Cell Biology Chapter: Membrane Proteins
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Questions and Answers

Which type of protein extends across the lipid bilayer?

  • Covalently attached proteins
  • Transmembrane proteins (correct)
  • Peripheral proteins
  • Lipid-anchored proteins

How are some membrane proteins anchored to the cytosolic half of the lipid bilayer?

  • By an amphipathic α helix (correct)
  • By a single β sheet
  • Through a transmembrane helix
  • Using hydrogen bonds

What connects some proteins to either side of the bilayer?

  • Hydrophobic interactions
  • Covalently attached lipid molecules (correct)
  • Hydrogen bonding
  • Electrostatic interactions

What type of interactions often attaches proteins to the membrane weakly?

<p>Noncovalent interactions (D)</p> Signup and view all the answers

Which type of protein association is characterized by being solely linked through weak interactions?

<p>Peripheral proteins (A)</p> Signup and view all the answers

What is the primary function of the plasma membrane?

<p>To serve as a continuous barrier between cytoplasm and the external environment (B)</p> Signup and view all the answers

Which of the following structures is involved in the production of ATP?

<p>Mitochondria (A)</p> Signup and view all the answers

Internal membranes within a cell are primarily responsible for which of the following?

<p>Dividing the cell into functional compartments (D)</p> Signup and view all the answers

What role do enzymes play in the internal membranes?

<p>They are involved in the cell's metabolism (A)</p> Signup and view all the answers

Which organelle is responsible for sorting and modifying proteins?

<p>Golgi apparatus (D)</p> Signup and view all the answers

What is the main characteristic of lipid-anchored membrane proteins?

<p>They are covalently attached to lipid chains. (D)</p> Signup and view all the answers

Which of the following proteins is an example of a GPI-linked protein?

<p>N-CAM (D)</p> Signup and view all the answers

How do peripheral proteins typically attach to the membrane?

<p>By electrostatic bonds with membrane lipids or interactions with other proteins. (D)</p> Signup and view all the answers

Which fatty acid is linked to protein kinases and growth hormone receptors as an anchor?

<p>Myristate (C)</p> Signup and view all the answers

What is a common function of G trimeric proteins?

<p>Coupling between primary effectors and membrane-associated enzymes. (C)</p> Signup and view all the answers

What is a primary characteristic of transmembrane proteins?

<p>They penetrate the hydrophobic interior of the lipid bilayer. (C)</p> Signup and view all the answers

Which of the following accurately describes the structure of transmembrane proteins?

<p>They usually consist of coiled helices formed by nonpolar amino acids. (A)</p> Signup and view all the answers

What role do oligosaccharides play in many transmembrane proteins?

<p>They are exposed on the surface and contribute to glycoprotein formation. (A)</p> Signup and view all the answers

In what form do sulfhydryl groups typically exist in the cytoplasmic domain of transmembrane proteins?

<p>They are usually maintained in their reduced form. (C)</p> Signup and view all the answers

What type of structure do transmembrane proteins primarily form?

<p>Beta-barrel structure (D)</p> Signup and view all the answers

How do some polypeptide chains traverse the lipid bilayer in a unique structure?

<p>They roll into a cylindrical structure known as a beta barrel. (D)</p> Signup and view all the answers

Which amino acid side chains are predominantly found inside the barrel of transmembrane proteins?

<p>Hydrophilic side chains (D)</p> Signup and view all the answers

In which type of membranes are beta-barrel proteins predominantly located?

<p>Bacterial and mitochondrial membranes (A)</p> Signup and view all the answers

What is a significant example of a beta-barrel structure?

<p>Porin proteins (D)</p> Signup and view all the answers

What is the role of integral monotopic proteins in relation to the lipid bilayer?

<p>They are associated with the cytoplasmic half of the lipid bilayer. (D)</p> Signup and view all the answers

What is one function of membrane proteins related to solute transport?

<p>Forming hydrophilic channels for specific solutes. (A)</p> Signup and view all the answers

Which function of membrane proteins involves interaction with the cytoskeleton?

<p>Anchoring the membrane to macromolecules. (A)</p> Signup and view all the answers

What percentage of the mass of most plasma membranes do carbohydrates comprise?

<p>5-10% (C)</p> Signup and view all the answers

What primarily constitutes the outer leaflet of lipid rafts?

<p>Cholesterol and sphingolipids (B)</p> Signup and view all the answers

Which proteins are primarily concentrated in the inner leaflet of lipid rafts?

<p>Src kinase and lipid-anchored proteins (D)</p> Signup and view all the answers

What are glycoproteins?

<p>Membrane proteins linked to oligosaccharides. (A)</p> Signup and view all the answers

What role do lipid rafts play in cellular function?

<p>They form signaling microdomains for certain receptors. (B)</p> Signup and view all the answers

Which of the following is NOT a function of membrane proteins?

<p>Storing genetic information. (C)</p> Signup and view all the answers

In the context of lipid rafts, which lipid molecule tends to concentrate alongside cholesterol in the inner leaflet?

<p>Glycerophospholipids with long saturated fatty acyl tails (D)</p> Signup and view all the answers

Which of the following is thought to stabilize lipid rafts?

<p>Proteins that bind to carbohydrates in the trans-Golgi network (C)</p> Signup and view all the answers

What percentage of the mass of most plasma membranes is constituted by carbohydrates?

<p>5-10% (B)</p> Signup and view all the answers

Which of the following describes glycoproteins?

<p>Proteins linked to short chains of sugars (D)</p> Signup and view all the answers

Where is the carbohydrate layer, or glycocalyx, located?

<p>On the outside of the plasma membrane (C)</p> Signup and view all the answers

Where are sugar residues added to glycosylated transmembrane proteins?

<p>In the lumen of the ER and Golgi apparatus (A)</p> Signup and view all the answers

What is the primary role of glycolipids in the plasma membrane?

<p>To form a sugar coating on the cell surface (C)</p> Signup and view all the answers

What role do carbohydrates play in the adhesion phenomena between cells?

<p>They contribute to cell adhesion through specific molecules. (C)</p> Signup and view all the answers

Which of the following statements about the immunological reactions of carbohydrates is true?

<p>They can act as antigens in blood group classification. (A)</p> Signup and view all the answers

How do carbohydrates influence the hydro-mineral environment of a cell?

<p>They regulate osmotic pressure and maintain cell hydration. (D)</p> Signup and view all the answers

What is a physiological role of carbohydrates related to specific membrane receptors?

<p>They participate in ligand recognition by specific membrane receptors. (D)</p> Signup and view all the answers

In what way do carbohydrates contribute to the insulation of certain axons?

<p>Galactocerebroside acts as a glycolipid in the insulating sheath of myelin. (A)</p> Signup and view all the answers

What is one of the primary functions of biomembranes?

<p>Compartmentalization of the cell contents (D)</p> Signup and view all the answers

Which characteristic of biomembranes contributes to their selective permeability?

<p>Asymmetric organization (A)</p> Signup and view all the answers

What is a role of biomembranes in relation to cells?

<p>Interacting between cells (A)</p> Signup and view all the answers

Which component is part of the structure of biomembranes?

<p>Double layer of phospholipids (A)</p> Signup and view all the answers

Which process is NOT directly associated with the functioning of biomembranes?

<p>Cell division (C)</p> Signup and view all the answers

Flashcards

Transmembrane proteins

Proteins that span the entire lipid bilayer, acting as channels or transporters for molecules.

Single α helix transmembrane protein

A type of transmembrane protein formed by a single α helix structure that crosses the membrane.

Multiple α helix transmembrane proteins

A type of transmembrane protein constructed from multiple α helices, arranged in a specific way to create a channel or pore.

Peripheral proteins anchored to the cytosolic side

Proteins attached to the inner (cytosolic) side of the membrane through an amphipathic α helix.

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Lipid-linked membrane proteins

Proteins linked to either side of the membrane by a lipid molecule, which acts as an anchor.

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Plasma membrane

A membrane that encloses the cell's cytoplasm and separates it from the external environment.

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Internal (Endocellular) Membranes

Internal membranes that create compartments within the cell, forming organelles.

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Selective Barrier

The plasma membrane acts as a selective barrier, allowing essential molecules to pass through, while blocking others.

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Enzyme Complexes

Mitochondria and chloroplasts have enzymes embedded in their membranes, which are essential for energy production.

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Increased Surface Area

Internal membranes create a larger surface area within the cell, allowing for more efficient metabolic reactions.

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Lipid-anchored membrane proteins

Membrane proteins attached to the lipid bilayer through lipid chains on the outer leaflet of the membrane. These chains can either be fatty acids or oligosaccharide linkers called GPI anchors.

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GPI-linked protein

A type of lipid-anchored membrane protein that is attached to the membrane through a GPI anchor, a complex oligosaccharide linker.

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Peripheral proteins

A class of membrane proteins that are not embedded in the lipid bilayer but are associated with the membrane surface.

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Direct attachment of peripheral proteins

Peripheral proteins can bind to the membrane by interacting with lipid molecules through electrostatic interactions.

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Indirect attachment of peripheral proteins

These proteins can bind to the membrane through interactions with other transmembrane proteins.

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What are transmembrane proteins?

Transmembrane proteins are embedded in the cell membrane, spanning the lipid bilayer with one or more domains.

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How do transmembrane proteins interact with the membrane?

They have hydrophobic amino acids that interact with the hydrophobic interior of the membrane, while hydrophilic amino acids interact with the aqueous environment on either side.

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What are transmembrane proteins often associated with?

They are often glycosylated, meaning they have sugar molecules attached, with these sugar molecules exposed on the cell surface.

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What is the common structure of transmembrane proteins?

They are often arranged in a helical structure to form channels, pumps, or transporters.

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What other structure can transmembrane proteins form?

Some transmembrane proteins form a barrel-like structure, with a hydrophilic interior that forms a channel through the membrane.

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Beta-barrel protein

A type of transmembrane protein where the polypeptide chain folds into a beta sheet, forming a cylindrical structure.

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Hydrophilic side chains in beta-barrels

In beta-barrel proteins, amino acid side chains lining the aqueous channel are hydrophilic, allowing water and other molecules to pass through.

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Hydrophobic side chains in beta-barrels

In beta-barrel proteins, amino acid side chains interacting with the hydrophobic core of the lipid bilayer are hydrophobic.

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Porin proteins

A common example of beta-barrel proteins that form large, water-filled pores in bacterial outer membranes.

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Integral monotopic proteins

Some membrane proteins are only partially embedded in the lipid bilayer, with their main structure residing in the cytosol.

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What are cell surface receptors?

Membrane proteins that bind to specific signaling molecules outside the cell and initiate a response inside.

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How do membrane proteins facilitate transport?

Membrane proteins help transport substances across the cell membrane, either passively or actively.

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What role do membrane proteins play in enzymatic activity?

Some membrane proteins act as enzymes, catalyzing chemical reactions within the cell or at the membrane surface.

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How do membrane proteins contribute to cell structure?

Membrane proteins attach to the cytoskeleton or extracellular matrix, providing structural support and anchoring.

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How do membrane proteins facilitate cell-to-cell interactions?

Membrane proteins mediate cell-to-cell adhesion, connecting cells and forming tissues.

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What are lipid rafts?

Small, specialized regions within the cell membrane enriched in cholesterol, sphingolipids, and specific proteins, forming platforms for signaling and other cellular processes.

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What is the composition of a lipid raft's outer leaflet?

The outer leaflet of a lipid raft primarily consists of cholesterol and sphingolipids, creating a unique environment for protein interactions.

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How are GPI-anchored proteins associated with lipid rafts?

GPI-anchored proteins, which are attached to the membrane by a glycolipid anchor, are often found concentrated in lipid rafts.

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Are lipid rafts only found in the plasma membrane?

Lipid rafts are not only found in the plasma membrane but also in the membranes of internal organelles like the Golgi apparatus, playing a role in protein sorting and trafficking.

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What kind of protein can be found in the inner leaflet of a lipid raft?

Src kinase, a protein involved in cell signaling, is often found in the inner leaflet of lipid rafts, suggesting its role in signal transduction.

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What is the glycocalyx?

A sugar coating on the outer surface of cell membranes, formed by carbohydrate chains attached to glycoproteins, proteoglycans, and glycolipids.

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What are glycolipids?

Carbohydrates attached to lipids, found on the outer layer of the plasma membrane.

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What are glycoproteins?

Proteins with short sugar chains attached to them, found in cell membranes.

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What are proteoglycans?

Proteins that contain long polysaccharide chains, found in cell membranes.

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Where are sugar residues added to transmembrane proteins?

The addition of sugar residues to proteins occurs within the lumen of the ER and Golgi apparatus.

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Selective Permeability

The cell membrane acts as a barrier to regulate what enters and leaves the cell. Only certain molecules can cross, making it 'selective'.

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Asymmetry of biomembranes

Biomembranes have two distinct layers composed of lipids and proteins. The molecules on each side of the membrane are not the same, showcasing 'asymmetry'.

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Compartmentalization

Biomembranes allow for the formation of distinct internal compartments within the cell. These compartments, known as organelles, perform specific functions.

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Signal reception in biomembranes

Biomembranes play a key role in signal reception. They recognize and respond to signals from both inside and outside the cell, facilitating communication.

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Endomembrane system

Biomembranes are dynamic structures that can connect transiently. This allows for the movement of materials between different compartments through a network of membranes called the 'endomembrane system'.

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Carbohydrates as cell signals

Carbohydrates on the cell surface can act as signals, allowing cells to recognize and interact with each other. This interaction is crucial for various cellular processes, such as cell adhesion and immunity.

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Carbohydrates as insulators

Carbohydrates function as insulators in some cells, such as the myelin sheath, which wraps around certain axons, preventing electrical signals from leaking out.

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Fluid-mosaic model

The fluid-mosaic model describes the plasma membrane as a dynamic structure with embedded proteins that move laterally within a lipid bilayer.

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Glycolipids and glycoproteins

Carbohydrates can be linked to lipids or proteins, forming glycolipids and glycoproteins, respectively. These molecules are important for various cellular functions, including cell recognition and adhesion.

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Carbohydrates in cell adhesion

Carbohydrates play a role in cell adhesion by interacting with other cells and the extracellular matrix. This interaction is mediated by cell adhesion molecules (CAMs) and substrate adhesion molecules (SAMs).

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