the critical role of membranes Flashcards
what are the two types of membrane
1) plasma/cell
2) intracellular membranes of organelles
what are the functions of cell membranes
1) to act as a permability barrier
2) organize organelle function
3) mediate transport processes
4) mediate interaction with external environment
5) cell-cell communication
outline the function of acting as a permeability barrier
- it can control substances inside and outside the cell
-compartmentalises specific functions
outline how the cell membrane organises and localises functions
1) hosts essential cellular functions such as the ETC, photosynthesis and translocation
2) the membrane has functional proteins embedded which help exploit gradients allowing specific biochemical reactions
outline how the cell membrane regulates transportation of solutes
1) passive transport such as simple diffusion, faciliated or osmosis
2) active transport processes
3) endo/exocytosis
outline how the cell detects signals
1) the receptor binds to a molecule
2) the binding generates a secondary messenger
3) the secondary messenger alters gene expression and function= produces a response
outline how the cell allows communication with other cells
1) joins cells of similar functions together
2) the cells connected allow component exchange e.g. plasmodesmata, septa and gap junctions
what are the two types of membrane proteins
1) integral
2) peripheral
what is an integral protein
1) proteins which span the membrane consisting of hydrophobic aminoacids, usually arranged in alpha helices allowing them to become embedded inside the membrane with hydrophili regions on the cytoplasmic face or outside
what are peripheral proteins
proteins which only have contact with the membrane temporarily and are easily removed, this allows cell signalling
what are the main components of plasma membranes
1) phosopholipids
2) sphingolipids
3) glycolipids
4) membrane proteins
5) sterols
what are the features of a phospholipids
1) amphipathic= both hydrophilic and phobic
2) self -assemble into bilayers in water
3) formation of micelles in water
what is a micelle
occurs when lipid molecules arrange themselves into a spherical form in aqueous solutions
what is the composition of a phospholipid
1) one glycerol molecule
2) 2 fatty acid non-polar tails
3) 1 phosphate group
what are the properties of biological membranes
1) frequent lateral movement
2) increased phospholipid movement leads to increased fluidity
3) high levels of unsaturated acids tails prevent molecular packing
4) cholesterol reduces fluidity
what is the fluid mosaic model
describes cell membranes as a tapestry of several types of molecules which are constantly moving. This movement helps the cell membrane to maintain its role as a barrier inside and outside the cell
outline the process of phosphlipid synthesis
1) membrane proteins have N-terminal sequences which direct ribosomes to the ER membrane
2) attachment of the signal recognition particle
3) ribosomes dock on a protein complex
4) polypeptide synthesis starts
5) a signal peptide is cleaves
6) full synthesis
7) folding
what are the three transmembrane proteins in the cell membrane which mediates transport
1) ATP powered pumps
2) ion channels
3) protein transporters
outline an ATP powered pump
- uses the energy released by ATP hydrolysis to power the movement of specific ions or small molecules against a gradient
= active transport
outline ion channels
protein channels which allow the movement of specific ions or hydrophilic molecules down their electrochemical gradient via facilitated diffusion in responce to a specific chemical or electrical signal
what are the tree types of protein transporters
1) uniporters
2) symporters
3) antiporters
what is a uniporter
a protein transporter which transports a single molecule down a conc gradient
outline how a uniporter works
1) binding of a molecule to outward facing site
2) this triggers a conformational change resulting in binding site facing inwards to cystol
3) molecule then released inside the cell
4) transporter undergoes the reverse conformational change
what is a symporter
a protein transporter which transports molecules and ions in the same direction
outline how a symporter works
1) simultaneous binding of molecules to the outwards facing binding site
2) causes a conformational change resulting in an inward facing site
3) dissociation of bound molecules allows it to revert back to original outward facing conformation
what is an antiporter
a protein transporter which transportes molecules and ions in the opposite direction
outline how an antiporter works
1) one molecule bind to the outward facing state causing it to switch to an inward facing state
2) on the inside the bound molecule is exchanged for a different one and the protein carrier reverts to outwards facing state
what is a vesicle
a self-contained structure consisting of fluid or gas surrounded by an outer membrane
what is endocytosis
the pinching off of the plasma membrane to form vesicles
what is exocytosis
the fusion of vesicles with the plasma membrane discharging contents into the extracellular space
