Proteins, Transport Mechanism Flashcards
The sum total of all chemical reactions and physical workings occurring in a cell
Metabolism
2 Types of Metabolism
Anabolism and Catabolism
- biosynthesis
- building complex molecules from simple ones
- requires energy (ATP)
Anabolism
- degradation
- breaking down complex to simple molecules
- generates energy (ATP)
Catabolism
- For a reaction to occur, an energy barrier must be surmounted
- the minimum quantity of energy which the reacting species must possess in order to undergo a specified reaction
Activation Energy
- Point when a reaction can easily run in either direction, to product or back to reactant
- Unstable at the highest energy level
- Substrate is bound most tightly to an enzyme in this state
Transition State
Enzymes consisting of proteins alone
Simple enzymes
Enzymes that contain protein (apoenzyme) and nonprotein (cofactors) molecules
Metallic Cofactors: iron, copper, magnesium
Conjugated Enzymes or holoenzymes
Enzyme-Substrate Interaction
a model for enzyme-substrate interaction suggesting that the enzyme and the substrate possess specific complementary geometric shapes that fit exactly into one another.
Lock and Key Model
a model for enzyme–substrate interaction to describe that the substrate is capable of inducing the proper alignment of the active site of the enzyme, causing the latter to subsequently perform its catalytic function.
Induced Fit Model
These are anabolic reactions to form covalent bonds between smaller substrate molecules, require ATP, release one molecule of water for each bond
Synthesis/condensation reactions
These are catabolic reactions that break down substrates into small molecules, requires the input of water
Hydrolysis Reactions
a type of chemical reaction that involves a transfer of electrons between two species.
Oxidation-Reduction Reaction
They convert one type of amino acid to another by transferring an amino group
Aminotransferases (or transaminases)
The transfer of phosphate groups, involved in energy transfer
Phosphorylation
Three types: Photophosphorylation, Substrate level phosphorylation, Oxidative phosphorylation
Control of Enzyme Activity Categories
- Control of enzyme activity directly
- Control of enzyme activity by regulating enzyme synthesis
Control of Enzyme Activity Directly
Occurs when a substance that resembles normal substrate competes with substrate for active site
Competitive Inhibition
Control of Enzyme Activity Directly
Characterized by a substance binding to the cofactor and distorts the shape of the active site
Noncompetitive Inhibition
Control of Enzyme Activity Directly
Control mechanism wherein the concentration of product at the end of a pathway blocks the action of a key enzyme
Feedback Inhibition
Control of Enzyme Activity by Regulating Enzyme Synthesis
always present, always produced in equal amounts or at equal rates, regardless of amount of substrate; enzymes involved in glucose metabolism
Constitutive Enzymes
Control of Enzyme Activity by Regulating Enzyme Synthesis
- not constantly present, produced only when substrate is present, prevents cell from wasting resources
- synthesis of these enzymes is induced by a metabolite
Induced Enzymes
Control of Enzyme Activity by Regulating Enzyme Synthesis
- enzymes that are not produced when the end product of the pathway is present
- synthesis of these enzymes is suppressed by a metabolite
Repressible Enzymes
enzymes transported extracellularly, where they break down large food molecules or harmful chemicals
* cellulase, amylase, penicillinase
Exoenzymes
enzymes retained intracellularly and function within the cell
Endoenzymes
- The ability of the cell membrane to differentiate between different types of molecules, only allowing some molecules through while blocking others
- “Small, nonpolar molecules get in. Ions and polar molecules don’t get in”
Selective Permeability
- A thin, polar membrane made of two layers of lipid molecules
- Acts as a barrier to the passage of molecules and ions into and out of the cell
Phospholipid Bilayer
- Reduces membrane fluidity at moderate temperatures by reducing phospholipid movement
- At low temperatures, it hinders solidification by disrupting the regular packing of phospholipids
Cholesterol
Membrane Proteins
- These proteins penetrate the hydrophobic inside of lipid bilayer
- most are transmembrane proteins
Integral Proteins
Membrane Proteins
- Proteins that attach to the lipid bilayer
- Appendages loosely bound to either surface
- Easily separable from the bilayer
Peripheral Proteins
Proteins that provide hydrophilic channels
Transport Proteins
Differentiate Uniport, Symport, and Antiport
- Uniport: type of membrane transport that transports one substance in one direction
- Symport: transports two substances in the same direction
- Antiport: transports two substances in opposite directions
Transport protein that acts like a pore in the membrane that lets water molecules or small ions through quickly
Channel Proteins
- Transport protein that is specific for an ion, molecule, or group of substances
- This type of protein carries the ion or molecules across the membrane by changing shape after the binding of the ion or molecule
Carrier Protein
Proteins that functions by binding a specific ligand molecule
Receptor Proteins
- Proteins that can freely move within the lipid bilayer because of its fluidity
- May also be confined to certain areas of the bilayer
Membrane Proteins
The diffusion of a substance across membrane with no energy investment
Passive Transport
- Random movement of molecules but has a net direction toward regions of lower concentration to reach equilibrium
- No work required: spontaneous because particles have KE and are in constant motion
- Both the solute and solvent move
Diffusion
Diffusion that does not require the assistance of membrane proteins
* Substances simply pass through the phospholipids
Simple Diffusion
Movement of molecules along the concentration gradient that requires the help of carriers
* Substances pass through channels instead of directly through the phospholipids
Facilitated Diffusion
Factors that affect the rate of diffusion
- Concentration Gradient
- Temperature
- Mass of Particles
- Solvent Properties
Movement of SOLVENT across a semipermeable membrane from high to low solvent concentration
* Only the solvent moves
Osmosis
Difference between Diffusion and Osmosis
Diffusion: movement of MOLECULES from high to low concentration (both solute and solvent move)
Osmosis: movement of SOLVENT from high to low solvent concentration (only solvent moves)
- Ability of a surrounding solution to cause a cell to gain or lose water
- Depends on concentration of solutes that cannot cross membrane relative to the concentration of all solutes in the cell
Tonicity
A higher concentrated solution is (?) to a lower concentrated solution
Hypertonic
A lower concentrated solution is (?) to a higher concentrated solution
Hypotonic
Two solutions with equal concentrations are (?)
Isotonic
- Transport of ions or molecules that require energy and assistance of enzymes
- Lower to higher concentration (against concentration gradient)
- Allows cell to maintain concentration gradients
- Similar to facilitated diffusion but requires energy
Active Transport
A difference in charge across membrane
Membrane potential
Cations move into the cell while anions move out
Electrical Gradient
- Transport proteins that generate voltage across a membrane
- Generation of voltage increases potential energy
Electrogenic Pumps
The major electrogenic pump in animal cells
Na+/K+/ATPase pump
The major electrogenic pump in plant cells
Proton pump
A type of secondary transport across a biological membrane in which a transport protein couples the movement of an ion (usually Na+ or H+) down its electrochemical gradient to the movement of another ion or molecule against a concentration or electrochemical gradient
Cotransport
a mode of transport of large quantities of materials and food particles across the membrane
Bulk Transport
Exo/Endocytosis
Process in which a cell transports molecules out of the cell
Exocytosis
Process in which substances are brought into the cell
Endocytosis
Phago and Pinocytosis
- is the process by which large particles, such as cells or relatively large particles, are taken in by a cell
- “Cell-eating”
Phagocytosis
- was named at a time when the assumption was that the cell was purposefully taking in extracellular fluid
- “Cell-drinking”
Pinocytosis
- a form of endocytosis in which receptor proteins on the cell surface are used to capture a specific target molecule
- allows cells to take in specifically what it needs
- specific ligands bind to specific membrane proteins
Receptor-Mediated Endocytosis
