Once pyruvate enters the matrix, a multienzyme complex, known as the pyruvate dehydrogenase complex, catalyzes the following three changes/steps:
Decarboxylation - pyruvate oxidized, CO2 is released
Redox - NAD+ is reduced by two H atoms to create NADH
Acylation - Coenzyme A is attached to the remaining acetic acid portion forming acetyl-CoA (thioester linkage)
**Remember this happens twice – once PER EACH pyruvate (there are 2 pruvates)**
Overall equation: 2 pyruvate + 2NAD+ + 2CoA 🡪 2 acetyl-CoA + 2NADH + 2H+ + 2CO2
areas of mitochondria
Outer Membrane (smooth)
behaves like a cell membrane
contains enzymes to convert fatty acids into forms that can be further metabolized
Inner Membrane (highly folded)
the folds are called cristae (singular: crista)
large surface area and is the site of reactions for the Electron Transport Chain (ETC)
has many proteins and enzymes both in the membrane itself and attached to the surface
Intermembrane space:
the fluid filled space between the inner and outer mitochondrial membranes
proton reservoir during ATP synthesis and it also contains various other enzymes that use ATP
Matrix:
the fluid that fills the inner space of the mitochondrion
highly concentrated mixture of proteins including those to break down proteins, lipids, and carbohydrates
About Krebs cycle: Location: mitochondrion matrix
Aerobic (requires oxygen)
Each step catalyzed by an enzyme
A cyclical metabolic pathway because the product of step 8 is the reactant of step 1
Acquires acetyl-CoA from pyruvate oxidation
Oxidizes acetyl-CoA to carbon dioxide
Regenerating the compound (oxaloacetate) that picks up more acetyl-CoA
converts released energy to ATP, NADH, and FADH2
Overall equation: Acetyl-CoA + 3NAD + FAD + H2O + ADP + Pi
🡪 3NADH + FADH + 2 CO2 + ATP
at the end of krebs...The original glucose molecule is entirely consumed
The six carbon atoms leave the process as six low-energy CO2 molecules, which are released by the cell as waste
The energy in glucose is now stored in the form of
4 ATP molecules (2 from glycolysis and 2 from Krebs cycle)
12 reduced coenzymes also store the free energy in NADH and FADH2 molecules will eventually be transferred to ATP in the next (and last) stage of cellular respiration
starting molecule: acetyl-CoA
Net product:
6 NADH
2 FADH2
2 ATP
4 CO2
ETC
What is it? A series of multiprotein complexes, electron shuttles, and ATP synthase embedded in the inner mitochondrial membrane
Two Main Goals of ETC
Convert the energy held in NADH and FADH2 from glycolysis, pyruvate oxidation and Kreb’s cycle into ATP
Transfer the final protons and electrons to oxygen to make water
COmpoments of ETC: Complex I = NADH dehydrogenase
Complex II = succinate dehydrogenase
(sometimes not shown in diagrams; does not pump H+)
Q = coenzyme Q = “ubiquinone”
Complex III= cytochrome bc1 complex
C = “cty c” = cytochrome c
Complex IV = cytochrome oxidase
* Q and cyt c = “mobile electron carriers”
ETC process
NADH is oxidized at protein complex I (NADH dehydrogenase)
NADH gives its 2 electrons to complex I
Mobile electron carrier, coenzyme Q, shuttles the electrons to complex III (cytochrome bc)
FADH2 skips complex I (NADH dehydrogenase)
FADH2 is oxidized at coenzyme Q
FADH2 gives its 2 electrons to complex Q
Mobile electron carrier, coenzyme Q, shuttles the electrons to complex III (cytochrome bc)
Electrons shuttle through the ETC like a baton handed from runner to runner in a relay race alternately reducing (gaining electrons) and oxidizing (losing electrons) the components
Electrons will continue to be moved and passed along through various proteins complexes and electron shuttles
As the electrons move through complex I, III, and IV, the complex uses the free energy from the electrons to pump a proton (H+) into the intermembrane space
In the end, the electrons will be accepted by oxygen (O2) and the oxygen will pick up some protons to create H2O
This process is to create the proton gradient that will be used to fuel the production of ATP in chemiosmosis - *the ETC generates no ATP directly
Subtopic
About: Occurs in the cristae is where ATP is made from ADP and Pi.
ATP synthase uses the energy of the proton gradient to power ATP synthesis
Electrical potential energy converted into chemical potential energy of ATP by complexes called ATP synthase
concentration gradient of H+ creates proton-motive force
The ATP synthase complexes are the only place H+ can diffuse back to the matrix (exergonic flow of H+).
Process: This flow of H+ is used by the enzyme to phosphorylate ADP to ATP - process called chemiosmosis.
Electrons move DOWN their concentration gradient
One molecule of ATP is made when a hydrogen ion passes through the ATP synthase enzyme from the intermembrane space to the matrix 🡪 1H+ = 1 ATP made
WHat is it: Process that uses energy in a hydrogen ion gradient across the inner mitochondrial membrane to drive oxidative phosphorylation of ATP
ATP yield
actual ATP yield (30-32) lower than theoretical yield (36-38)
Why? Depends on electron shuttle (“aspartate malate” vs “glycerol phosphate”)
Lost as thermal energy / heat
Ratio is not exact for NADH : ATP and FADH2 : ATP
Difference between aerobic and anaerbic: Respiration in which an inorganic molecule other than oxygen (O2) is the final electron acceptor.
Some prokaryotes and some organisms that live in anoxic conditions
Anaerobic = oxygen is not present/available
A cellular respiration pathway that transfers electrons from NADH to an organic acceptor molecule
An alternative set of reactions that allows glycolysis to occur in the absence of oxygen as a final electron acceptor - allows cells to regenerate NAD+ for glycolysis
Efficiency
Less efficient than aerobic cellular respiration (i.e. produces less energy) because there is no Krebs cycle and no ETC
Only produces a net of 2 ATP per glucose molecule generated in glycolysis
Ethanol Fermentation
NADH passes its hydrogen atoms to acetaldehyde, a compound formed when a carbon dioxide molecule is removed from pyruvate by the enzyme pyruvate decarboxylase
This forms ethanol, the alcohol used in alcoholic beverages
Lactate fermentation
NADH that is reduced during glycolysis cannot be re-oxidized to NAD+ by ETC as fast as its being reduced – therefore, muscles run out of NAD+ and glycolysis will stop -so we need a different way to re-oxidize NADH
In lactate fermentation…
NADH produced in glycolysis transfers its hydrogen atoms to pyruvate in the cytoplasm of the cell, regenerating NAD+ and allowing glycolysis to continue
Pyruvate changes into lactate
application : Under normal conditions, animals such as humans catabolize glucose by aerobic respiration
During heavy exercise, ATP production will switch from aerobic respiration to anaerobic respiration
During intense exercise, oxygen cannot be delivered to muscle cells fast enough to supply energy
Must RELY on glycolysis for energy because glycolysis occurs in anaerobic conditions
About glycolysis Location – Cytoplasm
Anaerobic/Aerobic? - Anaerobic (does not use oxygen)
Each step catalyzed by a specific enzyme
Glycolysis = “sugar splitting”
10 enzyme-catalyzed reactions
one 6C glucose is split into two 3C pyruvate molecules
net energy gain of 2 ATP
2 NAD+ are reduced to NADH
3 stages of glycolysis
Energy Investment (reactions #1-3)
Cleavage (reactions #4-5)
Energy Pay-off (reactions #6-10)
energy yield: 2 ATP are used per glucose
4 ATP are produced per glucose
overall net yield of 2 ATP per glucose
overall 2 NADH per glucose molecule (will be used in Stage 4 - ETC to form ATP)
product created: 2 pyruvates
2 ATP
2 NADH
2 H2O
starting molecule: 1 molecule of glucose
Metabolism is the sum of all chemical reactions that occur in the cell of an organism
A metabolic pathway is:
a sequence of chemical reactions in living cells
begins with a specific molecule and ends with a product
each step is catalyzed by a specific enzyme
Energy is the capacity to do work (cause change)
forms of energy
Kinetic Energy is energy associated with motion
Heat (thermal energy) is kinetic energy associated with random movement of atoms or molecules
Potential Energy is stored energy
Chemical energy is potential energy stored in bonds
The Laws of Thermodynamics
The First Law of Thermodynamics says that the energy of the universe is constant
Second Law of Thermodynamics says that:
Disorder in the universe (entropy) is continuously increasing
i.e. disorder is more favoured than order
Gibbs free energy
∆G = ∆H – T∆S
Process that uses the Sun’s energy to make simple sugars
6 CO2 + 6 H2O + sunlight 🡪 C6H12O6 + 6 O2
Photosynthesis occurs in the chloroplast
Terminologies : When matter absorbs light energy, light is absorbed in the form of packets of energy called photons
A compound that absorbs certain wavelengths of visible light is called a pigment (wavelength determines colour)
Chlorophyll is the main type of pigment in plants
two step
photosynthesis: Light Dependent Reactions
Occur within the thylakoids
Involves three steps:
Excitation of photosystems by light energy
Production of ATP via an electron transport chain
Reduction of NADP+ and the photolysis of water
Step 1: Excitation of Photosystems by Light Energy
Photosystems are groups of pigments embedded within the thylakoid membrane
Photosystems are named according to their maximal absorption wavelengths (PS I = 700 nm ; PS II = 680 nm)
When a photosystem absorbs light energy, electrons within the pigments become energised or ‘excited'
These excited electrons are transferred to carrier molecules within the thylakoid membrane
Step 2: Production of ATP via an Electron Transport Chain
Excited electrons from Photosystem II (P680) are transferred to an electron transport chain within the thylakoid membrane
As the electrons are passed through the chain they lose energy, which is used to move H+ ions into the thylakoid
This build up of protons within the thylakoid creates an electrochemical gradient
The H+ ions return to the stroma (along the proton gradient) via ATP synthase (chemiosmosis)
tep 3: Reduction of NADP+ and the Photolysis of Water
Excited electrons from Photosystem I are transferred to a carrier molecule and used to reduce NADP+
This forms NADPH – which is needed (together with ATP) for the light independent reactions
The electrons lost from Photosystem I are replaced by de-energised electrons from Photosystem II
The electrons lost from Photosystem II are replaced by electrons released from water via photolysis:
photosynthesis: Light Indpendent Reactions
The light independent reactions use the chemical energy derived from light dependent reactions to form organic molecules
The light independent reactions occur in the fluid-filled space of the chloroplast called the stroma
The light independent reactions are collectively known as the Calvin cycle and involve three main steps:
Carboxylation of ribulose bisphosphate
Reduction of glycerate-3-phosphate
Regeneration of ribulose bisphosphate
In the Calvin Cycle, energy and electrons from the Light Reactions (in the form of ATP and NADPH) and carbon dioxide from the atmosphere are used to produce organic compounds.
The Calvin Cycle occurs in the stroma inside the chloroplasts (inside the cells).
Reactants: carbon dioxide, ATP and NADPH
Product: organic compounds (G3P) → eventually glucose