5.1 - The Structure And Function Of Membranes Flashcards
Compartmentalisation
Formation of separate membrane bound areas in a cell.
Why is compartmentalisation vital
Metabolism includes many different and incompatible reactions.
Separate parts allows specific conditions required for cellular reactions to be maintained
(e.g. chemical gradients)
Protects vital cell components
Plasma membrane
Cell surface membrane that separates cell from external environment
What are membranes formed by
Phospholipid bilayer
Structure of phospholipid bilayer
Hydrophilic phosphate head
Forms the inner and outer surface of membrane
Fatty acid tails are hydrophobic
Form hydrophobic core inside membrane
How are phospholipids perfectly suited for their role as a membrane
Cell exist in aqueous environments.
Organelles in aqueous environment
Hydrophilic phosphate heads can interact with water
When were membranes first scene
After invention of electron microscope.
Images taken in ‘50s show two black parallel lines
Supported earlier theory that membranes were made up of a bilayer
Fluid-mosaic model
1972 Singer and Nicolson
Proteins occupy various positions in the membrane
Fluid - phospholipids are free to move within layer relative to each other.
Gives membrane flexibility
Mosaic - Proteins embedded in bilayer vary in size, shape, and position.
Two types of membrane protein
Intrinsic
Extrinsic
Intrinsic
Transmembrane proteins
Embedded in both layers
Amino acids with hydrophobic R groups on external surface
Interact with hydrophobic core keeping them in place
Intrinsic proteins involved in transport across the membrane
Channel proteins
Carrier proteins
Channel proteins
Hydrophilic channel
Passive movement of polar molecules and ions down a concentration gradient through membranes
Interact with hydrophobic core due to amino acids with hydrophobic R groups on outer surface, keeping them in place
Carrier proteins
Passive transport and active transport
Involves shape of protein changing
Glycoproteins
Intrinsic Embedded in cell surface membrane Carbohydrate chains of varying lengths and shapes Cell adhesion Receptors for chemical signals
Cell communication / signalling
Chemical bonds to receptor
Elicits response from cell
Either direct or sets off chain of events inside cell
Examples of cell communication
Receptors for neurotransmitters (acetylcholine) at nerve synapses
Binding of neurotransmitters triggers or prevents impulse in next neurone
Receptors for peptide hormones (insulin)
Affect uptake and storage of glucose in cells.
Glycolipids
Lipids
Attached carbohydrate chains
Cell markers or antigens
Recognised by immune system as self or non self
Extrinsic proteins
One side of bilayer
Hydrophilic R groups on outer surface
Interact with polar heads or intrinsic proteins
Present in either layer and can move between
Example of extrinsic protein
Cholesterol
Cholesterol
Lipid Hydrophilic end interacts with phosphate Hydrophobic end interacts with fatty acid tails Regulates fluidity of membranes Adds stability without making rigid Positioned between phospholipids Pulls heads and tails together Prevent membrane from becoming too solid by stopping phospholipids from grouping too close together and crystallising
Particular position of proteins
Proteins need to be in particular positions for chemical reactions to take place
Example of proteins needing to be in particular places
Electron carriers and enzyme ATP synthase have to be in correct positions within cristae for production of ATP in respiration
Enzymes of photosynthesis are found on membrane stacks within chloroplasts
