Cell Biology Chapter Quiz

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Questions and Answers

Which component of the eukaryotic cell is responsible for making ribosomes?

Lysosome

Cytoplasm

Nucleus (correct)

Vacuole

What is the primary function of the Rough Endoplasmic Reticulum?

Synthesizes proteins (correct)

Detoxifies substances

Produces ribosomes

Stores nutrients

Which organelle is primarily known for energy production in eukaryotic cells?

Golgi Apparatus

Chloroplast

Mitochondria (correct)

Peroxisome

What distinguishes plant cells from animal cells?

Presence of chloroplasts Signup and view all the answers

What is the role of the Golgi apparatus in a eukaryotic cell?

Sorting and shipping proteins Signup and view all the answers

Which of the following options correctly identifies a function of lysosomes?

Removal of waste material Signup and view all the answers

What does the cell membrane primarily do?

Separates the cell from its environment Signup and view all the answers

Which structure is involved in the detoxification of substances within the cell?

Smooth Endoplasmic Reticulum Signup and view all the answers

What are the three modes of active transport?

Coupled transport, ATP-driven transport, light-driven transport Signup and view all the answers

How does the Na+/K+ ATPase pump function?

For every molecule of ATP hydrolyzed, 3 Na+ are pumped out and 2 K+ are pumped in. Signup and view all the answers

What is the primary function of aquaporins in the cell membrane?

Allow the rapid passage of water while blocking ions. Signup and view all the answers

Which statement best describes the selectivity filter of aquaporins?

It blocks the passage of H+ because the pore is too small for hydrated ions. Signup and view all the answers

Which ion is commonly mentioned as being actively transported into the lumen, facilitating osmotic pressure?

Na+ Signup and view all the answers

What is one of the primary functions of the plasma membrane?

Acts as a selective barrier Signup and view all the answers

Which of the following best describes phospholipids?

Amphiphilic molecules with both hydrophilic and hydrophobic parts Signup and view all the answers

How does cholesterol affect membrane fluidity at different temperatures?

Decreases fluidity at high temperatures and increases fluidity at low temperatures Signup and view all the answers

What defines the cell and contributes to its shape and strength?

Plasma membrane Signup and view all the answers

Which type of fatty acids increases the fluidity of the membrane?

Unsaturated fatty acids Signup and view all the answers

What are the main components of the plasma membrane?

Lipids, proteins, and sterols Signup and view all the answers

What role do sterols play in the plasma membrane?

Stabilize membrane fluidity Signup and view all the answers

Which of the following describes the structure of phosphoglycerides?

Consist of a polar head group and two non-polar tails Signup and view all the answers

What is the main role of the glycocalyx on the cell surface?

Provides mechanical and chemical protection Signup and view all the answers

Which of the following accurately describes a characteristic of membrane transport proteins?

Undergo conformational changes to transport solutes Signup and view all the answers

Active transport requires energy because it:

Transports substances against their concentration gradient Signup and view all the answers

Which type of transporters are involved in moving two molecules in the same direction across the membrane?

Symporters Signup and view all the answers

Which of the following correctly differentiates simple diffusion and transporter-mediated transport?

Transporter-mediated transport occurs along the concentration gradient Signup and view all the answers

What defines a uniporter in transport mechanisms?

Transports one type of molecule across the membrane Signup and view all the answers

Which of the following statements is true regarding membrane permeability?

Polarity, charge, and size affect membrane permeability Signup and view all the answers

Which is a characteristic of passive transport mechanisms?

Can involve channel proteins or simple diffusion Signup and view all the answers

What is the primary function of lipid rafts in the cell membrane?

To form platforms for protein interactions and signaling Signup and view all the answers

Which characteristic differentiates transmembrane proteins from peripheral proteins?

Transmembrane proteins are fully integrated into the membrane. Signup and view all the answers

What role does the hydropathy index play in relation to membrane proteins?

It indicates the hydrophobic regions in a polypeptide chain. Signup and view all the answers

In what condition can disulfide bonds form in membrane proteins?

In the lumen of the ER and Golgi apparatus Signup and view all the answers

What is a common characteristic of most transmembrane proteins?

They contain hydrophobic amino acids. Signup and view all the answers

What best describes the nature of the cell membrane as it relates to lipid rafts?

The membrane is thicker in areas of lipid rafts. Signup and view all the answers

What is the typical length range of the transmembrane part of a membrane protein?

20-30 amino acids Signup and view all the answers

Which statement about membrane proteins is true?

Most membrane proteins are glycosylated. Signup and view all the answers

What is the primary function of the Na+/K+ pump?

To maintain high Na+ outside the cell and high K+ inside the cell Signup and view all the answers

What does the resting potential of a neuron typically measure?

-70 mV Signup and view all the answers

When do voltage-gated Na+ channels open during an action potential?

At the action potential threshold of -55 mV Signup and view all the answers

Which of the following ions primarily contributes to the repolarization phase of an action potential?

K+ Signup and view all the answers

What is the outcome when K+ leaks out of the cell until its electrochemical gradient is zero?

The resting membrane potential is maintained Signup and view all the answers

How does the plasma membrane of excitable cells respond to stimuli?

It contains voltage-gated ion channels that respond to various signals Signup and view all the answers

How does the Na+/K+ pump contribute to the resting membrane potential?

It establishes and maintains ion concentration gradients Signup and view all the answers

What major change occurs during the depolarization phase of an action potential?

Voltage-gated Na+ channels open and Na+ enters the cell Signup and view all the answers

Study Notes

Cell Biology Lesson & Book Notes

Lesson 1: Cells & Organelles, Membrane Structure
- Eukaryotic cells contain components and functions detailed in the next slide
- Animal cells differ from plant cells:
  - Plant cells have a cell wall, central vacuole, and chloroplasts, but no centrosomes.
Cellular Components
- Nucleus: Stores genetic information.
- Nucleolus: Makes ribosomes.
- Cytoplasm: Contains the contents of the cell; matrix holding water and nutrients.
- Cytosol: The liquid portion of the cytoplasm.
- Cytoskeleton: Structure, support, and transport.
- Ribosomes: Synthesize proteins (all cells)
- Rough Endoplasmic Reticulum: Makes proteins for the endomembrane system
- Smooth Endoplasmic Reticulum: Detoxifies the cell; makes lipids.
- Golgi Apparatus: Sorts and ships proteins.
- Mitochondria: Makes energy; removes unwanted material and waste.
- Lysosomes: (animal cells only) Removes unwanted material and waste; regulates biochemical pathways involving oxidation.
- Peroxisome: Removes unwanted material and waste; regulates biochemical pathways involving oxidation.
- Vacuoles: Stores water and nutrients.
- Vesicles: Transport materials around the cell.
- Cell Membrane: A thin flexible barrier separating the cell from its environment; all cells have.
- Cell Wall: Rigid barrier protecting the cell; plants, fungi, and prokaryotes have.

Endosymbiosis Theory

An ancestral anaerobic predator cell (an archaeon) engulfed the bacterial ancestor of mitochondria, initiating a symbiotic relationship.
An early eukaryotic cell, possessing mitochondria, engulfed a photosynthetic bacterium (a cyanobacterium), sustaining a symbiotic relationship; present-day chloroplasts are traced to this ancestor.

The Plasma Membrane

Functions: Defines the cell; provides shape and strength (with cytoskeleton); forms a selective barrier.
Properties: Consists of lipids, proteins, and sterols (cholesterol); forms a fluid lipid bilayer, held together via noncovalent interactions.

Phospholipids

Consist of:
- Polar head group containing a phosphate group
- Two non-polar hydrocarbon tails (usually fatty acids)
Amphiphilic: have both hydrophilic and hydrophobic parts (important in membrane structure.)
Important classes of phospholipids:
- Phosphoglycerides (derived from glycerol)
- Sphingolipids (derived from sphingosine)

Sterols

Cholesterol stabilizes membrane fluidity at high temperatures and lessens fluidity and permeability at low temperatures
Cholesterol immobilizes the upper part of the fatty acid chain. This leads to a less deformable membrane and lessened permeability.
Saturated fatty acids make the membrane less fluid; Higher ratio means relatively more saturated fatty acids.

Lipid Rafts

Cell membranes are not completely homogenized.
Lipid rafts are dynamic structures rich in cholesterol, sphingolipids, glycolipids, and certain proteins.
Lipid rafts are thicker than other parts of the membrane.
Lipid rafts form platforms for protein interactions and signalling.

Transmembrane/Integral Proteins

Integrated into the entire membrane
- Single-helix
- Multiple-helix
- Barrel

Peripheral Proteins

Attached to the outside of the cell membrane.
Attached via an a helix
Bound to a lipid chain
Bound by other proteins

Membrane Proteins

Give functional properties to the cell membrane.
Can associate with the membrane in various ways.
Are amphiphilic.
- Containing hydrophilic and hydrophobic amino acids.
- Most transmembrane proteins cross the lipid bilayer with an alpha-helix. Peptide bonds in alpha-helices form hydrogen bonds, maximizing efficiency.
- Transmembrane part is 20 to 30 amino acids long
- Transmembrane alpha helices interact with each other to form proper structures.

Hydropathy Plots

Predict membrane proteins using amino acid composition to forecast transmembrane regions.
Hydropathy index = free energy required to transfer segments of a polypeptide chain from a non-polar solvent to water.
Hydropathy index is plotted on the Y-axis versus the amino acid number on the X-axis.
Peaks in hydropathy index reflect hydrophobic segments in the amino acid sequence.

Membrane Proteins (Cytosolic vs Non-cytosolic)

Most membrane proteins are glycosylated
Sugar residues are added in the ER and the Golgi
Disulfide (S-S) bonds form between cysteines on the non-cytosolic side of the membrane.
Carbohydrate layer on the surface (glycocalyx) helps protect the cell from chemical & mechanical stress.
Glycocalyx helps prevent unwanted cell-cell interactions.

Lesson 2: Membrane Transport

Cell membranes are selectively permeable based on polarity, charge, and size.
Membrane transport proteins:
- Multipass membrane proteins: Specific to one or a few molecules
Channel proteins: Interact weakly with solute; form narrow pores which can be open or closed; faster transport.
Transporters: Bind more strongly to solute; undergo sequential conformational changes; slower transport; never open on both sides.

Types of Transporters

Uniporters
Symporters (coupled transport)
Antiporters (coupled transport)
Passive transport: no energy required (along concentration gradient, simple diffusion, via channels/transporters)
Active transport: costs energy (against concentration gradient, via transporters).
Transport of essential substances into the cell or removal of waste even when the concentration is higher outside the cell. Maintains ions (K+, Na+, Ca2+, H+) concentration

Active Transporters

Three modes of active transport:
- Coupled transport (secondary active transport)
- ATP-driven (primary active transport)
- Light-driven (primary active transport)
Sodium-Potassium pump (Na+/K+ ATPase): Creates high Na+ outside the cell, high K+ inside the cell.

Transport of Water

Water can pass the cell membrane via aquaporins, which are essential for rapid transport.
Aquaporins are passive channels that allow water passage.
Some cells have mechanisms to control the passage of specific ions via selective filtering of pores (such as in kidneys & glands)
Asparagine selectivity filter: Prevents passage of H⁺.
Water follows the osmotic gradient in active transport by ions (for example, Na⁺ and Cl⁻).

Ion Channels

Function in transport of ions across the membrane.
Selective for specific ions.
Conformations (open and closed)
Respond to electrical, mechanical, and chemical signals.
The K⁺ leak channel & Na⁺/K⁺ pump play a paramount role in maintaining resting membrane potential.

Transport Channels

Different types of ion channels such as voltage-gated, ligand-gated, and mechanically-gated channels, vary in their method of activation

Neurons & Voltage-gated Channels

Plasma membrane of excitable cells contain voltage-gated ion channels; critical for action potentials and signal transport.
Depolarization: shift in membrane potential to a less negative value inside the cell.
Action potentials in neurons:
- Resting potential (-70 mV)
- Action potential threshold (-55 mV)
- Voltage-gated Na⁺ channels open/depolarization (+30 mV)
- Voltage-gated K⁺ channels open/repolarization (<70 mV and hyperpolarization)
- Na⁺/K⁺ pump restores resting potential

Presynaptic & Postsynaptic Cells

Neuronal signals transmit to next cell via synapses.
Transmitters are released through voltage-gated channels
Neurotransmitters (e.g., Dopamine, Serotonin, Acetylcholine) act as messengers between neurons.

ABC Transporter

Transporters (609-611, Chapter 11).

Neuromuscular Transmission

Process of signal transmission between a neuron and a muscle fiber.

Lesson 3: Intracellular Compartments & Protein Transport

Proteins and other macromolecules are transported within the cell by:
- Gated transport (through nuclear pores)
- Transmembrane transport (via translocators)
- Vesicular transport (packaged into vesicles)
Signal sequences direct proteins to their destinations (organelles or the exterior environment.)

Transport into the Nucleus: Gated Transport

The nuclear envelope is formed by two membranes with selective gates (nuclear pores).
Proteins with a nuclear localization signal bind to import receptors.

Nuclear Import & Export

Similar: cargo transported by receptors, energy via GTP hydrolysis, Ran-GTP/GDP for transport.
Different: Direction of transport affects binding/releasing of Ran, influencing import and export specificity.

Transport into Mitochondria: Transmembrane Transport

Proteins destined for the mitochondrial matrix pass through two membranes using protein translocators.
These proteins must be unfolded for transport.
Signal sequences mark mitochondrial proteins for import. These sequences have a positively charged side and a hydrophobic side (recognized by TOM complex).

Transport into Mitochondria: Energy Cost

Chaperones bind to mitochondrial proteins to prevent folding,
Release of chaperones demands energy in form of ATP.
Positive charge in the signal sequence is drawn into the matrix by the membrane potential.
Chaperones are released when ATP is hydrolyzed.

Transport into the ER: Transmembrane Transport

Synthesis occurs in the ER of folded proteins, carbohydrates, and lipids.
ER is a storage site for calcium.
Detoxification occurs in the smooth ER through cytochrome P450 family enzymes.
Proteins and lipids are synthesized, stored, and potentially secreted in the ER.

Protein Synthesis at ER-bound Ribosomes

Signal recognition particles (SRPs) bind to signal sequences on proteins, halting translation.
Proteins are directed to ER translocators when the signal sequence binds to the translocator.
SRPs are then released.
Translation continues.

Synthesis of Soluble Proteins in the ER

Proteins cross the ER membrane and enter the lumen.
Signal sequences are cleaved (by signal peptidase).
These soluble proteins are released into the ER lumen.

Synthesis of Membrane-bound Proteins in the ER

Partly translocated and remain partly embedded in the membrane.
The sequences used to synthesize membrane-bound proteins are start- and stop transfer sequences.

What Happens to Proteins Translated in the ER?

Some proteins stay in the ER (involved in lipid synthesis, protein glycosilation, protein folding).
Others are transported to other organelles/membranes/outside the cell using vesicular transport.
Proteins undergo glycosylation in the ER for better structure, solubility, and folding.
Disulfide bonds are formed.
Lipid anchors (e.g., GPI anchors) are added.

Proper Protein Folding in the ER

Chaperones facilitate protein folding.
Unfolded/misfolded proteins are degraded in proteasomes in the cytosol.

Export & Degradation of Misfolded ER Proteins

ER quality control mechanisms eliminate misfolded proteins.
Misfolded proteins are marked for degradation via ubiquitination.
The complexes are exported to the cytosol for degradation by the proteasome.

Vesicular Transport

Membrane proteins are concentrated in specialized patches of the membrane, forming vesicles.
Outer and inner coat proteins shape to vesicle membrane.
Three types of coated vesicles: clathrin, COPI, COPII.
Vesicles transfer materials (e.g. proteins, lipids) between compartments.
Compartments communicate with each other and the outside of the cell via transport vesicles.
- Secretory pathway: materials from ER to plasma membrane/lysosome
- Endocytic pathway: extracellular material to lysosome
- Retrieval pathway: recycled components back to ER/Golgi.

Transport of Vesicles to Their Target Membranes

Specificity of vesicle transport is regulated by Rab proteins and SNARE proteins (v-SNARE & t-SNARE) for membrane fusion.
These are crucial for vesicle docking and fusion onto target membrane.

Protein Glycosylation in the Golgi

Oligosaccharides added to proteins and lipids in the Golgi.
Influence protein structure and function .
Sorting of proteins for various destinations (constitutive secretory pathway and regulated secretory pathway).
Transport to extracellular space via exocytosis.
Export of proteins in regulated secretory pathway are stored in secretory vesicles until signal.

Transport From Cell Exterior into the Cell: Endocytosis

Endocytic vesicles (with materials or components) fuse to early endosomes.
Sorting and recycling/degradation occur.
Late endosomes fuse with lysosomes for degradation.
Acid hydrolases are crucial for degradation of components.

Lesson 4: Cell Signaling

Four forms of intercellular signaling:
- Paracrine: short-range signaling between nearby cells.
- Synaptic: specialized signaling between nerve cells.
- Endocrine: long-distance signaling via hormones.
- Contact-dependent: direct cell-cell signaling via membrane-bound signal molecules

Principle of Cell Signaling

Extracellular signal is spread via signal transmission.
Signaling involves an extracellular signal activating a receptor, which triggers a series of intracellular signaling molecules and effector proteins, eventually altering cell behavior.
Intracellular signaling pathways relay, amplify, integrate, and distribute signals to produce various cell responses.

Extracellular Signal Molecules

Signal molecules themselves have very little information, but can induce varied responses in different target cell types.
Examples of signal molecules include various hormones and neurotransmitters depending on whether the communication is of local or long distance nature.

Three Classes of Receptors in Signaling

Ion channel-coupled
G-protein-coupled
Enzyme-coupled (protein kinases)

Scaffold Proteins

Compact protein “modules” that bind to different protein/lipid motifs.
Phosphotyrosine-binding (PTB) domains bind to phosphorylated tyrosine.
Src homology 2 (SH2) domains bind to phosphorylated tyrosine residues.
Src homology 3 (SH3) domains bind to short, proline-rich amino acid sequences.
Pleckstrin homology (PH) domains bind to charged groups of modified phospholipids.

G-protein Coupled Receptors

Largest family of cell-surface receptors.
Responds to signals from the world around us (sight, smell, taste, etc)
7 transmembrane domains.
A deep ligand binding site at its center.
G-protein couples the receptor to enzymes or ion channels via GTP / GDP binding

Signaling Of GPCRs via Cyclic AMP

Some G proteins modulate cyclic AMP (cAMP) production.
cAMP (second messenger) is generated from ATP by adenylyl cyclase.
cAMP is degraded by cAMP phosphodiesterase.
cAMP usually activates protein kinase A (PKA).
cAMP pathways involve many signaling molecules, which eventually modify transcription of target genes.

GPCRs & Ca²+ Signalling

Gq activates plasma membrane-bound phospholipase C-β (PLC-β) leading to 2nd messenger release, Ca²⁺.
Leads to Ca²+ release from the endoplasmic reticulum.
Ca²+ then activates protein kinase C (PKC)

Enzyme-Coupled Receptors

Each subunit often contains one transmembrane region
Works via intrinsic enzyme activity or via a direct association with enzymes
Protein phosphorylation is a common mechanism of signal transduction and regulation of protein activity in signaling pathways
Two main types:
- Serine/threonine kinases (e.g., PKA, PKC)
- Tyrosine kinases (e.g., RTKs)

Receptor Tyrosine Kinases (RTKs)

Most common class of enzyme-coupled receptors.
Important for cell survival, proliferation, and differentiation.
Often involved in tumors.
Interaction domains (e.g., PTB, SH2, SH3, PH) bind to phosphorylated tyrosines to activate downstream signals.

Ras Activates the MAP Kinase Pathway

Activated Ras initiates the MAP kinase pathway, often involving a complex of kinases.
Results in changes of gene expression.
Implicated in cancers

PI3K-Akt Signalling Pathway

Growth factors initiate RTK activation, leading to recruitment of PI3K to cell membrane.
Converts membrane PIP2 to PIP3.
PIP3 then activates kinase Akt—promoting cell survival.

JAK-STAT Signaling Pathway

Cytokine binding to cytokine receptors activates JAKs.
JAKs phosphorylate STATs.
STATs bind to each other and translocate to nucleus, modifying gene transcription.
Crucial for signaling biological responses.

Lesson 5: Cytoskeleton & Extracellular Matrix

Cytoskeleton: dynamic network of protein filaments (actin, microtubules, intermediate filaments).
Actin filaments (microfilaments): Cell shape maintenance and movement; roles in muscle contraction.
Microtubules: Intracellular transport, intracellular organization, and the mitotic spindle.
Intermediate filaments: Providing mechanical strength and cell-cell connections.

Microtubules

Properties
Structure
Functions
Polarity
Growth rate

Microtubules Binds to GTP

Dynamic instability: rapid assembly and disassembly of microtubules by GTP hydrolysis.
Catastrophe: GTP hydrolysis faster than tubulin addition.
Rescue: GTP-tubulin addition faster than hydrolysis.
Used as a target for cancer drugs.

Motor Proteins Drive Intracellular Transport

Dynein: moves cargo towards the minus end of microtubules.
Kinesins: moves cargo towards the plus end of microtubules.
ATP plays a vital role in energy provision for transport along microtubules.
Leading and lagging head group: different stages of ATP binding and hydrolysis causing conformational changes required for proper movement along the microtubles.

Actin Filaments (Microfilaments)

Functions: determining shape of the cell, cell movement, cytokinesis, and organizing structures for muscle contraction.
Actin & myosin drive contraction structures that generate force.

Intermediate Filaments (IF)

Main function: absorbing mechanical stress in the cell
Examples: keratin, vimentin, neurofilaments.
Found in tissues throughout the body; e.g., epithelial cells.

Lesson 6: Cell Cycle & Apoptosis

Cell cycle phases: G1, S, G2, and M.
Interphase: G1, S, and G2 phases.
M phase: Mitosis and cytokinesis.
Checkpoints during G1 and G2 phases ensure proper replication and cell division.

Cyclin-dependent kinases (Cdks)

Function: phosphorylate intracellular proteins to regulate cell-cycle events.
Activity regulators: Cyclins (different cyclins active at different stages of cell cycle), CDK inhibitor Proteins (p27)
Inhibition: Via phosphorylation and proteolysis of cyclin.

Regulators of CDK activity

Cyclin-dependent kinase activity is regulated by:
Phosphorylation/dephosphorylation.
Binding to inhibitory proteins or cyclins
Proteolytic degradation of cyclins.

Regulation of CDK activity via p53

Activation of p53 due to DNA damage initiates a signaling cascade stopping the cell cycle until damage is repaired or apoptosis occurs.

Stages of Mitosis

Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis

Chromosome Spindle Attachment

Steps describing chromosome positioning and attachment during different phases of mitosis.

Motor Proteins of the Spindle

Kinesins and dyneins use energy from ATP hydrolysis to drive chromosome movement during different stages of mitosis.

Apoptosis: Genetic Regulated Cell Death

Importance in embryonic development, immunity, and preventing diseases.
Morphological changes (cells shrink and condense, nuclear envelope disassembles, chromatin condenses, cell breaks into apoptotic bodies).
Caspases: proteases that execute and regulate apoptosis; initiator and executioner caspases.

Intrinsic Pathway of Apoptosis

Cytochrome c release from mitochondria
Cytochrome c promotes apoptosome formation, activating caspases and triggering apoptosis.

Extrinsic Pathway of Apoptosis

External signals (e.g., Fas ligand) activate death receptors.
Initiator caspase activation.

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