Biology Chapter on Plasma Membrane

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Questions and Answers

What does the prefix 'glyco' refer to in glycoproteins?

Lipid

Carbohydrate (correct)

Protein

Nucleic Acid

In the context of proteoglycans, which statement is correct?

There is equal sugar and protein content.

Proteoglycans contain no carbohydrates.

There is more sugar than protein. (correct)

There is more protein than sugar.

What role do glycoproteins play on the external surface of the plasma membrane?

Enhance membrane fluidity

Facilitate nutrient absorption

Act as cell markers for identification (correct)

Provide energy storage

What is one of the primary functions of antibodies, which are a type of glycoprotein?

Interaction with antigens Signup and view all the answers

What characteristic describes a selectively permeable membrane?

Certain molecules can pass while others cannot. Signup and view all the answers

Which factors influence the permeability of a cell membrane?

Molecule composition and membrane properties Signup and view all the answers

What happens to impermeable molecules trying to cross a membrane?

They require assistance to move across. Signup and view all the answers

How does the membrane composition affect molecule movement?

It determines which molecules can and cannot cross. Signup and view all the answers

What is the main function of the plasma membrane as a physical barrier?

To regulate the entry and exit of certain molecules. Signup and view all the answers

What role do peripheral proteins play in the plasma membrane?

They are located only on one side of the membrane and do not transport substances. Signup and view all the answers

How does the arrangement of phospholipids in the plasma membrane contribute to its function?

It forms a lipid interior with hydrophilic heads that interact with the environment. Signup and view all the answers

Which of the following is NOT one of the four basic roles of the plasma membrane?

Nutrient Storage Signup and view all the answers

What does the term 'regulation of exchange' refer to regarding the plasma membrane?

It describes the control of substance movement into and out of the cell. Signup and view all the answers

In the analogy of a cell's plasma membrane as a fence around a yard, what does the mailbox represent?

The communication function of the plasma membrane. Signup and view all the answers

Why is the plasma membrane considered fundamental to cell responses and function?

It interacts continuously with the external and internal environments. Signup and view all the answers

What structure in the plasma membrane allows for the movement of larger substances in and out?

Gaps in the membrane Signup and view all the answers

What role do structural proteins play in the plasma membrane?

They maintain cell shape by linking the cytoskeleton to the plasma membrane. Signup and view all the answers

Which of the following is true about cell adhesion molecules?

They form part of the connections that hold tissues together. Signup and view all the answers

What is the function of enzymes associated with the plasma membrane?

They perform chemical reactions fixed on the membrane surface. Signup and view all the answers

What typically occurs when a ligand binds to a receptor on the plasma membrane?

It causes direct changes to the plasma membrane's ion permeability. Signup and view all the answers

Which type of molecules require transporters to cross cell membranes?

Hydrophilic molecules such as amino acids and ions. Signup and view all the answers

What is a common problem associated with spherocytosis?

Cells develop a spherical shape instead of a biconcave shape. Signup and view all the answers

What role do transporters play in maintaining homeostasis?

They facilitate the transport of essential molecules across cell membranes. Signup and view all the answers

How do receptors function in the body's chemical signaling system?

They bind specific signals to trigger cellular responses. Signup and view all the answers

What type of molecules can primarily pass through protein channels?

Small ions and water Signup and view all the answers

Which characteristic of protein channels affects the selectivity of molecules that can pass through?

The diameter of the channel Signup and view all the answers

How does the speed of transport through protein channels compare to that of protein carriers?

It is faster because there is no binding required Signup and view all the answers

Which of the following statements about protein channels is correct?

Protein channels often allow only specific ions to pass through. Signup and view all the answers

What distinguishes protein channels from protein carriers in terms of functionality?

Protein carriers bind to their substrates. Signup and view all the answers

Which of the following best describes the structure of protein channels?

Water-filled pores that allow small molecules through Signup and view all the answers

What role do electrical charges lining the inner channel play in protein channels?

They restrict movement of some charged particles. Signup and view all the answers

Which of the following molecules is likely to pass through a protein channel?

Sodium ion (Na+) Signup and view all the answers

What is the function of the apical end of epithelial cells?

It faces the lumen of a tube or canal. Signup and view all the answers

What is a key feature of the basal end of epithelial cells?

It faces the underlying connective tissue. Signup and view all the answers

How do Na+ and glucose transport occur in epithelial cells?

The Na+/glucose symport brings them into the cell at the apical end. Signup and view all the answers

What drives the Na+/glucose symport mechanism in epithelial cells?

A gradient created by continuous Na+ ejection via Na+-K+-ATPase. Signup and view all the answers

Which of the following correctly describes transepithelial movement?

It involves transport proteins at both apical and basal ends. Signup and view all the answers

What is the role of the Na+/K+-ATPase in glucose transport across epithelial cells?

It helps maintain the Na+ gradient necessary for symport. Signup and view all the answers

How can epithelial cells adjust their permeability based on transport needs?

By inserting or withdrawing membrane proteins. Signup and view all the answers

Which characteristic is NOT associated with glucose transport across epithelial cells?

Glucose crosses the membrane through simple diffusion. Signup and view all the answers

Study Notes

Plasma Membrane

The plasma membrane acts as a physical barrier, regulating exchange, providing structural support, and facilitating communication and cell identification.
The membrane is composed of a phospholipid bilayer with hydrophilic heads facing the internal and external aqueous environments and hydrophobic fatty acid tails in the interior.
Proteins are embedded in the membrane, some spanning the entire bilayer (transmembrane proteins) acting as transporters, while others are peripheral proteins located on one side of the membrane.
Cholesterol molecules are found within the lipid interior of the membrane.

Function of Plasma Membrane Proteins

Structural Proteins: Maintain cell shape by linking the cytoskeleton to the plasma membrane. Examples include microvilli and the biconcave shape of red blood cells.
Cell Adhesion Molecules: Form cell-to-cell connections holding tissues together. Membrane-spanning proteins link the cytoskeleton to the extracellular matrix. Collagen is a common fibrous protein involved in cell adhesion.
Enzymes: Catalyze chemical reactions on either side of the membrane. Examples include enzymes involved in digestion in the small intestine and adenylyl cyclase involved in signal transduction.
Receptors: Act as receivers for chemical signals, binding to specific ligands. Ligand binding can trigger events like ion channel opening or closing.
Transporters: Facilitate the movement of molecules across the membrane. Most hydrophilic molecules require transporters to cross.

Protein Transporters

Protein Channels: Act as water-filled channels, allowing passage of small molecules like water and ions (K+, Na+, Cl-, Ca2+). Their structure can restrict the passage of certain molecules based on size and electrical charge.
Protein Carriers: Bind to specific molecules and facilitate their movement across the membrane. This process is slower than protein channels.

Examples of Transport Mechanisms

Transepithelial transport: Movement of molecules across epithelial linings, often involving specific transporters at the apical and basal ends of the cell.
Glucose Transport: Glucose, a large polar molecule, is transported across epithelial cells through two mechanisms:
- Secondary active transport: Utilizes the Na+/glucose symport to facilitate glucose uptake from the gut lumen into the cell. This is driven by the continual active transport of Na+ out of the cell by the Na+/K+-ATPase.
- Facilitated diffusion: Glucose can also move across the membrane through specific glucose transporters down its concentration gradient.

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Description

This quiz covers the structure and function of the plasma membrane, including its components such as phospholipids, proteins, and cholesterol. It also explores the various roles of membrane proteins, including structural support and cell adhesion. Test your knowledge on this essential aspect of cell biology.