Cellular Respiration

Ch. 9

Overview

Respiration has three metabolic stages: Glycolysis Krebs Cycle Electron Transport Phosphorylation

Glycolysis and Krebs Cycle decompose glucose and other organic fuels

90% of ATP is produced in Electron Transport Phosphorylation step

Glycolysis

Glycolysis means “splitting of sugar”

Glucose (6 carbon sugar) is split into two 3-carbon sugars These smaller sugars are oxidized and rearranged to form

two molecules of pyruvate

Ten total steps in glycolysis First set of steps is “energy investment” Second set of steps is “energy payoff” Net energy gain for every glucose molecule is 2 ATP and 2

NADH

Some energy is made with “substrate-level phosphorylation”

Transfer of a phosphate from substrate creates ATP

Produces small amount of energy

Krebs Cycle

Glycolysis only releases a small amount of the energy in glucose

Most of the energy is still stored in the pyruvate

If O2 is present, pyruvate enters mitochondrion where the Krebs Cycle will complete the oxidation of the fuel

First thing the mitochondrion will do is convert the pyruvate into acetyl CoA

Step 1: Carboxyl group removed (CO2 given off) Step 2: Oxidized to form acetate (loses electrons) Step 3: Coenzyme A attached to the acetate

FADH2 and NADH created by Krebs Cycle will relay electrons to the electron transport chain

Also a small amount of ATP created by substrate-level phosphorylation (just like glycolysis)

Electron Transport Phosphorylation

Electrons delivered to transport systems of inner mitochondrial membrane

As electrons move through the system, they set up H+ gradients, which drive ATP production

This is the real “money maker” of ATP production

ATP synthase is powered by the flow of hydrogen ions

Like active transport in reverse

Can be found in the mitochondrial and chloroplast membranes of eukaryotes

Can also be found in plasma membrane of prokaryotes.

Fermentation

Anaerobic pathway (does not require O2)

Extension of glycolysis that can generate ATP by substrate-level phosphorylation ONLY as long as there is enough NAD+ to accept electrons

Pyruvate (end product of glycolysis) serves as an electron acceptor for oxidizing NADH back to NAD+ which can then be reused in glycolysis

One example is alcohol fermentation