Biol Ch5 Hw
Due to the constant random motion of its atoms and molecules, a substance will exhibit net movement from a region where it has a higher concentration to a region where it has a lower concentration. This net movement is called
Diffusion
Net movement of a substance from a region where it has a higher concentration to a region where it has a lower concentration is called which of the following?
Diffusion
Which of the following is not one of the four main components of all plasma membranes?
Extracellular matrix
Which region of a phospholipid molecule is hydrophobic?
Fatty acid hydrocarbon chains
Because individual lipids and unanchored proteins are relatively free to move around laterally within the membrane, the membrane is said to be .
Fluid
Why do phospholipids form bilayers when mixed with water?
It allows the nonpolar tails to avoid contact with water.
Which of the following describe(s) the interior of a phospholipid bilayer?
It is nonpolar. It is hydrophobic. It contains the fatty acid tails.
Select the statements that describe the structure shown in blue.
It is open at both ends, forming a channel that allows specific ions or molecules to pass through the membrane. It is a pore protein. It is a transmembrane protein.
Which of the following describe(s) the surface of a phospholipid bilayer?
It is polar or charged. It is hydrophilic.
The outer leaflet of the membrane in an animal cell can contain up to 50% cholesterol. What is the effect of this on the membrane's properties?
It is stronger. It is less permeable. It has intermediate fluidity.
Some bacteria have evolved enzymes that introduce double bonds into the fatty acid chains that make up the membrane. These enzymes are used to do which of the following?
Maintain a relatively constant membrane fluidity in spite of changes in temperature
Select the components of phospholipids.
One phosphate group A backbone derived from glycerol 2 fatty acid chains
This diagram is best described as which of the following?
Phospholipid
Which of the following makes up the bilayer of every cell membrane?
Phospholipids
Which of the following accurately describes plant cell membranes?
Plant cell membranes contain sterols but typically have little or no cholesterol.
Which of the following describes the structure of the fluid mosaic model of membranes?
Proteins float in or on a phospholipid bilayer.
What is the function of this membrane protein? (The area on the left is outside the cell and the area on the right is inside the cell.)
Receive external chemical messages
Phospholipids form bilayers when mixed with water due to which of the following?
Their nonpolar tails repel water. Their polar heads are attracted to water.
Which of the following describe transmembrane proteins?
They actually span the membrane's lipid bilayer. They are anchored in the membrane because their nonpolar regions are "pushed" into the interior of the membrane by hydrophobic exclusion.
Which of the following describe pore proteins?
They are transmembrane proteins. They have extensive nonpolar regions that are folded into beta-pleated sheets. They create openings or channels in the membrane that allow specific ions or molecules to pass through.
Which of the following accurately describe the functions of transmembrane proteins?
They can transport molecules across the membrane. They transmit information into the cell.
Which of a following is the major function of the phospholipid bilayer of a plasma membrane?
To impose a barrier to permeability.
Select the statement that is true of transmembrane domains.
Transmembrane domains are composed of hydrophobic amino acids.
Proteins which are embedded in the membrane are called _____________membrane proteins, while proteins which are attached to the surface of the membrane are called ____________ proteins.
integral peripheral
A typical cell membrane is structurally supported by a(n) ___________ protein _______________ The proteins in this support structure can link to cytoskeleton fibers, such as actin fibers. Listen to the complete question
interior Network
Membrane proteins can be attached to the surface of the membrane by special phospholipid-associate molecules. These molecules are
modified lipids.
A membrane that has a larger percentage of unsaturated fatty acids will most likely be
more fluid than a membrane with a lower percentage of saturated fatty acids.
Globular proteins are inserted in the lipid bilayer with their _____________ segments interacting with the interior of the lipid bilayer, and their ___________________segments protruding from the membrane surface.
nonpolar Polar
Transmembrane proteins must span the lipid bilayer at least ____________ time(s) to be anchored in the interior of the cell membrane.
one
Fat molecules (triglycerides) and phospholipids are similar because they both have which of the following?
A backbone derived from glycerol
When phospholipids are placed in water, they spontaneously form which of the following?
A bilayer
Fat molecules (triglycerides) and phospholipids are different because only phospholipids have which of the following?
A phosphate group attached to 1 carbon atom in the backbone A polar "head" and 2 nonpolar "tails"
The hydrophobic region of a transmembrane protein which extends through the lipid bilayer to the nonpolar interior of the membrane is composed of which of the following?
Amino acids
The protein marked with A on this diagram is which of the following?
An integral protein
What is the function of this membrane protein? (The area on the left is outside the cell and the area on the right is inside the cell.)
Attach the membrane to the cytoskeleton
What is the function of this membrane protein? (The area on the left is outside the cell and the area on the right is inside the cell.)
Carry out chemical reactions on the interior of the cell
What is the function of this membrane protein? (The area on the left is outside the cell and the area on the right is inside the cell.)
Cell-surface identity marker
Select the ways in which phospholipids can vary.
The type of polar organic group that is attached to the phosphate group The type of fatty acid chains present
This series of diagrams illustrates which of the following processes?
Simple diffusion
The two faces of the lipid bilayer of most cellular membranes are asymmetrical. How is this symmetry achieved?
Special enzymes transport lipids from one of the faces to the other.
Diffusion is caused by which of the following?
The constant random motion of all atoms and molecules
Select the accurate statement concerning membrane fluidity.
The degree of membrane fluidity varies depending on the composition of lipids in the membrane.
What would happen to the fluidity of bacterial plasma membrane if a bacterium is placed in a refrigerator?
The fluidity will decrease.
Why does a plasma membrane act as a barrier to the free passage of water-soluble substances?
The interior of the lipid bilayer is hydrophobic.
If a phospholipid that has only phosphate as its polar head is chemically modified by attaching a sugar to the phosphate, how will the behavior of this phospholipid change if placed in water?
The modified lipid will spontaneously form bilayers, just as before the chemical modification.
This experiment best supports which of the following hypotheses?
The plasma membrane is fluid.
The ___________________ formed by these membrane proteins may be temporary or permanent.
bond
Transmembrane proteins include:
carriers channels receptors
This membrane protein receives ___________ messages.
chemical
The lipid bilayer that forms the core of a cell's membranes is composed primarily of .
phospholipids
This transmembrane membrane protein is a _________ protein; it assists molecules in crossing the plasma membrane by forming a channel. (The area on the left is outside the cell and the area on the right is inside the cell).
transporter
The structure shown in blue is formed as a result of folding of what?
β-pleated sheets
Which of the following correctly describes this molecule?
A phospholipid with two fatty acids
Which of the following are examples of how an interior protein network structurally supports the membrane?
A protein in red blood cells called spectrin links proteins in the plasma membrane to actin filaments. Intracellular proteins anchor membrane proteins
Which of the following statements accurately describe transmembrane proteins?
A specific class of proteins has a consistent number of transmembrane domains. Proteins vary in the number of transmembrane domains they have.
Of the following substances, which one will be able to easily cross the lipid bilayer of a cell membrane without the help of transport proteins?
A steroid hormone
The plasma membrane's cell surface markers include which of the following?
Glycolipids Glycoproteins
What is the function of these membrane proteins?
Hold adjacent cells together
Which of the following describe(s) the blue regions (circled on the diagram) of this transmembrane protein?
Hydrophobic Nonpolar
Each membrane-spanning region of a transmembrane protein is called a _______________________
Transmembrane domain
What is the function of this membrane protein? (The area on the left is outside the cell, the area on the right is inside the cell).
Transport substances across the membrane
In a living cell, the plasma membrane does not allow the free passage of water-soluble substances. Why?
Water-soluble substances are repelled by the interior of the lipid bilayer.
Animal cells have membranes that are have intermediate fluidity but are more durable and less permeable. This is due to the presence of up to 50% __________________ in the outer leaflets of those membranes.
cholesterol
The membranes of animal cells usually contain significant amounts of a steroid molecule called
cholesterol
These membrane proteins are anchored to the actin filaments of the
cytoskeleton
Some bacteria have increased their tolerance to cold by evolving enzymes that introduce _________ bonds into the fatty acid chains present in their membranes.
double
When driven by diffusion, the net movement of a substance will be
down its concentration gradient.
These membrane proteins located on the surface of the cell are cell-surface _____________ markers. (The area on the left is outside the cell, and the area on the right is inside the cell).
identity
All cell membranes are composed of ___________ in a bilayer which provides a flexible _______________ and acts as a barrier to permeability.
phospholipids matrix
Transmembrane β-sheets can form a motif through the membrane that allows molecules to pass through the membrane. This type of protein is called a
pore protein.
According to the fluid mosaic model of membrane structure, a mosaic of ______________ floats in or on a fluid ____________
proteins lipid bilayer
ells can use wedge-shaped transmembrane proteins called _________ to bend membranes. These proteins are found in great concentrations in tubular regions of the membrane.
reticulons
How do cells stabilize flat regions of their membranes?
By coating membranes with proteins
Which of the following best describes membrane fluidity?
Individual phospholipids and unanchored proteins are relatively free to move around laterally within the membrane.
Which of the following best describes the proteins which are inserted into the lipid bilayer of the plasma membrane?
Integral proteins
Identify the four main components of all eukaryotic membranes.
Interior protein network Transmembrane proteins Cell surface markers Lipid Bilayer
In cell membranes, the interior of the lipid bilayer repels which of the following?
Ions Hydrophilic molecules Polar molecules
Molecules and ions dissolved in water diffuse across the plasma membrane due to which of the following?
Molecules and ions dissolved in water move down their concentration gradient until equilibrium is reached. Molecules and ions dissolved in water are in constant random motion.
Which of the following can cross the lipid bilayer of a cell membrane most easily without the help of transport proteins?
Oxygen gas
Which regions of a phospholipid molecule are hydrophilic?
Phosphate group Polar or charged molecule attached to the phosphate group
Which of the following statements about transmembrane domains are ture?
Proteins need only a single transmembrane domain to be anchored to the membrane, but they often have more than one They are usually shaped like alpha-helices. They act to anchor transmembrane proteins to the lipid bilayer. They are the regions of a transmembrane protein that actually pass through the lipid bilayer.
Which of the following are key functions carried out by membrane proteins?
Receive external chemical messages Attach the membrane to the cytoskeleton Connect adjacent cells and hold them together _________________ Catalyze specific chemical reactions on the surface of the membrane Transport specific ions and molecules across the membrane Function as cell-surface identity markers
Which of the following describes the placement of membrane proteins?
The nonpolar regions are inserted into the membrane and the polar regions protrude from its surface.
In phospholipids, a polar or charged organic molecule is often attached to which of the following?
The phosphate group
Which of the following statements are true concerning the substructure of the plasma membrane?
The plasma membrane contains areas with distinct lipid and protein composition. The distribution of lipids within the plasma membrane is not symmetrical. The plasma membrane is not homogeneous.
When phospholipids are placed in water, they spontaneously form a bilayer with which of the following?
The polar heads on the surface and the nonpolar tails in the interior
Some membrane proteins are attached to the surface of the membrane by special molecules that associate strongly with phospholipids. Which of the following describes the anchoring molecules?
They are modified lipids. They have chemical bonding domains that link them directly to the membrane proteins.
This membrane protein carries out ________ reactions within the interior of the cell membrane.
chemical
Because individual lipids and unanchored proteins are relatively free to move around laterally within the membrane, the membrane is said to be .
fluid
In this experiment, human and mouse cells were fused. Examination of hybrid cells that resulted from the fusion of these two cell types revealed that unanchored membrane proteins within the two cell types had become intermixed. Based on these results it can be concluded that the plasma membrane is , __________not rigid.
fluid
The endoplasmic reticulum adds sugar molecules to membrane proteins and lipids to form different varieties of___________ and ____________ on the surface of the cell.
glycoprotein glycolipid
When the concentration of a substance varies from one region to another, the net movement of the substance will continue down its concentration _____________ until the concentration is the same in all regions.
gradient
his diagram illustrates the net movement of ink molecules from an area of _________ concentration to an area of __________ concentration.
high low
The top part of this molecule, which is shaped like a circle, is
hydrophilic. polar or charged.
The lower part of this molecule, which contains two very long chains of carbon atoms (18 C atoms in each), is
hydrophobic Nonpolar
If a bacterium is moved from the refrigerator to a 37oC incubator,
its plasma membrane will become more fluid.