Chapter 4 Cell Membrane and Transport Flashcards
(29 cards)
Describe the fluid mosaic model of membrane structure
- 7nm thick phospholipid bilayer containing protein molecules
- hydrophilic heads that face water
- hydrophobic tails that avoid water
- arrange into a bilayer
- proteins are scattered throughout the surface of the membrane
Features that increase fluidity
- The more unsaturated
- shorter fatty acid tails
- higher temperatures
What do the words “ fluid mosaic “ mean?
FLUID: both phospholipid and proteins can move about by diffusion
MOSAIC: the pattern produced by the scattered protein molecules when the surface of the membrane is viewed from above
Importance of cholesterol
- strengths membrane by getting in between the phospholipid molecules reducing fluidity
- prevent ions or polar molecules from passing through the membrane
- prevents phospholipid tails from packing closely together at low temperatures
Importance of glycolipids and glycoproteins
- receptor proteins: signalling receptors, recognize messengers molecules like hormones and neurotransmitters
- cell markers: cell- to-cell recognition, growth and development, and for immune response
Importance of proteins
- transporter proteins: provide hydrophilic channels or passageways for ions and polar molecules to pass through the membrane
- enzymes: catalyse the hydrolysis of molecules
- cytoskeleton: maintain and decide the shape of the cell
What is cell signalling?
The molecular mechanisms by which cells detect and respond to external stimuli
Process of cell signalling
- secretion of ligands from cells
- transport of ligands to target cells
- binding of ligands to cell surface receptors on target cells
- signal brings about a conformational change in the shape of the receptor, spanning the membrane
- the message is passed to the inside of the cell (transduction)
- changing the shape of the receptor allows it to interact with G-protein
- release of a second message
- activates a cascade of enzyme catalyzed reactions
- involves ATP use
What is a Visking tubing?
- It is a partially permeable, non-living membrane made of cellulose
- It has molecular-sized pores which are small enough to prevent the passage of large molecules, such as starch and surcose
- allows diffusion of smaller molecules such as glucose
Demonstrating diffusion using Visking tubing
- fill a length of visking tubing with a mixture of starch and glucose solutions
- suspend the tubing in a test tube of water for a period of time
- test the presence of starch and glucose
- results should indicate that glucose has diffused out of the tubing, and no sucrose
Factors affecting rate of diffusion
- the steepness of the concentration: steeper, faster
- temperature: higher, faster
- the nature of the molecules or ions: non-polar, diffuse more easily that polar molecules
- surface area: greater, faster
Trend between surface area: volume and 3D object size
The surface area: volume ratio decreases as the size of any 3D object increases
Define transduction
Occurs during cell signalling and is the process of converting a signal from one method of transmission to another
Define diffusion
- The net movement of molecules or ions from a region of higher concentration to a region of lower concentration down a concentration gradient
- Passive process
Define facilitated diffusion
The diffusion of a substance through a transport protein in a cell membrane; the protein provides hydrophilic areas that allows the molecule or ion to pass through the membrane
What are channel proteins?
- A membrane protein of fixed shape that has water-filled pores that allow charged substances to diffuse through the membrane.
- does not use ATP
What are carrier proteins?
- A membrane protein which changes shape to allow the passage into or out of the cell of ions or molecules
- uses ATP
Define osmosis
The net diffusion of water molecules from a region of higher water potential (less negative) to a region of lower water potential (more negative), through a partially permeable membrane
What happens when an animal cell is immersed in a hypotonic solution?
- water flows into the cell because the inside of the cell has a lower water potential
- cell swells due to influx of water
- cell can burst due to too much water
What happens when an animal cell is immersed in a hypertonic solution?
- water flows out of the cell to the more concentrated solution
- cell shrinks
What happens when a plant cell is immersed in a hypotonic solution?
- water flows into the cell
- the vacuole fills with water
- cell swells
- cell becomes turgid
What happens when a plant cell is immersed in a hypertonic solution?
- water leaves the vacuole and cytoplasm
- cell membrane pulls away, plasmolysis
- cell becomes flaccid
Define incipient plasmolysis
- The point at which plasmolysis is about to occur when a plant cell or prokaryote cell is losing water
- protoplast no longer exerts pressure on the cell wall
Define active transport
The movement of molecules or ions through transport proteins across a cell membrane, against their concentration gradient, using energy from ATP
