Cell Biology Lecture 29 p.568-583 Chapter 12 Mitochondria, Chloroplast, Peroxisome, E.R.

Most proteins of mitochondrion, chloroplast = nuclear encoding.

Chloroplast from inside to out: Thylakoid space, thylakoid membrane, matrix space (stroma), inner membrane, intermembrane space, outer membrane. Mitochondrion lacks thylakoid.

How proteins targeted? Signal peptide (12 a.a. min.) amphipathic(⁺ one side, hydrophobic other) helix + ATP(mito and chloroplast) + PMF ([mitoch]H⁺ from matrix to intermembrane space) cytosolic protein to matrix, crossing both membranes at once, with hsp70 forms on each side; signal clipped off.

Some proteins = cytosol to matrix, back to intermembrane; others = stop ½ way through. If hydrophobic section clipped off, intermembrane protein. If not, inner membrane protein.

Thylakoid: cross 2 membranes (chloroplast signal sequence) then, stromal peptidase exposing thylakoid signal sequence.

Peroxisomes: All proteins imported, most functions duplicated by mitochondrion. Peroxidase to detoxify. Acetaldehyde concentrations in alcoholics, siblings of alcoholics, identical twins, etc.

Glyoxylate cycle = 2 acetyl CoA to succinate in plants. Animals can't convert fats to sugars(no gluconeogenesis). Photorespiration also. 3 a.a. signal = into peroxisome.

E.R. More than ½ total cell membrane. Lipid + protein biosynthesis. Cotranslational import.

P450 of liver = detoxification of various molecules. ER signal peptide = ribosome to ER.

Rough and smooth microsomes. Sucrose gradients

Amino terminal signal peptides guide all proteins made by ER.

Signal-recognition particle + "docking Protein guide ribosome to ER.