Transport Across Cell Membranes (Chapter 4) Flashcards
Describe the cell membrane
Partially permeable. Contains phospholipid bilayer, intrinsic proteins (span membrane), extrinsic protein (on surface), Cholesterol (stability) and glycolipids (recognition site)
Which molecules can diffuse through the membrane?
Lipid soluble molecules, water and other small substances.
Water soluble and larger molecules (e.g. glucose) can’t .
Define Diffusion
Net movement of particles from an area of high concentration to low concentration.
Passive process as its down a concentration gradient.
Describe Phospholipid
2 fatty acids/glycerol/phosphate
Hydrophobic tail and hydrophilic head so bilayer
Why it is described as a fluid mosaic?
Fluid = molecules are moving
Mosaic =Made up of proteins and phospholipids
What factors increase the rate of diffusion?
Bigger surface area, short diffusion pathway, bigger concentration gradient and higher temperature.
Higher temp as particles have more kinetic energy so move faster.
Define Facilitated Diffusion
When a molecule is too large to diffuse across membrane so can go by protein channels/carriers. Involves proteins that are specific to substance crossing.
Why are carrier proteins a limiting factor?
The can become fully saturated with molecules so can’t carry anymore across membranes.
Define Osmosis
Net movement of water particles from an area of high concentration to low, across a partially permeable membrane.
Passive/no carrier proteins/down a concentration gradient
What is the connection between water and water potential?
Water moves to more negative water potential.
More concentrated solution (e.g. more solutes) = lower the water potential.
Describe how substances move across across membranes via carrier proteins?
1) Ion binds to carrier proteins on receptor sites.
2) On inside of membrane, ATP binds to protein and is then hydrolysed to form ADP and Pi.
3) Ion is released.
4) Pi is released from protein so it changes back to original shape.
Define Active Transport
Net movement of molecules/ions from an area of low concentration to high concentration using energy and carrier proteins.
Requires ATP (active) - (lots of mitochondria)/uses carrier proteins/against concentration gradient
Describe the active transport of glucose
Co-Transport
1) Sodium ions actively transported form ileum epithelium cell to blood by Na/K pump.
2) Maintains/forms a diffusion gradient for sodium to enter cells from gut (and with it glucose)
3) Glucose enters by facilitated diffusion/co-transport with sodium ions.
