Week Three Flashcards
What are the main component of cell membranes
Lipids
Are there proteins in membranes?
yes proteins are often associated with or embedded in the cell membrane
What is the role of proteins associated or embedded in cell membranes?
they preform important functions such as transporting molecules
Where are the carbohydrates which are usually found in cell membranes attached?
they are usually attached to lipids(glycolipids) and proteins (glycoproteins)
What are most phospholipids made up of?
a glycerol backbone attached to a phosphate group and two fatty acids
Is the phosphate head group on phospholipids hydrophilic or hydrophobic?
hydrophilic (polar)
Are the fatty acid tail groups on phospholipids hydrophilic or hydrophobic?
hydrophobic (nonpolar)
Define amphipathic
Having both hydrophilic and hydrophobic regions.
Molecules with both hydrophobic and hydrophilic regions are called….?
amphipathic
Define micelle
A spherical structure in which lipids with bulky heads and a single hydrophobic tail are pakded
Define bilayer
A two-layered structure of the cell membrane with hydrophilic “heads” pointing outward toward the aqueous environment and hydrophobic “tails” oriented inward, away from water.
The shape amphipathic molecules in a aqueous environment is caused by…?
the polar heads interacting with the water on the outside and the hydrophobic nonpolar tails hiding from the water on the inside
The shape amphipathic molecules in a aqueous environment is dependent on…?
The bulkiness of the head group relative to the hydrphobic tails
Why are bilayers the most effective cell membranes?
because bilayers form closed structures with an inner spaces since free edges would expose the hydrophobic chains to the aqueous environment
Why are cell membranes formed by bilayers self healing?
Small tears in a membrane are rapidly sealed by the spontaneous rearrangement of the lipids surrounding the damaged region because of the tendency of water to exclude nonpolar molecules
What does a liposome look like?
a sphere with a hollow center
bilayers from spontaneously without the action of an enzyme as long as…?
the concentration of free phospholipids is high enough and the pH of the solution is similar to that of a cell
What do micelles look like?
solid spheres
define liposomes
An enclosed bilayer structure spontaneously formed by phospholipids in environments with neutral pH, like water.
why is pH important to the formation of bilayers?
beacuse in ensures that the head groups are in their ionized (charged) form and thus suitably hydrophilic
Why do lipids freely associate with one another?
becuase of their extensive van der waals forces between their fatty acid tails
Why are cell membranes dynamic?
the weak van der waals interactions between fatty acid tails are easily broken and reformed so phospholipids can easily move transnationally, rotate around their vertical axis and flex or bend
Define fluid
Describes lipids that are able to move in the plane of the cell membrane.
why are membranes called fluid?
because of the lipids’s ability to move in the plane of the membrane
What is the degree of fluidity of the cell membrane dependent on?
the type of lipid which makes up the membrane
what other lipid besides phospholipids do cell membranes often contain?
cholesterol
Does cholesterol influence membrane fluidity?
yes
define cholesterol
An amphipathic lipid that is a major component of animal cell membranes.
What is the hydrophilic region in cholesterol made up of?
a hydroxyl group (-OH)
what is the hydrophobic region in cholesterol made up of?
4 interconnected carbon rings with an attached hydrocarbon chain
What does the structure of cholesterol allow it to do?
it allows it to insert into the lipid bilayer so that the head group interacts with the hydrophilic head group of the phospholipids while the 4 rings interacts (by van der waals attractions) with the fatty acid chains
When does cholesterol decrease membrane fluidity? and how?
at temperature typically found in a cell. it does so because the rigid rings interact with the fatty acid tails of two different phospholipids decreasing the phospholipids mobility
When does cholesterol increase the fluidity of of the membrane? and how?
At low temperatures it increases the membranes fluidity. It does this by preventing phospholipids from packing tightly with other phospholipids
because of cholesterol’s ability to make the membrane more fluid at low temperatures and less fluid at normal temperatures it helps the cell to…?
maintain a consistent state of membrane fluidity by preventing dramatic transitions from a fluid to solid state
Define lipid rafts
Lipids assembled in a defined patch in the cell membrane.
Are membranes always a uniform fluid bilayer?
no because lipid rafts can form creating regions with discrete components
define transporter
Membrane proteins that move ions or other molecules across the cell membrane.
define receptor
A molecule on cell membranes that detects critical features of the environment. Receptors detecting signals that easily cross the cell membrane are sometimes found in the cytoplasm.
Define enzymes
A protein that functions as a catalyst to accelerate the rate of a chemical reaction; enzymes are critical in determining which chemical reactions take place in a cell.
define anchor
A membrane protein that attaches to other proteins and helps to maintain cell structure and shape.
name 4 different roles proteins can play in the cell membrane
trasporter
receptor
enzyme
anchor
Define integral membrane protein
A protein that is permanently associated with the cell membrane and cannot be separated from the membrane experimentally without destroying the membrane itself.
Define peripheral membrane protein
A protein that is temporarily associated with the lipid bilayer or with integral membrane proteins through weak noncovalent interactions.
Define transmembrane proteins
Proteins that span the entire lipid bilayer; most integral membrane proteins are transmembrane proteins
Integral membrane proteins have _____ regions? What are these regions?
three regions
to hyrdophilic regions protruding from either side of the membrane and one hydrophobic region that spans the inside of the membrane
How do peripheral membrane proteins associate with the membrane?
by week noncovalent interactions such as hydrogen bonding
what roles can peripheral membrane proteins play in the cell?
transmitting information received from external signals, limit the ability of transmembrane proteins to move within the membrane, or assist proteins in clustering in lipid rafts.
Define fluid mosaic model
A model that proposes that the lipid bilayer is a fluid structure that allows molecules to move laterally within the membrane and is a mosaic of two types of molecules, lipids and proteins.
define plasma membrane
The membrane that defines the space of the cell, separating the living material within the cell from the nonliving environment around it.
Define cell wall
A defining boundary in many organisms, external to the cell membrane, that helps maintain the shape and internal composition of the cell.
Define homeostasis
The active regulation and maintenance of a stable internal physiological state in the face of a changing external environment.
Define selectively permeable (or semipermeable)
Describes the properties of some membranes, including the plasma membrane, which lets some molecules in and out freely, lets others in and out only under certain conditions, and prevents other molecules from passing through at all.
What causes the membrane to be able to act as a barrier?
the combination of lipids and proteins
What molcules/atoms does the hydrophbic interior of the lipid bilayer prevent from crossing?
ions, charged or polar molecules
What types of macromolecules are too large to cross the plasma membrane on their own?
Things such as polysaccharides or proteins
What are some molecules/atoms that can freely across the lipid bilayer?
gases, lipids, and small polar molecules
How does the cell import and export molecules that cannot cross the membrane on their own?
protein transporters
What is the simplest form of movement into and out of cells?
passive transport
How does passive transport work?
Diffusion
Define diffusion
The random motion of individual molecules, with net movement occurring where there are areas of higher and lower concentration of the molecules.
Diffusion leads to a net movement of the substance from one region to another when there is a _____ _____ in the distribution of a molecule
concentration gradient
Name two gases which freely diffuse across the plasma membrane
oxygen and carbon dioxide
Give an example of a hydrophobic molecule which can diffuse through the plasma membrane.
triacylglycerols
why can hydrophobic molecules diffuse across the plasma membrane (sometimes)
because the lipid layer is hydrophobic as well
Define facilitated diffusion
Diffusion through a membrane protein, bypassing the lipid bilayer.
Is facilitated diffusion still a result of a concentration gradient?
yes
How to molecules diffuse through facilitated diffusion?
by diffusing through a membrane transport (kind of like going through a tunnel?)
Define channel
A transporter with a passage that allows the movement of molecules through it.
Define carrier
A transporter that facilitates movement of molecules.
How do membrane transporter channels work?
by providing an opening between the inside and outside of the cell within which certain molecules can pass, depending on their shape and charge.
How do gated membrane transporter channels work?
they open in response to some sort of signal, which may be chemical or electrical
How do membrane transporter carriers work?
They bind to and the transport specific molecules
What are the two membrane carriers conformations?
one that is open to the outside of the cell and one that is open to the inside of the cell
The binding of the transported molecule induces…?
a conformational change in the membrane protein (open to one side originally and then moves so it is now open to the other)
How does water move in and out of cells?
through passive transport
How is it possible for water molecules to move via passive transport through the hydrophobic plasma membrane
water molecules are small enough to passively diffuse to a small extent
What other way can water enter the cell that is not passive diffusion?
by being transported through aquaporins
Define aquaporin
A protein channel that allows water to flow through the plasma membrane more readily by facilitated diffusion.
Define osmosis
The net movement of a solvent, such as water, across a selectively permeable membrane toward the side of higher solute concentration.
The diffusion of water (a solvent) from high water (solvent) concentration to low water (solvent) concentration can be equivalently said as…?
The diffusion of water (a solvent) from low solute concentration to high solute concentration
Define active transport
The “uphill” movement of substances against a concentration gradient requiring an input of energy.
What function carried out by proteins in the plasma membrane takes up most of the energy in a cell
keeping the inside of the cell different from the environment outside the cell
define primary active transport
Active transport that uses the energy of ATP directly.
where does the chemical energy come from to move ions?
ATP
what are protein transporters that move two ions in different directions called?
Antiporters
Define electrochemical gradient
A gradient that combines the charge gradient and the chemical gradient of protons and other ions.
Define secondary active transport
Active transport that uses the energy of an electrochemical gradient to drive the movement of molecules.
How do cells create an elctrochemical gradient using hydrogen ions?
they pump the hydrogen ions (protons) out of the cell to build up a postive charge outside the cell
Why do cells pump protons (hydrogen ions) out of the cell?
to build up an electrochemical gradient. This then allows the transporter proteins to move a molecule from low concentration to high concentration without the use of ATP.
What is a hypertonic solution?
a solution with a higher solute concentration that that inside the cell
What is a hypotonic solution?
a solution with lower solute concentration than that inside the cell
When a cell is placed in a hypertonic solution what occurs?
The cell shrinks as the water leaves the cell by osmosis
When a cell is placed in a hypotonic solution what occurs?
The cell lyses (or bursts) as water moves by osmosis into the cell
What does it mean to keep intercellular fluid isotonic?
It means that the solute concentration is the same on the inside of the cell as it is in the extracellular fluid
Define contractile vacuole
A type of cellular compartment that takes up excess water and waste products from inside the cell and expels them into the external environment (via contraction).
The ___ ___ plays a critical role in the maintenance of cell size and shape
cell wall
The ___ ___ provides structural support and protection to the cell.
cell wall
Define turgor pressure
Pressure within a cell resulting from the movement of water into the cell by osmosis and the tendency of the cell wall to resist deformation.
What is another name for turgor pressure?
hydrostatic pressure
how does the cell wall contribute to the stability of a cell via turgor pressure?
The wall resists expansion, allowing the water that enters via osmosis to build up pressure creating a rigidity
How does turgor pressure explain why plants wilt?
Turgor pressure is water pressure built up inside a cell which pushes against the cell wall creating rigidity. So when a plant is dehydrated, the pressure decrease causes a decrease in rigidity
What types of cells have vacuoles?
Fungi and plant cells
Define vacuole
A cell structure that absorbs water and contributes to turgor pressure.
What do the cell wall of plants contain which is different from other cell walls?
polysaccharides (such as cellulose, a polymer of the sugar glucose)
What do the cell wall of algae contain which is different from other cell walls?
Some contain cellulose like plants but others contain silicon or calcium carbonate
What do the cell wall of fungi contain which is different from other cell walls?
chitin (a polymer made of sugar)
What are the cell wall of bacteria made up of?
primarily peptidoglycan, a mixture of amino acids and sugars
