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Lecture 5

BIOL 1F90 Lecture 5: chapter 7 two


Department
Biological Sciences
Course Code
BIOL 1F90
Professor
Douglas Bruce
Lecture
5

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Rate-Limiting Step of a Pathway
-slowest step in a metabolic pathway
-often subject to a cellular or biochemical regulation
(inhibition of the rate limiting step eciently and quickly controls a pathway)
Cellular Respiration
-process by which living cells obtain energy from organic molecules
-primary aim is to make ATP and NADH
-when oxygen is used it is called the process of aerobic respiration (O2 consumed
and CO2 released)
-focus on glucose but other organic molecules also used
Glucose Metabolism
C6H12O6 + 6Os  6CO2 + 6H2O
-four metabolic pathways
1. Glycolysis (occurs in cytosol)
2. Breakdown of pyruvate
3. Citric acid cycle
4. Oxidative phosphorylation (pathways 2-4 occur in mitochondria)
Stage 1: Glycolysis
-glycolysis can occur in the presence of oxygen, aerobically or in the absence of
oxygen, anaerobically
-steps are nearly identical in all organisms (glycolysis arose early in evolution of life)
-10 steps in 3 phases
1. Energy investment; 2. Cleavage 3. Energy liberation

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3 Phases of Glycolysis
1. Energy investment (steps 1-3)
-2 ATP hydrolyzed to create fructose-1, 6 biphosphate
2. Cleavage (steps 4-5)
-6 carbon molecule broken into two 3 carbon molecules of glyceraldehyde-3-
phosphate
3. Energy liberation (steps 6-10)
-two glyceraldehyde-3-phosphate molecules broken down into 2 pyruvate
molecules producing
2 NADH and 4 ATP
*net yield in NADH of 2; net yield in ATP of 2
Net Reaction of Glycolysis
C6H12O6 + 2 NAD+ + 2 ADP + 2 Pi 2 CH3(C=O)COO− + 2 H+ + 2 NADH + 2 ATP
+ 2 H2O
-net yield of NADH is 2 molecules
-net yield of ATP is 2 molecules
-when enough ATP is produced… ATP acts as a feedback inhibitor; inhibits rate
limiting step of glycolysis; target is an early enzyme in the pathway, the third
enzyme … phosphofructokinase
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