Chapter 11 Assembly of Biomolecules

We’ve looked at the construction of monomers for the four classes of biomolecules. Now we will turn to how some of thosemonomers are turned into useful cell components, using proteins as examples

CO2

or othercarbon source

NH3

Also SO4-

Metabolic precursors

Amino Acids

Polypeptides

Mature, Functional Proteins

Modification, transport, etc.

Protein Structure

--- Proteins took over most of the catalytic and structural rolesin cells because of the greater chemical diversity ofamino acids (20) vs. nucleotides ( 4-5)

--- Most proteins get their biological activity from their complexthree dimensional shape

--- The three dimensional shape of a protein is largely determinedby its primary structure or amino acid sequence

--- Most proteins have plastic three dimensional shapes that areconstantly changing in at least small ways and the energybarriers to larger structural changes can be quite small

Factors Affecting Protein Structure:

Temperature, pH, solvent effects (ionic strength/ polarity)

Levels of Protein Structure and the Forces That Hold Them Together

Structural Force Components Level _____ ___________

1 peptide bond amino acids

2 hydrogen bonds -helices, -sheets, turns, etc.

3 Hydrophobic forces domains H-bonds, ionic, disulfides

4 as in 3 above whole active protein

Secondary Structure Elements

Alpha-Helix

Beta-Sheet

Stringing TogetherSecondary Structural Elements (Tertiary Structure)

Making Proteins Useful: (Getting Them Where They Need to be)

Secretion: (General Secretory Pathway, GSP) --- Moving proteins across the cytoplasmic membrane--- Requires protein machinery and energy--- Protein is moved across membrane while unfolded

Posttranslational modifications:Disulfide formationSignal Sequence CleavageCo-Factor insertionLipidation (Lipo-proteins)Cleavage

Start ofProtein

“Signal Sequence”in proteins to beexported across thecytoplasmic membrane

Cleavage

Family # of Proteins Energy Source MovesABC (I SP) 3-4 ATP proteins

Sec (II SP) ca. 12 ATP & pmf proteins general secretory

Fla/Path (III SP) 30+ ATP toxins

Conjugative >10 ATP DNA (IV SP)

OM AutoTrans. 1* ? proteins (V SP)

Tat (VI SP) 2-4 pmf folded (RR system) proteins

Secretion Systems in Bacteria

ABC Transporter

General Secretory Pathway (Type II)