Chapter 7 (respiration)

• Energy flow and chemical recycling in ecosystems:

  • Energy enters an ecosystem as sunlight and leaves it as heat
  • the chemical elements essential for life are recycled

  
• the principle of redox reactions (reduction-oxidation):

  • reduction: the process of gaining electrons
  • Oxidation: the process of losing electrons
  • reducer: the substance that is able to give electrons
  • oxidizer: the substance that is able to take electrons

  
• oxidation:

  • oxidization of organic molecules in cells is similar to burning of fuel such as methane gas

  
• stepwise oxidation of sugar in cells:

  • in a cell, enzymes catalyze the breakdown of sugars via a series of small steps -> a portion of the free energy released is captured by the formation of activated carriers

  
• direct burning of sugar:

  • the direct burning of sugar in nonliving systems generates more energy than can be stored by any carrier molecule -> this energy is released as heat

  
• catabolism and anabolism

  
• carrier molecules in activated forms:

  • monomers of RNA:
  • ATP
  • GTP (same function as ATP but not as common)
  • (just read over the image)

  
• catabolic reactions:

  • gradual oxidation of energy-rich molecules
  • to obtain energy -> food is broken down into simpler organic molecules, which later become substrates for cellular respiration
• stage 1 of catabolism:

  • energy extraction from food is digestion
  • specialized enzymes in:
  • mouth (neutral ph)
  • stomach (Acidic ph) - digestion of proteins
  • intestine (Basic ph) - digestion of polysaccharides
  • Acids in stomach participate in hydrolysis
  • absorption through specialized cells in small intestine -> bloodstream -> body cells
  • Enzymes in lysosomes for internal cellular digestion
  • after digestion, the small organic molecules derived from food enter cytosol of a cell -> gradual oxidative breakdown begins
• Stage 1 of catabolism:

  
• the four major domains of cellular respiration:

  • Glycolysis - in cytosol
  • pyruvate oxidation - in mitochondria
  • citric acid cycle - in mitochondria
  • oxidative phosphorylation: electron transport and chemiosmosis - in mitochondria
• Glycolysis - in cytosol

  • glucose -> pyruvate
  • produces substrate-level phosphorylation (little ATP)
  • electrons via NADH from this stage are weaker than the others because it is produced outside the mitochondria
• • pyruvate oxidation - in mitochondria
  • pyruvate -> acetyl CoA
  • releases CO2 (IMPORTANT TO KNOW THE STAGE)
  • electrons are carried from this stage via NADH
• citric acid cycle - in mitochondria

  • produces substrate-level phosphorylation (little ATP)
  • releases CO2 ( IMPORTANT TO KNOW THE STAGE)
  • electrons are carried from this stage via NADH and FADH2
• oxidative phosphorylation: electron transport and chemiosmosis - in mitochondria

  • accepts the electrons transported from other stages by NADH and FADH2
  • produces oxidized phosphorylation
  • produced through usage of proton gradient
  • produces 10 to 20 more ATP here
• substrate-level phosphorylation:

  • produces very few ATP molecules compared with oxidative phosphorylation

  
• energy input and output of glycolysis:

  • energy investment phase
  • split glucose composition into 2
  • 2 ATP is consumed -> produces 2 ADP + 2 P
  • (look at the image)

  
• overall energy outcome of glycolysis :

  glucose -> 2 pyruvate + 2H2O

  4 ATP formed - 2 ATP used -> 2 ATP

  2 (NAD+) + 4 (e-) + 4H+ -> 2 NADH +2H+
• overall purpose of glycolysis:

  • oxidation of carbonyl groups of sugars to carboxyl groups of organic acids

  
• oxidation of pyruvate to acetyl CoA:

  • carboxyl group of pyruvate is completely oxidized and removed -> has very little energy
  • releases CO2 - first place in respiration where CO2 is released
  • the remaining 2 carbon fragments still have much chemical energy
  • part of the remaining energy is given to NAD+ for storage
  • the rest of the energy is preserved in the form of acetic group bound to coenzyme A -> given to next step for further oxidation

  
• Glycolysis and TCA:

  • they provide precursors for cells to synthesize many important organic molecules (in anabolic pathways)
• oxidative phosphorylation:

  • is the final stage of cell respiration
  • uses energy of the stored electrons for ATP synthesis with the help of chemiosmosis
• Aerobic respiration:

  • oxygen is needed only as an agent that can accept low energy electrons at the end of the electron transport chain to make electrons flow through the system
• anaerobic respiration (nonaerobic):

  • some microbes can "breathe" without respiration
  • they use one of the following terminal electron acceptors instead of O2
  • Sulfate
  • nitrate
  • sulfur
  • fumarate (deprotonated version of HOOC-CH=CH-COOH)
• chemiosmosis theory:

  • same mechanism is working in chloroplast (thylakoid membrane)
  • the energy to power to proton pump comes from light

  
• chemiosmotic proton flow energizes

  • mitochondria membrane
  • chloroplast membrane
  • inner membranes of gram negative bacteria (including photosynthetic bacteria)

  
• elements essential for ETC and cellular respiration

  • iron (Fe)
  • copper (Cu)
  • Sulfur (S)
• ATP synthase :

  • produces ATP similar to how a hydroelectric power generator produces electricity
  • enzyme present in
  • chloroplast
  • mitochondria
  • plasma membrane of bacteria
  • produces more than 100 molecules of ATP/sec - 3 molecules of ATP/revolution

  
• ATP synthase is a reversible coupling device

  • can operate in reverse (functions as a H+ pump)
  • uses energy of ATP hydrolysis to pump protons against their electrochemical gradient across the membrane
  • working as an ATP synthesis of ATP hydrolysis depends on the magnitude of the electrochemical gradient across the membrane

  
• ATP yield per molecule of glucose at each stage of cellular respiration:

  
• theoretical ATP yield per glucose molecule:

  • theoretical ATP yield of respiration 6ATP molecules higher
  • this maximal output is never reached because of the partially damaged state of the membrane at physiological conditions