Membrane (cell bio) Flashcards
CELL MEMBRANE
No biological membranes = No ?!
* regulates the movement of material into and out of the cell
* facilitates ? signaling between cells
* defines the boundaries of ? and separates complex ? reactions
? differing functions
cell membranes: good fences make good neighbours
CELL MEMBRANE
No biological membranes = No life!
* regulates the movement of material into and out of the cell
* facilitates electrical signaling between cells
* defines the boundaries of organelles and separates complex chemical reactions
multiple differing functions
cell membranes: good fences make good neighbors
CELL MEMBRANE
Plasma membrane, cytoplasmic membrane
Define the ? boundaries of a cell
Are ? to allow for growth and movement, ? and ? to polar solutes
Regulate the ? across boundary
In eukaryotic cells: ? to segregate processes and compartments
Are central to both biological ? and cell-to-cell ?
Can break and re-seal for ? or ?
Serve as attachment surface for “ * ? * “ and extracellular structures
CELL MEMBRANE
Plasma membrane, cytoplasmic membrane
Defines the external boundaries of a cell
Are flexible to allow for growth and movement, self-sealing and selectively permeable to polar solutes
Regulate the molecular traffic across boundary
In eukaryotic cells: compartmentalization to segregate processes and compartments
Are central to both biological * energy and cell-to-cell communication*
Can break and re-seal for * fusion or fission *
Serve as attachment surface for cytoskeleton and extracellular structures
THE EUKARYOTE CELL: A “Membranous”
Unit
Cellular compartmentalization:
? separation within the cell
- Plasma membrane
- Nuclear membrane (inner and outer)
- ER membrane
- Golgi apparatus membrane
- Mitochondrial membrane (inner and outer)
- Peroxisomes and Lysosomes
(ETC (oxidative phosphorylation) and TCA occur in which part of mitochondria?)
sER: lipids are sort by enterocytes (** ? ** process)
rER: post-transitional modification of
GA: also some modifications of ?
THE EUKARYOTE CELL: A “Membranous”
Unit
Cellular compartmentalization:
functional separation within the cell
- Plasma membrane
- Nuclear membrane (inner and outer)
- ER membrane
- Golgi apparatus membrane
- Mitochondrial membrane (inner and outer)
- Peroxisomes and Lysosomes
(ETC (oxidative phosphorylation) and TCA occur in which part of mitochondria?)
sER: lipids are sort by enterocytes (** re-esterifaction ** process)
rER: post-transitional modification of
GA: also some modifications of proteins
CELL MEMBRANE -COMPARTMENTALIZATION
- Separation of ? processes
* i.e. anabolic and catabolic processes can be held in ? compartments avoiding competition for the ? or
interference in the ?
Example: Fatty acid synthesis in ? and fatty acid oxidation in ? - Separation of similar reactions serving different ?
* i.e. similar reactions for different purposes and must therefore be held in ? compartments
Example: fatty acid oxidation
* in mitochondria for ? production
* in peroxisomes for ? production - ? of different reactions which are involved in the same pathway (energy efficiency)
Example: TCA and electron transport chain are the central point of ? metabolism in cells and are located in the mitochondria
CELL MEMBRANE -COMPARTMENTALIZATION
- Separation of antiparallel processes
* i.e. anabolic and catabolic processes can be held in separate compartments avoiding competition for the substrate or
interference in the rxn
Example: Fatty acid synthesis in cytosol and fatty acid oxidation in mitochondria - Separation of similar reactions serving different purposes
* i.e. similar reactions for different purposes and must therefore be held in independent compartments
Example: fatty acid oxidation
* in mitochondria for energy production
* in peroxisomes for heat production - coordination of different reactions which are involved in the same pathway (energy efficiency)
Example: TCA and electron transport chain are the central point of energy metabolism in cells and are located in the mitochondria
CELL MEMBRANE - PROPERTIES
- ? the cellular interior from the exterior
- ? information with the environment in a controlled manner
- Membranes are extremely ?
- Membranes get information from the cell about ? status
- Membranes are ?, allow ? transport of molecules into and out of the cell
- Membranes contain ?, ?, ? and other proteins
CELL MEMBRANE - PROPERTIES
- separates the cellular interior from the exterior
- exchanges information with the environment in a controlled manner
- Membranes are extremely dynamic
- Membranes get information from the cell about metabolic status
- Membranes are selective barriers , allow selective transport of molecules into and out of the cell
- Membranes contain receptors, transporters, ENZYMES and other proteins
Membrane Fusion and Fission
Central to ? cellular processes involving organelles and the plasma membrane.
Membrane Fusion:
2 separate ? merge to become one.
*Example: Transport vesicles from the ER fusing with ?
Membrane Fission:
Involves splitting of a membrane into 2 parts
* Example: formation of ? by ER/Golgi apparatus to transport ? and ? to other organelles and to cell ?
Both processes involve ? without loss of continuity.
Membrane Fusion and Fission
Central to many cellular processes involving organelles and the plasma membrane.
Membrane Fusion:
2 separate lipid bilayers merge to become one.
*Example:Transport vesicles from the ER fusing with Golgi membranes
Membrane Fission:
Involves splitting of a membrane into 2 parts
* Example: formation of vesicles by ER/Golgi apparatus to transport lipids and proteins to other organelles and to cell membrane
Both processes involve membrane organization without loss of continuity.
CELL MEMBRANE - COMPONENTS
*Lipids - phospholipids, ?, glycolipids
about ?% of the ? of most animal cell membranes
*? (transmembrane, peripheral)
*? (glycan groups)
?
? (Ca2+, Mg2+)
CELL MEMBRANE - COMPONENTS
*Lipids - phospholipids, sterol, glycolipids
about 50% of the ? of most animal cell membranes
*proteins (transmembrane, peripheral)
*carbohydrates (glycan groups)
water
divalent cations (Ca2+, Mg2+)
CELL MEMBRANE
Proteins that are part of or interact with biological membranes
- Most ? are transmembrane and mediate many functions such as ? and ? (enzymes)
- Some transmembrane proteins serve as ? connecting the cytoskeleton through the lipid bilayer to either the ? or to an ? cell
- Others serve as ? to detect and transduce signals
Numerous different proteins are necessary for proper cell ? and ?
-> 30% of human ? proteins are membrane proteins
-> Membrane proteins are ** ? ** of over ?% of all modern ? drugs
CELL MEMBRANE
Proteins that are part of or interact with biological membranes
- Most membrane protiens are transmembrane and mediate many functions such as transporting and catalysing of reactions (enzymes)
- Some transmembrane proteins serve as “structural links” connecting the cytoskeleton through the lipid bilayer to either the extracellular links or to an adjacent cell
- Others serve as receptors to detect and transduce signals
Numerous different proteins are necessary for proper cell function and interaction
-> 30% of human genome’s proteins are membrane proteins
-> Membrane proteins are ** TARGETS ** of over 50% of all modern medicinal drugs
CELL MEMBRANE - LIPIDS
The lipid bilayer is a relatively ? barrier to most ?-soluble (polar) molecules
Lipid molecules make up about ?% of the mass of most animal cell membranes.
- Three main lipids:
? (phosphoglycerides and sphingolipids)
? (cholesterol in eukaryotic cells, not in prokaryotes!!!)
?
All lipid molecules in cell membranes are ?:
one hydrophilic (? end)
one hydrophobic (? end)
CELL MEMBRANE - LIPIDS
The lipid bilayer is a relatively impermeable barrier to most water-soluble (polar) molecules
Lipid molecules make up about 50% of the mass of most animal cell membranes.
- Three main lipids:
phospholipids (phosphoglycerides and sphingolipids)
sterol (cholesterol in eukaryotic cells, not in prokaryotes!!!)
glycolipids
All lipid molecules in cell membranes are amphiphatic:
one hydrophilic (polar end)
one hydrophobic (? end)
CELL MEMBRANE
Universal basis for membrane structure:
The bilayer structure results from special properties of ? molecules that cause their ? assemblage into bilayers.
Common general structure: very ? film (average 5nm thick) of ? and ? molecules, held together mainly by covalent or noncova? interactions
Easily seen by ? microscopy.
Specialized techniques are necessary (x-ray diffraction, freeze- fracture) to study the ? of its organization.
Fluid, ? structures with most their molecules able to move in the plane of the membrane -> ? ? MODEL
CELL MEMBRANE
Universal basis for membrane structure:
The bilayer structure results from special properties of lipid molecules that cause their spontaneous assemblage into bilayers.
Common general structure: very thin film (average 5nm thick) of lipid and proteins molecules, held together mainly by noncovalent interactions
Easily seen by electron microscopy.
Specialized techniques are necessary (x-ray diffraction, freeze- fracture) to study the ? of its organization.
Fluid, dynamic structures with most their molecules able to move in the plane of the membrane -> FLUID MOSAIC MODEL
CELL MEMBRANE
A red blood cell’s membrane–Thin layer
Viewed in cross-section:
All cell membranes share a characteristic ** ? ** appearance: plasma membrane appears as three-layer structure, 5-8 ?thick
Trilaminar image consists of two ?-dense layers separated by a ? dense central region.
CELL MEMBRANE
A red blood cell’s membrane–Thin layer
Viewed in cross-section:
All cell membranes share a characteristic ** TRI-LAMINAR ** appearance: plasma membrane appears as a three-layer structure, 5-8 nm thick
Trilaminar image consists of two electron-dense layers separated by a less dense central region.
CELL MEMBRANE–
Prokaryotes vs Eukaryotes
Prokaryotic plasma membranes are often composed:
one main type of ?
contain no ? (with some rare exceptions)
(Their mechanical stability is steadied by an overlying cell wall)
Most eukaryotic cells are more varied, composed:
mixtures of different ?
large amounts of ?
CELL MEMBRANE–
Prokaryotes vs Eukaryotes
Prokaryotic plasma membranes are often composed:
one main type of phospholipid (PL)
contain no cholesterol (with some rare exceptions)
(Their mechanical stability is steadied by an overlying cell wall)
Most eukaryotic cells are more varied, composed:
mixtures of different PL
large amounts of cholestrol
(plants: phytosterol; animal cell: cholestrol)
Micelles and bilayers
Shape and amphipathic nature of lipid molecules:
causes their formation into bilayers ? in ? environments
RECAP:
* Hydrophilic molecules: dissolve readily in water due to their ? groups, or ? groups, which form either favourable ? interactions, or ? bonds, with water molecules
* Hydrophobic molecules are insoluble in water due to most or all of their atoms being uncharged and nonpolar and therefore unable to form ? interactions with water molecules
Lipid molecules assemble with their hydrophobic tails in the interior and hydrophilic heads outside to water
Can do this in two ways:
1. Spherical ?
2. Bimolecular sheets- ?
Micelles and bilayers
Shape and amphipathic nature of lipid molecules:
causes their formation into bilayers spontaneoously in aqeuous environments
RECAP:
* Hydrophilic molecules: dissolve readily in water due to their charged groups, or uncharged polar groups, which form either favourable electrostatic interactions, or H bonds, with water molecules
* Hydrophobic molecules are insoluble in water due to most or all of their atoms being uncharged and nonpolar and therefore unable to form energitically favorable interactions with water molecules
Lipid molecules assemble with their hydrophobic tails in the interior and hydrophilic heads outside to water
Can do this in two ways:
1. Spherical *micelles
2. Bimolecular sheets- bilayers
CELL MEMBRANE
Lipids spontaneously form micelles or bilayers in an ? environment
- Cone-shaped amphipathic molecules (* ? *) form micelles,
- Cylinder-shaped molecules (* ? *) form bilayers
The spontaneous closure of a phospholipid bilayer to form a sealed compartment is energetically most favorable.
Why?
Closed structure is ? as it avoids the exposure of the ? hydrocarbon ? to water (which would be energetically ?).
This provides the bilayer‘s * ? *: all free edges are avoided by closing in on itself.
CELL MEMBRANE
Lipids spontaneously form micelles or bilayers in an aqueous environment
- Cone-shaped amphipathic molecules (*i.e. FATTY ACIDS *) form micelles,
- Cylinder-shaped molecules (* PLs *) form bilayers
Why?
Closed structure is stable as it avoids the exposure of the hydrophobic hydrocarbon tails to water (which would be energetically unfavourable).
This provides the bilayer‘s self-healing property: all free edges are avoided by closing in on itself.
CELL MEMBRANE
Techniques for visualizing cells:
Electron microscopy (EM)
1. Scanning electron microscope (SEM): directly produces an image
of the ?-dimensional structure of the ? of a specimen
- Transmission electron microscope (TEM): a ? of electrons is transmitted through a specimen to form an ?, capturing fine ?
- Freeze-fracture and freeze-? electron microscopy: provide ? of surfaces ? the cell
CELL MEMBRANE
Techniques for visualizing cells:
Electron microscopy (EM)
1. Scanning electron microscope (SEM): directly produces an image
of the 3-dimensional structure of the surface of a specimen
- Transmission electron microscope (TEM): a beam of electrons is transmitted through a specimen to form an image, capturing fine detail
- Freeze-fracture and freeze-etch electron microscopy: provide views of surfaces inside the cell
pic: In the TEM image the cells’ cytoplasm is rich in filaments of the protein cytokeratin (dark brown).
CELL MEMBRANE
- Polar head group and two hydrophobic hydrocarbon tails (? ?)
- Tails can differ in ? (normally: 14-24 C)
- One tail usually contains one or more ?-double bonds (unsaturated), while other does not (?)
- Double bond creates small ? in tail
- Differences in ? and ? of fatty acid tails affect the ability of phospholipid molecules to pack together, and so guarantee the ?
what attaches hydrocarbon tail to phosphate? and what is attached to phosphate?
CELL MEMBRANE
- Polar head group and two hydrophobic hydrocarbon tails (FAs)
- Tails can differ in length (normally: 14-24 C)
- One tail usually contains one or more cis-double bonds (unsaturated), while other does not (saturated)
- Double bond creates small kink in tail
- Differences in length and saturation of fatty acid tails affect the ability of phospholipid molecules to pack together, and so guarantee the membrane fluidity.
what attaches hydrocarbon tail to phosphate? = GLYCEROL and what is attached to phosphate? = choline
