Chemical energy is contaiend within food substances, and may be converted into another form.
All life can convert energy into different forms e.g. green plants can convert light into chemical.
Glucose is broken down by means of enzymes, releasing small quantities of enegy at a time. This energy is used to make ATP.
- it is a nucleotide.
- 1 organic base= adenine
- 3 phosphate groups
- pentose sugar = ribose
Energy is required to form ATP from ADP and Pi, and this is an endergonic reaction (energy is taken up.)
ATP stores and releases energy via the unstable bond between phosphate groups.
They are easily broken to release energy when and where it is needed. This break down is called HYDROLYSIS.
In living cells the thrird phosphate group is usually removed by enzyme ATPase.
ATP +water >>>> ADP + Pi + 30.5kj of energy
This is also a reversible reaction; re-adding the phopshate group is called phosphorylation.
The break down of ATP is an exergonic reaction.
ATP: How is it made
Protons: H+ ions
Electron: sub atomic particle with a relative charge of -1.
ATP is produced across the internal membranes of mitochondria and chloroplasts.
has an internal mebrane that separates the intemembranal space from the matrix. In chloroplats, the corresponding membrane separates the thylakoid space from the chloroplast stroma.
There must be high concentration of protons in the intermembrane space, and these are replenished by proton pumps. They then flow down the concnetration gradient through the enxymes ATP synthetase.
The proton umps are fuelled by electron energy.
ATP: 3 Types of Phosphorylation
Occurs on the inner membrane of mitochondria during respiration e.g. electron transport chain.
Occurs on chloroplasts inner membrane during photosynthesis.
When phosphate grouos are transferred from donor molecules to ADP to make ATP e.g. Glycolysis and the Krebs cycle.
ATP: Importance and advantages
ATP controls the release of energy. If the breakdown of glucose was uncontrolled, the cell would overheat and die.
Advantages of ATP:
- Hydrolysis of ATP only has one reaction and so is efficient for when energy is needed quickly. Glucose require many reactions to release energy.
- Hydrolysis of ATP only needs one enzyme, whereas Glucose needs loads.
- ATP releases a small amount of energy when and where needed. This allows greater control over energy, whereas glucose could end up in wasting energy and overheating the cell.
- ATP is a common energy currency for all cells allowing greater efficiency and 'trading' between cells and functions.
It is the 'universal energy currency' as all cells use it.
ATP has 5 main uses for the WJEC exam:
- Active transport
Energy is required to move ins and molecules against a concentration gradient.
- Muscle contraction
- Metabolic pathways
ATP is used to build up larger molecules, or break them down.
- Nerve transmission
Sodium and potassium ions need to be actively pumped across synapses.
ATP plays a big role in processing and packaging secretion vesicles.
Respiration: in organisms
Respiration is a series of enzyme catalysed reactions which release chemical energy from organic molcules in order to synthesise ATP.
All organisms fall into one of these three repsiration catergories.
- Obligative aerobes:
Can only respire in the presence of oxygen.
- Faculative aerobes:
Can respire aerobically and anaerobically.
- Obligative anaerobes:
Cannot respire in the presence of oxygen.
The phosphorylation of glucose,making 6C hexose posphate> trisose phosphate which are oxidised to make pyruvate, ATP and NADH.
In the cytoplasm of the cell. 'splitting of sugar'. SUBSTRATE LEVEL.
- Glycogen is the animal store of glucose. First, it is split down into Glucose, which has 6 carbons.
- 2 ATPs are used to activate/phosphorylate the glucose into hexose phosphate.
- This is much more reactive than glucose, and so breaks down.
- Hexose phosphate is split into two, making two triose phosphates.
- The triose phosphate is dehydrogenated, releasing hydrogen ions, which are picked up by NAD, to become 2 reduced NAD.
- This reduction procides enough enegry for substrate level phosphorylation of 4 ADP molecules.
4 ATP molecules are produced, but 2 are used up so NET ATP PRODUCTION =2
Respiration: The Link Reaction
Matrix of Mitochondria. Converts pyruvate into acetyl Coenzyme A (2C).
- Pyruvate diffuses from the cytoplasm to the mitochondria matrix.
- Decarboxylate and dehydrogenate the pyruvate, to make Acetyl.
- This joins onto a coenzyme A moelcule.
- The hydrogen is picked up once again to make reduced NAD.
- Acetyl contains the two carbons- the coenzyme is a separate molecule.
PRODUCES: CO2 and 2rNAD
PYRUVATE IS DECARBOXYLATED AND OXIDISED.
Respiration: The Krebs Cycle
Matrix of the mitochondria. 2C- Acetyle CoA combined and then broken down to release Hydrogen atoms to reduce NAD and FAD.
- Acetyl coenzyme A is combined with a 4C compound, to make a 6C compound.
- This 6C compound is decarboxylated and dehydrogenated- (latter used to reduced rNAD).
- The remaining 5C compund is also decarboxylated, dehydrogenated and dephosphorylated - a bit of ATP is made by SUBSTRATE LEVEL PHOSPHORYLATION (Pi taken from 5C compound)
- The 4C compound is then dehydrogenated to make reduced FAD.
- Dehydrogenated again to make NADH.
- This 4C compound is recycled back into the cycle, combining with another acetyl CoA.
TURNS TWICE FOR ONE GLUCOSE MOLECULE (for each pyruvate molecule) The krebs cycle is a series of decarboxylations and dehrydrogenations where an acetate fragment is completely broken down and the 4C is regenerated via 6C and 5C intermediates.
4C + acetyl >> 6C -2H(NAD) - CO2 >> 5C -ATP -CO2 - 2H(NAD) >>> 4C - 2H(FAD) >> 4C -2H (NAD) >> 4C
FOR EACH ROTATION: one ATP molecule >> 2 ATP moelcules per glucose
Respiration: Electron Transport Chain
Inner membrane of mitochondria. Series of redox reactions along a chain of electron carriers, using oxygen. An example of chemiosmosis.
- The reduced NAD and FAD are used here. There are proteins intrinsic in the membrane which make up the electron transport chain.
- The rNAD is oxidised and releases all its hydrogens, as H+'s, at the beginning of the chain, in the matrix. Electrons are also released.
- The H+'s are then actively pumped up the proton pump proteins and into the inter membrane space. The electrons sit on the electron carriers on the pump, providing energy.
- The pump is oxidised, and the electron moves onto a a electron acceptor, and then the next pump, giving it a bit of energy, and letting it pump more H+'s into the intermembrane space. The electron then moves to the next pump and the same happens. These are redox reactions.
- There is a build up of H+ ions on the inter membrane space, creating a chemical concentration gradient between the space and the matrix.
- The H+'s then diffuse down the stalked particle with ATP synthase, making the stalked particle rotate. This mechanical energy is converted to chemical energy e.g. ATP.
- Once out the stalked particle. Hydrogen ion + Oxygen +electron >> 1/2water
Aerobic repsiration combines substrate level (Glycolysis and Krebs Cycle) and oxidative phosphorylation (ETC).
Glycolysis: Creates 4 ATP, but two are used up. NET per glucose = 2ATP and 2 rNAD (=6ATP)
Link reaction: No ATP produced, but NET per glucose = 2 rNAD (=6ATP).
The Krebs Cycle: 1 ATP produced, 3 rNAD and 1 rFAD for each cycle. NETper glucose= 2ATP, 6 rNAD (18ATP) and 2rFAD )4ATP).
Electron Transport Chain: One rNAD can produce 3 ATP, we have 10 so 30ATP. Each rFAD produces 2 ATP. We have 2 so 4 ATP. 2 ATP made by directly sublevel phosphorylation.
NET = 34 ATP by oxidative phosphorlation. +2 each (substrate levl photophosphorylation in glycolysis and ETC) = 38.
NET OVERALL= 38 ATP.
NET overall for ECF = 34
Anaerobic respiration stops before the krebs cycle, so only produces the 2ATP from glycolysis.
Some energy is lost as heat energy.
Concentration gradient between matrix and inner membrane isn't maintained, so electron transport chain stops. The NAD and FAD are locked up with hydrogens, so the Krebs cycle stops also.
For glycolysis to continue, pyruvate and hydrogen must be removed to liberate rNAD from hydrogen (so triose phosphate can be converted to pyruvate.) Solution: Pyruvate accepts hydrogen from rNAD.
Path 1: animals
- Pyruvate is then converted to lactic acid, mainly in muscle tissues during exercise.
Glucose is dehydrogenated and phosphorylated, reducing NAD and creating pyruvate. This pyruvate recombines with the hydrogen from NAD to make lactate.
Path 2: micro-organisms and some plant cells
Pyruvate is decarboxylated, and converted to ethanal, which is then reduced by H's from NAD to make ethanol ==== FERMENTATION.
PYRUVATE + 2H >>> CO2 + C2H5OH
Alternative Respiratory Substances
- First, hydrolysed into glycerol and fatty acids.
- Glycerol is phosphorylated by ATP (to make ADP) and dehydrogenated (by NAD) and converted into triose phosphate, which then continues in normal glycolysis pathway.
- Long fatty acid chains are split into 2C fragments which enter the Krebs Cycle as Acetyl CoA
- Huge amounts of ATP are built up with lipids, as there are many hydrogens on the fatty acid chains, which are then fed into the ECT.
- Only used in extreme circumstances.
- First, the polypetide is hydrolysed into amino acids, which are the deanimated in the liver.
- The amino group is converted to urea and excreted.
- The rest of it is converted to acetyl CoA, pyruvic acid or another Krebs cycle intermediate.
Similarities between chloroplast and mitochondria
-both create proton gradients across a membrane (inner mitochondrial membranes v thylakoid membrane)
-both use ATP synthestase to convert electrochemical potential energy into mechanical energy and then chemical energy-- ATP.
-Both create an electrohemical gradient by pumping H+ into a intermembranal space.
-electrons fuel the electron pumps.
- If there is no Oxygen, the gradient disintegrates, and stalked particle doesnt work. Oxygen is the final electron acceptor.
- NAD and FAD cannot be reoxidised, so the link recation and krebs cycle will stop.
enzymes and co-enzymes
- Link reaction and Krebs
- Glycolysis, link reaction, Krebs
- Combines with acetyl group
- In Krebs Cycle
NAD + FAD
- Act as hydrogen carriers
- Krebs Cycle
ALSO ELECTRON CARRIERS IN THE ELECTRON TRANSPORT CHAIN