Cell Membranes

Question 1

What are the components of a cell membrane?

Answer 1

Phospholipids, Cholesterol, Proteins, Glycoproteins/Glycolipids

Question 2

What is the 2 types of proteins found in the cell membrane?

Answer 2

Integral/intrinsic proteins and Peripheral/Extrinsic proteins

Question 3

What are the 2 types of integral/intrinsic proteins?

Answer 3

Unilateral (reach partway across membrane)
Transmembrane (completely span across the thickness of membrane)

Question 4

What are the functions of proteins in cell membrane?

Answer 4

• Function as channels/carriers for faciliatated diffusion and active transport
• Function as enzymes
• Function as receptor proteins
• Function to stabilise membrane structure

Question 5

What are the functions of glycolipids/glycoproteins in cell membrane?

Answer 5

Carbohydrate chains can
- Function as markers/recognition sites in cell-cell recognition and adhesion
- Function as receptors

Question 6

Explain the fluid mosaic model in cell membranes.

Answer 6

Fluid as cell membranes consists of phospholipids and proteins which are free to move laterally within a layer. Mosaic as random arrangement of proteins embedded amongst the phospholipid molecules resemble a mosaic pattern.

Question 7

What are the functions of membranes?

Answer 7

• Regulate movement of substances as membranes are a selectively permeable barrier
• Membranes allow for compartmentalisation
• Membranes act as a surface for chemical reactions to occur in a sequential manner
• Membranes have increased surface area for chemical reactions
• Membranes surface topography enable communication between cell and its surroundings

Question 8

Explain how simple diffusion occurs.

Answer 8

Simple diffusion is the movement of non-polar molecules and small polar water molecules directly through the membrane, down its concentration gradient without assistance of any transport protein. This does not require ATP.

Question 9

What are the factors affecting simple diffusion?

Answer 9

• Molecular size
• Solubility in lipid bilayer
• Concentration gradient
• Kinetic energy of molecules
• Surface area of cell membrane
• Distance

Question 10

Explain how facilitated diffusion occurs.

Answer 10

Faciliatated diffusion is a passive process where substances move down concentration gradient with no usage of ATP, with the need for transport proteins (Channel/Carrier Protein).

Question 11

Describe a channel protein.

Answer 11

It is a transmembrane protein that provides a hydrophilic pore which only specific ions or polar molecules can diffuse readilty through from one side of membrane to the other

Question 12

Describe a carrier protein

Answer 12

It is a transmembrane protein that exists in 2 alternate conformations. Binding of solute results in conformational change of protein and solute is now exposed to other side of membrane

Question 13

Explain osmosis.

Answer 13

Osmosis is the movement of water molecules from a region of higher water potential to a region of lower water potential through a selectively permeable membrane.

Question 14

Explain how active transport occurs.

Answer 14

Active transport is the transport of polar molecules or ions across a memebrane against a concentration gradient with the expenditure of ATP. It involves specialised carrier proteins called pumps.

Question 15

Explain bulk transport.

Answer 15

Bulk transport is an active process as ATP is used to mobilise the movement of membranes. It is not considered active transport.

Question 16

What are the different types of bulk transport?

Answer 16

Endocytosis, Exocytosis

Question 17

What are the different types of endocytosis?

Answer 17

Phagocytosis, Pinocytosis and Receptor-mediated endocytosis

Question 18

Describe process of phagocytosis.

Answer 18

• “Cell eating”
• Material taken up is in solid form.
• Filaments in cytoskeleton are rearranged to form pseudopodia, which are extensions of the membrane which wraps around and engulf the particles.
• Ends of extension of membrane fuse and a vesicle containing the solid matter is pinched off and moves into cytoplasm

Question 19

Describe process of pinocytosis.

Answer 19

• “Cell drinking”
• Material taken up is in liquid form
• Small area of plasma membrane invaginates to form tiny vesicles within the cell

Question 20

Describe process of receptor-mediated endocytosis

Answer 20

• It is a specific transport that involves protein receptors embedded in membranes that are exposed to the extracellular fluid
• Extracellular substances that bind to receptors are called ligands
• Invagination of membrane forms vesicles containing ligand-receptor complexes which are transported within the cell

Question 21

Describe exocytosis.

Answer 21

It is the secretion of macromolecules by the fusion of vesicles with plasma membrane

Question 22

Describe the process of exocytosis

Answer 22

A transport vesicle budded from the Golgi apparatus moves to the cell surface where the membrane of vesicle fuses with cell surface membrane to release contents of the vesicle to the extracellular environment.