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?

<p>Presence of chloroplasts (A)</p> Signup and view all the answers

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

<p>Sorting and shipping proteins (C)</p> Signup and view all the answers

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

<p>Removal of waste material (D)</p> Signup and view all the answers

What does the cell membrane primarily do?

<p>Separates the cell from its environment (D)</p> Signup and view all the answers

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

<p>Smooth Endoplasmic Reticulum (A)</p> Signup and view all the answers

What are the three modes of active transport?

<p>Coupled transport, ATP-driven transport, light-driven transport (D)</p> Signup and view all the answers

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

<p>For every molecule of ATP hydrolyzed, 3 Na+ are pumped out and 2 K+ are pumped in. (C)</p> Signup and view all the answers

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

<p>Allow the rapid passage of water while blocking ions. (D)</p> Signup and view all the answers

Which statement best describes the selectivity filter of aquaporins?

<p>It blocks the passage of H+ because the pore is too small for hydrated ions. (D)</p> Signup and view all the answers

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

<p>Na+ (B)</p> Signup and view all the answers

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

<p>Acts as a selective barrier (D)</p> Signup and view all the answers

Which of the following best describes phospholipids?

<p>Amphiphilic molecules with both hydrophilic and hydrophobic parts (C)</p> Signup and view all the answers

How does cholesterol affect membrane fluidity at different temperatures?

<p>Decreases fluidity at high temperatures and increases fluidity at low temperatures (D)</p> Signup and view all the answers

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

<p>Plasma membrane (A)</p> Signup and view all the answers

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

<p>Unsaturated fatty acids (B)</p> Signup and view all the answers

What are the main components of the plasma membrane?

<p>Lipids, proteins, and sterols (B)</p> Signup and view all the answers

What role do sterols play in the plasma membrane?

<p>Stabilize membrane fluidity (B)</p> Signup and view all the answers

Which of the following describes the structure of phosphoglycerides?

<p>Consist of a polar head group and two non-polar tails (B)</p> Signup and view all the answers

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

<p>Provides mechanical and chemical protection (A)</p> Signup and view all the answers

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

<p>Undergo conformational changes to transport solutes (A)</p> Signup and view all the answers

Active transport requires energy because it:

<p>Transports substances against their concentration gradient (B)</p> Signup and view all the answers

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

<p>Symporters (B)</p> Signup and view all the answers

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

<p>Transporter-mediated transport occurs along the concentration gradient (A)</p> Signup and view all the answers

What defines a uniporter in transport mechanisms?

<p>Transports one type of molecule across the membrane (D)</p> Signup and view all the answers

Which of the following statements is true regarding membrane permeability?

<p>Polarity, charge, and size affect membrane permeability (C)</p> Signup and view all the answers

Which is a characteristic of passive transport mechanisms?

<p>Can involve channel proteins or simple diffusion (A)</p> Signup and view all the answers

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

<p>To form platforms for protein interactions and signaling (D)</p> Signup and view all the answers

Which characteristic differentiates transmembrane proteins from peripheral proteins?

<p>Transmembrane proteins are fully integrated into the membrane. (D)</p> Signup and view all the answers

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

<p>It indicates the hydrophobic regions in a polypeptide chain. (B)</p> Signup and view all the answers

In what condition can disulfide bonds form in membrane proteins?

<p>In the lumen of the ER and Golgi apparatus (D)</p> Signup and view all the answers

What is a common characteristic of most transmembrane proteins?

<p>They contain hydrophobic amino acids. (B)</p> Signup and view all the answers

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

<p>The membrane is thicker in areas of lipid rafts. (C)</p> Signup and view all the answers

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

<p>20-30 amino acids (A)</p> Signup and view all the answers

Which statement about membrane proteins is true?

<p>Most membrane proteins are glycosylated. (C)</p> Signup and view all the answers

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

<p>To maintain high Na+ outside the cell and high K+ inside the cell (A)</p> Signup and view all the answers

What does the resting potential of a neuron typically measure?

<p>-70 mV (A)</p> Signup and view all the answers

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

<p>At the action potential threshold of -55 mV (D)</p> Signup and view all the answers

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

<p>K+ (C)</p> Signup and view all the answers

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

<p>The resting membrane potential is maintained (C)</p> Signup and view all the answers

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

<p>It contains voltage-gated ion channels that respond to various signals (B)</p> Signup and view all the answers

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

<p>It establishes and maintains ion concentration gradients (B)</p> Signup and view all the answers

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

<p>Voltage-gated Na+ channels open and Na+ enters the cell (C)</p> Signup and view all the answers

Flashcards

Nucleus

The control center of the eukaryotic cell, containing the genetic material (DNA) and regulating cellular activities.

Nucleolus

A small, dense region within the nucleus responsible for making ribosomes.

Cytoplasm

The gel-like substance that fills the cell, containing water, nutrients, and organelles.

Cytoskeleton

A network of fibers that provides support, shape, and movement within the cell.

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Ribosome

The organelle that makes proteins, essential for cell function.

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Endoplasmic Reticulum (ER)

A network of membranes that synthesizes proteins and lipids and plays a role in detoxification.

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Golgi Apparatus

A stack of flattened membrane-bound sacs that sorts, modifies, and packages proteins for transport.

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Mitochondria

The organelle that produces energy (ATP) for the cell.

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Lipid rafts

Specialized regions within the cell membrane enriched in cholesterol, sphingolipids, glycolipids, and certain proteins. They are thicker than the surrounding membrane and act as platforms for protein interactions and signaling.

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Transmembrane/integral proteins

Proteins that are embedded within the entire cell membrane. They can have single or multiple alpha-helices spanning the membrane or form beta-barrel structures.

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Peripheral proteins

Proteins that are loosely attached to the exterior of the cell membrane. They may be bound via an alpha-helix, lipid chains, or other proteins.

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Membrane proteins

Proteins that are embedded within the cell membrane and give functional properties to the membrane. They have both hydrophilic and hydrophobic regions, allowing them to interact with both the watery environment and the lipid bilayer.

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Hydropathy plots

A method used to predict transmembrane regions in proteins based on their amino acid composition. It calculates the free energy required to transfer segments of a polypeptide chain from a nonpolar solvent to water, thus identifying hydrophobic segments likely embedded in the membrane.

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Glycosylation of membrane proteins

The addition of sugar residues (glycosylation) to proteins, primarily occurring on the non-cytosolic side of the membrane in the ER and Golgi apparatus. This results in sugar residues being found on the extracellular side of the protein.

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Disulfide bonds in membrane proteins

Chemical bonds that form between cysteine amino acids, primarily on the non-cytosolic side of the membrane. They are not typically found on the cytosolic side due to the reducing environment.

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Amino acid arrangement in membrane proteins

The arrangement of amino acids in a protein influences its structure and function. Transmembrane proteins often use alpha-helices to cross the membrane because they are more efficient in forming hydrogen bonds with each other in the absence of water.

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What is the function of the plasma membrane?

The plasma membrane is the outermost boundary of a cell, acting as a selective barrier that controls what enters and leaves. It also provides structural support and facilitates communication between cells.

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What is the structure of the plasma membrane?

The plasma membrane is made up of a phospholipid bilayer, a double layer of lipids with hydrophilic heads facing the outside and hydrophobic tails facing inwards. Proteins embedded within this bilayer contribute to various functions.

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What are phospholipids and why are they important to the plasma membrane?

Phospholipids are major components of the plasma membrane. They have a polar head group containing a phosphate and two non-polar hydrocarbon tails, making them amphiphilic.

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What is the role of cholesterol in the plasma membrane?

Cholesterol, a type of sterol, is embedded in the plasma membrane. It helps regulate membrane fluidity by decreasing fluidity at high temperatures and increasing fluidity at low temperatures.

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How do saturated and unsaturated fatty acids affect membrane fluidity?

Saturated fatty acids make the plasma membrane less fluid and more rigid, while unsaturated fatty acids make it more fluid and flexible. The ratio of saturated to unsaturated fatty acids in the membrane can vary depending on the cell's environment and function.

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What is the endosymbiotic theory?

The endosymbiotic theory proposes that mitochondria and chloroplasts were once free-living bacteria that were engulfed by early eukaryotic cells and established a symbiotic relationship. Evidence for this theory lies in the fact that these organelles have their own DNA and ribosomes.

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How are cyanobacteria related to chloroplasts?

Cyanobacteria, a type of bacteria that performs photosynthesis, are believed to be the ancestors of chloroplasts. These organisms were engulfed by early eukaryotic cells, eventually leading to the development of plant cells with chloroplasts.

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Explain the dual bacterial and archaeal inheritance of eukaryotic cells.

All eukaryotic cells, including plants and animals, inherit genetic information from both bacteria and archaea, hinting at a mixed ancestry. This is evidenced by the presence of genes in the eukaryotic nucleus that are more closely related to archaeal genes, while other genes are more similar to bacterial genes.

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Glycocalyx

A layer of carbohydrates, often attached to proteins and lipids, that covers the surface of cells.

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Selectively permeable

The cell membrane allows some substances to pass through while blocking others.

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Passive transport

Movement of substances across a membrane without requiring energy.

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Active transport

Movement of substances across a membrane that requires energy.

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Membrane transport proteins

Membrane proteins that help move substances across the cell membrane.

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Uniporter

A type of membrane transport protein that moves one substance across the membrane.

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Symporter

A type of membrane transport protein that moves two substances in the same direction across the membrane.

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Antiporter

A type of membrane transport protein that moves two substances in opposite directions across the membrane.

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Coupled transport (secondary active transport)

A type of active transport where the energy for movement of molecules across the membrane is derived from the concentration gradient of another molecule, often facilitated by a membrane protein.

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ATP-driven transport (primary active transport)

A type of active transport where the energy for movement of molecules across the membrane is derived directly from ATP hydrolysis.

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Light-driven transport (primary active transport)

A type of active transport where the energy for movement of molecules across the membrane is derived from light energy, often used by photosynthetic organisms.

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Na+/K+ ATPase pump

A transmembrane protein that pumps sodium ions out of the cell and potassium ions into the cell, creating electrochemical gradients across the membrane.

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Aquaporin

A specialized channel protein that facilitates the rapid movement of water across cell membranes, playing a crucial role in maintaining osmotic balance and fluid secretion.

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Osmotic gradient

The difference in concentration of a substance across a membrane. Water moves from areas of high water concentration (low solute concentration) to areas of low water concentration (high solute concentration).

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K+ leak channel

A type of membrane protein that allows potassium ions (K+) to passively leak out of the cell, contributing to the resting membrane potential.

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Na+/K+ Pump

An active transport protein that pumps sodium ions (Na+) out of the cell and potassium ions (K+) into the cell, using energy from ATP. This maintains the concentration gradients of these ions, essential for generating the resting membrane potential.

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Resting membrane potential

The electrical potential difference across the cell membrane when the cell is at rest. It is typically negative inside the cell compared to the outside.

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Action potential

A sudden, rapid change in the membrane potential of a neuron or muscle cell, caused by the opening and closing of voltage-gated ion channels. It is a signal that travels along the cell's membrane.

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Voltage-gated ion channel

A type of ion channel that opens and closes in response to changes in the membrane potential. It plays a crucial role in generating action potentials.

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Depolarization

The process of making the inside of the cell more positive relative to the outside. It is the first step in generating an action potential.

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Repolarization

The process of restoring the membrane potential back to its resting value after an action potential. It is the second part of the action potential.

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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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Cell Bio Notes PDF

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Test your knowledge on eukaryotic cell structures and their functions with this quiz. Explore topics including ribosome production, the role of the Rough Endoplasmic Reticulum, and the distinctions between plant and animal cells. Perfect for students studying cell biology and related fields.

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