Biology Ch. 5
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Cell membrane bilayer of phospholipids with embedded and attached proteins.
What steroid helps stabilize the cell membrane?
What message-transfer process is the binding of a signaling molecule that triggers a change in the protein, then relays the message into the cell, activating molecules that perform specific functions?
Allows some substances to cross the cell membrane more easily than others.
Review the six different types of functions that proteins in a plasma membrane can perform.
- 1. Attachment to the cytoskeleton and ECM
- 2. Signal Transduction
- 3. Enzymatic Activity
- 4. Cell-Cell Recognition
- 5. Intercellular Joining
- 6. Transport
What are the key ingredients of biological membranes?
What is a basic requirement for the life of a cell?
That the plasma membrane allows cells to regulate their exchanges with the enviornment.
Thermal Motion (heat)
Molecules that vibrate and move randomly.
The tendency for particles of any kind to spread out evenly in an available space.
How does diffusion work?
The solute diffuses down it's concentration gradient and eventually with have equal concentrations on each side.
- When molecules diffuse across a membrane without having to do any work, like diffusion.
- Nonpolar, hydrophobic molecules can dissolve in the lipid bilayer of a membrane and cross it with ease.
- The driving force is the concentration gradient.
What is osmosis?
The diffusion of water across a membrane. One of the most important substances that crosses a membrane by passive transport.
What is a solute?
A substance that dissolves in a liquid solvent, producing a solution.
Refers to the ability of a surrounding solution to cause a cell to gain or lose water.
Referring to a solution that, when surrounding a cell, has no effect on the passage ofwater into or out of the cell.
Referring to a solution that, when surrounding a cell, will cause the cell to take up water.
Referring to a solution that, when surrounding a cell, will cause the cell to lose water.
The control of water balance. A cell must have a way to prevent excessive uptake or excessive loss of water.
A type of passive transport. Polar or charged substances have to move across a membrane with the help of specific transport proteins.
Discovered by Peter Agre in 2003. A protein channel that very rapidly diffuses water into and out of certain cells.
When a cel must expend energy to move a solute against its concentration gradient (across a membrane toward the side where the solute is more conentrated.)
Define the process of active transport.
- 1. Solute molecule attaches to specific binding sites on the transport protein.
- 2. ATP transfers a phsphate group to the transport protein.
- 3. The protein changes shape in a way that solute is released on the other side of the membrane.
- 4. The phosphate group detaches, and the transport protein returns to its original shape.
How do large molecules cross cell membranes?
Through exocytosis and endocytosis.
(Greek: exo: outside, kytos: cell)
Process to export bulky materials such as proteins and polysaccharides. The vesicle fuses with the plasma membrane and its contents spill out of the cell when the vesicle membrane becomes part of the plasma membrane.
(Greek: endo: inside, kytos: cell)
A transport process that is the opposite of exocytosis. A cell takes in large molecules when a depression in the plasma membrane pinches in and forms a vesicle enclosing material that has been outside the cell.
Name three types of endocytosis.
- 1. Phagocytosis
- 2. Pinocytosis
- 3. Receptor-Mediated Endocytosis
What is phagocytosis?
"Cellular eating." A cell engulfs a particle by wrapping extensions called pseudopodia (a temporary extension) around it and packaging it within a membrane-enclosed sac large enough to be called a vacuole.
What is pinocytosis?
"Cellular drinking." The cell gulps droplets of fluid into tiny vesicles. Pinocytosis is not specific; it takes in any and all solutes dissolved in the droplets.
Highly selective receptor proteins for specific molecules are embedded in regions of the membrane that are lined by a layer of coat proteins. The plasma membrane indents to form a coated pit, whose receptor proteins have picked up particular molecules from the surroundings. The coated pit then pinches closed to form a vesicle that carries the molecules into the cytoplasm.
The capacity to cause change or to perform work.
Name two types of energy.
- 1. Kinetic energy
- 2. Potential energy
The energy of motion. Moving objects can perform work by transferring motion to other matter.
Heat (Thermal Energy)
A type of kinetic energy associated with the random movement of atoms or molecules. Energy is converted to head in most energy transformations, a disordered form of energy.
The second main form of energy, matter that possesses as a result of its location or structure. ATP is potential energy, or water behind a dam.
The most important type of energy for living organisms; it is the energy that can be transformed to power the work of the cell. The potential energy available for release in a chemical reaction.
- The study of energy transformations that occur in a collection of matter.
- System - the matter under study
- Surroundings- everything outside the system
First Law of Thermodynamics
- Known as the law of energy conservation.
- States that the energy in the universe is constant. Energy can be transferred and transformed, but it cannot be created or destroyed.
Quantity of disordered energy or randomness. The more randomly arranged a collection of metter is, the greater its entropy.
Second Law of Thermodynamics
Energy conversions increase the entropy (disorder) of the universe.
Chemical energy stored in organic molecules that are converted to a form that the cell can use to perform work. Cells release energy from fuel molecules.
Name two types of chemical reactions.
Exergonic and Endergonic
A chemical reaction that releases energy. Begins with reactants whose covalent bonds contain more energy than those in the products. The reaction releases to the surroundings an amount of energy equal to the difference in potential energy between the reactants and the product.
Yield products that are rich in potential energy. Starts out with reactant molecules that contain relatively little potential energy. Energy is absorbed from the surroundings as the reaction occurs, so the products of an endergonic reaction contain more chemical energy than the reactants did.
The total of an organism's chemical reactions.
A series of chemical reactions that either builds a complex molecule or breaks down a complex molecule into simpler compounds.
The use of energy released from exergonic reactions to drive essential endergonic reactions. It is a crucial ability of all cells.
What molecules are key to energy coupling?
ATP (Adenosine Triphosphate)
What powers nearly all forms of cellular work?
ATP (Adenosine Triphosphate)
Define the parts of ATP.
- Adenosine part: consists of adenine, a nitrogenous base, and a ribose, a five-carbon sugar.
- Triphosphate part: three negatively charged phosphate groups. These groups are unstable and can readily be broken by hydrolysis.
How is ADP created.
ADP (Adenosine Diphosphae) is created when the bond to the third phosphate group of ATP is broken by hydrolysis and energy is released (phosphate.)
The phosphate transfer from ATP to some other molecule. Nearly all cellular work depends on ATP energizing molecules by phosphorylating them.
Name three types of cellular work.
- 1. Chemical work
- 2. Mechanical work
- 3. Transport work
The phosphorylation of reactants provides energy to drive the endergonic synthesis of products.
The transfer of phosphate groups to special motor proteins in muscle cells causes the proteins to change shape and pull on protein filaments, in turn causing the cells to contract.
ATP drives the active transport of solutes across a membrane against their concentration gradient by phosphorylating transport proteins.
Explain how ATP transfers energy from exergonic to endergonic processes in the cell.
Exergonic processes phosphorylate ADP to from ATP. ATP transfers energy to endergonic processes by phosphorylating other molecules.
What speeds up the cell's chemical reactions by lowering energy barriers.
- A molecule that functions as a biological catalyst, increasing the rate of a reaction without being consumed by the reaction.
- Almost all enzymes are proteins, although some RNA molecules can also function as enzymes.
- An enzyme speeds up a reaction by lowering the Ea needed for the reaction to begin.
- Is very selective in the reaction it catalyzes.
- As a protein, an enzyme has a unique three-dimensional shape, and that shape determines the enzyme's specificty.
The specific reactant that an enzyme acts on.
- The region of an enzyme where a substrate fits into.
- Typically a pocket or groove on the surface of an enzyme formed by only a few of the enzyme's amino acids.
What do most enzyme names end with?
- Many are named for their substrate.
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