Cell Organelles: Peroxisomes, Vacuoles, Golgi, Lysosomes, and ER

Flashcards covering the structure, function, and formation of peroxisomes, vacuoles, the Golgi apparatus, lysosomes, the nucleus, and the endoplasmic reticulum, as well as their roles in cellular processes.

What is the primary function of peroxisomes regarding hydrogen peroxide?

Peroxisomes use the enzyme catalase to break down hydrogen peroxide (H₂O₂) into water (H₂O) and oxygen gas (O₂).

How is a premature peroxisome formed?

Vesicles bud from the ER membrane and fuse with each other to form a premature peroxisome.

What makes a premature peroxisome mature?

The import of additional proteins and lipids results in a mature peroxisome.

Why is it beneficial for cells to break down H₂O₂ using catalase rather than metal ions?

In the presence of metals like iron (Fe²⁺), H₂O₂ can break down to form highly reactive and damaging hydroxide free radicals (•OH), which catalase avoids.

Describe the general characteristics of vacuoles.

Vacuoles are prominent organelles in plant cells, fungal cells, and certain protists, containing fluid and sometimes solid substances, formed by the fusion of smaller membrane vesicles.

What are the two important purposes of a large central vacuole in mature plant cells?

It stores large amounts of water, enzymes, inorganic ions, proteins, and pigments, and it performs a space-filling function by exerting turgor pressure on the cell wall.

How do contractile vacuoles in some protists, like paramecia, maintain cell volume?

They expand as water enters the cell and then fuse with the plasma membrane to expel excess water, preventing the cell from bursting.

What is the role of vacuoles in degradation?

Some protists engulf food into food vacuoles containing hydrolytic enzymes, and in animals, phagocytic vacuoles fuse with lysosomes to destroy ingested substances like bacteria.

Who discovered peroxisomes and when?

Christian de Duve discovered peroxisomes in 1965.

What type of cells in mammals contain a large number of peroxisomes and why?

Liver cells contain a large number of peroxisomes because toxic molecules accumulate there and are broken down.

Who discovered the Golgi apparatus and when?

The Golgi apparatus was discovered by Italian microscopist Camillo Golgi in 1898.

Describe the structure of the Golgi apparatus.

It consists of a stack of flattened membranes, each enclosing a single compartment called a cisterna.

What are the three compartments of the Golgi apparatus based on their orientation?

The cis Golgi (near the ER), the medial Golgi (in the middle), and the trans Golgi (closest to the plasma membrane).

According to the cisternal maturation model, how do materials move through the Golgi?

Vesicles from the ER fuse to form a new cisterna at the cis face, and then the cisternae themselves mature and move progressively from the cis to the trans face.

What are the three overlapping functions of the Golgi apparatus?

Protein sorting, processing (glycosylation and proteolysis), and secretion.

What process occurs in the Golgi apparatus where enzymes cut proteins into smaller polypeptides?

Proteolysis, for example, converting proinsulin into functional insulin.

What is the secretory pathway?

The route by which proteins destined for secretion are synthesized into the ER, travel through the Golgi, and are then transported by vesicles to the plasma membrane to be released outside the cell.

What are lysosomes and what is their primary function?

Lysosomes are small organelles found in animal cells that are involved in the intracellular digestion and breakdown of molecules and macromolecules.

What type of enzymes do lysosomes contain, and at what pH do they function optimally?

Lysosomes contain many acid hydrolases, which are hydrolytic enzymes that function optimally at an acidic pH, approximately 4.8.

Why is the cell protected from significant damage if a lysosomal membrane breaks?

If lysosomal acid hydrolases are released into the cytosol, they are not very active because the cytosolic pH is neutral (approximately pH 7.0) and buffered.

What are the primary functions of the nucleus?

The protection, organization, replication, and expression of the genetic material, as well as the assembly of ribosomal subunits.

What is the nucleolus and what happens there?

The nucleolus is a droplet organelle within the nucleus where ribosomal subunits are assembled from imported ribosomal proteins and RNA molecules.

Describe the structure of the endoplasmic reticulum (ER).

The ER is a network of membranes forming flattened, fluid-filled tubules (cisternae) that enclose a single continuous internal space called the ER lumen.

What is the relationship between the ER membrane and the nuclear envelope?

The ER membrane is continuous with the outer nuclear membrane.

What gives the rough endoplasmic reticulum (rough ER) its bumpy appearance?

Its outer surface is studded with ribosomes.

List key functions of the rough ER.

Protein sorting, insertion of membrane proteins, and glycosylation (attachment of carbohydrates to proteins and lipids).

What is a main difference between rough ER and smooth ER?

Rough ER is studded with ribosomes, while smooth ER lacks ribosomes.

List key functions of the smooth ER.

Metabolism (e.g., detoxification in liver cells), storage of Ca2+, and lipid synthesis and modification (e.g., phospholipids, steroid hormones).

What is the nuclear envelope?

The nuclear envelope is a double-membrane structure that encloses the nucleus.

What is the function of nuclear pore complexes?

They provide passageways for the movement of molecules and macromolecules into and out of the nucleus.

What two components make up the nuclear matrix?

The nuclear lamina (intermediate filaments lining the inner nuclear membrane) and an internal nuclear matrix (connected to the lamina, filling the nucleus interior).

What is chromatin?

Chromatin is the complex formed between DNA and many types of proteins (like histones) that compact the chromosomes inside the nucleus.

What concept describes how chromosomes are organized within the nucleus?

Each chromosome is located in a distinct, nonoverlapping chromosome territory within the nuclear matrix.

List the components of the endomembrane system.

The nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, peroxisomes, and the plasma membrane.