Unit 1: Cell Biology
ATP and Energy Release
Name: __________________ - 1Teacher: ________________
Structure of Adenosine Triphosphate (ATP)
Adenosine triphosphate (ATP) is the energy molecule of the cell.
A molecule of ATP is composed of a complex organic molecule, adenosine, to
which three inorganic phosphates are attached. Draw a molecule of ATP
Chemical energy is stored in the bonds between the inorganic phosphate
molecules. This stored energy is released when the bond attaching the last
phosphate is broken by enzyme action. This results in the formation of
Adenosine Diphosphate (ADP) and inorganic phosphate (Pi). See below:
Adenosine Pi Pi + Pi
Energy is needed to regenerate ATP from ADP and inorganic phosphate.
During an energy releasing reaction ATP is generated from ADP and an
inorganic phosphate molecule using the energy released by that
Adenosine Pi Pi Pi Adenosine Pi Pi + Pi
There are 3 types of energy releasing reactions in which a cell can produce
ATP from ADP and Pi (phosphorylation): These are:
1) Photosynthetic phosphorylation (light energy to chemical)
2) Respiratory phosphorylation (chemical energy to chemical energy)
3) Oxidative phosphorylation (chemical energy to chemical energy)
Use the words/phrases below to complete the passage:
Phosphorylation; terminal phosphate; adenosine; phosphates;
reduced; glucose ; oxidised; adenosine diphosphate (ADP); broken.
ATP is a molecule composed of____________________ and three
_______________. Energy is fixed into the molecule when the bond joining
the ____________ ___________ to the rest of the molecule is made. Energy
is released when the bond is _____________. The synthesis of ATP by the
making of the bond is called ______________________ and is achieved by
the linking of inorganic phosphate to____________ ____________. This
bond-making process occurs in cells when an energy rich compound such as
_________________ is broken down by enzymes during respiration.
The Importance of ATP
ATP is found in all living cells. ATP was originally found in muscle fibres. Since
then it has been shown to fuel many processes such as transmission of nerve
impulses, muscle contraction, synthesis of new molecules and luminescence (fire
In muscle cells ATP is the chemical which acts as the immediate energy
molecule. During respiration glucose is broken down and the energy released is
used to make ATP. This ATP can then be broken down and the energy released
can be used by the cell
The results below show the effect ATP has on muscle tissue:
Muscle strand in Muscle strand in Muscle strand in
distilled water glucose solution ATP solution
Initial length (mm) 12 11 13
Final length (mm)
12 11 8
Reduction in length
1. Complete the table.
2. What is the conclusion for this experiment?
3. How can the results be made more reliable?
4. What is the purpose of the water and the glucose treatment?
The Role of ATP
Use Torrance page 20 (old) page 26 (new) to find out cellular processes that
require energy from ATP.
It takes a lot of energy to make large molecules e.g. fats from fatty acids and
Metabolism has two parts:
1) Synthesis reactions requiring energy: The process of synthesising large
molecules from smaller ones is called anabolism. The energy comes from
2) Breakdown reactions releasing energy: The energy stored in the ATP
molecule came from energy releasing reactions called catabolic reactions.
Metabolism can be defined as the sum of all the chemical reactions both
anabolic and catabolic that take place in a cell.
ATP is the molecule which transfers energy from breakdown to synthesis
1. Highlight the energy flow from glucose to ATP to protein.
2. Copy and complete Fig. 3.5 on page 22 (old), Fig 3.3 p26 (new) of your text
Oxidation and Reduction
Oxidation: The molecule is oxidized when it loses a hydrogen.
Reduction: The molecule is reduced when it gains a hydrogen.
NB. Remember: OIL RIG
(oxidation is loss,
reduction is gain)
Now answer TYK questions 1-4 p22 (old), p27 (new).
The mitochondrion is a sausage shaped organelle. It is the site of aerobic
The mitochondrion has a double membrane, the outer one is smooth whilst the
inner one is greatly folded into cristae which project into the fluid filled cavity
called the matrix.
Label the diagram below:
The energy used for the synthesis of ATP from ADP plus inorganic phosphate
(Pi) becomes available during tissue respiration. Throughout this process
glucose is gradually oxidised during a series of enzyme controlled reactions.
Such a series of reactions is referred to as a metabolic pathway. Each
reaction in such a series of reactions is catalysed by its own enzyme.
Respiration is an example of a metabolic pathway which occurs in all living cells
at all times. For the complete oxidation of glucose, aerobic respiration must
occur, this requires the presence of oxygen.
During respiration, glucose is broken down (oxidised) in a series of steps.
Each of these steps is under the control of a different enzyme.
Some of these steps involve the release of hydrogen. Each of these steps is
controlled by a dehydrogenase enzyme. There are many different types of
dehydrogenase depending on the substrate.
Other reactions in the respiration pathway involve the removal of carbon in the
form of carbon dioxide. These reactions are controlled by a series of enzymes
Respiration can be divided into THREE major stages that can be studied
1. Glycolysis 2. Krebs cycle 3. Cytochrome system
Stage 1: Glycolysis (breakdown of glucose)
Glycolysis is the name given to the first stage in the breakdown or oxidation of
glucose. In animals this glucose, if not already present in the blood, can be
derived from the breakdown of stored glycogen. In plants the equivalent food
store is starch.
1. During glycolysis, Glucose (a 6 carbon molecule) is broken down to 2
molecules of Pyruvic acid (a 3 carbon molecule)
2. Glycolysis takes place in the cytoplasm of the cell.
3. Oxygen is not required to be present for Glycolysis to occur.
4. During Glycolysis enough energy is released for the production of 4
molecules of ATP. However, as 2 ATP molecules are used up to start the process
the net production of ATP from Glycolysis is only 2 ATP molecules for each
glucose molecule broken down.
5. Two hydrogen ions are released. These immediately combine with one of
the hydrogen carriers in the cell (a co-enzyme) called NAD (Nicotinamide
adenine dinucleotide). NAD = hydrogen carrier/acceptor, NADH2 = reduced
Answer the following questions
1) What substance results from the breakdown of a glucose molecule during
2) What other substance is released during glycolysis?
3) What is NAD and what is its purpose?
4) Complete the flow diagram for the reduction of NAD: -
5) Why is this termed a reduction reaction?
6) Complete the Glycolysis summary below.
Stage 2: The Krebs Cycle OR Citric Acid Cycle
After glycolysis, the process can only proceed if there is a supply of oxygen.
The cycle of reactions by which citric acid is gradually converted back to a 4-
carbon compound is called the Krebs cycle.
1. If oxygen is present, pyruvic acid molecules diffuse into the mitochondria,
where they are converted into a 2-carbon Acetyl group.
2. These Acetyl groups then join with Co-enzyme A molecules to form Acetyl
Co-enzyme A (Acetyl CoA).
3. These compounds then become involved in a cyclical sequence of reactions
known as the Krebs Cycle or Citric Acid Cycle.
4. In the Krebs Cycle Acetyl CoA reacts with a 4 carbon compound to form
citric acid (6 carbon compound).
5. This 6C compound is converted, by enzyme controlled reactions, to a 5C
compound, this is then converted into a 4C compound. This 4C compound is then
converted into two further 4C compounds. Two molecules of carbon dioxide are
6. At certain stages of the cycle hydrogens are released. These hydrogens are
immediately picked up by the carrier NAD and taken to the cytochrome system.
7. The Krebs Cycle occurs in the matrix of the mitochondria.
Draw a summary of the Kreb’s Cycle on the next page
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The Kreb’s Cycle
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Use the notes from the previous pages and your Torrance textbook page 26
(old), page 31 (new) to help you answer the questions below.
(i) Explain how citric acid is formed, and state how many carbon atoms are
(ii) In which region of a mitochondrion is citric acid formed?
(i) Name 2 enzymes involved in the Krebs cycle and their roles.
(ii) What happens to the hydrogen released during the Krebs cycle?
(iii) What happens to the carbon dioxide formed during this cycle?
Stage 3: The Cytochrome System
During both Glycolysis and the Krebs Cycle many compounds are oxidised by the
removal of hydrogen. This hydrogen never occurs as free atoms or molecules
but is immediately picked up by the carrier NAD.
1. The NAD transports the hydrogen to the Cytochrome System as NADH2.
2. The Cytochrome System occurs on the Cristae of the mitochondria.
3. As hydrogen passes along the carrier molecules of the cytochrome system
enough energy is released for the production of ATP. At the end of the
cytochrome system the hydrogen combines with oxygen to form water.
Oxygen is often referred to as the final hydrogen acceptor.
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The total number of ATP molecules generated during the Cytochrome
System is 36ATP, making the over all ATP production for 1 glucose
Cytochrome (Hydrogen Transfer) System
If oxygen is not present to act as the terminal hydrogen acceptor, hydrogen
cannot pass through the system so the cytochrome system and the Krebs Cycle
Now answer the questions below and on the next page.
(i) What is the basic function of the cytochrome system?
(ii) Where is the cytochrome system located in a mitochondrion.
(i) Explain how ATP is synthesised as hydrogen passes along the cytochrome
(ii) Explain why the production of ATP on the cytochrome system is called
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c) State the total number of ATP produced from the complete oxidation of
ONE molecule of glucose and explain where that total comes from.
(i) Identify the final hydrogen acceptor in the aerobic respiration.
(ii) Explain why it is termed the final hydrogen acceptor.
(iii) What is formed as a result?
Summary Table of Aerobic Respiration
Reaction Site of reaction of ATP Other Products
fate of pyruvic
Compound Number of carbon Atoms
Acetyl Co A
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Draw a summary of all 3 stages of Respiration below
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Alternative Respiratory Substrates
Glucose is the normal substrate which is broken down by enzymes in tissue
respiration to release energy. Sometimes however, there is not enough starch
or glycogen to provide sufficient glucose to meet the energy requirements. In
these cases other substrates must be used. The diagram below shows how
fats and proteins are converted into substances which can enter the
respiratory pathway. Carbohydrates, fats and proteins can all be oxidised to
produce ATP in respiration.
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Absence of Oxygen
Glycolysis occurs when oxygen is absent, but krebs cannot proceed. The pyruvic
acid has an alternative fate.
Glucose 2 x Pyruvic Acid 2 Ethanol + Carbon Dioxide
(6C) (3C) (2C) (1C)
Glucose Acid (3C)
Due to the only partial breakdown of glucose, little energy is derived. There are
only 2ATP molecules released during anaerobic respiration – these are those
produced during Glycolysis.
Read Torrance page 29 (old), page 34 (new), ‘Anaerobic Respiration’.
Complete this table to show the contrasts between aerobic and anaerobic
Number of ATP produced
Waste products (animals)
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Examine the diagram below then answer the questions below.
1) What is the purpose of the oil layer?
2) What waste products would be found in the flask after 24 hours?
3) What would happen to the lime water after 24 hours?
4) Give a suitable control for this experiment.
Another way of studying respiration is to measure the rate of uptake of oxygen
using devices known as respirometers. These can be set up in various ways but
nearly all work on the same principles. The idea is that a substance, usually
soda lime or a strong alkali (like potassium hydroxide) is placed in a sealed
container along with a living organism. The alkali absorbs any carbon dioxide
produced by the organism.
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The oxygen used up by the organism causes a reduction of volume and pressure
of gas inside the container, this is measured in one of a number of different
ways. If the time lapsed during the experiment is also measured, then a value
for the quantity of oxygen absorbed per unit of time can be obtained.
Read Torrance p28 (old), ‘Measuring Rate of Respiration’ and study fig 4.5
or page 33 & fig 4.6 page 34 (new).
The apparatus below was set up to investigate rate of oxygen consumption in a
1. What is the purpose of tube B?
2. Complete the diagram to show the missing contents of tube B.
3. Why is the soda lime included?
4. What is the purpose of the stopcocks?
5. How can the effect of room temperature be reduced?
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Now answer AYK questions 1-4 & 6 pages 30-32 (old), pages 35-37 (new) of Torrance.
Learning Outcome I can find I can
this in my do this
State that ATP is the energy source for cells
Write the equation for the formation of ATP
State two examples of the use of ATP in a cell
State that ATP is formed during respiration
Name the three stages of aerobic respiration
List the names of the main compounds in aerobic respiration and
give the numbers of carbon atoms in each (glucose, pyruvic acid,
acetyl-Co-A and citric acid)
State that Glycolysis takes place in the cytoplasm
State that Glycolysis is the breakdown of glucose into pyruvic acid
with a net gain of 2ATP
State that pyruvic acid breaks down into acetyl-CoA with the
release of carbon dioxide
Draw the Krebs cycle
Identify the stages at which carbon dioxide is released
Identify the stages at which hydrogen is released
Name the carrier (NAD) which accepts the hydrogen
State that the Krebs cycle takes place in the matrix of the
Describe the Hydrogen Transfer System (Cytochrome System) by
referring to oxidation, reduction, carriers, hydrogen, ADP, Pi, ATP,
oxygen and water
State that for complete oxidation to take place oxygen must be
State that the Hydrogen Transfer System takes place in the
cristae of the mitochondrion
State that energy may be released from a few individual steps in
the overall process, but most of the energy is made available by the
Compare Aerobic and Anaerobic respiration (mention products,
conditions required, energy released, and the difference between
anaerobic respiration in plants and animals
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