Energy Production - Stages 3 & 4 Flashcards
What are the products of the TCA cycle?
- NADH
- FADH2
- GTP
- CO2
- Intermediate metabolites e.g. Citrate, α-ketoglutarate
Why are some reactions of the TCA cycle irreversible?
DECARBOXYLATION of some compounds where C is lost as CO2
What can the intermediates of the TCA cycle be used for?
- Amino acid synthesis e.g. α-ketoglutarate
- Fatty acid synthesis e.g. Citrate, Malate
- Synthesis of haem and glucose (Succinate and oxaloacetate)
How is the rate of the TCA cycle controlled?
- ALLOSTERIC ACTIVATION AND INHIBITION OF SPECIFIC RATE DETERMINING ENZYMES
- α-ketoglutarate dehydrogenase
- Isocitrate dehydrogenase
How many molecules of NADH, FADH2 and CO2 are produced from the TCA cycle per molecule of glucose?
- 6 NADH
- 2 FADH2
- 4 CO2
What is the role of NADH and FADH2 in energy production?
Contain high energy electrons that can be transferred to oxygen via a series of carrier molecules to release LARGE AMOUNTS OF FREE ENERGY
Where does oxidative phosphorylation occur?
Electron transport chain of the inner mitochondrial membrane
Explain what is meant by ‘electron transport’
Electrons in NADH and FADH2 are transported through a series of carrier molecules to produce a STEPWISE RELEASE OF FREE ENERGY
Explain the formation of the proton motive force (PMF)
- Inner mitochondrial membrane is impermeable to protons (H+)
- 3/4 electron carriers also act as PROTON TRANSLOCATING COMPLEXES (PTC)
- PTC use free energy from electron transport to pump H+ across the inner membrane into the intermembrane space, forming a proton gradient
- THE CHEMICAL BOND ENERGY OF ELECTRONS IS TRANSFORMED INTO ELECTROCHEMICAL POTENTIAL DIFFERENCE OF H+
What is the role of the PMF? Explain how it performs this role
- COUPLES electron transport to ATP synthesis
- Chemical bond energy produced via stepwise transition of electrons through carrier proteins is transformed into electrochemical potential difference of H+
- Proton gradient produced in intermembrane space
- Potential difference of H+ is used to drive the synthesis of ATP by diffusion of H+ through ATP synthase complex
Why is there more potential energy produced from NADH compared to FADH2?
NADH uses all 3 of the PTC, whereas FADH2 only uses 2
Why can both stages 3 and 4 not occur in the absence of oxygen?
- Oxygen acts as the TERMINAL ELECTRON ACCEPTOR and is therefore responsible for the reoxidation of NADH and FADH2
- Absence of oxygen means the ETC stops and a PMF cannot be set up, therefore ATP synthesis cannot occur
- Lack of reoxidation of NADH and FADH2 means there is less substrate available for reactions of the TCA cycle, therefore the rate of TCA cycle decreases
List 4 differences between oxidative phosphorylation and substrate level phosphorylation
- OP is mitochondrial, SLP is cytoplasmic
- OP energy coupling occurs indirectly through utilisation of PMF, SLP energy coupling occurs directly through phosphoryl group transfer
- OP is major process for ATP production, SLP is minor process for ATP production
- OP cannot occur in the absence of O2, SLP can occur to an extent in the absence of O2
Give two examples of UNCOUPLERS and explain how they work
- Dinitrophenol
- Dinitrocresol
- INCREASE PERMEABILITY OF THE INNER MEMBRANE TO H+
- Dissipates potential energy of PMF as HEAT ENERGY
- ET can continue but ATP synthesis does not occur
What is the role of UCP1?
- THERMOGENIN
- Expressed in brown adipose tissue
- Involved in NON SHIVERING THERMOGENESIS and heat production in hibernating mammals and babies
