Cell Bio Homework

Each of the following is a function of membranes except

information storage

Of the following molecules, which would you predict diffuses most readily across membranes?

Oxygen

Each of the following is typical characteristics of an integral membrane protein transmembrane segment except

amphipathic

A colleague gives you two tubes containing membrane fractions from an animal cell lysate. One tube contains the plasma membrane fraction, and the other tube contains the mitochondrial inner membrane fraction, but the tubes are not labeled. When you analyze the macromolecule composition of the samples, you are confident that the second tube contains the mitochondrial fraction, because the sample has

a higher protein to lipid ratio.

In response to temperature changes, cell membranes change state to become more solid or more fluid by undergoing

a phase transition

Imagine a new type of cell was discovered on Mars in an organism growing in benzene, a nonpolar liquid. The cell had a lipid bilayer made of phospholipids, but its structure was very different from that of our cell membranes.

Describe what might be a possible structure for this new type of membrane.

non polar groups, non polar solvent, hydrophilic interior

Imagine a new type of cell was discovered on Mars in an organism growing in benzene, a nonpolar liquid. The cell had a lipid bilayer made of phospholipids, but its structure was very different from that of our cell membranes.

What might be characteristic features of the phospholipid head groups?

Equal positively & negatively charged groups

Membrane proteins embedded in the membrane would likely have hydrophilicregions spanning the membrane with hydrophobic groups protruding from both sides. Protein transporters would be required for hydrophobic compounds that could not otherwise pass through the hydrophilic membrane interior.

hydrophilic, hydrophobic, hydrophobic, hydrophilic

How might you isolate and visualize these unusual membranes?

It may require hydrophilic solvents to solubilize these membranes and release embedded proteins prior to visualization by conventional means.

The composition of lipids in the outer and inner monolayers of cell membrane lipid
bilayers is

asymmetrical, different in each monolayer

The most prominent lipids in animal cell membranes are

phospholipids

Which of the following would you expect to find predominating in the plasma membrane of a unicellular eukaryotic organism thriving in glacier ice?

16 carbon long fatty acids with 3 double bonds

Cholesterol

buffers membrane fluidity by increasing fluidity at low temperature and decreasing fluidity at high temperature.

Using a laser beam to inactivate fluorescence dye molecules connected to proteins or lipids on a cell membrane is called

photobleaching

Which of the following would best be used to determine the lipid content of an isolated membrane fraction?

thin-layer chromatography

Naturally occurring unsaturated fatty acids typically

contain double bonds primarily in the cis configuration

FRAP has revealed that some proteins move in cell membranes much slower than they move in reconstituted liposomes. Which of the following could account for limited mobility of proteins in cell plasma membranes?

Anchorage to the extracellular matrix

Association with lipid rafts

Anchorage to the cell cytoskeleton

Association with other proteins in a large complex

All could limit protein mobility.

Each of the following molecules move across membranes by simple diffusion except

glucose

Requires the presence of an integral membrane protein.

facilitated, active

Depends primarily on solubility properties of the solute.

simple

Doubling the concentration gradient of the molecule to be transported will double the rate of transport over a broad range of concentrations.

simple diffusion

Involves proteins called ATPases

active transport

work is done during the transport process

active transport

applies only to small, non polar solutes

simple diffusion

only to ions

none

transport can occur either in direction across the membrane, depending on the prevailing concentration gradient

simple

facilitated

delta G 0

All

Km

Facilitated & Active

Which of the following types of transport occur across the erythrocyte membrane?

O₂ and CO₂ passive diffusionaquaporin water transportCl ^- bicarbonate ion antiportglucose uniportAll of the above are correct.

All of the following are active transporters except

permeases

Each of the following is an example of facilitated diffusion except

oxygen transport

Cystic fibrosis is the result of a malfunction of a cellular ABC transporter that transports

Cl-

Each of the following is a characteristic of active transport mechanisms except

nondirectionality for moving a solute in either direction across a membrane depending on the solute concentration gradient.

Which of the following is an example of indirect active transport?

Na+/Glucose support

The primary difference between active transport and facilitated diffusion is that active transport is the only one of the two in which

the direction of transport is [S]_low → [S]_high.

Active transport makes it possible for cells to

maintain nonequilibrium intracellular concentrations of ions such as Na+, K+, Ca2+, and H+.

transport out secretory products and waste material against concentration gradients.

establish an electrical potential across the membrane.

take up nutrients from the environment against concentrations gradients.

All of the above are correct.

Each of the following is true for the mechanism of the Na⁺/K⁺ ATPase pump except

K⁺ triggered dephosphorylation of the pump stabilizes the E2 conformation.

Which of the following is false for the mechanism of the 2Na⁺/glucose symporter?

Binding of 2 Na⁺ to the symporter on the inside of the cell causes the symporter to open to the outside of the cell and release of the Na⁺ ions.

In which of the following organelles would you expect to first find a protein destined to be secreted from a cell?

endoplasmic reticulum

Comparing cells synthesizing secretory proteins and cells secreting steroid hormones, the cells synthesizing the steroid hormones have

more smooth ER

Each of the following is an endoplasmic reticulum function except

All are endoplasmic reticulum functions

peptide folding, addition of carbohydrate to proteins to make glycoproteins

the export of protein that cannot be folded into the cytoplasm for destruction

the assembly of multimeric proteins

Explain why the carbohydrate groups of membrane glycoproteins are always found on the outer surface of the plasma membrane.    

Outer monolayer originally faced the interior of the rough ER and Golgi, where the enzymes involved in glycosylation are located.

What assumption did you make about biological membranes in order to answer the queston in Part B?

Membrane asymmetry is maintained throughout the rough ER, Golgi, and plasma membrane.

A protein that is normally localized in the cytoplasm has been engineered so that it will be secreted from the cell instead. Which of the following represents the most likely pathway for the protein after it has been completely synthesized?

rough ER → Golgi → secretory vesicle → environment

How do proteins become embedded in the membrane of the endoplasmic reticulum?

Via stop- and start-transfer sequences that stop and start translocation of a polypeptide through the ER membrane, resulting in transmembrane proteins

The continuous release of mucus by the epithelial cells lining the respiratory tract is an example of

constitutive secretion.

The vesicles that are anchored to the plasma membrane at a nerve cell presynaptic site are specialized for

polarized secretion

In receptor-mediated endocytosis, each of the following is a fate for the receptors and/or vesicle contents except

release from the vesicle into the nucleus.

Pancreatic acinar cells produce and store hydrolytic enzymes in zymogen granules until hormones signal the cell to release the enzymes in a process known as

regulated secretion

Which of the following molecules forms the coat during receptor-mediated endocytosis-coated pit formation?

clathrin

Each of the following is a component involved in the SNARE hypothesis model mechanism except

all are involved

The low pH of lysosomes is established by

ATP-dependent proton pumps

The transfer of polypeptides into the ER is called

cotranslational import