Download Cellular Respiration NOTES

Cellular Respiration / (Aerobic (with oxygen)) Respiration
Cellular respiration converts the energy stored in the bonds of the glucose into
energy in ATP.
Why is it important? – all living organisms need to convert the energy in the food
they eat (or in the case of plants in the food they produce through photosynthesis)
into a form of energy that is easy to use – ATP. Plants must also undergo cellular
respiration to make ATP. ATP fuels all chemical reactions & process in living
organisms.
Cellular respiration 3(and ½) stages:
1) Glycolysis – In Cytoplasm of cells
Splits 1 glucose into 2 Pyruvic Acid molecules. The splitting of glucose releases
energy:
Makes 2 ATP.
Releases electrons and Hydrogen ions. Electrons & Hydrogen ions are taken by the
electron carrier NAD+ (NAD+ + H ions + electrons → NADH) to stage 3.
1.5) Link Reaction – In matrix of mitochondria
Link reaction occurs where pyruvic acid is converted into Acetyl Coenzyme-A. Acetyl
Co-A will then enters the Kreb’s cycle.
In the process of the link reaction, carbon dioxide is released and more NADH is
made and will be used in stage 3.
2) Krebs Cycle – Mitochondria
Pyruvic Acid broken down to Carbon Dioxide. The splitting of pyruvic Acid releases
energy:
Makes 2 ATP.
Releases electrons and Hydrogen ions. Electrons & Hydrogen ions are taken by the
electron carriers: NAD+ (NAD+ + H ions + electrons → NADH) and FAD2+ (FAD2+ + 2H ions +
2electrons → FADH2) to stage 3.
3) Electron Transport Chain – Mitochondria
NADH from glycolysis & the Krebs cycle delivers the electrons and Hydrogen ions to
an electron transport chain (ETC) which is embedded in the inner membrane of the
mitochondria. As the electrons move through the chain they release lots of energy to
pump H+ ions into the intermembrane space. In doing so, a steep concentration
gradient is formed and H+ ions will flow back into the matrix through the membrane
protein ATP synthase. In flowing back through the H+ provide the energy to the ATP
synthase to link a ADP to P and make ATP, a lot of it! (ADP + P + energy → ATP).
Makes 34 ATP. Kreb’s cycle releases the last of the carbon from the glucose
molecule as carbon dioxide.
When the Hydrogen and electrons have finished moving through the ETC they
combine with O2 to form H2O. Oxygen is the final electron (and hydrogen) acceptor.
Net Respiration Reaction
Glucose + Oxygen + → Carbon Dioxide + Water + ENERGY (in the form of ATP)
C6H12O6 + 6O2 → 6CO2 + 6H2O + 38 ATP
Carbon dioxide & water are the waste products of cellular respiration. They are
released from the mitochondria and then exhaled from the body.
The ATP is used by the cell as a source of energy to perform cellular work: move,
grow, repair, produce cellular products, active transport, reproduce, etc..
Fermentation/Anaerobic Respiration
When NO OXYGEN is available, organisms have to use another pathway called
fermentation (or ANaerobic) respiration. Regardless of the organism (bacteria to
human), all organisms use glycolysis as an initial step.
Remember, glycolysis results in a net gain of 2 ATP (useful) and 2 NADH (without
oxygen, not very useful) and the pyruvate molecules. So, in order to recycle the
NAD+ (so more glycolysis can still occur) and to take care of the pyruvate, organisms
will convert the pyruvate into either: lactic acid (as we humans do) or into carbon
dioxide and alcohol (like bacteria and yeasts).
Note that fermentation does not result in any more ATP, so the only ATP is the 2
gained when glucose is split. So, humans cannot use this system very long, and
organisms who ONLY use fermentation cannot get very big (bacteria and yeast).