32 Questions
What is the term for the loose carbohydrate coat on the outside surface of a cell?
Glycocalyx
What is the function of the negatively charged carbohydrate moieties on the cell surface?
Repelling other negative objects
What type of junction allows for the exchange of nutrients and wastes between adjacent cells?
Gap junctions
What is the function of carbohydrate moieties as receptor substances?
Binding to hormones
What is the term for the protein attachments between adjacent cells?
Desmosomes
What is the function of the glycocalyx in immune reactions?
Entering into immune reactions
What is the structure inside the plasma membrane of a desmosome?
Disk-shaped structure
What is the purpose of cell junctions?
To join adjacent cells
What is the orientation of the hydrophilic ends of lipid bilayer molecules in a cell membrane?
Exposed to the exterior of the cells and the aqueous cytoplasm
What type of substances can easily pass through the lipid bilayer membrane?
Lipid-soluble substances such as oxygen and alcohol
What is the primary function of integral proteins that provide structural channels?
To allow diffusion of water-soluble substances, especially ions
Where are peripheral proteins typically attached in a cell membrane?
To the inner surface of the membrane
What is the primary function of carrier proteins in a cell membrane?
To transport substances such as sodium and potassium
What is the main characteristic of the hydrophobic ends of lipid bilayer molecules?
They are relatively insoluble
What is the function of receptors in a cell membrane?
To bind to water-soluble chemicals, such as peptide hormones
What is the primary function of peripheral proteins in a cell membrane?
To catalyze chemical reactions in the cell
What is the main function of the cell membrane?
To regulate the transport of materials entering and exiting the cell
What is the approximate percentage of proteins in the cell membrane?
55%
What is the purpose of receptors on the cell membrane?
To receive and respond to hormonal signals
What is the basic structure of the cell membrane?
A lipid bilayer with embedded protein molecules
What percentage of the cell membrane is composed of carbohydrates?
3%
What is the primary function of the lipid bilayer in the cell membrane?
To act as a barrier to the outside environment
What is the role of cholesterol in the cell membrane?
To maintain the fluidity of the membrane
What is the characteristic of the cell membrane that allows it to control the movement of substances?
Semipermeability
What is the primary function of desmosomes in tissues?
To hold together tissues that undergo considerable stress
What is the characteristic of tight junctions?
They are found in cells lining the digestive tract
What is the primary function of gap junctions?
To allow the passage of ions and small molecules between cells
What is a key function of the cell membrane?
To maintain the shape and structure of cells
What is the function of connexons in gap junctions?
To allow the passage of ions and small molecules between cells
What is the function of desmosomes in the heart muscle?
To hold together tissues that undergo considerable stress
What is a characteristic of tight junctions in the digestive tract?
They prevent the movement of materials between cells
What is a function of the cell membrane related to cell movement?
Directed cell movement
Study Notes
Cell Physiology
- The cell membrane is a biological membrane that separates and protects the interior of a cell from the outside environment.
Cell Membrane Composition
- The cell membrane is composed of approximately 55% proteins, 25% phospholipids, 13% cholesterol, 4% other lipids, and 3% carbohydrates.
Cell Membrane Structure
- The basic structure of the cell membrane is a lipid bilayer, interspersed with large globular protein molecules.
- The lipid bilayer has hydrophilic (polar) heads and hydrophobic (nonpolar) tails, which face inward and outward, respectively.
Cell Membrane Permeability
- The lipid bilayer membrane is highly permeable to lipid-soluble substances, such as oxygen, carbon dioxide, and alcohol.
- It acts as a major barrier to water-soluble substances, such as ions, glucose, and urea.
Cell Membrane Proteins
- There are two types of membrane proteins: integral proteins and peripheral proteins.
- Integral proteins protrude all the way through the membrane, providing structural channels (pores) for water-soluble substances and acting as carrier proteins for transporting substances.
- Peripheral proteins are attached to the inner surface of the membrane and function as enzymes that catalyze chemical reactions in the cell.
Carbohydrates in the Cell Membrane
- Membrane carbohydrates occur in combination with proteins or lipids in the form of glycoproteins or glycolipids.
- The carbohydrate moieties attached to the outer surface of the cell have several functions:
- They have a negative electrical charge, giving most cells an overall negative surface charge.
- They attach cells to one another.
- They act as receptor substances for binding hormones.
- They participate in immune reactions.
Cell Junctions
- There are three kinds of cell junctions: desmosomes, tight junctions, and gap junctions.
- Desmosomes are protein attachments between adjacent cells, acting like spot welds to hold together tissues that undergo stress.
- Tight junctions are tightly stitched seams between cells, preventing the movement of material between cells.
- Gap junctions are narrow tunnels that directly connect the cytoplasm of two neighboring cells, allowing the passage of ions and small molecules.
Functions of Cell Membrane
- The cell membrane maintains cell shape and structure.
- It performs a transport function, regulating the movement of materials into and out of the cell.
- It facilitates intercellular communication.
- It enables intracellular adhesion.
- It directs cell movement.
This quiz assesses knowledge of cell membrane definition, composition, and structure, as well as its two types of proteins. Learn about cell physiology and its importance in clinical biochemistry.
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