Class test 2 Flashcards
What do membranes do?
Provide the structural basis for metabolic order. Each membrane has its own proteins and precsise enzymatic solution and functions.
what are the functions of the plasma membrane?
-Seperates living cells from their surroundings
- Maintains a constantly controlled intracellular environment
- Selectively permeable (takes up required substances and disposes of unwanted wastes)
What makes up the plasma membrane?
- phospholipid bilayer
- proteins
- steroid lipids
What is characterisitic of the phospholipid bilayer structure
It is ampiphatic: Both hydrophboic and hydrophilic
- Hydrophilic head is made of phosphate group
- Hydrophobic tails made of fatty acid chains
define selective permeability
- the plasma membrane allows some substances to cross more easily than others and blocks passage of somesubstances completley. Type of transport used depends on the type of molecule looking to cross
What is a factor of membrane fluidity?
- depends on the lipid components (staurated or unsaturated hydrocarbons)
- in a living cell, the bilayer has the consistency of salad oil. at lower temperatures, it is more rigid and the motion of the datty chains slow down
define homeoviscous adaptation
when the temperature goes down, the proportion of unsaturated fatty acids goes up and the membrane stays fluid
the longer the fatty acid chains…
the less fluid the membrane is likely to be
what steroid has an effect on plasma mebrane fluidity?
- chloesterol
at high temps, cholesterol stabalizes the membrane, the polar OH groups on cholesterol bind to the phosphate groups pf the phospholipid which restricts its motion. AT low temps, it acts as a spacer between the chain which prevent van der waals interaction.
There are two types of membrane proteins, what are they?
- integral proteins: firmly bound to the membrane, penetrating the core of the lipid bilayer
- ampiphatic (hydrophilic region extends out of the cell, hydrophobic regions inereact with the fatty acid tails)
- some doe not extend fully through the membrane (transmembrane proteins)
- examples are aquaproteins (allow water in and out of the cell) and glycoproteins - peripheral proteins: not embedded in the lipid bilayer. They are located on the inner and outer surface of the membrane
- may be receptors of the cell or enzymes associated with the inner membrane
why is it said that the bilayer is asymmetric?
- there are more protiens attached to one side more than the other
- each side of the membrane has specific characterisitics due to the types of porteins attached
- proteins are asymmetrically oriened, this is produced by the specific way every protein is inserted in the bilayer
how are plasma membrane proteins made?
- peripheral proteins are made byfree ribosomes in the cytoplasm
-integral proteins are made by the ribosomes embedded in the rough ER
what are the 6 main functions of membrane proteins?
- transport
- enzymatic activity
- signal transduction
- cell-to-cell recognition
- intercellular joining
- attachement to the cytoskeleton and ECM
what is the point of cell-to-cell recognition ?
- provides identifucation tags to cells, allows them to be distinguisged among other cells.
what happens when the body lacks cell-to-cell recognition?
- when antiobodies fail to recognize what cells are not freign to our body, the body is said to suffer from an autoimmune disease
ex; rhumatoid arthritis, MS
what is the point of intercellular joining?
allow cells to communicate and forms barriers
-ex: plant cell junctions like the plasmodesmata allows for communication between cells
what is the plasmodesmata ?
- channels that allow rapid chemical communication and sharing of materials between plant cells
- not only ridge the plasma membrane of adjacent cells, but alos their cell walls
what are desmosomes
IN ANIMALS
- attach animla cells to eachother or the ECM without inhibiting the passage of materials between cells.
- very strong
why dont plants have desmosomes
THE REASON WHY PLANTS CELLS DONT HAVE DESMOSOMES IS BECAUSE THEY HAVE A CELL WALL FOR STRENGTH
how do desmosomes fucntion
- dsmosomes have a pair of button-like discs that bind to the cytosolic side of the plasma membrane of adjacent cells and the intercellular protein filaments that connect them
- the intermediate filaments in the cells are attached to the discs and are connected to toher desmosomes
-the intermediate filaments of adjacent cells are therefore connected, so mechanical stresses are districuted throughou the tissue
what are tight junctions
form of interceullar joining that is so tight it prevents substances from leaking between them
- proteins that form tight junctions hold the cells together in actual physical contact, forming a sheet of tissue
ex: tight junctions are often found in the stomach to avoid strong acids from injuring nearby organs and tissues
what are gap juncitons
intercellular joining that bridge the space between animal cells like desmosomes, but the space they span is narrower. contain channels that conect the cytoplasm of adjacent cells, allowing communication
ex: these allow for elctrical communication between animal cells (gap junction in heart permit the flow of ions to synchronize contractions)
what is the point of the attachement of the cytoplasm to the ECM ?
- some proteins do not move freely within the plasma membrane they are fixed and help keep the membrane in place
- these proteins are non-covalently bonded to the cytoskeleton and to fibers of the adjacent ECM
what is the ECM?
ECM is made of extracellular fluid, a gel-like substance made of carb and fibrous proteins
- the most prominent protein is collagen
- fibronectins (glycoprotein) heps organize the matrix and also aid cells in attaching to the matrix by binding to proteins that extend from the plasma membrane