Cell Biology Quiz - Organelles and Signaling

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Questions and Answers

Which organelle is primarily responsible for the synthesis of steroid hormones and maintaining calcium homeostasis?

Golgi Apparatus

Lysosome

Smooth Endoplasmic Reticulum (correct)

Rough Endoplasmic Reticulum

What cellular structure serves as a barrier and electrical insulator, as well as an interface between intra and extracellular fluids?

Cytoplasm

Nucleus

Cytoskeleton

Cell Membrane (correct)

Which organelle is often referred to as the 'powerhouse of the cell' and is involved in initiating apoptosis?

Peroxisome

Lysosome

Mitochondria (correct)

Golgi Apparatus

What role do ribosomes play in the cell?

Protein synthesis and folding Signup and view all the answers

Which cellular component is responsible for breaking down aging cells and engaging in phagocytosis?

Lysosome Signup and view all the answers

What is required for the activation of epidermal growth factor receptors (EGFRs)?

Dimerization of the receptors Signup and view all the answers

What type of phosphorylation is primarily involved in the signaling pathway activated by EGFR?

Phosphorylation of tyrosine residues Signup and view all the answers

Which component does the intracellular portion of cytokine receptors bind to after activation?

Janus Kinase (JAK) Signup and view all the answers

How do mutated JAK proteins affect cellular activity in relation to cytokine receptors?

They can lead to abnormal cell signaling and are implicated in some cancers Signup and view all the answers

What role does the extracellular portion of the EGFR play?

Providing a binding site for ligands Signup and view all the answers

Which signaling molecules are primarily involved in the excitatory effects on heart rate?

Acetylcholine and Norepinephrine Signup and view all the answers

What role do primary messengers play in the signaling pathway of GPCRs?

They activate second messengers that influence cellular responses. Signup and view all the answers

What effect do inhibitory receptors have on GPCRs?

They limit the intensity and duration of GPCR effects. Signup and view all the answers

What describes the process of autophosphorylation in enzyme-linked receptors?

Each receptor chain phosphorylates the other after dimerization. Signup and view all the answers

Which mechanism is responsible for terminating the action of second messengers?

Hydrolysis of cyclic AMP Signup and view all the answers

Which of the following accurately describes G protein–coupled receptors (GPCRs)?

They can activate multiple types of second messengers. Signup and view all the answers

In the context of GPCRs, what is the role of protein kinases?

They phosphorylate intracellular proteins to alter their activity. Signup and view all the answers

What distinguishes enzyme-linked receptors from G protein-coupled receptors?

Enzyme-linked receptors possess intrinsic kinase activity. Signup and view all the answers

What is the primary function of the sodium-potassium pump?

To transport sodium out of the cell and potassium into the cell Signup and view all the answers

Which transport mechanism allows glucose to enter the cell without the use of ATP?

Facilitated diffusion with GLUT transporters Signup and view all the answers

What role do calcium ATPases play in cellular function?

They maintain calcium gradient and restore low intracellular calcium levels. Signup and view all the answers

Secondary active transport relies on which primary mechanism?

Sodium-potassium pump Signup and view all the answers

In secondary active transport, what does the term 'cotransport' refer to?

Both Na+ and another molecule moving into the cell Signup and view all the answers

Which statement best describes facilitated diffusion?

It utilizes carrier proteins to move polar and hydrophilic substances into the cell. Signup and view all the answers

What types of molecules are primarily transported by SGLT transporters?

Glucose molecules Signup and view all the answers

Drugs that inhibit gastric acid secretion target which type of transport?

Primary active transport Signup and view all the answers

Which type of cell death is characterized by cells swelling and rupturing?

Necrosis Signup and view all the answers

What triggers the intrinsic pathway of apoptosis?

Mitochondrial release of cytochrome C Signup and view all the answers

Which characteristic distinguishes apoptosis from necrosis regarding nuclear fate?

Nucleus shrinks in apoptosis Signup and view all the answers

Which process involves the maintenance and recycling of cellular components during malnourishment?

Autophagy Signup and view all the answers

What is the primary distinction in cell content removal between apoptosis and necrosis?

Apoptosis packages cellular contents into apoptotic bodies Signup and view all the answers

Which type of signaling is associated with the extrinsic pathway of apoptosis?

Extracellular signal binding to TNF Signup and view all the answers

Under severe malnutrition, what is the ultimate fate of a cell undergoing autophagy?

The cell dies Signup and view all the answers

How do cytotoxic T cells initiate the apoptosis of infected or cancerous cells?

By activating the apoptotic pathway Signup and view all the answers

What is the primary role of troponin in muscle contraction?

To help expose actin for myosin binding Signup and view all the answers

Which of the following correctly describes the structure of skeletal muscle fibers?

Long fibers containing multiple nuclei Signup and view all the answers

During the crossbridge formation, what initiates the exposure of actin binding sites?

Intracellular Ca++ binding to Troponin C Signup and view all the answers

What distinguishes cardiac muscle cells from skeletal muscle fibers?

Cardiac cells have one nucleus and are connected mechanically and electrically Signup and view all the answers

Which mechanism explains the contraction of smooth muscle?

Latch-bridge mechanism Signup and view all the answers

What is the effect of calcium ions in muscle contraction?

They bind to Troponin C facilitating actin exposure Signup and view all the answers

How do skeletal muscle fibers generate action potentials?

Via acetylcholine released at the neuromuscular junction Signup and view all the answers

What characterizes the length-tension relationship in skeletal muscle?

Longer fibers initially generate greater tension Signup and view all the answers

Which statement best describes smooth muscle?

It is found in the GI tract and blood vessels, lacking striations Signup and view all the answers

What is the function of tropomyosin in muscle contraction?

To block actin binding sites when the muscle is relaxed Signup and view all the answers

Study Notes

Clinical Pathophysiology of the Cell

This presentation covers the clinical pathophysiology of the cell, focusing on cell components, membrane transport, and cell mechanisms.

Objectives Part 1

Identify cellular organelles, their structure, and function.
Describe the cell membrane structure and function.

Cell Components

This section details various components of the cell.

Cell Membrane

Phospholipid bilayer separates intracellular and extracellular fluids.
Polar/hydrophilic heads and nonpolar/hydrophobic tails.
Functions include barrier, electrical insulation, and an interface.
Key components: integral proteins, peripheral proteins, cholesterol, and carbohydrates (glycoproteins/GPI-anchored proteins).

Cell Components (Cytoplasm, Nucleus, Ribosomes & ER, Smooth ER)

Cytoplasm: protein synthesis and transport of proteins.
Nucleus: houses cell DNA and typically has one per cell. Synthesis of ribosomes.
Ribosomes & Rough ER: protein synthesis and protein folding.
Smooth ER: involved in metabolic processing, steroid synthesis, and calcium homeostasis.

Cell Components (Golgi Apparatus, Mitochondria, Lysosomes, Peroxisomes, Cytoskeleton)

Golgi Apparatus: packages proteins and lipids.
Mitochondria: energy powerhouse.
Lysosomes: break down aging cells (phagolysosome).
Peroxisomes: generate and scavenge free radicals.
Cytoskeleton: protein filaments responsible for cellular movement.

Question 1

The correct answer is the rough endoplasmic reticulum (ER).
Rough ER is made in the nucleus and attached to messenger RNA (mRNA) for protein synthesis.

Mechanism of Membrane Transport

Objectives Part 2: Briefly describe membrane transport mechanisms, including diffusion, endocytosis, exocytosis, facilitated diffusion, active transport, primary, secondary, and ion channels.

Concentration Gradients in a Typical Cell

A table providing concentrations of various solutes both inside and outside a typical cell.

Diffusion

No specific transport proteins required.
Movement down the concentration gradient.
Key characteristic: small, non-polar, hydrophobic molecules.
Follows Fick's first law of diffusion.

Endocytosis

Extracellular fluid is engulfed and brought into the cell.
Three processes: phagocytosis, pinocytosis, receptor-mediated endocytosis.
Includes mechanisms for environmental surveillance and familial hypercholesterolemia.

Exocytosis

Extracellular release of intracellular contents.
Includes examples such as liver, plasma, and neuron functions.
Can be regulated via protein or molecule release depending on needs.

Facilitated Diffusion

Many substances that need to enter cells are polar and hydrophilic.
Membrane transport proteins facilitate movement down the concentration gradient.
Example: GLUT (1-5) transporters—important in gut function.

GLUT Facilitated Diffusion

SGLT is a sodium-dependent glucose transporter.
GLUT is a facilitated glucose transporter.

Active Transport

Transport against the concentration gradient.
Requires energy input.
Examples include sodium-potassium pump, calcium ATPase, and proton pump.

Sodium-Potassium (Na+/K+) Pump

Transports sodium out of the cell and potassium into the cell against their gradients.
Important for maintaining cellular potential energy.

Calcium ATPase Pump

Found in cell membranes and ER.
Maintains the calcium gradient and restores low intracellular calcium levels.

Proton Pump

Found on gastric parietal cells, involved in secreting hydrochloric acid in the stomach.
Maintains acid-base balance.
Drug targets.

Secondary Active Transport

Relies on the established gradient from the Na+/K+ pump.
Does not directly require ATP.
Two types: cotransport/symport and antiport/countertransport.

Secondary Active Transport: Cotransport

Multiple substances are moved across the membrane simultaneously.
Example: Glucose absorption in the gut.

Question 2

The correct answer is primary active transport.
Drugs that inhibit gastric secretion target the proton pump (a type of primary active transport).

Ion Channels

Transmembrane proteins allowing movement down the concentration gradient.
Selective for one type of ion.
Crucial for all body cells, especially excitable ones.
Contribute significantly to resting membrane potential.

Transporter Names and Locations

Table detailing various transporters and their locations in the body.

Transport Mechanism

Details of various transport modes, examples, and locations.

Mechanisms of Cellular Signaling

The presentation examines the detailed mechanisms of cell signaling.

Objectives Part 3

Plasma membrane receptor roles and functions.
Signal transduction pathways (adenylyl cyclase and phospholipase C-linked pathways).
Mechanisms and sequences of signal transduction and tyrosine kinase enzyme receptors.

Autonomic Nervous System Signaling: GPCRS

Autonomic nervous system: rapid regulatory system.
Parasympathetic: preganglionic neurons in brainstem and sacral spinal cord, and postganglionic neurons are cholinergic.
Sympathetic: preganglionic neurons in thoracic and lumbar spinal cord, and postganglionic neurons are adrenergic.

G-Protein Coupled Receptors (GPCR)

Common structural elements (seven transmembrane-spanning alpha helices).
Ligand binding: conformational change.

GPCR: Adenylyl Cyclase: (AC)

AC converts ATP to cAMP and amplifies the signal.
cAMP diffuses to activate protein kinase A (PKA).
PKA phosphorylates target proteins, altering cellular activity.

GPCR: Phospholipase C (PLC)

PLC splits the membrane phospholipid PIP₂ into DAG and IP₃.
DAG stays in the membrane.
IP₃ diffuses to the cytoplasm and releases calcium.
Stimulates cell contraction and increases blood pressure.

Question 3

The correct answer is the action of second messengers is terminated by off-switches.

Enzyme-Linked Receptors

Intrinsic enzyme activity instead of needing a G protein.
Tyrosine kinase activity: target proteins are phosphorylated; dimerization, autophosphorylation.

Epidermal Growth Factor Receptor (EGFR)

EGFRs turn on signaling pathways leading to gene expression and translation.
Dimerization is required for activation.
Extracellular ligand-binding site and intracellular tyrosine kinase component.

Cytokine Receptors

Cytokines are protein messengers of the immune system.
Their receptors are activated by binding and initiate downstream signal transduction.

Question 4

The correct answer is the phosphorylation of cell proteins on tyrosine residues.

Mechansim of Contractile Cells

Objectives Part 4: Describe the basics of interactions between the contractile proteins myosin and actin. Compare the mechanisms of contraction of striated (skeletal and cardiac) and smooth muscle cells.

Types of Contractile Cells

1. Cardiac
1. Smooth
1. Skeletal

Sarcomeres of Skeletal and Cardiac Muscle

Striated appearance: alternating dark (A bands) and light (I bands).
Sarcomeres: span from Z-disc to Z-disc.
Key Proteins: Actin (contains repeating subunits), Myosin (two light chains and two heavy chains).

Mechanism of Myofibril Crossbridge Formation

Goal: shortening of the muscle.
Actin binding sites are blocked by tropomyosin.
Troponin complex regulates tropomyosin: high sensitivity cardiac (troponin I, troponin C, and troponin T)

Steps of Crossbridge Formation

1. Myosin binds to ADP and a free phosphate.
1. Muscle fiber stimulated, causing depolarization.
1. Sarcoplasmic reticulum increases intracellular calcium levels.
1. Calcium binds to troponin.
1. Tropomyosin shifts, exposing actin.
1. Myosin binds to actin, forming a crossbridge.
1. Myosin head moves closer to actin.
1. Crossbridge formation is complete.

Cell Renewal, Stress, and Cell Death

Objectives Part 5: Describe cell renewal, cell stress, and mechanisms of cell stress. Identify major types of cell adaptations and their common causes. Describe cell responses to severe injury and their biochemical mechanisms. Explain the purpose and examples of physiological apoptosis and the reasons why a programmed death pathway is necessary for optimal body function.

Cell Renewal, Maintenance, and Adaptation

Many cells die and are replaced by self-renewing stem cells.
Cell renewal can occur via removal of damaged proteins through new protein synthesis.
Cells can adapt to injury, infection, or malnutrition via hypertrophy, atrophy, hyperplasia, or metaplasia.

Cell Death Pathways

Necrosis: caused by lack of nutrient supply (e.g., stroke, myocardial infarction).
Rapid ATP loss, Ca2+ overload, membrane rupture, and activation of degradative enzymes.

Apoptosis

Programmed cell death.
Key examples: autoreactive lymphocytes, cytotoxic T cells, infected cells.
Two mechanisms: intrinsic and extrinsic.

Necrosis vs. Apoptosis

Table comparison: cell size, nucleus fate, DNA fragmentation size, and cell membrane fate.

Autophagy

Adaptations to malnutrition.
Vacuole forms within the cell, engulfing cellular contents.
Digested back into building blocks (amino acids, carbohydrates, and fats).

Question 6

The correct answer is necrosis.
Cells undergoing hypoxic insults exhibit decreased ATP production, acidosis, and increased ROS, resulting in necrosis.

Question 7

The correct answer is activation of new protein synthesis.

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Description

Test your knowledge on key cell structures and their functions with this quiz. From the synthesis of steroid hormones to the intricacies of signaling pathways, challenge yourself on the essential roles of organelles and cellular components. Perfect for biology students looking to reinforce their understanding of cell biology concepts.