Module 7: Cellular Respiration Flashcards
What can cellular respiration do?
- Can utilize carbs, lipids and proteins
- converts energy in fuel molecules into ATP
- Allows the cell to do work
What are the two types of phosphorylation?
- substrate level
- oxidative
What is Stage 1 of Cellular Respiration?
Glycolysis
- occurs in the cytoplasm
- glucose is partially broken down and small amount of energy is released
- forms pyruvate
What is Stage 2 of Cellular Respiration?
Pyruvate Oxidation
- occurs in the mitochondria
- pyruvate is produced from the breakdown of glucose in glycolysis and converted to acetyl-CoA and CO2
What is Stage 3 of Cellular Respiration?
Citric Acid Cycle
- occurs in the mitochondria
- Acetyl-CoA from the end of stage 2 is broken down
- this releases CO2, small amount of energy and electron carriers
What is Stage 4 of Cellular Respiration?
Oxidative Phosphorylation
- occurs in the mitochondria
- all the electron carriers from stages 1-3 release their high energy electrons to the electron transport chain
- this produces ATP
What mechanisms generate ATP?
Substrate level phosphorylation is the process by which ATP is synthesized by a hydrolysis reaction involving enzyme/substrate complex
- a small amount of ATP is generated
- the energy is transferred to electron carriers which carry energy from one reaction to another
- the electron carriers transport electrons to the respiratory ETC, which transfers electrons acoross membrane associated proteins to a final acceptor
- Oxidative Phosphorylation is the process where the proteins harness the energy released to produce ATP
The majority of ATP is produced using OP
substrate level phosphorylation is a direct phosphorylation of ADP with a phosphate group by using the energy obtained from a coupled reaction whereas oxidative phosphorylation is the production of ATP from the oxidized NADH and FADH2.
Oxidation Reactions in Cellular Respiration
- NAD+ and FADH are important electron carriers in cellular respiration
- in CR the energy stored in glucose is harnessed in electron carriers as glucose is oxidized into CO2
- In the breakdown of glucose, glucose is oxidized to CO2 and O2 is reduced to H2O
- oxidation = Loss of e-
- reduction = gain e-
What is the final electron acceptor in cellular respiration?
Oxygen
When O2 is reduced it turns into what?
forms H2O
What is the original electron donor in cellular respiration?
glucose
How do electrons move from one molecule to the next during cellular respiration?
reduction reactions
What are the two important electron carriers?
NAD+/NADH & FADH/FADH2
- the oxidized forms of these carriers are NAD+ and FADH
- the reduced forms are NADH and FADH2
- through glycolysis, pyruvate oxidation, and the citric acid cycle, the form of the electron carrier accepts electrons and becomes reduced
- the reduced form of the electron carriers has high potential energy
- this is used to synthesize ATP in the final stage of cellular respiration
What type of pathway is glycolysis?
Catabolic
How many chemical reactions does it take to break down glucose?
10
- goes from six carbon glucose to 2 three carbon pyruvates
Where does glycolysis occur?
cytosol
What is glycolysis relationship with O2?
occurs in the presence or absence of O2
What are the three phases of glycolysis?
- Preparatory Phase
- where energy is consumed - Cleavage Phase
- where glucose is split into two - Payoff Phase
- where ATP is one of the products
Glycolysis Phase 1
Preparatory Phase
- the preparation of glucose for the next two phase’s happens here
- add two phosphate groups to glucose, producing fructose 1,6-biphosphate
- this process requires an input of energy in the form of two molecules of ATP
- the phosphorylation of glucose traps the molecule inside the cell and destabilizes it so that i is ready for phase 2
Glycolysis Phase 2
Cleavage Phase
- cleavage of fructose 1,6 biphosphate into two molecules
– glyceraldehyde 3-phosphate
– dihydroxyacetone phosphate (which is quickly converted into another molecule of glyceraldehyde 3-phosphate)
Glycolysis Phase 3
Payoff Phase
- two molecules of pyruvate are formed
- two molecules of the electron carrier NADH are produced
four molecules of ATP are produced
What is the net gain of ATP in glycolysis?
2
- produces 4 ATP, but uses 2
What is the makeup of the mitochondria?
- the inner membrane
- the outer membrane
- these define the two spaces - inter membrane
- space between the two membranes - mitochondrial matrix
- space inside inner membrane
Pyruvate Oxidation
- when oxygen is present, pyruvate can be oxidized to produce carbon dioxide and NADH
- Ultimately to Acetyl-CoA
- these reactions occur in the mitochondrial matrix
- pyruvate is converted to Acetyl CoA and then further broken down in the citric acid cycle
- the pyruvate is initially oxidized to form CO2 and an acetyl group
Where is the acetyl group in pyruvate oxidation transferred to?
- the acetyl group is transferred to coenzyme A, which carries the acetyl group to the citric acid cycle
What enzymes catalyze the reactions in pyruvate oxidation?
pyruvate dehydrogenase complex
Overall what does one molecule of pyruvate produce?
1 CO2
1 molecule of NADH
1 molecule of acetyl-CoA
but remember glycolysis produces 2 molecules of pyruvate, thus, at the end of this process for each GLUCOSE molecule there are
2 CO2
2 molecules of NADH
2 molecules of acetyl-CoA
Why is the Citric Acid cycle called a cycle?
- because the first reactant (oxaloacetate) in the process is also regenerated at the end
During the citric acid cycle what happens to the fuel molecules?
they are completely oxidized
Where does the citric acid cycle happen?
In the mitochondrial matrix
What happens during the citric acid cycle?
the citric acid cycle completes the oxidation of glucose and turns it into CO2 (produces 2)
What does the citric cycle produce?
- undergoes substrate level phosphorylation to produce ATP
- 3 NADH
- 1 FADH
How are intermediates used in reference to the citric acid cycle?
some organisms can use products from different steps in the citric acid cycle as intermediates in other metabolic pathways
Why do we exhale CO2?
the oxidation of acetyl-CoA produces the carbon dioxide we exhale
What do NADH and FADH2 produce?
they produce transfer electrons to other carriers in the electron transport chain (ETC)
- produced though redox reactions in the first 3 stages of cellular respiration
CO2 produced from citric acid
- there is a transfer of the potential energy stored in acetyl-CoA to be stored in NADH and FADH2
- also the production of GTP is catalyzed by substrate level phosphorylation
Where is the ETC?
in the mitochondrial inner membrane
Overview of ETC
- electrons enter and move from donors to acceptor until they reach the final electron acceptor, oxygen
- when oxygen accepts the electron it is reduced to H2O
Where are electrons moved?
- electrons are moved from energy storage molecules to proteins in the ETC
How do electrons move?
they move through a sequence of redox processes which contributes to the formation of the proton gradient
- this stores potential energy for ATP synthesis
What happens with protons near the membrane and what is their distribution?
- protons are pumped across the membrane and a gradient is formed across the membrane
- the distribution is as follows:
1. in the intermembrane space there is HIGH [protons]
2. in the mitochondrial matric there is LOW [protons] - the protons cannot diffuse across the membrane (can’t go on own), the proton concentration gradients contains high potential energy
What does the proton gradient power?
the proton gradient powers ATP synthase, a molecular machine
How does ATP synthase work?
-protons flow down their concentration gradient
- as protons pass through a channel it rotates a protein subunit
- this converts one form of energy into energy in bonds of ATP
Summary of CR
- Overall the energy of glucose is released slowly in a series of reactions
- some of the energy is released by substrate-level phosphorylation
- some is generated through redox reactions that transfer energy to the electron carriers NADH and FADH2
- these carriers donate electrons to the ETC, forms the proton gradient to drive ATP synthase
– this is oxidative phosphorylation - thus the complete oxidation of GLUCOSE forms 32 molecules of ATP
What happens if oxygen is not available?
If O2 is not available, the cell is under anaerobic conditions
- the pyruvate produced from glycolysis can be reduced by a fermentation process
In animal and bacteria cells what happens if there is no Oxygen?
the pyruvate is reduced to lactic acid
- this regenerates NAD+ which can then be reduced in glycolysis
- ATP is still synthesized in small amounts for use by the cell
Glucose + 2 ADP + 2 Pi -> 2 lactic acid + 2 ATP + 2 H2O
What happens in plants and fungus if there is no oxygen?
they undergo ethanol fermentation
- the pyruvate releases CO2 to form acetaldehyde, the electrons from NADH are transferred to acetaldehyde to produce ethanol and NAD+
- regeneration of NAD+ is important so that at least small amounts of ATP can be generated during ethanol fermentation
glucose + 2 ADP + 2 Pi -> 2 ethanol + 2 CO2 + 2 ATP + 2 H2O
Excess sugar storage
- plants and animals can store excess glucose for use in glycolysis later as branched polymers of glucose
- glucose monomers are cleaved one at a time and enter glycolysis as an intermediate
- plants store it as STARCH
- animals store it as GLYCOGEN
– stored in muscle cells for energy to power contraction
– stored in liver for the whole body
What about other sugars?
- the carbohydrates that are digested can produce a variety of disaccharides and monosaccharides
- may produce glucose or other glycolysis intermediates
What about other energy sources?
- lipids are an excellent energy source, rich in C-C bonds and C-H bonds
- fatty acids absorbed after a meal, or produced from excess glucose can be used by cells
– they are shortened through beta-oxidation
What is beta-oxidation?
in beta-oxidation lipids are broken down into glycerol and acetyl-CoA
– ATP is not produced directly
– NADH and FADH2 are produced and can enter
