How are eukaryotic cell organelles classified by membrane number?
As nonmembranous, one-membrane, or two-membrane structures.
Which structures are nonmembranous in eukaryotic cells?
Ribosomes, microtubules, microfilaments, and chromosomes.
What organelles are included in the endomembrane system?
The nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vesicles, and plasma membrane.
What is the endoplasmic reticulum?
A convoluted membranous network extending from the nuclear surface through much of the cytoplasm.
How does the endoplasmic reticulum's membrane surface compare to the plasma membrane?
It has up to 30 times greater membrane surface than the plasma membrane.
What distinguishes rough endoplasmic reticulum from smooth endoplasmic reticulum?
Rough ER has membrane-bound polyribosomes; smooth ER lacks attached ribosomes.
What proteins does the rough endoplasmic reticulum produce?
Membrane-associated proteins, proteins of membranous organelles, and secreted proteins.
What does the smooth endoplasmic reticulum synthesize?
Phospholipids and steroids.
What detoxification role does the smooth endoplasmic reticulum have?
It detoxifies potentially harmful exogenous molecules.
How does the smooth endoplasmic reticulum regulate calcium ions?
It sequesters and controls the release of Ca2+ ions.
What are ribosomes composed of?
Many different proteins and at least three ribosomal RNAs.
Where do free ribosomes generally synthesize proteins?
In the cytoplasm.
What do ribosomes bound to the endoplasmic reticulum synthesize?
Proteins exported from the cell or incorporated into membranes.
What particle detects the amino acid sequence in cotranslational sorting?
The signal recognition particle.
Where does cotranslational sorting direct proteins first?
To the endoplasmic reticulum.
After the ER, where are proteins directed in cotranslational sorting?
To the Golgi complex, lysosomes, secretory vesicles, or plasma membrane.
What happens to improperly folded proteins in ER-associated degradation?
They are translocated back into the cytosol.
How are proteins marked for degradation in ER-associated degradation?
They are conjugated to ubiquitin.
Who discovered the Golgi apparatus and when?
Camillo Golgi discovered it in 1898.
What is the Golgi apparatus composed of?
Stacked membranous cisternae.
What is the function of the Golgi apparatus?
It processes and packages proteins from the rough ER.
What is the role of the cis face of the Golgi apparatus?
It is the receiving region.
What does the medial region of the Golgi apparatus contain?
Intermediate cisternae.
What is the function of the trans face of the Golgi apparatus?
It is the exit and sorting region.
Where do proteins enter the Golgi apparatus?
Proteins enter the cis face in transport vesicles.
Through which Golgi region do proteins move for enzymatic modification?
Proteins move through medial cisternae for enzymatic modification.
From which Golgi face do proteins leave in vesicles?
Proteins leave from the trans face in vesicles.
What are the three main functions of the Golgi apparatus?
The Golgi modifies secretory products, sorts them, and forms transport vacuoles.
Name two important modifications performed by the Golgi apparatus.
Sulfation and many glycosylation reactions are important Golgi modifications.
Which coat proteins guide vesicle movement in the Golgi?
Coat proteins COPII and COPI guide vesicle movement.
What are lysosomes in cells?
Spherical membrane-enclosed vesicles for intracellular digestion.
How many types of hydrolytic enzymes do lysosomes contain?
More than 40 types of hydrolytic enzymes.
Which enzyme in lysosomes degrades proteins, nucleic acids, carbohydrates, and lipids?
Acid phosphatase.
At what pH do lysosomal enzymes function optimally?
Approximately pH 5.0, an acidic environment.
Why does the cytosol's less acidic pH protect it from lysosomal digestion?
Because lysosomal enzymes are inactive at the cytosol's higher pH.
How many lysosomes can a typical animal cell contain?
Up to 100 lysosomes.
How many lysosomes can phagocytic macrophages contain?
Up to 1000 lysosomes.
What is heterophagy in lysosomal pathways?
The lysosomal breakdown of foreign substances absorbed by endocytosis.
What does autophagy break down in lysosomal pathways?
The cell's own storage nutrients, macromolecules, or nonfunctional organelles.
What is autolysis in cell pathology?
Digestion of cells caused by pathology or aging after lysosomal membrane breakdown.
Where do primary lysosomes originate and what do they contain?
They emerge from the Golgi apparatus with inactive acid hydrolases.
How are secondary lysosomes formed?
By fusion of primary lysosomes with endocytic vesicles containing material to be digested.
What happens to digestion products from secondary lysosomes?
They are released into the cytoplasm for reuse.
What do residual bodies contain in lysosomal digestion?
Condensed vesicles containing indigestible molecules.
What causes lysosomal diseases and their main effects?
Deficiency of a lysosomal enzyme causing macromolecule accumulation, enlarged lysosomes, cellular dysfunction, and CNS damage.
Test your knowledge with 20 questions on Eukaryotic Cell Organelles.
1. Which classification best describes the major categories of eukaryotic cell organelles?
2. Which set contains components of the eukaryotic endomembrane system?
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