Chapter 5 & 8 Flashcards
What are general functions of the plasma membrane?
Provide a selectively permeable barrier, transport solutes in and out of membrane, bind ligands to communicate extracellular cell signals and regulate interactions between cells
What are the three dynamic properties of the cell membrane?
Movement, division, fusion
What does the fluid-mosaic model say about the plasma membrane?
Describes function:
-Main function is to transport solutes in and out of membrane and maintain permeability
Describes fluidity:
-It says that phospholipids are free to move within the bilayer
Describes structure:
-There are two opposite facing leaflets that contain polar heads and an inner leaflet that contains hydrophobic tails
- There are also integral proteins embedded in the membrane and peripheral proteins loosely associated with the membrane on the outside and inside of the cell
How do cell plasma membranes vary across different cells in the body?
Different cells contain different composition of their plasma membrane. For example, the ratio of lipid to protein varies depending on the type of cell membrane.
What kinds of molecules make up the plasma membrane?
The majority are phospholipids, then fatty acids, triacylglycerols, steroids, cholesterol, sphingolipids, and waxes.
What are the two types of passive transport across the cell membrane?
Simple diffusion and facilitated diffusion
What is simple diffusion?
It’s when a substance moves from an area of high concentration to an area of low concentration, directly through the semipermeable membrane without assistance of other proteins. All nonpolar molecules like carbon dioxide & O2 can diffuse freely through membrane. Even big nonpolar molecules.
What is facilitated diffusion??
When a substance moves from an area of high concentration to an area of low concentration, with the help of a membrane protein such as a channel protein or carrier protein.
-charged and POLAR substances use this method of passive transport.
What are the three types of facilitated diffusion?
Ungated channel, voltage-gated channel, ligand-gated channel
Ungated facilitated diffusion
There is no regulation required here, the molecule merely travels through the protein channel. An example is potassium leak channel which contributes to the negative resting membrane potential of the cell.
Voltage gated facilitated diffusion
The protein channel that allows the molecule to pass through is activated and deactivated by the membrane potential change. For example, depolarization of the membrane causes sodium channels to open and sodium to rush into the cell.
Ligand gated facilitated diffusion
This involves the binding of a ligand which causes the protein channel to open or close. An example is a Cl- channel which activates when the neurotransmitter GABA binds to it, causing hyper polarization of the cell.
What are lipid rafts?
A collection of similar lipids clustered, and regions of the membrane that serves as attachment points for other signaling biomolecules. Contain a lot of cholesterol in them. They don’t travel as fast as single phospholipids throughout the membrane.
What are micelles?
Closed lipid monolayers with fatty acids tails pointing towards the middle and the polar head groups on the outside.
What are liposomes?
Donut shaped lipid bilayer. Hydrophilic heads on the outside layer and innnermost layer both pointing to aqueous solution. Inside of the donut has hydrophobic fatty acid tails.
Describe the two uncatalyzed movements of phospholipids in the membrane.
- Lateral diffusion - phospholipids diffuse across the cell membrane within one leaflet moving up/down and side to side. This movement is fast and common.
- Flip-flop trans-bilayer diffusion - phospholipids move between two membrane leaflets. This movement is very slow and rare.
Describe the catalyzed movement of phospholipids in the membrane that uses ATP.
Using ATP, the flippase enzyme flips the phospholipid from the outer leaflet to inner leaflet. The floppase enzyme flips the phospholipid from the inner leaflet to the outer leaflet.
Describe the catalyzed movement of phospholipids in the membrane that doesn’t use ATP.
The scramblase enzyme, which doesn’t use ATP flips one phospholipid in one direction and another phospholipid in the opposite direction.
What are the three factors that affect membrane fluidity?
Temperature, cholesterol, fatty acids
How does temperature affect membrane fluidity?
High temperature causes increased membrane fluidity. Low temperature causes decreased membrane fluidity.
Why does cholesterol decrease membrane fluidity at high temperatures?
At high temperatures, the phospholipids are spaced far apart. Cholesterol inserts itself between the phospholipid, making it harder for them to move.
Why does cholesterol increase membrane fluidity at low temperatures?
At low temperatures, phospholipids are tightly packed together. Cholesterol inserts itself between the tightly packed phospholipids thus creating a larger space for them to move and increasing membrane fluidity.
How do fatty acids affect membrane fluidity?
Saturated fatty acids decrease membrane fluidity because there are no double bonds, causing phospholipids to be packed tightly.
Unsaturated fatty acids have double bonds which create kinks, increasing the space between phospholipids and increasing membrane fluidity.
_______ proteins are located in the lipid bilayer.
Integral
What are the two types of integral proteins?
Transmembrane proteins that pass completely through the lipid bilayer.
Embedded proteins that only pass through one leaflet of the lipid bilayer and protrude either intracellularly or extracellularly.
________ proteins don’t touch the lipid bilayer, they are located on the intracellular side or extracellular side.
Peripheral
How are peripheral proteins bound to the lipid bilayer?
They are bound through noncovalent interactions to G proteins, polar head groups, other integral proteins, and in lipid raft regions.
What are lipid-anchored proteins?
They are proteins covalently anchored on the plasma membrane to hydrocarbon fatty acids in the lipid bilayer.
Where are carbohydrates located in the cell membrane and what role do they play?
Carbohydrate sugars are attached to proteins on the extracellular surface of the cell, forming a glycoprotein coat when interacting with water. They play an important role in cell signaling, “giving face to the cell”.
Where are gap junctions most prevalent in the body?
They are prevalent in the heart where they allow the rapid spread of ion current through cardiac muscle and between smooth muscle cells.
What are gap junctions made of?
They are channel proteins made of six connexin protein subunits arranged in a ring formation with a central opening. They pass through the lipid bilayers of cells connecting 2 cells together.
What is the function of gap junctions?
They allow for the passage of ions, amino acids, cAMP, ATP, and nucleosides between cells. These channels are regulated by phosphorylation.
Where are tight junctions found?
They are found in epithelial cells in the stomach, intestine, bladder, and capillaries in the blood brain barrier.
What is the function of tight junctions?
They are integral proteins that form continuous bands around the cell to prevent solute from leaking into the extracellular space between cells. They create a water-tight seal.
Where are desmosomes primarily found?
They are found in epithelial skin cells (epidermis), heart muscle, and the intestines.
What is the main function of desmosomes?
They aid in structural support and tensile strength of tissue. They connect cells together by binding to intermediate filaments in the cytoplasm and connecting cells via cadherin bridges in the ECM.
What is the main function of hemidesmosomes?
They are integrin protein sites involved in attaching cells to the ECM. Usually, hemidesmosomes connect to the basement membrane of the epithelium.
What are hemidesmosomes made of?
They are made of a dense plaque like proteins with projecting keratin filaments on the intracellular side, with a membrane spanning integrin protein that connects to laminin in the ECM.
What is the structure of sphingolipids?
Sphingolipids have a sphingosine backbone which is made of a long hydrocarbon chain with a double bond connecting to 2 alcohol groups and an amine group. A fatty acid chain connects to the amine group and a polar head group connects to the outermost OH group.
What is the structure and function of vitamin A?
Also known as “carotene”. It is composed of an unsaturated hydrocarbon chain, and its functions include vision, growth, development, and immune function.
A metabolite of vitamin A is retinal which is part of the photoreceptor transduction pathway in the human eye.
What is the structure and function of vitamin D?
Also known as “cholecalciferol”. It is part vitamin/part hormone. It had several rings as well as side chains. Vitamin D is converted to its active form in the liver and kidneys. Its function is to increase calcium and phosphate uptake in the intestines. it is important for the growth and development of bones and teeth.
What is the structure and function of vitamin E?
Also known as tocopherol and tocotrienol. it is composed of a hydrophobic substituted, aromatic ring, with a long isoprenoid side chain.
It functions as a biological antioxidant that reacts with free radicals to prevent oxidative damage in the body.
What is the structure and function of vitamin K?
There are different groups of vitamin K called “phylloquinone and menaquinone” . They are composed of a long hydrocarbon chain with 2 cyclohexanes at the end.
They are vital in posttranslational modifications to form prothrombin, which is a clotting factor in the blood.
