Respiration Flashcards
Why do we need to respire?
We need energy to drive biological processes; this energy is provided by respiration
Define metabolism
All the reactions that take place within an organism
Define anabolic
Metabolic reactions that build large molecules
Define catabolic
Metabolic reactions that break down large molecules in hydrolysis. Often releases heat that helps organisms maintain necessary temperatures for enzymes
What metabolic processes need energy?
Active transport; Secretion (exocytosis); Endocytosis; Anabolic reactions; DNA replication; Movement
Describe the structure of ATP
Full name: adenosine triphosphate
Purine (2 rings) nitrogenous base adenine attached to 5 carbon sugar ribose which has 3 phosphates attached to it. If adenine is attached to carbon 1, the phosphates are attached to carbon 3.
What is the function of ATP
Provides the immediate source of energy for biological processes
Why are coenzymes needed in respiration?
There are many redox reactions in respiration with removal of hydrogens by dehydrogenase enzymes. Enzymes aren’t so great at catalysing redox reactions, so the hydrogen ions are combined with NAD that carries the H until needed. Coenzyme A is needed to carry acetate groups to the Krebs cycle.
Where does glycolysis take place?
In the cytoplasm
Describe the stages in glycolysis
ATP is hydrolysed, and a phosphate attaches to carbon 6 of glucose, making glucose 6-phosphate
Glucose 6-phosphate is changed to fructose 6-phosphate
ATP is hydrolysed and a phosphate attaches to carbon 1 making fructose 1,6-bisphosphate
Energy from the ATP activates the sugar, and prevents it from being transported out of the cell
Hexose bisphosphate is split into 2 molecules of triose phosphate
Triose phosphate is oxidised by the removal of 2 hydrogen atoms, aided by coenzyme NAD, becoming NADH. 2 molecules of ATP are formed
Triose phosphate is transformed into pyruvate, making 2 more molecules of ATP
What are the products of glycolysis?
2 molecules of ATP were used; and 4 molecules of ATP were created: net gain of 2 ATP
2 molecules of NADH were produced
2 molecules of pyruvate were formed
What happens to the pyruvate produced at the end of glycolysis in anaerobic respiration?
Actively transported into the mitochondria
What are the 3 ways ATP can be produced?
Photophosphorylation; Oxidative phosphorylation and Substrate level phosphorylation
How big are mitochondria?
2-5um long; 0.5-1um in diameter
How is the matrix of the mitochondria designed to carry out its function?
Matrix is where the link and Krebs cycle occurs.
Has enzymes to catalyse the stages of these reactions
Molecules of NAD
Oxaloacetate
Mitochondrial DNA (coding for mitochondrial enzymes and other proteins)
Mitochondrial ribosomes for making of these proteins
How is the outer membrane of the mitochondria designed to carry out its function?
Composed of phospholipids with proteins which form channels or carriers that allow passage of molecules such as pyruvate
How is the inner membrane of the mitochondria designed to carry out its function?
Folded into cristae for large SA for oxidative phosphorylation
Many electron carriers and ATP synthase enzymes embedded
Impermeable to small ions
Describe the structure and function of the electron transport chain in mitochondria
Each electron carrier is an oxidoreductase enzyme associated with a cofactor - a haem group. The haem group can accept and donate electrons because the iron atoms can be oxidised and reduced (Fe2+ or Fe3+)
Some also have a coenzyme that uses the energy of passing electrons to pump proton into the intermembrane space (inner membrane is impermeable to small ions); build up of protons
Describe the structure and function of ATP synthase enzymes
Protrude from inner membrane into the matrix
Allow passage of protons down the proton concentration gradient (chemiosmosis)
The flow drives a rotation that converts ADP + P(i) to ATP
Where does the link reaction take place?
In the mitochondrial matrix
Describe the link reaction
Pyruvate dehydrogenase removes hydrogen atoms from pyruvate, reducing NAD, forming NADH
Pyruvate decarboxylase removes a carbon group, forming CO2
Left with acetate which is accepted by coenzyme A, giving acetyl coenzyme A which is then transported to the link reaction
What are the products of the link reaction per molecule of glucose?
2 NADH; 2 CO2; 2 acetyl coenzyme A
Where does the Krebs cycle take place?
The mitochondrial matrix
Describe the Krebs cycle
Acetate is offloaded from coenzyme A and binds to 4 carbon oxaloacetate, making 6 carbon citrate
Citrate is decarboxylated and dehydrogenated, forming CO2 and NADH and a 5 carbon compound
This is decarboxylated and dehydrogenated forming CO2, NADH and a 4 carbon compound
The 4 carbon compound is changed into another 4 carbon compound, and ADP is phosphorylated to produce ATP in substrate level phosphorylation
This is transformed into another 4 carbon compound, removing hydrogens and reducing FAD to FADH
This is dehydrogenated, reducing NAD to NADH, forming oxaloacetate again.
What are the products of the Krebs cycle a) in one turn b) per molecule of glucose?
a) 3 NADH; 1 FADH; 2 CO2; 1 ATP
b) 6 NADH; 2FADH; 4 CO2; 2 ATP
Describe the process of oxidative phosphorylation; electron transfer chain
NADH and FADH are oxidised with the removal of hydrogen
The electron carrier chain in the mitochondrial cristae (inner membrane) accepts the electron, and the proton goes into the mitochondrial matrix
The first electron acceptor is NADH - coenzyme Q reductase (also known as NADH dehydrogenase)
Oxygen acts as the final electron acceptor, with an oxygen molecule receiving 4 H+ and 4 e- to form water
As electrons move down the chain, energy is released which is used to pump protons into the inner membrane space at electron carries 1, 3 and 4
Describe the process of oxidative phosphorylation; chemiosmosis
As electrons move down the chain, energy is released which is used to pump protons into the inner membrane space at electron carries 1, 3 and 4
A proton gradient is formed (also a pH and electrochemical gradient)
Protons diffuse back through inner membrane via ion channels in chemiosmosis. Channels are associated with ATP synthase enzymes.
As protons flow through the enzyme, a rotation is driven which aids the combination of ADP and P(i) to ATP. Voila.
Why is the maximum yield of ATP in aerobic respiration (approx. 30 molecules per molecule of glucose) rarely achieved?
Some protons leak across the mitochondrial membrane, reducing the number of protons to generate the proton motive force
Some ATP produced is used to actively transport pyruvate into the mitochondria
Some ATP is used for the shuttle to bring hydrogen from reduced NAD made during glycolysis, in the cytoplasm, into the mitochondria
Define proton motive force
The force of the kinetic energy of the flow of protons down their concentration gradient
Why does anaerobic respiration have a much lower yield of ATP than aerobic respiration?
If there is insufficient oxygen, the only stage of respiration that can occur is glycolysis. This produces 2 molecules of ATP, so can sustain the concentrations needed for a while; however it also requires NAD. So, we need to oxidise NADH. This process of oxidation doesn’t produce any ATP, resulting in a much lower yield.
Describe anaerobic respiration in mammals
Pyruvate formed in glycolysis acts as a hydrogen acceptor, converting one molecule of NADH into NAD, producing lactate (lactic acid) as a by-product. The lactate then goes to the liver where it can be converted back into pyruvate or converted into glucose/glycogen when more oxygen is available. The NAD goes back to glycolysis, where ATP is produced.
Describe anaerobic respiration in yeast
Pyruvate formed in glycolysis looses a carbon dioxide molecule, forming ethanal. This is catalysed by enzyme pyruvate decarboxylase
Ethanal accepts hydrogen atoms from reduced NADH, being reduced to ethanol (catalysed by ethanol dehydrogenase). The NADH becomes NAD to go back to glycolysis
Define respiratory substrate
An organic substance that can be used for respiration
Why do lipids release more energy than proteins, which release more energy than carbohydrates in aerobic respiration?
In aerobic respiration, the majority of the ATP is produced in chemiosmosis, involving protons. Therefore, the more hydrogen ions a molecule has, the more protons it will release and the more ATP will be produced due to the flow of protons through ATP synthase. Lipids have more hydrogen atoms than proteins which have more hydrogen atoms than carbohydrates. Therefore, lipids release the most ATP and carbohydrates the least. Note: only for aerobic respiration, as lipids and proteins can’t undergo glycolysis.
