Unit 2 - Plasma membranes Flashcards
State 4 functions of plasma membranes
Options:
-recognition of other cells
-separates cell contents from the outside (barrier between cells and its environment)
-controls the passage of materials in and out
-allow cell communication
-phagocytosis
-cell to cell attachment
State 4 functions of membranes inside cells
Options:
-isolates DNA
-acts as an intracellular transport system
-compartmentalises reactions
-can be the site of chemical reactions
-ribosomes attach
-protection from lysosomes
-forms vesicles
Define semi-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 ,
-sandwhiching the fatty acid tails to form a hydrophobic core
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)
Define glycoprotein
Extrinsic membrane proteins with attached carbohydrate molecules of varying lengths and shapes
Define glycolipid
Cell-surface membrane lipids with attached carbohydrate molecules of varying lengths and shapes
Define phospholipid
Modified triglycerides, where one fatty acid has been replaced with a phosphate group
What are channel proteins?
Membrane proteins that provide a hydrophilic channel through a membrane
What are receptor proteins?
Extrinstic glycopoteins that bind chemical signals, triggering a response by the cell
What are carrier proteins?
Membrane proteins that play a part in the transport of substances through a membrane
What are the functions of cholesterol in cell surface membranes?
-regulates fluidity and adds stability to membranes
-prevents phospholipids from crystallising
What are the functions of phospholipids in cell surface membranes?
-forms basic structure
-acts as partially permeable barrier
-allows the passage of lipid soluble molecules
-prevents water soluble molecules from moving across
What are the functions of glycoproteins in cell surface membranes?
-receptors for chemical signals
-cell adhesion
-when chemical binds to the receptor, events inside the cell are set off
-binding sites for chemical e.g hormones
-Hydrogen bonds to water to stabilise membrane
What are the functions of glycolipids in cell surface membranes?
-act as antigens that can be recognised by the immune system
-form hydrogen bond with water molecules to stabilise membrane
What are the functions of carrier proteins in cell surface membranes?
-have an important role in both passive movement of polar molecules and ions down a concentration gradient
-this involves the shape of the protein changing
What are the functions of channel proteins in cell surface membranes?
-provide a hydrophillic channel that allows passive movement of polar molecules and ions down a concentration gradient
Define cell adhesion
The process by which cells make contacts with each other
Describe 2 ways in which cholesterol regulates membrane fluidity
-hydrophillic end of cholesterol interact with phosphate heads
-hydrophobic end of cholesterol interacts with fatty acid tails
-pulling the phospholipids together
-prevents membranes from becoming too solid and crystallising by preventing the phospholipids from getting too close together
What 3 factors affect membrane structure?
Temperature
Solvents
Cholesterol
How does an increase in temperature affect cell membranes?
-increases membrane fluidity
-increases membrane permeability
-carrier and channel proteins are denatured at higher temperatures
-membrane loses its structure
Why does an increase in temperature increase membrane permeability?
-more temperature means phospholipids move more
-because they have a higher kinetic energy
-makes it easier for things to pass through
