Membrane Structure Flashcards
What is a cell membrane?
- Structure that gives cells it shape.
- Separates extracellular environment from intercellular environment.
- Dynamic in shape and keeps changing
- Allows transport of substances into and out of the cell
- In eukaryotes each organelle has a membrane
- Has multiple functions: signal transduction, cell communication, complex reaction sequences, energy transduction
What is a cell membrane made of?
- phopholipid bilayer
2. proteins
What is the phospholipid bilayer?
Made up of phospholipids. They had a hydrophillic head with a polar group. Also have a hydrophobic fatty acid tail. The head interacts with the extra/inter cellular environments.
The tails provides structure.
Has two leaflets, the outer and inner.
What are Lipids?
Building blocks of membranes.
Non-covalently linked.
Insoluble in water.
Amphipatic - head and tail
What are the different types of lipids?
- Fatty Acids
- Glycerolipids
- Glycerophospholipids
- Sphingolipids
- Sterol Lipids
- Prenol Lipids
- Saccarolipids
- Polyketides
Function of Lipids?
- Structural - membrane components and protein modification.
- Metabolic - energy storage
- Other Functions - cell signalling, hormones, enzyme cofactors, electron carriers, pigments
Effects of chain length on lipids?
The longer the chain the higher the melting point.
The longer the chain = more stable = more rigid.
Solubility in water will decrease as chain length increases.
Effects of double bonds on lipids?
Lipids contain long chains of carbon, therefore there can sometimes be double bonds.
An increase in the number of double bonds decreases the melting point.
Double bonds usually found in cis configuration. Causes kink in chain and unable to pack in as tightly.
Difference between saturate and unsaturated fats?
Saturated fats have no double bonds and are packed in tightly. Have a higher melting point than unsaturated fats.
Unsaturated fats have lipids that contain double bonds. The double bonds cause kinks so the lipids aren’t able to pack in as tightly. This causes a lower melting point than saturated.
Structure of Glycerophospholipids
- Glycerol backbone
- fatty acid tails often unsaturated
- Phosphate and alcohol head group - OH on head group is polar
Glycerophsopholipid head groups?
Serine Ethanolamine Choline Glycerol Inositol
What is the importance of glycerophospholipids?
Structural component for cell membrane - forms bilayer
What are Sphingolipids?
- Major membrane components
2. Derivatives of the amino alcohol sphingosine
Importance of sphingolipids?
- Forms a mechanically stable and chemical resistant outer leflet of the cell membrane.
- Linked to cell signalling and cell recognition
What are steroids?
Mostly of eukaryotic origin.
Most common in cholesterol (a sterol)
Cholesterol is a mjor component of cell membrane.
Has a small head group able to easily bind/interact with membrane
What are the properties of a cell membrane?
- Flexible
- self-sealing
- selectivly permeable
- two dimensional
What is the Fluid Mosaic Model?
- Every membrane differs in lipid composition. Typically have asymmetrical distribution between leaflets except for cholesterol.
- Lipids are in constant motion
- Proteins can move laterally
- Microdomains - within a leaflet different sections with varying distributions of lipids. Sphingolipids and cholesterol form lipid rafts which are involved in signalling proteins
What are the different formations of biomembranes?
- Micelle - individual lipids are wedged shaped and they form a single layer ball.
- Bilayer - most common, two layers of cylindrical lipids, flat
- Vesicle - bilayer but forms a small globular structure
Stability of different formations of biomembranes?
Determined by: size of chains, degree of saturation, size of head group and temperature
How is the bilayer held together?
Ionic bonds between the head groups.
Head groups form hydrogen bonds with water in surrounding envirnment.
Van der Waals interactions between fatty acid tails.
How can lipid bilayers be made in the lab?
- treat cells with solvent to remove proteins
- disperse left over phospholipds in water
- liposome will form
What are the different type of lipid motion in the bilayer?
- Spinning - they can rotate without changing location
- lateral diffusion - move within the same leaflet. This occurs 10^7 times per second.
- transverse diffusion - flip flopping between different leaflets this is very rare