Photosynthesis and cellular respiration
Plants and Animals.
Photosynthesis.
Light reaction.
Calvin cycle.
Cellular respiration.
Glycolysis.
Krebs cycle.
Electron transport phosphorylation.
Plants and Animals.
Plants and animals, are the two major types of life.
Plants and animals, including human beings, are very different from each other.
Yet there is a strong bond, that links them together.
Animals including human beings, are heterotrophs.
Heterotrophs cannot make their own food.
Plants are Autotrophs.
Autotrophs can make their own food.
Heterotrophs are dependent on Autotrophs, for food.
There is a clear interdependence between these types of life.
Plants use the energy from sunlight,
and carbon dioxide from the atmosphere, to produce food.
They give out oxygen.
Animals consume the food, made by plants.
Animals breathe in oxygen, and breathe out carbon dioxide.
They eat the food made by plants, and derive energy from it.
Without this energy, animals including human beings, cannot survive.
Animals need plants for food.
Plants need the sun, as a source of energy.
The sun, the plants, and animals,
are thus closely connected, in the web of life.
Animals indirectly source their energy from the sun,
via., the food synthesised by plants.
Plants synthesise food, by a process called photosynthesis.
Photosynthesis basically uses sun’s energy, carbon dioxide, and water,
to synthesise carbohydrates which it stores in fruits, vegetables,
grains, nuts and other parts, of its body.
Synthesis involves building larger molecules, from smaller molecules.
For example, synthesising glucose from carbon dioxide.
Such synthesising reactions are called, as anabolic reactions.
These reactions require energy to take place.
Such reactions, which require energy, are called as endergonic reactions.
Carbon dioxide is sourced from the atmosphere.
Water is sourced from the soil.
We can write this basic process, as a chemical reaction.
6CO2 + 6H2O + sun’s energy, results in,
C6H12O6 + 6O2.
C6H12O6 is the sugar glucose, which is the basic carbohydrate.
6 molecules of carbon dioxide, combine with 6 molecules of water,
and use the sun’s energy, to produce,
1 molecule of glucose, and 6 molecules of oxygen.
Animals breathe in oxygen, and breathe out carbon dioxide.
This process takes place in the lungs.
We call it breathing.
This process is called respiration.
This happens at the macro level.
Animals are composed of microscopic living cells.
Cellular respiration takes place, in each cell.
Cells take in oxygen, and give out carbon dioxide.
Cellular respiration creates energy.
It acts like a micro engine.
The efficiency of cellular respiration engine, is about 40%.
The efficiency of a typical car engine, is about 25%.
The mitochondria in the cell, is the centre of energy production.
Mitochondria have their own DNA, like chloroplasts.
Many micro-organisms have mitochondria.
It is possible that animals, incorporated these, during evolution.
Each cell takes in oxygen and nutrients,
and gives out carbon dioxide and water.
The blood circulation system brings in the oxygen and nutrients,
and transports out the carbon dioxide, and other waste products.
The basic nutrient that the cell ingests, is glucose.
This glucose is metabolised, to extract energy.
This basic metabolic process, can be written as a chemical equation.
C6H12O6 + 6O2 results in,
6CO2 + 6H2O + energy.
If we examine this equation, we can easily make out,
that this is exactly the opposite, of what happens in photosynthesis.
Photosynthesis harvests, the sun’s energy and stores it in glucose.
Cellular respiration, breaks down the glucose, to derive energy for living.
These simple equations, highlight our intimate relationship with plants.
We also note, that we breathe in the oxygen, given out by plants.
Plants and animals, including humans, have a symbiotic relationship.
Photosynthesis.
Photosynthesis takes place in plants.
It also takes place in algae, and certain types of bacteria.
We will focus on plants.
The leaves in the plants, are the main site, for photosynthesis.
Trees and plants have so many leaves, which are specially designed,
to harvest the sun’s energy, using photosynthesis.
We can notice that leaves have a large surface area,
to maximise its exposure, to sunlight.
There are two main processes, in photosynthesis.
One is the light dependent reactions.
These reactions, harvest sunlight, and create energy molecules,
called ATP, and NADPH.
They also breakdown water, H2O, into hydrogen ions, and oxygen.
The water is extracted, from the soil, by the roots.
The oxygen is released, into the atmosphere.
The second main process, is called the Calvin cycle.
The Calvin cycle, is a series of biochemical reactions.
Basically it uses the carbon dioxide,
and energy from the energy storehouse molecules, ATP and NADPH,
and synthesise glucose from it.
It stores the glucose in the form of carbohydrates,
in fruits, vegetables and other parts of the plant.
Sunlight.
Light is part of the large spectrum, of electromagnetic radiation.
Light can be viewed from two perspectives.
From the particle perspective, light comprises of photons.
Each photon, has energy.
From the wave perspective, light can be viewed, as a wave.
Each wavelength, corresponds to a particular colour.
Sunlight comprises of infra red light, visible light and ultra violet light.
Plants are sensitive to only visible light.
Visible light has a wave length from 400 nano meters to 700 nano meters.
We perceive sunlight, as white in colour.
Actually visible sunlight has the entire spectrum of colours,
Violet, Indigo, Blue, Green, Yellow, Orange and Red.
Each colour corresponds to a particular wave length.
Most leaves absorb all these wave lengths, or colours,
except green.
Green colour is reflected back.
That is why leaves, appear green.
Leaves have a molecule called chlorophyll.
These molecules are responsible for absorbing light.
Plants also have other pigments, which can reflect other colours of light.
Plants use these pigments, to produce colourful flowers.
Flowers attract insects, which help to propagate pollen.
Plants also use colour pigments to produce fruits and vegetables.
Fruits attract animals, and help to propagate seeds.
Light is a form of energy.
When leaves absorb sunlight, they are harvesting the energy of the sun.
This energy is converted to chemical energy, present in the bonds,
of molecules like glucose.
Glucose is a source of food and energy for animals.
Glucose is a sugar molecule.
Sucrose and maltose are also sugar molecules.
Plants are also capable of synthesising sugars, carbohydrates,
proteins, fats, and nucleic acids.
Algae and cyanobacteria are also capable of photosynthesis.
Oxygen is a byproduct of photosynthesis.
Life started out as simple, unicellular organisms.
Scientists believe that all of life, evolved from a common ancestor cell.
This cell is called Last Universal Common Ancestor,
or ‘LUCA’ in short.
About 2.3 billion years ago, there wasn’t much oxygen in the atmosphere.
It is ancient organisms like cyanobacteria, which oxygenated the atmosphere.
Algae and plants, evolved later.
Thanks to these organisms, we now have an oxygen rich atmosphere.
This is what created an environment, for animals to evolve.
Animals require oxygen to live.
Sunlight and photosynthesis, played a crucial role, in the evolution of life.
Structure of a leaf.
A leaf typically has a flat structure.
This increases the surface area of the leaf.
The surface of the leaf, is covered, with a waxy layer, called the cuticle.
The cuticle is waterproof.
It has an epidermis, under the cuticle.
The epidermis has tightly packed cells.
There are small openings, called stomata, in the surface of the leaf.
These openings help the leaf, to breathe in carbon dioxide,
and breathe out oxygen.
Veins in the leaf, are vascular bundles, which transport materials,
through out the leaf.
The leaf is packed with organelles, called chloroplasts.
Chloroplasts are the centres, of photosynthesis, of the leaf.
Chloroplasts are possibly the most important part of a plant.
Chloroplasts have there own DNA.
It is possible, that plants evolve from micro-organisms, having chloroplasts.
Chloroplasts, have an outer membrane, and an inner membrane.
The chloroplast, is filled with a fluid called stroma.
The stroma is where the Calvin cycle takes place.
Inside the chloroplast, there are stacks of thylakoid membranes.
The thylakoid membranes, are carpeted with chlorophyl molecules.
A stack of thylakoid membrane, is called as a Granum.
Many granum, are called as Grana.
Chlorophyl molecules, are light sensitive molecules.
These are the molecules, which capture sunlight,
and start the light reactions.
Light reaction.
Light reactions is also called, as light dependent reactions.
There are some main steps in the light reaction.
Capture of sunlight.
Hydrolysis of water.
Electron transport chain.
Creation of NADPH molecule.
Creation of ATP molecule.
Capture of sunlight.
Sunlight enters the leaf, and reaches the thylakoid membrane,
in the chloroplast.
The thylakoid membrane is lined with chlorophyl molecules.
Chlorophyl is the main light absorbing pigment molecule.
Chlorophyl and other pigment molecules, absorb the photons, from sunlight.
Photons have energy.
This energy of the photon, is transferred to the electron in chlorophyl.
The electron gets excited, and reaches a high energy state.
This causes it to move out of the chlorophyl molecule,
and enter the electron transport chain.
The chlorophyl and other pigment molecules,
mainly absorb light in the red and the blue wavelength bandwidth.
Green light is reflected back from the leaf.
This is why leaves look green.
Hydrolysis of water.
Electrons in the chlorophyl molecules, reach a higher energy state,
and leave the chlorophyl molecule, to enter the electron transport chain.
This lost electron, has to be replaced.
The chloroplast does this, by breaking down water molecules.
H2O molecules are split into H+ ions, oxygen, and free electrons.
The electrons replace, the lost electrons, in the chlorophyl molecule.
The oxygen atom, combines with another oxygen atom to form O2.
This oxygen diffuses out of the leaf via tiny openings, called the stomata.
The oxygen is released into the atmosphere.
This is the oxygen that animals, and we breathe.
Hydrogen ions are left behind, inside the thylakoid membrane.
Hydrogen ions, are nothing but protons.
We can refer to them, as protons.
Protons are positively charged.
Electron transport chain.
There is a chain of proteins, embedded in the thylakoid membrane.
These carrier proteins are the pathways, for the electron transport chain.
High energy electrons, move from one protein to another.
As they move from one protein to another in the electron transport chain,
they lose a little energy, in every step.
This energy is used to pump hydrogen ions, or protons, across the membrane.
This function is carried out by special proteins.
This contributes to the proton gradient inside the membrane.
This proton gradient, will be made use of later,
to create the energy storehouse molecules, ATP.
ATP is created from ADH.
The process so far can be considered as part of photosystem 2.
After passing through photosystem 2, electrons lose their energy,
before they go to photosystem 1, which is the next step in the process.
Creation of NADPH molecule.
Low energy electrons, reach photosystem 2.
Photosystem 2, also absorbs photons, from sunlight.
These photons, are used to re-energise the electron.
These electrons are used to reduce NADP+ to NADPH.
NADP+ is a product of the Calvin cycle.
The equation can be represented as,
NADP+ + electron + H results in NADPH.
The electrons released, by breaking up of H2O molecules,
ultimately end up in the NADPH molecule.
NADPH is a energy carrier molecule.
It is used to supply energy, in the Calvin cycle.
Creation of ATP molecule.
The electron transport chain, creates a positively charged proton gradient,
inside the thylakoid membrane.
These ions cannot normally permeate the membrane.
There is a special protein, called ATP synthase, through which,
hydrogen ions or protons can pass through.
The protons enter the thylakoid membrane, through ATP synthase.
During this passage, ADP is phosphorylated, to ATP.
This process is called as Chemiosmosis.
ADP stands for adenosine diphosphate.
Phosphorylation is the process of adding a phosphate group.
ATP stands for adenosine triphosphate.
ATP is an energy storehouse molecule.
This molecule has an adenine component,
a ribose component, and 3 phosphate groups.
ATP generates energy, when it loses 1 phosphate group.
It stores potential energy, in the phosphate bonds.
ATP can be broken down, to ADP, to release energy.
The Calvin cycle uses ATP, to derive energy.
Calvin cycle.
The first main process in photosynthesis, is the light reaction.
These reactions are dependent on sunlight.
The second main process, is the dark reactions,
or the light independent reactions.
This is commonly referred to as the Calvin cycle.
Carbon is the most common element, in bio chemical molecules.
Numerous carbon compounds, can be found in many bio chemical processes.
Energy is stored, in the chemical bonds of carbon compounds.
These bonds can be broken down to derive energy.
One of the most basic, and commonly found carbon molecule is glucose.
Glucose is a six carbon molecule, with the formula C6H12O6.
The most basic function of the Calvin cycle,
is to synthesise glucose from CO2.
CO2 is absorbed from the atmosphere, by the leaf.
The energy for synthesising glucose,
is derived from the ATP, and NADPH molecules,
produced in the light reactions.
Calvin cycle, like the name implies, is a cycle.
It starts with a 5 carbon molecule, called RuBP.
RuBP stands for Ribulose bisphosphate.
The formula for RuBP is C5H12O11P2.
At the end of the cycle, RuBP that was used is regenerated.
The chloroplast, is filled with a fluid called stroma.
The Calvin cycle takes place in the stroma.
During photosynthesis, multiple Calvin cycles,
simultaneously takes place in the stroma.
The first step is called carbon fixation.
The 5 carbon RuBP molecule is attached to CO2.
This results in a 6 carbon molecule.
This 6 carbon molecule is unstable.
It breaks down into two 3 carbon molecules, called PGA.
The next step is known as reduction.
ATP is broken down to derive energy.
ATP is converted to ADP, releasing a phosphate group.
The phosphate group, helps in phosphorylating PGA.
ADP is used in the light reaction.
Addition of a phosphate group, is called as phosphorylation.
PGA is phosphorylated, to form BPGA.
NADPH is broken down to derive energy.
NADPH and BPGA react to form G3P.
G3P stands for Glyceraldehyde 3-phosphate.
NADPH is converted to NADP+.
This NADP+, is used in the light reaction.
G3P is an important precursor molecule to produce,
sugars, starch, etc.
G3P is a 3 carbon molecule.
Plants that produce this, are called 3 carbon or 3C plants.
G3P is the base molecule, to produce glucose.
2 G3P 3-carbon molecules, are used to produce,
one 6 carbon glucose molecule, with the formula C6H12O6.
Some of the G3P produced, goes on to synthesise glucose.
The rest of the G3P is used, to regenerate the RuBP,
that was used in the beginning of the cycle.
The cycle is now complete.
During photosynthesis, this cycle keeps repeating.
To account for the main molecules, we will imagine that,
6 Calvin cycles are taking place simultaneously.
We will walk through the 6 Calvin cycles,
and trace the main molecules involved.
6 molecules of CO2, combines with 6 molecules of RuBP.
This results in 6 molecules, of a 6 carbon unstable molecule.
The unstable molecule breaks up to produce 12 molecules of PGA.
PGA is a 3 carbon molecule.
12 molecules of PGA is phosphorylated,
to form 12 molecules of BPGA.
12 molecules of BPGA, is used to produce,
12 molecules of G3P.
Now the cycle branches of into 2 pathways.
In one pathway 2 of the 12 molecules, of G3P,
is used to produce one molecule of glucose, C6H12O6.
This pathway comes out of the Calvin cycle.
The basic purpose of the Calvin cycle, is to synthesise glucose.
The second pathway continues and completes the cycle.
This pathway regenerates RuBP.
10 of the 12 molecules of G3P,
is used to produce 6 molecules of RuBP.
10 G3P molecules, has 30 carbon atoms.
6 RuBP molecules, has 30 carbon atoms.
The 6 carbon atoms in CO2, is now present,
in one molecule of glucose, C6H12O6.
All the carbon atoms, are now accounted for.
The cycle started by using 6 RuBP molecules,
by the end of the cycle, the 6 RuBP molecules, are regenerated.
That is the reason why, this chain of biochemical reactions,
is called a cycle.
All photosynthetic plants, use the Calvin cycle.
It is probably the most important biochemical process, in the plant kingdom.
Photosynthesis harvests the sun’s energy.
It produces oxygen, glucose and other nutrients.
Energy is stored in the carbon bonds, of glucose.
Cellular respiration, by animals, use the oxygen,
and nutrients, produced by photosynthesis.
They breakdown the carbon bonds in glucose, to derive energy.
This energy is used for living.
Animals and human beings, use the sun’s energy,
processed by plants, to get energy to live.
Cellular respiration.
Cellular respiration takes place in animal and plant cells.
In animals cellular respiration uses,
the product of photosynthesis in plants.
Plants produce glucose molecules, which store energy.
Animals break down glucose, by cellular respiration,
to get energy for living.
Cellular respiration involves breaking down glucose.
This is called, as a catabolic reaction.
These reactions release energy.
Such reactions are called as exergonic reactions.
Cellular respiration has three main stages.
1. Glycolysis.
2. Krebs cycle.
3. ETC or Electron transport chain.
The cell.
The cell is the basic unit of living organisms.
We will discuss the anatomy of a animal cell,
with relevance to cellular respiration.
The cell has a phospholipid membrane.
The cell is filled with a fluid, called as the cytoplasm.
Glycolysis takes place in the cytoplasm.
There are many organelles, inside the cell.
The mitochondria is one such organelle.
It is the energy factory, of the cell.
A single cell can contain many mitochondria.
Cells which have to do more work, like muscle cells, have more mitochondria.
The mitochondria produces ATP.
ATP is the universal molecule for energy storage.
Even small single cellular organisms, use ATP for energy.
It is believed that LUCA, Last Universal Common Ancestor,
used ATP for energy storage, billions of years ago.
Even today the cells use the same ATP.
The mitochondria, has an outer membrane,
and an inner membrane.
The region between the outer and inner membrane,
is called as the inter membrane space.
The outer membrane, is permeable to oxygen and glucose.
The inner membrane, is highly folded.
It is called as cristae.
This increases its surface area, for the electron transport chain,
or ETC processes.
ATP is synthesised in the electron transport chain.
The inside of the inner membrane, is called as the matrix.
This is where, the Krebs cycle, takes place.
Cellular respiration processes.
Cellular respiration has 3 main processes.
Glycolysis.
Krebs cycle.
Electron transport phosphorylation.
The main purpose of cellular respiration,
is to use food energy molecule like glucose,
and generate energy for living.
Energy is generated, in the form of a molecule called ATP.
The basic formula for cellular respiration is:
C6H12O6 + 6O2 results in,
6CO2 + 6H2O + 38 ATP.
This process takes place, in many steps,
in the 3 main processes listed above.
Glycolysis starts with glucose, and ends with the molecule, called pyruvate.
This process generates 2 ATP, energy storehouse molecule.
This process also generates, 2 NADH molecules.
NADH can be considered as an energy carrier molecule.
NADH helps to produce ATP, in the last main process,
which is electron transport phosphorylation.
Glycolysis is an anaerobic process.
This means that, typically no oxygen is involved in glycolysis.
The Krebs cycle, is also called as the citric acid cycle.
This process starts with pyruvate, and it produces CO2.
It produces some energy storehouse molecule, ATP.
It also produces many energy carrier molecules,
called NADH and FADH.
The NADH and FADH energy carrier molecules,
helps to produce ATP, by electron transport phosphorylation,
in the third main process.
The electron transport phosphorylation, is the final main process.
It happens in the electron transport chain, located in the cristae.
In this process, the energy carrier molecules, NADH and FADH,
are used to produce ATP.
The process also uses oxygen, and releases water.
This completes the cellular respiration process.
Glycolysis.
Glycolysis takes place in the cytoplasm.
Glycolysis is an anaerobic process.
Glucose is the starting point of glycolysis.
Most of the glucose comes from the blood stream.
The cell absorbs glucose.
Glucose is broken down, using ATP.
It is split into 2 G3P molecules.
The cost of this process is 2 ATP molecules.
This is called as the energy investment stage.
2 G3P molecules help reduce NAD+ to NADH.
2 G3P molecules are converted to 2 BPGA,
or biphosphoglycerate.
2 NADH molecule produced, are energy carriers.
They move on to the electron transport chain.
BPGA phosphorylates ADP to ATP.
2 BPGA results in 2 PGA, + 2 ATP.
We have now produced 2 ATP molecules.
The 2 PGA phosphorylates, another 2 ADP molecules, to ATP molecules.
Now we have produced 2 more ATP molecules.
In this process 2 PGA molecules, are converted to 2 Pyruvate molecules.
We have now produced a total of 4 ATP molecules,
and 2 NADH molecules.
In the investment stage 2 ATP molecules was spent.
So the net energy molecules produced in glycolysis,
is 2 ATP molecules, and 2 NADH molecules.
Pyruvate or pyruvic acid, a 3 carbon molecule, is the end product of glycolysis.
Pyruvate enters the Krebs cycle.
Krebs cycle.
Before starting the Krebs cycle, a preparatory step,
called the prep step is involved.
An enzyme called coenzyme A, binds the pyruvate to oxaloacetate.
NAD+ is reduced to NADH.
Carbon dioxide, CO2 is released.
A series of reactions takes place, and the end product is acetyl CoA.
Acetyl CoA is a two carbon molecule.
It is acetyl CoA, which enters the Krebs cycle.
The molecule oxaloacetate, is a substrate molecule,
which facilitates the Krebs cycle.
Oxaloacetate is a four carbon molecule.
At the end of the cycle the oxaloacetate used,
is regenerated.
2 acetyl CoA combines, with 2 oxaloacetate molecules,
to produce 2 citrate molecules.
In this step coenzyme A, is released.
Citrate is also called as citric acid.
This is reason that the Krebs cycle, is also called as the citric acid cycle.
Citric acid is an 6 carbon molecule.
The citric acid cycle, strips the citrate of carbon molecules,
and harvests the energy, in the carbon bonds.
This is the basic principle of deriving energy,
from carbon back bone molecules.
First, 2 carbon molecules is stripped, from the citrate molecule.
This carbon combines with oxygen, to produce 2 CO2 molecules.
CO2 is released, as a by-product.
2 NAD+ molecules are reduced, to produce 2 NADH molecule.
NADH molecule are energy carrier molecules.
What is left is an 4 carbon intermediate A molecule.
In this discussion, for simplicity,
we will not name all the intermediate molecules.
We will simply refer to them, as intermediate A, B, C, and D.
Next, 2 more carbon molecules is stripped, from the intermediate A molecule.
CO2 is released as a by-product.
2 NAD+ molecules are reduced to 2 NADH molecules.
This produces a 2 carbon intermediate B molecules.
The two, 2 carbon intermediate B molecules, phosphorylates 2 ADP to 2 ATP molecules.
This is called substrate level phosphorylation.
What is left is another 2 carbon intermediate C molecule.
The two intermediate C molecules, reduce 2 FAD molecules,
to 2 FADH molecules.
FADH molecules are energy carrier molecules.
What is left is a 2 carbon intermediate D molecule.
The two intermediate D molecules, reduce 2 NAD+ molecules,
to 2 NADH molecules.
Oxaloacetate molecules, is regenerated with the intermediate D molecules.
The Krebs cycle started with oxaloacetate molecule.
It ends with regenerating the same molecule.
The Krebs cycle systematically breaks down,
the carbon bonds, in citrate.
This energy is stored in energy storehouse molecules, ATP,
and energy carrier molecules NADH, and FADH.
CO2 is generated, as a bi-product, and is released.
NADH and FADH move on, to the electron transport chain,
and help to generate ATP.
For this discussion we have taken glucose, as an example.
Energy molecules are derived from glucose.
Fats and proteins also enter the Krebs cycle after some processing.
Fats are converted to glucose.
Proteins are broken down to amino acids,
and then converted to acetyl CoA.
So, all forms of food, ultimately end up in the Krebs cycle,
to produce energy molecules.
We can summarise, what has happened in cellular respiration, so far.
In glycolysis,
2 ATP molecules,
2 NADH molecules and,
2 pyruvate molecules are produced.
In the prep stage,
2 CO2 molecules,
2 NADH molecules and,
2 acetyl CoA molecules are produced.
In the Krebs cycle,
4 CO2 molecules,
2 ATP molecules,
6 NADH molecules and,
2 FADH molecules are produced.
The 6 carbon atoms in glucose, combines with oxygen,
and is released as 6 CO2 molecules.
We have so far produced 4 energy storehouse ATP molecules.
We have also produced a total of,
10 NADH and,
2 FADH energy carrier molecules.
These 12 energy carrier molecules,
will help produce more ATP in the electron transport chain.
Electron transport phosphorylation.
Electron transport phosphorylation, takes place in the,
electron transport chain.
The electron transport chain, or ETC in short, takes place,
in the inner membrane or cristae of the mitochondria.
The electron transport chain, is a series of enzymes or proteins embedded in the cristae.
The cristae is highly folded, to increase its surface area,
which facilitates electron transport phosphorylation.
High energy carrier molecules, enter the electron transport chain.
The NADH molecule undergoes oxidation.
NADH becomes NAD++ H+ + 2 electrons.
NAD+ is used in the Krebs cycle.
The NADH drops off the high energy electron, in the ETC.
This causes the H+ ions, or protons, to be pumped,
from the inner compartment to the outer compartment,
via the cristae.
The high energy electron moves from protein to protein, in the ETC.
In each step it loses some energy.
This energy is used to pump the protons, to the outer compartments.
All the 10 NADH and and 2 FADH energy carrier molecules ,
participate in this process.
This is why they are called as energy carrier molecules.
They carry energy from glycolysis, and the Krebs cycle, to the ETC.
Here they lose their energy, to create a proton gradient, in the membrane.
This creates a high concentration, of protons outside the membrane.
The matrix has a low concentration of protons.
This causes a proton gradient across the membrane.
There is a pressure for the protons to enter the membrane.
In the next step, the protons, outside the membrane,
try to re-enter the membrane.
They can only do so, by passing through a special protein,
called ATP synthase.
The protein ATP synthase, acts like a pump.
As the protons move through it, it phosphorylates ADP to ATP.
This process is called as chemiosmosis.
ATP is the final energy storehouse molecule.
One NADH molecule results in the production of 3 ATP molecules.
One FADH molecule results in the production of 2 ATP molecules.
Ten NADH, and two FADH molecules, results in the production of,
30 + 4, which is 34 ATP molecules.
ATP is used by the cell, for various functions of living.
The objective of cellular respiration. is to generate ATP,
from food like glucose.
This has been achieved.
At the end of the electron transport chain,
the electron combines with the hydrogen ion, and oxygen ,
to produce H2O or water.
H2O is a byproduct of cellular respiration.
In photosynthesis H2O is split up.
H2O molecules are split into H+ ions, oxygen, and free electrons.
In photosynthesis H2O is the electron donor.
In cellular respiration, oxygen is the electron receptor.
2H++ O + 2 electrons results in H2O.
Cellular respiration summary.
We can now account for the main molecules,
in each step of cellular respiration.
We started with one molecule of glucose.
In glycolysis,
this glucose molecule was converted to, two molecules of pyruvate.
In the process 2ATP and 2NADH molecules, was produced.
In the prep stage,
2 Pyruvate molecules was converted to acetyl CoA molecules,
and 2 CO2 molecules.
In the process 2 NADH molecules are produced.
In the Krebs cycle,
the 2 acetyl CoA molecules are converted to 4 CO2 molecules.
In the process, 6 NADH, 2 FADH and 2ATP molecules are produced.
In the electron transport chain,
10 NADH and 2 FADH produces 38 ATP molecules.
The summary chemical equation of cellular respiration is,
C6H12O6 + 6O2 results in,
6CO2 + 6H2O + 38 molecules of ATP energy.
In practice, less than 38 molecules of ATP is produced.
The basic chemical equation, summarises the essence of cellular respiration.
Summary.
In this module, we have traced the energy from the sun,
in a photon, to the ATP molecules used by us, for living.
There is an intimate relationship, between the energy of the sun,
plants, the food we eat, and the ATP energy, we derive from it .
The web of life on earth, is intimately inter-related.