1.5 The Cell Membrane Flashcards
What is the main function of the cell membrane?
Controlling the exchange of materials between the internal and external environments. It separates the internal environment from its surroundings.
Mostly consists of what two molecules?
- Phospholipids (and other lipids such as cholesterols)
- Membrane proteins
What is used to describe the structure of the cell membrane?
Fluid Mosaic Model
Describe the Fluid-Mosaic Model of the cell membrane, including the role of phospholipids and proteins:
It is a bilayer of phospholipids with proteins embedded in it. The role of the phospholipids is to create the barrier between the internal and external cell and to control the movement of materials in and out of the cell. The role of the protein is to help transport materials in and out of the cell which can’t get through the phospholipid bilayer directly.
Where are hydrophilic phospholipid ‘heads’ positioned?
Towards the outer edge of the cell membrane. Hydrophilic heads are water loving/attracting.
Where are hydrophobic phospholipid ‘tails’ positioned?
Inwards towards the centre of the bilayer. Hydrophobic tails are water repelling/hating.
Explain phospholipid
The phospholipids have a hydrophilic head containing phosphates and hydrophobic tails derived from fatty acids.
What are membrane proteins, and examples?
They help transport materials in and out of the cell which can’t get through the phospholipid bilayer directly. There are larger proteins which span the width of the membrane and smaller proteins that sit within the bilayer. Channel and integral proteins are larger. Peripheral proteins are smaller.
Glycoproteins:
Membrane proteins with a carbohydrate chain attached to them.
Glycolipids:
Phospholipids with carbohydrate chains attached to them.
Cells need to exchange materials:
With their external environment. Exchanged materials include gases, nutrients and waste products.
The structure of the cell membrane allows it to control the exchange of materials.
What is the membrane described as and why?
The membrane is described as semi-permeable because it can control substances that pass through it.
What are the three factors influencing transportation?
- Size: Only very small molecules such as gases, like oxygen and carbon dioxide are freely exchanged, larger molecules such as many proteins cannot.
- Charged ions: Atoms or molecules with a charge can only be exchanged if the specific membrane proteins (transport proteins) are used.
- Water solubility: Water and hydrophilic molecules can only be exchanged if specific membrane proteins are used.
The two characteristics of the membrane that allow for selective exchange of materials are:
- Lipid nature of the membrane
- Proteins embedded in the lipid bilayer
How does the cell need to be controlled to ensure the cells function properly?
Intracellular environments need to be controlled to ensure the cell functions properly.It’s substances such as pH, glucose concentrations, water and solute (ion concentration needs to be balanced and highly controlled.
What is passive transport?
Passive transport occurs by atoms or molecules moving from high concentration to low concentration solutions. The movement of the atoms is called passive transport as it does not require energy in order to pass the membrane.
What is diffusion?
Diffusion is the transport of a substance from a region of high concentration to a region of low concentration until an equilibrium has been reached (both regions have the same concentration).
What is a solution with a high solute concentration defined as:
It is defined as one that has fewer water molecules than that of a low solute concentration.
What is simple diffusion?
Simple diffusion is where no energy is required and no protein is needed for transportation passed the membrane. Small uncharged molecules, such as oxygen and carbon dioxide, pass the membrane by using it.
What is facilitated diffusion?
The passive transport of substance across a membrane through a transport protein. They cannot pass the membrane without the protein to facilitate the diffusion. These are by substances that are hydrophilic such as glucose and some ions
What is osmosis?
Osmosis is the movement of water molecules from a solution with a high concentration of water molecules to a solution with a lower concentration of water molecules, through a cell’s semipermeable membrane.
What is solute?
Solute is the substance dissolved in the water.
What is a rate of exchange factor?
- Surface area to volume ratio of the cell
Why is surface area to volume ratio used?
To explain the amount of external surface area of the cell to the volume of the cytoplasm.
