5.1 Structure & Function of Plasma Membranes Flashcards
What is the main function of membranes?
separate their contents
from environment
What is compartmentalisation?
formation of separate, membrane-bound areas
within a cell
What is the importance of compartmentalisation within a cell?
Allows cytoplasm to be divided into separate membrane-bound compartments
can provide separate environment & conditions for different reactions
which require specific pH, temperature, enzymes etc
Describe the structure of a phospholipid:
-
AMPHIPATHIC - contain both hydrophilic & hydrophobic parts
-
hydrophilic phosphate group “head”
- hydrophilic due to negatively charged phosphate
-
hydrophobic fatty acid “tails”
- 1 saturated + 1 unsaturated
- hydrophobic due to no charge
-
hydrophilic phosphate group “head”
Describe the structure of phospholipids within the phospholipid bilayer with reference to their environment:
- 2 LAYERS OF PHOSPHOLIPIDS
- HYDROPHILIC HEADS FACE OUTWARDS
- can interact with water in aqueous environment
- HYDROPHOBIC TAILS FACE INWARDS
Do hydrophilic or hydrophobic molecules interact with water molecules? Explain why.
Hydrophilic molecules interact with water:
Water is a polar molecule, hydrophilic molecules also have (at least partial) separation of charge
∴ opposite charges on neighbouring molecules can attract
What is facilitated diffusion?
net movement of particles
across a membrane
down a concentration gradient
via a membrane protein
What are intrinsic membrane proteins?
transmembrane proteins
embedded through both layers within the phospholipid bilayer
What are examples of intrinsic membrane proteins & what are their functions?
-
CHANNEL PROTEINS - provides hydrophilic channel through protein
- hydrophilic channel
- selective, specific to certain type of molecule
-
CARRIER PROTEINS - transport substances through membrane
- Active transport:
- Target molecules bind to active site,
- ATP binds to carrier protein >> conformational change
- Allows molecules into cell
- Facilitated diffusion:
- Target molecules bind to active site
- Conformational change occurs without ATP, due to molecules naturally diffusing down concentration gradient
- Active transport:
What are extrinsic membrane proteins?
proteins present on only 1 side of phospholipid bilayer
can move between layers
What is the function of glycolipids?
act as antigens
allows cells to be recognised by immune cells as self or non-self
What is the function of glycoproteins?
- CELL ADHESION
- cells join using glycoproteins
- RECEPTORS during CELL SIGNALLING
- cellA releases chemical by exocytosis
- diffuses & binds to complementary glycoprotein receptor on cellB
- elicits response
What are examples of extrinsic membrane proteins & what are their functions?
-
GLYCOLIPIDS - lipid with attached carbohydrate chain
- ANTIGENS: molecules which can be recognised by immune cells as self or non-self
-
GLYCOPROTEINS - protein with attached carbohydrate chain
- CELL ADHESION: cells join using glycoproteins to form tight junctions
- RECEPTORS during CELL SIGNALLING: cellA releases chemical by exocytosis, binds to specific complementary glycoprotein receptor on cellB, eliciting response
Carrier proteins can transport molecules through the membrane either by _____ or
_____ depending on whether ATP is required.
active transport, facilitated diffusion
What is the difference between active transport & facilitated diffusion within carrier proteins?
Conformational change occurs due to different reasons:
In facilitated diffusion, caused by molecules diffusing naturally down concentration gradient
In active transport, caused by ATP binding to carrier protein.
∴ transport via carrier proteins can be active or passive
What makes cholesterol molecules amphipathic?
Hydrophilic due to polar OH
Hydrophobic due to non-polar carbon rings
