B2.1 Membrane Proteins & their functions Flashcards
What are the definitions of hydrophobic and hydrophilic?
Hydrophobic = does not mix with water. Hydrophilic = does mix with water.
How does insulin affect specific cell types?
Insulin will only interact with cells which have a surface receptor for insulin.
What is the structure of a lipid bilayer?
Sheet-like bilayers formed by amphipathic lipids in water.
What is selective permeability in the context of lipid bilayers?
The ability of the lipid bilayer to regulate the movement of substances.
What is the role of aquaporins?
Transporting water across cell membranes.
What are the two main types of membrane proteins?
- Integral proteins
- Peripheral proteins
What is the fluid mosaic model?
A model describing the structure of membranes with integral and perpheral proteins embedded in a fluid lipid bilayer.
Describe the permeability of membranes.
Dependent on the size and hydrophobic nature of molecules.
What is simple diffusion?
The movement of small molecules like oxygen and carbon dioxide directly through the lipid bilayer.
What are integral proteins?
Transmembrane proteins that are embedded through both layers of the membrane.
What are peripheral proteins?
Proteins that do not span the membrane and are located on its surface.
What is osmosis?
The movement of water from a region of higher water potential to lower potential
What is facilitated diffusion?
The process allowing polar or large molecules to pass through membranes via channel or carrier proteins.
What is the difference between active transport and passive transport?
Active transport requires energy to move substances against their concentration gradient.
What is endocytosis?
The process where the cell membrane engulfs material to form a vesicle.
What is exocytosis?
The process where vesicles fuse with the cell membrane to release contents outside the cell.
What are gated ion channels?
Channels that open or close in response to stimuli, allowing specific ions to pass.
What are cell-adhesion molecules (CAMs)?
Glycoproteins that mediate the binding of cells to each other.
Fill in the blank: Phospholipids are considered _______ molecules.
[amphipathic]
True or False: Charged particles can diffuse easily across a membrane.
False
What are the two types of active transport?
- Direct active transport
- Indirect active transport (cotransport)
What factors affect membrane fluidity?
- Fatty acid composition
- Presence of cholesterol
What is the role of cell junctions?
Connect cells to each other, allowing intracellular transport and communication
They play important roles in cell proliferation, cell migration, and prevent unregulated movement of materials between cells.
What are the three types of cell junctions found in animals?
- Adhesive junctions
- Tight junctions
- Gap junctions
What are adhesive junctions?
Junctions present in epithelial and cardiac cells that facilitate cell–cell adhesion and ensure structural stability
Also called anchoring junctions.
What do tight junctions do?
Form a tight seal between two neighboring cells, preventing unregulated movement of molecules
They act as occluding junctions.
What are gap junctions?
Intracellular channels that connect neighboring cells for the movement of molecules
Often called communicating junctions.
What are the main components of biological membranes?
- Lipids
- Proteins
- Small amounts of cholesterol
What is an example of direct active transport?
Sodium–potassium pumps
What is an example of indirect active transport?
Sodium-dependent glucose cotransporters
Voltage gated ion channels
Nerve signalling
1. stimulus causes temporary reversal in pot. diff. = action potential
2. voltage-gated sodium channel opens = defuse = depolarisation (less -)
3. VGSC opens = diffuse = repolarisation (more -)
4. Treshold value = gate closes
5. channel inactivation = particle blcosk opening = prveents reopening
Role of cholesterol in membrane
- stuffens & reduces lateral movement = less fluidity
- at high temp = stabilises
- at low temp = prevents fatty acid chains form coming close (cant become solid)
Use of active transport
- uptake of glucose & AA in small intestine
- excretion of H+ & urea
- absorption of mineral ions by plant roots
Ligand gates channels - Nicotonic Acetyl choline receptor
- binding creates conformational change => channel opens
- sodium diffuses down conc grad. = depolarisation = enzyme cholinestrase breaks down acetylcholine => channel close
Nictoine can activate this
Difference between direct vs indirect sodium potassium pump
Direct = in cell membrane & generates energy + 3Na & 2K bidnign sites
Indirect = two way solute transport
Indirect sodium potassium pump
- Na+ bind to bidning site on oiter surface
- simultaneously glucose molecule binds on cotransporter
- conformational change => transports both inside
Direct sodium potassium pump
- Pump opens to inside = Na+ binds
- Bond triggers ATP hydrolysis =>attaches => conformational change to outside facing
- pump releases Na+ to exterior
- 2 x K+ bind & phosphate latter detaches
- conformational change back to original form
