Download the krebs cycle

MIDDLETOWN HIGH
SCHOOL SOUTH
BIOLOGY
BOOKLET 10
NAME: _________________________________
CLASS: _____________
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LEARNING OUTCOMES
The role and production of ATP
(a) Importance, role and structure of ATP
(b) Regeneration of ATP from ADP and inorganic Phosphate.
(c) Energy from ATP comes from the breaking of the bond between the
second and third inorganic phosphates
Glycolysis
(c) The location and significance of Glycolysis
(d) Describe what happens during Glycolysis.
(e) State that Glycolysis does not require Oxygen
Krebs (Tricarboxylic Acid, Citric Acid) Cycle
(f) The location and significance of Krebs cycle
(g) Describe what happens during Krebs cycle
(h) Krebs cycle only occurs in the presence of oxygen
Cytochrome System
(i) The location and significance of the cytochrome system
(j) Describe what happens during cytochrome system.
(k) Describe the role of oxygen in the cytochrome system
Aerobic and Anaerobic Respiration
(l) Distinguish between Aerobic and Anaerobic Respiration with reference to
the levels of ATP production and final metabolic products in plant and
animals.
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ADENOSINE TRIPHOSPHATE

ATP or Adenosine triphosphate is a high-energy molecule that stores
the energy we need to do just about everything.

ATP is made up of one adenosine group and three inorganic
phosphates.
Energy is stored in this bond

ATP is made from two low energy molecules called ADP and Pi or
adenosine diphosphate and one inorganic phosphate.

The combining of ADP + Pi to make ATP is an energy consuming
process. This is because the energy is stored in the bond between
inorganic phosphate 2 and 3.
+
energy

The breakdown of ATP to ADP + Pi is an energy releasing process.
This occurs when the bond between inorganic phosphate 2 and 3 is
broken.

The energy required for the formation of ATP from ADP + Pi comes
from the respiration of glucose.

ATP is the energy source for:
o Muscle contraction
o Cell division
o Building up (synthesis) of proteins
o Transmission of nerve impulses
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
When ATP is broken down into ADP + Pi, energy is released. This
energy is transferred to another molecule so a chemical process can
take place, for example, a muscle contracting.
1
ATP
3
2
Muscle
Contraction
ADP + Pi
Stage 1: ATP is being broken down into ADP + Pi. The bond between the
terminal inorganic phosphate and the second is broken. This releases
energy.
Stage 2: The energy released from ATP is transferred into another cellular
process. In this example it is the contract of muscle fibres.
Stage 3: If there is energy present, ADP + Pi can become bonded back
together again to form ATP. This process requires energy and will no t occur
without it. This shows that the formation of ATP from ADP + Pi is a
reversible process
KEY FACTS

Respiration is a chemical process in which energy is released from
food molecules in cells.

The cell’s main energy source is glucose.

Energy is released from glucose using a series of enzymes to control
each stage of the breakdown process.

Enzymes are needed so that our cells do not use all their energy at
once or release it too slowly.

The energy released from glucose is converted into high energy
ATP molecules, which are “recharged” from ADP + Pi.
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AEROBIC RESPIRATION

Aerobic respiration is the process by which energy is released from
glucose in cells using oxygen.

There are two stages involved in the breakdown of glucose.

The first stage is the splitting of
glucose – this is known as glycolysis.
Glycolysis occurs in the cytoplasm of a
cell.

Glucose is a 6-carbon sugar. In respiration, it is broken down in a
series of enzyme catalysed reactions, to two 3-carbon molecules
called pyruvic acid.

To start the process of splitting glucose apart, energy is needed. The
body uses energy in the form of ATP molecules.

The series of reactions eventually produces four ATP molecules, so
there is a net gain of two ATPs from glycolysis.

During the transformation of glucose into pyruvic acid, the hydrogen
that is removed is bound to a substance known as a co-enzyme called
NAD (nicotineamide adenine dinucleotide) which is reduced to NADH2.
In a later process of cell respiration, the energy from the NADH2 will be
used to produce ATP.

The co-enzyme NAD is a molecule that acts as a hydrogen acceptor
and carrier.

The process of glycolysis in an anaerobic process. This means that it
does not require oxygen.
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Task 3: Complete the questions that follow. Make sure that you check
with your teacher to ensure you have the correct answers.
1. Using the notes on the previous page, complete the flow diagram of
glycolysis.
2. What is the role of NAD?
3. Where does glycolysis take place in a cell?
4. What is the total number of ATP produced in glycolysis?
5. Why is there only a net gain of two ATP molecules?
6. What does the term “glycolysis” mean?
7. Glycolysis requires anaerobically. What does the term anaerobic
mean?
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THE KREBS CYCLE

In the presence of oxygen, cell respiration continues on from
glycolysis in the mitochondria of the cell.

Mitochondria are ideally suited to their function in cell respiration as
their inner membrane is highly folded to form cristae, presenting a
large surface area for the reactions of Krebs cycle to occur.

In addition, the fluid-filled interior of a mitochondrion (the matrix) is
packed with the enzymes that are required for the process.
The site of ATP production in the mitochondria is proved by particles
on the cristae.

Since mitochondria are the 'energy producing ' organelles of cells, they
are present in large numbers in cells that require lots of energy, such
as muscle cells, liver cells, sperm cells, and nerve cells.
The events of the Krebs cycle (also known as the tricarboxylic acid cycle or
the citric acid cycle) are summarised below.

Pyruvic acid (produced in glycolysis) diffuses into the matrix of the
mitochondrion where it is converted into a 2C carrier called acetyl coenzyme A (acetyl CoA)

The conversion of pyruvic acid to acetyl CoA releases hydrogen that is
bound to NAD to form NADH 2.

Each acetyl CoA combines with a 4C molecule to form a 6C molecule
called citric acid.
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THE KREBS CYCLE

During the Krebs cycle, citric acid is converted through a series of
enzyme-catalysed reactions back into the 4C molecule.

In the process, both carbon (in the form of carbon dioxide) and
hydrogen are released.

Hydrogen becomes bound to NAD to form NADH 2. This will be used
in the next stage of respiration to release energy for ATP production.
(In one case, the hydrogen becomes bound to a coenzyme called FAD
rather than NAD.)

Carbon dioxide diffuses out the cell as a waste product that is
expired from the organism by breathing out or by diffusion over the
body surface.
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Task 4: Complete the questions that follow. Make sure that you check
with your teacher to ensure you have the correct answers.
1. Complete the diagram of the Krebs cycle below using the boxes on the
right of the page. Use your notes to help you.
2. The diagram below shows a mitochondrion surrounded by cytoplasm.
Where does glycolysis take place?
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3. In respiration, the sequence of reactions resulting in the conversion of
glucose to pyruvic acid is called
a. the Krebs cycle
b. the citric acid cycle
c. glycolysis
d. the cytochrome chain.
4. The diagram below represents a summary of respiration in a mammalian
muscle cell.
Which box represents ATP?
5. The diagram below shows an outline of respiration in yeast cells.
(a) State the location of glycolysis in yeast cells.
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(b) Name one substance, other than glucose, which must be present
for glycolysis to occur.
______________________________
(c) Name compounds R.
______________________________
(d) What is the name of the stage of aerobic respiration that follows on
from glycolysis and where does this stage take place?
Name____________________________
Site_____________________________________________________
(e) What is the name of the 6-carbon compound formed during the
middle phase of aerobic respiration?
________________________________________________________
(f) What does the term “aerobic respiration” refer to?
________________________________________________________
________________________________________________________
(g) What is the function of the molecule NAD?
________________________________________________________
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THE CYTOCHROME SYSTEM

This third and final stage of aerobic respiration occurs on the stalked
particles, called the cristae of the mitochondrion.

Most of the energy produced during respiration is made by the
cytochrome system. In this stage of aerobic respiration, the NADH2
molecules produced during glycolysis and the Krebs cycle transfer the
hydrogen ions to the cytochrome system.

This is a system of hydrogen carriers located on the cristae of the
mitochondrion and this stage also requires oxygen, which acts as
the final hydrogen acceptor.

The oxygen and the hydrogen combine to form metabolic or respiratory
water.

If oxygen is not present to act as the final hydrogen acceptor, the
hydrogen cannot pass through the system and complete oxidation
cannot take place
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Task 5: Complete the questions that follow. Make sure that you check
with your teacher to ensure you have the correct answers.
1.
(a)The diagram shows the role of the cytochrome system in aerobic
respiration.
(i)
State the exact location of the cytochrome system in a cell.
_____________________________________________
(ii)
Name the carrier that brings the hydrogen to the cytochrome
system.
______________________________________________
(b) Name molecules X, Y and Z.
X _____________________
Y ___________________
Z _____________________
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2. The diagram below represents stages in aerobic respiration in mammalian liver cells.
(a)
Name the storage carbohydrate in liver cells.
___________________________________________
(b)
Other than carbohydrate, name an alternative respiratory substrate.
____________________________________________
(c)
State the exact location within a liver cell of:
1.
Glycolysis _______________________
2.
Krebs cycle ______________________
(d)
State the net gain of ATP molecules from the breakdown of a glucose molecule to
pyruvic acid.
______________________________________________
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3. The pathway below represents an outline of stages in respiration in a mammalian cell.
(a)
Complete the table below by inserting the number of carbon atoms present in each
substance.
Substance
Glucose
Pyruvic acid
Acetyl group
(b)
Number of carbon atoms
Explain why the gain of 2ATPs in STAGE I is described as being a net gain.
_________________________________________________
_________________________________________________
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(c)
Name cycle X in STAGE II
Name __________________________________
(d)
Name the carrier that transfers hydrogen to the cytochrome system.
Name __________________________________
(e)
Name the final hydrogen acceptor in STAGE III.
Name __________________________________
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ANAEROBIC RESPIRATION

When anaerobic respiration occurs there is no oxygen to act as the
final hydrogen acceptor and so the hydrogen cannot pass through the
cytochrome system.

As a result, both the Krebs cycle and the cytochrome system stages
cannot take place:

The only ATP produced is formed during glycolysis, that is, 2 ATP.

During glycolysis, glucose is partially broken down to pyruvic acid and
releases only two ATP molecules.
THE FATE OF THE PYRUVIC ACID DIFFERS ACCORDING TO
ORGANISM

In plants and fungi, the pyruvic acid is converted to ethanol and
carbon dioxide (a process also known as fermentation).
In plants: pyruvic acid

Ethanol (2C) + Carbon Dioxide (CO2)
In animals, pyruvic acid is converted to lactic acid.
In animals: pyruvic acid

Lactic Acid (3C)
During the formation of lactic acid in animal cells, an oxygen debt
accumulates that is repaid when oxygen becomes available and the
lactic acid is reconverted to pyruvic acid.
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SUMMARY OF ATP PRODUCTION
Type of
respiration
Total number
of ATP
produced per
1 glucose
molecule
Does
glycolysis
occur?
Does the
Krebs cycle
occur?
Does the
cytochrome
system
occur?
Yes
Yes
Yes
36
Yes
No
No
2
Yes
No
No
2
Aerobic
(oxygen
present)
Anaerobic
(animals)
(NO oxygen
present)
Anaerobic
(plants and
yeast)
(NO oxygen
present)
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Task 6: Complete the questions that follow. Make sure that you check
with your teacher to ensure you have the correct answers.
1. Complete the summary of anaerobic respiration below using the boxes
at the bottom of the page. Use your notes to help you.
2. Which line in the table describes correctly both aerobic respiration and
anaerobic respiration in human muscle tissue?
Aerobic Respiration
Anaerobic Respiration
A
There is a net gain of ATP
Carbon dioxide is not produced
B
There is a net gain of ATP
Oxygen is required
C
Carbon dioxide is produced
There is a net loss of ATP
D
Lactic acid is formed
Ethanol is formed
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3. During anaerobic respiration in muscle fibres what is the fate of pyruvic acid?
a. It is converted to lactic acid
b. It is broken down by the mitochondria
c. It is broken down to carbon dioxide and water
d. It is converted to citric acid
4. Three different strains of yeast each lacked a different respiratory enzyme
involved in the complete breakdown of glucose.
Strain X- cannot produce carbon dioxide from pyruvic acid
Strain Y – cannot form pyruvic acid
Strain Z – cannot reduce oxygen to form water
Which of the strains could produce ethanol?
a. Strains X and Y
b. Strains X and Z
c. Strain Y only
d. Strain Z only
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5(a)
The diagram below shows the pathway of anaerobic respiration in human
muscle tissue.
Glucose
Process X
Pyruvic acid
Compound S
Name Process X and Compound S.
Process X _______________ Compound S ____________
(b) Complete the boxes in the diagram to show the number of carbon atoms present
in glucose and pyruvic acid.
(c) Aerobic respiration in human muscle tissue involves the Krebs cycle and the
cytochrome system.
For each statement in the table below, tick (√) a box to show the process to which it
applies.
Statement
Krebs cycle
Cytochrome system
Carbon dioxide is produced
Occurs on the cristae of the mitochondria
Involves the formation of NADH2
Involves the formation of citric acid
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6.
The diagram shows a mitochondrion from a human muscle cell.
(a)
Name regions A and B.
A _________________________
B __________________________
(b)
The table shows some substances involved in respiration.
(i)
Complete the table by inserting the number of carbon atoms present in each
substance.
Substance
Pyruvic acid
Acetyl group
Citric acid
Number of carbon atoms present
(ii) To which substance is the acetyl group attached before it enters the citric acid
cycle?
___________________________________________
(c)
In region B, hydrogen is passed through a series of carriers in the cytochrome
system as shown in the diagram below.
(i) Name carrier X.
____________________________________________
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(ii)
Name the final acceptor of hydrogen.
____________________________________________
(iii)
Describe the importance of ATP cells.
____________________________________________
____________________________________________
(iv) The quantity of ATP present in the human body remains relatively constant yet
ATP is continually being broken down.
Suggest an explanation for this observation.
________________________________________________________
________________________________________________________
(v) Name the final metabolic product of anaerobic respiration in a muscle cell.
____________________________________________
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Task 7: Your teacher will assess your knowledge of the following key
terms. Make sure you understand what these words mean.
Adenosine Triphosphate (ATP)
Supplies chemical energy for cellular
processes
Respiration
A chemical process in which energy is
released from food molecules in cells
The cell’s main energy source
Glucose
The process by which energy is released
from glucose in cells using oxygen
Aerobic respiration
Anaerobic respiration
The process by which some energy is
released from glucose in cells in the
absence of oxygen
Pyruvic acid
Formed as a result of the first stage of
the respiration of glucose
Stage of respiration that occurs in the
cytoplasm and does not require oxygen
Glycolysis
Stage of respiration that occurs in the
matrix of the mitochondria and does
require oxygen
Krebs cycle
Also known as the electron transport chain.
The stage of aerobic respiration
where the majority of ATP are
synthesised from ADP and Pi
Cytochrome system
Oxygen
The final hydrogen acceptor
The products of anaerobic respiration in
plants and yeast cells
Carbon dioxide and ethanol
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Lactic Acid
The product of anaerobic respiration in
animals. This can be reversed when
oxygen is present.
Oxygen debt
The build up of lactic acid causes this
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