Topic 2B: Cell Membranes Flashcards
What is the main structural component of the cell membrane?
The phospholipid bilayer.
Why is the cell membrane described as a fluid-mosaic model?
It is fluid because phospholipids move are constantly moving, proteins are scattered throuhg the bilayer like tiles in a mosaic and contain other molecules such as cholesterol, glycolipids, Proteins( channel, carrier, glycoproteins and receptor proteins)
What is the function of phospholipids in the cell membrane?
They form a barrier that is selectively permeable, allowing small, non-polar molecules to diffuse through.
What is the role of cholesterol in the membrane?
It increases membrane stability by reducing fluidity, especially at high temperatures.
What are the two types of membrane proteins, and their functions?
~Intrinsic proteins (integral proteins): Span both bilayers of the plasma membrane and aid transport (e.g., carrier and channel proteins).
~Extrinsic proteins (peripheral proteins): Found on the surface of the plasma membrane, involved in cell signaling and recognition (e.g. receptor proteins).
What is the role of glycoproteins and glycolipids in the membrane?
~Glycoproteins functions as the receptors for chemical signaling.
~Glycolipids facilitate cellular recognition.
How does temperature affect membrane permeability?
~Low temperatures: Membrane becomes rigid, reducing permeability.
~High temperatures: Phospholipids move more, making the membrane more permeable; extreme heat can denature proteins.
What is diffusion?
The passive net movement of molecules from a high concentration to a low concentration down a concentration gradient.
What type of molecules can diffuse directly through the phospholipid bilayer?
Small, non-polar molecules (e.g., oxygen, carbon dioxide).
What is facilitated diffusion?
The movement of larger or charged molecules across the membrane via carrier or channel proteins.
How do channel proteins work?
They provide a hydrophilic pathway for specific ions to pass through the membrane.
How do carrier proteins work in facilitated diffusion?
They change shape when a molecule binds, allowing it to cross the membrane.
What factors affect the rate of diffusion?
~Concentration gradient: A steeper gradient increases the rate.
~Surface area: A larger surface area increases the rate.
~Thickness of membrane: A thinner membrane increases diffusion speed.
~Temperature: Higher temperatures increase kinetic energy and diffusion speed.
What is osmosis?
The diffusion of water from an area of high water potential to low water potential through a partially permeable membrane.
What is water potential measured in?
Kilopascals (kPa).
What is the water potential of pure water?
0 kPa (the highest possible water potential).
How does adding solutes affect water potential?
It lowers the water potential (makes it more negative).
What happens to an animal cell in a hypotonic solution (higher water potential outside)?
Water enters the cell, causing it to swell and possibly burst (lysis).
What happens to an animal cell in a hypertonic solution (lower water potential outside)?
Water leaves the cell, causing it to shrink (crenation).
What happens to a plant cell in a hypotonic solution?
It becomes turgid (swollen but does not burst due to the cell wall).
What happens to a plant cell in a hypertonic solution?
It becomes plasmolysed (the cytoplasm pulls away from the cell wall).
What is active transport?
The movement of molecules against a concentration gradient using ATP and carrier proteins.
How do carrier proteins work in active transport?
They bind to the molecule, change shape, and transport it across the membrane using ATP.
How does ATP provide energy for active transport?
ATP is hydrolyzed into ADP + Pi, releasing energy.
What is co-transport?
A form of indirect active transport, where one molecule moves down its gradient while another moves against it.
How does sodium-potassium pump work in active transport?
It pumps 3 Na⁺ ions out and 2 K⁺ ions in, maintaining a concentration gradient.
What is an example of co-transport in the body?
The absorption of glucose in the small intestine using sodium ions (Na⁺).
How does glucose enter intestinal epithelial cells?
~Sodium-potassium pump actively transports Na⁺ out of the cell.
~Sodium-glucose co-transporter brings Na⁺ and glucose in together.
~Glucose moves into the blood by facilitated diffusion.
What is a Cell membrane?
A selectively permeable barrier that controls what enters and exits the cell.
What is Phospholipid bilayer?
The double-layered structure of the membrane, with hydrophilic heads and hydrophobic tails.
What is Cholesterol?
A lipid that stabilises the membrane by reducing fluidity.
What is Water potential?
The ability of water to move, measured in kPa.
What is a Hypertonic solution?
A solution with a lower water potential than the cell, causing water to leave the cell.
What is a Hypotonic solution?
A solution with a higher water potential than the cell, causing water to enter.
What does turgid mean?
A plant cell full of water, pressing against the cell wall.
What is Plasmolysis?
The shrinking of the cytoplasm away from the cell wall in a plant cell.
What is a Sodium-potassium pump?
A protein pump that moves Na⁺ out and K⁺ in, using ATP.
