Lecture 10- Pathways that harvest chemical energy Flashcards
What is the difference between slow twitch and fast twitch muscle fibers?
Slow twitch: lots of mitochondria to form ATP
Fast twitch: Fewer mitochondria, generate ATP in short bursts in absence of O2
What protein breaks down fat in fat tissues and leads to ‘marathon mouse’? (increase in slow twitch muscle fibers)
PPARδ
What are fuels?
Molecules whose stored energy can be released for use
How are molecules such as fats or proteins able to supply energy?
They are converted into glucose or intermediate compounds
Complex chemical transformations in the cell occur…
in a series of separate reactions that form metabolic pathways
Each reaction in a metabolic pathway is
catalyzed by a specific enzyme
Metabolic pathways are
similar in all organisms, from humans to bacteria
Metabolic pathways are comp_____
Compartmentalized in eukaryotes (certain reactions occur in specific organelles)
Each metabolic pathway is regulated by…
Key enzymes that can be inhibited or activated to determine how fast a reaction can go
C6H12O6 +6O2 —>
6CO2 + 6H20 + free energy
What is the function of the glucose metabolism pathway?
To trap stored energy of glucose into ATP molecules
What is the reaction that traps free energy into ATP molecules?
ADP + Pi + free energy –> ATP
What is the change in free energy from the complete conversion of glucose and oxygen into carbon dioxide and water?
-686 kcal/mol (exergonic)
What are the three metabolic processes that harvest energy from glucose?
Glycolysis
Cellular respiration
Fermentation
What is glycolysis?
The first step in glucose metabolism in all cells and produces two three carbon pyruvates
Does glycolysis use oxygen?
No
What is cellular respiration?
Aerobic
Converts each pyruvate molecule into three CO2 molecules
Energy stored in covalent bonds is transferred into ADP and Pi to form ATP
What is fermentation?
Anaerobic
Converts pyruvate into lactic acid or ethanol (energy rich molecules)
Why does fermentation not release as much energy as cellular respiration?
Lactic acid or ethanol is produced. Glucose break down is incomplete, less energy is released
What four pathways operate when oxygen is present as the final electron acceptor?
Glycolysis,
Pyruvate oxidation
Citric acid cycle
Electron transport chain
What 2 pathways operate in the absence of oxygen?
Glycolysis
Fermentation
What is a redox reaction?
A reaction in which one substance transfers one or more electrons to another substance
What type of reaction is the addition of phosphate to ADP to make ATP?
Endergonic
In redox reactions, what type of agent is glucose and what type of agent is oxygen?
Glucose is a reducing agent
Oxygen is a oxidizing agent
What are co-enzymes?
Small molecules that assist in enzyme-catalyzed reactions
How is ADP a coenzyme?
It picks up energy released in exergonic reactions and uses it to form ATP
Other than ADP, what molecule acts as a coenzyme in redox reactions?
NAD acts as an electron carrier
What does NAD stand for?
Nicotinamide adenine dinucleotide
What is the oxidized and reduced form of NAD?
Oxidized: NAD+
Reduced: NADH + H+
What is the equation for the reduction of NAD+?
NAD+ + 2H –> NADH + H+
What is transferred to NAD+ to form NADH?
A hydride ion, H-
Why does oxygen readily accept electrons from NADH?
It is highly electronegative
What is the equation for the oxidation of NADH?
NADH +H+ +1/202 –> NAD+ +H20
What is the delta G value for oxidation of NADH?
-52.4 kcal/mol
What type of reaction is the oxidation of NADH?
Exergonic
Other than NAD, name another electron carrier in cells.
FAD
What does FAD stand for?
Flavin adenine dinucleotide
Where does glycolysis and fermentation occur in eukaryotes?
external to mitochondria
Where does glycolysis occur in prokaryotes?
In the cytoplasm
Where does fermentation occur in prokaryotes?
In the cytoplasm
Where does the citric acid cycle occur in prokaryotes?
In the cytoplasm
Where does the electron transport chain occur in eukaryotes?
The inner membrane of the mitochondria
Where does the electron transport chain occur in prokaryotes?
Plasma membrane
Where does the citric acid cycle and pyruvate oxidation occur in eukaryotes?
The matrix of the mitochondria
Where does pyruvate oxidation occur in prokaryotes?
On the plasma membrane
Does glycolysis generate CO2?
no
How many enzyme catalysed reactions are there in glycolysis?
10
What does glycolysis produce?
2 molecules of pyruvate
4 molecules of ATP
2 molecules of NADH
What are the two stages of glycolysis?
Energy investment reactions
Energy harvesting reactions
What are the first 5 energy investment reactions of glycolysis?
Endergonic
In what two reactions in glycolysis is ATP invested?
1 and 3
What happens during reaction 1 and 3 of glycolysis?
Two phosphate groups are attached to the glucose molecule using energy from ATP
What is the result of investing 2 ATP molecules during glycolysis?
Fructose 1,6-bisphosphate
What is the free energy of fructose 1,6 bisphosphate compared to that of glucose?
Higher
What enzyme catalyzes reaction 1 of glycolysis?
hexokinase
What is a kinase?
An enzyme that catalyzes the transfer of a phosphate group from ATP to another substrate
What enzyme catalyzes reaction 3 of glycolysis?
Phosphofructokinase
What does reaction 4 of glycolysis do?
Opens up the six-carbon ring structure and cleaves it into two different three carbon sugar phosphates
In summary, what is the end product of the energy investing reactions of glycolysis?
- Two molecules of ATP have been invested
- Two three carbon sugar phosphate molecules have been produced
What is the name of the 3 carbon sugar phosphate produced by the energy investing glycolysis reactions?
Glyceraldehyde 2-phosphate (G3P)
What is the drop in free energy for reaction 6 of glycolysis?
100kcal/mol
What type of reaction is reaction 6 of glycolysis?
Oxidation
How is the energy released in reaction 6 of glycolysis stored?
Reducing 2 molecules of NAD+ to NADH + H+
What happens if NAD is not recycled?
Glycolysis comes to a stop because its is present only in small amounts
What happens in reaction 7-10 of glycolysis?
2 phosphate groups are transferred to ADP
What is the name of the enzyme-catalyzed transfer of phosphate groups from donor molecules to ADP molecules to form ATP?
Substrate-level phosphorylation
What happens in reaction 7 of glycolysis?
Phosphoglycerate kinase catalyzes the transfer of a phosphate group from BPG to ADP
How many ATP molecules are produced per glucose molecule in the energy harvesting reactions?
4 (2 net)
At the end of glycolysis, each glucose molecule yields…
2 pyruvate
2 NADH +H+
2 ATP
What does pyruvate oxidation link?
Glycolysis and the citric acid cycle
What is Coenzyme A?
A complex molecule responsible for binding two-carbon acetate molecule
Acetyl coenzyme A formation is a
multi step reaction
What is acetyl coenzyme A formation catalysed by?
Pyruvate dehydrogenase complex
What is pyruvate dehydrogenase complex?
A multi-enzyme complex attached to the inner mitochondrial membrane
What happens after pyruvate diffuses into the mitochondrion?
Pyruvate is oxidised to a two carbon actyl group (acetate) and CO2 is released
What happens after pyruvate is oxidised to become acetate?
Part of the energy from the oxidation is captured by reducing NAD+ to NADH + H+
How is the rest of the energy from oxidation of pyruvate into acetate stored?
Temporarily, by combining the acetyl group with CoA to form acetyl CoA
What is the overall reaction for the pyruvate oxidation reaction?
pyruvate + NAD+ CoA –> acetyl CoA + NADH +H+ +CO2
What does the citric acid cycle do?
Completes the oxidation of glucose to CO2
What is the starting molecule of the citric acid cycle?
Acetyl CoA
How many reactions are there in the citric acid cycle?
8
The citric acid cycle is maintained in a ________
steady state
What does it mean that the citric acid cycle is maintained in a steady state?
The concentration of the intermediates does not change
What is the first reaction of the citric acid cycle?
oxaloacetate and energy stored in Acetyl CoA forms citrate
What is removed during the first reaction of the citric acid cycle?
Coenzyme A
What is the second reaction of the citric acid cycle?
Citrate is rearranged to form isocitrate
What is the third reaction of the citric acid cycle?
Isocitrate is converted to alpha-ketoglutarate
2 hydrogen atoms and 1 CO2 is removed
NADH + H+ forms
What is the 4th reaction in the citric acid cycle?
alpha-ketoglutarate is oxidised to succinyl CoA
Catalysed by a multi-enzyme complex
What is the 5th reaction in the citric acid cycle?
GDP +Pi–>GTP
Succinyl CoA releases CoA to become succinate
What does GTP stand for?
Guanosine triphosphate
What is the reaction of GDP +Pi –> GTP an example of?
Substrate level phosphorylation
What is GTP used for?
To make ATP from ADP
What is the 6th reaction of the citric acid cycle?
Succinate is oxidised to fumarate
FAD –> FADH2
What is the 7th reaction of the citric acid cycle?
Fumarate and water react, malate is formed
What is the final reaction of the citric acid cycle?
Malate is oxidised to oxaloacetate
NADH + H+
How many times does the citric acid cycle operate for each molecule of glucose?
Twice
What is the input for each citric acid cycle?
Acetate (actyl CoA)
Water
Oxidised electron carriers
What is the output for each citric acid cycle?
CO2
reduced electron carriers
ATP
How is the citric acid cycle regulated?
Electron carriers that were reduced must be oxidized
What two chemical pathways oxidize electron carriers so that the citric acid cycle can proceed?
Fermentation
Oxidative phosphorylation
At the end of the citric acid cycle, each molecule of glucose yields from all three stages:
6 CO2
10 NADH + H+
2 FADH2
4 ATP
What does fermentation use to reduce pyruvate?
NADH +H+
What are the two most understood fermentation pathways?
Lactic acid fermentation
Alcoholic fermentation
What serves as the electron acceptor in lactic acid fermentation?
Pyruvate
Why does lactic acid build up in muscles cause problems?
The acid ionizes
pH of the cell is lowered
Cellular activities reduce
Where does alcoholic fermentation take place?
Certain yeasts
Some plant cells
How does alcoholic fermentation metabolize pyruvate?
two enzymes
What is the first step in alcoholic fermentation?
carbon dioxide is removed from pyruvate to make acetaldehyde
What is the second step in alcoholic fermentation?
Acetaldehyde is reduced by NADH +H+ to produce ehtanol and NAD+
What is net yield of ATP from fermentation?
two ATP’s
