Cell Biology: Membrane Transport Concepts

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Questions and Answers

What percentage of living matter by weight is accounted for by small molecules such as water and organic ions?

25 - 30%

50 - 60%

75 - 80% (correct)

90 - 95%

Which of the following best describes the primary function of small molecules in cells?

They serve mainly as storage for genetic information.

They primarily assist in cellular structure formation.

They act as precursors for the synthesis of macromolecules. (correct)

They regulate cellular temperature.

What type of molecules can primarily passively diffuse across the phospholipid bilayer of the plasma membrane?

Polypeptides

Ionic compounds

Large, charged molecules

Small, hydrophobic molecules (correct)

Facilitated diffusion is characterized by which of the following statements?

It is always energetically downhill. Signup and view all the answers

What is the primary role of carrier proteins in facilitated diffusion?

To bind and transport solutes across the membrane Signup and view all the answers

What distinguishes channel proteins from carrier proteins in membrane transport?

Only carrier proteins undergo conformational changes. Signup and view all the answers

Which type of transport occurs spontaneously due to a positive delta S value and a negative delta G?

Simple diffusion Signup and view all the answers

What type of molecules does facilitated diffusion particularly allow to cross the plasma membrane?

Polar and charged molecules Signup and view all the answers

What is the primary function of uniporters in cellular transport?

Transport a single type of molecule down its concentration gradient Signup and view all the answers

What distinguishes gated ion channels from non-gated channels?

Gated channels open in response to specific signals Signup and view all the answers

Which type of ion channel opens in response to mechanical vibration or pressure?

Mechanically-gated channels Signup and view all the answers

What drives the process of primary active transport?

Coupled reactions like ATP hydrolysis Signup and view all the answers

What characteristic allows aquaporins to facilitate rapid water movement across membranes?

They provide a hydrophilic pathway for water molecules Signup and view all the answers

Which biological process is facilitated by cotransporters?

Utilizing the energy of an electrochemical gradient Signup and view all the answers

What is the role of ion pumps in a cell's plasma membrane?

Maintaining gradients of ions across the membrane Signup and view all the answers

Which type of transport is characterized by molecules moving from areas of high concentration to areas of low concentration without the use of energy?

Facilitated diffusion Signup and view all the answers

Which statement accurately describes sphingolipids?

They contain a long-chain fatty acid attached to sphingosine amino group. Signup and view all the answers

What is the basic structure of sterols?

A four-ring hydrocarbon structure. Signup and view all the answers

Which type of membrane protein interacts with the hydrophobic core of the phospholipid bilayer?

Integral membrane proteins. Signup and view all the answers

Which function of the plasma membrane involves enclosing the contents of the cell?

Compartmentalization. Signup and view all the answers

Where are carbohydrate chains located on transmembrane proteins?

In the exoplasmic face of the membrane. Signup and view all the answers

What type of membrane proteins are bound covalently to one or more lipid molecules?

Lipid-anchored proteins. Signup and view all the answers

What characteristic do peripheral membrane proteins lack?

Spanning the phospholipid bilayer. Signup and view all the answers

Which of the following is a role of the plasma membrane in response to external stimuli?

Signal transduction. Signup and view all the answers

What is the primary role of the rough endoplasmic reticulum (ER)?

Protein synthesis Signup and view all the answers

Which organelle is responsible for the destruction of a cell's own organelles?

Lysosomes Signup and view all the answers

Which of the following functions is NOT associated with the Golgi apparatus?

Synthesis of steroid hormones Signup and view all the answers

What characterizes phosphoglycerides as a class of lipids?

They are the most abundant lipids in membranes. Signup and view all the answers

Which component of the endomembrane system is involved in protein transport and modification?

Golgi apparatus Signup and view all the answers

What process do lysosomes participate in besides autophagy?

Phagocytosis Signup and view all the answers

What specific function does the smooth endoplasmic reticulum serve?

Lipid synthesis Signup and view all the answers

Which statement about amphipathic molecules is true?

They contain both hydrophilic and hydrophobic regions. Signup and view all the answers

What mechanism allows eukaryotic cells to take up macromolecules from their environment?

Endocytosis Signup and view all the answers

Which type of endocytosis is characterized by the uptake of soluble materials?

Pinocytosis Signup and view all the answers

What triggers the process of phagocytosis?

Binding of large particles to surface receptors Signup and view all the answers

Which type of phagocyte is NOT considered a professional phagocyte in mammals?

Eosinophils Signup and view all the answers

What forms the intracellular vesicles during receptor-mediated endocytosis?

Clathrin-coated pits Signup and view all the answers

How does the process of phagocytosis ultimately lead to digestion of engulfed materials?

By fusing phagosomes with lysosomes to form phagolysosomes Signup and view all the answers

What characterizes receptor-mediated endocytosis in terms of selectivity?

It selectively targets macromolecules that bind to cell surface receptors. Signup and view all the answers

What is the primary role of the LDL receptor in relation to cholesterol?

To facilitate the uptake of cholesterol into cells. Signup and view all the answers

What do clathrin-coated pits on the plasma membrane primarily facilitate?

Selective uptake of extracellular materials Signup and view all the answers

What condition is associated with a variant in the LDLR gene?

Familial hypercholesterolemia. Signup and view all the answers

Which statement best describes the process of constitutive exocytosis?

It continually releases materials without specific triggers. Signup and view all the answers

What triggers regulated exocytosis in β cells of the pancreas?

Increase in blood glucose concentration. Signup and view all the answers

What is the ultimate outcome of exocytosis?

Contents are released into the extracellular fluid. Signup and view all the answers

Which type of exocytosis occurs randomly and continuously?

Constitutive exocytosis. Signup and view all the answers

Which of the following best describes clathrin-coated vesicles?

They are involved in receptor-mediated endocytosis. Signup and view all the answers

What molecular change triggers the exocytosis of insulin from β cells?

Closure of K+ channels. Signup and view all the answers

Study Notes

Molecular Transport - Transport of Small Molecules

Small molecules (water, inorganic ions, and relatively small organic molecules) make up 75-80% of living matter by weight
Cells import ions, water and small organic molecules
Cells make and alter small organic molecules through various chemical reactions
Small molecules perform several functions:
- Precursors for macromolecule synthesis
- Energy storage and distribution
- Signaling

Transport Across the Plasma Membrane

Plasma membranes are selectively permeable
Permeability is determined by size, charge, and solubility
Small, relatively hydrophobic molecules diffuse across the phospholipid bilayer
Larger or charged molecules cannot readily pass through

Passive Transport

Includes simple and facilitated diffusion
- Simple diffusion: Molecules dissolve into the phospholipid bilayer, diffuse across, and then dissolve into the aqueous solution on the other side
- Facilitated diffusion: Uses protein channels or carriers to move polar or charged molecules across the membrane down their concentration gradient
- Facilitated diffusion - Carrier proteins:
  - Bind to a solute
  - Undergo conformational changes to transport the solute across the membrane
  - Uniporter, symporter, antiporter
- Facilitated diffusion - Channel proteins:
  - Form hydrophilic passageways
  - Allow water or specific ions and small molecules to pass along their concentration or electric potential gradients
  - Non-gated (always open) and gated (open in response to signals)
  - Aquaporins help water move quickly across the membrane

Active Transport

Requires energy (often ATP) to move molecules against their concentration or electrochemical gradient
- Primary active transport: ATP directly fuels the transport
  - Ion pumps (e.g., Na+/K+ ATPase)
- Secondary active transport (Cotransport): Uses energy stored in an electrochemical gradient created by primary active transport to move other molecules
  - Symporters move molecules in the same direction
  - Antiporters move molecules in opposite directions

Ion Channel Properties

Transport through channels is very rapid
Ion channels are highly selective (size and charge)
Non-gated ion channels are permanently open
Gated ion channels are not permanently open
- Ligand-gated ion channels: Open in response to ligands (signaling molecules)
- Voltage-gated ion channels: respond to changes in membrane potential
- Mechanically-gated ion channels: respond to mechanical stimuli

Cystic Fibrosis (CF)

CF is a genetic disorder caused by mutations in the CFTR gene
CFTR encodes a chloride channel in plasma membranes
Defective CFTR channels disrupt ion transport, leading to thick mucus in the lungs and other organs, impacting function and leading to issues in health
Mutations in CFTR genes influence stability, folding, quantity and insertion of the protein into the membrane

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Description

Test your understanding of membrane transport concepts in cell biology. This quiz covers small molecules, passive diffusion, facilitated diffusion, and the roles of various transport proteins. Challenge yourself with questions about the mechanisms driving these essential processes.