GLYCOLYSIS

1. Glycolysis- it is the first stage of cellular respiration. It is derived from the Greek word “glyco” meaning
sweet/sugar, “lysis” meaning to split. So, glycolysis literally means breaking something sweet or breaking sugar.
This stage takes place in the cell’s cytoplasm.It does not require oxygen in the process and produces 4 ATP.

• The Glycolysis stage is present in both aerobic and anaerobic respiration. Extraction of energy from the glucose
(food you intake) is done in this process.

• It is important to know that two molecules of ATP are being utilized initially to break the glucose and that ATP is
borrowed from the cell. It is then paid after, since the said stage can produce four ATP’s minus the borrowed
ATP, will yield to two ATP gain. When glucose are splits during glycolysis pyruvate molecule are formed .

• The glucose (6-carbon molecule) will split into two molecules of pyruvate (three-carbon molecule) with the
production of two molecules of ATP.

• In this process, some of the electrons from the glucose are transferred to an electron carrier molecule known as
NADH.

2. Citric acid/ Kreb’s Cycle- The pyruvate molecules produced by glycolysis are transformed into a molecule
called coenzyme A to form acetyl coenzyme A or simply acetyl CoA, which enters the Krebs cycle. Pyruvates
are oxidized before it enters the Krebs cycle .

• (Fact: this cycle is named after its discoverer, Hans Adolf Krebs, a German- born British physician and
biochemist).

• Since there are two molecules of acetyl CoA ( serves as a fuel for Kreb cycle ) from one glucose molecule, there
are two ( 2) complete turns or rounds of Krebs cycle.

• Hence, the end products are four ATP molecules, ten NADH molecules, and two FADH2 molecules. The cell
ejects CO2 as waste.

3. Electron Transport Chain and Chemiosmosis- In this phase, the high-energy electrons within NADH and
FADH2 will be passed to a set of membrane-bound enzymes in the mitochondrion, collectively known as the
electron transport chain

• Electron transport chain is a series of electron carriers existing in an oxidized form.

• Electrons pass across carrier molecules in a series of exergonic redox reaction.

• It comprises an enzymatic series of electron donors and acceptors.

• Each electron donor will pass the electrons to more electronegative acceptor which in turn donates these
electrons to another acceptor.

• As the hydrogen ions move from high concentration to low concentration through the ATP synthase complex in
the mitochondrion, the enzyme ATP synthase adds phosphate to adenosine diphosphate (ADP+) which yields
ATP.

• Since ADP is phosphorylated to ATP using the energy of hydrogen oxidation, the entire process is known as
oxidative phosphorylation a process which produces the most ATP molecules per glucose molecule . ADP
phosphorylation is endergonic .

• Chemiosmosis is an event that proceeds after what take place in the electron transport chain. In chemiosmosis,
the free energy from the series of redox reactions is used to pump hydrogen ions (protons) across the
membrane and the movement of hydrogen ions across the mitochondrial membrane .
• The process of ATP synthesis using free energy obtained when electrons are passed to several ETC

• It occurs in the inner mitochondrial membrane. The uneven distribution of H+ ions across the membrane
establishes both concentration and electrical gradients (thus, an electrochemical gradient), owing to the
hydrogen ions’ positive charge and their aggregation on one side of the membrane.

• In summary, photosynthesis and cellular respiration depend on each other. The oxygen released by the plants
during photosynthesis is needed by animals to breathe and the carbon dioxide animals release is one of the
reactants in photosynthesis. Just like a cycle, right? Another one is that the organisms that photosynthesize give
glucose to organisms that eat them and use this in cellular respiration to produce energy.

PHOTOSYNTHESIS

Photosynthesis is a process where the energy from the sun, water, and carbon dioxide is used to produce sugar,
and oxygen (Energy Transformation: Photosynthesis vs. Cellular Respiration

• Photosynthesis is the process by which the energy of sunlight is converted into the energy of glucose

• The main site of photosynthesis is in chloroplast

• Most of the plant cells (specially in leaves) contain chloroplast

• The chloroplast contains a semi-fluid medium which is the stroma (mix up of enzyme and water).

• Embedded in the stroma is a complex network of stacked sacks.

• Each stack is known as granum. A granum consists of disk-shaped interconnected sacs called thylakoids

• Chlorophyll is the pigment inside the chloroplast that absorbs light for photosynthesis

• The organs for photosynthesis of plants always contain assortment of pigments.

• Each pigment absorbs only certain rays of light. One of the most known pigment is chlorophyll which makes the
color of plants green.

• Chlorophyll absorbs different wavelength than the chloroplast

• Green light is not absorbed but reflected, making the plant appear green.

• No plant was found to be capable of photosynthesis without the presence of chlorophyll a.

• Caretonoids are photosynthetic pigments that prevents chlorophyll from photo damage

• Chlorophyll b is an accessory pigment and acts indirectly in photosynthesis by transferring light it absorbs to
chlorophyll a. It is present in higher plants and in green algae.

• Chlorophyll c is found in certain marine algae, including the photo++synthetic chromista (ex. Diatoms, brown +

• +algae and dinoflagellates).

• Phycobilins are photosynthetic pigments efficient at absorbing red, orange, yellow and green light, wavelengths
that are not well absorbed by chlorophyll a.

• They are water-soluble pigments, and are found in the cytoplasm, or in the stroma of the chloroplast. They
occur only in cyanobacteria and rhodophyta.
 LIGHT DEPENDENT REACTION

• There are two stages in photosynthesis: light and dark reaction. LIGHT-DEPENDENT REACTIONS come first and
use light energy (as the name implies) from the sun to make two (2) molecules of ATP and NADPH (nicotinamide
adenine dinucleotide phosphate). It happens in the thylakoid membrane of the chloroplasts. It has an electron
transport chain and chemiosmosis that uses and produces ATP. Photosystem I contains more chlorophyll a than
chlorophyll b. The first stage of the photosynthesis is the light-dependent reaction. Here, energy from the light is
trapped and converted into chemical energy through thylakoids present in the chloroplasts.

• This process is made possible by the help of different pigment molecules that forms cluster which is known as
photosystems.

• The first state of light dependent reaction is the excitation of electrons which occurs in PS I and PS II

• The reaction begins in a group of pigments and proteins called photosystem. Photosystems exist in the
membranes of thylakoids, i.e., photosystem II and photosystem I in eukaryotes and some prokaryotes.

• A pigment molecule in the photosystem absorbs individual light packet called photon.

• As the photon of light travels and reaches a molecule of chlorophyll in photosystem II, the electrons become
excited . Photosystem II transfers the free electrons along a series of proteins called electron transport chain. In
photosystem II an electron is transferred to an electron acceptor where water molecule supplies the lost
electron in the reaction center .

• Light-dependent reactions convert light energy and the splitting of water to chemical energy (ATP) and release H
and oxygen which is release into the atmosphere The product of light-dependent reaction are ATP and NADPH

• Light-independent reactions use the energy from the light-dependent reaction to convert CO2 and H to sugar ,

• The second stage energy from the electrons fuel membrane pumps that move hydrogen ions against the
concentration gradient from the stroma to the thylakoid space and the synthesis of ATP will be affected

• As the energy is used, electrons will be accepted by another pigment molecule in photosystem I, causing them
to break away from the atom of the chlorophyll molecule.

Water is split in a process called photolysis , providing a source of electrons and protons (hydrogen ions, H+ -
continues to be used in the process) and giving off O2 as a by-product.

■ The electrons leave the transport system (ETC) with very low energy that enters the reaction system of
Photosystem I, where they gain again energy when pigment absorb light energy. The excited electrons are
passed on to the primary electron acceptor of Photosystem I and along the transport chain of PS I until they will
reach Nicotinamide Adenine Dinucleotide phosphate (NADP+), also an electron carrier. NADP+ picks up electron
together with the hydrogen ion from the water to become NADPH which means that NADP+is reduced to
NADPH. The product of Light Reactions are ATP and NADPH. Oxygen is also released as a by-product .

■ CALVIN CYCLE

• The products of the first photosynthesis will be used in LIGHT-INDEPENDENT REACTIONS (also known as Calvin
Cycle): ATP and NADPH.

• The initial reactant needed here is the carbon dioxide to make 3-carbon sugar and this process is assisted by ATP
and NADPH. This reaction happens in stroma of the chloroplasts .

1. Carbon Fixation - This is the initial incorporation (fixation) of carbon into a large inorganic molecule.

This reaction is catalyzed by the enzyme rubisco, which attaches a carbon molecule with the ribulose biphosphate
(RuBP) molecule.
This reaction produces six-carbon molecule that quickly break down into 3-phosphoglycerate (3-PGA) molecules which is
the reason why Calvin cycle is often referred to as C3 pathway.

This process requires two molecules of ATP

2.Synthesis of G3P

■ - In this stage, ATP and NADPH are used to convert the 3-PGA molecules into molecules of a three-carbon sugar,
Glyceraldehyde-3-Phosphate (G3P) which has 3 carbon atoms .

■ The two molecules of the phosphoglyceraldehyde (PGAL), a 3-carbon compound. PGAL is the first stable product
of photosynthesis

3. Regeneration of RuBP

■ -Some G3P molecules go to make glucose, while others must be recycled to regenerate the RuBP acceptor.

■ Regeneration requires ATP and involves a complex network of reactions, which my college bio professor liked to
call the "carbohydrate scramble."

■ In order for one G3P to exit the cycle (and go towards glucose synthesis), three CO2 molecules must enter the
cycle, providing three new atoms of fixed carbon.

■ When CO2 molecules enter the cycle, six G3P molecules are made. One exits the cycle and is used to make
glucose, while the other five must be recycled to regenerate three molecules of the RuBP acceptor.

These two stages of photosynthesis are referred to as ANABOLIC reactions. These are chemical reactions that
used to store energy or create molecules.

• Cellular respiration is a catabolic reaction where the molecules (complex) are broken down to release energy. In
the initial stage, glycolysis uses glucose and oxygen to make ATP, and carbon dioxide is released as a waste
product.

Cellular respiration is a metabolic pathway that converts glucose into energy and it breaks down carbohydrates
to provide energy for the cell. Heterotrohs and autotrophs are organism that can go through cellular respiration.

• The succeeding stages are Krebs cycle and oxidative phosphorylation (electron transport chain and
chemiosmosis) that produce 2 ATP and 28 ATP respectively. These processes happen in mitochondria except for
glycolysis that occurs in the cytoplasm.

• Aerobic Respiration- the process of converting glucose into energy with the presence of oxygen.
 • Anaerobic respiration- the process of converting glucose into energy without oxygen.

• Cellular respiration can occur both aerobically and anaerobically. Aerobic respiration occurs in the cytoplasm as
well as in the mitochondria. It is a set of reactions occurring in the presence of oxygen.

• Anaerobic respiration is a set of reactions occurring in the absence of oxygen which breaks down food into
simple organic compounds, generating energy in the form of ATP. It occurs in the cytoplasm. It involves the use
of an alternative final electron receptor other than oxygen to complete ETC .

• Anaerobic respiration is a set of reactions occurring in the absence of oxygen which breaks down food into
simple organic compounds, generating energy in the form of ATP. It occurs in the cytoplasm.

• The process of lactic acid fermentation replaces the process of aerobic respiration so that the cell can have a
continual source of energy, even in the absence of oxygen

• If no oxygen is available, cells can obtain energy through the process of anaerobic respiration.

• A common anaerobic process is fermentation.

• Fermentation is not an efficient process and results in the formation of far fewer ATP molecules than aerobic
respiration.It is a pathway that consists glycolysis with some extra reaction in the tail end .

• Pyruvate is a by-product of glycolysis needed to proceed to fermentation even without oxygen.

• There are two primary fermentation processes:

1. Lactic Acid Fermentation

Ex. Pain or burning sensation in the muscles

The process of lactic acid fermentation replaces the process of aerobic respiration so that the cell can have a
continual source of energy, even in the absence of oxygen

2. Alcohol Fermentation

Wine , vinegar making , soy sauce , beer

Alcohol fermentation occurs in yeasts and some bacteria.

Pyruvic acid formed during glycolysis is broken down to produce alcohol and carbon dioxide and is released (which is
used to form ATP

• The Pyruvic acid formed during Glycolysis each gain a hydrogen from NADH.The new hydrogen turn the
Pyruvate into lactic acid and energy is released (which is used to form ATP).Glucose → Pyruvic acid → Lactic acid
+ energy

• In Fermentation the Pyruvate made during Glycolysis loses another carbon making carbon dioxide.The two sets
of carbons left each gain a hydrogen from NADH. This turns the two carbon chains into Ethyl Alcohol

• ATP stands for ADENOSINE TRIPHOSPHATE, and is the energy used by an organism in its daily operations. It
consists of an adenosine molecule and three inorganic phosphates. After a simple reaction breaking down ATP
to ADP, the energy released from the breaking of a molecular bond is the energy we use to keep ourselves alive.

• Energy stored in ATP are in the bonds between phosphate and the energy from ATP is released when
phosphate group is removed

ATP -ADP CYCLE

• This complex molecule provides us, living organisms, energy for the mechanical functions of cells. This ATP
contains the nucleoside adenine and a tail consisting of three phosphates (reason for Triphosphate). The basic
building blocks of the said complex molecule are carbon, hydrogen, nitrogen, oxygen and phosphorous.

• ATP transport chemical energy within cells for metabolism. The stored energy within its chemical bonds diffuses
throughout the cell when it’s broken, transporting the energy to the place where energy is needed. The release
of energy is when the third phosphate in ATP is removed leaving adenosine diphosphate (ADP

• ATP is linked to a process called coupled reactions. It means the two reactions occur at the same time and at
the same place, usually utilizing the same enzyme complex. All biological reactions either give off energy
(exothermic) or take in energy (endothermic).

• In this coupled reaction, an exothermic reaction supplies the energy needed to drive the endothermic reaction.
For example, in plants, through the sunlight emitted by the sun (exothermic reaction), high-energy glucose
molecules are synthesized from carbon dioxide and water (endothermic reaction )

• This coupled reactions (endothermic and exothermic reactions) happen in various places within a cell, with the
help of ATP the terminal phosphate group then transferred by hydrolysis to another compound, a process called
phosphorylation, producing inorganic Phosphate (Pi), ADP and energy

• ADP also called adenosine diphosphate, is a molecule formed in living cells. It is often converted to adenosine
triphosphate (ATP), a high-energy molecule used in various biochemical reactions. ADP is made up of adenine (a
nucleobase), ribose (a simple sugar), and two phosphate molecules (phosphorous ions

• The molecular structure of ADP is comprised of:

• 1 adenine: A purine derivative nucleobase. Adenine is widely known as one of the four bases present in nucleic
acids, the building blocks of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA is the genetic code for
every living organism, and RNA is essential for the synthesis of proteins, among other processes.

• 1 ribose: A 5-carbon simple sugar. Ribose is also present in RNA.

• 2 phosphate molecules: The majority of ADP's energy is stored within the phosphate-phosphate bond. This
explains why ATP is such a high-energy molecule since it has three phosphate groups.

• ADP, through adenosine, is a component of DNA.

• When used as an intermediate for ATP, it plays an essential role in providing energy for muscle contraction,
firing neurons (nerve cells), and intracellular signaling.

• ADP enhances blood clotting and wound healing when a blood vessel is punctured. ADP is stored in platelet-rich
granules. At the time of injury, ADP is released from platelets and used to promote the clotting cascade.

• Most importantly, it stores and releases energy for essential biochemical reactions. ATP is also regenerated
through the use of ADP in cellular respiration. Cellular respiration is a series of biochemical pathways that
produce energy in the cell.