Metabolic Pathways and Enzymes • Cellular reactions are usually part of a metabolic pathway , a series of linked reactions • Illustrated as follows: E1 E2 E3 E4 E5 E6 A → B → C → D → E → F → G • Letters A-F are reactants or substrates , B-G are the products in the various reactions, and E1-E6 are enzymes . http://highered.mcgraw-hill.com/sites/0072437316/student_view0/ chapter8/animations.html
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Metabolic Pathways and Enzymes Cellular reactions are usually part of a metabolic pathway, a series of linked reactions Illustrated as follows: E 1 E 2.
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Metabolic Pathways and Enzymes• Cellular reactions are usually part of a
metabolic pathway, a series of linked reactions• Illustrated as follows:
E1 E2 E3 E4 E5 E6
A → B → C → D → E → F → G• Letters A-F are reactants or substrates, B-G are
the products in the various reactions, and E1-E6 are enzymes.
• Temperature and pH:• As the temperature rises, enzyme activity
increases. • If the temperature is too high, enzyme activity
declines rapidly because the enzyme is denatured.• When enzyme is denatured, its shape changes and
it can no longer attach to the substrate.• Each enzyme has an ideal temperature and pH at
which the rate of reaction is highest.• Change in pH can alter the structure of the
enzyme, and can eventually cause enzyme to denature.
Rate of an enzymatic reaction as a function of temperature and pH
•Rates and concentration:
•Reaction rate depends on the number of enzyme-substrate complexes that can be formed.
•When all available enzymes and active sites are filled, the rate of activity cannot increase further.
•Substrate concentration•Enzyme activity increases as substrate concentration increases because there are more collisions between substrate molecules and the enzyme.
•Enzyme concentration•Enzyme activity increases as enzyme concentration increases because there are more collisions between substrate molecules and the enzyme.
Overview of Cellular Respiration• Makes ATP (potential energy) from glucose
(chemical energy)• Releases energy in 4 reactions
• Glycolysis, Transition reaction, Citric acid cycle (Kreb’s cycle), and Electron transport system
• An aerobic process that requires O2
• If oxygen is not available (anaerobic), glycolysis is followed by fermentation
Coupled Reaction
The four phases of complete glucose breakdown
Where does each step occur?
•Outside the mitochondria•Step 1 - Glycolysis
•Inside the mitochondria•Step 2 - Transition reaction (matrix)•Step 3 – Citric acid cycle (matrix)•Step 4 – Electron transport system (cristae)
Structure of mitochondria:•Has a double membrane, with an intermembrane space between the two layers.•Cristae are folds of inner membrane•The matrix, the innermost compartment, which is filled with a gel-like fluid.
•It is an oxidation-reduction reaction, or redox reaction for short.•Oxidation is the loss of electrons; hydrogen atoms are removed from glucose.•Reduction is the gain of electrons; oxygen atoms gain electrons.•Remember OIL RIG (oxidation is loss, reduction is gain)
Reaction that Occurs in Cellular Respiration
Enzymes involved:
• NAD+
• Nicotinamide adenine dinucleotide
• Accepts H+ to become NADH
• FAD
• Flavin adenine dinucleotide (sometimes used instead of NAD+)
• Accepts 2H+ to become FADH2
The NAD+ cycle
Step 1. Glycolysis
• Occurs in the cytoplasm (outside the mitochondria)
Energy Yield from Electron Transport Chain• Per glucose molecule:
– 10 NADH take electrons to the ETS 3 ATP from each
– 2 FADH2 take electrons to the ETS 2 ATP from each
• Electrons carried by NADH produced during glycolysis are shuttled to the electron transport chain by an organic molecule (mechanism of delivery may vary # of ATP produced by ETS).
Accounting of energy yield per glucose molecule breakdown
Fermentation• Occurs when oxygen is not available.
• During fermentation, the pyruvate formed by glycolysis is reduced to lactic acid .
• Fermentation uses NADH and regenerates NAD+.
• Occurs in anaerobic bacteria, fungus, & human muscle cells.