4 Transportation across cell membranes
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Why are membranes described as fluid-mosaic?
The mixture and movement of phospholipids, proteins, glycoproteins and glycolipids
Fluid
individual PL molecules can move relative to one another, making it flexible and constantly changing shape
Mosaic
Proteins that are embedded in the PL bilayer very in shape
What does a phospholipid bilayer create?
Partially permeable membrane
How is the phospholipid bilayer created (2)
Due to the hydrophilic heads being attracted to the water And the hydrophobic tails being repelled by water
What molecules can pass through the cell membrane? (2)
Lipid-soluble substances (e.g some hormones like oestrogen) Very small molecules
What molecules cannot pass through the cell membrane? (2)
Water soluble (polar) substances like sodium ions Large molecules like glucose
What is cholestrol (3)
Type of lipid that restricts lateral movement of other molecules in the membrane Makes the membrane less fluid at higher temperatures Prevents water and dissolved ions from leaking out the cell
Peripheral proteins (2)
Provide mechanical support Connected to carbohydrates to make glycoproteins
Function of glycolipids and glycoproteins
Cell recognition as receptors
Integral proteins
Protein carries or channel proteins involved in the transport of molecules across membranes
Channel proteins
Form tubes that fill with water to enable water-soluble ions to diffuse
Carrier proteins (2)
Bind to other ones and large molecules, such as glucose and amino acids Change shape to the other side of the membrane
What are the 5 different types of transport
SImple diffusion Facilitated diffusion Osmosis Active transport Co-transport
How are cells adapted for rapid transport across internal and external membranes (2)
An increase in surface area An increase in the number of protein channels and carrier molecules in their membranes
Simple diffusion (2)
The net movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached Does not require ATP
How do the molecules move by simple diffusion (3)
Kinetic energy to be able to constantly move in fluids Lipid soluble Small
Passive process
goes down the concentration gradient and does not require energy
Facilitated diffusion
Movement of polar molecules using down concentration gradient via carrier proteins
Facilitated diffusion by protein channels (2)
1.Protein channels form tubes that fill with water 2. Which enables water-soluble ions to pass through membrane
Why are protein channels selective
Only open in the presence of certain ions which bind to protein
Facilitated diffusion by carrier protein
• Bind with a molecule such as glucose • Causes a change in shape of the protein • Enables molecule to be released to the other side of the membrane
Osmosis
The movement of water from an area of higher water potential to an area of lower water potential across a partially permeable membrane, down concentration gradient
Water potential
Pressure created by water molecules