colleges, which does not endorse the WikiPremed Course.


Creative Commons License
The work of WikiPremed is published under a Creative Commons Attribution Share Alike 3.0 License. There are elements of work here, such as a subset of the images in the archive from WikiPedia, that originated as GNU General Public License works, so take care to follow the unique stipulations of that license in printed reproductions. You can use the resources here for commercial or non-commercial purposes, but please give attribution and a link to the production credits and edit history of the resource. For the works here which began as my individual work, please attribute "John Wetzel, an author at wikipremed.com".