GLYCOLYSIS
• Glycolysis is the first step in the biochemical pathway of respiration
• Overall a molecule of glucose is broken down into two pyruvate molecules
• Glycolysis actually involves a large number of individual reactions which are carefully
Pyruvate Pyruvate
Reactions of glycolysis
• 1.Glucose is phosphorylated to make a 6C sugar
phosphate (fructose diphosphate). 2 ATPs are used to supply the phosphate groups.
• 2.The 6C sugar phosphate breaks down to form 2, 3-carbon sugar phosphates, called triose phosphates (TP).
• 3.Hydrogen is removed from each of the 2 TP
molecules. The hydrogens are passed to 2 NADs – this means that the NADs are reduced.
• 3.Hydrogen is removed from each of the 2 TP molecules. The hydrogens are passed to 2 NADs – this means that the NADs are reduced.
• 4. 2 ATPs are made directly from the conversion of each TP to pyruvate as the phosphate groups are removed, therefore in total 4ATP is made.
Summary
Into Glycolysis Out of glycolysis
1 glucose 2 pyruvates
2 NAD 2 reduced NAD
(NADH)
2 ATP 4 ATP
The link reaction
(in the matrix of the mitochondria)
Pyruvate
The Link Reaction
• The pyruvate molecules enter the mitochondrion.
• CO2 and hydrogen are removed from each
pyruvate to create 2-C molecules. The hydrogen is transferred to NAD
THE KREB’S CYCLE
• 1. Each acetyl CoA (2C) combines with oxaloacetate (4C) to make a 6C compound (citrate).
• 2. In a series of steps, for each acteyl coA: 2 CO2 molecules are released
3 NAD molecules are reduced (3 NADH) 1 FAD molecules are reduced (1 FADH2) 1 ATP molecule is made
• 3. The 4C compound is regenerated (by the removal of the 2 Cs in 2 CO2 molecules) so that the cycle can begin again joining
What co-enzymes are
• Co-enzymes are small molecules that carry chemical groups between enzymes.
• NAD and FAD are examples of co-enzymes
• The most important product of the Kreb’s cycle is
NADH and FADH2 which are passed to the final stage
of respiration, the electron transport chain.
Summary of the Kreb’s cycle
Into Kreb’s Out of Kreb’s
2 acetyl co A 2 oxaloacetate
4CO2
6NAD 6 reduced NAD (6 NADH)
2FAD 2 reduced FAD
(2 FADH2)
• Reduced FAD and NAD produced as a result of oxidation now pass to chains of protein
molecules located on the internal membranes of the mitochondria
• These chains of molecules are known as the electron transport chains
• The H is removed from NAD and FAD and is split into H+ and electrons.
Hydrogen atoms from the NADH and FADH2 split into hydrogen ions and electrons
• NADH NAD + H
+
+• The electrons pass from one molecule to the next on the electron transport chain through a series of redox reactions
• At each transfer, a small amount of energy is released
• This energy is used to pump H+ ions through the inner mitochondrial membrane into the
• The H+ concentration therefore increases, forming
an electrochemical gradiednt.
• This means that the H+ ions have electrical potential
energy. H+ then flows back down the gradient into
the matrix through protein channels.
• Associated with each channel is an enzyme, ATP
synthetase. As the H+ ions flow through, their
energy is used to make ATP.
• Oxygen acts as the final electron acceptor in the chain, so the oxygen, electrons and hydrogen ions combine together to form water.
Anaerobic Respiration
• Under conditions of low oxygen, cells have to produce ATP by anaerobic respiration
• The only stage in the anaerobic process which produces ATP is glycolysis.
The problem with NAD
• Reduced NAD is normally converted back to NAD when its hydrogen is transferred in the electron transport chain.
• This will only happen if oxygen is present
where H+ and electrons from the ETC combine
• When oxygen is not present the hydrogen from NADH is donated to pyruvate.
• This forms either lactate in animal cells or ethanol and CO2 in plants and micro-organisms.
• Anaerobic respiration allows NAD to be reformed which is necessary for the continuation of glycolysis.
Plants and Fungi:
Pyruvate + NADH Ethanol + CO2 + NAD
Animals:
The respirometer to calculate the
rate of respiration
• Normally the volume of oxygen used equals the volume of carbon dioxide produced so there is no volume change
• The volume of oxygen used can be calculated using the manometer. The position of the
liquid in the manometer is noted at the
beginning and the end of the experiment. The distance the liquid travels is calculated.
Describe how the inner mitochondrial membrane is well adapted to its function of producing ATP
• The inner mitochondrial membrane is the site of oxidative phosphorylation and the electron transport chain
• The membrane is selectively permeable. This means it is
possible to create an electrochemical gradient of H+ as they are unable to diffuse through the membrane by simple
diffusion
• The inner mitochondrial membrane has ATP synthetase for making ATP from ADP and Pi
• The membrane is folded so this increases the surface area so there is a greater area for ATP synthetase stalked particles • The membranes keep enzymes is a small space
Using different respiratory substrates
• A respiratory substrate is the substance that is the starting point for respiration. So far we
have looked at glucose being the respiratory substrate.
• Amino acids and lipids can also be used • We can estimate which substances an
Calculating RQ
RQ = CO2 produced
O2 consumed
RQ Respiratory Substrate
0.7 (7/10) Triglycerides
0.9 (9/10) Amino acids and proteins
