lecture 4 - plasma membrane Flashcards
What are the key functions of organelles?
They provide seperate environments with specific conditions for substances to react/be transported.
What are the key organelles present in a plant and animal cell?
Nucleus, endoplasmic reticulum, golgi apparatus, mitochondrion.
What is the key organelle that is unique to the animal cell?
Lysosome
What are the key organelles that are unique to the plant cell?
Central vacuole, chloroplast
What covers the surface of plant and animal organelles?
Membranes
How many membranes do mitochondria have?
2
What is the key component of a cell/organelle plasma membrane?
Phospholipid bilayer
Why is the size of a cell limited?
Cells are small because the bigger they get, the smaller the surface area to volume ratio, meaning there is insufficient area of membrane for transport of the substance required to serve the large cell volume.
What is the phospholipid bilayer?
A double layer of phospholipids, which have their hydrophilic heads outside, and their hydrophobic tails imbedded within the membrane.
What is the structure of a phospholipid?
Hydrophilic head (glycerol and phosphate) with two hydrophobic tails (fatty acids)
How do the tails of phospholipids determine the fluidity of the bilayer?
Saturated tails pack together increasing viscosity, while unsaturated tails prevent packing, creating fluidity.
How is viscocity of the animal cell membrane regulated?
Cholesterol is embedded within the phospholipid bilayer. It immobilises the outer surface and lowers permeability of water soluble molecules. Prevents the phospholipids from packing together stiffly during cold temperatures, and stabilises the membrane at high temperatures
Does cholesterol lower or raise membrane permeability?
Lower - it is worse than phospholipids at shielding hydrophobic interactions.
What are the four types of transport across the cell membrane?
Diffusion, facilitated diffusion, active transport and co-transport.
What types of membrane transport are passive?
Diffusion and facilitated diffusion
What types of membrane transport require energy?
Active transport and co-transport
What type of molecules are involved with diffusion across a phospholipid bilayer membrane?
Lipid soluble molecules.
How do lipid soluble molecules move through the membrane?
The concentration gradient drives the movement. They move through from higher concentration to lower concentration (down the gradient).
What molecules pass through the membrane via facilitated diffusion?
Hydrophilic substances (water soluble molecules and ions).
How are particles moved in facilitated diffusion?
They are moved through protein channels or carriers.
What are channels and carriers?
Proteins which traverse the width of the cell membrane and aid the movement of hydrophilic substance from higher concentration to lower concentration.
Why is facilitated diffusion passive?
Requires no energy because substances move down their concentration gradient.
How do carriers move molecules across the membrane?
They change shape.
What is the facilitated diffusion of water?
Osmosis is the process of moving water from high water(low solute) concentration to low water (high solute) concentration. Water moves through protein channels called aquaporins.
What are the protein channels that water passively moves though?
Aquaporins
Osmosis is what type of transport?
Facilitated diffusion
What is active transport?
Transport that requires energy input (in the form of ATP) to move substances against their concentration gradient.
The sodium-potassium pump is involved in what kind of transport?
Active transport
What are the key steps of active transport?
Molecules/ions bind to transport protein. ATP transfers phosphate group to transport protein, which changes shape and moves the substance to the other side of the membrane. Another substance may then be transported back across the membrane before the phosphate group is released and the process can begin again.
The sodium-potassium pump transfers ions in which directions?
Na+ leaves the cell, and K+ is brought into the cell.
What is co-transport?
Indirect active transport, where an initial active transport process uses ATP to transfer a substance up its concentration gradient. The substance then pushes another substance against its concentration gradient (with no energy input), to restore the initial concentration of the first substance.
What is the H+/sucrose cotransporter?
A transport protein which uses H+ ions to push sucrose molecules into the cell against its concentration gradient.
What are the roles of membrane proteins, excluding transport proteins? (4)
Signal transduction, cell recognition, intercellular joining, and linking cytoskeleton and extracellular matrix.
What is signal transduction of membrane proteins?
When proteins relay messages from the body or environment to the cell.
How are signals brought to the cell from the body?
signal transduction - Signalling molecules bind to receptors in the cell membrane
What is the cell recognition role of membrane proteins?
Glycoproteins act as identifiers to recognise other cells, such as pathogens for the immune system.
What are glycoproteins?
Proteins with added sugars that aid in cell recognition
How do membranes join with other cells?
Via intercellular joining, where proteins in neighbouring cells bind together.
What is the cytoskeleton of a cell?
A structure inside the cell which provides structural support.
How is the cytoskeleton linked to the extracellular matrix?
Via proteins in the cell membrane
What is the thickness of the plasma membrane?
5-10nm
