Cellular Respiration

Cellular respiration is a metabolic process your cells use to break down glucose and release chemical energy, in the form of ATP, for functioning. Cells convert the food we eat/nutrients to produce energy. It occurs in almost every living cell. In eukaryotic cells, it takes place in the mitochondria (the powerhouse of the cell!) and in prokaryotes in occurs in the cytoplasm.

Aerobic Respiration

The process is as follows:

C₆H₁₂O₆ + 6O₂ = 6CO₂ + 6H₂O + ATP

Glucose + Oxygen = Carbon Dioxide + Water + Energy

Aerobic respiration is divided into 4 stages: glycolysis, link reaction, kreb cycle, and finally electron transport chain.

Glycolysis

Occurs in cytoplasm
Universal step in all living organisms
No oxygen required
Breaks down glucose into 2 pyruvate molecules
Final results: 2 ATP, 2 NADH and 2 pyruvates

Link Reaction (intermediate step):

Pyruvate is transported to the mitochondrial matrix.
2 pyruvates are oxidized and converted to 2 Acetyl Coenzyme A.
2 Carbon Dioxide is released
2 NADH are produced

Krebs Cycle

The Krebs cycle consumes pyruvate and produces three things: CO2, ATP, and NADH and FADH (electron carriers)
Pyruvate is broken down completely

Electron Transport Chain

Occurs in Inner mitochondrial membrane
NADH and FADH give up electrons to the chain
Energy is captured and released as electrons move from high energy to low energy, using a set of proteins (ATP synthase) embedded in the membrane of mitochondria.
Oxygen is terminal acceptor
Final results of ETC – 32-34 ATPs
Water is released as a byproduct

ATP Synthase

Adds a phosphate to ADP to turn into ATP
Protons travel down the electrochemical gradient to the ATP synthase, powering it.

Anaerobic Respiration

Without oxygen, aerobic respiration switches to fermentation or anaerobic respiration. There are two types of fermentation: alcoholic fermentation and lactic acid fermentation. Both start with glycolysis in which two molecules of ATP are produced from one molecule of glucose.

Anaerobic respiration produces far less ATP than does aerobic cellular respiration, but it has the advantage of being much faster. For example, it allows muscles to get the energy they need for short bursts of intense activity. When the body cannot supply the cells with the oxygen needed to break down glucose, it has to carry out anaerobic respiration.

Alcohol Fermentation

Alcoholic fermentation is carried out by single-celled organisms, including yeasts and some bacteria. We use alcoholic fermentation in these organisms to make biofuels, bread, and wine.

Equation:

C₆H₁₂O₆ → 2 ATP + 2 C₂H₅OH + 2 CO₂

Glucose → ATP + Ethanol + Carbon Dioxide

Lactic Acid Fermentation

Lactic acid fermentation is undertaken by certain bacteria, including the bacteria in yogurts, and also by our muscle cells when they are worked hard and fast.

Starts with glycolysis
Occurs in animals muscle cells and some one-celled organisms
Produces 2 ATP & lactic acid
Produces soreness when built up in muscles
Production in yogurt, cheese and other milk products

Equation:

C₆H₁₂O₆ → 2 ATP + 2 C₃H₆O₃

Glucose → ATP + Lactic Acid

When anaerobic respiration takes place, the lactic acid produced soaks the muscle cells and prevents muscle from doing their job. This causes fatigue and sometimes cramps. After activity that has led to anaerobic respiration, the person involves pants and breath heavily. This happens because they need lots of oxygen to get rid of the lactic acid that has built up in their body.

Differences Between Aerobic & Anaerobic

Aerobic	Anaerobic
Needs Oxygen	No oxygen needed
30-38 ATP molecules	2 ATP molecules
Products – CO₂, H₂O, ATP	Products – ATP, Ethanol or lactic acid
Reactants – C₆H₁₂O₆ + O₂	Reactants – C₆H₁₂O₆ + Electron acceptor
Cytoplasm and mitochondria	Cytoplasm
Glycolysis, Link Reaction, Krebs cycle, ETC	Glycolysis, Fermentation

LifeLine