Cellular Membrane

Question 1

What is the main function of phospholipids?

Answer 1

To selectively isolate the cell’s (or organelle’s) internal content from the external environment.

Question 2

What are the main functions of proteins?

Answer 2

1. Regulates the flow of material into and out of the cell.
2. Allows for interaction with other cells and the extracellular environment.
3. Regulate some biochemical reactions.
4. Help cells attach together.

Question 3

What are the four main classes of membrane proteins and their functions?

Answer 3

1. Adhesion proteins: attach the cell to other cells or non-living protein surfaces.
2. Enzymes: catalyze chemical reactions that occur at a cell membrane.
3. Transport proteins: move substances across the membrane that would not normally be able to cross on their own.
4. Receptor proteins: involved in cell-cell communication, recognize and bond to specific molecules in the extracellular environment.

Question 4

What is the function of enzymes?

Answer 4

To catalyze chemical reactions that occur at a cell membrane.

Question 5

What is the function of adhesion proteins?

Answer 5

To attach the cell to other cells or non-living protein surfaces.

Question 6

What is the function of transport proteins?

Answer 6

To move substances across the membrane that would not normally be able to cross on their own.

Question 7

What are the two kinds of transport proteins?

Answer 7

1. Carrier proteins.
2. Channel proteins.

Question 8

What are the four major components of cellular membrane?

Answer 8

1. Two layers of phospholipids (lipid bilayer).
2. Proteins.
3. Carbohydrates.
4. Cholesterol (a steroid lipid).

Question 9

What is the function of receptor proteins?

Answer 9

Involved in cell-cell communication, recognize and bond to specific molecules found in the extracellular environment, and relay messages to relevant locations in the cytoplasm.

Question 10

What are the characteristics of the (potentially) diffusing molecule to consider?

Answer 10

1. Polarity (polar or non-polar).
2. Size (small or large).

Question 11

The membrane is said to be __________ in order to make diffusion across membranes possible.

Answer 11

Selectively permeable.

Question 12

What characteristics can make diffusion across membranes easier?

Answer 12

1. Hydrophobic (non-polar).
2. Small.

Question 13

What are the aspects of passive transport?

Answer 13

1. The molecule crosses the membrane without the use of energy.
2. May be transported using a molecule or may diffuse across on its own.
3. The molecule is moving DOWN its concentration gradient.

Question 14

What is used in active transport?

Answer 14

Energy (often from ATP).

Question 15

Active transport is used for transport when…

Answer 15

1. Going up the concentration gradient.
2. Many molecules are transported at the same time.
3. The object is relatively large.

Question 16

For active transport, does the rate of transport depend on concentration gradient magnitude?

Answer 16

No.

Question 17

What are the 3 types of passive transport? What are their characteristics?

Answer 17

1. Simple diffusion: The molecule diffuses on its own through the lipid bilayer.
2. Facilitated diffusion: The molecule uses a channel or carrier to cross.
3. Osmosis: Movement of water across the membrane.

Question 18

For passive transport, how does facilitated diffusion work?

Answer 18

1. Binding of cargo molecules to binding site on carrier protein.
2. Carrier proteins change shape.
3. Release of large molecules on the other side of the membrane.
4. Carrier returns to its original shape.

Question 19

What are the three types of active transport?

Answer 19

1. Channel or carrier protein pumps.
2. Endocytosis.
3. Exocytosis.

Question 20

How do protein pumps work?

Answer 20

1. Binding of cargo molecules to binding site on carrier protein, ATP also bonds to its own binding site.
2. A phosphate group is broken off ATP, providing the energy required for the carrier to change shape.
3. The cargo molecule is released on the other side of the membrane and ADP + phosphate are released from the ATP binding site.
4. Carrier returns to its original shape.

Question 21

How does endocytosis work?

Answer 21

Large objects or many molecules are taken into the cell (membrane) at the same time by being enclosed in a vesicle.

Question 22

How does exocytosis work?

Answer 22

A cell transports substances (like proteins or waste) out of the cell by packaging them in a vesicle, which then fuses with the cell membrane and releases the contents outside.

Question 23

What are exergonic biochemical reactions?

Answer 23

They release energy because the products have less energy than the reactants. These reactions are spontaneous.