26 Questions
What is the primary function of receptors in membrane proteins?
To recognize and transmit signals
What is the effect of increasing short chain fatty acids on membrane fluidity?
It increases membrane fluidity
What is the structure of transmembrane spanning domains in integral membrane proteins?
α-helices or β-sheets
What is the characteristic of lipid rafts in terms of their fluidity?
They are less fluid and more ordered
Which type of protein is deeply embedded in the bilayer?
Integral membrane protein
Which type of membrane protein is involved in catalyzing chemical reactions?
Enzymes
What is the function of spectrin in erythrocytes?
It is an important structural protein on the cytoplasmic surface
What is the effect of high cholesterol content on membrane fluidity?
It restricts the random movement of polar heads and decreases fluidity
Which treatment can remove peripheral, anchored, and integral proteins from the membrane?
Detergent
What is the primary function of integral proteins in the membrane?
To span the entire lipid bilayer
What is the characteristic of kinks in unsaturated fatty acids in terms of membrane fluidity?
They reduce van der Waals interactions with other lipids and increase fluidity
What is the site of action of phospholipase A1?
sn-1
Which type of protein is attached to the membrane surface by interactions with other membrane proteins?
Peripheral protein
What type of membrane protein is involved in the import and export of substrates?
Transporters
What is the function of phospholipases in the cell?
They selectively hydrolyse components of phospholipids
What is the characteristic of the fluid mosaic model of the cell membrane?
It is a fluid and dynamic structure
What is the main characteristic of phospholipids that allows them to spontaneously form a bilayer in an aqueous environment?
They have a polar head group and a non-polar fatty acid tail
What is the ratio of protein to lipid in the plasma membrane?
1:1
What is the main function of membrane fluidity?
Regulating membrane function
Which lipid component is most abundant in the nuclear membrane?
Phosphatidylcholine (PC)
What is the orientation of phosphatidylcholine (PC) in the lipid bilayer?
Facing the extracellular environment
What is the primary function of glycolipids in the membrane?
Mediating cell-cell interactions
What is the term used to describe the movement of lipid molecules within the plane of the bilayer?
Membrane fluidity
What is the characteristic of integral membrane proteins?
They are embedded in the lipid bilayer
What is the primary function of cholesterol in the membrane?
Maintaining membrane structure
What is the term used to describe the 'islands of protein in a sea of lipid' model of membrane structure?
Fluid mosaic model
Study Notes
Composition of Membranes
- Phospholipids are the main components of all membranes, forming a bi-layer in aqueous environments.
- Composed of a polar head group attached to a glycerol backbone through a phosphate group, with two fatty acyl side chains linked to the glycerol backbone via ester bonds.
- Phospholipids are amphipathic, with polar head groups and non-polar fatty acid tails.
Fluid Mosaic Model of Membrane Structure
- Describes membranes as "islands of protein in a sea of lipid".
- Membranes are composed of a lipid bilayer with embedded proteins.
Variation in Composition of Cellular Membranes
- Different membranes have varying compositions of carbohydrates, proteins, and lipids.
- Examples include plasma membranes, outer mitochondrial membranes, inner mitochondrial membranes, and nuclear membranes.
Lipid Bilayers
- Are asymmetrical, with two halves of the bilayer having different lipid compositions.
- PC and SPH face the extracellular environment, while PS and PE face the cytosolic side.
Membrane Fluidity
- Refers to the ease with which lipid molecules move about in the plane of the bilayer.
- Important in regulating membrane function, such as movement of proteins, signaling, and exocytosis.
Regulation of Fluidity
- Lipid composition of the membrane defines its fluidity.
- Increasing short chain fatty acids reduces van der Waals interactions, increasing fluidity.
- Kinks in unsaturated fatty acids reduce van der Waals interactions, increasing fluidity.
- High cholesterol content restricts the random movement of polar heads, ordering the lipid bilayer and decreasing fluidity.
Lipid Rafts
- Specialized membrane microdomains with increased order and less fluidity.
- Characterized by increased levels of cholesterol, sphingomyelin, and gangliosides.
- Allows close interaction between receptors and signaling molecules.
Types of Membrane Proteins
- Structural proteins: involved in cell-cell contact and attachment of cytoskeleton.
- Receptors: involved in signal recognition and transmission.
- Ion channels: maintain ionic gradients and transmission.
- Transporters: import and export substrates.
- Enzymes: catalyze reactions.
Organisation of Membrane Proteins
- Integral proteins: embedded in the lipid bilayer, most span the entire bilayer.
- Anchored proteins: covalently linked to fatty acid chains or glycolipids.
- Peripheral proteins: attach to the membrane surface by ionic interactions.
Removal of Proteins from Membranes
- Different treatments can be used to remove proteins from membranes, such as high salt, urea, detergents, and phospholipases.
- The type of protein affects its removal from the membrane.
This quiz covers the main classes of lipid structures, including saturated and unsaturated fatty acids, triacylglycerols, phospholipids, and glycolipids. It is part of the Foundations of Medical Science course in the Faculty of Life Science and Medicine.
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