Biol 162 Cell membrane

When phospholipids are placed in water, they spontaneously form which of the following?

A bilayer

Which of the following correctly describes this molecule (typically found in a biological membrane)?

A phospholipid with two fatty acids

All cell membranes contain a phospholipid which provides a flexible matrix and a barrier to .

Blank 1: bilayer Blank 2: permeability

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.

Blank 1: integral or intrinsic Blank 2: peripheral

The lack of double bonds in phospholipids with saturated fatty acids allow them to pack together tightly, and therefore the membrane is fluid. Kinks introduced by double bonds in lipids with unsaturated fatty acids prevent them from packing together tightly, and therefore the membrane is fluid.

Blank 1: less Blank 2: more

Transmembrane proteins must span the lipid bilayer at least time(s) to be anchored in the interior of the cell membrane.

Blank 1: one or 1

The thin structure made of a bilayer of lipids with embedded proteins that surrounds all cells is called the .

Blank 1: plasma, cell, or cellular Blank 2: membrane

According to the fluid mosaic model of membrane structure, a mosaic of floats in or on a fluid .

Blank 1: proteins Blank 2: lipid or phospholipid Blank 3: bilayer

Although a eukaryotic cell membrane can contain many different lipids, they can be classified in three groups: glycerol phospholipids, , and .

Blank 1: sphingolipids Blank 2: sterols

Which of the following are key functions carried out by membrane proteins?

Catalyze specific chemical reactions on the surface of the membrane Receive external chemical messages Function as cell-surface identity markers Transport specific ions and molecules across the membrane

What are lipid rafts in cellular membranes heavily enriched in?

Cholesterol Sphingolipids

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.

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

Which of the following describe(s) the circled regions on this diagram of a transmembrane protein.

Hydrophobic Nonpolar

Which of the following best describes the proteins which are inserted into the lipid bilayer of the plasma membrane?

Integral proteins

Which of the following describe(s) the interior of a phospholipid bilayer?

It contains the fatty acid tails. It is nonpolar. It is hydrophobic.

Identify the four main components of all eukaryotic membranes.

Lipid bilayer Cell surface markers Interior protein network Transmembrane proteins

Which of the following are typical components of biological membranes?

Lipids Proteins

Select the true statements concerning the organization of the plasma membrane.

Lipids can exist in either an ordered or disordered phase within the membrane. The plasma membrane contains areas with distinct lipid and protein composition. The plasma membrane is not homogeneous.

Which part of a membrane protein is found in contact with the interior of the lipid bilayer?

Nonpolar segment

What biological molecule found in membranes is depicted in this simple diagram?

Phospholipid

Which of the following makes up the bilayer of every cell membrane?

Phospholipids

Which of the following can relatively easily move laterally within the plasma membrane?

Phospholipids and unanchored proteins

Which structure surrounds all cells?

Plasma membrane

Which regions of a phospholipid molecule are hydrophilic?

Polar or charged molecule attached to the phosphate group Phosphate group

Which component of the plasma membrane is responsible for transport of materials and communication across the membrane?

Proteins

Which of the following best describes the fluid mosaic model of membrane structure?

Proteins float in or on a phospholipid bilayer.

Choose all functions typically carried out by membrane proteins.

Receive external chemical messages Connect adjacent cells and hold them together Attach the membrane to the cytoskeleton

How does lipid composition affect membrane fluidity?

Saturated fatty acids tend to make the membrane less fluid because they pack together well. Sphingolipids tend to make the membrane less fluid.

Choose the three groups of lipids found in eukaryotic cells.

Sphingolipids Sterols Glycerol phospholipids

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.

Which part of the lipid bilayer is responsible for the ability of membranes to act as impermeable barriers to the passage of any water-soluble substances?

The nonpolar interior

This experiment showing protein movement in membranes of fused cells best supports which of the following hypotheses?

The plasma membrane is fluid.

When phospholipids are placed in water, they spontaneously form a bilayer. Why?

The polar heads on the surface of the bilayer interact with water, while the nonpolar tails in the interior of the bilayer do not come into contact with water.

Which of the following is a defining feature of biological membranes?

The presence of two phospholipid sheets

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 describe pore proteins?

They create openings or channels in the membrane that allow specific ions or molecules to pass through. They are transmembrane proteins. They have extensive nonpolar regions that are folded into beta-pleated sheets.

Which of the following is one of the main functions of the membrane's phospholipid bilayer?

To impose a barrier to permeability.

Select the accurate statements concerning membrane fluidity.

Unanchored proteins are relatively free to move laterally within the membrane. Phospholipids are relatively free to move laterally within 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.

Phospholipids that contain unsaturated fatty acids typically have

cis-unsaturated fatty acids

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

On this diagram of a transmembrane protein, the circled region can be described as Blank______.

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 Blank______.

hydrophobic nonpolar

The top part (shaped like a circle) of this molecule, is Blank______.

polar or charged hydrophilic

Transmembrane β-sheets can form a motif through the membrane that allows molecules to pass through the membrane. Proteins with such a structure are known as Blank______.

pores