8.2 Cell respiration Flashcards
What is ATP?
A high energy molecule that functions as an immediate power source for cells
What does one molecule of ATP contain three of?
Three covalently bonded phosphate groups
What do the three covalently bonded phosphate groups store in their bonds?
Potential energy
Why is ATP a readily reactive molecule that contains high energy bonds?
Because phosphorylation makes molecules less stable
What happens to the energy when ATP is hydrolysed?
It is stored in the terminal phosphate bond and released for used by the cell
What are the two functions of ATP in the cell?
- functions as the energy currency of the cell by releasing energy when hydrolysed to ADP
- transfers phosphate groups to other organic molecules
What is ATP synthesised from?
ADP
What are two sources of energy used to synthesise ATP?
Solar energy
Oxidative processes
What is solar energy?
Photosynthesis converts light energy into chemical energy that is stored as ATP
What are oxidative processes?
Cell respiration breaks down organic molecules to release chemical energy that is stored as ATP
What is cell respiration?
The controlled release of energy from organic compounds to produce ATP
What does anaerobic respiration involve?
The incomplete breakdown of organic molecules for a small yield of ATP
No oxygen is required
What does aerobic respiration involve?
The complete breakdown of organic molecules for a larger yield of ATP
Oxygen is required
How does the breakdown of organic molecules occur?
Via a number of linked processes
What does staggering the breakdown into several processes do?
Reduces the energy requirements
What happens to released energy during the overall breakdown of organic molecules?
It is transferred to activated molecules via redox reactions
How is chemical energy transffered when organic molecules are broken down by cell respiration?
Redox reactions
What do redox reactions involve?
The oxidation of one chemical species and the reduction of another
What do most redox reactions typically involve?
The transfer of electrons, hydrogen or oxygen
What is reduction?
Gain of electrons/ hydrogens or the loss of oxygen
What is oxidation?
The loss of electrons/ hydrogen or the gain of oxygen
What does cell respiration transfer to carrier molecules?
Hydrogen atoms and electrons
What is the energy stored in the organic molecule transferred with to the carrier proteins?
Protons and electrons
What are carrier molecules called?
Hydrogen carriers or electron carriers
What is the most common hydrogen carrier?
NAD+
What is an example of a less common hydrogen carrier?
FAD
What do hydrogen function to do?
Transport the electrons to the cristae of the mitochondria
What is the site of the electron transport chain?
The cristae
What does the electron transport chain use the energy transferred by the carriers to do?
Synthesise ATP
What type of respiration can generate ATP from hydrogen carriers?
Aerobic respiration
What is the main organic compound used in cell respiration?
Carbohydrates
Why are lipids not preferentially used in cell respiration?
As they are harder to transport and digest
Why are proteins not preferentially used in cell respiration?
As they release potentially toxic nitrogenous compounds when broken down
What is the first step in the controlled breakdown of carbohydrates?
Glycolysis
Where does glycolysis occur?
In the cytosol of the cell
What is the main point of glycolysis?
A hexose sugar is broken down into two molecules of pyruvate
What are the four key events of glycolysis?
Phosphorylation
Lysis
Oxidation
ATP formation
What happens at the phosphorylation stage of glycolysis?
A hexose sugar is phosphorylated by two molecules of ATP to form a hexose biphosphate
How does the phosphorylation in glycolysis affect the molecule?
It makes it less stable and more reactive
Prevents diffusion out of the cell
What happens at the lysis stage of glycolysis?
The hexose bisphosphate is split into two triose phosphates
What happens at the oxidation stage of glycolysis?
Hydrogen atoms are removed from each of the 3C sugars via oxidation to reduce NAd+ to NADH
What is produced at the oxidation stage of glycolysis?
Two molecules of NADH
In ATP formation in glycolysis, what is some of the energy released from the sugar intermediates used to do?
Directly synthesise ATP
In ATP formation at glycolysis what is the direct synthesis of ATP called?
Substrate level phosphorylation
What is produced during glycolysis by substrate level phosphorylation?
4 molecules of ATP
What two reactions have occurred in glycolysis?
Glucose has been broken down into two molecules of pyruvate
Two hydrogen carriers have been reduced via oxidation
What is the net total of ATP molecules produced in glycolysis?
Two
What type of process is glycolysis?
An anaerobic process
Depending on the availability of oxygen what are the two processes pyruvate may be subjected to?
Aerobic respiration which results in the further production of ATP
or
Fermentation where no more ATP is produced
Where is the pyruvate transported to after glycolysis if oxygen is present?
The mitochondria for further breakdown
What does the further oxidation after glycolysis generate?
Large numbers of reduced hydrogen carriers
What can reduced hydrogen carriers release in the presence of oxygen?
Their stored energy to synthesise more ATP
What three processes occur in aerobic respiration?
The link reaction
Krebs cycle
The electron transport chain
Where does the pyruvate remain if oxygen is not present?
The cytosol
What is pyruvate converted into in animals if no oxygen is present?
Lactic acid
What is pyruvate converted into in plants and yeast if no oxygen is present?
Ethanol and carbon dioxide
Is the conversion of pyruvate in none oxygen conditions reversible?
Yes
Why is the conversion of pyruvate in non oxygen conditions important?
To ensure that glycolysis can continue to produce small amounts of ATP
In the absence of oxygen what will glycolysis quickly deplete to prevent further glycolysis?
Available stocks of NAD+
What type of reaction does fermentation of pyruvate involve?
A reduction reaction that oxidises NADH
What is the first stage of aerobic respiration?
The link reaction
What does the link reaction do?
Transports pyruvate into the mitochondria
What does aerobic respiration use available oxygen to do?
Further oxidise the sugar molecule for a greater yield of ATP
Why is the link reaction named that way?
Because it links the products of glycolysis with the aerobic processes of the mitochondria
In the link reaction, where is pyruvate transported into?
The mitochondrial matrix
In the link reaction, how is the pyruvate transported into the mitochondrial matrix?
By carrier proteins on the mitochondrial membrane
In the link reaction, what does the pyruvate lose?
A carbon atom which forms a carbon dioxide molecule
In the link reaction, what does the now 2C compound form?
An acetyl group when it loses hydrogen atoms via oxidation
In the link reaction what does the acetyl compound combine with?
Coenzyme A to form acetyl coenzyme A
How many times does the link reaction occur per molecule of glucose?
Two
Why does the link reaction need to go twice?
As glycolysis splits glucose into two pyruvate molecules
What does the link reaction produce per glucose molecule?
2x acetyl CoA
2xNADH + H+
2x Co2
What is the second stage of aerobic respiration?
The Krebs cycle
Where does the kreb cycle occur?
In the matrix of the mitochondria
What happens in the krebs cycle?
acetyl CoA transfers its acetyl group to a 4C compound to make a 6C compound
Once the coenzyme A is released what can it do?
It can return to the link reaction to form another molecule of acetyl CoA
In the krebs cycle what is broken down to form the original 4C compound?
The 6C compound
What are the reactions that occur in the Krebs cycle?
Two carbon atoms are released via decarboxylation to form two molecules of carbon dioxide
Multiple oxidation reactions result in the reduction of hydrogen carriers
One molecule of ATP is produced directly via substrate level phosphorylation
Why does the krebs cycle occur twice?
As the link reaction produces two molecules of acetyl CoA
What are the products of the Krebs cycle?
4x Co2
2x ATP
6x NADH + H+
2x FADH2
What is the final stage of aerobic respiration?
The electron transport chain
Where is the electron transport chain stage located?
In the inner mitochondrial membrane
Where is the electron transport chain stage located?
In the inner mitochondrial membrane
What is the inner mitochondrial membrane arranged into?
Folds/Cristae
What does the folds increase?
Surface area available for the transport chain
What does the electron transport chain release in order to synthesise ATP?
The energy stored within the reduced hydrogen carriers
Why is it called oxidative phosphorylation?
As the energy to synthesise ATP is derived from the oxidation of hydrogen carriers
What are the three steps of oxidative phosphorylation?
- proton pump create an electrochemical gradient
- ATP synthase uses the subsequent diffusion of protons to synthesise ATP
- oxygen accepts electrons and protons to form water
When generating a proton motive force, what causes the release of high energy electrons and protons?
The hydrogen carriers are oxidised
When generating a proton motive force, where are the high energ electrons transferred to?
The electron transport chain
What does the electron transport chain consist of?
Several transmembrane carrier proteins
As electrons pass through the electron transport chain, what do they lose?
Energy
In the electron transport chain, how is the energy that is lost from the electrons used?
By the chain to pump protons from the matrix
What creates an electrochemical gradient in the electron transport chain?
The accumulation of H+ ions within the inter membrane space
What does the proton motive force cause H+ ions to dd?
To move down their electrochemical gradient and diffuse back into the matrix
What is the diffusion of protons called?
Chemiosmosis
What facilitates chemiosmosis?
The transmembrane enzyme ATP synthase
What do H+ ions trigger as they move through ATP synthase?
The molecular rotation of the enzyme which synthesises ATP
What must happen in order for the electron transport chain to continue functioning?
The de-energised electrons must be removed
In the electron transport chain, what does oxygen act as?
The final electron acceptor
Why does oxygen remove the de-energised electrons in the electron transport chain?
To prevent the chain from becoming blocked
What does oxygen bind with to form water?
Free protons in the matrix
What does removing matrix protons maintain?
The hydrogen gradient
In the absence of oxygen, what cannot happen?
Hydrogen carriers cannot transfer energised electrons to the chain and ATP production is halted
How much ATP is produced per glucose consumed?
36 ATP
Where are 32 ATP produced?
In the electron transport chain
What do hydrogen carriers produce different amounts of ATP depend on?
Where they donate electrons to the transport chain
Mitochondria are the ____ of the cell?
Power plants
What do aerobic prokaryotes use to perform oxidative phosphorylation?
The cell membrane
What are mitochondria once though to have been?
Independent prokaryotes that were internalised by eukaryotes
What are the proof of mitochondria via endosymbiosis?
- double membrane structure
- own circular DNA and 70S ribosomes
- metabolic processes are susceptible antibiotics
What are the five key structures of the mitochondria?
Outer membrane
Inner membrane
Cristae
Intermembrane space
Matrix
What is the outer membrane?
The outer membrane contains transport proteins that enable the shuttling of pyruvate from the cytosol
What is the inner membrane?
Contains the electron transport chain and ATP synthase
What is the Cristae?
The inner membrane is arranged into folds that increase the SA:Vol ratio
What is the intermembrane space?
Small space between membranes maximises hydrogen gradient upon proton accumulation
What is the matrix?
Central cavity that contains appropriate enzymes and a suitable pH for the Krebs cycle to occur
What may cause the appearance of a mitochondrion in electron micrographs?
Depending on where the cross-section occurs
What is electron tomography?
A technique by which the 3D internal structure of a sample can be modelled
