Membranes Flashcards
Q: What are the major membrane systems in eukaryotic cells?
A: Plasma membrane, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, endosomes, mitochondria, chloroplasts (in plants), and nuclear envelope.
Q: What are the principal lipids found in eukaryotic membranes?
A: Phospholipids, cholesterol, glycolipids.
Q: List four major functions of cell membranes.
A: 1. Compartmentalization
2. Selective transport of molecules
3. Signal transduction
4. Cell-cell recognition and adhesion
Q: Name and describe the three major groups of membrane ion transport proteins.
A:
Pumps (ATPases): Use ATP to move ions (e.g., Na⁺/K⁺-ATPase)
Coupled transporters: Use electrochemical gradients to move substances (e.g., glucose-sodium symporter)
Ion channels: Allow passive ion flow (e.g., voltage-gated Na⁺ channels)
Q: Give one example of pump,
A:
Pump: Na⁺/K⁺-ATPase (animal cells)
Q: What is the principal ion pump in animal cells, and what gradient does it generate?
A: Na⁺/K⁺-ATPase; generates a Na⁺ gradient (high outside, low inside)
Q: What is the principal ion pump in plant and fungal cells, and what gradient does it generate?
A: Proton (H⁺)-ATPase; generates a proton gradient (high H⁺ outside)
Q: What is a coupling-ion circuit and how is it used in cells?
A: It’s the use of electrochemical gradients (e.g., Na⁺ or H⁺) to drive the transport of other solutes like sugars, amino acids, and nutrients.
Q: What role does cholesterol play in eukaryotic membranes?
A: Cholesterol modulates membrane fluidity and stability by fitting between phospholipids.
Q: How do membrane proteins contribute to membrane function?
A: They facilitate transport, signal transduction, enzymatic activity, cell recognition, and intercellular joining.
Q: What percentage of cellular metabolism is estimated to support solute and nutrient transport?
A: Around 30%.
What do membranes have high permeability for?
Small hydrophobic molecules and gases, O2
What do membranes have low permeability for?
Water, ions e.g K+ and large solutes e.g. glucose
Q: How do cations and anions behave in an electrochemical gradient across a membrane?
Cations (e.g., Na⁺, K⁺, Ca²⁺) are positively charged and tend to move into the cell, attracted by the typically negative inside.
Anions (e.g., Cl⁻, HCO₃⁻) are negatively charged and tend to move out of the cell unless actively transported, as they’re repelled by the negative interior.
The electrochemical gradient combines both concentration and electrical differences across the membrane.
What are transport proteins for passive transport?
pumps, co-transport system
What are transport proteins for active transport?
channels, carriers
Q: What is a co-transporter and how does it work?
A co-transporter is a membrane protein that moves two or more substances together across a membrane. It uses the energy from one ion’s movement down its electrochemical gradient (usually Na⁺ or H⁺) to transport another substance against its gradient.
Symporter: both substances move in the same direction
Antiporter: substances move in opposite directions
Co-transporters are examples of secondary active transporters.
