M1 Topic 3: Plasma membrane Flashcards
(24 cards)
What is the plasma membrane?
Divides the inside of the cell from the outside and regulates what can enter or exit the cell
Structure of the plasma membrane
- Lipid bilayer (two layers of lipids)
- Membrane proteins
Which end of the lipid is hydrophilic?
The head
Which end of the lipid is hydrophobic?
The tail
Membrane proteins
Proteins can either be stuck to one side of the membrane, or penetrate the whole way through
- Channels
- Carriers
- Receptors
- Enzymes
Channel proteins
Form pores or holes through PM, allowing ions to pass from one side to the other
- Can sometimes have gate which opens/closes
Carrier proteins
Proteins that facilitate movement of substances across the membrane by changing shape to funnel them across
Receptor proteins
Cell recognition sites with receptors which recognises and binds a specific type of molecule, may trigger receptor to change in some way
Enzymes
Proteins that catalyse specific chemical reactions
Attributes of lipids
- Non-polar
- Non-polar molecules are more attracted to other non-polar molecules and polar molecules are attracted to other polar molecules
- Polar molecules and non-polar molecules repel each other
Selective permeability
PM ability to allow some substances through, whilst blocking others
- Lipid bilayer is permeable to non-polar, uncharged molecules, allowing small particles that are neutral to cross
- Protein channels and carriers increase PM permeability, are highly selective where specific ions or molecules can use particular channels/carriers
- Larger molecules too big for these methods, thus must use vesicular transport
Diffusion
Random movement of particles along a concentration gradient
- From an area of high concentration to an area of low concentration
Categories of transport mechanisms
Passive transport
- Simple diffusion
- Osmosis
- Facilitated diffusion - diffusion using channel or carrier protein
Active transport
- Primary active transport
- Vesicular transport
What is passive transport?
Transport requires no energy (ATP) as substances always moving with concentration gradient
Simple diffusion
- Substances move directly through the phospholipids of the PM along concentration gradient
- No need of energy from ATP hydrolysis.
Facilitated diffusion (using a channel protein)
- Substances move through protein channels embedded in lipid bilayer
- Move with concentration gradient
- No need for ATP hydrolysis energy
Facilitated diffusion (using a carrier protein)
- Substance attach to one side of protein, which then changes shape to push substance to other side of PM
- Move with concentration gradient
- No need for ATP hydrolysis energy
Osmosis
Water moves through membrane (both through channels and directly through membrane) with concentration gradient
Active transport
Requires energy to move something from one side of PM to other
Primary active transport
Protein pump hydrolyses ATP molecule, uses energy released from this reaction to move substance against concentration gradient
Example of primary active transport
Sodium-potassium pump
Pump has binding sites for 3 sodium and 2 potassium ions
- 3 intracellular sodium ions bind to carrier protein
- ATP molecule is split (hydrolysis), phosphate binds to carrier protein, changing its’ shape
- 3 sodium ions are moved to extracellular space
- 2 extracellular potassium ions bind to carrier protein, changing its’ shape, and releasing the phosphate molecule
- Potassium ions are released into the cytoplasm
For every 3 sodium ions leaving cell, 2 potassium ions enter
Vesicular transport
Used to transport larger substances across PM
- Exocytosis
- Endocytosis
Exocytosis
Extrude contents of cellular vesicles into the extracellular spaces
Endocytosis
Take substances into the cell from extracellular space by producing a vesicle
