Membranes - The Structure and Function of Membranes Flashcards
What is the primary role of membranes in cells?
Membranes separate cells from their environment and organelles from the cytosol.
State 4 functions of plasma membranes
- separates cell contents from the outside (barrier between cells and its environment)
- controls the passage of materials in and out
- allow cell communication
- recognition of other cells
State 4 functions of membranes inside cells
- isolates DNA
- can be the site of chemical reactions
- compartmentalises reactions
- ribosomes attach
- protection from lysosomes
What is compartmentalisation?
Compartmentalisation is the formation of membrane-bound areas within cells, allowing incompatible reactions to occur in separate areas with specific conditions.
Why is compartmentalisation useful in cells?
- incompatible reactions occur within the cell
- isolates reactions making them more efficient
- allows reaction conditions to be maintained (e.g., chemical gradients)
- protects cell components
Define partially permeable
A membrane that allows some substances to cross but not others
Define cell signalling
A complex system of intercellular communication
Define phospholipid bilayer
- arrangement of phospholipids found in cell membranes
- the hydrophilic phosphate heads form the inner and outer surface of a membrane ,
- sandwiching the fatty acid tails to form a hydrophobic core
What is the structure of membranes in cells?
All membranes have a phospholipid bilayer with hydrophilic phosphate heads on the outer surfaces and hydrophobic fatty acid tails in the core.
Why are phospholipid bilayers ideal for membranes?
Their hydrophilic heads interact with aqueous environments inside and outside the cell, while the hydrophobic core provides a barrier.
How were membranes first visualized, and what did it confirm?
Electron microscopy in the 1950s showed membranes as two black parallel lines, supporting the lipid bilayer theory.
Who proposed the fluid mosaic model, and when?
American scientists Singer and Nicolson proposed it in 1972, building on earlier lipid bilayer models.
Why is the model called the “fluid mosaic model”?
The phospholipids move fluidly within the bilayer, allowing flexibility, and the embedded proteins vary in size, shape, and position like tiles in a mosaic.
What does the fluid mosaic model describe about membrane structure?
It explains the dynamic and flexible nature of membranes, with a lipid bilayer hosting various proteins in specific positions.
Why is the fluid mosaic model important today?
It forms the foundation of our current understanding of membrane structure and function.
Why are membranes referred to as having a ‘fluid-mosaic structure’ ?
the phospholipids are able to move freely relative to each other (fluid)
the proteins embedded in the bilayer vary in shape, size, and position (mosaic)
What do plasma membranes contain, and how do they vary?
Plasma membranes contain specific proteins and lipids, with types and numbers unique to each cell type.
Define glycoprotein
Extrinsic membrane proteins with attached carbohydrate molecules of varying lengths and shapes
