Biological membranes Flashcards
1
Q
Plasma membranes
A
- Barrier between cell and environment controlling which substances enter and leave the cell
- Partially permeable
- Substances can move by diffusion, osmosis and active transport.
- They allow cell signalling
2
Q
Membranes within cells
A
- Divide cell into different compartments act as barrier
- Form vesicles to transport substances and control what goes in and out of the cells
3
Q
Fluid mosaic model
A
- Fluid- Phospholipids are constantly moving
- Mosaic- Protein molecules scattered in the bilayer contain glycoproteins
4
Q
Phospholipids
A
- Has a hydrophilic head and hydrophobic tail
- Arrange themselves into a phospholipid bilayer
- Centre of bilayer is hydrophobic so water soluble substances cannot pass through
5
Q
Cholesterol
A
- Fits in between the phospholipid molecules binding to the hydrophobic tails causing them to pack more tightly together making the membrane more ridged
- At lower temperatures it prevents the phospholipids from packing too close together increasing fluidity
6
Q
Proteins
A
- Some form channels in the membrane allowing small charged particles through.
- Some transport molecules and ions across the membrane by active transport and facilitated diffusion
- Also act as receptors for molecules in cell signalling when a molecule binds a chemical reaction is triggered in the cell.
7
Q
Glycolipids and glycoproteins
A
- Stabilise the membrane by forming HYDROGEN BONDS with surrounding water molecules
- Also sites where drugs and hormones binds and act as receptors for the cell aswell as antigens
8
Q
How do messenger molecules work?
A
- One cell releases the molecule eg a hormone
- Molecule travels to another cell eg in the blood
- Messenger molecule detected by cell because it binds to a receptor on the membrane
9
Q
Receptor proteins
A
- They have a specific shape and only complementary messenger molecules can bind to them
- Different cells have different types of receptors and respond to different molecules
- Target cell is a cell which responds to a particular messenger molecule
10
Q
Diffusion
A
- Passive process
- Net movement of particles across a membrane to the area of lower concentration and continues until particles are evenly distributed
11
Q
Facilitated diffusion
A
- Uses carrier and channel proteins
- Moves particles down a concentration gradient and is passive.
12
Q
Active transport
A
- Molecule attaches to carrier protein and protein changes shape and moves molecule across membrane releasing it on the other side
- Energy is used to move it against the cpnc gradient
13
Q
Endocytosis
A
- Cell surrounds a substance with a section of its plasma membrane
- Membrane then pinches off to form a vesicle inside the cell containing the substance
- Uses ATP
14
Q
Exocytosis
A
- Vesicles containing substances pinch off from the sacs of the golgi apparatus and move towards plasma membrane
- Vesicles fuse with plasma membrane and release contents outside of the cell and requires ATP.
15
Q
Osmosis
A
- Diffusion of water molecules across a partially permeable membrane down a water potential gradient
16
Q
Hypotonic solution
A
- Solution with higher water potential than the cell net movement of water molecules into the cell
- In animals the cell bursts
- In plants cell becomes turgid- (swollen)
17
Q
Isotonic solution
A
- Solution with the same water potential as the cell
- Water molecules pass in and out the cell in equal amounts
- Cell stays the same in animal and plant cells.
18
Q
Hypertonic solution
A
Solution with a lower water potential than the cell
- Net movement is out of the cell7
- Cell shrinks in animals and becomes flaccid in plants plasmolysis
