nucleotides: composition and structure

• DNA: deoxyribonucleic acid
• RNA: ribonucleic acid

• mRNA: carries genetic information from the nucleus and into cytosol 
• tRNA: carries the amino acids to ribosomes
• rRNA (ribosomal RNA): is the structural component of ribosomes where protein is synthesized. 
• snRNA (small nuclear RNA): component of small nuclear ribonucleoprotein particles which process heterogeneous RNA (hnRNA) into mature mRNA.
• in viruses, RNA stores genetic information

stores genetic information used for the synthesis of proteins

• sequence of nucleotides defines primary structure of DNA and RNA.
• linked by phosphodiester bonds of 5' carbon to 3' carbon
• oxygen and nitrogen atoms in the backbone give DNA and RNA "polarity"
• 

• pairing of bases where A-T, G-C by hydrogen bonds
• 
• G-C pair: 3 H bonds
• A-T pair: 2 H bonds
• The secondary structure of DNA consists of two complementary polynucleotide chains wrapped to form a double helix. Orientation of helix is usually in B-form (right handed with 10 nucleotides per turn). Contain major and minor grooves

B-form: right handed with 10 nucleotides per turn

C bind with G and A bind with T. Equal number of C to G and equal number of A to T

at the grooves were the functional groups on the bases are exposed

Consists of a single polynucleotide where folding occurs between complementary regions, resulting in both single and double stranded regions. The strands are antiparallel and assume a helical shape the helices are of the A-form.

contains multiple single stranded stem loop structures.

via exo and endo nucleases that cleave RNA and DNA via methylation

cleave nucleic acids from the ends

cleave at specific sequences within or near their sequences. The resulting fragments can be joined to other fragments to create new combinations of DNA sequences

DNA can be reversibly denatured enzymatically, chemically, or by heat.

• hyperchromic effect: increasing heat breaks the H bonds that holds the strands together and exposes the bases.
• The higher percentage of GC bonds the higher the Tm required to melt DNA because GC bonds have 3 H bonds compared two 2 hydrogen bonds from AT

the temperature at which 50% of DNA is denatured

Two DNA strands must be in contact to one another initiating base base pairing and must occur when temperature is below Tm

• cations (Na+,K+,Mg2+): decrease repulsion of negatively charged phosphate backbones of two DNA strands.
• Renaturation only occurs if the temperature is below the Tm

• occurs between nucleic acids from different sources (animals) resulting in a heteroduplex. 
• heteroduplexes indicates homology of DNA (similarity)
• DNA and RNA can hybridize with one another to form heteroduplexes.