Cell Biology: Membrane Structure and Function

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Questions and Answers

Explain how cholesterol affects membrane fluidity and stability.

Cholesterol increases membrane stability by breaking up closely packed phospholipids, reducing fluidity, and decreasing permeability to some water-soluble ions.

Describe the difference between integral and peripheral membrane proteins.

Integral proteins are embedded within the entire membrane and stick out on both sides, whereas peripheral proteins are only on the outside of the membrane.

What is the main function of glycolipids and glycoproteins found in cell membranes?

Glycolipids and glycoproteins are primarily cell identification tags and are used for cell-to-cell adhesion and recognition.

How do transport proteins facilitate the movement of molecules across the cell membrane?

Transport proteins create channels or have binding sites, allowing specific ions or molecules to move in and out of the cell. Signup and view all the answers

What role do receptor proteins play in cell communication?

Receptor proteins bind to signal molecules (ligands) and relay messages, triggering responses within the cell. Signup and view all the answers

What is the name of the random molecular motion that is essential to passive transport?

Brownian motion Signup and view all the answers

What type of energy is used directly in passive transport?

Kinetic energy Signup and view all the answers

What is the term for the movement of molecules from an area of higher concentration to an area of lower concentration?

Diffusion Signup and view all the answers

What is the term for the diffusion of water across a selectively permeable membrane?

Osmosis Signup and view all the answers

What is the term for a solution that causes a cell to shrink due to water loss?

Hypertonic Signup and view all the answers

What is the function of aquaporins in a cell membrane?

Fast water transport Signup and view all the answers

What type of molecules use carrier proteins during facilitated diffusion?

Large, unchanged polar molecules. Signup and view all the answers

What are the three types of gated channels found in cell membranes?

Mechanically-gated, voltage-gated, ligand-gated Signup and view all the answers

What is the source of chemical energy for active transport?

ATP Signup and view all the answers

What type of transport moves molecules from areas of lower concentration to higher concentration?

Active transport Signup and view all the answers

What type of protein facilitates both active and facilitated transport?

Carrier protein Signup and view all the answers

How many sodium and potassium ions are exchanged in the sodium-potassium pump in each cycle?

Three sodium ions out, two potassium ions in. Signup and view all the answers

What is the name of the process by which cells export bulky materials?

Exocytosis Signup and view all the answers

What type of endocytosis involves the engulfment of large particles by the cell?

Phagocytosis Signup and view all the answers

In receptor-mediated endocytosis, what role do membrane receptors play?

Binding specific solutes Signup and view all the answers

What is exocytosis and what type of materials does it export?

Exocytosis is a cellular process used to export bulky materials like proteins and polysaccharides. Signup and view all the answers

Define kinetic energy and give an example.

Kinetic energy is the energy of motion; an example is light energy, which can be harnessed during photosynthesis. Signup and view all the answers

What does the law of energy conservation state?

The law of energy conservation states that energy cannot be created or destroyed, only transformed from one form to another. Signup and view all the answers

Differentiate between exergonic and endergonic reactions.

Exergonic reactions release energy, while endergonic reactions require an input of energy to proceed. Signup and view all the answers

Explain the concept of ATP and its role in cellular work.

ATP, or Adenosine Triphosphate, powers nearly all forms of cellular work by releasing energy when its third phosphate group is transferred. Signup and view all the answers

What is activation energy, and why is it important?

Activation energy is the minimum energy needed for a reactant to reach a high-energy state and initiate a chemical reaction. Signup and view all the answers

What role do enzymes play in biochemical reactions?

Enzymes act as biological catalysts that increase the reaction rate by lowering the activation energy required. Signup and view all the answers

Describe the process of enzyme-substrate interaction.

The substrate binds to the enzyme's active site, leading to an induced fit that converts the substrate into products, which are then released. Signup and view all the answers

What factors affect enzyme activity?

Temperature and pH are key factors that influence enzyme activity and optimal conditions vary for different enzymes. Signup and view all the answers

What is an enzyme inhibitor, and how does it affect enzyme activity?

An enzyme inhibitor is a substance that interferes with the enzyme's activity, reducing its productivity in catalyzing reactions. Signup and view all the answers

What is the significance of cofactors in enzymatic reactions?

Cofactors are non-protein helpers that bind to enzymes and aid in catalysis, enhancing their activity. Signup and view all the answers

How does energy coupling work in cells?

Energy coupling uses energy released from exergonic reactions to drive endergonic reactions, commonly involving ATP. Signup and view all the answers

Explain the ATP cycle in cellular metabolism.

The ATP cycle involves the breakdown of ATP to release energy, which is then used to regenerate ATP from ADP in an endergonic reaction. Signup and view all the answers

Give an example of a useful enzyme inhibitor and its application.

Ibuprofen is an example of an enzyme inhibitor that inhibits an enzyme involved in pain and inflammation pathways. Signup and view all the answers

Study Notes

Membrane Structure and Function

Membranes are fluid mosaics, with embedded proteins in a phospholipid bilayer.
Phospholipids: Polar heads (hydrophilic) face outwards, nonpolar tails (hydrophobic) face inwards. Fluidity allows phospholipid movement.
Cholesterol: Found in eukaryotic membranes, increases stability, reduces fluidity, and permeability to water-soluble ions.
Integral proteins: Embedded throughout the membrane, exposed on both sides; act as channels for transport.
Peripheral proteins: Exposed on one side, may link to cytoskeleton, act as enzymes, binding/receptor sites.
Glycolipids/glycoproteins (ID tags): Carbohydrates attached to proteins or lipids, on the extracellular surface; for cell-cell adhesion and recognition.

Types of Membrane Proteins

Transport proteins: Allow ion/molecule passage.
Enzymes: Clustered for sequential reactions.
Junction proteins: Link adjacent cells.
Attachment proteins: Connect to cytoskeleton or extracellular matrix. Coordinate internal/external changes.
Receptor proteins: Bind signal molecules (ligands), triggering intracellular responses.

Membrane Transport

Membrane transport is crucial for homeostasis; requires energy.
Potential energy & kinetic energy (molecules in Brownian motion).
Chemical energy (ATP from cellular respiration).
Concentration gradient: Quantitative measure of solute concentration on either side of the membrane.
Dynamic equilibrium: Movement continues until concentrations are equal.

Passive Transport

Movement down the concentration gradient, no energy required.
Types:
- Simple diffusion: Small, nonpolar molecules (e.g., O₂, CO₂, benzene, N₂). Fat-soluble molecules readily cross.
- Osmosis: Water diffusion across a selectively permeable membrane. Attempts to equalize solute concentration.
- Tonicity: Surrounding solution's ability to affect cell volume.
  - Isotonic: No net water movement.
  - Hypotonic: Water moves into cell (animal cells potentially burst).
  - Hypertonic: Water moves out of cell (animal cells shrink).
- Osmoregulation: Maintaining water balance.
- Aquaporins: Water channel proteins for rapid water movement (discovered by Dr. Peter Agre).

Facilitated Diffusion

Passive transport through channel proteins.
Carrier proteins: For large, polar molecules (amino acids, sugars, nucleotides). Protein changes shape to facilitate movement.
Ion channels: Transport ions through selective protein channels. Can be gated (closed/open). - Leakage channels: Always open. - Mechanically gated: Opened by membrane stretching. - Voltage-gated: Opened by electrical changes. - Ligand-gated: Opened by specific molecules binding.

Active Transport

Movement against the concentration gradient, requires energy (ATP).
Membrane pumps:
- Carrier proteins actively move molecules, changing shape with ATP.
- Example: Na⁺-K⁺ pump (3 Na⁺ out, 2 K⁺ in).
Bulk transport:
- Exocytosis: Exporting bulky materials (vesicles).
- Endocytosis: Taking in bulky materials.
  - Phagocytosis: Cell engulfs particle (vacuole formation).
  - Pinocytosis: Bulk transport of molecules.
  - Receptor-mediated endocytosis: Selective uptake of specific molecules.

Energy and Chemical Reactions

ATP (Adenosine Triphosphate): Powers cellular work (mechanical, transport, chemical).
Hydrolysis: Releasing energy from ATP by removing a phosphate.
Regeneration: ATP is continuously used and regenerated.
Enzymes: Speed up reactions by lowering activation energy.
Activation energy: Initial energy input needed for a reaction.
Factors Affecting Enzyme Activity:
- Temperature: Optimal temperature, excessive heat can harm proteins.
- pH: Optimal pH is near neutrality.
Cofactors/coenzymes: Non-protein helpers to enzymes, inorganic or organic.
Inhibitors: Interfere with enzyme activity.
- Competitive inhibitors: Block the active site.
- Non-competitive inhibitors: Bind elsewhere, change active site shape.
Metabolic pathways: Series of reactions, building or breaking down molecules.

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Description

Test your knowledge on the structure and function of cell membranes. This quiz covers important concepts such as phospholipid bilayers, types of membrane proteins, and the role of cholesterol in membrane stability. Understand how these elements contribute to cellular function and communication.