essay 2 - Nucleotides – composition and structure. Free nucleotides of biologic significance. Nucleic acids – composition and structure. DNA and RNA. Levels of organization of DNA – nucleosomes and chromosomes. Types of RNA molecules – mRNA, tRNA, rRNA, miRNA.

section

• nucelotides

• function of nucelotides

• nucleic acid

• dna and rna difference

• dna organisation levels

• types of rna molecules

• nucelotides

• made up of: nitrogenous base, pentose group, phosphate group

• purine base is either adenine or guanine base

• pyrimidine base has either cytosine or thymine or uracil (in RNA)

• pentose group is either ribose or deoxyribose

• nitrogenous base is bonded to ribose via glycosidic bond

• ribose group bonded to phosphate group via phosphodiester bond

• function of nucelotides

• building blocks on nucleic acid

• metabolic role

• regulators

• allosteric effectors

• nucleic acid

• nucleic acids are polynucleotides, lots of nucleotides joined together by phosphodiester bonds

• phosphodiester bond between 5’ hydroxyl group on one sugar to 3 hydroxyl group on next sugar in chain

• phosphodiester bonds found in both dna and rna

• direction of nucleic acid is 5’-3’

• nucleic acid is read in same 5’-3’ direction

• dna and rna difference

• dna organisation level

• DNA is a double-stranded helix with antiparallel strands

• Held together by hydrogen bonds:

  • A–T has 2 hydrogen bonds

  • G–C has 3 hydrogen bonds

• Most DNA helices are right-handed, except Z-DNA (left-handed)

• DNA is packaged into chromosomes

• Chromosomes are made of DNA tightly coiled around histone proteins

• Histones are positively charged proteins that bind to negatively charged DNA

• DNA + histones form nucleosomes, which help compact DNA into the nucleus

• types of rna molecules

• mRNA (messenger RNA)

• tRNA (transfer RNA)

• rRNA (ribsoomal RNA)

• miRNA (micro RNA)