Module 2 - cell membranes and transport Flashcards
(34 cards)
Describe the structure of a phospholipid bilayer
These bilayers contain phospholipids which have hydrophilic heads that face outwards and hydrophobic tails that face inwards.
Why are membranes important and provide an example
Cell membranes are important for the exchange of materials, interface for communication and protection. Lysosomes have a membrane so that hydrolytic enzymes don’t break down cellular organelles.
What is the difference between intrinsic proteins and extrinsic proteins?
Intrinsic are embedded in the membrane with its arrangement determined by hydrophobic/hydrophilic regions. Extrinsic are found on the outer and inner surface of a membrane
Briefly describe the fluid-mosaic model
Membranes are fluid because individual phospholipids can diffuse within their monolayer and thus move around. It is a mosaic because the scattered proteins make it look like a mosaic
What is the role of cholesterol in cell membranes
Same structure as phospholipids and are in between phospholipids in the membrane. Increases fluidity and prevents it from becoming rigid at low temperatures. Stops phospholipids from packing to close together.
What is the role of glycoproteins and glycolipids in cell membranes.
Both have carbohydrate chains acting as a receptor so it can bind to substances on cell surface. Signals for hormones and transmitters, receptors involved in endocytosis and involved in adhesion/stabilisation
What is the role of proteins in cell membranes
Transport proteins create hydrophobic channels allowing ions and polar molecules to travel through the membrane.
Each protein is specific to a particular ion/molecule.
Membranes become less fluid when there is…
Increase number of saturate fatty acids as chains pack tightly, high number of intermolecular forces. Low temps molecules have less energy not moving as freely cause structure to be more closely packed.
Membrane becomes more fluid when there is…
Increased number of unsaturated fatty acids, chains are bent meaning less tightly packed together so less intermolecular forces. At high temperatures, more energy, move freely so more fluid
What is diffusion?
Net movement as a result of the random motion of its molecules or ions, of a substance from a region of its higher concentration to a region of its lower concentration. Moves down the conc gradient
Rate depends on several factors which include…
Temperature (more kinetic energy), surface area, properties of molecules/ions and steepness
Explain how surface area can increase the rate of diffusion
More molecules/ions can pass in a period of time increasing rate. Folding increases surface area. As cell size increase, surface: volume ratio decreases, slowing rate as distance for diffusion increases
Explain how the properties of molecule/ions increase the rate of diffusion
Large molecules diffuse slower as required more energy to move. Non-polar diffuse quicker than polar as they are soluble in non-polar phospholipid layer.
Explain how the steepness of the conc gradient will increase the rate
A greater difference in conc means greater difference in number of molecules passing in 2 direction and so faster rate of diffusion
What is facilitated diffusion?
Large molecules and ions cannot pass through the phospholipid bilayer so only pass through with the help of certain proteins that are highly specific to one type of molecule/ion
What are channel proteins?
Water-filled pores allowing charged substances to diffuse through the cell membrane. They are gated so open and close to control the exchange of ions.
What are carrier proteins
Switch between shapes. Open up at the binding site then the carrier protein switches shape. Once inside the other side of the carrier protein opens up.
What is osmosis?
The net movement of water molecules from a region of higher water potential to a region of lower water potential. A dilute solution has a higher water potential and a concentrated solution has a lower water potential.
What happens when a plant cell is placed in pure water or a dilute solution?
Water passed into the cell as it moves from high water potential to low water potential. This means that the vacuole of the cell fills up with water so the volume of the cell increases. The expanding protoplast against the cell wall and pressure builds. Once the cell is fully inflated, the cell is fully turgid
why are cells being turgid important?
Ensures plant strength and to provide support allowing them to remain upright with leaves held out to catch the sunlight
What happens if a plant is placed in a solution of high water potential?
The water from within the cell will move out, the vacuole will being to shrink and the volume of the plant cell will being to decrease. The protoplast will shrink and no longer exerts pressure on the cell wall.
What is plasmolysis
This is when the protoplast pulls away from the cell wall after it has shrunk.
What happens when an animal cells is placed in a hypertonic environment?
This is when the concentration of solutes is higher outside of the cell than inside meaning water potential is lower. This will cause water to move out, the cell will shrink and therefore shrivel.
What happens when an animal cell is placed in a hypotonic environment?
This is when the concentration of solutes is lower outside of the cell than inside the cell meaning outside as a higher water potential. This caused water to move into the cell. Without the cell wall, the cell can may undergo cytolysis aka burst.
