Chapter 9 (Cell Biology)
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Why do eukaryotic cells require membrane-enclosed organelles?
To isolate incompatible reactions, enhance local reactant concentrations, and allow specialized functions to occur simultaneously.
What property of membranes allows them to create isolated environments within cells?
Selective permeability.
Name three benefits of cellular compartmentalization.
Efficient reactions; Controlled environments; Separation of incompatible processes.
What is a hallmark feature of eukaryotic cells not found in prokaryotes?
Presence of membrane-bound organelles.
How do different organelles maintain unique internal environments?
By specific sets of lipids, proteins, and enzymes tailored to their functions.
What is the main function of the nucleus?
Housing and protecting genetic material; site of DNA and RNA synthesis.
What is the nuclear envelope and what is its special feature?
A double membrane surrounding the nucleus; its outer membrane is continuous with the ER membrane.
How does the nucleus communicate with the cytosol?
Through nuclear pores embedded in the nuclear envelope.
What are the two types of ER and how do they differ structurally?
Rough ER has ribosomes and flattened sheets; Smooth ER lacks ribosomes and forms tubular structures.
What are microsomes?
Vesicular fragments of ER that form spontaneously during cell homogenization.
List three key functions of the Rough ER.
Protein synthesis (membrane + soluble), initial glycosylation, folding and assembly of multimeric proteins.
What are three main roles of the Smooth ER?
Lipid biosynthesis, detoxification, and calcium storage.
On which ER surface does lipid biosynthesis occur?
Cytosolic (outer) monolayer of the Smooth ER membrane.
What is the Golgi apparatus composed of?
A stack of flattened membrane sacs called cisternae.
What is the primary function of the Golgi?
Sorting, processing, and packaging of proteins for secretion or delivery to organelles.
Where do ER vesicles enter and exit the Golgi?
Enter at the cis face, exit from the trans face.
What biochemical process does the Golgi complete that begins in the ER?
Protein glycosylation (modification of carbohydrate groups).
What is the primary function of lysosomes?
Controlled intracellular digestion of macromolecules and worn-out organelles.
What maintains the acidic pH of lysosomes?
ATP-driven proton (H+) pumps.
What are heterophagic vs. autophagic lysosomes?
Heterophagic digest materials from outside; autophagic digest internal organelles.
Why are lysosomes considered safe despite their destructive enzymes?
Enzymes only work at low pH, are made as inactive zymogens, and are contained within membranes.
What are lysosomal storage diseases and give an example.
Disorders caused by enzyme deficiency in lysosomes; e.g., Gaucher’s disease (lack of glucocerebrosidase).
What is the main function of mitochondria?
ATP production — the cell’s power plants.
Describe the structure of mitochondria.
Double membrane with inner folds (cristae) and an internal matrix.