Cell Biology: Plasma Membrane Structure

46 Questions

What is the estimated number of cells in the average adult human body?

Trillions

What is the term for the process by which cells become specialized in function?

Differentiation

What is the primary function of the plasma membrane?

Regulating the passage of materials into and out of the cell

What is the term for the proteins attached to the phospholipid bilayer?

Peripheral proteins

What is the term for the movement of molecules through the plasma membrane?

Passive transport

What is the term for the proteins that span the phospholipid bilayer?

Transmembrane proteins

What is the typical thickness of membranes?

Between 7.5 to 10 nm

What is the primary component of the phospholipid bilayer?

Phospholipids

What is the primary function of cholesterol in the plasma membrane?

To restrict the movement of phospholipid fatty acids

What is the term for the carbohydrates attached to phospholipids and proteins?

Oligosaccharides

Which type of protein is incorporated directly within the lipid bilayer?

Integral protein

What is the primary mechanism of transport for small, nonpolar molecules across the plasma membrane?

Diffusion through the lipid bilayer

What is the approximate proportion of proteins in the plasma membrane by weight?

50% by weight

What is the role of transmembrane proteins in the plasma membrane?

To recognize and respond to signals from the environment

What is the orientation of the hydrophobic fatty acid chains in the phospholipid bilayer?

Towards the center of the bilayer

Which type of molecule can diffuse through the membrane readily?

Lipophilic molecule

What is the purpose of channel-linked receptors?

To open associated channels to promote transfer of molecules or ions across the membrane

What type of receptors bind to hydrophilic signaling molecules?

Transmembrane receptors

What occurs when a ligand binds to a G-protein–coupled receptor?

The receptor stimulates associated G-proteins which then bind the guanine nucleotide GTP

What type of protein is usually associated with hydrophilic signaling molecules?

Transmembrane protein

What is the function of enzymatic receptors?

To induce catalytic activity in associated peripheral proteins

What are cells that bear receptors for a specific ligand referred to as?

Target cells

Match the following components with their functions in the plasma membrane:

Phospholipids = Form the lipid bilayer Cholesterol = Modulate fluidity of membrane components Integral proteins = Span the phospholipid bilayer Peripheral proteins = Bind to the cytoplasmic side of the membrane

Match the following types of molecules with their ability to diffuse through the plasma membrane:

Lipophilic molecules = Diffuse readily through the membrane Hydrophilic molecules = Diffuse very slowly through the membrane Polar molecules = Cannot diffuse through the membrane Nonpolar molecules = Diffuse slowly through the membrane

Match the following types of proteins with their location in the plasma membrane:

Integral proteins = Incorporated directly within the lipid bilayer Peripheral proteins = Bound to the cytoplasmic side of the membrane Transmembrane proteins = Span the phospholipid bilayer Lipid-anchored proteins = Attached to the outer leaflet of the membrane

Match the following components with their roles in the plasma membrane:

Phospholipid bilayer = Forms a selective barrier for molecules Cholesterol = Maintains membrane fluidity Proteins = Perform specific recognition and signaling functions Lipid anchors = Attach proteins to the membrane

Match the following mechanisms with their functions in the plasma membrane:

Diffusion = Transports small, nonpolar molecules Active transport = Uses energy to transport molecules Passive transport = Transports molecules without energy Osmosis = Regulates water balance in the cell

Match the following characteristics with the phospholipid bilayer:

Amphipathic molecules = Have hydrophilic and hydrophobic regions Hydrophilic heads = Face the outer and inner leaflets of the membrane Hydrophobic tails = Face the middle region of the membrane Phosphate groups = Bear a negative charge

Match the following components with their proportions in the plasma membrane:

Proteins = Comprise approximately 50% of the membrane by weight Phospholipids = Comprise approximately 30% of the membrane by weight Cholesterol = Comprises approximately 20% of the membrane by weight Carbohydrates = Comprise approximately 10% of the membrane by weight

Match the following functions with the plasma membrane:

Cell signaling = Occurs through transmembrane proteins Cell-cell recognition = Occurs through membrane proteins Cell-environment interactions = Occurs through the plasma membrane Cell division = Occurs through the cytoskeleton

Match the components of the plasma membrane with their functions:

Phospholipids = Form the structural framework of the membrane Cholesterol = Regulate the fluidity of the membrane Proteins = Facilitate the transport of specific molecules Oligosaccharide chains = Participate in cell-cell recognition

Match the plasma membrane functions with their descriptions:

Selective barrier = Regulating the passage of materials into and out of the cell Transport facilitation = Maintaining the ion content of the cytoplasm Cell signaling = Enabling communication between cells Waste removal = Excreting cellular waste products

Match the plasma membrane structures with their characteristics:

Phospholipid bilayer = Hydrophobic tails facing inward Transmembrane proteins = Spanning the entire membrane thickness Oligosaccharide chains = Covalently linked to phospholipids and proteins Cholesterol = Embedded within the phospholipid bilayer

Match the following mechanisms with their description:

Diffusion = Movement of substances across membranes against concentration gradients Channels = Transmembrane proteins that bind small molecules and translocate them across the membrane Carrier proteins = Passive movement of substances across membranes down a concentration gradient Membrane pumps = Movement of substances across membranes down a concentration gradient due to kinetic energy

Match the plasma membrane roles with their consequences:

Ion content regulation = Maintaining a stable cytoplasmic environment Selectivity = Controlling the movement of molecules into and out of the cell Cell signaling = Influencing cell behavior and response Waste removal = Preventing cellular toxicity

Match the plasma membrane components with their interactions:

Phospholipids = Interacting with cholesterol to regulate fluidity Proteins = Interacting with oligosaccharide chains for cell-cell recognition Cholesterol = Interacting with phospholipids to influence membrane structure Oligosaccharide chains = Interacting with proteins to facilitate cell signaling

Match the following types of proteins with their function:

Transmembrane proteins = Forming transmembrane pores through which ions or small molecules pass selectively Carrier proteins = Engaged in active transport, utilizing energy from ATP hydrolysis Receptors = Attached to the phospholipid bilayer, detecting extracellular molecules and physical stimuli Gap junctions = Coupling adjacent cells and allowing exchange of ions and small molecules

Match the plasma membrane functions with their relationships to the cell:

Selective barrier = Defining the cell's outer limit Transport facilitation = Regulating the exchange of materials with the extracellular environment Cell signaling = Influencing cell behavior and response to stimuli Waste removal = Maintaining cellular homeostasis

Match the following terms with their description:

Active transport = Movement of substances across membranes against concentration gradients, using ATP energy Passive transport = Movement of substances across membranes down a concentration gradient, using kinetic energy Signal reception = Detection of extracellular molecules and physical stimuli by receptors Signal transduction = Response to signals detected by receptors

Match the following components with their location:

Phospholipid bilayer = The main component of the plasma membrane Transmembrane proteins = Attached to the phospholipid bilayer, spanning the membrane Receptors = Attached to the phospholipid bilayer, detecting extracellular molecules and physical stimuli Gap junctions = Forming channels between adjacent cells

Match the plasma membrane structures with their functions in cell signaling:

Transmembrane proteins = Enabling communication between cells Oligosaccharide chains = Participating in cell-cell recognition Phospholipid bilayer = Providing a platform for signaling molecule interactions Cholesterol = Influencing the fluidity of the signaling environment

Match the plasma membrane components with their effects on membrane structure:

Cholesterol = Increasing the fluidity of the membrane Phospholipids = Forming the structural framework of the membrane Proteins = Influencing the membrane's permeability Oligosaccharide chains = Affecting the membrane's rigidity

Match the following processes with their description:

Ion channels = Forming transmembrane pores through which ions pass selectively Carrier-mediated transport = Transmembrane proteins that bind small molecules and translocate them across the membrane Facilitated diffusion = Passive movement of substances across membranes down a concentration gradient Osmosis = Movement of water molecules across the membrane

Match the following types of transport with their characteristic:

Passive transport = Does not use ATP energy Active transport = Uses ATP energy to move substances against concentration gradients Facilitated diffusion = Uses carriers to move substances down concentration gradients Simple diffusion = Movement of substances across membranes without carriers

Match the following molecules with their function:

ATP = Energy source for active transport Adenosine = Component of ATP, used for active transport Ligands = Binding to receptors to trigger signal transduction Ions = Moving across membranes through ion channels

Match the following structures with their function:

Gap junctions = Allowing exchange of ions and small molecules between adjacent cells Plasma membrane = Regulating movement of substances in and out of the cell Receptors = Detecting extracellular molecules and physical stimuli Ion channels = Forming transmembrane pores through which ions pass selectively

Study Notes

The Plasma Membrane – Structure

Membranes range from 7.5 to 10 nm in thickness and are only visible in the electron microscope.
Phospholipids are amphipathic, consisting of two nonpolar fatty acid chains linked to a charged polar head with a phosphate group.
Phospholipids are most stable when organized into a double layer (bilayer) with hydrophobic fatty acid chains in the middle and hydrophilic polar head groups contacting water.
Cholesterol molecules insert among phospholipid fatty acids, restricting their movements and modulating membrane fluidity.

Lipids & Cholesterol in the Membrane

Proteins make up ~50% by weight in the plasma membrane.
Integral proteins are incorporated directly within the lipid bilayer, while peripheral proteins are bound to one of the two membrane surfaces, particularly on the cytoplasmic side.

The Plasma Membrane – Transmembrane Proteins & Membrane Transport

The plasma membrane is the site where materials are exchanged between the cell and its environment.
Small molecules cross the membrane through diffusion, which transports nonpolar molecules directly through the lipid bilayer.
Lipophilic (fat-soluble) molecules diffuse through membranes readily, while water diffuses very slowly.

Cell Differentiation

The average adult human body consists of nearly 40 trillion cells, which exist as hundreds of histologically distinct cell types, all derived from the zygote.
The first zygotic cellular divisions produce cells called blastomeres, which give rise to all tissue types of the fetus.
Most cells of the fetus undergo a specialization process called differentiation, where they express specific genes that mediate cytoplasmic activities, becoming efficiently organized in tissues with specialized functions.

The Plasma Membrane – Roles/Functions

The plasma membrane functions as a selective barrier regulating the passage of materials into and out of the cell.
One important role of the cell membrane is to keep constant the ion content of cytoplasm, which differs from that of the extracellular fluid.

The Plasma Membrane – Signal Reception & Transduction

Each cell type in the body contains a distinctive set of cell surface and cytoplasmic receptor proteins that enable it to respond to a complementary set of signaling molecules in a specific, programmed way.
Receptors for hydrophilic signaling molecules, including polypeptide hormones and neurotransmitters, are usually transmembrane proteins in the plasmalemma of target cells.
Three important functional classes of receptors are:
- Channel-linked receptors that open associated channels upon ligand binding to promote transfer of molecules or ions across the membrane.
- Enzymatic receptors that induce catalytic activity in associated peripheral proteins upon ligand binding.
- G-protein–coupled receptors that stimulate associated G-proteins upon ligand binding, which then bind guanine nucleotide GTP and are released to activate other cytoplasmic proteins.

Cell Structure and Differentiation

The average adult human body consists of nearly 40 trillion cells.
These cells exist as hundreds of histologically distinct cell types, all derived from the zygote.
The process of cell differentiation leads to cells specializing in specific activities and changing their shape accordingly.

The Plasma Membrane

The plasma membrane (cell membrane or plasmalemma) consists of phospholipids, cholesterol, and proteins.
The membrane has oligosaccharide chains covalently linked to many of the phospholipids and proteins.
The plasma membrane defines the outer limit of the cell and regulates the passage of materials into and out of the cell.

Roles and Functions of the Plasma Membrane

The plasma membrane functions as a selective barrier, facilitating the transport of specific molecules.
It keeps the ion content of the cytoplasm constant, which differs from that of the extracellular fluid.
Membrane proteins perform recognition and signaling functions, playing a key role in cell interactions.

Structure of the Plasma Membrane

The membrane ranges from 7.5 to 10 nm in thickness and is only visible in the electron microscope.
Membrane phospholipids are amphipathic, consisting of nonpolar fatty acid chains linked to a charged polar head.
Phospholipids are most stable when organized into a double layer (bilayer) with the hydrophobic fatty acid chains located in a middle region away from water.

Lipids and Cholesterol in the Membrane

Molecules of cholesterol, a sterol lipid, insert at varying densities among the closely-packed phospholipid fatty acids, restricting their movements and modulating the fluidity of all membrane components.

Proteins in the Membrane

Proteins are major constituents of membranes (~50% by weight in the plasma membrane).
Integral proteins are incorporated directly within the lipid bilayer, whereas peripheral proteins are bound to one of the two membrane surfaces, particularly on the cytoplasmic side.

Transmembrane Proteins and Membrane Transport

The plasma membrane is the site where materials are exchanged between the cell and its environment.
Small molecules cross the membrane by diffusion, channels, and carrier proteins.
Diffusion transports small, nonpolar molecules directly through the lipid bilayer.
Channels are multipass proteins forming transmembrane pores through which ions or small molecules pass selectively.
Carrier proteins bind small molecules and translocate them across the membrane via conformational changes.
Membrane pumps are enzymes engaged in active transport, utilizing energy from the hydrolysis of ATP to move ions and other solutes across membranes.

Signal Reception and Transduction

Cells in a multicellular organism communicate with one another to regulate tissue and organ development, control growth and division, and coordinate their functions.
Cells form communicating gap junctions that couple the cells and allow exchange of ions and small molecules.
Cells use different types of receptors to detect and respond to various extracellular molecules and physical stimuli.

Learn about the structure and composition of the plasma membrane, including phospholipid bilayers and cholesterol molecules.

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