L and D isomers of amino acids

Ionization state as a function of pH

• Trans and cis • Peptide bonds

• Trans and cis X-Pro• Peptide bonds

Rotation about bonds in a polypeptide

Ramachandran diagram

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 PrP, 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