Respiration Flashcards
What is glycolysis
Breakdown of glucose by enzymes
Occurs in the cytoplasm
Anaerobic process (doesn’t require oxygen); the first stage of aerobic and anaerobic respiration.
Glycolysis process
Phosphorylation of glucose to glucose phosphate using the inorganic phosphates from 2ATP
Glucose phosphate hydrolysed to 2 X triose phosphate
2 X Triose phosphate oxidised to 2 X pyruvate where 2NAD is reduced (collects hydrogen ions) and 4ATP is regenerated
4 gained – 2 used = net production of 2ATP
After glycolysis if no oxygen present (anaerobic respiration)
Pyruvate converted to lactate (animal cells, some bacteria) or ethanol (plants, yeast)
Reduced NAD is oxidised so that NAD is regenerated
Glycolysis, which uses NAD, can continue
Some energy still in lactate (incomplete breakdown of glucose)
Anaerobic respiration is much less efficient than aerobic respiration; the ATP yield is lower. The majority of ATP is formed in oxidative phosphorylation
After glycolysis if oxygen present (aerobic respiration)
Pyruvate actively transported into the mitochondrial matrix
Stages of aerobic respiration:
1. Glycolysis
2. Link reaction
3. Krebs cycle
4. Oxidative phosphorylation
Aerobic respiration stage 2: Link reaction
Occurs in mitochondrial matrix
Pyruvate oxidised and decarboxylated which produces acetate
CO2 and reduced NAD produced
Acetate combines with coenzyme A which produces Acetyl Coenzyme A
Per glucose molecule, 2 X Acetyl CoA, 2 X CO2 and 2 X reduced NAD produced
Aerobic respiration stage 3: Krebs cycle
Occurs in mitochondrial matrix
Acetyl coenzyme A reacts with a 4-carbon molecule (oxaloacetate), producing a 6-carbon molecule (citrate) that enters the Krebs cycle. Coenzyme A released back into the link reaction to be used again
6C molecule converts to 5C, which in turn converts to 4C molecule (4C molecule regenerated) through a series of oxidation-reduction reactions
Decarboxylation and dehydrogenation occurs where CO2 is removed and coenzymes NAD and FAD are reduced (key point - important for oxidative phosphorylation)
ATP produced by substrate level phosphorylation (direct transfer of Pi from intermediate compound to ADP)
Aerobic respiration stage 4: Oxidative phosphorylation
On the cristae of mitochondria, reduced NAD/FAD is oxidised to release H atoms and are split into protons (H+) and electrons (e-)
Electrons transferred down the electron transport chain (a chain of carriers at decreasing energy levels) by redox reactions
Energy released by electrons used in the production of ATP from ADP + Pi (chemiosmotic theory):
a. Energy used by electron carriers to actively transport protons from the matrix to the intermembrane space
b. Protons diffuse down an electrochemical gradient, via ATP synthase (embedded in the inner mitochondrial membrane) back into the matrix
c. Releasing energy to combine ADP + Pi to ATP
In the matrix at the end of the electron transport chain, oxygen is the final electron acceptor – protons, electrons and oxygen combine to form water
Why is oxygen needed for the production of ATP on the cristae of the mitochondrion?
Oxygen is the terminal electron acceptor for electrons passing along the electron transport chain
The electron transport chain releases the energy for the formation of (most) ATP (from ADP + Pi)
No oxygen to accept them so electrons can’t be passed along the electron transport chain
The Krebs cycle and link reaction also stop in the absence of oxygen because NAD and FAD (converted from reduced NAD/FAD as they release their H atoms for the ETC,) cannot be produced.
Other respiratory substrates
Other respiratory substrates include the breakdown products of lipids and amino acids, which enter the Krebs cycle. For example:
Fatty acids from the hydrolysis of lipids are converted to Acetyl Coenzyme A
Amino acids from the hydrolysis of proteins are converted to intermediates in Krebs cycle
