BIO 181 Chapter 5
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
In order to survive, grow, and reproduce, a cell must
exchange materials and information with its environment
Diffusion that is assisted by a channel protein or carrier protein is called __________ diffusion.
facilitated
Cells continually exchange materials and information with their environment. This exchange is crucial
for all the processes occurring in a cell.
The endoplasmic reticulum adds sugar molecules to membrane proteins and lipids to form different varieties of ________ and ________ on the surface of the cell.
glycoproteins glycolipids
When the concentration of a substance varies from one region to another, this substance is said to exhibit a concentration _______.
gradient
Transport that occurs without a cell expending any of its own energy is called _______ transport.
passive
The lipid bilayer that forms the core of all cell membranes is composed primarily of
phospholipids
The thin structure made of a bilayer of lipids with embedded proteins that surrounds all cells is called the ______ _______.
plasma, cell, or cellular membrane
The major barrier to crossing a biological membrane is the hydrophobic interior of the membrane that repels what kind of molecules?
polar
Transmembrane β-sheets can form a motif through the membrane that allows molecules to pass through the membrane. This structure is called a
pore protein.
Membranes are structurally supported by intracellular ______ that reinforce the membrane's shape.
proteins
According to the fluid mosaic model of membrane structure, a mosaic of ____________ floats in or on a fluid _______________ ______________.
proteins lipid or phospholipid bilayer
What is the function of the membrane protein shown? (The area on the left is outside the cell and the area on the right is inside the cell.)
receive external chemical messages
Transport proteins that have a hydrophilic interior space through which specific substances can move across the membrane in either direction are called _______.
transport proteins
This transmembrane membrane protein assists molecules in crossing the plasma membrane by forming a channel. Such proteins are known as
transporters.
Which of the following is not one of the four main components of all plasma membranes?
Extracellular matrix
When a channel protein or carrier protein assists in diffusion, which of the following is observed?
Facilitated diffusion
Which region of a phospholipid molecule is hydrophobic?
Fatty acid hydrocarbon chains
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
Which method of microscopy is illustrated in this drawing?
Freeze-fracture microscopy (Pg. 96)
The plasma membrane's cell surface markers include which of the following?
Glycoproteins Glycolipids
The top part of this molecule, which is shaped like a circle, is which of the following (choose all that apply)?
Hydrophilic Polar or charged
Which of the following best describes the proteins which are inserted into the lipid bilayer of the plasma membrane?
Integral proteins
Why do phospholipids form bilayers when mixed with water?
It allows the nonpolar tails to avoid contact with water.
Which of the following describes passive transport?
It does not require an expenditure of energy by the cell itself.
Which of the following describe(s) the surface of a phospholipid bilayer?
It is hydrophilic. It is polar or charged.
Which of the following describe(s) the interior of a phospholipid bilayer?
It is hydrophobic. It contains the fatty acid tails. It is nonpolar.
Diffusion is caused by which of the following?
The constant random motion of all atoms and molecules
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.
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
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.
Transport proteins that actually bind to the specific substance being transported across the membrane are called ___________ proteins.
carrier
Transport proteins that have a hydrophilic interior space through which specific substances can move across the membrane in either direction are called _________ proteins.
carrier
Proteins which are embedded in the membrane are called Blank 1Blank 1 trans , Incorrect Unavailable membrane proteins, while proteins which are attached to the surface of the membrane are called Blank 2Blank 2 glyco , Incorrect Unavailable proteins.
integral peripheral
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
Many substances that are repelled by the hydrophobic interior of the lipid bilayer can readily diffuse across the plasma membrane with the help of specific _________ proteins or __________proteins. These transporter proteins are typically transmembrane proteins.
channel carrier
Phospholipids that contain unsaturated fatty acids typically have
cis-unsaturated fatty acids
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
The relative concentration of substances inside and outside the cell along with the ability of a substance to cross the membrane determines the rate of ___________ across the plasma membrane.
diffusion
Each membrane-spanning region of a transmembrane protein is called a transmembrane ____________.
domain
Examination of cell membranes using the two types of _______ microscopy has allowed biologists to visualize the lipid bilayer of the membrane.
electron
If a concentration difference exists for a nonpolar molecule across a biological membrane, it will move across the membrane until the concentration is _______ on both sides.
equal
If a concentration difference exists for a nonpolar molecule across a biological membrane, it will move across the membrane until the concentration is ___________ on both sides.
equal
The rate of diffusion of a substance across the plasma membrane depends on which of the following?
the concentration of the substance inside the cell the concentration of the substance outside the cell how easily the substance can cross the membrane
What type of microscope can be used to see the two phospholipid layers in a plasma membrane?
Electron
Select the true statements about cell membranes.
- Individual lipids and unanchored proteins are relatively free to move around laterally within the lipid bilayer. - The degree of membrane fluidity varies depending on the composition of the membrane.
How does lipid composition affect membrane fluidity?
- Sterols, such as cholesterol, can either increase or decrease membrane fluidity depending on temperature. - Saturated fatty acids tend to make the membrane less fluid because they pack together well.
Select the accurate statements concerning membrane fluidity.
- The degree of membrane fluidity varies depending on the composition of the membrane. - Unanchored proteins are relatively free to move around laterally within the membrane. - Phospholipids are relatively free to move around laterally within the membrane.
Select the true statements concerning the organization of the plasma membrane (Select all that apply).
- The plasma membrane contains areas with distinct lipid and protein composition. - The plasma membrane is not homogeneous. - Lipids can exist in either an ordered or disordered phase within the membrane.
Select the true statements concerning the organization of the plasma membrane.
- The plasma membrane is not homogeneous. - Lipids can exist in either an ordered or disordered phase within the membrane. - The plasma membrane contains areas with distinct lipid and protein composition.
Which of the following describe transmembrane proteins? Choose all that apply.
- 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 regions of a phospholipid molecule are hydrophilic?
-Phosphate group -Polar or charged molecule attached to the phosphate group
Which of the following describe pore proteins? Choose all that apply.
-They have extensive nonpolar regions that are folded into beta-pleated sheets. - They are transmembrane proteins. - They create openings or channels in the membrane that allow specific ions or molecules to pass through.
What type of microscope can provide images that clearly show both layers of a membrane's lipid bilayer?
Electron microscope
When phospholipids are placed in water, they spontaneously form which of the following?
A bilayer
When the concentration of a substance varies from one region to another, this is called which of the following?
A concentration gradient
A defining feature of biological membranes is the presence of which of the following?
A lipid bilayer
Which of the following correctly describes this molecule?
A phospholipid with two fatty acids
Oxygen diffuses across the plasma membrane due to which of the following?
All oxygen molecules are in constant random motion.
Of the 2 types of transport proteins that mediate facilitated diffusion, only __________ proteins actually bind with the substance being transported while ________ proteins simply provide a hydrophilic space for the substance to move through.
Blank 1: carrier Blank 2: channel
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.)
Catalyze chemical reactions
Which of the following are key functions carried out by membrane proteins?
Catalyze specific chemical reactions on the surface of the membrane Function as cell-surface identity markers Transport specific ions and molecules across the membrane Receive external chemical messages
Which of the following are key functions carried out by membrane proteins?
Connect adjacent cells and hold them together Receive external chemical messages Attach the membrane to the cytoskeleton
Different proteins can cross the membrane in different ways. What is the primary difference between transmembrane proteins in terms of how they cross the membrane?
Different proteins can cross the membrane a different number of times.
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
Place the following molecules in order according to their capability to cross the lipid bilayer of the plasma membrane without the help of transport proteins. Start with molecules that cross most easily on top.
Nonpolar molecules Small polar molecules Large polar molecules
Which part of a membrane protein is found in contact with the interior of the lipid bilayer?
Nonpolar segment
How do carrier proteins differ from channel proteins?
Only carrier proteins actually bind to the substance being transported.
Compared to the ER membrane, the plasma membrane contains more of which of the following (choose all that apply)?
Phosphatidylcholine Sphingomyelin Cholesterol
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 structure surrounds all cells?
Plasma membrane
In cell membranes, the interior of the lipid bilayer repels which of the following?
Polar molecules Hydrophilic molecules Ions
Which of the following are typical components of biological membranes?
Proteins Lipids
Which of the following transmembrane proteins are likely to be found in membranes that form tubular structures?
Reticulons
Plasma membranes allow some substances to pass through easily while other substances only pass through very slowly or not at all. For that reason, plasma membranes are considered which of the following?
Selectively permeable
Substances that cannot easily cross the lipid bilayer can still diffuse across the plasma membrane with the help of which of the following?
Specific channel proteins or carrier proteins
What are lipid rafts in cellular membranes heavily enriched in?
Sphingolipids Cholesterol
The ER membrane is typically more fluid than the plasma membrane and it contains more curvature. Why?
The ER membrane contains mainly unsaturated phospholipids.
During facilitated diffusion, how do carrier proteins transport solutes across the membrane?
They bind specifically to the solute being transported.
What is the function of transmembrane proteins called reticulons?
They can cause a membrane to bend or even form a tube.
Which of the following accurately describes the polar heads of glycerol phospholipids?
They can have both a negative and a positive charge, or they can be primarily negatively charged.
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 the following is true of channel proteins?
They have a hydrophilic interior through which polar molecules can pass.
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 have chemical bonding domains that link them directly to the membrane proteins. They are modified lipids.
Which of the following is the major function of the phospholipid bilayer?
To impose a barrier to permeability.
Identify the four main components of all eukaryotic membranes.
Transmembrane proteins Lipid bilayer Cell surface markers Interior protein network
What is the function of this membrane protein?
Transport substances across the membrane
The lack of double bonds in saturated fats allow them to pack together tightly, and therefore the membrane is __________ fluid. The presence of double bonds in unsaturated fats prevent them from packing together tightly, and therefore the membrane is _________ fluid.
less more
Cellular __________ are said to be selectively _____________ because they allow some substances to pass through easily while other substances pass through very slowly or not at all.
membrane permeable
Some membrane proteins are anchored to the surface of the membrane by molecules that associate strongly with phospholipids and insert into the lipid bilayer. These molecules are
modified lipids.
Transmembrane proteins must span the lipid bilayer at least __________ time(s) to be anchored in the interior of the cell membrane.
one
Transmembrane proteins include:
receptors channels carriers
Although a eukaryotic cell membrane can contain many different lipids, they can be classified in three groups: glycerol phospholipids, ____________ and ______________
sphingolipids sterols
The hydrophobic region of a transmembrane protein which extends through the lipid bilayer contacting the nonpolar interior of the membrane might be composed of which of the following (choose all that apply)?
β pleated sheets containing non-polar amino acids α helices containing non-polar amino acids
