Cellular Respiration
1. Recognize the reactants and products of glycolysis
2. Summarize the major steps in the Kreb’s cycle.
3. Describe the electron transport system
4. Contrast the energy output of aerobic and anaerobic respiration |
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- Cellular Respiration is an
ATP-producing catabolic process in which the eventual electron acceptor
is an inorganic molecule, such as oxygen
- Living things get their energy
from the cellular respiration process. This process takes glucose
present in a cell and breaks it down to release its energy.
- The two types are aerobic
respiration (oxygen required) and anaerobic respiration (no oxygen used).
- Energy that is produced is
stored in the bonds of an adenosine and phosphate molecule.
ADP has 2 phosphate groups, while another phosphate group (with the energy
stored in the connecting bond) is added to produce an ATP. When energy
is needed, a bond breaks and energy is released (ATP >ADP).
| Aerobic Respiration |
Glucose
+ Oxygen ---------------> Carbon Dioxide
+ Water + Enegry
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- Aerobic respiration produces
much more energy (ATPs) than anaerobic respiration ... about 20x more.
- One molecule of glucose produces
a net total of 36 ATPs. Note: if you add 2 ATPs produced by GTP
in the Krebs Cycle, the total is 38 ATPs.
- Feedback inhibition controls
the reactions of respiration. If the products of a reaction start piling
up, a signal is sent to stop the reaction from occuring.
- Aerobic respiration involves
3 steps: glycolysis, Krebs cycle, electron transport chain.
1) Glycolysis - 1
glucose molecule => 2 pyruvate molecules + 2 ATPs
- the first step of all cellular respiration (aerobic and anaerobic)
[detailed diagram]
- In glycolysis, one molecule of glucose (a simple sugar) is converted
into two pyruvate molecules.
> First, one 6-carbon glucose molecule is split into two 3-carbon sugars.
> Second, the two 3-carbon sugars are oxidized.
> Third, rearrangement of the two 3-carbon sugars produces two pyruvate
molecules
- This occurs in the cytoplasm of the cell.
- Though four ATP molecules are produced, two are used up; so there is
a net production of two ATP molecules.
- Oxygen is not needed for this step.
- This step is exergonic, producing 140 kcal/mol. |
2) Krebs cycle - the second step in aerobic
respiration
- IF oxygen is present, the pyruvate molecules enter the mitochondria to
be oxidized in this 2nd step.
- It's sometimes called the citric acid cycle.
- A carbon dioxide molecule is removed from the pyruvate along with H+
ions, leaving behind an acetyl group.
- This acetyl group is added to a four carbon compound present in
the mitochondrion and produces citric acid.
- Citric acid is then broken down in a number of stages back to the original
four carbon compound releasing 2 CO2
molecules, 2 ATP molecules, and numerous H+ions.
- CO2 is released
as a waste product (this is where the carbon dioxide we exhale comes from)
- The H+ ion is added to NAD with an electron to form the coenzyme NADH.
- GTP and coenzyme FADH2 produce
a small part of the energy.
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3) Electron transport chain - the third
step in aerobic respiration
- Most of the energy produced by aerobic respiration (34 ATPs) is produced
in this step.
- Occurs in a series of nine steps in the inner membrane of the mitochondria.
- The NADH releases electrons down a series of receptors (the electron
carrier chain).
- As the electrons move down the chain, they release energy (stored in
ADPs to create ATPs).
- Oxygen is needed in this step (this is why we need to breathe in oxygen).
- Oxygen is first combined with the electrons, but then quickly combines
with the H+ ions to form water. |
Anaerobic Respiration
- After glycolysis, anaerobic
respiration does not produce any more energy.
- Only two ATP molecules (net)
are produced from anaerobic respiration (from the glycolysis step).
- A common next step in anaerobic
respiration is fermentation.
- In fermentation, the pyruvate
molecules are converted to lactic acid or ethyl alcohol (plus carbon dioxide
and water), but no ATPs are produced.
- Ethanol fermentation occurs
in yeast and in some types of bacteria.
- Lactic acid fermentation occurs
in some types of bacteria and in animal muscles (when they need energy
faster than the blood can supply oxygen).
- Some types of anaerobic respiration
also use the electron transport phosphoylation, but they use other inorganic
molecules as the final electron acceptor instead of oxygen.
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