Biological Membranes Flashcards
(24 cards)
What is the structure of the plasma membrane?
A phospholipid bilayer with embedded proteins, cholesterol, glycolipids, and glycoproteins.
What is the fluid mosaic model?
Describes the membrane as a fluid phospholipid bilayer with proteins floating in it.
What are the functions of the plasma membrane?
Controls entry/exit of substances, communication, compartmentalisation, site of chemical reactions.
What is the role of phospholipids in membranes?
Form a bilayer that acts as a barrier to most water-soluble substances.
What is the role of cholesterol in membranes?
Stabilises membrane fluidity and adds mechanical strength.
What is the role of glycoproteins and glycolipids?
Involved in cell recognition, signalling, and adhesion.
What are intrinsic proteins?
Proteins that span the membrane and are involved in transport (e.g., channel and carrier proteins).
What are extrinsic proteins?
Proteins on the surface of the membrane involved in signalling or enzymatic activity.
What is passive transport?
Movement of substances down their concentration gradient without energy (e.g., diffusion, osmosis, facilitated diffusion).
What is diffusion?
The passive movement of molecules from a region of high to low concentration.
What is facilitated diffusion?
Diffusion of substances through channel or carrier proteins in the membrane.
What is osmosis?
The diffusion of water from high water potential to low water potential across a partially permeable membrane.
What is water potential?
The potential of water to move; pure water has the highest value (0 kPa).
What happens to animal cells in hypotonic solutions?
They swell and may burst (lysis) due to water influx.
What happens to plant cells in hypotonic solutions?
They become turgid as water enters the cell, but cell wall prevents bursting.
What happens to animal cells in hypertonic solutions?
They shrink or crenate as water leaves the cell.
What happens to plant cells in hypertonic solutions?
They become plasmolysed as the cell membrane pulls away from the cell wall.
What is active transport?
Movement of substances against their concentration gradient using ATP and carrier proteins.
What is endocytosis?
The process of taking substances into the cell by engulfing them in a vesicle.
What is exocytosis?
The process of removing substances from the cell by vesicle fusion with the membrane.
How does temperature affect membrane permeability?
High temperatures increase fluidity and permeability; low temperatures make membranes rigid.
How does solvent concentration affect membrane permeability?
Ethanol and other solvents can disrupt the membrane, increasing permeability.
What is the importance of membranes within cells?
Separate organelles, create concentration gradients, and provide surfaces for reactions (e.g., cristae in mitochondria).
