Cell Membrane, Part 1 Flashcards
- biological membranes in the cell: functions and properties - importance of cell membranes for cellular function - structure of cell membranes: phospholipid bilayer - components of cell membranes - different membrane proteins and their roles - role of phospholipids and the 4 main types - cell organelles that possess cell membranes
1
Q
cell membranes (plasma membranes)
A
- define external boundaries of cell
- regulate molecular traffic across boundary
- eukaryotic cells: compartmentalization
- central to energy conservation and cell-to-cell communication
- flexible, self-sealing and selectively permeable to polar solutes and to allow growth and movement
- can break and re-seal for fusion (exocytosis) or fission (endocytosis, cell division)
- attachment surface
2
Q
compartmentalization
A
- separation of antiparallel processes
- ex: anabolic and catabolic processes can be held in separate compartments – avoiding competition for substrate or interference in reactions
FA synthesis in cytosol, FA oxidation in mitochondria)
- ex: anabolic and catabolic processes can be held in separate compartments – avoiding competition for substrate or interference in reactions
- separation of similar reactions serving different purposes
- ex: similar reactions for different purposes, thus must be held in different compartments
- fatty acid oxidation:
- in mitochondria: energy production
- in peroxisomes: heat production
- fatty acid oxidation:
- ex: similar reactions for different purposes, thus must be held in different compartments
- coordination of reactions which are involved in the same pathway (energy efficiency)
- ex: TCA and ETC are central point of energy metabolism in cells and are located in mitochondria
3
Q
cellular compartmentalization in eukaryotic cell
A
functional separation within the cell:
- plasma membrane
- nuclear membrane (inner and outer) 2
- ER and Golgi apparatus membrane
- mitochondrial membrane (inner and outer)2
- peroxisomes and lysosomes
4
Q
plasma membrane FUNCTION
A
- regulates movement of material into and out of cell
- facilitates electrical signaling btwn cells
- defines boundaries of organelles and separates complex chemical reactions
- -> multiple differing functions
5
Q
plasma membrane STRUCTURE
A
- very thin film of lipid and protein molecules held together mainly by non covalent interactions
- fluid, dynamic structures with most of their molecules able to move about in plane of membrane (fluid mosaic model)
- arranged as continuous double layer (lipid bilayer)
- relatively impermeable barrier to most water-soluble molecules (polar)
- 3 main lipids: phospholipids, glycolipids and cholesterol
- most membrane proteins span both parts of lipid bilayer some will only be in one layer
6
Q
plasma membrane PROPERTIES
A
- separates cellular interior from exterior
- exchanges information with environment in controlled manner
- membranes are dynamic
- membranes get information from cell about metabolic status
- selective barriers, allow selective transport of molecules in and out of cell
- contain enzymes
- contain receptors
7
Q
membrane fusion
A
- fusion of 2 membranes central to many processes involving organelles and plasma membrane
- vesicles bud from ER to transport synthesized lipids and proteins to other organelles and plasma membrane
- processes involve membrane reorganization, fusion of 2 membrane segments without loss of continuity
8
Q
trilaminar appearance
A
- plasma membrane appears as 3-layer structure (osmium bound to the inner and outer surfaces of the membrane) separated by a less dense central region
9
Q
cell membrane COMPONENTS
A
- lipids (phospholipids, glycolipids, sphingolipids)
- proteins (integral, peripheral)
- carbohydrates
- water
- divalent cations
- cholesterol (not present in most prokaryotes)
10
Q
cell membrane PROTEINS
A
- proteins that are part of or interact with membranes
- span lipid bilayer and mediate many functions of membranes: transport and catalysis of reactions
- some transmembrane proteins serve as structural links that connect cytoskeleton through lipid bilayer to either ECM or to adjacent cell
- others serve as receptors to detect and transduce signals
- membrane proteins are targets of over 50% of all modern medicinal drugs
11
Q
bacterial plasma membrane
A
- often composed of one main type of phospholipid and contain NO CHOLESTEROL
- mechanical stability is steadied by overlying cell wall
12
Q
eukaryotic plasma membrane
A
- contain large amounts of cholesterol and mixture of different phospholipids
- different sterols in different organisms
13
Q
lipid bilayer
A
- universal basis for membrane structure
- bilayer structure is result of special properties of lipid molecules that cause spontaneous assemblage
- lipid molecules make up about 50% of mass of most animal cell membranes, remainder is proteins
- all lipid molecules in cell membranes are amphipathic: one hydrophilic (polar) head and hydrophobic (non polar) tail
- most abundant membrane lipids -> phospholipids
14
Q
phospholipids
A
- polar head group and 2 hydrophobic hydrocarbon tails (FAs)
- tails can differ in length
- one tail usually contains 1 or more cis-double bonds (unsaturated), while other does not (saturated)
- double bond creates small kink in tail (important in formation of bilayer)
- differences in length and saturation of fatty acid tails affect ability of phospholipid molecules to pack together and guarantee membrane fluidity
15
Q
lipid molecules assemble in 2 ways:
A
- spherical micelles (energy favorable shape)
2. bimolecular sheets - bilayers
