Plant Cells and Osmoregulation

• Plant cells in a hypotonic solution are in a normal state, with the cell swelling and becoming turgid as the central vacuole stores water.
• The cell wall prevents the plant cell from bursting in a hypotonic solution, and cytoplasmic streaming aids the swollen cell.
• In a hypertonic solution, plant cells shrivel due to plasmolysis, where the cell membrane shrinks around the cytoplasm and detaches from the cell wall; this process is reversible.
• Plant cells become flaccid in isotonic solutions, resulting in a limp or droopy plant, though plants prefer a turgid state; this condition is also reversible.

Adaptations – Osmoregulation

• Human kidneys maintain isotonic solutions in the body.
• Single-celled organisms use contractile vacuoles as water pumps to absorb and expel water, while the cell wall provides structural support.

Active Transport

• Active transport requires energy to move solutes from areas of low concentration to high concentration, using transport proteins.
• The sodium-potassium pump is an example of primary active transport that directly uses ATP to move ions against their concentration gradients.
• The pump, a membrane protein, is open toward the inside of the cell, and 3 Na⁺ ions from inside the cell bind to specific sites on it.
• ATP phosphorylates the pump, causing a shape change that opens the pump to the outside of the cell and releases the 3 Na⁺ ions.
• The shape change allows 2 K⁺ ions from outside the cell to bind to the pump.
• Removal of the phosphate group resets the pump to its original shape, forcing the 2 K⁺ ions inside the cell and releasing them due to the shape change.
• Membrane potential refers to the voltage difference across the membrane.

Bulk Transport

• Exocytosis involves substances exiting the cell, while endocytosis involves substances entering the cell.
• Phagocytosis, or "cell eating," is a non-specific process where the cell engulfs large substances, forming a vesicle.
• Amoebas use phagocytosis to engulf food, and white blood cells in animals use it to engulf pathogens.
• Pinocytosis, or "cell drinking," is a non-specific process.
• Receptor-mediated endocytosis is where receptors specifically bind to molecules, which then end up inside the vesicle.

Energy

• Energy is the capacity to cause change or perform work.
• Kinetic energy is the energy of motion, while potential energy is the energy associated with location or chemical structure.
• Chemical energy is stored in bonds or chemical compounds and is either released or absorbed during chemical reactions.
• Cells transform energy when performing work, such as converting potential energy to kinetic energy or utilizing the potential energy in sugar for kinetic activities.
• The first law of thermodynamics states that energy cannot be created or destroyed, only converted from one form to another.

Chemical Reactions

• Exergonic reactions release energy through the breaking of covalent bonds, which is catabolism.
• Endergonic reactions absorb energy through the formation of bonds, which is anabolism, like in photosynthesis.
• A metabolic pathway is a series of chemical reactions that form and break bonds.
• Adenosine triphosphate (ATP) is the usable energy in cells, containing two high-energy bonds with negatively charged phosphates that repel each other, making it unstable.
• When ATP bonds break, energy is released, forming adenosine diphosphate (ADP).
• AMP stands for adenosine monophosphate.
• ATP hydrolysis occurs when going from ATP to ADP and from ADP to AMP.
• Dehydration synthesis occurs when going from AMP to ADP and from ADP to ATP.

Cellular Work

• Chemical work involves adding a phosphate and energy to a reactant to trigger a chemical reaction.
• Mechanical work involves the movement of motor proteins.
• Transport work involves transport proteins facilitating solute movement.
• Energy coupling is the use of energy released from an exergonic reaction to drive an endergonic reaction.

How Enzymes Function

• Enzymes are proteins that speed up chemical reactions.
• Enzymes speed up chemical reactions because A+B need to find each other, A+B need to collide strongly and A+B need to collide with proper orientation.
• Each enzyme speeds up only one specific type of reaction.
• Activation energy is the energy invested in reactants to make them unstable and ready to react.

Enzyme

• Enzymes decrease activation energy, requiring less kinetic energy to destabilize reactants.
• Enzymes only affect activation energy, not the starting or ending points of a reaction.
• A catalyst is a substance that speeds up reactions.
• An enzymatic reaction: Sucrase enzyme.
• A substance binds to the enzyme with induced fit
• Only sucrose can bind to the active site of sucrase.
• The substrate is converted to products through a chemical reaction, using hydrolysis to break the bond by adding water.
• Once the active site is empty, new substrates bind, continuing the cycle.
• induced fit model: enzyme “clasps” (surrounds) the substrate(s) and enzyme changes its shape to start the chemical reaction and then the product is released with the enzyme going back to its original form.
• Different enzymes function at different temperatures and pH levels depending on their environment and function.
• Very high temperatures break bonds and denature enzymes, causing them to unravel and lose their essential shape.
• pH 1 is acidic, pH 14 is basic/alkaline, goes by 10x each pH
• A coenzyme or a cofactor must bind to the active site for chemical reactions to occur; cofactors are metal ions, while coenzymes are vitamins.
• Inhibitors are molecules that bind to enzymes and stop reactions.
• Competitive inhibition involves more competition for the active site and more inhibitor than substrates, eventually releasing the inhibitor without a chemical reaction.
• Non-competitive inhibition: A molecule that binds to an allosteric site causes a shape change that alters the enzymes active site
• Bind to the enzyme somewhere other than the active site (allosteric binding site).
• Feedback inhibition: when E binds allosterically and prevents A (non-competitively) from preventing too much of E from being made.

Cellular Respiration

• Cellular respiration converts food, such as sugars and fats, into usable energy.
• It is a metabolic pathway of chemical reactions that form and break bonds.
• O2 enters the cell and CO2 exits the cell.
• Glucose(high energy in bonds) undergoes catabolism to produce usable energy (ATP).
• Cellular respiration occurs in the mitochondria.
• The metabolic pathway has many steps, so sugar doesn't explode when the bonds are all released at once.
• Oxidation-reduction(redox) reactions allow for the slow capture and storage of energy from glucose.
• High-energy electrons in bonds are transferred with hydrogen.
• High-energy molecules are organic and include hydrogen and carbon.
• LEO says GER
• Loss of electrons is oxidation, while gain of electrons is reduction.
• NAD+ temporarily stores hydrogen and high-energy electrons; it is a coenzyme containing the vitamin nicotinamide.

Phase 1: Glycolysis

• It takes place in the cytoplasm
• Does not require oxygen but can occur in the presence of oxygen
• Glycolysis, or "splitting of sugar," produces 2 pyruvate, 2 NADH, and a net gain of 2 ATP (4 ATP produced, but 2 ATP are used).

Plant cells react differently to hypotonic, hypertonic, and isotonic solutions. Osmoregulation adaptations like contractile vacuoles and the role of the kidneys maintain cellular balance. Active transport and the use of transport proteins, are also an integral part of this homeostatic process.