Membranes and membrane transport Flashcards
What are cell membranes formed of?
Cell membranes are primarily composed of lipid bilayers formed by phospholipids and other amphipathic lipids.
What are phospholipids, and how do they contribute to membrane structure?
Phospholipids have hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails, which allow them to arrange themselves into a bilayer in aqueous environments.
How do amphipathic lipids behave in water?
Amphipathic lipids naturally form continuous sheet-like bilayers in water, with hydrophilic heads facing the aqueous environment and hydrophobic tails oriented inward.
Why is the lipid bilayer crucial for cell membranes?
The lipid bilayer acts as a barrier that separates the interior of the cell from the external environment, maintaining homeostasis and allowing selective permeability.
What role does the fluidity of the lipid bilayer play in membrane function?
- Flexibility: The fluid nature of the lipid bilayer allows the membrane to bend and change shape, enabling cellular processes like endocytosis and exocytosis.
- Movement of proteins: Membrane fluidity permits lateral diffusion of proteins within the bilayer, facilitating their function in processes such as cell signaling and transport.
- Self-healing: The fluid structure of the lipid bilayer enables spontaneous rearrangement of phospholipids to seal small tears, maintaining the integrity of the cell membrane.
How does temperature affect the lipid bilayer?
Temperature changes can influence the fluidity of the lipid bilayer; higher temperatures increase fluidity, while lower temperatures can make it more rigid.
What are some functions of membrane proteins embedded in the lipid bilayer?
Membrane proteins facilitate transport, act as receptors for signaling molecules, provide structural support, and assist in cell recognition.
How do cholesterol molecules influence membrane structure?
Cholesterol molecules interspersed within the lipid bilayer help stabilize membrane fluidity, making membranes less permeable to very small water-soluble molecules that might otherwise pass freely through.
What is meant by “selective permeability” in relation to cell membranes?
Selective permeability refers to the ability of cell membranes to allow certain substances to pass while restricting others, enabling cells to maintain their internal environment.
Why is understanding lipid bilayers important in biology?
Understanding lipid bilayers is crucial for comprehending how cells interact with their environment, how substances are transported across membranes, and how various cellular functions are regulated.
What is the primary function of lipid bilayers in cell membranes?
Lipid bilayers function as effective barriers between aqueous solutions, preventing the passage of certain substances.
Why do hydrophobic hydrocarbon chains form a barrier in membranes?
The hydrophobic hydrocarbon chains create a core that is impermeable to large molecules and hydrophilic particles, including ions and polar molecules.
How does the structure of a lipid bilayer contribute to its barrier properties?
The arrangement of hydrophilic heads facing outward and hydrophobic tails facing inward prevents water-soluble substances from easily crossing the membrane.
What types of molecules have low permeability across lipid bilayers?
Large molecules, ions, and polar molecules cannot easily pass through the hydrophobic core of the lipid bilayer due to their charge or polarity. The hydrophobic core repels these molecules, creating an energetic barrier that prevents their passage through the membrane without the aid of specialized transport proteins.
How do small non-polar molecules interact with lipid bilayers?
Small non-polar molecules can easily pass through lipid bilayers due to their compatibility with the hydrophobic interior of the membrane.
What role do membrane proteins play in relation to lipid bilayer barriers?
Membrane proteins facilitate transport across the lipid bilayer, allowing specific ions and molecules to enter or exit the cell despite the barrier properties of the bilayer. The barrier properties of the lipid bilayer refer to its ability to selectively restrict the passage of molecules and ions, primarily due to its hydrophobic core which repels water-soluble substances. Large molecules, ions, and polar molecules cannot easily pass through the hydrophobic core of the lipid bilayer due to their charge or polarity. The hydrophobic core repels these molecules, creating an energetic barrier that prevents their passage through the membrane without the aid of specialized transport proteins.
How does the selective permeability of lipid bilayers benefit cells?
Selective permeability allows cells to maintain homeostasis by controlling the internal environment and regulating the entry and exit of substances.
What happens when a substance cannot cross the lipid bilayer directly?
Substances that cannot cross the lipid bilayer directly may require transport proteins or vesicular transport mechanisms to enter or leave the cell.
Why is it important for membranes to act as barriers?
- They maintain cellular homeostasis by controlling the movement of substances in and out of cells.
- They protect the cell’s internal environment from harmful external substances and pathogens.
- They allow for the establishment of concentration gradients, which are essential for many cellular processes, including energy production and signal transduction.
- They enable the compartmentalization of cellular functions, allowing different biochemical reactions to occur in specific organelles.
- They provide structural integrity to cells and organelles, maintaining their shape and organization.
How do variations in lipid composition affect membrane permeability?
- Longer phospholipid tails increase membrane thickness, reducing permeability
- Higher unsaturation (e.g., polyunsaturated lipids like DHA) increases fluidity and permeability
- Reduces permeability in unsaturated membranes by increasing lipid order but increases permeability in saturated membranes
What is simple diffusion?
Simple diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentration without the need for energy or transport proteins.
How do lipid bilayers facilitate simple diffusion?
Lipid bilayers allow small non-polar molecules and gases, such as oxygen and carbon dioxide, to pass through easily due to their hydrophobic core.
What is an example of simple diffusion involving oxygen?
Oxygen molecules diffuse across the phospholipid bilayer from areas of higher concentration (outside the cell) to lower concentration (inside the cell) to enter cells for respiration.
How does carbon dioxide move across cell membranes via simple diffusion?
Carbon dioxide molecules diffuse out of cells into the surrounding environment, moving from areas of higher concentration inside the cell to areas of lower concentration outside.