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BIOLOGY - 12
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UNIT–1 : Biological energetics
• Introduction :
Organic compounds store potential energy.
With the help of enzymes a cell systematically breaks-down
complex organic molecules ( E ↑ ) to simpler substances ( E↓ )
Some of energy released can be used to do work.
The rest ( most ) lost as heat.
Complex org. molec. ( E ↑ )
Systematic
breaking-down
Cellular activities
energy
Heat
simple substances ( E↓ )
Mitochondria
Respiration
• Respiration : breaking-down of food molecules
to produce energy.
• There are two types of respiration :
Aerobic respiration
Anaerobic respiration
Breaking-down of food molecules
In the presence of oxygen
to produce energy
Breaking-down of food molecules
in the absence of oxygen
to produce energy
Glucose + oxygen  carbon dioxide + water + energy
C6H12O6 + O2  6CO2 + 6 H2O + 38 ATP
Glucose  lactic acid + energy
C6H12O6  2 C3H5O3 + energy
Glucose  alcohol + CO2 + energy
C6H12O6  2 C2H5OH + 2 CO2 + energy
Respiration
Compare between aerobic and anaerobic respiration.
Type of respiration
Oxygen
Oxidation of glucose
Energy yield
Products
Aerobic
Anaerobic
With
Without
Complete
Incomplete
High
Low
CO2 and H2O
Lactic acid or alcohol
+ CO2
Respiration
•
Energy produced in respiration can be used in :
1. Muscle working.
2. Active transport.
3. Nerve impulses.
4. Biosynthesis.
5. Keeping body temperature constant.
•
BUT
remember that : not all energy is used up
a lot is lost as heat.
Respiration
• Compare respiration with combustion :
Respiration
Combustion
Inside the cell
Outside the cell
Enzyme regulated
No enzymes
Energy produced
step-by-step
Energy produced
at once
Slow
Fast
Anaerobic respiration
•
Occur in the absence of O2.
•
Occur totally in cytoplasm.
•
The cell is incompletely oxidize glucose.
•
Produce little amount of energy ( 2 ATP )
so most of the energy remains in the organic molecule.
•
•
It is a 2 stages process :
1.
Glycolysis.
2.
Regeneration of NAD+.
Two types :
1. Lactic acid fermentation ( in animals ).
2. Alcoholic fermentation
( in plants ).
Anaerobic resp.
• Note : only the first stage of anaerobic resp. produces ATP,
so what is the importance of the second stage?
•
[ If the supply of NAD stops anaerobic respiration stops ]
The second step Regenerate NAD from NADH by reduction of pyruvate.
so production of ATP continue.
GLYCOLYSIS
Glucose
Regeneration of NAD
NAD
NADH
ATP
Pyruvic acid
Lactic acid
Lactic acid fermentation
• Why does the athlete breathe heavily for several minutes
after the race?
During the rapid exercise the body can`t supply
enough oxygen to the muscle.
( developing oxygen dept )
So, the muscle begin to produce ATP by lactic
acid fermentation.
Building of lactic acid cause a painful sensation.
• What is the fate of lactic acid?
Oxidised by liver.
ATP structure and function
ATP ( Adenosine triphosphate )
-
A nucleotide.
Acts as an energy currency of the cell.
-
( intermediary molecule between energy producing
and energy consuming reactions )
Structure :
1. Adenine base.
2. Ribose sugar.
3. Three phosphate groups.
-
How does ATP synthasize in respiration?
1. Substrate level phosphorylation ( in glycolysis & krebs cycle )
2. Oxidative level phosphorylation ( in electron transport chain )
Aerobic respiration
1. Glycolysis
• Occur in the cytoplasm of all living organisms.
• No need for oxygen.
• Glucose is broken down into two pyruvates.
• This process consists of three stages:
Glycolysis
Activation stage
Glucose
C C C C C C
ATP
ADP
C C C C C C P
Glucose phosphate
C C C C C C
P
Fructose phosphate
P
Fructose-1,6-diphosphate
ATP
ADP
P C C C C C C
Splitting stage
PGAl
P C C C
NAD
NAD
ADP
ATP
Oxidation anf rearrangement
ADP
NADH
NADH
C C C
C C C P
Pyruvate
ATP
C C C
Glycolysis
1.
Glucose molecule activated by 2 ATP to form hexose
diphosphate.
2.
The hexose diphosphate split into 2 triose phosphate.
3.
The trioses oxidised in energy yielding phase to
produce 2 pyruvate.
4.
4 ATP and 2 NADH2 produced
2 Pyruvate
Glucose
2 ATP ( 4 - 2 )
2 NADH2
The link reaction
In the presence of oxygen pyruvic acid enters the matrix of mitochonderia
and three things happen :
1. Decarboxylation : CO2 molecule removed from the pyruvic acid.
2. Dehydrogenation : hydrogen removed and transferred to NAD+ to form
NADH.H+.
3. The resulting acetate ( 2C ) combines with coenzyme A ( CoA ) forming :
acetyle CoA which enters the krebs cycle.
CO2
Pyruvate ( 3C )
NAD+
NADH.H+
CoA
Acetyle CoA ( 2C )
Remember : - 2 pyruvate molecules are formed from each glucose molecule.
- So, the reaction happen twice and 2 Acetyle CoA resulted with 2 NADH.H+
Krebs cycle
It takes place in the matrix of mitochondria and includes the following
reactions :
1. Acetyle CoA combine oxaloacetate ( 4C ) to form 6C compound ( citrate ).
• A series of reactions takes place where the citrate both decarboxylated
and dehydrogenated.
– CO2 is released as waste product.
– Hydrogen is picked up by 2 electron acceptors ( NAD & FAD )
• As a result the oxaloacetate is regenerated to combine with more acetyl
CoA.
Krebs cycle
Krebs cycle
For each 1 turn of Krebs cycle :
For each 2 turns of Krebs cycle :
- 3 NADH.H+ produced.
- 6 NADH.H+ produced.
- 1 FADH2 produced.
- 2 FADH2 produced.
- 1 ATP molecule produced.
- 2 ATP molecule produced.
- 2 CO2 molecules released.
- 4 CO2 molecules released.
Electron transport chain
Where does the energy that was in the glucose molecule has gone?
- Most is still in the reduced coenzymes ( NADH, FADH )
- Only 4 ATP molecules produced directly ( by substrate level phosphorylation )
from 1 glucose molecule ( 2 from glycolysis + 2 from krebs cycle )
What is the final stage of aerobic respiration? What is its importance?
electron transport chain ( e.t.c. )
importance : - couples the transport of electrons with the production of ATP
- most of ATP is produced during this stage
by oxidative phosphorylation
Electron transport chain
Where in the cell does e.t.c. occur?
in the cristae of the inner membrane of mitochondria.
Components of the e.t.c. :
- group of carrier proteins
( cytochromes )
- ATP synthase protein.
Cytochrome complexes
Electron transport chain
How does the mitochondria couple the transport of electrons with ATP synthesis?
( CHEMIOSMOSIS )
- High energy electrons from NADH and FADH2 are passed to e.t.c.
- These electrons are passed from carrier protein to the next .
- At the end of the chain there is an enzyme that combine these electrons with H+
and oxygen to form water.
- As the electrons passes along the chain, they lose most of their energy.
- This energy is used to pump hydrogen ions across the inner membrane
( from the matrix to the intermembrane space ).
- H+ gradient is created across the inner membrane.
- H+ diffuses down the proton gradient through the ATP synthase protein.
- The diffusion of H+ drives the phosphorylation of ADP to ATP
Chemiosmosis
Electron transport chain
How many ATP molecules produced for each :
- 1 NADH  3 ATP
- 1 FADH2  2 ATP
What is the function of oxygen in respiration?
oxygen serves as the final electron acceptor in the electron transport chain.
so oxygen is essential for getting rid of low-energy electrons and hydrogen
ions, the wastes of cellular respiration.
What is the importance of e.t.c.?
1. release energy from NADH and FADH2 to be stored ( temporary ) in ATP.
1. Regenerate NAD and FAD so that the process of respiration proceeds
from glycolysis to link-reaction and krebs cycle.
Why does the an aerobic respiration stops after glycolysis ? ? ! !
TOTALS
2 ATP
Glycolysis
2 NADH
2 ATP
Link reaction
2 NADH
2 ATP
2 ATP
Krebs cycle
6 NADH
2 FADH2
e.t.c.
4ATP
4 ATP directly produced
18ATP
6ATP 6ATP
34 ATP indirectly produced
38 ATP is produced / 1 glucose
-
Food gives us energy.
-
Carbohydrates and fats are high energy foods.
-
Energy of food is measured in kJ ( 1 kJ = 1000J ).
65
-
To measure the amount of energy in food :
20 ml
1. Burn the food to give-out energy.
28.5
2. Use energy to heat-up water.
3. The hottest water the more
energy content.
3.5 g
RESULTS
mass of peanut ( g )
Temp. of water ( start )
Temp. of water ( end )
Temp. rise
Of water
3.5
28.5
65.0
??
Calculations :
Temperature rise ( ΔT )
= end temp. – start temp.
= 65
- 28.5
= 36.5 C
Energy ( J )
= temperature rise X 20 X 4.2
= 36.5 X 20 X 4.2
= 3066 J
Energy content ( J/g )
= energy give ( J ) / weight of peanut ( g )
= 3066 / 3.5
= 876 J/g
= 0.876 kJ/g