Cell Biology: Plasma Membrane Quiz

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Questions and Answers

What is the approximate total thickness of the plasma membrane?

8-10 nm (correct)

2-4 nm

12-14 nm

5-7 nm

Which type of microscopy is required to discern the detailed structure of the plasma membrane?

Light microscopy (LM)

Transmission electron microscopy (TEM) (correct)

Scanning electron microscopy (SEM)

Confocal microscopy

When viewed with TEM, how does the plasma membrane appear?

As a single electron-lucent layer.

As two electron-lucent layers sandwiching an electron-dense layer.

As two electron-dense layers separated by an electron-lucent layer. (correct)

As a single electron-dense layer.

Which of the following is NOT a major component of the plasma membrane?

Glycogen Signup and view all the answers

Which best describes the arrangement of phospholipids in the plasma membrane?

A bilayer with hydrophilic heads facing both the inner and outer surfaces and hydrophobic tails meeting in the middle. Signup and view all the answers

What are lipid rafts?

Localized thick regions of the plasma membrane containing high concentrations of cholesterol, glycosphingolipids, and membrane-associated proteins. Signup and view all the answers

Which feature of lipid rafts makes them less fluid than the surrounding membrane?

High concentration of cholesterol. Signup and view all the answers

What role do lipid rafts potentially play in bacterial or viral infections?

They facilitate pathogen entry by acting as contact points and enabling cellular hijacking of signalling mechanism. Signup and view all the answers

Which type of membrane transport involves the movement of molecules down a concentration gradient, without the assistance of a transport protein?

Simple diffusion Signup and view all the answers

The movement of glucose into a cell, with the help of a carrier protein, is an example of what type of transport?

Passive transport Signup and view all the answers

Which of the following best describes the function of channel proteins in membrane transport?

To create regulated pores through the membrane allowing specific molecules to pass Signup and view all the answers

What is the general term for the processes of vesicular transport, in which substances enter a cell?

Endocytosis Signup and view all the answers

Which type of vesicular transport involves the transport of macromolecules from the apical to the basolateral plasma membranes?

Transcytosis Signup and view all the answers

What role does dynamin play in micropinocytosis?

It acts as a guanosine triphosphatase (GTPase) that 'scissiors' off the vesicle from the membrane Signup and view all the answers

Which of the following is NOT a mechanism of endocytosis?

Exocytosis Signup and view all the answers

What is a distinctive feature of micropinocytosis?

It is a non-specific ingestion of fluid and small protein molecules Signup and view all the answers

In which of the following scenarios are ligand-gated ion channels predominantly involved?

Muscle contraction at the neuromuscular junction Signup and view all the answers

What cellular component is essential for the formation of vesicles during vesicular transport?

Plasma membrane Signup and view all the answers

Which of the following is NOT a primary function of the cell membrane?

Generating ATP for cellular energy needs. Signup and view all the answers

According to the fluid mosaic model, the plasma membrane is BEST described as:

A plane of phospholipids where lateral movement of membrane proteins is controlled. Signup and view all the answers

What is the immediate consequence for a cell if its plasma membrane is severely damaged?

The cell will likely die within seconds. Signup and view all the answers

Which of these is an example of an intracellular membrane?

The membrane surrounding the nucleus. Signup and view all the answers

Why is the prevention of ATP loss from the cell crucial?

ATP is the energy reserve of the cell. Signup and view all the answers

Which of the following does the cell membrane prevent the loss of?

Amino Acids. Signup and view all the answers

What is one of the major components of the cell membrane, in addition to phospholipids and proteins?

Cholesterol Signup and view all the answers

What does the cell membrane use to maintain interactions with its environment?

Cell recognition and signaling Signup and view all the answers

Which process is characterized by the formation of membrane ruffles and the subsequent trapping of extracellular fluid?

Macropinocytosis Signup and view all the answers

What is the primary function of cargo receptors in receptor-mediated endocytosis?

To bind specific molecules for cellular uptake Signup and view all the answers

Which type of endocytosis is associated with the uptake of large particles, such as bacteria and cell debris?

Phagocytosis Signup and view all the answers

What protein is responsible for coating vesicles during receptor-mediated endocytosis?

Clathrin Signup and view all the answers

What is the function of dynamin in receptor-mediated endocytosis?

To sever the vesicle from the plasma membrane Signup and view all the answers

Which vesicle type is primarily involved in retrograde transport from the Golgi to the endoplasmic reticulum (ER)?

COP-I coated vesicles Signup and view all the answers

In which cellular structure does most vesicle trafficking within the cell occur?

Endosomes Signup and view all the answers

Which type of cellular projection is characterized by a core of microtubules and is motile in certain locations?

Cilia Signup and view all the answers

What feature primarily characterizes early endosomes in a cell?

They are confined to areas near the plasma membrane. Signup and view all the answers

Which of these endocytosis mechanisms are actin-dependent?

Macropinocytosis and phagocytosis Signup and view all the answers

What is the main function of flotillins within planar lipid rafts?

To facilitate signaling pathways and recruit specific membrane proteins. Signup and view all the answers

Which type of membrane protein is directly involved in forming tight junctions?

Structural proteins Signup and view all the answers

What is the role of cholesterol in the plasma membrane?

To limit membrane fluidity in warm temperatures and prevent freezing in cold temperatures. Signup and view all the answers

Which of the following best describes the glycocalyx?

A carbohydrate-rich coat on the external surface of the plasma membrane. Signup and view all the answers

Integrins are responsible for interactions between which of the following structures?

Cell cytoskeleton (actin filaments) and the extracellular matrix. Signup and view all the answers

Which type of membrane transport requires the use of a specific protein to facilitate the movement of substances across the membrane?

Transport through carrier proteins Signup and view all the answers

How are caveolar rafts different from planar lipid rafts?

Caveolar rafts are invaginations of the plasma membrane, whereas planar rafts are flat. Signup and view all the answers

Which of these is NOT a function of a membrane protein?

Replication of DNA. Signup and view all the answers

What is a characteristic of a membrane with a high proportion of phospholipids containing unsaturated fatty acid tails?

It is more fluid than a membrane with saturated fatty acid tails. Signup and view all the answers

The apical plasma membrane is primarily responsible for which function?

Nutrient and water intake, secretion, and protection. Signup and view all the answers

Which of the following describes fully transmembrane (multi-pass) integral proteins?

Their polypeptide chains span through the lipid bilayer many times. Signup and view all the answers

How does the chemical structure of phospholipids influence membrane fluidity?

Unsaturated tails prevent packing and increase membrane fluidity. Signup and view all the answers

What is the purpose of using freeze-fracture technique in the context of biological membranes?

To split the membrane leaflets and visualize integral proteins. Signup and view all the answers

Which function is primarily associated with the lateral plasma membrane domain?

Cell contact, cell communication and pumping. Signup and view all the answers

In the context of the plasma membrane, what does 'anchored' mean in reference to some integral proteins?

They are attached to either the outside or inside lipid bilayer. Signup and view all the answers

Study Notes

Cell Membrane

The cell membrane separates the cell from its environment.
It forms distinct functional compartments within the cell (e.g., nucleus, organelles).
Key functions include maintaining the ion content of the cytoplasm, preventing the loss of essential cellular materials (like proteins, nucleic acids, carbohydrates), and preventing the loss of ATP (cellular energy).
The outermost membrane is called the plasma membrane or plasmalemma.
The bilayer of phospholipids, within which proteins and cholesterol molecules are embedded, constitutes the cell membrane.

Learning Objectives

Describe the structure of the cell membrane.
Describe what lipid rafts are within the cell membrane.
State the role of cholesterol in membrane fluidity.
Describe transmembrane proteins.
State the categories of transmembrane proteins and define their functions.
Describe the glycocalyx coat and define its functions.
Explain the types of membrane transport.
Describe the types of vesicles.
Define endocytosis, exocytosis, and transcytosis and relate them to vesicular transport.
State the types of cell surface modifications (e.g., microvilli, microtubules, basolateral folding) and relate these modifications to the specialized function of the cell.

Plasma Membrane Structure

Total thickness is 8-10 nm.
Details are not visible with light microscopy (LM).
Transmission electron microscopy (TEM) is needed to see the details of the membrane.

Plasma Membrane Structure (continued)

It contains a large volume of phospholipids, cholesterol, and proteins.
Phospholipids have hydrophilic heads and hydrophobic tails, arranged in a bilayer.
The hydrophobic tails form a middle layer, while the hydrophilic heads face the outer and inner sides of the membrane.
Cholesterol is present which helps control membrane fluidity in varying temperatures.

Lipid Rafts

Lipid rafts are localized thick regions within the membrane.
They have a high concentration of cholesterol, glycosphingolipids, and membrane-associated proteins.
They are less fluid than the surrounding membrane.
Lipid rafts can be mobilized to different regions of the membrane with stimulation.
They play important roles in signal transduction, T-lymphocyte activation, and HIV entry.
In bacterial and viral infections, some bacteria take advantage of lipid rafts for entry into cells.

Two Types of Lipid Rafts

Planar Lipid rafts (Flotillin Lipid Rafts).
Caveolar Lipid rafts (Caveolin Rafts).

Caveolar Lipid Rafts

These are small flask-shaped invaginations of the plasma membrane.
Contain integral membrane proteins (Caveolins).
They form vesicles by micropinocytosis.

Membrane Proteins

These are crucial for cellular functions, and they span the lipid bilayer.
Integral proteins are classified as transmembrane proteins that pass through the lipid bilayer.
Two types of transmembrane proteins: Single-pass and multi-pass.
There are partially lipid-anchored proteins that are attached to either the inner or outer side of the lipid bilayer.
Peripheral proteins are located outside the lipid bilayer and interact with the integral proteins.

Integral Membrane Protein Categories

Pumps: Transport ions, amino acids, sugars.
Channels: Allow the passage of small ions and water.
Receptors: Allow recognition and localized binding of ligands (eg. receptors to hormones, antibodies).
Linker proteins: Anchor the intracellular cytoskeleton to the extracellular matrix.
Enzymes: Various roles (e.g., ATPases in ion pumping.)
Structural proteins: Form junctions with neighboring cells.

Integrins

Transmembrane linker proteins, composed of α and β subunits.
Responsible for specific interactions between the cell cytoskeleton and extracellular matrix proteins.

Membrane Fluidity

The ability of membrane molecules to move within the plane of the membrane.
Three features provide fluidity: Loose attachment of phospholipids, proteins, and carbohydrates, chemical structure of the phospholipids, and presence of cholesterol in the membrane.

Cell Coat or Glycocalyx

A fuzzy, carbohydrate-rich coat on the external surface of the plasma membrane.
Composed of carbohydrates from glycoproteins/glycolipids.
Varies in composition with cell type.
Contains tissue and cell-specific antigens (e.g. the major histocompatibility complex (MHC)).
Plays a role in organ transplant compatibility.
Present in the apical microvilli of the intestinal epithelium.

Membrane Shapes

The glycoproteins of the glycocalyx influence the shape of the plasma membrane.
The shapes can be flat, blebs, tubes, or pearls.

Vesicular Transport

Includes three main types: Endocytosis, Exocytosis, and Transcytosis.
Endocytosis is the processes that allow substances to enter the cell.
Exocytosis is the processes that allow substances to leave the cell.
Transcytosis is the transport of macromolecules from one side of a cell to the other.

Endocytosis Mechanisms

Includes pinocytosis (fluid consumption), micropinocytosis, and phagocytosis (cell consumption).

Pincocytosis

Nonspecific ingestion of fluids and small proteins.
Almost all cells use this process.
Involves vesicles being associated with caveolin and flotillin.

Macropinocytosis

Nonspecific uptake of extracellular fluids, nutrients, and other molecules.
Actin-dependent and independent processes.
This involves actin cytoskeleton reorganization.
Commonly used process by immune cells.

Phagocytosis

Ingestion of large particles (e.g., bacteria, debris).
Nonselective process.
Plasma membrane sends out pseudopodia.
Performed by cells of the Mononuclear Phagocytotic System (MPS).
Uses receptor-mediated pathways.

Receptor-mediated Endocytosis

Specific uptake method, employing cargo receptors for specific molecules (e.g., LDL).
Receptors are found in certain regions of the cell membrane (e.g., lipid rafts).
Molecules enter through coated pits (coated by clathrin).
The vesicle is formed from the plasma membrane.
This is a clathrin-dependent process.

Endosomes

Membrane-enclosed compartments within the cytoplasm, involved in endocytotic pathways.
Two types: Early endosomes (near the cell membrane, initially receive vesicles) and Late endosomes (move to the interior of the cell, eventually fuse into lysosomes).

Plasma Membrane Domains

Apical: faces the lumen/outside of organs, regulates nutrient absorption, secretion, and protection.
Lateral: contact with other cells, communication and intracellular transport.
Basal: contact with the underlying tissues or extracellular matrix, allows cell-substratum adhesion.

Plasma Membrane Modifications

Microvilli (finger-like projections) increase surface area.
Cilia (hair-like appendages) are usually motile, used for movement.
Basolateral folds increase surface area.

Summary Of Vesicle Types

Clathrin-coated vesicles are for receptor-mediated endocytosis.
Coatomer-coated vesicles are for transport between the endoplasmic reticulum (ER) and Golgi apparatus, and Golgi to other locations.
Caveolin-coated vesicles are in cell regions with caveolin proteins, involved in micropinocytosis.

Membrane Transport

Simple Diffusion: Fat-soluble molecules cross the membrane down their concentration gradient; important for O2, CO2.
Carrier Proteins: Help transport water-soluble molecules across the membrane; highly selective and may require energy.
Channel Proteins: Allow specific ions to pass across the membrane, often gated (regulated by signals).

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Description

Test your understanding of the plasma membrane with this quiz, covering its structure, components, and transport mechanisms. Questions explore topics such as lipid rafts and types of microscopy used for observation. Perfect for students studying cell biology and membrane dynamics.