Chapter 5 Flashcards
Can you identify six different types of functions of proteins in a plasma membrane?
—attachment to the cytoskeleton and ECM
—signal reception and relay
—enzymatic activity
—cell-cell recognition
—intercellular joining
—transport
In the origin of a cell, why would the formation of a simple lipid bilayer membrane not be sufficient? What else would have to be part of such a membrane?
The membrane would need embedded proteins that could regulate the movement of substances into and out of the cell
Why is diffusion across a membrane called passive transport?
The cell does not expend energy to transport substances that are diffusing down there concentration gradients
Predict the net water movement between two solutions— a 0.5% sucrose solution and a 2% sucrose solution— separated by a membrane not permeable to sucrose
Water will move from the 0.5% sucrose solution (lower concentration) to the 2% sucrose solution (higher concentration)
Explain the function of the contractile vacuoles in a freshwater Paramecium in terms of what you have just learned about water balance in cells.
The pond water in which Paramecium lives is hypotonic to the cell. The contractile vacuoles expel the water that constantly enters the cell by osmosis.
How do transport proteins contribute to a membrane’s selective permeability?
Because they are specific for the solutes they transport, the numbers and kinds of transport proteins affect a membrane’s permeability to various solutes.
Why did the researchers use frog eggs to test the function of this unknown protein? Why did they also monitor the behavior of control eggs in the hypotonic solution?
Frog eggs are quite impermeable to water. The control eggs confirmed this trait and provided a comparison to the bursting of the eggs that were making aquaporins.
Cells actively transport Ca2+ out of the cell. Is calcium more concentrated inside or outside of the cell? Explain.
Outside: Active transport moves calcium against its concentration gradient.
As a cell grows, its plasma membrane expands. Does this involve endocytosis or exocytosis? Explain.
Exocytosis: When a transport vesicle fuses with the plasma membrane, its contents are released and the vesicle membrane adds to the plasma membrane.
How does the second law of thermodynamics explain the diffusion of a solute across a membrane?
Diffusion across a membrane results in equal concentrations of solute, which is a more disordered arrangement (higher entropy) than a high concentration on one side and a low concentration on the other.
Remembering that energy must be conserved, what do you think becomes of the energy extracted from food during cellular respiration?
Some of it is stored in ATP molecules; the rest is released as heat.
Explain how ATP transfers energy from exergonic to endergonic processes in the cell.
Exergonic processes phosphorylate ADP to form ATP. ATP transfers energy to endergonic processes, often by phosphorylating other molecules.
Explain how an enzyme speeds up a specific reaction.
An enzyme lowers the activation energy needed for a reaction when its specific substrate enters its active site. With an induced fit, the enzyme strains bonds that need to break or positions substrates in an orientation that aids the conversion of reactants to products.
Explain an advantage of feedback inhibition to a cell.
It prevents the cell from wasting valuable resources by synthesizing more of a particular product than is needed.
What determines whether enzyme inhibition is reversible or irreversible?
If the inhibitor binds to the enzyme with covalent bonds, the inhibition is usually irreversible. When weak chemical interactions bind inhibitor and enzyme, the inhibition is reversible.
