Chapter 5 BIO 2770

Overall Chemical Reaction for Cellular Aerobic Respiration

C6H12O6 + 6O --> 6H2O + 6CO2

Endergonic reactions

require energy to occur

Exergonic Reactions

release energy

Connection between exergonic and endergonic

as energy released from exergonic reactions fuels endergonic reactions, which can then later release energy

Oxidation

loss of electrons

Reduction

gain of electrons (negative charge reduces total charge)

Hydrogens come along when

electrons are exchanged, Follow hydrogen and see where it goes

Enzyme activity

-Enzymes are catalyst

-Catalysts lower the activation energy of a reaction but are not consumed in the reaction

-Ribozymes are RNA catalysis

Enzymes target

is its substrate, which binds to the active site of an enzyme

Denaturation of enzyme

by heat or pH destabilized the shape and inhibits function

Completive inhibition

inhibitors binds to its site

non-completive inhibitors

inhibitors bind elsewhere

Why does cell use inhibition?

to turn enzyme of when not needed

Feedback inhibition

involves a product of metabolic pathway inhibiting enzymes in the pathway, prevents cell from making too much of any one product

NAD+ and FAD

they are electron carriers (and H+) from catabolism

Glycolysis (metabolic pathway note)

-breakdown of glucose

-Forms pyruvate, ATP, and NADH

Entner-Doudoroff

-Breakdown of a non-glucose sugar molecule (catabolic)

-Forms Pyruvate, ATP, NADH, NADPH

Pentose Phosphate Pathway

Uses intermediates of glycolysis or ED to build organics (anabolic)

What are used to form carbon bonds?

NADPH (electron donor [reducing agent]), ATP (energy)

Glycolysis

-Occurs in cytoplasm

-Glucose is phosphorylated twice, expanding 2 ATP molecules

-Glycolysis breaks glucose (6C) down to two pyruvate molecules (3C)

• used to phosphorlate 4 ADP molculesmolecules

-SLP: directly phosphorylate via enzyme

-Produces 2NADH and 2 ATP ( 4 ATP uses 2 to begin)

-Once pyruvate is produces, the pathway split depending on oxygen level

Anaerobic Fermentation (oxygen absent)

-NAD+ is required for glycolysis, cell reverts NADH to NAD+ to continue

-The electrons from NADP are donated to pyruvate (or a metabolite of pyruvate), creating lactate, CO2, alcohol, or many other products

-NO ATP produced, regenerates the NAD+

Lactic Acid Fermentation (CO2 formed)

-NADH and H+ attach 2 hydrogens to pyruvate, forming lactic acid

Ethanol Fermentaion

-Decarboxylates pyruvate forming acetaldehyde and CO2

-Then NADH and H+ attach 2 hydrogens to acetaldehyde forming ethanol

The remaining C-C bond hold a lot of energy, but

the cell cannot take advantage of it without a highly electronegative acceptor

Cellular Respiration (Aerobic)

-If the cell has enough oxygen the pyruvate can be further catabolized

-The electrons and hydrogens will be removed and sent to an electron transport system (ETS) and the carbons will form CO2

Pyruvate Transition Step (Decarboxylation)

-In order to enter the citric acid cycle, pyruvate must be chemically modified

-A coenzyme (Coenzyme A or CoA) is bonded to the carbons of pyruvate forming acetyl CoA

-This process also releases a CO2 and forms an NADH for each pyruvate (2 for each glucose molecule)

Citric Acid Cycle

-Acetyl-CoA (2 carbons) is bonded to Oxaloacetate (a 4-carbon molecule) to form citrate (6 carbons)

-This cycle extracts energy by removing the new carbon atoms to regenerate the Oxaloacetate

-Carbon bonds are broken to release energy and CO2 molecules

-2 ATP and high energy electrons via NADH & FADH2 molecules

-These electrons are then fed into the electron transport chain in the membrane of a prokaryote or the inner membrane of mitochondria

Electron Transport Chain

- A series of membrane bound proteins

-These proteins accept high energy electrons and slowly release the energy by passing them around

-Many of these molecules are proton pumps, they pump H+ with the energy they release

-As the H+ molecules are pumped across the membrane they build up a diffusion gradient

-ATPase is a protein which allows H+ ions to flow across the membrane

-As the H+ ions flow down their gradient, ATPase uses this energy to bond ADP to Phosphate making ATP

-In aerobic respiration, the terminal electron acceptor is oxygen (anaerobes use alternative electron acceptors)

Following oxidative phosphorylation

The cells produce around 30 ATP per glucose, as opposed to the fermentation which produces 2 glucose

Photosynthesis (Light Reaction)

-Require sunlight to function

-Pigment embedded in the thylakoid membrane of chloroplast absorb photons of light.

• pigments absorb specific wavelengths of light

-Chlorophyll pigments absorb red and blue light, reflecting green light.

-This light excites electrons which are harnessed for energy

Calvin Cycle (“dark reactions”)

-Do not require light or photosynthesis, but use products of light reaction, ATP, and NADPH

-The Calvin cycle fixes inorganic carbon from CO2 by adding it to an organic molecule (RuBP) and is thus “Fixed.”

• The new carbon molecules are modified to make them suitable for glucose synthesis.

• Most of the carbon is recycled to continue the cycle.

-ATP is stored in carbon bonds

-1 G3P is generated each round of the cycle 2, 2 are required to make one glucose