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Cell Biology Exam 2 Flash Cards
Terms in this set (85)
What is the universal basis for cell membrane structure?
The Lipid Bilayer
What percentage of cell membranes are composed of lipids and proteins?
What is the most common phospholipid in cell membranes?
What two molecules compose the polar head of Phosphatidylcholine?
a phosphate group, and choline
What does the erm amphipathic mean?
Having both hydrophilic and hydrophobic properties
Would a phospholipid bilayer prefer a flat sheet or closed ball arrangement?
Closed ball. This minimizes contact of hydrophobic lipid tails with water.
Closed phospholipid vesicles are known as...
Lipid hydrocarbon chains within a simgle layer rotate about their axis with a speed up to how many rpm?
Fluidity in the bilayer depends on what two aspects of hydrocarbon tails?
Their length and degree of unsaturation. Shorter length provides less tail interaction so more fluid. Double bonds create kinks which keep tails from tight packing. Therefore unsaturated tails with doubke bonds create more fluidity.
What experimental technique is used to measure fluidity and movement in the lipid bilayer?
FRAP - flourescent recovery after photobleaching. Proteins are uniformly labeled across membrane surface, a small region is bleached, with lasers and rate of seepage of proteins into this region is measured.
Cholesterol molecules are short and rigid. What does this do to membrane?
Decreases fluidity by stiffening.
What experimental technique uses gold coated antibodies to determine membrane fluidity?
Single Particle Tracking (SPT) microscopy. Individial or single proteins labeled with gold coated antiodies appear black and can be monitored via video.
True or False: the lipid bilayer's inner and outer sides are strikingly different in composition, particularly of phospholipids and glycolipids.
What enzyme flips exterior phsopholipids into the interior?
Flippases. Some are selective and only flip particular phsopholipids, which are created in ER inside cell and bud off in vesicles to reach membrane.
Glycolipids are found only on what side of the cell membrane?
The non-cytosolic (outide). They form the glycocalyx
Where do glycolipids acquire their sugar groups?
In the Golgi apparatus. Enzymes that add sugars are confined to the inside of the Golgi.
Proteins constitute what percent of the mass of the lipid bilayer?
Transporters, anchors, receptors, and enzymes are all...
A beta sheet or alpha helix of one or multiple strands are examples of what type of membrane protein?
Where are the hydrophilic regions of transmembrane proteins found?
They are exposed to the aqueous environment on either side of the membrane. Hydrophobic are on the interior of the membrane.
Are peptide bonds in transmembrane alpha helices polar are nonpolar?
Polar. They associate together by hydrogen bonding hydrophilically while hydrophobic side chains associate with lipids in membrane
How do transmembrane alpha helices form an aquatic pore?
By lining up multiple helices in a circle with hydrophilic side chains in middle and hydrophobic side chains facing lipids of membrane.
True or false: Beta barrels can only form thin channels.
False, they can only form wide channels due to their limited ability to curve. Beta sheets fold into curved barrels in this type of channel.
What type of transmembrane protein is common in mitochondria and bacterial membranes?
Detergents are amphipathic molecules that aggregate into what structure rather than a bilayer?
How do detergents interact with membrane bilayers and their integrated proteins?
The hydrophobic ends of detergent molecules bind to the membrane spanning hydrophobic region of the transmembrane proteins, as well as to the hydrophobic tails of phospholipid molecues. thereby disrupting the lipid bilayer and separating the proteins from most of the phospholipids. Proteins are then bounds as protein-detergent complexes while lipids are in lipid-detergent micelles. Protein-detergent complexes can then be separated and the functional protein placed into an artificial bilayer for study.
The cell cortex is a structure on what side of the cell membrane?
The cytosolic side. It's like the supportive chain-link fence. It provides support for the membrane and maintains cell shape. Spectrin forms the cell cortex of a Red Blood Cell's membrane.
Short chains of sugars (oligosaccharides) linked to proteins on the surface of cell membranes are called...
Cell membrane proteins with long polysaccharide chains are called...
All of the carbohydrate on the glycoproteins, proteoglycans, and glycolipids is located on one side of the membrane which is the...
What layer is formed by glycoproteins, proteoglycans, and glycolipids?
The Carbohydrate Layer
What is the purpose of the carbohydrate layer?
It protects the cell surface from mechanical and chemical damage and also acts in cell-cell recognition and adhesion. It also serves as a distinctive clothing which other cells recognize. (Uniform)
Lectins on a cell surface recognize what feature of white blood cells that have come to deal with an infection?
Lectin's recognize the cell surface carbohydrates on white blood cells.
By mixing membrane proteins of mice and humans, what was discovered about the lipid bilayer?
It's fluidity. The proteins of the mice membranes and human membranes ended up mixed together within a plane after 40 minutes.
The lateral mobility of the plasma membrane can be restricted in what ways?
1) Proteins are tethered to cortex inside cell
2) Proteins are linked to fixed structures in the extracellular matrix
3) Proteins are tethered to proteins on the surface of other cells.
4) Proteins are prevented from moving by barriers that restrict movement.
True or False: Proteins are limited to particular domains in the cell membrane where the partake in various tasks and are frequently blocked from entering other domains by structures such as tight junctions.
The rate at which a molecule diffuses across a synthetic lipid bilayer depends on what two factors?
The size and solubility of the molecule
How do water and small non-polar molecules such as O2 and CO2 cross the membrane?
By simple diffusion
True or False: Lipids are permeable to ions and charged molecules if they are small.
False. Lipids are highly impermeable to ions and all charged molecules, such as H+, K+ Cl-, Ca2+
What are required to bring ions, sugars, nucleotides and other cell metabolites into the cell?
What are the two classes of transport proteins?
1) Carrier Proteins - undergoes a series of conformational changes to transfer molecules
2) Channel Proteins - forms a hydrophilic pore across the bilayer through which specific inorganic ions can diffuse
The main difference between carrier proteins and channel proteins is...
the way they discriminate between solutes
Can carrier proteins facilitate passive or active transport?
They facilitate both passive and active transport. Each carrier protein is highly selective, usually transporting only one type of molecule.
Glucose carrier proteins, which bind glucose outside, then change comformations to open the glucose into the cell, play what role in determining direction of transport for uncharged molecules?
None. They simply change conformations and allow the solute to flow in the direction of the concentration gradient.
The sum of the concentration gradient and the voltage across the membrane forms what?
The Electrochemical gradient
The electrochemical gradient determines the direction of what type of transport?
True or False: Voltage and concentration can work in the same direction, creating a steep gradient.
True, as in the case of Na+ They can also work against one another. A concentration gradient with an opposing voltage gradient would be slower than if gradients were in same direction.
What type of transport moves solutes against their electrochemical gradients?
Active transport by the uphill transport of one solute linked to the downhill transport of another is accomplished via...
Active transport coupled to the hydrolysis of ATP is done via...
Active transport coupled to the input of light energy is done via...
The Na+ K+ pump is an example of what kind of pump?
ATP-driven pumps. Na binding causes phosphate to bind, which lets Na through other side and K in. K in causes phosphate to dissociate and lets K in. Cycle starts over.
Transport of only one type of solute across cell membrane by a carrier protein is known as...
Movement of one solute coupled to the movement of another solute in the same direction is known as...
Movement of one solute coupled to the movement of another solute in the opposite direction is known as...
The glucose-Na+ transport is what type of transport: uniport, symport, or antiport?
Symport. A carrier symport protein actively pumps glucose using the influx of Na+ down its gradient to drive glucose transport. Glucose hitches a ride on Na+
After glucose is transported into the cell via symport with Na+, what type of transport releases it from the cell.
Uniport transport down its concentration gradient. The two types of glucose transporters are segregated by tight junctions in the cell membrane.
Movement of water from a region of low solute concentration to a region of high solute concentration is known as...
How do cells prevent from bursting due to the osmosis effect?
They use Na+-K+ pumps to control the solute level in the cell, so as not to draw in too much water.
What controls the opening and closing of channels in cell membranes?
An external stimulus, or by conditions within the cell.
A channel's rate of transfer is how much faster than a carrier protein?
1000 times faster
True or False: Ion channels couple the ion flow to an energy source to carry out active transport
False. They cannot couple ion flow to an energy source, thus cannot accomplish active transport.
How do ion channels select only ions that are supposed to be let in?
Via a selectivity filter, which is typically a narrow portion of the channel with a particular size and charge that will only accommodate a particular molecule, such as a K+ molecule. Na+, being too small to interact with carbonyl groups on side of K+ channel, would not pass.
In what two ways do ion channels differ from each other?
1) Ion slectivity - in what type of ions they allow to pass
2) Gating - the conidtions that influence their opening and closing
What type of gated channels open in response to a change in the voltage across a membrane?
Voltage Gated channels
What type of gated channels open in response to the binding of a chemical ligand to the channel?
Ligand-gated channel (extracellular or intracellular)
What type of gated channels open in response to mechanical stimulation?
Mechanically gated or Stress activated channels
Auditory hair cells in the ear are an example of cells that depend on what type of gated channel?
Stress activated (mechanicallly gated) channels. Sound acts as the mechanical force which activates stress activated channels.
What technique uses voltage passed through membrane channels to see if ions pass or not, showing ion channel activity.
Patch-Clamp Recording. Example of acetylcholine binding to channel, which opens and closes intermittently.
The distribution of ions on either side of the bilayer gives rise to...
the membrane potential
What do K+ leak channels do?
They open and allow K+ to flow out of the cell down its concentration gradient until the inside of the cell has a negative charge and the outside has an excess of positive charge.
Despite the meaning of a signal sent through a neuron, the form of the signal is always the same in what manner?
It is always a change in the electrical potential across the neuron's plasma membrane.
What is triggered by a rapid change in membrane potential?
An action potential.
What type of gated channel usually mediates action potentials?
Voltage-gated Na+ channels
The membrane at its resting potential is also known as the...
Steady state level
When a membrane is at rest (highly polarized) is the open or closed conformation more stable in voltage gated Na+ channels?
The closed is more stable when polarized and at rest.
When a membrane is depolarized, is the open or closed conformation more stable in voltage gated Na+ channels?
The open state is more stable, however the inactivated state is even more stable, so the channel becomes inactivated soon!!!
True or false: An action potential weakens as it travels along an axon.
False. Action potentials do not weaken as they travel along axons. Voltage measurements remain constant.
Does lipid solubility speed or slow transmission of electrical impulses?
Speed up transmission
Utilizing synapses, voltage-gated Ca2+ channels convert electrical signals into what type of signals?
A chemical signal is converted back into an electrical signal by what type of ion channels at a synapse?
Transmitter-gated ion channels. These are neurotransmitter receptors.
The acetycholine receptor is an example of what type of gated ion channel?
A Transmitter-gated ion channel
True or False: Synapses can be excitatory, but not inhibitory?
False, synapses can be both excitatory or inhibitory.
Influx of Cl- that keeps a membrane polarized would be excitatory or inhibitory?
Influx of Na+ that depolarizes a membrane would be excitatory or inhibitory?
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