Flashcards in Anaerobic Respiration incl. rice , Mitochondria + Respiratory Substrates (Chapter 12) Deck (62)
What happens when oxygen is not present?
1) hydrogen cannot be disposed of by combination with oxygen
2) ∴ the ETC stops working and no further ATP is formed by OP
3) the link reaction, Krebs cycle and OP do not take place (but glycolysis does)
What is necessary for a cell to gain even the 2 ATP for each glucose yielded by glycolysis?
To pass on the hydrogens from the molecules of reduced NAD that are made in glycolysis
What are the two different anaerobic pathways that solve the problem of 'dumping' the hydrogen?
Alcoholic and lactic
Where do both of the anaerobic pathways take place?
In the cytoplasm of the cell
What happens during alcoholic fermentation?
1) first, the pyruvate is decarboxylated to ethanal
2) then, the ethanal is reduced to ethanol (C2H5OH) by alcohol dehydrogenase
3) the H from reduced NAD is passed to ethanal (CH3CHO) when it forms ethanol
4) this releases the NAD and allows glycolysis to continue
Summarise alcoholic fermentation
Conversion of glucose to ethanol
In what microorganisms does alcoholic fermentation happen?
Yeast and in some plant tissues
What happens in during lactic fermentation?
1) pyruvate acts as the H acceptor and is converted to lactate by lactate dehydrogenase
2) again, the NAD is released and allows glycolysis to continue
Why does anaerobic respiration only buy time?
1) they allow the continued production of ATP even though oxygen is not available as the hydrogen accepter
2) however, bc the products of anaerobic respiration (ethanol/lactate) are toxic, these reactions cannot continue indefinitely
Can the alcoholic pathway be reversed?
No, ∴ the remaining chemical potential energy is wasted
How is the lactate pathway reversed in mammals?
1) most of the lactate is carried by the blood plasma to the liver and converted back into pyruvate
2) the liver oxidises some (20%) of the incoming lactate to CO2 and H2O via aerobic respiration when oxygen is available again
3) the remaining lactate is converted to glycogen by the liver
How does a person build up an oxygen deficit?
1) standing still, a person absorbs oxygen at a resting rate of 0.2 dm3/min
2) when exercise begins, more oxygen is needed to support aerobic respiration in the person's muscles. increasing the overall demand to 2.5dm3/min
3) however, it takes 4 mins for the heart and lungs to meet the demand and during this time, lactic fermentation occurs in the muscles ∴ the person builds up an oxygen deficit
4) after this time, enough oxygen is supplied
What happens when exercise stops?
The person continues to breathe deeply and absorb oxygen at a higher rate than when at rest
What is the oxygen debt?
The post-exercise uptake of extra oxygen, which is paying back the oxygen deficit
What is the extra oxygen needed for post-exercise?
1) the conversion of lactate to glycogen in the liver
2) reoxygenation of haemoglobin in the blood
3) a high metabolic rate, as many organs are operating at above resting levels
What is the mitochondrion the site of in eukaryotic organisms?
The site of the Krebs cycle and the ETC
Describe the features of mitochondria
- Rod-shaped or filamentous organelles
- 0.5-1 µm in diameter
- Not rigid and can change their shape
What does the number of mitochondria in a cell depend on?
The cell's activity e.g. a liver cell has many mitochondria as it is very active
Describe the structure of mitochondria
- Each mitochondrion is surrounded by an envelope of 2 phospholipid membranes (like chloroplast)
- The outer membrane is smooth, but the inner membrane is very folded to give cristae
What do the cristae give the inner membrane?
A large total surface area
What do mitochondria from more active cells have?
Longer, more densely packed cristae than those from less active cells
What is the difference between the two membranes?
The outer membrane is relatively permeable to small molecules, whereas the inner membrane is less permeable
Describe the inner membrane
- The inner membrane is studded with tiny spheres (9nm diameter) called stalked particles which are the enzyme ATP synthase and are attached to the inner membrane by stalks
- The inner membrane is the site of the ETC and contains the proteins necessary for this
Why does the intermembrane space in a mitochondrion have a lower pH than the matrix?
Due to the protons that are released into the intermembrane space by the activity of the ETC
Describe the matrix of the mitochondrion
- The site of the link reaction and the Krebs cycle ∴ has the enzymes needed for these reactions
- Contains small (70s) ribosomes and several identical copies of looped mitochondrial DNA
Where and how is ATP formed in mitochondria?
- ATP is formed in the matrix by the activity of ATP synthase on the cristae
- The energy for the production of ATP comes from the proton gradient between the intermembrane space and the matrix
What is ATP produced in mitochondria used for?
All the energy-requiring reactions of the cell, both inside and outside the mitochondrion
For what cells is glucose the essential respiratory substrate?
Neurones in the brain
What can cells such as RBCs and lymphocytes also oxidise and how?
- Lipids and amino acids
- When lipids are respired, carbon atoms are removed in pairs (as acetyl CoA) from the fatty acid chains and fed into the Krebs cycle
- When amino acids are respired, the C-H skeletons of amino acids are converted into pyruvate or acetyl CoA