Molecular BiochemistryBioc.432

Lab 1: Introduction to nucleic acids (Structural properties)

Nucleotide Structure

• Nucleic acids are polymers of nucleotides

• Nucleotides consist of– sugar

• RNA - ribose

• DNA - deoxyribose

– phosphate group– nitrogenous base

Nitrogenous Bases

• Purines - double carbon-nitrogen (bicyclic rings)

• Pyrimidines - single carbon-nitrogen ring (monocyclic rings)– uracil - RNA only– thymine - DNA only

Complementary Base Pairing

• Nitrogenous bases form hydrogen bonds

• Base pairs– A-T and C-G

• Law of complementary base pairing– one strand determines

base sequence of the other

Su

gar-ph

osph

ate back

bon

e

Su

gar-ph

osph

ate back

bon

e

Segment of DNA

DNA Structure: Twisted Ladder

DNA Function

• DNA is located in nucleus but small amount in the mitochndria.

• Serves as code for protein synthesis, cell replication and reproduction

• Gene - sequence of DNA nucleotides that codes for one polypeptide

• Genome - all the genes of one person

RNA Structure and Function

• Only one nucleotide chain• RNA forms globular conformations, in

which regions of helical structure are formed by intramolecular hydrogen bonds (secondary structure)

RNA

• RNA much smaller than DNA transfer RNA (tRNA) has 70 - 90 bases messenger RNA (mRNA) has over 10,000 bases DNA has over a billion base pairs

• Ribose replaces deoxyribose as the sugar• Uracil replaces thymine as a nitrogenous base

• Essential function:1. Interpret DNA code2. Direct protein synthesis

Types of RNA• Messenger RNA – mRNA - re-writes DNA

(transcription) and takes it out of the nucleus to the ribosome.

• Transfer RNA – tRNA -Carries amino acids in the cytoplasm to the ribosomes.

• Ribosomal RNA - rRNA- Building blocks of ribosomes. Assembled in the nucleolus.

• Small nuclear RNA- snRNA- small RNA molecules found in the nucleus. Important in number of processes including the maintenance of telomeres.