Eukaryotic Test Lecture 2

• 1. Found in animal cells NOT in plants
• 2. pH in lysosomal compartment ~4.6
• 3. Contain about 50 diff. acid hydrolases
• 4. Vary in size (25nm-1000nm) in diameter
• 5. Carbohydrate chains of highyl glycosylated integral proteins protect the membrane from attack by enzymes

Heterophagy: Breakdown of materials brought into the cell from Extracellular environment

Autophagy: Regulated turnover of cell's organelles

As much as 90% of volume of many cells is occupied by a single membrane-bound, fluid-filled central vacuole

• 1. Storage of cell's solutes and macromolecules, including ions, sugars, AAs, proteins, and polysaccharides
• 2. A number of active tranport systems are in the vacuole membrane. Provides turgor (hydrostatic pressure)
• 3. Sites of intracellular digestions

• 2 basic processes:
• 1. Endocytosis: Cells internalize cell surface receptors and bound extracellular ligands
• 2. Phagocytosis: Uptake of particulate matter

Bulk-Phase endocytosis (Pinocytosis): Nonspecific uptake of EC fluids. Primarily functions in the recycling of membrane between cell surface and interior compartments

Receptor-mediated endocytosis: Uptake of specific EC macromolecules (ligands) following their binding to receptors on surface of the PM

Each clathrin molecule consists of 3 heavy and 3 light chains

triskelions join together to form lattice of hexagons. When lattice is curved, some hexagons are converted to pentagons

A layer of Adaptor Complexes (AP2) situates between clathrin lattice and surface of the vesicle

GGA adaptor has a single subunit w/several domains.

• AP2 adaptor contains multiple subunits having diff. functions
• -(u) subunit bind cytoplasmic tail of specific PM receptors
• -(b) subunit binds and recruits clathrin molecules

Dynamin is a GTP-binding protein, required for release of a clathrin coated vesicle from a membrane

• 1. Endocytic vesicles fuse w/each other to form early endosomes. pH in lumen is lowered to ~5.9 by H(+)-ATPases in membrane
• 2. Different types of receptors & ligands are sorted & directed along diff. pathways
• 3. pH continues to drop to 5.0-6.0. Vesicles fuse w/vesicles from TGN which carry lysosomal enzymes to form late endosomes
• 4. Most of materials inside are degraded in late endosomes
• 5. Late endosomes fuse w/lysosomes (pH 4.6) to digest those not digested in late endosomes. Lysosomes are end products of endocytosis

Carried out by a few types of cells specialized for the uptake of relatively large particles (>0.5 um )

• 1. Many single-celled protists (amoebas and ciliates) use phagocytosis as a mode of feeding
• 2. Most animals use phagocytosis as a protective mechanism

Engulfment of phagocytosis is driven by contraction of actin-containing microfilaments that underlie PM

Hollow, cylindrical, protein-degrading machines found in both nucleus and cytosol of cells

-(B) subunits functions as proteolytic enzymes

A Polyubiquitin chain is covalently attached to proteins to be degraded by proteasomes

Short signal peptide chain directs posttranslational transport of a protein

Some signals peptides (targeting signals/signal sequences) are cleaved from protein by peptidases after proteins are transported in

AA sequences of signal peptides direct synthesized proteins in cytosol into certain organelles such as nucleus, mitochondrial matrix, chloroplast, and peroxisome

1. Signal peptide: Peroxisomal Targeting Signal (PTS) for matrix or mPTS for peroxisomal membrane protein

2. PTS receptors bind to peroxisome-destined proteins in cytosol & shuttle them to peroxisome membrane

3. Peroxisomes are able to import peroxisomal matrix proteins in native, folded, compartments, even those having multiple subunits

1. Majority of mit. & chlo. proteins are encoded by nuclear genome, synthesized in cytosol, & imported post-translationally

2. Outer & inner envelope contain distinct translocation complexees that work together during import (TOM & TIM for mit. & TOC & TIC for chlo.)

3. Chaperones aid in unfolding of polypeptides in cytosol & folding of proteins in mit. & chloro.

• 4. Proteins are synthesized w/signal peptide: removable N-terminal sequence or internal targeting sequence
• a. Matrix: removable N-terminal transit peptide
• b. IMM: integral targeting sequence remain as part of molecule
• c. thylakoid: thylakoid transfer domain in transit peptide