Term
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Definition
separates the internal contents of cell from its external environment. It’s extremely thin.
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Term
What does structure determine?
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Definition
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Term
Two primary components of membranes
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Definition
Phospholipids- form the basic matrix/framework of a membrane.
Proteins-embedded in the membrane or loosely attached to its surface.
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| A third component of membranes |
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Definition
| Carbohydrates- may be attached to membrane lipids and proteins. |
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| Most abundant lipids found in proteins |
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Definition
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| What kind of molecules are phospholipids? |
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Definition
| amphipathic-head is hydrophilic (water-loving) and tail is hydrophobic (water-fearing) |
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| How much of each component does a membrane typically have? |
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Definition
50% protein by mass and majority of rest is lipids.
Lipid molecules are more in number than protein |
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Term
| How do cytosolic and extracellular leaflets compare? |
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Definition
| They are highly asymmetrical- certain lipids may be more abundant in one leaflet than another. |
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Definition
Lipids with carbohydrate attached. Good ex of asymmetry: Carbs are primarily on extracellular leaflet.
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Term
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Definition
| protein with a carbohydrate covalently attached |
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Term
| Integral Membrane protein |
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Definition
a.k.a intrinsic membrane protein
cannot be released from the membrane unless the membrane is dissolved with an organic solvent or detergent (diruption of the membrane) |
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Term
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Definition
- type of integral membrane protein
- has one or more regions that are physically inserted into the hydrophobic region of the phospholipid bilayer |
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Term
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Definition
- regions of proteins
- stretches of nonpolar amino acids spanning from leaflet to leaflet
- usually folded into alpha helix structure
- stable; nonpolar interacts with hydrophobic fatty acyl tails |
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Term
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Definition
- type of integral membrane protein
- lipid molecule attached to an AA side chain within the protein |
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Term
| Peripheral membrane proteins |
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Definition
- aka extrinsic proteins (in cytosol)
- no hydrophobic interior interaction
- noncovalently bound to regions of integral membrane proteins that project out from membrane OR bound to polar head groups of phospholipids |
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| How can peripheral proteins be removed? |
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Definition
- By varying pH or salt concentration
- can remove without destroying membrane |
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Definition
- protein in the ER membrane that drugs bind to
- necessary for synthesis of chemicals that help with inflammation and pain sensation |
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Term
| Biomembranes have fluidity |
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Definition
| the individual molecules remain in close association yet have the ability to readily move within the membrane |
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Term
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Definition
| quality of motion within biomembranes; considered 2D because movement occurs only within the plane of the membrane |
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Term
| How are fatty acyl tails kept within hydrophobic interior? |
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Definition
| - Rotational and lateral movements |
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Term
| Typical lipid molecules exchange places with its neighbors about ... |
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Definition
| 107 times per second (at 37 C) |
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Term
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Definition
- enzyme flippase: provides energy from the hydrolysis of ATP
- transports lipids from one leaflet to the other leaflet without going through hydrophobic interior
-does not happen spontaneously |
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Term
| What can make a membrane more fluid? |
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Definition
- more double bonds and shorter fatty acyl tails
- changing cholesterol concentration (increase) |
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Term
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Definition
- a group of lipids that floar together as a unit within a larger sea of lipids.
- raft has different lipid composition than surrounding lipids.ex: high amt of cholesterol
-unique lipid-anchored and transmembrane proteins.
- may play important role in endocytosis and cell signaling. |
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Term
| Lipid concentration affects membrane fluidity |
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Definition
-length of fatty acyl tails (14-24 C atoms); the shorter the more fluidity
-presence of double bonds in acyl tails; double bonds (make lipid unsaturated) creates kink in tail, makes neighboring tail less likely to interact = more fluidity
-presence of cholesterol;only found in animals; at high temps, makes it LESS fluid and at low temps/icy water = more fluid
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Term
| Why doesn't flip flop of transmembrane of proteins occur? |
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Definition
| - because the proteins also contain hydrophilic regions that would not pass through the hydrophobic portions. |
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Term
| Not all transmembrane proteins are capable of movement |
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Definition
-10-70% of proteins may be restricted in their movmt
- can be bound to components of cytoskeleton; restricts proteins from moving
- attached to molecules outside of cell; ex: interconnected network of proteins that forms extracellular matrix of animal cells. |
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Term
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Definition
| - process of covalently attaching a carbohydrate to a lipid or a protein |
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Term
| Function of Glycosylation |
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Definition
- serve as recognition signals for other cellular proteins; ex: protein destined for lysosome gets glycosylated
- cell surface recognition; embryonic dvlpmt indiv. cells & cell layers properly migrated via recognition of carbs on their cell surfaces
-determine blood type
-cell coat/glycocalyx = protective. carb rich zone on certain cell surfaces. protects proteins in plasma membr. |
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Term
| Where does lipid synthesis occur? |
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Definition
-At the ER membrane
- at cytosolic leaflet of SER |
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Term
| What are the building blocks for a phospholipid and how are they made? |
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Definition
- 2 fatty acids each w/ and acyl tail
- 1 glycerol molecule
-1 phosphate
-a polar head group
-made by: enzymes in cytosol or taken into cells from food |
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Term
| Lipids in ER can be transferred to other membranes |
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Definition
- diffuse laterally to nuclear envelope
- transported via vesicles to gogli, lysosomes, vacuoles, or plasma membrane
-lipid exchange proteins-extract lipid from one membrane, diffuse through cell, and insert lipid into another membrane |
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Term
| Where are transmembrane proteins first inserted? |
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Definition
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Term
| Where does glycosylation of proteins occur? |
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Definition
| - in the ER (N-linked) and Golgi apparatus (O-linked) |
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Term
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Definition
| movement of ions and molecules across biological membranes |
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Definition
-lets essential molecules in (i.e. glucos and AA)
- metabolic intermediates remain in
-waste products exit |
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Term
| Substances can move across a membrane in 3 ways |
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Definition
1. Diffusion
2. Passive transport
3. Active transport
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Term
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Definition
- When a substance moves from region of high to low concentration
- some substances can move directly through bilayer
-type of passive transport (high to low)
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Term
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Definition
- transport protein provides a passageway for the substance to cross the membrane
-type of passive transport (high to low) |
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Term
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Definition
- moves a substances from low to high concentration with help of a transport protein; against concentration gradient
-requires input of of energy (ATP hydrolysis)
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Term
| Which can and cannot diffuse across bilayer? |
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Definition
-can: gases and a few uncharged molecules
-cannot: ions, larger polar molecules (sugars), macromolecules (proteins & polysaccharides)
-diethylurea (much more hydrophobic) is about 50 times faster than urea in crossing hydrophobic interior |
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Term
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Definition
concentration of solute is higher on one side of a membrane than the other
ex: eat a bunch of carbs; concentration of glucose is higher outside of your cells compared to inside |
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Term
| Gradients involving ions have which two components? |
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Definition
| - electrical and chemical |
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Term
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Definition
- dual gradient with electrical and chemical components
- occurs with solutes of net negative or positive charge
- electrical: differences in amts of different types of ions across membrane i.e. Na+, K+, Cl+
-chemical: difference in one ion concentration across membrane i.e. Na+
(Na+ outside is greater than inside)
- formation of input requires input of energy (active trans) |
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Term
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Definition
| when the solute concentrations on both sides of the membrane are equal |
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Term
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Definition
| solute concentration outside the cell is higher compared to inside |
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Term
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Definition
| lower concentration outside the cell than inside |
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Term
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Definition
-when water diffuses across a membrane from hypotonic compartment to hypertonic compartment.
- solutes cannot readily move across membrane, so water does |
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Term
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Definition
-cells use them to sense changes in cell volume and allow necessary movements of solutes across membrane
-prevents osmotic changes
- keeps cell shape |
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Term
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Definition
- cell in hypotonic environment:
when a cell takes up so much water that is ruptures |
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Definition
-cell in hypertonic environment:
water exits cells via osmosis and cell shrinks |
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Term
| How does osmosis affect cells with a rigid cell wall, such as bacteria, fungi, algae, and plant cells? |
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Definition
- when extracellular is hypotonic, cell takes up small amount of water b/c wall prevents major changes in cell shape
-when extracellular is hypertonic, water exits cell and plasma membrane pulls away from cell wall = plasmolysis |
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Term
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Definition
- hydrostatic pressure required to stop the net flow of water across a membrane due to osmosis.
-turgor pressure: osm. press. in plants where plasma membrane is pushed against rigid cell wall.
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Term
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Definition
- some freshwater microorganisms have them, ex: amoebae and paramecia
- these vacouls prevent osmotic lysis. (they can freely live in hypotonic environments)
- fuses with plasma membrane to discharge water taken up by cytosol |
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Term
| transport proteins defintion |
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Definition
- transmembrane proteins that provide a passageway for movmt of ions and hydrophilic molecules across membranes
- role in selective permeability
- 2 classes: channels and transporters |
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Term
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Definition
- transmembrane proteins that form an open passageway for facilitated diffusion of ions or molecules across membrane.
-gated channels: regulates movement of solutes
-Ex: ligand-gated channels: noncovalent binding of ligands (sm. molecules; hormones, neurotrans.) important in transmission of signals betw. cells |
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Term
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Definition
- aka carriers
- bind their solutes in a hydrophillic pocket and undergo a conformation change that switches the exposure of the pocket from one side of membrane to other side
- slower than channels
-key role in uptake of organic molecules: sugars, AA, nucleotides
-key role in export: waste products, ex. lactic acid removal after exercise
- named according to # ions and direction: uniporters, symporters/cotransporters, & antiporters |
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Term
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Definition
-requires a pump- a type of transporter that directsly uses E to transport solute against a gradient.
-can est. large H+
-uses ATP to pump H+ across gradient
- exports |
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Term
| Secondary active transport |
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Definition
- uses pre-existing gradient to drive the active transport of another solute.
- ex: H+/sucrose symporter can use H+ gradient, est. by an ion pump, to move sucrose agtainst its conentr. gradient (only sucrose is actively transported)
- in animals, pump that exports Na+
-imports |
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Term
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Definition
- actively transports Na+ (inport) and K+ (export) against their gradients by using energy from ATP hydrolysis.
- every time 1 ATP hydrolyzed--> Na+/K+-ATPase functions as antiporter; pumps 3 Na+ into extracellular environment & 2 K+ into cytosol.--> net export of 1 pos. chrge = electrogenic pump (generates electrochemical gradient) |
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Term
| What is the common energy source to drive ion pumps? |
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Definition
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Term
| Important functions of electrochemical gradients |
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Definition
1. Transport of ions and molecules
2. production of E intermediates
3. Osmotic regulation
4. Nerve Signaling
5. Muscle contraction
6. Bacterial swimming |
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Term
| How are macromolecules and large particles transported? |
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Definition
| Via Exocytosis and Endocytosis |
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Term
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Definition
- material inside cell packaged into vesicles and excreted into extracellular environ.
- vesicles usually derived from golgi apparatus
- protein coat, cargo = vesicle formation in golgi
- protein coat sheds in cytosol
- 'naked' vesicle fuses with plasma membrane & releases cargo into outside environ.
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Term
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Definition
- plasma membrane invaginates or folds inward to form a vesicle that brings substances into cell
- receptor mediated endocytosis: receptor in plasma membr. is specific for a given cargo.
- cargo, protein coat = vesicle
- when protein coat shed in cytosol, 'naked' vesicle then fuses with an organelle (ex. lysosome) --> organelle releases cargo into cytosol whole or breaks it down |
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Term
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Definition
- endocytosis 'cell drinking'
- formation of membrane vesicles from plasma membrane as a way for cells to internalize extracellular fluid
- allows sampling of extracellular solutes
- important in nutrient absorption cells: ex. cells lining intestines in animals |
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Term
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Definition
- extreme endocytosis 'cell eating'
- forms enormous vesicle called a phagosome; engulfs lg particle such as a bacterium
- only some cells have capability
- ex: macrophages (cells of immune system) use phagocytosis to kill bacteria
- once inside cell, fuses with lysosome--> digestive enzymes within lysosome destroy bacteria |
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