Transport in Cells Flashcards
(17 cards)
Describe the fluid-mosaic model of cell and organelle membranes.
The fluid-mosaic model describes the structure of cell and organelle membranes as a mixture and movement of phospholipids, proteins, glycoproteins, and glycolipids. Cholesterol is also present in some membranes, restricting the lateral movement of other molecules in the membrane, making the membrane less fluid at high temperatures, and preventing water and dissolved ions from leaking out of the cell.
How do phospholipids align in a cell membrane?
Phospholipids align as a bilayer in a cell membrane due to the hydrophilic heads being attracted to water and the hydrophobic tails being repelled by water.
Define peripheral and integral proteins in the context of a cell membrane.
Peripheral proteins in a cell membrane do not extend completely across the membrane and provide mechanical support or connect to proteins or lipids to make glycoproteins and glycolipids. Integral proteins span across from one side of the bilayer to the other and are involved in the transport of molecules across the membrane.
Explain the role of protein channels and carrier proteins in a cell membrane.
Protein channels in a cell membrane form tubes that fill with water to enable water-soluble ions to diffuse. Carrier proteins bind with other molecules and larger molecules, such as glucose and amino acids, and change shape to transport them to the other side of the membrane.
What is a partially permeable membrane?
A partially permeable membrane is the cell-surface membrane created by the arrangement of molecules within the phospholipid bilayer. It allows certain molecules or ions to pass through it by diffusion.
Define simple diffusion as a mode of transport in and out of cells.
Simple diffusion is the net movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached. It is one of the five key modes of transport in and out of cells.
Describe the process of simple diffusion.
Simple diffusion is a passive process that does not require ATP. Molecules move due to their kinetic energy, allowing them to constantly move in fluids. For molecules to diffuse across the membrane, they must be lipid-soluble and small. Examples of such molecules include oxygen and carbon dioxide.
Define facilitated diffusion and how it differs from simple diffusion.
Facilitated diffusion is also a passive process that does not require ATP, but it differs from simple diffusion as proteins are used to transport molecules. The movement of ions and polar molecules, which cannot simply diffuse, can be transported across membranes by facilitated diffusion using protein channels and carrier proteins.
How do protein channels and carrier proteins function in facilitated diffusion?
Protein channels form tubes filled with water, enabling water-soluble ions to pass through the membrane. They only open in the presence of certain ions when they bind to the protein. Carrier proteins bind with a molecule, such as glucose, causing a change in the shape of the protein. This shape change enables the molecule to be released to the other side of the membrane.
Define osmosis and explain the concept of water potential.
Osmosis is the movement of water from an area of higher water potentials to an area of lower water potential across a partially permeable membrane. Water potential is the pressure created by water molecules, measured in kPa and represented with the symbol Ψ. Pure water has a water potential of zero, and when solutes are dissolved in water, the water potential becomes negative. The more negative the water potential, the more solute must be dissolved in it.
What is an isotonic solution?
An isotonic solution is when the water potential is the same in the solution and the cell within the solution.
What does it mean when a solution is hypotonic?
A solution is hypotonic when the water potential of the solution is more positive (closer to zero) than the cell.
Define the term ‘Hypertonic’ in the context of cell biology.
Hypertonic refers to a solution with a more negative water potential than the cell. In such a solution, both animal and plant cells will shrink and become shrivelled due to large volumes of water leaving the cell by osmosis.
Describe what happens to an animal cell when placed in a hypotonic solution.
When an animal cell is placed in a hypotonic solution such as pure water, a lot of water will move into the cell by osmosis. Since animal cells do not have a cell wall, the pressure will cause the cell to burst.
Explain the process of active transport in cell biology.
Active transport is the movement of molecules and ions from an area of lower concentration to an area of higher concentration (against the concentration gradient) using ATP and carrier proteins. The carrier proteins act as pumps to move substances across the membrane. This process is very selective, as only certain molecules can bind to the carrier proteins to be pumped.
How does ATP and carrier proteins function in active transport?
Certain molecules can bind to the receptor site on carrier proteins. ATP binds to the protein on the inside of the membrane and is hydrolysed into ADP and Pi. This causes the protein to change shape and open towards the inside of the membrane, releasing the molecule on the other side. The Pi molecule is then released from the protein, causing the protein to revert to its original shape.
Describe the process of co-transport in the context of sodium and glucose ions absorption.
In co-transport, sodium ions are transported by active transport from the epithelial cells to the blood via a protein carrier. This lowers the concentration of sodium in the epithelial cell, creating a concentration gradient between the ileum and the epithelial cell.
