Untitled Quiz

The plasma membrane consists of a phospholipid bilayer, proteins, carbohydrates, and cholesterol.
The phospholipid bilayer is composed of amphipathic molecules, meaning they have both hydrophilic (water-loving) and hydrophobic (water-fearing) regions.
The hydrophilic heads are composed of polar phosphate groups and are located in the outside and inside surfaces of the membrane.
The hydrophobic tails are composed of non-polar fatty acids and face each other in the interior region of the membrane.
Proteins are embedded in the phospholipid bilayer, either partially or wholly, and can be classified as integral or peripheral proteins.
Integral proteins are embedded in the phospholipid bilayer and span the membrane with their hydrophobic regions while their hydrophilic regions protrude from both surfaces.
Peripheral proteins are found only on the cytoplasmic side of the membrane and can be held in place by attachments to protein fibers of the cytoskeleton (inside the cell) or fibers of the extracellular matrix (ECM) (outside the cell).
Carbohydrate chains are attached to the outside surface of the membrane and project into the extracellular matrix (ECM).

Channel proteins form channels within the phospholipid bilayer, allowing small water-soluble molecules to pass through.
Carrier proteins have binding sites for specific molecules, change shape when a molecule binds, and transport the substance across the membrane.
Cell recognition proteins (glycoproteins and glycolipids) serve as surface receptors for cell recognition and identification, playing a crucial role in the immune system.
Receptor proteins act as binding sites, especially for hormones, and trigger cell responses through signaling pathways.
Enzymatic proteins embedded in membranes attract reacting molecules to the membrane surface, allowing enzymes needed for metabolic pathways to be aligned for efficient reactions.
Junction proteins (Cell Adhesion Proteins) facilitate cell-to-cell junctions, such as tight junctions, which allow cells to adhere to each other.

Only animal cells have an ECM, composed of various protein fibers and complex carbohydrate molecules.
The ECM supports the plasma membrane and aids communication between cells.
Both phospholipids and proteins can have attached carbohydrate chains, forming glycolipids and glycoproteins, respectively.
In animal cells, the carbohydrate chains of proteins create a "sugar coat" called the glycocalyx, which protects the cell and has various functions.

Cholesterol is a lipid found in the animal plasma membrane.
Cholesterol maintains the stability of the plasma membrane and affects its fluidity.

The fluid-mosaic model describes the plasma membrane as a fluid structure with embedded proteins.
The fluidity of the membrane is attributed to its lipid component, with the phospholipid bilayer having the consistency of olive oil at body temperature.
The membrane's fluidity increases with a higher concentration of unsaturated fatty acid residues.
Cholesterol stiffens the membrane at higher temperatures and prevents it from freezing at lower temperatures.
The mosaic nature of the membrane arises from its protein content, which can vary in number and type.

The plasma membrane regulates the movement of materials into and out of the cell, including gases, water, minerals, food, and waste products.
Transport can be passive (no energy required) or active (requires energy).

Passive transport involves the movement of molecules down their concentration gradient, from high concentration to low concentration.
Simple diffusion is a passive process where small, non-polar, non-charged, and lipid-soluble molecules move directly through the phospholipid bilayer.
Osmosis is the movement of water molecules across a semipermeable membrane from a region of higher water concentration to a region of lower water concentration.
Facilitated diffusion involves the movement of large polar molecules (e.g., glucose, amino acids) or ions through protein channels or carriers down their concentration gradient.

Active transport moves ions or other substances against their concentration gradient, from low concentration to high concentration.
Active transport requires energy, such as that supplied by ATP.
An example of active transport is the Na-K Pump.

Bulk flow refers to the movement of large molecules in cells, using vesicles or vacuoles.
Bulk flow requires energy.

In exocytosis, a cytoplasmic vesicle merges with the plasma membrane and releases its contents to the outside of the cell.
Exocytosis is involved in secretion of proteins and waste products.

Endocytosis involves the plasma membrane sinking inward, pinching off, and forming a vesicle to bring large particles into the cell.
The vesicle often merges with the Golgi body for processing and sorting of its contents.

Phagocytosis ("cell eating") involves the membrane engulfing solid particles, such as bacteria, cell debris, or food.
Pinocytosis ("cell drinking") involves the cell bringing in fluids containing suspended materials, such as movement of blood.