Download How do cells regulate the speed of reactions?

Two Ways to Generate ATP
1) Chemiosmosis: occurs in membrane
2) Substrate-level phosphorylation
• Cell maintains 10x more ATP than ADP
• This produces even more energy
when ATP is then broken down
• Energy required to make ATP again
after removing phosphate group
• Another exergonic reaction used
How do cells regulate the speed
of reactions?
• Enzymes- protein catalysts that affect
the speed of reactions without being
consumed.
• All reactions require energy to initiate
the breaking of existing bonds and begin
the reaction – activation energy needed
to get over the energy barrier.
• Enzymes lower the energy barrier
i.e. reduces the activation energy
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Cellular Respiration
catabolism: breaking down organic
molecules to extract energy
Two Catabolic Pathways
1) Fermentation (anaerobic)
2) Cellular Respiration (aerobic)
ATP = Adenosine TriPhosphate
• Oxidation (loss of e- = LEO) & reduction (gain e-)
drive cellular respiration
Redox Reactions
Four Main Steps in Cellular Respiration
1) Glycolysis (“sugar breaking”)
- in cytosol
2) Formation of acetyl coenzyme A
3) Citric Acid Cycle (Krebs Cycle)
4) Electron transport chain and
chemiosmosis
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Four Main Steps in Cellular Respiration
1) Glycolysis (“sugar breaking”)
- in cytoplasm
- break glucose into 2 molecules of
pyruvic acid
- Two ATP’s used in reaction; 4 ATP’s
generated (net gain = 2 ATP &
2 NADH)
NADH = reduced form of NAD+
(nicotinamide adenine dinucleotide)
- carries H atoms & ultimately loses e-
Glycolysis
Four Main Steps in Cellular Respiration
1) Glycolysis (“sugar breaking”)
- in cytosol
2) Formation of acetyl coenzyme A
Four Main Steps in Cellular Respiration
2) Formation of acetyl coenzyme A
- occurs in mitochondria (of eukaryotes)
- pyruvic acid is oxidized
- one C atom is removed & leaves as CO2
- coenzyme A is added to modified
pyruvic acid
Getting Ready for the Krebs (Citric Acid)
Cycle
Result of last reaction = acetyl coenyme A
(Acetyl CoA) = high energy fuel that is
now ready to enter the next step
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Four Main Steps in Cellular Respiration
3) Krebs (Citric Acid) Cycle
- in matrix of mitochondria
For each turn in the cycle:
2 CO2 leave
3 NADH made
1 FADH2 made
1 ATP made
FADH2 = reduced form of FAD (flavin
adenine dinucleotide); same function as
NADH = hydrogen carrier
Four Main Steps in Cellular Respiration
4) Electron Transport Chain
- NADH & FADH2 transported to
mitochondria cristae
- electron carriers = membrane proteins
Four Main Steps in Cellular Respiration
4) Electron Transport Chain
- NADH & FADH2 transported to
mitochondria cristae
- electron carriers = membrane proteins
- chemiosmosis
- cascading effect – protons travel
down an energy gradient
How Does Electron Transport Chain Work?
+
-
• NADH & FADH2 oxidized with H+ by-product
• H+ gradient results in electrical gradient
• Flow of H+ through ATP synthase = ATP
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Four Main Steps in Cellular Respiration
4) Electron Transport Chain
- NADH & FADH2 transported to
mitochondria cristae
- electron carriers = membrane proteins
- chemiosmosis
- cascading effect – protons travel
down an energy gradient
- 32-34 ATP generated
Anaerobic Conditions (Fermentation)
Alcoholic (Glycolysis) – 2 ATP’s made
Glucose ------ 2 Ethanol
Lactic Acid (Glycolysis) – 2 ATP’s made
Glucose ------ 2 Lactic Acid
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