Chapter 4 Biology 1010 - How Cells Obtain Energy

Cells Transform Energy

* Energy is the capacity to perform work
* Two kinds of energy:
* 1.) Kinetic Energy
* Energy of motion
* 2.) Potential Energy
* Stored chemical energy

ATP

* Main energy currency
* **A**denosine **T**ri**p**hosphate powers nearly all forms of cellular work
* Consists of
* Nitrogen Base
* Sugar
* Phosphate
* Hydrolysis of ATP releases energy by transferring its third phosphate from ATP to some other molecule in. a process called phosphorylation
* Most cellular work depends on ATP energizing molecules by phosphorylating them

Enzymes

* Are biological catalyst
* Speed up the cells' chemical reaction by lowering energy barriers
* Although biological molecules possess much potential energy, it is not released spontaneously
* An energy barrier must be overcome before a chemical reaction can begin
* This energy is called the Activation Energy (Ea)
* Enzymes help lower activation energy
* They are a type of protein

Specific Enzyme Catalyzes Each Cellular Respiration

* An enzyme:
* Is very selective in the reaction it catalyzes
* Shape determines the enzyme's specificity
* The specific reactant that an enzyme acts on is called the enzyme's substrate
* Substrate fits into a region of the enzyme called active site
* Enzymes are specific because their active site fits only specific substrate molecules

Feedback Inhibition

* Enzyme inhibitors are important in regulating cell metabolism
* In some reactions, the product may act as an inhibitor of one of the enzymes in the pathway that produced it

Cellular Respiration

* In Eukaryotes, cellular respiration
* Harvests energy from food
* Yields large amounts of ATP
* Uses ATP to drive cellular work
* Basically, make ATP from food we eat

Respiration and Cellular Respiration

* Respiration relates to breathing, not the same cellular respiration, but are connected
* Respiration, breathing sense, refers to an exchange of gases. Usually an organism brings in oxygen from environment and releases waste CO2
* Cellular Respiration is aerobic (oxygen requiring) harvesting of energy from food molecules by cells

Cellular Respiration Banks Energy in ATP Molecules

* Cellular Respiration is an exergonic process that transfers energy from the bonds of glucose to form ATP
* Cellular Respiration:
* Produces up to 32 ATP molecules form each glucose molecule
* Captures only about 34% of the energy originally stored in glucose
* Other foods (organic molecules) can also be used as a source of energy
* Glucose (C6H12O6) + 6 Oxygen (O2) --> ---> --> 6 Carbon Dioxide (O2) + 6 Water (H2O) + ATP + Heat

Electron Carriers

* Enzymes are necessary to oxidize glucose and other foods
* NAD+
* An important co-enzyme in oxidizing glucose
* Accepts electrons + becomes NADH
* Electron carrier molecules (NADH/FADH2)
* These electron carries collectively are called the electron transport chain
* As electrons are transported down the chain, ATP is generated

Three Stages of Cellular Respiration

* Stage 1: Glycolysis
* Little ATP, 2
* Cytoplasm, does NOT need oxygen
* Stage 2: Pyruvate Oxidation + Citric Acid Cycle (also known as Krebs Cycle)
* Little ATP, 2
* Matrix in Mitochondria, requires oxygen
* Stage 3: Oxidative Phosphorylation
* A lot of ATP, 28
* Inner Membrane @ mitochondria, there is electron transport chain
* Oxygen is final electron receptor
* Makes water