Respiration Flashcards
what happens when hydrogen atoms become available?
NAD and FAD accept these hydrogen atoms- they are reduced
What is the role of FAD and NAD?
To transfer the hydrogen atoms (hydrogen ions and electrons) from the different stages of respiration to the electron transport chain on the inner mitochondrial membrane, the site where hydrogens are removed from the coenzymes
Sources of reduced NAD
2 x 1 = 2 from Glycolysis
2 x 1 = 2 from the Link Reaction
2 x 3 = 6 from the Krebs cycle
Sources of FAD
2 x 1 = 2 from the Krebs cycle
Where does oxidative phosphorylation take place?
inner mitochondrial membrane
What does oxidative phosphorylation take place
production of many molecules of ATP and the production of water from oxygen
What is the model of phosphorylation?
chemiosmosis theory
What does the model state?
Hydrogen atoms are donated by reduced NAD (NADH) and reduced FAD (FADH2) 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
What happens in the electron transport chain?
The electron transport chain is made up of a series of membrane proteins/ electron carriers
They are positioned close together which allows the electrons to pass from carrier to carrier
The inner membrane of the mitochondria is impermeable to hydrogen ions so these electron carriers are required to pump the protons across the membrane to establish the concentration gradient
Why is oxygen so important for aerobic respiration
Oxygen acts as the final electron acceptor. Without oxygen the electron transport chain cannot continue as the electrons have nowhere to go. Without oxygen accepting the electrons (and hydrogens) the reduced coenzymes NADH and FADH2 cannot be oxidised to regenerate NAD and FAD, so they can’t be used in further hydrogen transport.
What are the several consequences when there is not enough oxygen available for respiration
-There is no final acceptor of electrons from the electron transport chain
-The electron transport chain stops functioning
-No more ATP is produced via oxidative phosphorylation
-Reduced NAD and FAD aren’t oxidised by an electron carrier
-No oxidised NAD and FAD are available for dehydrogenation in the –Krebs cycle
-The Krebs cycle stops
How is there is still a way for cells to produce some ATP in low oxygen conditions?
through anaerobic respiration
What happens during anaerobic respiration?
-Some cells are able to oxidise the reduced NAD produced during glycolysis so it can be used for further hydrogen transport
-This means that glycolysis can continue and small amounts of ATP are still produced
-Different cells use different pathways to achieve this
-Yeast and microorganisms use ethanol fermentation
-Other microorganisms and mammalian muscle cells use lactate fermentation
What happens through ethanol fermentation
-In this pathway reduced NAD transfers its hydrogens to ethanal to form ethanol
-In the first step of the pathway pyruvate is decarboxylated to ethanal
Producing CO2
-Then ethanal is reduced to ethanol by the enzyme alcohol dehydrogenase
-Ethanal is the hydrogen acceptor
-Ethanol cannot be further metabolised; it is a waste product
What happens during lactate fermentation
-reduced NAD transfers its hydrogens to pyruvate to form lactate
-Pyruvate is reduced to lactate by enzyme lactate dehydrogenase
-Pyruvate is the hydrogen acceptor
-The final product lactate can be further metabolised
