Question 1

Which of the following molecules add stiffness and strength to the plasma membrane?

Accepted Answer

Cholesterol stiffens and strengthens the membrane. The other things are present in membranes but do not fulfill that function.

Question 2

Proteins do NOT pass through cell membranes because

Accepted Answer

Proteins are too large to pass through the membrane. Proteins do contain nitrogen and may digest the cell but that does not explain why they cannot pass through the membrane. The membrane is made of proteins and phospholipids but again, that does not explain why proteins cannot pass. Proteins do not cause emulsification.

Question 3

In certain cancerous cells,the cell divides continuously even in the absence of a growth factor (signaling molecule)that indicates the cell should divide.Which of the following could NOT explain this?

Accepted Answer

The cell is behaving as if a signal has bound to a receptor even when one has not. This could be due to any of the products of a signaling pathway being activated when it should not be. The only thing it could not be is a receptor that is inactive or turned off.

Question 4

The cell membrane is composed of

Accepted Answer

The plasma membrane is a phospholipid bilayer in which protein molecules are embedded. Actin filaments and microtubules make up the cytoskeleton.

Question 5

Which statement is false concerning movement of molecules across the cell membrane?

Accepted Answer

The membrane is differentially permeable. Liipids, small uncharged molecules, water, and gases have no difficulty passing through the membrane. Charged molecules do not pass through easily.

Question 6

The inside and outside of the plasma membrane are

Accepted Answer

The phospholipid bilayer is identical but the proteins on each side of the membrane are different. The cytoskeleton is attached to the interior face while glycolipids and carbohydrates are attached to the outside face of the membrane.

Question 7

The same signaling molecule that binds to the receptor on the outside of the cell is used to alter gene expression in the nucleus.

Accepted Answer

The signaling molecule initiates a transduction pathway that results in altered gene expression, but it is not the same molecule that causes the end result.

Question 8

Which is a correct association of protein types?

Accepted Answer

Enzymatic proteins carry out metabolic reactions. Carrier proteins combine with a substance to help it move across a membrane. Variations in cell recognition proteins cause tissue transplant rejection. Channel proteins provide a pathway for substances to move across the membrane. Receptor proteins allow a specific molecule to bind to it and may cause a cell response.

Question 9

Certain individuals with a Y chromosome develop into females because testosterone is not able to induce the formation of male sexual characteristics.This is most likely due to a defect in

Accepted Answer

These individuals lack receptors for testosterone. Although the testosterone is produced and is functional, it cannot bind to the cells and cause altered gene expression resulting in male sexual characteristics. These individuals develop as females.

Question 10

Red blood cells come in many blood types including A,B,AB and type O (lacking proteins A and B),Rh positive,Rh negative (lacking Rh+),and many others.If blood is transfused,the recipient detects any new or foreign proteins.The blood type proteins are

Accepted Answer

In order to be used as cell recognition proteins, the red blood cell surface markers must be present on the outer surface of the red blood cell membrane.

Question 11

Which components of a cell membrane are used for cell-to-cell recognition?

Accepted Answer

Proteins in a cell membrane are used for cell recognition. The others are present in the membrane but do not function in this way.

Question 12

Permeability refers to

Accepted Answer

The ability of a membrane to allow substances to pass through is permeability. The movement of molecules from greater to lesser concentration is diffusion. The amount of solute in a solution is concentration. The state of being permanent is permanence. It is not possible to establish a permanent solute level in a solution.

Question 13

Which of the following is not a function of the cell membrane?

Accepted Answer

The endoplasmic reticulum is the site for protein synthesis.

Question 14

According to the fluid-mosaic model of membrane structure,

Accepted Answer

The fluid mosaic model states that proteins form a mosaic pattern just outside or within the phospholipid layer of the membrane. Cholesterol is found in membranes but it is not the main constituent. Glycolipids are on the outside of the cell.

Question 15

Which type of membrane protein will be used to bind to hormones?

Accepted Answer

Hormones are signal molecules that bind to receptor proteins. The others are types of membrane proteins but they do not function in this way.

Question 16

Which function does the lipid bilayer component of the plasma membrane NOT provide for the cell?

Accepted Answer

The membrane is not impermeable. Many things cross the membrane in both directions.

Question 17

What property of phospholipids make them suitable for the formation of the double layer found in membranes?

Accepted Answer

Because phospholipids have both a hydrophobic and a hydrophilic end, the hydrophobic ends interact to form a bilayer with the hydrophilic ends facing the exterior. Phospholipids are charged. The remaining statements are true but do not explain why phospholipids can form a bilayer.

Question 18

Our body recognizes the foreign nature of a parasite or disease agent and we soon build up antibodies.A few parasites can change their identity to evade our immune system.How could cells do this on a regular basis?

Accepted Answer

Cell recognition membrane markers are usually proteins, so new proteins, similar enough to the host proteins to not be recognized by antibodies, need to be made and presented on the membrane. This procedure must occur fairly quickly or the immune system will recognize and destroy the invader.

Question 19

In the new procedures developed to clone a mammalian cell,the nucleus is removed from an egg cell and the nucleus from the adult to be cloned is injected inside this cell.If we did this process with a basketball,we would permanently damage the shell.What property of the cell repairs this damage?

Accepted Answer

Because of the fluid-mosaic nature of the membrane it is self sealing. Cell membrane proteins do diffuse in the membrane but they are not responsible for the self sealing property. Carrier proteins do not restore lipids and the outer and inner sides of the plasma membrane do not have identical carbohydrate chains. Isotonic solutions do not damage the cell membrane but they do not seal it either.

Question 20

Radioactive isotopes are used to tag proteins in the cell membranes of mouse cells.These cells are then fused with human cells in cultures.What is the likely consequence of the tagged mouse proteins?

Accepted Answer

Once the membranes fuse, proteins are free to move around the membrane within the phospholipid bilayer. This is a consequence of the fluid mosaic nature of the membrane.

Quiz 4: Membrane Structure and Function