How Cells Make ATP: Glycolysis and Respiration

1
How Cells Make ATP Glycolysis and Respiration

• Ali Afrasiabi
• Period 1
• 04-05

2
An Overview of Glucose Oxidation

• Oxidation- loss of an electron
• Reduction- gain of an electron
• In the oxidation of glucose, carbon-carbon bonds,
  carbon-hydrogen bonds, and oxygen-oxygen bonds
  are exchanged for carbon-oxygen bonds and
  hydrogen-oxygen bonds, as oxygen atoms attract
  and hoard electrons. This oxidation takes place
  in glycolysis and respiration
• C6H12O6 6O2?CO2 6H2O

3
Glycolysis

• In glycolysis, the 6-carbon glucose molecule is
  split into 2 molecules of a 3-carbon compound,
  pyruvic acid. 4 hydrogen atoms are removed from
  the glucose molecule in this process and the
  electrons and 2 of the protons are accepted by
  the NAD molecules, while the other 2 protons
  remain in solution as hydrogen ions (H), this
  all takes place in the cytoplasm of the cell,
  this is the beginning of aerobic cellular
  respiration. This is where prokaryotes
  (bacteria) get their energy because they have no
  nucleus, thus they cant do steps 2,3, and 4 of
  cellular respiration.

4
9 Steps of Glycolysis

• Step 1 Input of energy required is supplied by
  coupling steps to the ATP/ADP system. The
  terminal phosphate group is transferred from an
  ATP molecule to the carbon in the 6th position of
  the glucose molecule, to make glucose
  6-phosphate.
• Step 2 The Molecule is reorganized. The 6-sided
  glucose ring becomes 5-sided fructose ring
• Step 3 Fructose 6-phosphate gains a 2nd
  phosphate by the investment of another ATP. The
  added phosphate is bonded to the 1st carbon,
  producing fructose with phosphates in the 1 and 6
  positions. The allosteric interaction between
  ATP and phosphofructokinase is a chief regulatory
  mechanism of glycolysis.

5
Glycolysis Contd

• Step 4 6 carbon sugar molecule is split into two
  3-carbon molecules, dihydroxyacetone phosphate
  and glyceraldehyde phosphate, this step completes
  the preparatory reactions of glycolysis.
• Step 5 Glyceraldehyde phosphate molecules are
  oxidized and NAD is reduced to NADH and H.
  Energy from this oxidation reaction is conserved
  in the attachment of a phosphate group to what is
  now the 1 position of the glceraldehyde phosphate
  molecule.
• Step 6 This phosphate is released from the
  diphosphoglycerate molecule and used to recharge
  a molecule of ADP, this is a highly exergonic
  reaction.
• Step 7 The remaining phosphate group is
  enzymatically transferred from the 3 position to
  the 2 position
• Step 8 Molecule of water is removed from the
  3-carbon compound, which creates energy in the
  vicinity of the phosphate group
• Step 9 The phosphate is transferred from a
  molecule of ADP, forming another molecule of
  ATP(2 molecules of ATP/glucose).

6
(No Transcript)
7
Anaerobic Pathways

• Anaerobic respiration- principal pathway of
  energy metabolism without the presence of oxygen
• Fermentation- formation of alcohol from sugar
• When oxygen is more abundant and ATP demand is
  reduced, the lactic acid is resynthesized to
  pyruvic acid and back again to glucose or
  glycogen, this occurs because it uses NADH and
  regenerates NAD without which glycolysis cannot
  go forward

8
(No Transcript)
9
Respiration

• Respiration- oxidation of food molecules by cells
• Takes place in Krebs cycle and electron transport
  system, which occur in the mitochondria of
  eukaryotic cells.
• Matrix- dense solution in mitochondria, which
  contains enzymes, coenzymes, water, phosphates,
  and other molecules involved in respiration
• The selective permeability of inner membrane of
  mitochondria is critical to the ability of the
  mitochondria to harness the power of respiration
  to the production of ATP.

10
Krebs Cycle

• Upon entering the cycle, 2-carbon acetyl group is
  combined with a 4-carbon compound to produce a
  6-carbon compound(citric acid).
• Occurs in mitochondria, is the common pathway to
  completely oxidize fuel molecules which mostly is
  acetyl CoA
• 2 acetyl CoA are transferred to electrons to NAD
  and FAD
• The net result is 24 ATP/glucose

11
(No Transcript)
12
Electron Transport

• Carbon atoms of the glucose molecule are now
  completely oxidized.
• Electron carriers NAD and FAD make up what is
  known as an electron transport chain, in which
  the electrons are held by NADH and FADH2
• Cytochromes- principal components of electron
  transport chain, which consist of a protein and a
  heme group

13
(No Transcript)
14
Chemiosmotic Coupling

• Oxidative phosphorylation- the way which ATP is
  formed from ADP and phosphate as electrons pass
  down the electron transport chain, this is
  regulated by the supply and demand of the cell
• Chemiosmotic coupling- process powered by a
  gradient of protons(H ions) established across
  the inner mitochondrial membrane
• ATP synthetase- large enzyme tunnel which
  provides for channel allowing protons to flow
  down the electrochemical gradient back into the
  matrix

15
Overall Energy Harvest

• Glycolysis yields 2 molecules of ATP directly and
  2 molecules of NADH, which is 6 ATP
• The transition reaction which converts pyruvic
  acid to acetyl CoA yields 2 molecules of NADH for
  each molecule of glucose and so produces 6
  molecules of ATP
• The Krebs Cycle yields 2 molecules of ATP, 6 of
  NADH, and 2 of FADH2, or a total of 24 ATP, for
  each molecule of glucose
• Maximum energy yield from the oxidation of one
  molecule of glucose is 38 ATP

16
(No Transcript)