Cellular Respiration

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Cellular Respiration
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INTRODUCTION TO CELLULAR RESPIRATION

• Nearly all the cells in our body break down
  sugars for ATP production
• Most cells of most organisms harvest energy
  aerobically
• The aerobic harvesting of energy from sugar is
  called cellular respiration
• Cellular respiration yields CO2, H2O, and a large
  amount of ATP

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Cellular respiration banks energy in ATP molecules

• Cellular respiration breaks down glucose
  molecules and banks their energy in ATP
• The process uses O2 and releases CO2 and H2O

ATP powers almost all cell and body activities
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Glycolysis

• There are two important ways a cell can harvest
  energy from food fermentation and cellular
  respiration.
• Both start with the same first step the process
  of glycolysis which is the breakdown or splitting
  of glucose (6 carbons) into two 3-carbon
  molecules called pyruvic acid (pyruvate)
• The energy from other sugars, such as fructose,
  is also harvested using this process. Glycolysis
  is probably the oldest known way of producing
  ATP. .

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Glycolysis Contd

• There is evidence that the process of glycolysis
  predates the existence of O2 in the Earths
  atmosphere and organelles in cells
• Glycolysis does not need oxygen as part of any of
  its chemical reactions. It serves as a first step
  in a variety of both aerobic and anaerobic
  energy-harvesting reactions.
• Glycolysis happens in the cytoplasm of cells, not
  in some specialized organelle.
• Glycolysis is the one metabolic pathway found in
  all living organisms.

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Summary Of Glycolysis

• Summary of the steps of Glycolysis
• a. 2 ATP added to glucose (6C) to energize it.
• b. Glucose split to 2 PGAL (3C). (PGAL
  phosphoglyceraldehyde)
• c. H and e- (e- electron) taken from each PGAL
  given to make 2 NADH.
• d. NADH is energy and e- carrier.
• e. Each PGAL rearranged into pyruvate (3C), with
  energy transferred to make 4 ATP (substrate
  phosphorylation).
• f. Although glycolysis makes 4 ATP, the net ATP
  production by this step is 2 ATP (because 2 ATP
  were used to start glycolysis). The 2 net ATP are
  available for cell use.
• g. If oxygen is available to the cell, the
  pyruvate will move into the mitochondria
  aerobic respiration will begin.

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Glycolysis
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Net Yield from Glycolysis

• Net Yield from Glycolysis
• 4 NADH2
• 2 CO2
• 4 ATP ( 2 used to start reaction)

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Fermentation

• If no oxygen is available to the cell
  (anaerobic), the pyruvate will be fermented by
  addition of 2 H from the NADH (to alcohol CO2
  in yeast or lactic acid in muscle cells).
• This changes NADH back to NAD so it is available
  for step c above. This keeps glycolysis going!
• In fermentation these pyruvic acid molecules are
  turned into some waste product, and a little
  bit of energy (only two ATP molecules per
  molecule of glucose actually four are produced
  in glycolysis, but two are used up) is produced.
• Out of many possible types of fermentation
  processes, two of the most common types are
  lactic acid fermentation and alcohol
  fermentation.

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Lactic Acid Fermentation

• Lactic acid fermentation is done by some fungi,
  some bacteria like the Lactobacillus acidophilus.
  in yogurt, and sometimes by our muscles.
• Normally our muscles do cellular respiration
  like the rest of our bodies, using O2 supplied by
  our lungs and blood. However, under greater
  exertion when the oxygen supplied by the lungs
  and blood system cant get there fast enough to
  keep up with the muscles needs, our muscles can
  switch over and do lactic acid fermentation.
• In the process of lactic acid fermentation, the
  3-carbon pyruvic acid molecules are turned into
  lactic acid.
• It is the presence of lactic acid in yogurt that
  gives it its sour taste, and it is the presence
  of lactic acid in our muscles the morning after
  that makes them so sore. Once our muscles form
  lactic acid, they cant do anything else with it,
  so until it is gradually washed away by the blood
  stream and carried to the liver (which is able to
  get rid of it), our over-exerted muscles feel
  stiff and sore even if they havent been
  physically injured.

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Lactic Acid Fermentation
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Alcohol Fermentation

• Alcohol fermentation is done by yeast and some
  kinds of bacteria.
• The waste products of this process are ethanol
  and carbon dioxide (CO2).
• Humans have long taken advantage of this process
  in making bread, beer, and wine.
• In bread making, it is the CO2 which forms and is
  trapped between the gluten (a long protein in
  wheat) molecules that causes the bread to rise,
  and the ethanol (often abbreviated as
  EtOH)evaporating that gives it its wonderful
  smell while baking.

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Alcohol Fermentation
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Cellular Respiration

• An analogy can be drawn between the process of
  cellular respiration in our cells and a car. The
  mitochondria are the engines of our cells where
  sugar is burned for fuel and the exhaust is CO2
  and H2O. Note that in a car that burned fuel
  perfectly, the only exhaust should theoretically
  be CO2 and H2O also.

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Cellular Respiration

• There are three steps in the process of cellular
  respiration glycolysis, the Krebs cycle, and the
  electron transport chain.
• Occurs in the mitochondria
• Pyruvic acid from glycolysis diffuses into matrix
  of mitochondria reacts with coenzyme A to for
  acetyl-CoA (2-carbon compound)
• CO2 and NADH are also produced

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Kreb's Cycle

• Named for biochemist Hans Krebs
• Metabolic pathway that indirectly requires O2 
• Kreb's Cycle is also known as the Citric acid
  Cycle
• Requires 2 cycles to metabolize glucose
• Acetyl Co-A (2C) enters the Kreb's Cycle joins
  with Oxaloacetic Acid (4C) to make Citric Acid
  (6C)
• Citric acid is oxidized releasing CO2 , free H,
  e- and forming ketoglutaric acid (5C)
• Free e- reduce the energy carriers NAD to NADH2
  and FAD to FADH2
• Ketoglutaric acid is also oxidized releasing more
  CO2 , free H, e-
• The cycle continues oxidizing the carbon
  compounds formed (succinic acid, fumaric acid,
  malic acid, etc.) producing more CO2, NADH2,
  FADH2, ATP
• H2O is added to supply more H
• CO2 is a waste product that diffuses out of cells
  
• Oxaloacetic acid is regenerated to start the
  cycle again
• NADH2 and FADH2 produced migrate to the Electron
  Transport Chain (ETC)

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Net Yield from Kreb's Cycle (2 turns)

• 6 NADH2
• 2 FADH2
• 4 CO2
• 2 ATP

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Electron Transport Chain

• Found in the inner mitochondrial membrane or
  cristae
• Contains 4 protein-based complexes that work in
  sequence moving H from the matrix across the
  inner membrane (proton pumps)
• A concentration gradient of H between the inner
  outer mitochondrial membrane occurs
• H concentration gradient causes the synthesis of
  ATP by chemosmosis
• Energized e- H from the 10 NADH2 and 2 FADH2
  (produced during glycolysis Krebs cycle) are
  transferred to O2 to produce H2O (redox reaction)
  
• O2    4e-    4H  2H2O

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Energy Yield from Aerobic Respiration

• Glycolysis
• 4 NADH2
• O FADH2
• 2 ATP
• Kreb's Cycle
• 6 NADH2
• 2 FADH2
• 2 ATP
• Total
• 10 NADH2 x 3 30 ATP
• 2 FADH2 x 2 4 ATP
• 4 ATP
• 38 ATP

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• Most cells produce 36- 38 molecules of ATP per
  glucose (66 efficient)
• Actual number of ATP's produced by aerobic
  respiration varies among cells

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ATP (Adenosine triphosphate )

• Energy carrying molecule used by cells to fuel
  their cellular processes
• ATP is composed of an adenine base, ribose sugar,
  3 phosphate (PO4) groups
• The PO4 bonds are high-energy bonds that require
  energy to be made release energy when broken
• ATP is made used continuously by cells
• Every minute all of an organism's ATP is recycled
  
• Phosphorylation refers to the chemical reactions
  that make ATP by adding Pi to ADP ADP Pi
  energy   ATP H2O
•  
• Enzymes  (ATP synthetase ATPase) help break
  reform these high energy PO4 bonds in a process
  called substrate-level phosphorylation
• When the high-energy phosphate bond is broken, it
  releases energy, a free phosphate group,
  adenosine diphosphate (ADP)