L2 Flashcards
(36 cards)
What does the plasma membrane do?
Coordinates interactions with the surrounding environment.
What are the five key functions of membranes?
Define boundaries and act as permeability barriers.
Sites of specific biochemical functions
Regulate transport of solutes
Detect and transmit electrical and chemicals signals
Mediate cell to cell communication and adhesion.
Plasma membranes - how do they act as boundaries and permeability barriers?
Control which substances are inside and outside of the cell. Compartmentalises specific functions.
Plasma membranes - site of what specific biochemical functions?
Hosting of essential cellular functions which include - ETC, photosynthesis, translation of specific proteins. Functional proteins are embedded in the membranes. Localise activity. Exploit gradients to drive processes.
Plasma membranes - how do they regulate transport of solutes?
Passive transport - does not require energy - simple diffusion, facilitated diffusion, filtration, osmosis. Active transport - requires energy. Endocytosis/exocytosis.
Plasma membranes - how do they detect and transmit electrical and chemical signals?
Signal transduction is where an extracellular signal is transmitted to the interior of the cell. Cell signalling is divided into three steps. Receptor binds a molecule, receptor binding generates secondary messengers, the secondary messengers alter gene expression and cell function.
Plasma membranes - how do they mediate cell to cell communication and adhesion?
Join cells together of similar function. Cells connected and components exchanged via : gap junctions (animals), plasmodesmata (plants), septa (fungi).
Why do cellular requirements impose a limit on size?
Cell size is often limited to maintain a favourable SA:V ratio. As cell volume increases, SA increases to maintain a sufficient nutrient flux. A cell that contains multiple small structures greatly increases the surface area. This allows for more sufficient solute exchange, allows biochemical processes to occur more efficiently, many cells have a modified surface area.
What types of membrane proteins are there?
Integral and peripheral
What are integral proteins?
Include transmembrane proteins that span the membrane. Membrane spanning regions consist of hydrophobic amino acids. Usually arranged into alpha helices. Cytoplasmic or extracellular parts are hydrophobic
What are peripheral proteins?
Contact the membrane temporarily, easily removed allows them to be involved in cell signalling.
What are the key structural features of membranes?
Very thin 8nm, a physical barrier - keeping contents in and external materials out, barrier must be insoluble in water. But cannot be completely impermeable as they must allow certain molecules and water to permeate through
What are the main components of membranes?
Phospholipids, sphingolipids, glycolipids, membrane proteins, sterols.
What can phospholipids be?
Amphipathic (hydrophilic and hydrophobic, self assemble in water into bilayers. Placed in water form into micelles.
What is the composition of phospholipids?
Glycerol molecule, two fatty acids which are uncharged nonpolar tails, which are hydrophobic. Phosphate group, negatively charged polar head, which is hydrophilic. That is modified by an headgroup.
What are membrane proteins?
Proteins in the plasma membrane - they can be partially inserted into the membrane, exposed on only one surface, span the entire membrane.
What are properties of biological membranes?
Lateral movement is frequent. Increased phospholipid movement leads to increased membrane fluidity. Composition of bilayer influences the movement of phospholipids. High levels of unsaturated fatty acids tails prevent tight molecular packing. Cholesterol reduces membrane fluidity.
Where is cholesterol inserted into in the plasma membrane?
Lipophilic interior
What is the fluid mosaic model?
Describes the cell membrane as a tapestry of several types of molecules that are constantly moving.
What happens in membrane synthesis?
Phospholipids are synthesised in the smooth ER. Membrane proteins have N-terminal sequences that direct ribosomes to the ER membrane. Attachment of the signal recognition particle (SRP). Ribosomes dock on a protein complex (translocon). Polypeptide synthesis starts. Signal peptide is cleaved. Full synthesis. Folding.
What is a signal recognition particle (SRP)?
Abundant, cytosolic, universally conserved ribonucleoprotein (protein-RNA complex) that recognises and targets specific proteins to the endoplasmic reticulum in eukaryotes and the plasma membrane in prokaryotes.
What happens with membrane transport?
The plasma membrane regulates the traffic of molecules into and out of the cell. Membranes are selectively permeable. With the exception of gases and small hydrophobic molecules, most molecules cannot diffuse across the phospholipid bilayer at rates sufficient to cellular needs.
What are the three classes of transmembrane proteins that mediate transport of ions, sugars, amino acids, and other metabolites across cell membranes?
ATP-powered pumps
Protein (ion) channels
Protein transporters
What are ATP-powered pumps and what do they do?
Pumps which utilise the energy released by ATP hydrolysis to power the movement of specific ions or small molecules against chemical concentration gradient. This process is active transport.
