GLYCOLYSIS
7 Glycolysis, the first stage of respiration, is the anaerobic decomposition of glucose to release energy
7.1 identify that the enzymes of glycolysis are found in cell cytoplasm and that glucose is the raw material for glycolysis
7.2 summarise the energy release in glycolysis and identify the form in which this energy is captured
7.3 identify the end product of glycolysis as 2-oxopropanoate (pyruvate)
7.5 process information from a simplified flow chart of biochemical pathways to analyse the total energy output from glycolysis
Glycolysis (stage 1)
–Occurs in the cytoplasm and relies on enzymes found in the cytoplasm.
–Is the first stage in both aerobic and anaerobic respiration.
–Begins with the molecule glucose and ends with two molecules of pyruvic acid (pyruvate). Its scientific name is 2-oxopropanoate. Draw the structural formulae for pyruvic acid
–Two molecules of ATP are used up, four molecules of ATP are produced, net gain of two ATP.
–NAD + (enzyme co-factor) acts as an oxidising agent and is reduced to 2x NADH. This reduced form can be used in the cytochrome chain or for the breakdown of pyruvic acid to lactic acid.
–Glycolysis occurs as a series of enzyme driven pathways. (10 step process)
–If no oxygen is present pyruvic acid will be converted to lactic acid in type 2 muscles ie. Pyruvate is reduced to the lactate ion and this is accompanied by the oxidation of NADH to NAD+
–Draw the structural formulae for lactic acid and write an equation to show the conversion of pyruvic acid to lactic acid
–An alternate pathway occurs in primitive organisms eg. Yeast where fermentation occurs N.B no oxygen present.
Fermentation :
Glucose pyruvic acid ethanol + CO2
Construct a flow chart below to show the steps involved and the products of GLYCOLYSIS
Before pyruvate enters the Krebs cycle it must be converted to Acetyl Co-A
THE KREB’S CITRIC ACID CYCLE
8. Gentle exercise uses type 1 muscles and involves aerobic respiration. The aerobic respiration of acetyl CoA releases much more energy
8.1 describe the tricarboxylic acid (TCA) cycle as another multi-enzyme system involved in respiration
8.2 outline the TCA cycle as oxidative decarboxylation with the addition of acetyl CoA as the energy source in each cycle
8.3 identify the products of the TCA cycle and explain the role of oxidation and reduction in the cycle
The Krebs Citric Acid or Tricarboxylic Acid Cycle (Stage 2)
–Occurs in and involves the enzymes in the matrix of the mitochondria.
–Acetyl Co A then enters the Krebs citric acid cycle (stage 2) ( tri-carboxylic acid cycle, TCA), where a series of compounds beginning with citric acid (C6) undergoes oxidative decarboxylation to produce C5 and C4 compounds. The process is cyclic ending with oxaloacetic acid which will then link with acetyl-Co A to produce citric acid and the cycle begins again.
–During this cycle 1 molecule of ATP is produced, 3x NADH and 1xFADH2 and also 2x CO2.
–The hydrogens and e- from the Co-factor molecules NADH and FADH2 now enter the cytochrome chain.(stage 3)
–The carbon atoms of the glucose molecules are now completely oxidised some of the energy of glucose has been used to produce ATP from ADP. Most of the energy remains in electrons removed from C-C and C-H bonds and has been passed to the electron carriers NAD+ and FAD. These electrons are still at a higher energy level. In the final stage of the oxidation of glucose these carrier molecules now NADH and FADH2 enter the cytochrome chain or the electron transport chain.
Construct a simplified Krebs citric acid cycle below
THE CYTOCHROME CHAIN
8.4 summarise the role of the cytochrome chain and identify the location of the chain of enzymes involved within the mitochondrion.
The Cytochrome chain and Oxidative phosphorylation (Stage 3)
–This occurs on the highly folded christae of the mitochondria and involves iron containing enzymes called cytochromes.
–At this stage high energy electrons are passed stepwise down an energy gradient enabling the formation of ATP molecules ie. Oxidative phosphorylation.
–This is a multi-stage pathway and for each NADH molecule that is oxidised to NAD+ three x ATP form and for each FADH2 two x ATP form.
–ie. The total production of ATP from the cytochrome chain is 34 ATP molecules.
–It is during this stage 3 that hydrogen from the carrier molecules is added to oxygen to produce H2O.
–Oxidative phosphorylation is defined as the process that couples the oxidation of NADH and FADH2 to the production of high energy phosphate bonds in ATP
–Another way of putting it is to say The use of electron energy released by NADH and FADH2 during cellular respiration to phosphorylate (add a phosphate group onto) ADP to yield energy rich ATP is called Oxidative Phosphorylation
The end result of the complete oxidation of one glucose molecule is 38 molecules of ATP ( 2 from Krebs, 2 from glycolysis and 34 from cytochrome chain ) 6 molecules of CO2 , and 6 molecules of H2O. This process is about 54% efficient with the remainder of the energy being lost as heat.
Glucose + 6 Oxygen 6 Carbon Dioxide + 6 Water + 38ATP
Construct a flow chart to summarise the chemistry of the cytochrome chain
8.5 describe the role of oxygen in respiration
Oxygen is reduced by the addition of hydrogen and electrons to form H2O accompanied by phosphorylation of ADP to ATP in the cytochrome chain producing 34 molecules of ATP.
Oxygen must be present for the Krebs cycle to proceed.
8.6 process information from a simplified flow chart of biochemical pathways to produce a flow chart summarising the steps in aerobic respiration
Construct your own flow chart
8.7 process information from a simplified flow chart of biochemical pathways to analyse the total energy output from glycolysis and compare it with the energy output from the TCA cycle
Glycolysis produced 2xATP and 2x NADH while TCA cycle produces 2xATP and 6xNADH and 2x FADH2 (For one glucose molecule).
9. ATP used in muscle contraction is continually regenerated
9.1 identify NADH and FADH2 as high energy compounds involved in respiration
9.2 describe the NADH/FADH2 reduction / ATP production as an oxidation/reduction process, explain how the
hydrogen is bonded to NAD+ and what happens to the electrons when these bonds are broken
NAD+ NADH + H+ (This is reduction)
FAD FADH2 ( Reduction)
Hydrogen is bonded to the NAD+by sharing a pair of electrons in a covalent bond. When NADH or FADH2 gives up its H to water they are oxidized. Now the electrons from the covalent bonds are transferred through a complex sequence of reactions down an energy gradient via the cytochromes and are used to combine with oxygen to make water ie the water is reduced because it both gains H’s and electrons
O2 + 4e- + 4H+ 2H2O (Reduction)
The energy lost by the electrons as they pass down the cytochrome chain is used to combine a phosphate group( Pi )to ADP to make ATP.
THE COMBINED PROCESS IS CALLED OXIDATIVE PHOSPHORYLATION
ie Oxidation of the NADH and FADH2accompanied by phosphorylation of ADP + Pi ATP
9.3 construct an equation to summarise the reduction/oxidation process in ATP regeneration
9.4 define oxidative phosphorylation as the process that couples the oxidation of NADH and FADH2 to the production of high energy phosphate bonds in ATP
Oxidative phosphorylation is defined as the process that couples the oxidation of NADH and FADH2 to the production of high energy phosphate bonds in ATP
Also see above equations
9.5 process information from a simplified flow chart of biochemical pathways to analyse the steps in oxidative phosphorylation
Can you complete the following flow chart