ap biology unit 3 notes

catabolism - break down of complex substances; releases energy; exergonic; catabolic pathways include fermentation and aerobic respiration

fermentation - partial degradation of sugars that occurs without the use of oxygen

aerobic respiration - most prevalent and efficient catabolic pathway in which energy from biological macromolecules is used to produce ATP, and oxygen is consumed as a reactant; usually cellular respiration refers to this

carbs, fats, and proteins all can break down to release energy in cell resp, but glucose is the most common

C(6)H(12)O(6) + 6O(2) → 6CO(2) + 6H(2)O + Energy (686 kcal/mol of glucose)

the exergonic release of energy from glucose is used to phosphorylate (attachment of a phosphate group to a molecule) ADP to ATP.

the reactions of cellular respiration are of a type termed oxidation-reduction (redox) reactions. in redox reactions, electrons are transferred from one reactant to another.

• oxidation - loss of one or more electrons from a reactant; when reactant is oxidized, it loses electrons and, consequently, energy

• reduction - gain of one or more electrons; when reactant is reduced, it gains electrons, and therefore, energy

SO reduced molecules is at higher energy state because of gaining an electrons

at key steps, electrons are stripped from glucose; each electron travels with a proton, thereby forming a hydrogen atom. hydrogen atoms are not transferred directly to oxygen, but are then passed to an electron carrier, the coenzyme NAD(+)

Within the cell, NAD(+) accepts two electrons, plus the stabilizing hydrogen ion, to form NADH. NADH has been reduced and has therefore gained energy.

START

glycolysis - inside of the cytosol; degradation of glucose begins as it is broken down into two pyruvate molecules; six-carbon glucose molecule is split into two three-carbon sugars, then altered to two three-carbon acids (pyruvate); there is an ATP consuming phase and an ATP producing phase

glycolysis ATP consuming phase - two atp molecules are consumed, helping to destabilize glucose and make it more reactive

glycolysis ATP producing phase - four atp molecules are produced; resulting in a net gain of two ato molecules. two NADH molecules are also produced, and they will be used in the electron transport system (aka oxidative phosphorylation) (which requires oxygen) to produce atp

after glycolysis, pyruvate is oxidized to acetyl CoA (LINK)

• a transport protein moves pyruvate from the cytosol into the matrix of the mitochondria

• in the matrix, an enzyme complex catalyzes three reactions: a CO(2) molecule is removed, electrons are stripped (oxidation) from pyruvate to convert NAD(+) to NADH, and coenzyme A joins with the remaining two-carbon fragment to form acetyl CoA

• two acetyl CoA molecules are produced per glucose molecule. Acetyle CoA now enters the enzymatic pathway termed the Krebs or “citric acid cycle”

CITRIC ACID CYCLE/KREBS CYCLE

• occurs in the mitochondrial matrix

• co2 is released as a waste product and this breaks down glucose

• each turn of the cyce acid cycle requires the input of one acetyl-CoA and the cycle must made two turns before the glucose is completely oxidized

• each turn produces 2co2. 3madj, 1 fadh(2), 1 atp

• THEREFORE - because each glucose yields two pyruvates, the total products of the citric acid cycle are usually listed as the result of two cycles

  • 4 co(2), 6 nadh, 2 fahd(2), and 2 atp

ELECTRON TRANSPORT SYSTEM

• electron transport chain is embedded in the inner membrane of the mitochondria;composed of 3 transmembrane proteins that work as hydrogen pumps and two carrier molecules that transport electrons between hydrogen pumps

• this chain is powered by electrons from the electron carrier molecules nadh and fadh2; as electrons flow thru the electron chain the loss of energy by the electrons is used to power the pumping of protons across the inner membrane

• at the end of the chain, the electrons combine with two hydrogen ions and oxygen to form water; O2 is the final electron acceptor

• hydrogen ins flow down their gradient thru a channel in the transmembrane protein known as atp synthase which harnesses the electrochemical gradient to phosphorylate adp, forming atp/

• the inner membrane of the mitochondria is impermeable to hydrogen ions

• an electrochemical gradient stores potential energy by a diffusion gradient and an electric charge gradient across a membrane

chemiosmosis - an energy-coupling mechanism that uses energy stored n the form of an H+ gradient across a membrane to drive cellular work (ATP synthesis); the electron transport chain and chemiosmosis together result in oxidative phosphorylation

fermentation - an expansion of glycolysis in which atp is generated without oxygen

alcohol fermentation - pyruvate is converted to ethanol, releasing co2 and oxidizing nadh in the process to create more nad+

lactic acid fermentation - pyruvate is reduced by nadh (nad+ is formed in the process) and lactate is formed as a waste product