Amino acids, proteins and DNA

Amino acids, proteins and DNA

11.1 Amino acids bifunctional molecules containing -NH2 and -COOH all natural occurring α-amino acids exist as optical isomers and occur as the ι-isomer naturally occurring 2-amino acids have similar structures, only R groups are different Acid-base properties: -COOH is weakly acidic -NH2 is weakly basic amino acids can act as both weak acids and weak bases zwitterion: existing simultaneously as an anion and cation isoelectric pH: the unique pH value at which a specific zwitterion exists relatively high mps: electrostatic attraction between oppositely charged parts of the ion

11.2 Proteins α-amino acid: an amino acid in which both -NH2 and -COOH groups are attached to the same C 2° structure: α-helix or β-pleated sheet: 2 possible structures of a protein 3° structure: determined by overall 3D shape in which 2° structure arranges itself disulphide bond: one of the strongest types of bond in proteins - occur between 2 cysteine amino acids peptide: compound formed from amino acids joined by peptide bonds (di=2, poly=many) one or more polypeptide form a protein peptide bond: formed when 2 amino acids join by condensation -CONH-

11.4 DNA made up of 2 polymer strands that are held together by H bonding (leading to double helix shape) the monomers are nucleotides which consist of a phosphate, sugar and base the 4 bases are: thymine, cytosine, adenine and guanine DNA is made by nucleotides linking together via the phosphate possible pairs: AT and CG (they fit exactly in terms of shape and size) the AT pair has 2x H bonds and the CG has 3 cell replication: double helix unwinds -> complementary nucleotides bind to 2 unwound chains (=2 copies)

11.5 Action of anti-cancer drugs - chemotherapy drugs that affect cell division do so by binding to DNA to stop replication cisplatin works by: a Cl- is replaced by water then by an N from a guanine base this creates a Pt-N bond this fixes drug to one strand of DNA a 2nd Cl- is lost from Pt, allowing a 2nd guanine base to bind this distorts shape of DNA, preventing replication side effects of cisplatin:-kidney damage-damage to intestinal cells-affect action of other molecules (enzyme action)-damage to hair follicles-nerve damage-damage to bone marrow-nauseatherefore, chemo is given:-in small quantities-at regular intervalsthis is to allow the body to recover