MCAT Cell Membranes

Phospholipid components

-Phosphate Head (hydrophilic, polar) -Glycerol backbone (holds the tails to the head) -2 Fatty Acid Tails (hydrophobic, non-polar)

cholesterol

A lipid that forms an essential component of animal cell membranes to maintain fluidity and acts as a precursor molecule for the synthesis of other biologically important steroids

amphipathic

A molecule that has both a hydrophilic (polar) region and a hydrophobic (non polar) region.

what is one disease that could be characterized by the disturbance of cell membranes leading to a disturbance in cell communication?

Alzheimer's Disease

How does cholesterol affect membrane fluidity?

At body temperature or higher, it makes the membrane less fluid; decreases fluidity

Which statement best describes how cholesterol affects cell membrane fluidity? Cholesterol increases fluidity at high temperatures and decreases fluidity at low temperatures. Cholesterol increases fluidity at high temperatures and increases fluidity at low temperatures. Cholesterol decreases fluidity at high temperatures and decreases fluidity at low temperatures. Cholesterol decreases fluidity at high temperatures and increases fluidity at low temperatures.

Cholesterol decreases fluidity at high temperatures and increases fluidity at low temperatures.

osmosis

Diffusion of water through a selectively permeable membrane

Which molecule diffuses through a membrane most quickly? Ethylene Benzene Urea Glucose

Ethylene

True or False: everything on the cell membrane is sedentary

FALSE things can move around on the surface of the cell membrane - fluid mosaic model

true or false: saturated fatty acids increase membrane fluidity

FALSE!!! saturated fatty acids decrease membrane fluidity because they allows the phospholipids to pack very tightly together

true or false: phospholipids are all the same

FALSE: phospholipids are very diverse because their polar head/phosphate group can bind many different molecules

Glucose typically enters the cell through which mechanism? Pinocytosis through a channel protein Active transport by a glucose transport protein Simple diffusion through the cell membrane Facilitated diffusion through a carrier protein

Facilitated diffusion through a carrier protein

The rate of osmosis across a cell membrane depends upon which of the following? I: Intracellular solute concentration II: Extracellular solute concentration III: Polarity of solutes IV: Molecular weight of solutes V: The presence of aquaporins

I, II, V

Which intermolecular process primarily drives the formation of a bilayer when phospholipids are added to water? Lipids cause water to arrange in an ordered, unfavorable cage-like structure. Forcing lipids into a bilayer reduces this effect. Phospholipids self-assemble into a bilayer due to the strong affinity they have for each other. The ordered arrangement of a bilayer is more favorable than the disordered state of individual free-floating phospholipids. A bilayer arrangement maximizes the strength of Van der Waals forces among phospholipids.

Lipids cause water to arrange in an ordered, unfavorable cage-like structure. Forcing lipids into a bilayer reduces this effect.

transbilayer diffusion

The flip-flopping of a fatty acid from the inner to outer leaflet, or vice versa, via the action of flippases (out->in) or floppases (in->out), which requires a catalyst because it needs ATP...or scramblase which takes one from the inner and one from the outer and flip-flops them without the use of ATP, so it happens more slowly

In nerve cells, sodium-potassium pumps exchange two K+ for three Na+ across the cell membrane. What is the primary purpose of this exchange? To propagate an action potential To store electrical and chemical potential energy To increase the concentration of Na+ inside the cell To increase the concentration of K+ outside the cell

To store electrical and chemical potential energy

True or false: cell membranes "self-assemble"

True!! with the help of water molecules encouraging the movement of hydrophobic towards the inside and hydrophilic to the outside

Which statement represents a notable difference between simple diffusion and facilitated diffusion? Unlike simple diffusion, facilitated diffusion can transport ligands against a concentration gradient. Unlike simple diffusion, the rate of facilitated diffusion is limited by the number of transport proteins in the membrane. Unlike simple diffusion, facilitated diffusion requires energy in the form of ATP. Unlike simple diffusion, facilitated diffusion can occur in any type of cell.

Unlike simple diffusion, the rate of facilitated diffusion is limited by the number of transport proteins in the membrane.

Compared to a typical animal cell, the cell membranes on the paw of a polar bear would most likely have an increased concentration of which macromolecule? Unsaturated phospholipids Saturated phospholipids Aquaporin proteins Potassium channel proteins

Unsaturated phospholipids

unsaturated fatty acid

a fatty acid whose hydrocarbon chain contains one or more double bonds

how does a cell increase membrane fluidity?

add more unsaturated phospholipids

what type of molecule binds to lipids or proteins in the cell membrane to act as a tag?

carbohydrates/sugars bind proteins to become glycoproteins or lipids to become glycolipids

Aquaporins

channel proteins that facilitate the passage of water

which type of bond-cis or trans-in the fatty acid tails will cause a "kink"?

cis bonds will cause a "kink", whereas trans bonds will keep the tail straight

osmotic pressure is what type of property?

colligative

the sodium potassium pump does what?

create an electrochemical gradient between the inside and outside of the cell by pumping 3 NA+ out of cell and 2 K+ into cell; increases K+ concentration and decreases the Na+ concentration inside the cell

in low temperatures, phospholipids exist in a _____________ state which ________ fluidity.

crystallized; decreases

what must a membrane have to function in high temperatures?

decreased membrane fluidity; long saturated fatty acid tails (no double bonds) to decrease membrane fluidity

what types of bonds are used to connect the various components of a phospholipid?

ester bonds connect the fatty acid tails to the glycerol and the glycerol to the phosphate head

give examples of molecules that cannot diffuse through a cell membrane.

glucose because it is large and polar ions because they are charged amino acids because they are large, polar, and usually charged

what is the main factor of how well a cell membrane functions?

how well phospholipid tails interact with one another through van der waals forces; how well they can pack together to reduce fluidity

creation of a phospholipid membrane is favorable because the entropy of water __________, while the entropy of the lipid molecules ____________.

increases; decreases

inner and outer leaflets

inner cell membrane - touching intracellular space outer cell membrane - touching extracellular space

which type of protein may use energy and can go against its concentration gradient?

integral carrier protein

which type of protein does not use energy and goes with its concentration gradient?

integral channel proteins

describe the types of cell membrane proteins

integral: stuck inside cell membrane; difficult to remove; help maintain homeostasis (channels, carriers) peripheral: on the outside of the cell membrane; come and go as they please, usually to perform a specific function lipid-bound: stuck on interior of cell membrane glyco-protein: sugar bound to any type of protein listed above; used for communication reasons

why is cholesterol considered a "buffer"?

it is a buffer because it allows cells to remain at a relatively stable and normal level of fluidity

why does glucose enter a cell through facilitated diffusion?

it is a large, polar molecule that needs help entering the cell-however, there is more glucose outside of a cell than inside it, so it moves down its concentration gradient, meaning it does not required ATP to enter the cell

what type of fatty acids are beneficial for cells/bacterium at high temperatures? how do they help?

long saturated fatty acid tails (no double bonds) help to decrease membrane fluidity because there is increased amount of surface area that the van der waals forces from other tails can act upon each other to pull the membrane closer together and lack of double bonds increase van der waals forces between tails

How does cholesterol function to affect membrane fluidity in high and low temperatures respectively?

low temps: it pushes itself between phospholipids that are very close together, which increases the distance between them, causing an increase in fluidity high temps: places itself between phospholipids that are already further apart, causing them to pull together due to the affinity they have for the cholesterol molecule-they want to attach to it. this decreases fluidity because they are pulling together and there is more "stuff" in the membrane

for a cell to function at low temperatures, what must occur?

membrane fluidity must increase

clathrate cage

molecular interaction water molecules will adopt when surrounding a molecule

at low temperatures, phospholipid tails are _________________. at high temperatures, phospholipid tails are _________________.

packed closely together; far apart

name the components of the cell membrane.

phopholipids proteins cholesterol

give example of an amphipathic molecule.

phospholipids (polar head, nonpolar tail)

Describe Alzheimer's disease

plaques form within the brain that stick to the lipid bilayer of neurons, which disturb the transmission of neural signals, eventually leading to memory loss and neuron cell death

lateral diffusion

process by which lipids and proteins move within the membrane bilayer

colligative properties

properties that depend on the concentration of solute to solvent particles but not on their identity

give examples of molecules that can diffuse through the cell membrane quickly and slowly, but without ATP.

quickly: small, nonpolar molecules like gases (O2, CO2) slowly: small, polar molecules (H2O, ethanol) and large, nonpolar molecules (benzene)

what are the functions of the proteins in the cell membrane?

receptors for communication channels for transportation

membranes have what important quality?

semipermeability

what are the three factors that affect membrane fluidity?

temperature presence of cholesterol presence of saturated vs. unsaturated fatty acid tails

what are factors that affect osmosis?

the rate of osmosis is affected by the ratio of intra- and extra- cellular concentration and presence of aquaporins

what is the function of carbohydrates (sugars) in the cell membrane?

they act as tags to let other cells know what type of cell it is

True or false: cholesterol increases the fluidity of membranes in cold weather and decreases the fluidity of membranes in warm weather

true

Which type of fatty acid has two or more carbon double bonds?

unsaturated

which type of fatty acid will increase membrane fluidity?

unsaturated fatty acids increase membrane fluidity because their double bonds in random places cause disturbances in the packing ability of the phospholipids, so there are spaces between them, increasing the fluidity

what are the intermolecular forces involved in cell membrane maintenance?

van der waals forces between the phospholipid tails stabilization through hydrogen bonding

when do you need ATP to cross a membrane?

when you are moving a molecule against its concentration gradient