L and D isomers of amino acids Ionization

L and D isomers of amino acids

Ionization state as a function of p. H

• Trans and cis • Peptide bonds • Trans and cis X-Pro • Peptide bonds

Rotation about bonds in a polypeptide

Ramachandran diagram

a-helix

Ferritin, an iron-storage protein

Antiparallel -sheet

A parallel -sheet

A fatty acid-binding protein

A leucine-zipper

Collagen triple helix

Collagen helix

Hemoglobin

Many sequences can adopt alternative conformations in different proteins.

Misfolding and aggregation • Neurological diseases can be transmitted purely by proteins • Bovine spongiform encephalopathy (mad cow disease) • Creutzfeldt-Jakob disease (CJD) in humans, Scrapie in sheep (Nobel prize in Physiology 1997)

Prion diseases • Transmissible agent consists of aggregated forms of a specific protein. • The protein aggregates are resistant to treatment with agents that degrade most proteins • The protein is lagely or completely derived from a cellular protein, called Pr. P, that is normally present in brain

Prion aggregation

A structure of amyloid fibers

Ribose and deoxyribose

Backbones of DNA and RNA

• The human genome 3 billion nucleotides 24 different chromosomes • Indian muntjak, 3 chromosomes

A prokaryotic and an eukaryotic cell

Gene expression