Topic 5.1 Cellular Respiration Flashcards
Energy definition
The capacity of a system to do work
Why do we need energy
-Metabolism
-Movement
-Active transport
-Maintenance/repair/division of cells
-Production of substances
-Maintenance of body temperature
Mononucleotide substance
ATP
Polynucleotide substance
DNA
ATP consists of:
-Adenine (a nitrogenous base)
-Ribose (a pentane sugar)
-Three inorganic phosphate groups
ATP reaction
ATP + water ⇌ ADP + Pi (energy)
Phosphorylation
A phosphate molecule is added to some organic compound (eg. glucose and ADP)
What is ATPase?
The enzyme that catalyses the breakdown of ATP
(ATP synthase catalyses the synthesis of ATP)
Where does the energy to produce ATP usually come from?
Usually from the breakdown (catabolic) or redox reactions.
Advantages of ATP
-Instant source of energy in the cell
-Releases energy in small amounts
-Resynthesised
-It is mobile and transports chemical energy to where it is needed in the cell
-Universal energy carrier and can be used in many chemical reactions
ATP is used in:
-Active transport
-DNA synthesis
-Protein synthesis
-RNA synthesis
-Photosynthesis
-Muscle contraction
-Control of cytoskeleton
Why is ATP suited to its function?
-Can be reformed (made again)
-Broken down in one step/immediate source of energy
-Release of energy is small manageable amounts
-Phosphorylation reduces activation energy
Aerobic respiration definition
Aerobic respiration refers to the cellular respiration that depends on oxygen
Aerobic respiration equation
Glucose + oxygen –> carbon dioxide + water
C6H12O6 + 6O2 –> 6CO2 + 6H2O
How do cells oxidise glucose?
Cells have to oxidise glucose in a much more controlled way so that the heat generated does not destroy them.
The heat is spread over many biochemical reactions which occur in a series of steps.
Labeled mitochondrion
Glycolysis
Glycolysis occurs in the cytosol of the cell
(Pyruvate enters the mitochondria via active transport).
Purpose of glycolysis
-To produce reduced coenzyme
-To produce a molecule which can enter the mitochondria as glucose is too large to enter
The Kreb’s cycle
-Consists of a series of enzyme- controlled reaction
-2C Acetyl CoA enters the circular pathway from the link reaction
-4C oxaloacetate accepts the 2C acetyl fragment from acetyl CoA to form the 6C citrate
-Citrate is then converted back to oxaloacetate through a series of redox reactions
Products of Kreb’s cycle
-2C
-3NADH
-FADH2
-ATP
The role of the Kreb’s cycle
- Completely oxidises pyruvate/acetyl CoA.
- To release as much energy as possible.
- To generate ATP.
- To produce reduced coenzyme/NADH
- So that ATP can be produced by oxidative phosphorylation.
The link reaction
Involves the conversion of pyruvate to form a compound acetyl coenzyme A
1) Pyruvate is oxidised in enzymes to produce acetate and CO2, requiring the reduction of NAD to NADH
2) Combination of acetate with conenzyme A (2C) to form acetyl coenzyme A
—>Acetyl coenzyme A can now enter the Kreb’s cycle.
(pyruvate + NAD + CoA –> acetyl CoA + NADH + CO2)
Products of link reaction
-Acetyl Coenzyme A
-CO2
-NADH
Oxidative phosphorylation requires:
The final stage of aerobic respiration
Requires:
-oxygen
-reduced NAD and FAD which are carrying hydrogen
-electron carriers (cytochromes)
What is a cytochrome?
Electron carrier
H –> H+ + e-
Hydrogen atoms are split into the protons and electrons
Electron Transport Chain
(A series of carrier proteins embedded in membrane off the cristae of mitochondria)
The four steps:
-glycolysis
-pyruvate oxidation
-the Krebs cycle
-oxidative phosphorylation
—> Oxygen acts as final electron acceptor.
Products of electron transport chain
-ATP
-Water
-NAD
-FAD
Oxidative phosphorylation
1) Hydrogen atoms are split into H+ ions and electrons by reduced NAD/FAD
2) The electrons enter the first coenzyme and give the energy needed for the H+ ions to move from the matrix to the inter membrane space by a series of redox reactions driven by oxygen as the terminal acceptor of electrons
3) a 1/2O2 molecule joins two H+ ions to form a H2O molecule
4) H+ flow back through stalked particles
5) This energy is used to synthesise ATP from ADP and inorganic phosphate by a condensation reaction.
Chemiosmosis
The process that moves hydrogen ions through the membrane along a concentration gradient.
It links the electron transport chain with production of ATP.
(ATP synthase catalyses ADP + Pi –> ATP)
Anaerobic respiration
(Partial breakdown of glucose in oxygen-deprived conditions to produce a limited ATP yield)
-Lack of oxygen
-Happens in the cytoplasm
-Produces lactic acid
-Includes glycolysis
-Generates ATP + NADH
-NADH is oxidised by a fermentation
Anaerobic fermentation: ethanol fermentation
1)Pyruvate is decarboxylated to ethanal (CO2 is produced)
2) Reduced NAD transfers its hydrogen to ethanal to form ethanol by enzyme alcohol dehydrogenase)
–Ethanal is a hydrogen acceptor
–Ethanol can’t be further metabolised so it is a waste product
Anaerobic fermentation: lactate fermentation
1) Reduced NAD transfers its hydrogen to pyruvate to form lactate
2) Pyruvate is reduced to lactate by enzyme lactate dehydrogenase
–Pyruvate is the hydrogen acceptor
–Lactate can be further metabolised
(Lactate is transported to liver in bloodstream; enters link reaction in liver cells or is converted to glycogen).
Anaerobic and aerobic similarities
-Both happen in the cytoplasm
-Both include glycolysis
-Both generate 2ATP, 2NADH and 2 pyruvate
-Both need glucose
Anaerobic and aerobic differences
-Aerobic is in the presence of oxygen, anaerobic isn’t
-Anaerobic produces lactic acid
-NADH in anaerobic respiration is oxidised by fermentation
The 4 main stages aerobic respiration and where do they occur?
-Glycolysis : cytoplasm
-Link reaction: mitochondrial matrix
-Krebs cycle: mitochondrial matrix
-Oxidative phosphorylation (via ETC): membrane of cristae
Advantage of producing ethanol/lactate during anaerobic respiration
Converts reduced NAD back into NAD so glycolysis can continue.
Disadvantage of producing ethanol during respiration
Dissolves cell membranes so cells die when concentration is above 12%.
Principle behind the respirometer
Pressure changes in the boiling tube due to CO2 production (anaerobic experiments) or O2 consumption (aerobic experiments) cause a drop of coloured liquid to move.
