Cell Biology Quiz on Organelles and Functions

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Questions and Answers

Which primary function is characteristic of non-membranous organelles?

Concentrating enzymes and reactants for increased efficiency

Synthesizing proteins for export from the cell

Providing structural support and organization within the cell (correct)

Isolating harmful molecules from the cytoplasm

What is the main role of the membrane surrounding certain organelles?

To facilitate direct interaction between the organelle's enzymes and cellular proteins

To separate the internal environment of the organelle from the external environment thereby increasing efficiency and isolating harmful substances (correct)

To decrease the presence of enzymes and reactants inside the cell

To allow free movement of all molecules into and out of the organelle

If a cellular process required the action of enzymes and concentration of reactants, what cellular component would primarily be responsible?

Non-membranous organelles

The cytosol itself

Membrane-bound organelles (correct)

Inclusions within the cell

How does the presence of membrane-bound organelles affect the biochemical efficiency of a cell?

By concentrating enzymes and reactants within specific compartments, optimizing reaction rates Signup and view all the answers

Which of the following best describes the relationship between the nucleus and cytoplasm?

The cytoplasm surrounds the nucleus Signup and view all the answers

In which part of the cell would you primarily find inclusions?

In the cytoplasm, freely floating and contained outside organelles Signup and view all the answers

A researcher identifies a cell component made up of specific macromolecules and organized to carry out complex functions, what is their description?

Organelle Signup and view all the answers

Which modification of a protein is essential for cell viability and is characterized by the attachment of glycans?

Glycosylation Signup and view all the answers

Where in a eukaryotic cell does the majority of post-translational protein modification initially occur?

Rough endoplasmic reticulum (rER) Signup and view all the answers

What is the primary structural difference between N-linked and O-linked glycosylation?

The atom to which the glycan is attached Signup and view all the answers

In light microscopy (LM), what characteristic visual aspect does the Golgi apparatus exhibit in protein-producing cells like plasma cells?

A lightly stained area in the cytoplasm Signup and view all the answers

Which of the following best describes the functional difference between the 'cis' and 'trans' faces of the Golgi complex?

The cis face is where substances enter for processing, and the trans face is where they exit in vesicles. Signup and view all the answers

Which of the following is NOT a component of the cytosol?

Endosomes Signup and view all the answers

What is a primary function of the cytoskeleton within the cytosol?

Organizing organelles and providing mechanical support Signup and view all the answers

Which of the following best describes the function of inclusions found in the cytosol?

They are products of metabolic activity and insoluble substances Signup and view all the answers

Which of the following is characterized as a double membrane-bound organelle that provides energy to the cell?

Mitochondrion Signup and view all the answers

In which of the following cell types would mitochondria likely be the LEAST abundant?

Erythrocytes Signup and view all the answers

What is the general size range for mitochondria based on width and length?

0.5-1 μm wide and 10 μm long Signup and view all the answers

Which of the following best describes the lifespan of a typical mitochondrion?

One to ten days Signup and view all the answers

Which of the following is a non-membranous organelle?

Centrioles Signup and view all the answers

The presence of which of the following would indicate the cell has high metabolic demands?

An abundance of mitochondria Signup and view all the answers

Which enzyme, when released into the cytoplasm, directly triggers programmed cell death?

Cytochrome C Signup and view all the answers

The mitochondrial matrix does not contain which of the following?

Translocases Signup and view all the answers

What is the primary function of the electron-dense matrix granules found within mitochondria?

Storage of $Ca^{++}$ Signup and view all the answers

Which type of cells are most likely to contain tubulo-vesicular cristae?

Steroid hormone-secreting cells Signup and view all the answers

Which of the following mitochondrial processes is NOT directly involved in ATP production?

Apoptosis Signup and view all the answers

What is the primary source for the majority of proteins found in the mitochondria?

Free ribosomes in the cell cytoplasm Signup and view all the answers

What are translocases responsible for in the context of mitochondria?

Transporting proteins into the mitochondrial matrix Signup and view all the answers

Which of these enzymes is located in the intermembrane space of the mitochondria?

Cytochrome C Signup and view all the answers

What is the direct role of caspases in the cell?

Inducing apoptosis Signup and view all the answers

What is the significance of the two types of cristae morphology in mitochondria?

Different morphologies correlate with different cell functions. Signup and view all the answers

What is the primary function of translocases in mitochondria?

To facilitate the movement of proteins across mitochondrial membranes. Signup and view all the answers

Which of the following best describes the structural organization of the endoplasmic reticulum (ER)?

A mesh-like interconnected network of branching tubes and flattened lamellae. Signup and view all the answers

What is the distinguishing feature that differentiates the rough ER from the smooth ER?

The presence of ribosomes on the outer surface of the rough ER. Signup and view all the answers

What term describes the flattened, membrane-limited sacs that are characteristic of the rough ER?

Cisternae Signup and view all the answers

What is one of the primary functions associated with the rough endoplasmic reticulum (rER)?

Protein synthesis and post-translational modification. Signup and view all the answers

What components are ribosomes, which are found on the rough ER, made of?

rRNA and proteins Signup and view all the answers

Which of the following is a post-translational modification that occurs in the rER?

Glycosylation Signup and view all the answers

What is the critical consequence of improper protein folding?

Loss of biological activity. Signup and view all the answers

What type of interactions stabilize the three-dimensional structure of proteins?

Various molecular interactions, including hydrogen bonds and ionic bonds. Signup and view all the answers

What is the role of protein folding?

To form a biologically active 3D structure Signup and view all the answers

Study Notes

Cell Organelles

Cellular components are divided into nucleus and cytoplasm
Cytoplasm contains organelles and cytosol
Organelles are complexes of macromolecules, carrying out specific functions, some are membrane-bound and others are not
Membrane-bound organelles concentrate enzymes and reactants, increase biochemical efficiency and isolate harmful proteins and molecules from the rest of the cell
Non-membranous organelles include microtubules, centrioles, and nucleoli
Cytosol is a gel-like substance containing dissolved macromolecules, organic compounds & ions, cytoskeleton (microtubules, actin filaments and intermediate filaments), which organizes organelles and provides mechanical support. Also contains inclusions—products of metabolic activity and insoluble substances, such as glycogen, lipid droplets, lipofuscin, hemosiderin, and crystals

Learning Objectives

Describe location, function and staining characteristics of cytoplasmic organelles
Differentiate between membrane-bound organelles (rough ER, smooth ER, Golgi complex, mitochondria, lysosomes, and peroxisomes) and explain their functions
Differentiate between free polyribosomes and membrane-bound polyribosomes and identify their roles in protein sorting
Determine the trafficking of different classes of protein to their destination
Describe autophagy and cytoplasmic protein degradation
Explain how faulty protein degradation leads to Alzheimer's disease
Describe proteasome-mediated protein degradation
Describe the functions of peroxisomes
Identify all cell organelles in a given electron micrograph, indicating the cell types in which they are abundant

Mitochondria

Double membrane-bound organelle
Provides energy to the cell (generating & expending energy) abundant in heart muscle, liver cells, and some kidney cells
Absent in erythrocytes and terminal keratinocytes/corneocytes
Spherical or filamentous, acidophilic structures (0.5-1µm wide and 10µm long)
Constantly turning over, lifespan of 1-10 days (varies)

Mitochondria Structure

Possesses two membranes separated by intermembrane space
Outer membrane contains large channels (e.g., porins), permits ions & small molecules to enter the intermembrane space.
Inner membrane is impermeable to ions but projects into the matrix to form numerous folds (cristae), increasing the surface area, and is responsible for oxidative phosphorylation and ATP synthesis
Attached to the inner membrane are ATP synthase particles (elementary particles)
Matrix contains soluble enzymes of the Krebs cycle, enzymes for fatty acid oxidation, electron-dense matrix granules that store Ca++, mitochondrial DNA, ribosomes and tRNA

Mitochondria cont. (Intermembrane Space)

Contains specific enzymes: creatine kinase, adenylate kinase, and cytochrome C.
When cytochrome C is discharged into the cytoplasm, it initiates apoptosis (programmes cell death)
Cytochrome C activates caspase, a key enzyme in cell death or apoptosis

Mitochondria cont. (Matrix)

Surrounded by the inner membrane
Contains soluble enzymes of the Krebs cycle and enzymes for fatty acid oxidation; electron dense matrix granules store Ca++ and mitochondrial DNA, ribosomes and tRNA

Mitochondria cont. (Cristae)

Two types of cristae: tubular or vesicular and plate-like
Most cells contain mitochondria with plate-like cristae. Steroid hormone-secreting cells (e.g., adrenal cortex cells, gonadal cells) have tubulo-vesicular cristae

Mitochondrial Enzymes System

Responsible for ATP generation in various metabolic pathways (oxidative phosphorylation, citric acid cycle, beta oxidation of fatty acids)
Mitochondrial DNA synthesizes only 1% of mitochondrial proteins
The remaining proteins are synthesized by free ribosomes in the cytoplasm and transported into the mitochondrial matrix through protein complexes called translocases (TOM and TIM)
Absence of translocases affects mitochondrial functions

Endoplasmic Reticulum (ER)

Mesh-like interconnected maze of branching tubes and flattened lamellae (cisternae)
Two types: rough (rER) and smooth (sER)
Rough ER: ribosomes attach to the outer surface and is involved in protein synthesis, post-translational modification, proper protein folding and initial glycosylation.
Smooth ER: outer surface ribosomes-free, involved in synthesis of steroid hormones, membrane lipids, breakdown of toxins & drugs, detoxification, synthesis of triglycerides from monoglycerides in intestinal epithelium, and calcium sequestration in striated muscle (sarcoplasmic reticulum)

Ribosomes

In the cytosol, ribosomes are connected by a strand of mRNA (polysomes)
Found in two forms: free polysomes (free in the cytosol) and bound polysomes (attached to the outer surface of rER cisternae)
Synthesize different classes of proteins
Ribosomes are responsible for cytoplasmic basophilia in Light Microscopy (LM)

Golgi Complex (Apparatus)

Group of flattened sacs with vesicles around the margins.
From one to hundreds in a cell, depending on the cell type.
Prominent in protein-secreting cells.
At the transmission electron microscopy (TEM) level, it appears to consist of three defined regions: cis, medial, and trans.

Golgi Complex cont.

Cis face: receiving/forming/entry face; substances enter from the endoplasmic reticulum for processing
Trans face: exit face; matured proteins exit in the form of small detached vesicles.
Involved in concentrating and maturing proteins. The process of protein maturation involves movement through the cis, medial, and trans regions. Each region has its unique enzymes involved in protein maturation. Mature proteins are then secreted in vesicles.

Golgi Complex functions

Posttranslational modifications of proteins (O-glycosylation)
Sorting and packaging of proteins

Lysosomes

Membrane-bound organelles containing around 40 different types of enzymes working in an acidic pH.
They contain acid hydrolases, inactive in the cytosol if they leak out (cytosol pH is 7.2).
Sites of intracellular digestion and turnover of cellular components.
Found in all cell types, abundant in phagocytic cells (e.g., neutrophils and macrophages)

Biogenesis of Lysosomes

Lysosomal enzymes synthesised in rER, modified, sorted and packaged in Golgi
Mannose-6-phosphate added to lysosomal enzymes in Golgi
Material for degradation brought to lysosomes by heterophagy (endocytosis & phagocytosis) and autophagy (degradation of cell’s senescent organelles and large denatured proteins)
Degraded materials either released into cytoplasm or removed by exocytosis

Lysosomes degrade cytoplasmic proteins and organelles via autophagy

Three autophagic pathways: macroautophagy, microautophagy, and chaperone-mediated autophagy.

Residual Bodies

Digested materials inside lysosomes are recycled or released to the outside.
Indigestible compounds stored are called residual bodies.
Appear as yellowish brown pigments around the nucleus (lipofuscins).
The unreleased indigestible compounds in long-living cells are called aging pigments; present in neurons and cardiac muscle cells

Lysosomal Storage Diseases

Absence of certain lysosomal enzymes leads to lysosomal storage diseases which is a pathological condition.
Caused by mutations in genes encoding lysosomal proteins.
Results in accumulation of undigested products.
Examples include Tay-Sachs disease (absence of lysosomal galactosidase), and Gaucher's disease/ Pompe disease (lack of enzyme that breaks down glycolipids / lack of acid maltase).

Peroxisomes (Microbodies)

Membrane-bound spherical or slightly ovoid structures (0.3-1.5 µm)
Regulate hydrogen peroxide levels in cells and contain catalase enzymes that break down hydrogen peroxide.
Involved in beta-oxidation of long-chain fatty acids, formation of bile acids and cholesterol. Synthesizes plasmalogen in nerve cells.
Abundant in liver cells (hepatocytes).
Peroxisomes differ from lysosomes in their self-replicating ability.

Peroxisome malfunction (Zellweger Syndrome)

Leads to over-accumulation of very long-chain fatty acids, affecting brain (hypotonia), liver (jaundice) and kidneys (polycystic kidney disease).
An example of a peroxisome-related disorder.

Proteasome-Mediated Protein Degradation

Lysosomes are not involved, but proteasomes are
Proteins must be tagged by ubiquitin.
Used by cells to destroy abnormal proteins (e.g., misfolded, denatured, or abnormal), cell cycle progression proteins (e.g., cyclins, transcription factors), and tumor suppressors/tumor progressors.
Protein degradation malfunction can lead to decreased protein degradation in some diseases (e.g., Alzheimer's and Angelman syndrome) or accelerated protein degradation in certain conditions (e.g. human papillomavirus infection).

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Description

Test your knowledge on the roles and structures of organelles in eukaryotic cells. This quiz covers non-membranous organelles, membrane functions, and protein modifications essential for cellular processes. Dive deep into the complexities of cell biology and enhance your understanding of cellular efficiency and organization.