Cellular Respiration [Harvesting Chemical Energy]

What is cellular respiration and its equation?

It is the process of releasing energy from food.

Equation: C₆H₁₂O₆ + 6O₂ --> 6CO₂ + 6 H₂O

(The energy is released from the bonds)

Name the 3 main stages of cell respiration and explain briefly

1) glycolysis

purpose: To split glucose and produce NADH and ATP

location: Cytoplasm (cytosol)

requirements: glucose, 2 ATP, 4 ADP, 2NAD+

products (net results): 2 pyruvic acids (3C acid), 2 ADP, 4 ATP, 2 NADH

a) Energy investment phase --> G3P (glycerolaldahyde, 3C sugar)

b) Energy harvest (payoff) phase --> pyruvate

krebs cycle (citric acid cycle)

--> doesn't require O2

purpose: oxidizing pyruvic acid to CO₂, production of NADH and FADH₂ (form of cell energy)

location: mitochondria matrix

requirements: pyruvic acid (3C acid), coenzyme A, 4 NAD^+, 1 ADP, 1 FAD (all double for each glucose)

products: 3 CO_2, acetyl CoA, 4 NADH, 1 ATP, 1 FADH₂

acetyl CoA --> acetyl coenzime A; the entry compound for the krebs cycle in celll respiration, formed from a fragment pyruvate attached to a coenzime

oxidative phosphorylation (electron transport chain)

purpose: converting NADH and FADH₂ into ATP

location: mitochondria cristae

ETC --> mitochondrial inner membrane (control of the energy transport)

requirements: NADH or FADH_2, ADP, O₂

products: NAD⁺ and FAD, ATP, H₂O (36-38 ATP --> total/ net result)

What is ATP synthase?

ATP synthase is a general term for an enzyme that can synthesize adenosine triphosphate (ATP) from adenosine diphosphate (ADP) and inorganic phosphate by using some form of energy. This energy is often in the form of protons moving down an electrochemical gradient, such as from the lumen into the stroma of chloroplasts or from the inter-membrane space into the matrix inmitochondria. The overall reaction sequence is:

ADP + P_i → ATP

5 facts:

- The energy stored in the organic molecules of food ultimately comes from the sun.

- To keep working, a cell must regenerate ATP.

- The electron transport chain is a collection of molecules embedded in the inner membrane of the mitochondria in eukaryotic cells.

- In prokaryotic cells, the krebs cycle occurs in the cytosol.

- At the end of electron transport chain, electrons are passed to oxygen, reducing it to water.

Key terms:

Aerobic respiration – the most relevant and efficient catabolic pathway

Anaerobic – no O₂

Cellular respiration – both aerobic and anaerobic processes

Oxidation – loss of electrons and energy

Oxidizing agent – the electron acceptor

Reduction – gain of electrons and energy

Reducing agent – the electron donor

NAD+ - electron carrier/acceptor, oxidizing agent in glycolisis

Chemiosmosis – energy-coupling mechanism

Fermentation – a way of harvesting chemical energy without using either oxygen or any ETC (no cell respiration)

Summary:

Cellular respiration allows organisms to use (release) energy stored in thechemical bonds of glucose. The energy in glucose is used to produce ATP. Cells use ATP to supply their energy needs. Cellular respiration is therefore a process in which the energy in glucose is transformed to ATP.

In respiration, glucose is oxidized and thus releases energy. Oxygen is reduced to form water. The carbon atoms of the sugar molecule are released as carbon dioxide.

The complete breakdown of glucose to carbon dioxide and water requires three major steps:

1)glycolysis; 2) krebs cycle; 3) oxidative phosphorylation

Glycolysis produces two ATP. Thirty-four more ATP are produced by aerobic pathways if oxygen is present.

Extra: Glucose Breakdown: RAP!