2.1.5 Biological membranes Flashcards
What is compartmentalisation?
Formation of separate membrane bound organelles
Why is compartmentalisation needed?
Allows for specific conditions such as chemical gradients to be maintained as reactions are contained to specific parts
Explain the fluid mosaic structure
- Phospholipids free to move giving membrane flexibility
- Proteins embedded in a random arrangement
What are intrinsic proteins? Give examples
- Proteins embedded in both layers of membrane
- Hydrophobic R-groups to interact with hydrophobic core
- E.g. carrier and channel proteins
What type of transport do channel proteins allow?
Passive transport of polar molecules
What type of transport do carrier proteins allow?
Active and passive transport which often involves shape of protein changing
What are glycoproteins?
- Proteins with attached carbohydrate chain
- Role in cell signalling e.g. neurotransmitters or peptide hormones
What are glycolipids?
- Lipid with attached carbohydrate chain
- Role in cell signalling e.g. antigens in immune system
What are extrinsic proteins?
- Proteins embedded in one side of the membrane
- Hydrophilic R-groups to interact with hydrophilic heads
- E.g. glycolipid or enzymes
What is the role of cholesterol in the phospholipid bilayer?
- Binds to phosphate heads
- Increases packing
- Reduces fluidity
What happens to phospholipid bilayer when temperature is increased?
- More kinetic energy
- More fluid membrane
- Increased permeability
- Carrier and channel proteins denatured
What happens to phospholipid bilayer when solvent is added?
- Less polar solvent will dissolve membrane
- More fluid
- More permeable
What is needed for facilitated diffusion?
Channel proteins
What type of molecule can pass through he membrane via simple diffusion?
Non-polar molecules with no charges
(Polar water can pass through but verryyyy slowly)
A greater SA:V ratio means a _____ rate of diffusion
Greater
The thinner a surface the _____ the rate of diffusion
Greater
What molecules can move down the concentration gradient in facilitated diffusion?
Polar molecules
Ions
What is needed for active transport?
Carrier proteins and ATP
How do carrier proteins function?
- Molecule to be transported bind to receptors on the side of the protein outside of cell
- ATP binds on the side of the protein inside of cell and is hydrolysed to ADP and P
- Protein changes shape and releases molecule to inside of cell
- P released and protein return to original shape
What is exocytosis
- Bulk transport of material out of cell
- Vesicles fuse to cell membrane and contents leave
What is endocytosis?
- Bulk transport of material into cell
- Phagocytosis: solids
- Pinocytosis: liquids
- Cell membrane bends inwards and fuses to form vesicle
The ____ concentrated the solution the ____ negative the water potential
More
More
What happens if an animal cell is placed in a solution of higher water potential
- Water moves in
- Increased hydrostatic pressure
- Cell swells and bursts
- Cytolysis
What happens if an animal cell is placed in a solution of lower water potential
- Water moves out
- Cell shrinks
- Crenation
Why do plant cells not burst due to high hydrostatic pressure?
Due to strong cellulose cell wall
What happens if a plant cell is placed in a solution of higher water potential
- Water moves in
- Cell membrane pushes against cell wall
- Cell becomes turgid
What happens if a plant cell is placed in a solution of lower water potential
- Water move out
- Cell membrane pulls inwards from cell wall
- Cell becomes plasmolysed
