Biology Chapter 9: Membrane Proteins

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Questions and Answers

What occurs shortly after an ATP molecule binds to an actin monomer during polymerization?

It forms a stable microtubule.

It is replaced by another ATP.

It remains bound indefinitely.

It hydrolyzes to ADP. (correct)

What is the primary structural characteristic of intermediate filaments?

They are comprised of a single type of protein subunit.

They consist of long, unbranched chains.

They have a diameter between 10-12 nm. (correct)

They are made up of only globular proteins.

Which of the following is an example of an intermediate filament in muscle cells?

Desmin (correct)

Neurofilaments

Cytokeratins

Vimentin

Where do intermediate filaments typically localize within most cells?

Surrounding the nucleus and extending throughout the cytoplasm. Signup and view all the answers

What role do stabilizing actin-binding proteins play in relation to actin filaments?

They assist in the polymerization of actin monomers. Signup and view all the answers

What characteristic makes intermediate filaments particularly useful in immunohistochemical determination of neoplastic cells?

Their stability, longevity, and cell-type specificity. Signup and view all the answers

What is the primary characteristic of peripheral membrane proteins?

They can be released in high-salt solutions. Signup and view all the answers

Which of the following is an example of a peripheral membrane protein in erythrocytes?

Spectrin Signup and view all the answers

What role does ankyrin play in the structure of erythrocyte membranes?

It links spectrin to protein-3-tetramer. Signup and view all the answers

Which of the following statements about membrane proteins is true?

Some peripheral proteins are globular in shape. Signup and view all the answers

How are peripheral membrane proteins associated with the lipid bilayer?

They are ionically associated with the membrane surface. Signup and view all the answers

What happens to peripheral membrane proteins in a high-salt solution?

They are released from the membrane. Signup and view all the answers

What feature distinguishes peripheral membrane proteins from integral membrane proteins?

Peripheral proteins are not embedded in the lipid bilayer. Signup and view all the answers

Which is NOT a function of peripheral membrane proteins?

Transporting ions across the membrane. Signup and view all the answers

Why is spectrin important for erythrocyte membranes?

It maintains overall membrane integrity. Signup and view all the answers

What is the primary function of exocytosis in cells?

To expel substances from the cell Signup and view all the answers

How does compartmentalization within the cytoplasm benefit cellular processes?

By preventing the intrusion of extraneous substances Signup and view all the answers

Which of the following statements best describes the role of membranes in enzymes' spatial-temporal organization?

They allow intermediates to be passed between enzymes in a particular order Signup and view all the answers

What happens during receptor-mediated endocytosis?

Specific receptors on the cell surface bind to molecules and initiate their uptake Signup and view all the answers

What is contained within the cytoplasm of a cell?

All material inside the cell membrane excluding the nucleus Signup and view all the answers

In what manner do vesicles participate in cellular functions?

They can store, transport, or secrete substances Signup and view all the answers

Which statement correctly represents one of the membrane functions?

Membranes selectively block most water-soluble substances Signup and view all the answers

What is one of the key benefits of maintaining local concentrations of intermediates in metabolic pathways?

It ensures that reactions occur in a timely manner Signup and view all the answers

What is the role of secretory granules during exocytosis?

To fuse with the plasma membrane for content release Signup and view all the answers

What distinguishes the cytoplasm from the nucleoplasm?

Cytoplasm is enclosed by the cell membrane while nucleoplasm is within the nuclear membrane Signup and view all the answers

What does the fluid mosaic model describe biological membranes as?

An arrangement of proteins in a lipid sea Signup and view all the answers

What is membrane asymmetry?

Differences in composition between the inner and outer layers of the bilayer Signup and view all the answers

Which molecule is typically helped across the membrane by a component during facilitated diffusion?

Glucose Signup and view all the answers

What is required for active transport across the cell membrane?

Energy from ATP Signup and view all the answers

Which phospholipid is more abundant in the inner half of the phospholipid bilayer?

Phosphatidyl serine Signup and view all the answers

What role do oligosaccharides play in membranes?

They occur only on the outer surface of the plasma membrane. Signup and view all the answers

What does selective permeability of cell membranes prevent?

Intrusion of harmful substances Signup and view all the answers

What type of diffusion occurs without energy expenditure for substances like water?

Passive diffusion Signup and view all the answers

What is one of the main functions of cell membranes regarding homeostasis?

To maintain optimal intracellular concentrations of ions and enzymes Signup and view all the answers

What is the primary structural component of microfilaments?

Globular actin proteins Signup and view all the answers

What ion is mentioned as playing a role in regulating the dynamics of actin filaments?

Calcium ions Signup and view all the answers

Which protein family is associated with the contraction of microfilaments?

Myosin proteins Signup and view all the answers

How do actin filaments in nonmuscle cells exist?

In soluble form Signup and view all the answers

Which of the following processes does NOT involve microfilaments?

Lysosomal digestion Signup and view all the answers

What is the core function of actin-binding proteins related to microfilaments?

Arranging microfilaments into networks Signup and view all the answers

Microfilaments tend to be less stable in which type of cells?

Nonmuscle cells Signup and view all the answers

What is the diameter range of microfilaments?

5–7 nm Signup and view all the answers

Which of the following statements is true regarding actin and myosin interactions?

Myosin must bind to actin to facilitate contraction Signup and view all the answers

What is a key characteristic that distinguishes microfilaments from microtubules?

Microfilaments are more flexible than microtubules Signup and view all the answers

Study Notes

Peripheral Membrane Proteins

Ionically associated with the inner or outer membrane surfaces.
Released in high-salt solutions; includes globular and filamentous types.
In erythrocytes, examples include spectrin (maintains membrane integrity) and ankyrin (links spectrin to protein-3-tetramer).

Membrane Organization

Fluid mosaic model describes membranes as "protein icebergs in a lipid sea".
Integral proteins can move laterally and rearrange due to interactions with peripheral proteins and cytoskeletal filaments.
Membrane asymmetry: differences in composition between inner and outer bilayer halves, with oligosaccharides only on the outer surface.
Outer layer contains more phosphatidyl choline and sphingomyelin; inner layer has more phosphatidyl serine and phosphatidyl ethanolamine.

Membrane Functions

Selective Permeability: Membranes protect internal environments, maintaining homeostasis by selectively allowing molecules to cross.
Transport Mechanisms:
- Passive Diffusion: Movement of substances along a concentration gradient without energy (e.g., water, lipids).
- Facilitated Diffusion: Passive transport of specific molecules like glucose, assisted by membrane components.
- Active Transport: Energy-dependent process (using ATP) for moving substances against a concentration gradient.
- Exocytosis: Process of ejecting substances from the cell without disrupting the membrane.

Compartmentalization

Cytoplasm contains membrane-limited compartments, protecting biochemical processes from unwanted intrusions and preventing substrate dilution.

Spatial-Temporal Organization

Mitochondrial and Golgi membranes have enzymes arranged to maintain the order of metabolic processes and control reaction rates.

Storage, Transport, and Secretion

Vesicles can store substances, transport them between compartments, or secrete them from the cell.

Cytoplasm

Comprises all materials within a cell, excluding the nucleus (the nucleoplasm is the material inside the nucleus).

Microfilaments

Thinnest cytoskeletal elements (5-7 nm), composed of globular actin; flexible and less stable compared to microtubules.
In muscle cells, they form stable structures in association with myosin.
Regulated by actin-binding proteins and calcium ions; involved in contractile functions.
Form an irregular mesh under the plasma membrane, with local accumulations in structures like microvilli.

Intermediate Filaments

Composed of ropelike structures (10-12 nm) made of protein subunits twisted together.
Example proteins include cytokeratins in epithelial cells, vimentin in mesenchymal cells, and neurofilaments in neurons.
Provide durability and tensile strength, important for cells under mechanical stress, stabilizing cell structure.
Typically form a network surrounding the nucleus, extending throughout the cytoplasm.

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Description

Explore the characteristics and functions of peripheral membrane proteins in this quiz. Learn how these proteins interact with the inner and outer surfaces of cell membranes and their role in cellular processes.