3.4 Plasma Membrane Structure and Function Flashcards
What is the function of the plasma membrane?
- separates the internal environment of the cell from the external environment
- regulates the entrance and exit of molecules from the cell
- helps the cell maintain homeostasis
What is the plasma membrane made up of?
primarily of phospholipids
What do the phospholipids of the membrane form?
a bilayer with the hydrophilic polar heads facing the outside and inside of the cell where water is present, and the hydrophobic nonpolar tails facing each other
What is the fluid consistency of the phospholipid bilayer?
comparable to light oil
What is the fluidity of the plasma membrane regulated by?
steroids such as cholesterol which serve to stiffen and strengthen the membrane
What are peripheral proteins?
proteins that are associate with only one side of the plasma membrane
What are peripheral proteins on the inside of the membrane often held in place by?
cytoskeletal filaments
What are integral proteins?
proteins that span the membrane and can protrude from one or both sides
they are embedded in the membrane but can move laterally, changing their position in the membrane
What do the proteins in the membrane form?
a mosaic pattern
What is the fluid-mosaic model?
combination of proteins, steroids, and phospholipids of the membrane structure
What are glycolipids?
phospholipids with attached carbohydrate chains
What are glycoproteins?
proteins with attached carbohydrate chains
What do glycolipids and glycoproteins play an important role in?
cellular identification
Why are the two halves of the membrane not identical?
the carbohydrate chains occur only on the outside surface and peripheral proteins occur asymmetrically on one surface or the other
Describe the fluid-mosaic model of the plasma membrane?
the membrane is composed of a phospholipid bilayer in which proteins are embedded (integral proteins) or associated with the cytoplasmic side (peripheral proteins)
steroids (cholesterol) help regulate the fluidity of the membrane
cytoskeleton filaments are attached to the inside surface by membrane proteins
What are the functions of peripheral proteins?
- structural role: help stabilize and shape the membrane
- signal pathways
What are the 5 types of integral proteins?
- channel
- carrier
- cell recognition
- receptor
- enzymatic
What are channel proteins?
- involved in the passage of molecules through the membrane
- have a channel that allows a substance to simply move across the membrane
Give an example of a channel protein function.
allows hydrogen ions to flow across the inner mitochondrial membrane
without this movement of hydrogen ions, ATP would never be produced
How must a gate be opened in a channel protein?
by the binding of a specific molecule to the channel
What is cystic fibrosis caused by?
a faulty chloride channel: chloride ion transport is reduced and so is the flow of sodium ions and water
researchers believe that the lack of water causes the mucus in the bronchial tubes and pancreatic ducts to be abnormally thick, therefore interfering with the function of the lungs and the pancreas
What are carrier proteins?
- involved in the passage of molecules through the membrane
- combine with other specific Dsubstances and help it move across the membrane
Give an example of a carrier protein function.
transports sodium and potassium ions across a nerve cell membrane, nerve conduction would be impossible without this carrier protein
What are cell recognition proteins?
glycoproteins that, among other functions, help the body recognize when its being invaded by pathogens so that an immune reaction can occur
Describe MHC (major histocompatibility complex) glycoproteins.
- different for each person, so organ transplants are difficult to achieve
- cells with foreign MHC glycoproteins are attacked by white blood cells responsible for immunity
What are receptor proteins?
- have a shape that allows a specific molecule to bind to it
- the binding of this molecule causes the protein to change its shape and thereby bring about a cellular response
Give an example of a receptor protein function.
the coordination of the body’s organs is totally dependent on receptor proteins
the liver stores glucose after it is signalled to do so by insulin
Why does dwarfism occur?
some type occur not because the body doesn’t produce enough growth hormone, but because the plasma membrane growth hormone receptors are faulty and cannot interact with growth hormone
What are enzymatic proteins?
- carry out metabolic reactions directly
- catalyzes a specific reaction
What do the integral membrane proteins of the electron transport chain do?
carry out the final steps of aerobic respiration
What are enzymes attached to?
some are attached to the various membranes of the cell
What can’t a cell do without the presence of enzymes?
a cell would never be able to perform the metabolic reactions necessary to its proper function
What membrane protein is involved in ATP metabolism?
adenylate cyclase
What does cholera do?
releases a toxin that interferes with the proper functioning of adenylate cyclase which eventually leads to severe diarrhea
