Physiology LE 1: Cell Structure and Function

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Questions and Answers

What is a characteristic of eukaryotic cells?

Their nucleus and most organelles are membrane-bound.

What is the primary function of the nucleus?

Storing the cell's hereditary material

Which of the following cells do not have a nucleus?

Mature human red blood cells

What is the result of transcription in the nucleus?

DNA to RNA Signup and view all the answers

What is the benefit of compartmentalization in eukaryotic cells?

It allows different organelles to perform different functions Signup and view all the answers

What is the role of the nucleus in regulating protein formation?

It regulates the formation of proteins and enzymes Signup and view all the answers

What is the term for the maintenance of a stable environment within a cell?

Homeostasis Signup and view all the answers

What is the importance of isotonicity in intravenous formulations?

It prevents cell lysis Signup and view all the answers

What is the role of lysosomes in the processing of materials for degradation?

To degrade foreign substances and cellular waste Signup and view all the answers

What is the process by which a cell engulfs a bacterium?

Phagocytosis Signup and view all the answers

What is the function of catalase in the lysosome?

To oxidize toxic substances Signup and view all the answers

What is the fate of the debris after degradation in the lysosome?

It is excreted into the extracellular environment Signup and view all the answers

What is the role of the Golgi apparatus in cellular degradation?

To modify and package proteins and lipids for transport Signup and view all the answers

What is the process by which cells bring in materials from the exterior?

Phagocytosis, pinocytosis, and receptor-mediated endocytosis Signup and view all the answers

What is the difference between macroautophagy and microautophagy?

Microautophagy is a type of autophagy that involves the degradation of small portions of the cell Signup and view all the answers

What is the function of early endosomes in the processing of materials for degradation?

To pre-process materials for degradation by the lysosomes Signup and view all the answers

What is the site of β oxidation of fatty acid molecules?

Peroxisomes Signup and view all the answers

What is the function of catalases in peroxisomes?

To detoxify harmful substances Signup and view all the answers

How are peroxisomes formed?

By breaking off from the smooth endoplasmic reticulum Signup and view all the answers

What is the function of proteasomes?

To degrade proteins Signup and view all the answers

What is the function of mitochondria?

To generate ATP Signup and view all the answers

What is the role of ubiquitin in proteasomes?

To serve as a degradation signal Signup and view all the answers

What is the difference between peroxisomes and lysosomes?

Peroxisomes have different contents Signup and view all the answers

What is the effect of inhibiting proteasomes?

Antitumor activity Signup and view all the answers

What is the main function of tight junctions?

To fasten cells together and promote strength and stability Signup and view all the answers

What type of cytoskeleton material is the smallest and most abundant in cells?

Thin filaments Signup and view all the answers

What is the diameter of thin filaments?

7nm Signup and view all the answers

What is the function of gap junctions?

To allow the passage of molecules between adjacent cells Signup and view all the answers

What type of junction is usually found on the apical surfaces of cells that line certain mucosa?

Tight junctions Signup and view all the answers

What is the function of zonula adherens?

To act as attachments of microfilaments or other cytoskeleton Signup and view all the answers

What type of junction attaches cells to the basal lamina?

Hemidesmosomes Signup and view all the answers

What is the function of desmosomes?

To attach intermediate filaments Signup and view all the answers

What is the name of the type of junction that allows the passage of some molecules through the paracellular route?

Tight junctions Signup and view all the answers

What is the function of microfilaments?

To form an elastic support for the cell membrane Signup and view all the answers

What is the function of Mitochondrial Ca2+ uniporter (MCU) and regulatory protein MICU?

To mediate the uptake of Ca2+ across the mitochondrial inner membrane Signup and view all the answers

What happens when cytosolic Ca2+ is elevated?

Ca2+ is released from mitochondrial stores Signup and view all the answers

What is the role of mitochondria in apoptosis?

To play a central role in programmed cell death Signup and view all the answers

What is the diameter of Microtubules?

25 nm Signup and view all the answers

What is the function of Intermediate Filaments?

To provide support and rigid physical structures Signup and view all the answers

What is the characteristic of Intermediate Filaments?

They are less dynamic than actin microfilaments or microtubules Signup and view all the answers

Why are they called Intermediate Filaments?

Because their average diameter is between that of narrower actin microfilaments and wider myosin filaments Signup and view all the answers

What is the function of actin and myosin filaments in muscle cells?

To organize into a special contractile machine Signup and view all the answers

Study Notes

Cellular Organelles

Peroxisomes: • Detoxify alcohol into acetaldehyde • Contain oxidases that combine oxygen and H+ to form H2O2 (hydrogen peroxide) • Used up by catalases to oxidize harmful substances • Site of β oxidation of fatty acid molecules and catabolism of D-amino acids, polyamines, and bile acids
Mitochondria: • Powerhouses of the cell – generate Adenosine triphosphate (ATP) • Total number varies depending on the cell type • Able to self-replicate, regulated by mitochondrial DNA
Proteasomes: • Specific to protein degradation • Regulate proteins that control cell-cycle progression and apoptosis • Work with ubiquitin, which serves as a degradation signal for numerous target proteins • Inhibition of the proteasome via antitumor activity (bortezomib)

Cell Structure and Function

Phagocytosis: • Important in phagocytosis – function of WBC • Bacterium is ingested → fuses with lysosome • Enzymes present in lysosomes degrade the bacterium • Debris will be excreted into the extracellular environment
Lysosomes: • Play a major role in processing materials for degradation inside the cell • Includes materials from the exterior brought in through phagocytosis, pinocytosis, and receptor-mediated endocytosis • Materials are pre-processed for degradation by the lysosomes • Eventually mature into the multivesicular body or late endosomes before fusing with the lysosome for enzymatic degradation of contents

Cytoskeleton

Intermediate Filaments: • 8-12 nm in diameter • Provide support and rigid physical structures • Also participate in cell division, cell motility, and movement of organelles
Microtubules: • 25 nm in diameter • Provide support and rigid physical structures • Participate in cell division, cell motility, and movement of organelles

Cell Cytoskeleton Materials

Thin Filaments (Actin Microfilaments): • Smallest; most abundant protein in cells (7nm) • Frequently in the ectoplasm, forming an elastic support for the cell membrane

Intercellular Connections

Tight Junctions (Zonula Occludens): • Found on the apical surfaces of cells that line certain mucosa and act as barriers (epithelium) • Fasten cells together and endow tissues with strength and stability • Allow the passage of some molecules through the paracellular route (“leaks”)
Zonula Adherens: • Usually continuous from the zonula occludens, acting as attachments of microfilaments or other cytoskeleton • “Adherens” = adhere
Desmosomes: • Apposed thickenings of two adjacent cells where intermediate filaments are attached
Hemidesmosomes: • Found on the basal surface, attaching cells to the basal lamina • Intracellularly, attachment for intermediate filaments
Gap Junctions: • Cytoplasmic “tunnels” between adjacent cells where molecules can pass through • Can open and close (water, ions, ATP, and action potentials pass through when it’s open)

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