Chapter 15: Intracellular Compartments and Protein Transport

Practice vocabulary flashcards covering intracellular compartments, protein sorting signals, and vesicular transport mechanisms as described in the Chapter 15 transcript.

Cytosol

The compartment responsible for metabolic pathways and protein synthesis, making up approximately $54\%$ of the total cell volume in a hepatocyte.

Nucleus

Contains the main genome and is the site of DNA and RNA synthesis; it occupies about $6\%$ of the liver cell volume.

Endoplasmic Reticulum (ER)

The most extensive membrane system in the cell; responsible for the synthesis of most lipids and the distribution of proteins.

Golgi apparatus

Organelle involved in protein and lipid modification for distribution, making up about $3\%$ of the total cell volume.

Lysosomes

Compartments used for intracellular degradation, with an approximate number of $300$ per liver cell.

Endosomes

Organelles responsible for sorting endocytosed materials; there are approximately $200$ per liver cell.

Mitochondria

Compartments with an approximate number of $1700$ per cell that perform ATP synthesis via oxidative phosphorylation.

Chloroplasts

Organelles in plant cells responsible for photosynthesis.

Peroxisomes

Organelles that function in the oxidation of toxic compounds, with approximately $400$ per cell.

K-D-E-L

The specific amino acid signal sequence located at the C-terminus required for a protein to be retained in the ER.

Nuclear localization signal

A sorting signal consists of a short stretch of lysines or arginines (positive charges) required for large molecules to pass through nuclear pores.

Ran

A GTPase (Ran-GTP & Ran-GDP) that provides energy through GTP hydrolysis for the active transport of proteins through nuclear pores.

Chaperonins

Also called chaperone proteins, they help re-fold proteins after they have been unfolded for transport across mitochondrial and chloroplast membranes.

Signal recognition particles (SRPs)

Cytosolic particles that recognize the ER signal sequence and, along with SRP receptors, direct proteins to the translocation channel.

Glycosylation

A protein modification in the ER involving the addition of a $14$-sugar oligosaccharide to an asparagine side group (N-linked).

Disulfide bond formation

The stabilization of protein structure through the oxidation of pairs of cysteine side chains in the ER.

Clathrin-coated vesicles

Vesicles with a protein coat that shapes the membrane into a bud and helps capture specific cargo molecules.

Adaptins

Proteins that trap transport receptors and anchor them to the clathrin coat.

SNARES

A family of transmembrane proteins including v-SNARES (vesicle markers) and t-SNARES (target receptors) that ensure specificity in target membrane fusion.

Constitutive exocytosis pathway

A default, continuous pathway that supplies new lipids and proteins to the plasma membrane and secretes proteins outside the cell.

Regulated exocytosis pathway

A pathway in specialized cells where secretory vesicles concentrate at the plasma membrane and only fuse when triggered by a signal.

Phagocytosis

Known as 'cellular eating,' it is the ingestion of large molecules or cells via large vesicles; macrophages scavenge about $10^{11}$ red blood cells per day.

Pinocytosis

Known as 'cellular drinking,' it is the indiscriminate ingestion of fluid and small molecules via small vesicles in all eukaryotic cells.

Receptor-mediated endocytosis

The uptake of specific molecules, such as cholesterol bound to low-density lipoproteins (LDL), via binding to complementary surface receptors.

Pseudopod

A sheet of plasma membrane extended by an activated phagocytic cell to engulf a target cell.