BIO_SC 2300 Midterm: Exam 3

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12 Sep 2017

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11/3/2016 3:33:00 pm: cell membrane is lipid bilayer. Phospho-lipids, cholesterol, and glycolipid are major components of the cell membrane. Typically has a hydrophilic polar head facing the aqueous environment and hydrophobic non-polar tails. Cholesterol stiffs the lipid bilayer: membranes: their structure, function, and chemistry. Membranes define the boundaries of a cell, and its internal compartments. Membrane play multiple roles in the life of a cell. Membranes separate the interior and exterior of cells and organelles. They are effective permeability barriers due to their hydrophobic interior. The pm surrounds the whole cell, whereas intracellular membranes compartmentalize functions within the cell: membranes are sites of specific proteins and therefore of specific functions. Membranes are associated w/ specific fx bc the molecules responsible for the fxs are embedded in or localized on membranes. The specific enzymes associated with particular membranes can be used as markers to identify the membranes during isolation: membrane proteins regulate the transport of solutes.

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Cholesterol is transported in the bloodstream in lipoproteinparticles. There are several classes of lipoprotein particles, butone of the most important classes is called Low-densitylipoproteins (LDL). LDL particles are composed of a single moleculeof a large protein called apolipoprotein, as well as thousands ofcholesterols molecules and phospholipids. Part of theapolipoprotein forms the surface of the particles and faces theaqueous phase, while other parts face the hydrophobic interior ofthe particle where they interact with cholesterol and thehydrophobic tails of the phospholipids. When cells need additionalcholesterol, they produce a receptor protein on the surface oftheir plasma membrane that binds to the apolipoprotein andinitiates the uptake of LDL particles into the cell via a processcalled endocytosis.

1. What is the likely reason that LDL particles are used totransport cholesterol in the blood stream?

a. Cholesterol in LDL particles easily inserts into lipidbilayers

b. Cholesterol id largely insoluble in aqueous solutions

c. Cholesterol is synthesized within LDL particles

d. LDL particles can form lipid rafts in the lipid bilayer

2. What is the most likely location of phospholipids in LDLparticles?

a. Bound to the hydrophilic domain of apolipoprotein

b. In the lipid bilayer that surrounds LDL particles

c. On the surface interacting with the aqueous environment aswell as interacting with the hydrophobic core of the particle

d. Within the hydrophobic core of the particle

3. What best describes the class of protein that apolipoproteinbelongs to?

a. Amphipathic proteins

b. Cell surface proteins

c. Membrane associated protein

d. Multipass membrane proteins

4. What kind of molecule on the surface of the cell would bemost likely to serve as a receptor for LDL particles?

a. a cholesterol binding protein

b. a glycolipid

c. a phospholipid

d. trans membrane protein

5. What conditions would be most likely to trigger increaseduptake of LDL particles by cells?

a. increased glycolipid synthesis

b. increased plasma membrane growth

c. increased protein secretion

d. increase protein synthesis

Hybridomas are the useful result of a fusion between _______________ and _________________ to obtain hybrid cells that can proliferate and produce _________________ against specific ________________.

	myeloma cells; B lymphocytes; monoclonal antibodies; epitopes
	myeloma cells; T lymphocytes; polyclonal antibodies; antigen
	T lymphocytes; B lymphocytes; monoclonal antibodies; antigen
	T lymphocytes; B lymphocytes; polyclonal antibodies; epitopes

With respect to mammalian cell culture, which of the following statements is true?

	Media used for cell growth contain proteases and a divalent cation chelator to help cells adhere to the surface.
	During the establishment of a cell line, senescence is the last stage of the cell's life.
	Rodent cells cultures undergo spontaneous transformation with similar frequency to human cell cultures.
	Embryonic cell lines do not undergo senescence nor do they have a finite life span.

Epithelial cells have distinct surfaces. Which of these surfaces tends to be involved in secreting proteins out of the cell and into the bloodstream?

	apical
	basal
	All of the answers are correct.
	lateral

Which of the following is NOT true of phospholipid bilayers?

		Phospholipid bilayers separate the cell from the exterior environment as well as from compartments within the cell.
		The interior of phospholipid bilayers is a highly hydrophobic environment.
		Membrane budding requires transient breakages in the bilayer membrane.
		The chemical properties of phospholipids lead to the spontaneous formation of bilayers.

Which of the following is true regarding membrane proteins?

		All peripheral membrane proteins contact the lipid bilayer by covalent attachment to the hydrophilic head groups on membrane lipids.
		Beta strands can assemble into a membrane-spanning barrel structure.
		Lipid-anchored membrane proteins always face the cell exterior.
		A protein with six hydrophobic helices is most likely a lipid-anchored membrane protein.

Which of the following statements is NOT true?

		The three types of lipid anchors responsible for tethering proteins to the bilayer are acylation, prenylation, and ubiquitinylation.
		Movement of lipids from the cytoplasmic to the exoplasmic leaflet of the membrane bilayer requires specialized transport proteins called flippases.
		Glycoproteins are the basis for blood type compatibility between donor and receiver.
		Glycoproteins are always oriented so that the carbohydrate moieties are exoplasmic.

A set of erythrocytes is placed in a beaker of 0.9% NaCl.Nothing appears to happen to the cells. Why?

0.9% NaCl is hypertonic to the cells.

Sodium blocks the movement of water.

0.9% NaCl is hypotonic to the cells.

0.9% NaCl is iostonic to the cells.

water has not moved at all.

Question 2

Select one answer.

Which substance would be mostlikely to pass through a lipid bilayer/plasma membrane withoutembedded proteins?

water

a steroid hormone

a large fatty acid

a large peptide hormone

a sodium ion

Question 3

Select all that apply.

Which of the following can cross the cellâs plasmamembrane without the assistance of protein transporters?Select all that apply.

large polar molecules

positively charged ions

small hydrophobic molecules

gasses

Question 4

Select one answer.

Biological Membranesare:

symmetrical.

impermeable.

static.

dynamic.

Question 5

Select one answer.

How does the selectivepermeability of the membrane help the cell.

This allows the cell to maintain the proper shape.

This allows the cell to regulate what enters and exits

This allows the cell to maintain a constant temperature.

All of these

Question 6

Select one answer.

What is the role of carbohydratesin the plasma membrane?

cellular identification

adhesion

transport materials across the membrane

help maintain fluidity

Question 7

Select one answer.

Which component of the plasmamembrane has the widest variety of functions?

sterols

carbohydrates

phospholipids

proteins

Question 8

Select one answer.

All of the following have aneffect on the fluidity of a membrane except:

interactions among fatty acids in the core of the bilayer

the cholesterol content

the ratio of saturated to unsaturated fatty acids

the presence of integral proteins in the membrane

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BIO_SC 2300 Midterm: Exam 3

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