2.2 Membrane Structure & Function

Question 1

What does the CFTR (cystic fibrosis transmembrane conductance regulator) protein do in healthy cells?

Answer 1

The CFTR protein is a membrane transport protein that moves chloride ions (Cl⁻) out of the cells lining the lungs and intestines. This process attracts sodium ions (Na⁺) and water, which moves by osmosis into the surrounding mucus, keeping it hydrated and moist.

Question 2

How does cystic fibrosis affect CFTRs function?

Answer 2

In Cystic Fibrosis, a mutant CFTR protein fails to transport chloride ions, which causes water to remain inside cells. This leads to thick, sticky mucus buildup in the lungs and intestines.

Question 3

How does the cholera toxin cause severe diarrhea?

Answer 3

The cholera toxin binds to cells in the small intestine, causing chloride and sodium ions to leave the cells. This imbalance pulls water out of the cells and into the intestine in an attempt to balance the concentration, which leads to watery diarrhea as the body tries to expel the excess fluid, causing dehydration.

Question 4

How do non-lipid, water-soluble molecules pass through the cell membrane?

Answer 4

Water-soluble molecules pass through the cell membrane via protein channels or transport proteins, as they cannot move through the hydrophobic lipid bilayer.

Question 4

What is membrane asymmetry?

Answer 4

Membrane asymmetry refers to the different composition and functions of the inner and outer layers of the lipid bilayer. The outer layer often contains carbohydrates for cell recognition, while the inner layer has proteins that bind to the cytoskeleton for structural support.

Question 5

What is the fluid mosaic model of the cell membrane?

Answer 5

The fluid mosaic model describes the membrane as a dynamic structure made of a lipid bilayer with embedded proteins and carbohydrates, where lipids and proteins can move sideways within the layer, giving the membrane flexibility.

Question 6

What factors influence the fluidity of the cell membrane?

Answer 6

Membrane fluidity is influenced by temperature, the presence of unsaturated fatty acid tails, the length of fatty acids, and cholesterol content.

(“CULT” –> cholesterol, unsaturated, length, temperature)

Question 7

What are the main functions of the cell membrane?

Answer 7

The cell membrane acts as a selective barrier, controls the movement of substances in and out of the cell (gatekeeping), provides receptor sites for signaling molecules like hormones, offers structural support, and assists in chemical reactions through membrane-bound enzymes.

Question 7

How does cholesterol contribute to membrane fluidity?

Answer 7

Cholesterol helps maintain membrane fluidity by preventing the membrane from becoming too rigid in cold temperatures and too fluid in high temperatures, allowing the cell to function across various conditions.

Question 8

What are the two main types of membrane proteins?

Answer 8

Integral proteins are embedded within the lipid bilayer and span the membrane, while peripheral proteins are attached to the surface of the membrane without penetrating it.

Question 9

What are the four functional categories of membrane proteins?

Answer 9

Transport Proteins: Facilitate the movement of substances across the membrane.

Enzymatic Proteins: Catalyze biochemical reactions.

Receptor Proteins: Trigger signals by binding to molecules like hormones, initiating cellular responses.

Structural Proteins: Provide attachment and recognition, connecting to the cytoskeleton or recognizing other cells to maintain cell shape and stability.

Question 10

How do transport proteins aid in the function of the cell membrane?

Answer 10

Transport proteins help facilitate the movement of specific molecules across the membrane, allowing the cell to control what enters and exits.

Question 11

How does the cell membrane provide structural support?

Answer 11

The cell membrane supports the cell’s shape by attaching to microfilaments of the cytoskeleton, helping to maintain its structure.

Question 12

How does the cell membrane contribute to cell signaling?

Answer 12

Receptor proteins in the membrane bind to external signaling molecules like hormones, which trigger changes inside the cell, such as opening channels or starting cellular processes.

Question 13

What role do glycolipids and glycoproteins play in the cell membrane?

Answer 13

They are involved in cell recognition and cell-to-cell interactions.

Question 14

What types of proteins are found in membranes?

Answer 14

Integral proteins (including transport proteins), peripheral proteins, glycoproteins, and glycolipids.

Question 15

Why are membranes described as “fluid”?

Answer 15

Lipid and protein molecules can move laterally within the two layers.

Question 16

What is the primary structure of a biological membrane?

Answer 16

Phospholipid bilayer with embedded proteins

Question 17

How does the structure of phospholipids contribute to membrane formation?

Answer 17

Phospholipids have hydrophobic fatty acid tails and a hydrophilic phosphate head, allowing them to form a bilayer in aqueous environments.

Question 18

What is the importance of the plasma membrane?

Answer 18

It regulates the movement of substances into and out of the cell.

Question 19

What is a key feature of eukaryotic cells related to internal membranes?

Answer 19

Eukaryotic cells have a nuclear envelope, an internal membrane that encloses the nucleus.

Question 19

Do all organelles have identical membranes? Give examples of similarities and differences.

Answer 19

No, not all organelles have identical membranes. For example, the plasma membrane is flexible and interacts with the external environment, while the mitochondrial membrane is specialized for energy production and contains different proteins and lipid compositions.

Question 19

Identify a sterol found in animal cell membranes but not in plants or prokaryotes.

Answer 19

Cholesterol is a sterol found in animal cell membranes but is absent in plant cells and prokaryotes.

Question 19

Describe integral and peripheral membrane proteins. How do they differ in chemical makeup and amino acid arrangement?

Answer 19

Integral membrane proteins are embedded within the lipid bilayer and often span the membrane, while peripheral membrane proteins are attached to the exterior or interior surfaces. Integral proteins typically have hydrophobic amino acids, while peripheral proteins usually contain hydrophilic amino acids.

Question 19

What is the function of sterols in cell membranes?

Answer 19

Sterols, like cholesterol, help maintain membrane fluidity, stability, and integrity by preventing the fatty acid chains from packing too closely together.

Question 19

Why is the cell membrane important for cell function?

Answer 19

The semipermeable membrane filters nutrients and waste, maintains an environment for metabolic processes, and allows for more complex cell functions by compartmentalizing processes with internal membranes.

Question 20

Is cholesterol polar or non-polar? Explain your answer.

Answer 20

Cholesterol is primarily non-polar due to its hydrophobic steroid ring structure, though it has a small polar hydroxyl group that makes it amphipathic.

Question 20

How are protein receptors and enzymes similar?

Answer 20

Both protein receptors and enzymes are specialized proteins that bind to specific molecules, with receptors often initiating a signal transduction pathway, while enzymes catalyze biochemical reactions.

Question 21

What are the basic components of a cell membrane? What are their functions?

Answer 21

Phospholipids: Form the bilayer and provide structural integrity.

Proteins: Serve as receptors, transporters, enzymes, and structural components.

Carbohydrates: Play roles in cell recognition and signaling.