Membrane structure and Function Flashcards
Why are cell membranes primarily composed of lipids?
Lipids are hydrophobic, which creates a seperation of water into internal (inside the cell) and external (outside the cell) environments.
What does the fluid mosaic model propose about the cell membrane?
That the structure of the cell membrane is not one rigid structure. Instead, it is a mosaic of various lipids, proteins and other molecules that move and flow.
True or false: Lipid molecules exist as a double layer (bilayer)
True.
Explain how lipid molecules form a bilayer structure
Phospholipids have a polar head (glycerol and phosphate) and a nonpolar tail (fatty acid).
The hydrophilic (polar head) section points outwards, while the hydrophobic (nonpolar tail) are point inwards away from the water.
The nonpolar tail from another phospholipid will bind through hydrophobic interactions to the first, forming two layers.
How do saturated fatty acids influence the fluid state of the cell membrane?
Saturated fatty acids form strong, rigid bonds because of the single bonded carbons. These bonds hold the membrane tightly together.
Too many saturated fatty acids results in a cell membrane that is too viscous. This hinders the ability for important molecules (Ex. O2) to diffuse across the membrane. It can also hinder the ability for membrane proteins to function.
How do unsaturated fatty acids affect the fluidity of the cell membrane?
Unsaturated fatty acids can decrease the attraction between fatty acids due to the double bonded carbons, which cause the nonpolar tails to curl. This increases the fluidity of the membrane.
Too many unsaturated fatty acids result in a cell membrane that is too fluid, which compromises it’s ability to act as a barrier. Too many substances will pass through the membrane, disrupting the internal environment of the cell.
How does temperature affect the saturated and unsaturated bonds in a cell membrane?
Colder temperatures: Saturated fatty acid tails pack more tightly together, forming a more rigid membrane.
Warmer temperatures: Unsaturated fatty acids spread out from one another, forming a more fluid membrane.
Why is it important to have both saturated and unsaturated fatty acids within a cell membrane?
Having both saturated and unsaturated bonds allows for a balance of structure and fluidity.
It’s also important for managing changes in temperature.
When it’s cold, unsaturated bonds help maintain membrane fluidity with their bends.
When it’s warm, saturated bonds keep the membranes structure stable with their strong bonds.
Why is cholesterol important to the cell membrane?
Helps the cell membrane maintain fluidity across a wide range of temperatures.
It works by keeping the hydrophobic tails seperated at low temperatures and stopping the tails from moving too far apart at higher temperatures.
What are the four categories of membrane proteins that can exist on the cell membrane?
Transport proteins.
Enzymatic proteins.
Signaling proteins.
Attachment and Recognition proteins.
What is the function of transport proteins?
To facilitate the movement of substances across the membrane that would otherwise be unable to diffuse across. This allows the uptake of nutrients and removal of waste from the cell.
Specifically useful for transporting charged and polar substances.
What is the function of enzymatic proteins?
To catalyze reactions near or at the membrane. They facilitate chemical reactions that are necessary for the functioning of the cell.
What is the function of signaling proteins?
Signaling proteins bind to specific chemicals, like neurotransmitters or hormones, which trigger internal mechanisms in the cell.
This allows a cell to respond to changes in it’s external environment.
What is the function of attachment and recognition proteins?
Attachment and recognition proteins span both the internal and external portion of the membrane.
The internal portion binds to the cell membrane of organelles, ensuring they maintain their position within the cell.
The external portion binds to cytoskeleton components of other cells, allowing for communication between different cells. They may also be involved in cell recognition (detecting whether a cell is normal or foreign) or attachment, as well as immune response.
What are the two types of membrane proteins?
Integral: Embedded within the lipid bilayer, and go all the way through the membrane.
Peripheral: Found on the internal or external surface.
What must an integral membrane protein contain in it’s structure?
It must contain at least one hydrophobic section so it can interact with the hydrophobic tails of the membrane.
What is the structure of a glycolipid and what does it do?
Structure: A lipid (usually a fatty acid) attached to a short carbohydrate chain (usually oligosaccharide).
Function: Immune system markers that aid in cell recognition (self vs foreign cells).
What is the structure of a glycoprotein and what does it do?
Structure: A protein with a carbohydrate chain attached.
Function:
Helps with cell adhesion to form tissues.
May also act as receptors to bind molecules and trigger cellular responses.
Also form antigens (form blood types).
