8.2 Cell respiration Flashcards
Define respiration
The controlled release of energy from organic compounds in cells to form ATP.
What is the chemical equation for glucose (an organic molecule)?
C6H12O6 (little numbers)
What is the equation for aerobic respiration?
Respiration consists of several different ___
Interlinked metabolic pathways.
What are the different metabolic pathways/cycles that respiration consists of?
Glycolysis –> link reaction –> Kreb’s cycle (metabolic cycle) –> electron transport chain –> chemiosmosis
What is oxidative phosphorylation?
- The process by which ATP synthesis is coupled to the movement of electrons through the mitochondrial electron transport chain and the associated consumption of oxygen.
- Oxidative phosphorylation = electron transport + chemiosmosis
Diagram of the a mitochondrion in a cell
If oxygen is present, reactions move to the ___
Mitochondria
Diagram of labelled mitochondria (drawn and real one)
Labelled 3d diagram of mitochondrion
Labelled diagram of mitochondrion under a microscope
What is electron tomography?
A technique for obtaining 3D structures of sub-cellular structures (e.g. active mitochondria) using electron micrographs
More info on electron tomography
- 3D internal structure
- Samples are repeatedly imaged using TEM
- After every image, the sample is tilted to a different angle relative to the e- (small -_ beam
- Images are compiled –> 3D representation (= tomogram)
What is electron tomography improving the understanding of?
Mitochondria’s structure and function
What are the different types of oxidation reactions?
- Electrons are lost
- Oxygen is added
- Hydrogen is lost
What are the different types of reduction reactions?
- Electrons are gained
- Oxygen is removed
- Hydrogen is gained
What are the electron carriers in cell respiration?
- The most common hydrogen carrier is NAD
- Another less frequently used hydrogen carrier is FAD
Diagram of NAD being oxidised/reduced
Diagram of NAD being oxidised/reduced
Diagram of FAD being oxidised/reduced
What is glycolysis?
The splitting of glucose into pyruvate
Diagram of the summary of glycolysis
How many stages are there of glycolysis?
What is phosphorylation?
A reaction where a phosphate group (PO43-) is added to an organic molecule.
(4 on bottom and 3- on top)
What does phosphorylation of molecules do to them and what does this allow them to do?
- Phosphorylation of molecules makes them less stable.
- The phosphorylated molecule is less stable and therefore reacts more easily in the metabolic pathway.
- Reactions that would otherwise proceed slowly and require energy into a reaction that happens quickly releasing energy.
Diagram of phosphorylation
Diagram of the coupled reduction-oxidation reactions
What are the two types of phosphorylation?
Substrate and oxidative
Diagram of chemicals in glycolysis
Summary of glycolysis
Summary of glycolysis
- Glycolysis occurs in the cytoplasm
- A hexose sugar (e.g. glucose) is phosphorylated using ATP
- The hexose phosphate is then split into two triose phosphates
- Oxidation occurs, removing hydrogen
- The hydrogen is used to reduce NAD to NADH
- Four ATP molecules are produced, resulting in a net gain of two ATP
- Two pyruvate molecules are produced at the end of glycolysis
Where does glycolysis occur?
In the cytoplasm
Where does the link reaction take place?
In the matrix of the mitochondrion
Diagram of the link reaction (NADH + H + is referred to as NADH for simplicity.)
What should you be able to analysie about the pathways of aerobic respiration?
- You should be able to analyze diagrams of the pathways of aerobic respiration to deduce where decarboxylation and oxidation reactions occur.
- One good example is the link reaction pathway.
Give an example of a decarboxylation reaction
- At the end of the glycolytic pathway, two molecules of pyruvate are formed, which are linked to acetyl CoA in the link reaction if oxygen is available.
- This is an example of a decarboxylation reaction because carbon is lost as carbon dioxide.
- Since pyruvate also loses hydrogen, it is oxidized to acetyl CoA.
- Overall, the conversion of pyruvate to acetyl CoA involves both decarboxylation and oxidation reactions.
Diagram of oxidative decarboxylation
Summary of the link reaction (oxidative decarboxylation)
- Pyruvate (from glycolysis) enters the mitochondrial matrix
- Enzymes remove one carbon dioxide and hydrogen from pyruvate
- Hydrogen is accepted by NAD to form NADH
- Removal of hydrogen is oxidation
- Removal of carbon dioxide is decarboxylation
- The link reaction is therefore oxidative decarboxylation
- The product is an acetyl group that reacts with coenzyme A
- Acetyl CoA enters the Krebs cycle
How can fatty acids be used in aerobic respiration?
- Fatty acids can also be a source of energy in respiration
- Fatty acids have a long chain of carbon atoms
- CoA can oxidise this chain- break it down
- It makes Acetyl CoA with two carbons
- And carries them to the Krebs cycle
- Glycolysis is not needed, but the reaction is slower
What happens during the Krebs cycle?
The Krebs cycle reduces electron carriers in preparation for oxidative phosphorylation (carbon is released as CO2 is a byproduct).
In the Krebs cycle, the oxidation of acetyl groups is coupled to the ___
Reduction of hydrogen carriers, liberating carbon dioxide.
Where does the Krebs cycle take place?
The matrix of the mitochondrion
Diagram of the Krebs cycle
Another diagram of the Krebs cycle
The reduced forms of NAD and FAD carry ___ and ___ to the ___, which is situatied in the ___
1) H+ ions
2) Electrons
3) Electron transport chain
4) Folds on the inner membrane, i.e. the cristae
Summary of the Krebs cycle
- Acetyl CoA enters the Krebs cycle
- Acetyl group (2C) joins the 4C sugar to form a 6C sugar
- Oxidative decarboxylation of the C5 compound to a 4C compound produces CO2
- The process is oxidative as NAD and FAD are reduced by the addition of hydrogen
- Two CO2 are produced per molecule of pyruvate/cycle
- One ATP is produced by substrate level phosphorylation (from ADP + Pi)
- NADH and FADH2 provide electrons to the electron transport chain
What is the final stage of aerobic respiration?
The electron transport chain
Summary of oxidative phosphorylation (the electron transport chain)
- The electron transport chain is situated on the inner mitochondrial membrane
- Hydrogen is transferred to the electron transport chain by hydrogen carriers (NADH and FADH2)
- The hydrogen carriers release electrons which are transferred between carriers. This releases energy.
- This energy is used to pump H+ ions (from the matrix) across the inner membrane, causing H+ ions to accumulate in the inter-membrane space, creating a concentration gradient
- H+ ions return to the matrix through ATP synthase down the electrochemical concentration gradient
- This produces ATP by chemiosmosis
- Oxygen is the final electron acceptor for the electron transport chain
- Oxygen combines with electrons and H+ ions to produce water
Explain how electrons are taken to the electron transport chain
The reduced forms of NAD and FAD carry the energy released by the oxidation reactions to the cristae of the mitochondria where they give off their electrons and hydrogen ions to special protein complexes (the electron transport chain).
How is ATP synthesized in the inner mitochondrial membrane?
In the inner mitochondrial membrane, another large protein complex, ATP synthase, uses a hydrogen ion (= proton) gradient to synthesise ATP.
The inner mitochondrial membrane is folded to form ___, which provide ___.
Cristae
An increased surface area
What do reduced FAD and NAD+ temporarily store?
Energy that is released during oxidation reactions of glycolysis, link reaction, and the Krebs cycle
Diagram of the electron transport chain and chemiosmosis (complicated)
How is a high concentration of H+ created in the intermembrane space during the ETC?
- As the inner mitochondrial membrane is impermeable to protons, this results in the development of a high concentration of H + in the intermembrane space (higher than the matrix).
- The potential energy in the gradient is used by ATP synthase to make ATP.
- This process is also referred to as chemiosmosis because it involves the movement of ions (protons) across a membrane.
Simplified diagram of the ETC in the mitochondrion
How is the mitochondrion enabled to produce ATP?
It is the combination of the ETC and the gradient of hydrogen ions (protons) that supplies the energy to ATP synthase, enabling the mitochondrion to produce ATP .
What is chemiosmosis?
This involves the pumping of protons (H + ions) into the intermembrane space of the mitochondria by using energy released by electron transport along the ETC, followed by diffusion of protons into the matrix down a concentration gradient through ATP synthase to produce ATP.
What is the role of oxygen in the ETC?
- As the last electron acceptor of the ETC, oxygen also helps in maintaining the hydrogen gradient in the matrix by binding with the free protons to form water.
- Oxygen accepts electrons and binds protons at the same time to form water.
What can each NADH + H+ and FADH2 give rise to?
- Each molecule NADH + H + and FADH 2 can give rise to three and two ATP molecules, respectively.
- The main reason FADH 2 generates fewer ATP molecules, is that it donates its electrons to the ETC at a later step.
What can each NADH + N+ and FADH2 give rise to?
- Each molecule NADH + H + and FADH 2 can give rise to three and two ATP molecules, respectively.
- The main reason FADH 2 generates fewer ATP molecules, is that it donates its electrons to the ETC at a later step.
Structure of a mitochondrion (drawn and electron micrograph)
What are Svedberg units?
- Svedberg units (S) are used to define the size of ribosomes. It is a measurement of sedimentation rate after centrifugation of RNA subunits.
- The bigger the ribosome, the larger the S value.
- Therefore, 70S is larger than 50S.
What are the different structures in a mitochondrion?
- Cristae
- Intermembrane space
- Matrix
- 70S ribosomes
- Outer mitochondrial membrane
- Protein-coated, circular DNA
How is the inner membrane (which folds into cristae) adapted to its function?
- It contains the integral proteins that make up the electron transport chain and ATP synthase (needed for ETC and chemiosmosis)
- It is hyperpermeable to H+ so a high concentration of protons is created in the intermembrane space so that it can move into the ATP synthase down a concentration gradient.
How are cristae adapted to their function?
They form a large surface area for the electron transport chain and ATP synthase.
How is the intermembrane space adapted to its function?
The small space allows fast accumulation of protons needed for chemiosmosis.
How is the fluid matrix (containing enzymes) space adapted to its function?
Contains enzymes for the Krebs cycle and link reaction, enabling them to proceed at an appropriate rate.
How are the 70S ribosomes adapted to their function?
They synthesize some of the proteins and enzymes needed within the mitochondrion for aerobic respiration.
How is the outer mitochondrial membrane adapted to its function?
Isolates the content of the mitochondrion from the cytoplasm to allow optimum conditions for reactions of aerobic respiration.
How is the protein-coated, circular DNA adapted to its function?
Codes for some of the mitochondrial proteins.
Give more detail about the adaptation of the inner membrane (cristae)
The cristae, invaginations of the inner mitochondrial membrane, create tiny compartments that increase surface area and may increase the proton concentration gradient necessary for ATP synthase to function.
Use of electron tomography in investigating mitochondria’s function and adaptation to cellular energy requirements
- Electron tomography imaging allows three-dimensional images of mitochondria to be made, supporting the idea of the dynamic nature and fluidity of the cristae.
- Additionally, proteins can be visualised within active mitochondria.
- An example is the protein import site complexes (which are themselves proteins) located on both the inner and outer mitochondrial membranes.
3D images of mitochondria
The circular red-yellow layer indicates the outer membrane of the mitochondrion while green, blue, orange and pink coloured structures represent the inner membrane and its arrangement.
Distinguish oxidation and reduction
- Oxidation and reduction reactions always take palce together
- They are called redox reactions
- The reactions of cell respiration and photosynthesis involve a series of redox reactions.
The table summarizes the ways in which a substance can be oxidized or reduced:
What is the role of electron carriers in cell respiration?
Outline the effect of phosphorylating molecules in metabolic pathways
- Molecules within a metabolic pathway may be phosphorylated
- Phosphorylation is the addition of a phosphate group, typically from ATP
- Phosphorylation is catalyzed by enzymes called kinases
- Phosphorylation makes molecules less stable.
- Example: the first step of glycolysis is the phosphorylation of glucose. The phosphorylated sugar is easier to split into two parts
Summarize the events of glycolysis (short)
- Linear metabolic pathway
- Each glucose is converted to 2 pyruvates
- It takes place in the cytoplasm
- The substrate is partly oxidies
- Oxygen is not required
- There is a small yield of ATP
Summarize the events of the link reaction (short)
- Pyruvate is converted to acetyl-CoA
- Takes place in the mitochondrial matrix
- Links glycolysis to the Krebs cycle
- The substrate is partly oxidized
- It only occurs in the presence of oxygen
Summarize the events of the Krebs cycle (short)
- CoA delivers acetyl group into a cycle of metabolic reactions
- Takes place in the mitochondrial matrix
- Substrate is fully oxidized
- Only occurs in the presence of oxygen
Summarize the events of oxidative phosphorylation (electron transport chain & chemiosmosis) (short)
- Takes place in the cristae of the mitochondria
- Uses the energy released from the oxidation of glucose to produce ATP
- The majority of ATP produced is via oxidative phosphorylation
- Only occurs in the presence of oxygen
What happens to the pyruvate formed in glycolysis?
If oxygen is present, pyruvate enters the mitochondria:
- Via two metabolic processes, (the link reaction and the Krebs cycle) pyruvate is completely oxidized to carbon dioxide.
- Much more energy is released, resulting in a high yield of ATP
If no oxygen is present, pyruvate is converted to ethanol and CO2 (in yeast) or lactic acid (in humans)
- This is anaerobic respiration
- There is no extra production of ATP
Fatty acids can be a source of energy in cell respiration.
Which process in cell respiration will fatty acids not go through?
Glycolysis
When glucose is not available, fatty acids will directly enter the link reaction and produce many molecules of acetyl CoA. Glycolysis will not take place.
Each molecule of acetyl CoA will enter the Krebs cycle. Electron transport chain will still take place.
