Cell Reactions: ATP & Cellular Respiration

Cell Reactions

ATP & Cellular Respiration

• Cell energy is needed for living things; this energy comes from food which originally comes from the sun.

• Autotrophs: Organisms that use light energy from the sun to produce food (auto = self). Examples include plants and some microorganisms (some bacteria and protists).

• Heterotrophs: Organisms that CANNOT use the sun's energy to make food. Examples include animals and most microorganisms.

• Cells are constantly making and using ENERGY; without energy, cells would not be able to grow, repair, reproduce, synthesize proteins and fats, and carry out their daily activities.

Cell Energy: ATP /ADP cycle

• Cells usable source of energy is called ATP

• ATP stands for adenosine triphosphate.

• It is a chemical molecule which is stored in cells.

• ATP has a high amount of ENERGY stored in the last phosphate bond.

• When the cell needs energy for its activities, the last phosphate bond is broken to release the energy required.

• Once the energy is released, the molecule left from ATP is called ADP (adenosine diphosphate) which is a low energy molecule.

• The cell cannot build up ADP as it requires a constant supply of energy in the form of ATP.

• It uses the reaction of RESPIRATION to join the inorganic phosphate group back onto the ADP molecule to create ATP.

• This process requires glucose and oxygen and occurs in the cell’s cytosol and mitochondria.

Cellular Respiration: Aerobic and Anaerobic

• Cellular respiration is the process by which the energy of glucose is released in the cell and converted to ATP to be used for life processes (movement, breathing, blood circulation, etc…)

• Respiration occurs in ALL cells and can take place either with or without oxygen present.

Aerobic Respiration

• Requires oxygen

• Occurs in the cytosol & mitochondria of the cell

• Total of 30 or 32 ATP molecules produced from each glucose molecule.

• Equations for aerobic respiration (worded and chemical) :

Mitochondria Structure

• Has a DOUBLE MEMBRANE

• Has its own DNA

• Can reproduce in the cell.

• Smooth outer Membrane

• Folded inner membrane

• Folds called Cristae

• Liquid between cristae called the Matrix

Stages of Cellular Respiration

• Glycolysis

• The Krebs Cycle

• The Electron Transport Chain

• $C<em>6H</em>{12}O<em>6 + 6O</em>2 \rightarrow 6CO<em>2 + 6H</em>2O + 30 \text{ or } 32 \text{ ATP}$

• Glucose + Oxygen → Carbon Dioxide + Water + 30 or 32 ATP

• Overall aerobic respiration is a three stage process:

  1. Glycolysis: starts outside the mitochondria in the cytosol where glucose is split into two pyruvate molecules ……….. 2ATP & NADH generated (NADH is a carrier of H+ ions)

  2. Krebs Cycle: occurs inside the mitochondrial matrix pyruvate is broken down in a series of reactions and $CO_2$ is released. 2ATP generated. More carriers are loaded with H+ ( NADH and FADH2) Pyruvate

  3. Electron Transport Chain occurs on the cristae of mitochondria (inner membrane). Uses $O_2$ to produce water. Loaded H+ carriers deliver and release their H+ ions. 26 or 28 ATP generated.

Factors affecting the rate of cellular respiration

1. Temperature

2. Glucose availability

3. Oxygen concentration

4. Temperature

   • As the temperature increases towards the optimum range, the rate of cellular respiration increases.

   • At the optimum temperature, cellular respiration will occur at the maximum rate.

   • At the temperatures above the optimum temperature, the rate of cellular respiration rapidly decreases as enzymes (controlling the rate of respiration) are denatured (lose their shape and function)

   • Cellular respiration rate and ATP production are highest when the temperature is at the enzyme’s optimal temperature.

5. Glucose availability

   • Glucose is an input (substrate) for glycolysis and so its concentration will affect the rate of cellular respiration.

   • Increasing the amount of glucose will increase the rate of respiration until a saturation point is reached.

   • A maximum rate is reached when the enzymes within the cells are operating at their maximum capacity.

6. Oxygen concentration

   • Increasing the concentration of oxygen will increase the rate of aerobic respiration.

   • Aerobic respiration requires oxygen for the electron transport chain to function

   • Oxygen is not needed for anaerobic fermentation.

   • When there are low levels of oxygen, cells switch to anaerobic fermentation and then switch back to aerobic once $O<em>2$ levels increase. More $O</em>2$ = faster rate of aerobic respiration

   • Remember: Rate of aerobic respiration reaches a maximum rate as enzymes are limited – even if more oxygen is available.

Anaerobic Respiration

• Occurs when no oxygen is available to the cell

• Also called fermentation (alcoholic and lactic acid)

• Much less ATP produced than in aerobic respiration

  • Alcoholic fermentation occurs in bacteria and yeast

    • Process used in the baking and brewing industry yeast produces $CO_2$ gas during fermentation to make dough rise and give bread its holes.

    • Glucose is converted into pyruvate with the release of 2ATP and then is converted into the final products of alcohol (ethanol) and carbon dioxide.

    • Glucose → alcohol + carbon dioxide + 2 ATP

  • Lactic acid fermentation occurs in muscle cells

    • Lactic acid is produced in the muscles during rapid exercise when the body cannot supply enough oxygen to the tissues causes burning sensation in muscles.

    • Glucose is broken down into pyruvate with the release of 2ATP and is then further converted into the final product of lactic acid ( most of the energy is still in the bonds of lactic acid)

    • glucose → lactic acid + 2 ATP

• Anaerobic respiration is also the first step of aerobic respiration : glycolysis

• Anaerobic respiration occurs only in the cytosol.

• The final products of anaerobic respiration in both plants (alcohol) and animals (lactic acid) are toxic to cells and need to be removed.

• This form of respiration is not sustainable long term for this reason.