Cellular Respiration

Photosynthesis Backwards
Complex Process in which cells make ATP by breaking down Organic Compounds
Anerobic Respiration
1. Glycolysis
  1. Yields a small amount of ATP
  2. 1st Step of Cellular Respiration
  3. If O2 is absent in the cell, the products of glycolysis may enter fermentation pathways that yield no additional ATP
    Nota:
    - Fermentation Pathways = Anerobic, since they work in absence of O2
    1. If O2 is present, glycolysis products enter pathways of Aerobic Respiration
      Nota:
      - Aerobic respiration produces a much larger amount of ATP than does glycolysis alone
  4. Pathway in which one 6-carbon molecule of glucose is osidized to produce 2 3-carbon molecules of pyruvic acid
    1. Steps of Glysolysis:
      1. Step 1: 2 Phosphate groups are attached to glucose, forming a new 6-Carbon Compound. These phosphate groups are supplied by two molecules of ATP, which are converted into two molecules of ADP during the process since they have lost a phosphate
        Step 2: The 6-Carbon compound formed is then split into two 3-Carbon molecules of G3P
        Step 3: The two G3P molecules are oxidized, and each receives a phosphate group. The product of this step is two molecules of a new 3-Carbon compound. The oxidization of G3P is accompanied by the reduction of 2 molecules of NAD+ to NADH.
        Step 4: The phosphate groups added in earlier are removed from the 3-Carbon compounds, which produces two molecules of Pyruvic Acid. Each of the phosphate groups are added in to ADP to make ATP. Since a total of 4 phosphate groups are added in, 4 molecules of ATP are produced
  5. Takes place in the cytosol of the cell
  6. Net yield of 4 ATP Molecules for every molecule of glucose converted to2 molecules of Pyruvic Acid
2. Fermentation
  1. In absence of oxygen, some cells convert pyruvic acid into other compounds through additional biomechical pathways that occur in the cytosol. The combination of Glycolysis + these additional biochemical pathways = fermentation
  2. Doesn't produce ATP, but does generate NAD+, which keeps Glycolysis going to make more ATP
  3. Lactic Acid Fermentation
    1. enzyme converts pyruvic acid into another 3-Carbon compound called Lactic Acid
    2. Involves the transfer of two hydrogen atoms from NADH and H+ to pyruvic acid. In the process, NADH is oxidized to form NAD+. The resulting NAD+ is used in glycolysis, where it is again reduced to NADH.
      1. The regeneration of NAD+ in lactic acid fermentation helps to keep glycolysis operating
    3. Lactic Acid Fermentation by microorganisms plays an essential role in the manufacture of food products such as yogurt and cheese
    4. Occurs in your muscle cells during very strenuous exercise . During these exercises, muscle cells use up oxygen more rapidly than it can be delivered to them. As O2 becomes depleted, the muscle cells begin to switch from aerobic respiration to Lactic Acid Fermentation. As a result, lactic acid accumulates in muscles, making cell's cytosol more acidic, which reduces a cell's capacity to contract, resulting in muscle fatigue, pain, and cramps. Eventually, the lactic acid diffuses into the blood and is transported to the lived, where it can be converted back to pyruvic acid when O2 is available again
  4. Alcoholic Fermentation
    1. converts pyruvic acid to ethyl Alcohol
    2. used by some plant cells and unicellular organisms
    3. Pathway requires two steps
      1. Step 1: A CO2 molecule is removed from pyruvic aci, leaving a 2-Carbon compounds
        Step 2: Two Hydrogen atoms are added to the 2-Carbon compound to form ethyl alcohol
        Nota:
        As for lactic acid fermentation, these hydrogen atoms come from NADH and H+, regenerating NAD+ for use in glycolysis
    4. The Basis of the wine and beer industries. Yeast cells are added to the fermentation mixture to provide the enzymes needed for alcoholic fermentation. As fermentation proceeds, ethyl alcohol acumulates in the mixture until it reaches a concentration that inhibits fermentation.
    5. In Bread, CO2 that is produced by fermentation makes the bread rise by forming bubbles inside the dough, and the ethyl alcohol evaporates during bakiing
3. Energy Yield
  1. Effieiency of Anerobic pathways at obtaining energy from Glucose and using it to make ATP from ADP
  2. Energy is measured in kilocalories (kcal). One kcal = 1,000 calories
  3. Complete Oxidization of a standard amount of glucose releases 686 kcal. In conditions that exist in most cells, production of standard amount of ATP from ADP absorbs about 12 kcal
  4. Efficiency of Glycolysis = Energy required to make ATP / Energy released by oxidation of Glucose
  5. Efficiency of Glucose = 3.5%
    1. This means that most of the energy obtained from Glycolysis is held by Pyruvic Acid
      1. Even if Pyruvic Acid is converted into Lactic acid or Ethyl Alcohol, no additional ATP is synthesized
  6. Efficiency of Glucose = ((2 molecules of ATP produces per glucose molecule broken down x 12 kcal) / 686 kal) x 100%
4. Not very efficient in transferring energy from Glucose to ATP
5. Probably evolved early on Earth with bacteria
6. By themselves, Anerobic pathways only provide enough energy for many present-day organisms, most of them being unicellular and some small multicellular ones. However, all of them have limited energy requirments
7. Lesson 7-1 Review:
  1. 1. A Complex process in which cells make ATP by breaking down Organic Compounds
    1. 2. Glycolysis begins with Glucose, and ends with Glysolysis
      1. 3. For each 6-Carbon molecule that begins glycolysis, 2 ATP molecules are used, and 4 ATP molecules are produced
        4. For a cell to engage in fermentation, there musn't be enough Oxygen for it to use
        5. Glysolysis produces 3.5% of the energy that it takes from glucose
        6. This inhibition will lower that amount of ATP in the cell over time since glycolysis will not be able to occur, therefore producing no additional ATP
8. Lesson 7-2 Review:
  1. 1. At the end of the Krebs Cycle,Oxaloacetic acid is formed. It combines with 2 and 4-Carbon compounds at the beginning of the the Cycle
    1. 2. The synthesis of ATP in Cellular Respiration and Photosynthesis are similar as in they both use the concentration of protons to power ATP synthase, which results in chimosmosis
      1. 3. In Aerobic Respiration, O2 makes sure that the electron transport chain never stops, and keeps running by accepting electrons from the last molecule of the chain. Ass a result of respiration, O2 becomes water
        4. The Krebs Cycle occurs in the Mitochondrial Matrix, while the Electron Transport chain is along the inner membrane of the Mitochondria
        5. 55%
        6. This would slow down the production of ATP
Aerobic Respiration
1. Occurs only if Oxygen is present in the cell
2. 2 Major parts - Krebs Cycle & the Electron Transport Chain
  1. In Prokaryotes, they take place in the cytosol of the cell
  2. In Eukaryotes, they take place inside the mitochondria of the cell
    1. The pyruvic acid produced from Glycolysis diffuses across the double membrane of a mitochondrion and enters the mitochondrial matrix, a space inside the inner membrane of a mitochondrion
      1. The mitochondrial matrix contains the enzymes needed to catalyze the reactions of the Krebs Cycle.
      2. When pyruvic acid enters the mitochondrial matrix, it reacts to a molecule called coenzyme A to form acetyl coenzyme A, abbreviated acetyl CoA. The Carbon atom that is lost in the conversion of pyruvic acid to acetyl CoA is released in a molecule of CO2. The reaction also reduces a molecule of NAD+ to NADH
3. The Krebs Cycle
  1. A biochemical pathway that breaks down acetyl CoA, producing CO2, hydrogen atoms, and ATP.
  2. Identified by Hans Krebs
  3. Has 5 Main Steps:
    1. Step 1: A 2-Carbon molecule of acetyl CoA combines with a 4-Carbon compound, oxaloacetic acid, to produce a 6-C compound called citric acid. * This reaction regenerates CoA
      1. Step 2: Citric Acid releases a CO2 molecule and a hydrogen atom to form a 5-C compound. By losing a hydrogen atom with its electron, citric acid is oxidized. The hydrogen atom is trasferred to NAD+, reducing it to NADH
        Step 3: The 5-C compound formed in Step 2 also releases a CO2 molecule and a hydrogen atom, forming a 4-C compound. Again NAD+ is reduced to NADH. * In this step, a molecule of ATP is also synthesized from ADP
        Step 4: The 4-C compound formed in Step 3 releases a hydrogen atom to form another 4-C compound. This time, the hydrogen atom is used to reduce FAD (a molecule similar to NAD+) to FADH2
        Step 5: The 4-C compound formed in Step 4 releases a hydrogen atom to regenerate oxaloacetic acid. which keeps the Krebs Cycle operating. The hydrogen atom reduces NAD+ to NADH
  4. One glucose molecule carries 2 turns of the Krebs Cycle
    1. These 2 turns produce 6 NADH, 2 FADH2, 2 ATP, and 4 CO2 molecules.
      1. CO2 = waste byproduct
        ATP = Energy
      2. * One Glucose molecule produces the same number of ATP molecules as does glycolysis
  5. At the end, for each glucose molecule broken down, in total, we have 10 NADH molecules, and 2 FADH2 molecules, which will later be used in the electron transport chain
  6. Occurs in Mitochondrial Matrix
4. Electron Transport Chain
  1. 2nd Stage of Aerobic Respiration
  2. lines the inner membrane of mitochondrian in Eukaryotic cells
    Nota:
    - the inner membrane has many folds called cristae
  3. Produces ATP when NADH and FADH2 release hydrogen atoms, regenerating NAD+ and FAD.
    1. The electrons in the hydrogen atoms released by NADH and FADH2 are at high energy levels
      1. As the electrons pass through a series of molecules, they lose some of their energy, which is used to create a concentration gradient of protons between the inner and outer mitochondrial membranes
        The concentration of protons helps power ATP synthase and allow for chemiosmosis, which makes ATP
        ATP can be synthesized by chemiosmosis only if electrons continue to more along transport chain
        Therefore, Oxygen accepts electrons from last molecule from trasport chain, allowing the flow of electrons to keep running and the chain to never stop
        As a result of respiration, O2 becomes water
5. Energy Yield
  1. Most Eukaryotic cells produce 38 ATP molecules per glucose molecule broken down
  2. Aerobic Respiration efficiency given cell generates 38 ATP molecules
    1. Efficiency of Aerobic Respiration = ((38 ATP molecules x 12 kcal) / 686 kal) x 100% = 66%
  3. 20 times more efficient than glycolysis alone
6. Equation = C6H12O6 + 6O2 = 6H2O + energy
Provides cells with ATP and Organic Compounds needed to function that food doesn't provide

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