Date post: | 15-Jul-2015 |
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Respiratory substrates
The usual respiratory substrate is glucoseSome cells can only respire glucose, such as brain neurones
Other cells can oxidize lipids or amino acids
Lipids
These are broken down to fatty acids and glycerol
Fatty acids are then broken into pairs of Carbon atoms As Acetyl CoA which enters the Krebs cycle
Fatty acids
These are then broken into pairs of Carbon atoms As Acetyl CoA which enters the Krebs cycle
The more hydrogens the more NAD reduced can be madeThis will form ATP in oxidative phosphorylation
Most of the energy from respiration is from oxidation of hydrogen to water
The more hydrogens there are, the more energy can be released
Fatty-acids therefore have a high energy value per unit mass
Glycerol can be phosphorylated to and finally incorporated into glycolysis
One molecule of glycerol will yield 19ATP
Proteins These are hydrolysed to amino-acidsThese are deaminated to remove the amino group or transaminated to transfer the amino group to another molecule
The hydrocarbon skeleton is then converted to pyruvate or Acetyl CoA which will enter the Krebs cycle
Energy Values of SubstratesThese are found using a CALORIMETER
A known mass of the substrate is burnt completely in the presence of oxygen
The energy given off as heat is used to raise the temperature of a known volume of water
The energy value per unit mass of the substrate can be found using the Specific Heat Capacity of water
The energy values of Substrates are:
Carbohydrates – 15.8 KJg-1
Lipids – 39.4 KJg-1
Protein – 17.0 KJg-1
Respiratory Quotients (RQ)These are used to determine the respiratiry substrate being used in resiration
For Carbohydrates:
C6H12O6 + 602 6CO 2 + 6H2O + ENERGY
02 IN : CO2 OUT 1 : 1
RQ = Volume of CO 2 OUT per unit time
Volume of 02 IN per unit time
Or RQ = moles of CO 2 out moles of 02 in
For example the RQ of glucose = 6/6 = 1.0
Oleic acid:C18H34O2 + 25.502 18CO2 + 17H2O + ENERGY
RQ = moles of CO2 out moles of 02 in
=18/25.5 = 0.7
For anaerobic respiration in yeast
C6H12O6 2C2H5OH + 2CO2 + 2ATP
RQ = moles of CO2 out moles of 02 in
= 2/0 = infinity
However because there is some aerobic respiration so some oxygen IN the RQ will be high less than 2
A high value for RQ will indicate some anaerobic respiration
Respirometer
This is used to measure oxygen uptake
And to find RQ values or to investigate rates of respiration
a sealed chamber and method to measure volume changes
CO2 is absorbed by soda lime or concentrated Potassium/ sodium hydroxide
Any decrease in air volume will be because oxygen is being taken up
The amount of oxygen used per unit time will give a rate
The temperature and pressure must be kept constant or accounted for using a control
If investigating the effect of a variable on the rate of respiration:All other factors must be constant
If finding the RQ of an organism to determine the respiratory substrates being used:
First find the volume of oxygen used in a specified time, e.g. xcm3min-1
Remove the soda lime and repeat under the same conditions
If carbohydrates are being respired the plunger will not move O2 used and CO2 made will be xcm3min-1
RQ = Volume of CO2 OUT per unit time Volume of 02 IN per unit time
= x/x
= 1
If there is some anaerobic respiration more CO2 will be made than O2 used
The plunger will move to the rightIf it moves y cm3min-1 then the total volume of CO2
will be (x + y)cm3min-1
If fats are being respired there will be less CO2 made than O2 used because there is no glycolysis or link reaction
The plunger will move to the left by z cm3min-1
The amount CO2 of made is (x - z)cm3min-1