Respiration-5.7 Flashcards
(28 cards)
What is the need for respiration?
-active transport
-endocytosis
-exocytosis
-synthesis of proteins (E.g. enzymes and antibodies)
-DNA replication
What are the 4 stages of aerobic respiration and where do they occur?
1- Glycolysis (cytoplasm)
2-Link reaction (mitochondrial matrix)
3-Krebs Cycle (mitochondrial matrix)
4-Oxidative phosphorylation (mitochondrial inner membrane cristae)
Label this
What is the function of the inner membrane of the mitochondria?
The inner membrane is:
Folded (cristae)
Less permeable (e.g. to small ions such as hydrogen ions)
The site of the electron transport chain (used in oxidative phosphorylation)
Location of ATP synthase enzymes (used in oxidative phosphorylation)
Has a large surface area for electron carriers and ATP synthase enzymes embedded in them
Describe the outer membrane of a mitochondria
-permeable to small molecules -it contains proteins some of which form channels or carriers that allow the passage of molecules such as pyruvate into the mitochondrion
Describe the matrix of a mitochondrion
Is an aqueous solution within the inner membranes of the mitochondrion
Contains ribosomes, enzymes and circular mitochondrial DNA necessary for mitochondria to function
What is the function of cristae in a mitochondrion?
-cristae (inner folds) increases surface area
-which enables the membrane to hold many electron transport chain proteins and ATP synthase enzymes
What are the stages of glycolysis?
-glycolysis is the first stage of respiration
Stages of glycolysis
-> PHOSPHORYLATION
-two molecules of ATP are hydrolysed, the released phosphate groups bind to glucose to make hexose bisphosphate
-> SPLITTING
-hexose bisphosphate (6 carbons) is split into two three carbon molecules of triose phosphate
->OXIDATION OF TRIOSE PHOSPHATE TO PYRUVATE
-dehydrogenase enzymes aided by coenzyme NAD remove hydrogens from triose phosphate, the two molecules of NAD accept the hydrogen atoms and become reduced
-two molecules of NADH are made for every molecule of glucose also four molecules of ATP are made for every two triose phosphate molecules undergoing oxidation
What are the products of glycolysis?
2x pyruvate
Net gain of 2 ATP
2x NADH
What are the stages of the Link Reaction?
Stage 2 of aerobic respiration
Stages of glycolysis:
->DECARBOXYLATION OF PYRUVATE (pyruvate was made during glycolysis)
-the carboxyl group is removed from from the pyruvate molecule
->NAD is reduced to form NADH
->the acetyl group combines with coenzyme a (CoA) to form Acetyl CoA
A teacher told his students that the human body makes the equivalent of its own mass in ATP every day
Explain why, at the end of the day only a small proportion of the student’s mass was ATP
(2 marks)
-because ATP is hydrolysed to ADP
-ATP is constantly recycled
(ATP used to provide energy for (active transport, exocytosis
ATP not stored long term/ used immediately)
Describe two ways in which the structure of mitochondrial membranes is related to the function of a mitochondrion
(2 marks)
Explain why early eukaryotes were able to grow more quickly than cells that did not possess mitochondria
(3 marks)
Where does the Krebs cycle occur?
In the mitochondrial matrix
Describe the stages of the Krebs cycle
1-the acetyl group released from acetyl CoA combines with a four carbon compound (oxaloacetate) to form a six carbon compound (citrate)
2-citrate is decarboxylated and dehydrogenated producing a five carbon compound, one molecule of carbon dioxide and one molecule of reduced NAD
3- this five carbon compound is further decarboxylated and dehydrogenated producing a four carbon compound, one molecule of carbon dioxide and one molecule of reduced NAD
4-this four carbon compound combines temporarily with and is then released from coenzyme A. At this stage substrate level phosphorylation takes place producing one molecule of ATP
5-the four carbon compound is dehydrogenated producing a different four carbon compound and a molecule of reduced FAD
6-rearrangement of the atoms in the four carbon molecule catalysed by an isomerise enzyme followed by further dehydrogenation regenerate a molecule of oxaloacetate
List the products per molecule of glucose in the link reaction and Krebs cycle
Describe the process of oxidative phosphorylation
->Hydrogen atoms are donated by reduced NAD (NADH) and reduced FAD from the Krebs Cycle
->Hydrogen atoms split into protons (H+ ions) and electrons
->The high energy electrons enter the electron transport chain and release energy as they move through the electron transport chain
->The released energy is used to transport protons across the inner mitochondrial membrane from the matrix into the intermembrane space
->A concentration gradient of protons is established between the intermembrane space and the matrix
->The protons return to the matrix via facilitated diffusion through the channel protein ATP synthase
->The movement of protons down their concentration gradient provides energy for ATP synthesis
Oxygen acts as the ‘final electron acceptor’ and combines with protons and electrons at the end of the electron transport chain to form water (4H+ +4e- + O2 —->H2O )
Describe the chemiosmotic theory
electrons release energy as they pass through the ETC. This energy is used to actively pump H+ from the mitochondrial matrix into the intermembrane space. The H+ then diffuses down gradient through ATP synthase enzymes that are in the inner membrane, the flow of protons causes a conformational change in the ATP synthase so that ADP and Pi can combine to form ATP (this is oxidative phosphorylation)
The flow of protons is called chemiosmosis.
What is the net gain of ATP per molecule of glucose in respiration?
Glycolysis- 2
The link reaction- 0
The Krebs cycle-2
Oxidative phosphorylation-28
Total-32
What happens if oxygen is absent during respiration?
If oxygen is absent
->oxygen cannot act as the final electron accepter at the end of oxidative phosphorylation. Protons diffusing through channels associated with ATP synthase are not able to combine with electrons to form water
->the concentration of protons increases in the matrix and reduces the proton gradient across the inner mitochondrial membrane
->oxidative phosphorylation ceases
->reduced NAD and reduced FAD are not able to unload their hydrogen atoms and cannot be reoxidised
->the Krebs cycle stops as does the link reaction
Describe anaerobic respiration in yeast
The ethanol fermentation pathway
-> each molecule of pyruvate produced during glycolysis is decarboxylated and converted to ethanal. This is catalysed by the enzyme pyruvate decarboxylase
->the ethanal accepts hydrogen atoms from reduced NAD, becoming reduced to ethanol. The enzyme ethanol dehydrogenase catalyses the reaction
-in this process the reduced NAD is re-oxidised and made available to accept more hydrogen atoms from triose phosphate, thus allowing glycolysis to continue
Describe anaerobic respiration in mammals
The lactate fermentation pathway
->pyruvate, produced during glycolysis, accepts hydrogen atoms from the reduced NAD, also made during glycolysis. The enzyme lactate dehydrogenase catalyses the reaction
-Pyruvate is reduced to lactate
-the reduced NAD becomes reoxidised
->the reoxidised NAD can accept more hydrogen atoms from triose phosphate during glycolysis and glycolysis can continue to produce enough ATP to sustain muscle contraction for a short period
What happens to the lactate produced during anaerobic respiration in mammals?
-the lactate produced in the muscle tissue is carried away from the muscles, in the blood, to the liver. When more oxygen is available the lactate may either:
-> be converted to pyruvate, which may enter the Krebs cycle via the link reaction
->be recycled to glucose and glycogen
-if lactate were not removed from the muscles tissues, the pH would be lowered and this would inhibit the action of many of the enzymes involved in glycolysis and muscle contraction
What is the ATP yield from anaerobic respiration?
-neither ethanol fermentation nor lactate fermentation produces any ATP, however because this allows glycolysis to continue the net gain of two molecules per ATP molecule of glucose is still obtained
In anaerobic respiration glucose is only partially oxidised meaning only some of its chemical potential energy is released and transferred to ATP
The only ATP producing reaction that continues is glycolysis (~2 ATP)
As there is no oxygen to act as the final electron acceptor none of the reactions within the mitochondria can take place
The stages that take place inside the mitochondria produce much more ATP than glycolysis alone (~36 ATP)
