PTT 106
ASSIGNMENT 1 & EXERCISES ANSWER SCHEME
Title: Microbial Nutrition and Growth
1.
Microorganisms require about 10 elements in large quantities for the synthesis of
macromolecules. State clearly all the elements.
[10 marks]
(2 marks for each point = 10 Marks)
Answer:
-
2.
Carbon
Oxygen
Hydrogen
Nitrogen
Sulfur
- Phosphorus
- Potassium
- Calcium
- Magnesium
- Iron
Describe energy and carbon requirements each of the following group of
microorganisms.
a)
Photoautotrophs
b)
Chemoautotrophs
c)
Photoheterotrophs
d)
Chemoheterotrophs
[20 marks]
Answer:
Photoautotrophs : Use light as their energy source; Use carbon from inorganic
sources
Chemoautotrophs: energy is from redox reactions involving inorganic and
organic chemicals; Use carbon from inorganic sources
Photoheterotrophs: Use light as their energy source: use carbon from organic
molecules (proteins, carbohydrates) they acquire from other organisms.
Chemoheterotrophs: Energy is from redox reactions involving inorganic and
organic chemicals: use carbon from organic molecules (proteins, carbohydrates)
they acquire from other organisms.
3.
Different species of microorganisms can grow in a wide range of environments and
their growth rates are influenced by physical and biochemical factors.
i.
Lists four physical factors that affect microbial growth.
[5 marks]
ii.
Define the term ‘acidophiles’ and ‘alkaliphiles’ and name one common
genus from each group.
[20 marks]
Answer:
a)
b)
c)
Temperature (1.5 marks)
pH (1.5 marks)
Physical effects of water (Osmotic Pressure and Hydrostatic pressure)(2 marks).
Term ‘acidophiles’ and ‘alkaliphiles’ are referred to types of microorganisms with
their preferred pH for optimum growth. (4 marks)
(2 marks each for other points)
- Acidophiles grow best in acidic habitats at pH 0 to 5.5.
- Some can go as low as 0.0 i.e chemoautotrophic bacteria that oxidize sulfur to
sulfuric acid.
- Obligate acidophiles die if pH approaches 7.0.
- Acid-tolerant microbes can survive without preferring it.
- Examples: fungi, photosynthetic protests
- Alkalophiles grow best in alkaline soils and water between 8.0 up to pH 11.5.
- extreme alkalophiles have growth optima at pH 10 or higher
- i.e Vibrio cholerae, the causative agent of cholera grow best at pH 9.0.
4.
Initial information obtained for bacteria found in contaminated milk is that they
belonged to photoheterotrophs group. The milk was pasteurized at 72oC and then
cultured on nutrient agar media. The bacteria colonies appeared after three days.
i.
What are the assumptions that can be made for their carbon and energy sources?
ii.
ii. Explain the appearance of colonies and suggest the bacteria group based on the
physical requirements.
Answer:
i. The bacteria may get their energy source from the light and carbon source
from organic compounds such as proteins, carbohydrates that they acquire from
other organisms.
[10marks]
ii. The bacteria are resistance at 72oC meaning that they can grow at that
temperature. This type of bacteria is group under hyperthermophiles that can
grow at temperature above 80oC
[10marks]
5)
Information on bacterial growth is very important in food and industrial microbiology.
i.
Draw and label a typical bacterial growth curve and describe the phases
involved.
[15 marks]
ii. Fifty cells of a bacterial species with a generation time of 25 minutes are
introduced into a fresh sterile medium at 9.00 AM. The culture is maintained at an
optimum growth temperature throughout the experimental period. Calculate the
number of bacterial cells that can be obtained in this experiment at 3.00 PM and the
number of generations by 6.00 PM. [10 marks]
Answer:
Lag Phase
During the lag phase the cells are adjusting to their new environment, and
synthesize enzymes to utilize novel nutrients in the medium.
[6marks]
Log Phase
During the log phase, the population increases logarithmically, and the
reproductive rate reaches a constant as DNA and protein syntheses are
maximized.
[7marks]
Stationary Phase
At the stationary phase, the rate of reproduction decreases (as nutrients are
depleted). Here, the number of dying cells = the number of cells being produced.
[6marks]
Death Phase
At the death phase, a population reaches a point at which cells die at a faster rate
than they are produced Here, the number of dying cells >> the number of new
cells produced
[6marks]
ii. g = 25 min
t = 9.00 am – 3.00pm = 6 hrs
= 9.00 am – 6.00 pm = 9 hrs
No = 50 cells
N = ? at 3.00 pm
n = ? at 6.00 pm
at 3.00 pm
n = 360/25
= 14.4
Number of generation, n = 3.3 (log N – No)
14.4 =3.3 (log N – log 50)
log N/50 = 14.4/3.3
log N/50 = 4.36
N = 1.14 x 106 .................................. 8 marks
n = 540/25 ......................................... 2marks
= 21.6
= 22
6)
An inoculum of 107 bacterial cells was introduced into a flask of culture medium and
the growth was monitored. No change was observed for the first 18 minutes; then
growth occurred rapidly. After a further 76 minutes, the population had increased to
4.32 × 108 cells. Calculate the doubling time (Td) of the culture?
[20 marks/markah]
Answer:
Given that Nt and No represent the number of cells at a “n” and “zero” time ,
then:
N= (log Nt-logN0)/0.301
N= (log 4.32 × 108 – log 107 )/0.301
N= (8.6-7)/0.301
N=1.6/0.301
N= 5.4 ( in 76 minutes).
Td = 76/5.4= 14 minutes.
[10marks]
[10marks]
The doubling time of the culture is 14 minutes.
Title: Introduction to Microbial World
1) In the 19th Century, a major controversy erupted concerning the theory of spontaneous
generation. It was proposed by Aristotle and was widely accepted for almost 2000 years until
experiment by Pasteur challenged it.
(i)
Define the theory of spontaneous generation.
Answer:
The theory of spontaneous generation (or abiogenesis) proposes that living organisms
can arise from nonliving matter.
(ii)
Explain how did Pasteur finally settle the spontaneous generation controversy?
[20 Marks/Markah]
Answer:
Pasteur placed a nutrient solution in flask, heated the neck in a flame. He bent
the flask neck into S-shape which allow air to enter but prevent the introduction
of dust and microbes. pasteur then boiled the solutions for a few minutes and
allowed them to cool. No growth took place even though the content of the flask
was exposed to the air. Pasteur point out that no growth occurred because dust
and germ had been trapped in the wall of bent neck. he tipped the flask so that
the sterile solution get contact with the dust on the bent neck. after short time,
microorganisms grow in the solution. Pasteur conclude that microbes in the
solution are the progeny of microbes that had been on the dust particles. The
theory of spontaneous generation was disproved by Pasteur’s experiment.
(iii) The debate over spontaneous generation led in part to the development of scientific
method. With the aid of flowchart, discuss the scientific method.
[30 Marks/Markah]
Answer:
Step 1:Observation
It is concern with objects or events that are observable, directly or indirectly.
Step 2:Hypothesis
It is a tentative explanation on what is observed and used as a basis for
predictions. All hypothesis can be tested.
Step 3:Experimentation
Scientific experiments should be conducted to test the hypothesis. The data
obtained is used to validate the hypothesis.
Step 4:Conclusion & Theory
To accept or to reject the hypothesis is based on experimental results. The
hypothesis will be accepted and can become a theory if results are in support to
hypothesis. The hypothesis should be rejected and new hypothesis can be
developed if the data is insufficient.
2) The study of the causation of disease were dominated by German physician Robert Koch
(1843-1910). Koch initiated microbiological techniques in his search for disease agents, such
as bacterium responsible for anthrax. Koch elucidated a series of four steps, called Koch’s
postulates for proving that a specific type of microorganism causes a specific disease.
Describe FOUR (4) steps in Koch’s postulates.
[20 Marks/Markah]
Answer:
 Koch elucidated a series of steps that must be taken to prove the cause of any
infectious disease.
 These four steps are now known as Koch’s postulates:
1. The suspected causative agent must be found in every case of the disease and be
absent from healthy hosts.
2. The agent must be isolated and grown outside the host.
3. When the agent is introduced to a healthy, susceptible host, the host must get the
disease.
4. The same agent must be reisolated from the diseased experimental host.
Answer:
4)
A microbiologist is given a poisonous food sample that is suspected to be caused by a
microbe. How would he verify the microbe is pathogenic?
[30 marks/markah]
Answer:
Koch’s Postulates:
(1x10=10)
1.
The suspected causal agent must be found in every case o the disease and
absent from healthy hosts
2.
The agent must be isolated and grown outside the host
3.
4.
When the agent is introduced to a healthy, susceptible host, the host must get
infected with the disease
The same agent must be reisolated from the diseased experimental host.
(4x5=20 marks)
Title: Microscopy
1)
The ultra structures of microorganisms can only be observed by using transmission
electron microscopy (TEM).
i.
ii
Explain why those structures cannot be seen under light microscopy.
State the advantages of TEM
[20 marks/markah]
i.
Light microscopy has the ability to distinguish between two objects at the
shortest of 200nm or resolution principle. Structures in microorganisms located closer
than that and therefore cannot be distinguished. Greater resolving power admits the
possibility of greater magnification.
[10marks]
ii.
TEM using electron not light to magnify objects. Electrons have wavelengths
between 0.01 nm and 0.001 nm and therefore the resolution is higher to observe cellular
structures of bacteria. Electron microscope can magnify objects 10,000X to 100,000X.
[10marks]
2)
After a process of simple staining, a microbiologist observed the specimen under
compound microscope and sees nothing.
i. What is probable step that the microbiologist has missed and why the procedure is
important.
[15 marks/markah]
ii. Suggest what steps shall be include if the microbiologist want to
change the procedure using differential staining.
[15 marks/markah]
Answer:
i.
The microbiologist may not carry out the fixation procedure. [5marks]
The procedure of fixing the specimen properly on the glass slide is important so
that they are not lost during staining. [10marks]
ii. In using differential staining, the microbiologists should include three more steps
such as
a. use iodine solution to smear the slide and rinse with water,
b. rinse the smear with solution of ethanol and acetone and rinse with water
and
c. flood the smear with safranin for 1 min and rinse with water.
[3x5=15marks]
3)
You are given a strain of bacteria which is expected to fall under genera Bacillus
based on morphology identification. One important features of Bacillus is it have
endospores.
(i)
Write a procedure to prepare the specimen for special staining starting from
pretreatment so that it can be prove as Bacillus by identification under
compound light microscope.
Answer:

Prior to staining, specimens need to be smear and fixed which involve following
steps:
1)
2)
3)
4)
making a thin film (smear) of the specimen on a slide
The smear is air dried
then either passing the slide through a flame (heat fixation)
(heat fixation preserve overall morphology but not structure within cell) or
applying a chemical (chemical fixation) to attach the specimen firmly to the
slide. (used to protect ethanol or formaldehyde)

Commonly used method to stain endospore = Schaeffer-Fulton procedure
1) heat bacteria with malachite green (very strong stain that can penetrate endospores)
2) rinsing
3) counterstain with safranin
(yield a green-stained endospore and pink to red-stained bacterial cells)
[20 Marks/Markah]
(ii)
Explain why do you need to do the pretreatment before staining?
[5 Marks/Markah]
Answer:
- to retain the structure of cell on the slide
4)
Light microscope limits the detailed studies of viruses and internal structure of
microorganisms. This problem had lead the scientist to invent electron microscope.
(i)
Explain THREE (3) important characteristics of scanning electron microscope (SEM).
[15 Marks/Markah]
Answer:
 SEM use magnetic lenses to focus a beam of primary electrons
 Primary electrons are scanned across the metal-coated surface of a specimen –
produced secondary electrons
 Secondary electrons are collected by a detector & their signal amplified and displayed
on a monitor
(ii)
Write a procedure on how to stain a specimen for viewing under scanning electron
microscope (SEM).
[10 Marks/Markah]
Answer:

Preparing sample for SEM
1)
Fixed specimen using chemicals
2)
Dehydrated using aseton & ethanol
3)
Dried sample in critical point drying for 24hrs (to preserve surface structure and
prevent collapse of the cells)
4)
Mounted and coated specimen with a thin layer of metal eg platinum or gold
Title: Prokaryote and Eukaryote Cell
1)
Explain the functions of the following eukaryote cell organelles:
[20 marks/markah]
2)
i.
Mitochondria
produce adenosine triphosphate (ATP) as source of energy for cellular
activities.
ii.
Ribosomes
sites of protein synthesis.
iii.
Golgi body
Package, store and distribute newly synthesised substances such as proteins
and lipid , and assist in their transport away from the cell.
iv.
Endoplasmic reticulum
involve in protein synthesis and production of glycogen, steroids.
(4 ans.x 5 marks=20)
Describe briefly the mode of locomotion in bacteria.
[20 marks/markah]
a) Many bacteria are able to move through liquids by means of tail like appendages
called flagella, or tiny hair like structures called cilia.
b) The bacterial flagellum is a helical structure that drives the cell through the media
like a propeller.
c) The structure is rigid and turned by a rotatory motor at the base where it connects
to the bacteria's body and is driven by a proton motive force resulting from a
gradient of protons.
d) Bacterial chemotaxis is brought about by alterations in the direction that the motor
rotates in; this in turn is controlled by phosphorylation. (4 pts.x 5 marks=20)
3)
Compare the cell walls of gram positive and gram-negative bacteria.
[20 marks/markah]
Gram-positive cell walls are relatively simple in structure, comprising several layers
of peptidoglycan connected to each other by cross-linkages to form a strong, rigid
scaffolding. In addition, they contain acidic polysaccharides called teichoic acids;
these contain phosphate groups that impart an overall negative charge to the cell
surface.
4)
Gram-negative cells have a much thinner layer of peptidoglycan, making the wall
less sturdy. The structure is made more complex by the presence of a layer of
lipoprotein, polysaccharide and phospholipid known as the outer membrane.
(2 ans.x 10 marks=20)
One of plasma membrane function is to separate the cell from its environment.
Discuss
the arrangement of a prokaryotic plasma membrane structure with
relation to the stated function.
[20 Marks/Markah]
-
5)
The model known as fluid mosaic model
The models are lipid bilayers within which proteins float.
Small spheres represent the hydrophilic ends of membrane phospholipids
and wiggly tails, the hydrophobic fatty acid chains.
Other membrane lipids such as hopanoids may be present.
The integral proteins floating in a lipid bilayer.
Peripheral proteins are associated loosely with the inner membrane surface.
(4 Marks for any of 5 points)
Explain how does the cell membrane control the passage of nutrients and substances
into and out of the cell.
[Jelaskan bagaimana membran sel mengawal laluan nutrien dan bahan-bahan ke dalam dan keluar
sel.]
[30 Marks/Markah]
Through pasive and active process............ 2 marks
Diffusion………………………..5 points x 2 marks
In simple diffusion, solutes move down a concentration gradient i.e., from an area of
high concentration to an area of low concentration.
- Spontaneous process, there is a net movement of solute until an equilibrium is reach.
-
-
Because there is no input of energy, transport occurs with a negative charge in free
energy.
In general, the higher the concentration gradient, the faster the rate of solute diffusion.
Example: diffusion of oxygen and carbon dioxide and osmosis of water. Diffusion of
organic molecules also depends on molecular weight and lipid solubility.
Facilitated diffusion……………4 points x 2 marks
Is the movement of a solute/ subtances down its concentration gradient across a
membrane that occurs through protein channels or carriers.
- Channel are tunnel-like transmembrane protein. Each type is designed for the
transport of specific solute.
- Many channels are chemically or voltage-regulated.
-
-
Chemically regulated channels open or close in response to a specific chemical signal.
e.g. A chemically gated Na+ channel in the nicotinic acetylcholine receptor complex
opens when acetylcholine binds.
Active transport……………..5 points x 2 marks
energy is required to move solutes/ substances across a membrane against the
concentration gradient. Most commonly ATP. Divided into 2:
- Primary active transport
- Energy is usually provided directly by ATP hydrolysis. The Na+-K+ pump is a
prominent example of a primary transporter.
- Secondary active transport
-
-
-
6)
Solutes are moved across a membrane by energy stored in a concentration gradient of
a second substance that has been created by ATP hydrolysis or other energygenerating mechanisms.
e.g. the Na+ gradient created by the Na+-K+ ATPase pump is used in kidney tubule
cells and intestinal cell to transport D-glucose.
Why Gram staining cannot be used on Mycobacterium leprae? If Gram staining were
done towards this bacterium, what would the Gram reaction be?
[20 marks/markah]
Gram staining cannot be used because M. leprae is acid-fast bacteria not
gram bacteria (5 marks). The high lipid content of acid-fast cell walls makes them
impermeable to most stains. If the primary stain penetrates, the Gram stain
decolorizer will not decolorize the cell (10 marks). Therefore, acid-fast bacteria
would be gram-positive if they could be Gram stained (5 marks).
7)
Describe the FOUR functions of plasma membrane in the cell structure of
microorganisms.
[20 marks]
Functions of plasma membrane
1. separation of cell from its environment
- It is the chief point of contact with the cell’s environment and thus is responsible for
much of its relationship with the outside world.
2. selectively permeable barrier
– some molecules are allowed to pass into or out of the cell
– transport systems aid in movement of molecules
3. location of crucial metabolic processes such as respiration, photosynthesis, and the
synthesis of lipids and cell wall constituents.
4. detection of and response to chemicals in surroundings with the aid of special
receptor molecules in the membrane
12)
Explain the characteristic of the bacteria, archaea and eukarya domain
[30 Marks/Markah]
Title: MICROBIAL NUTRITION, GROWTH AND CONTROL
1)
Microorganisms require about 10 elements in large quantities for the synthesis of
macromolecules. State clearly all the elements.
[10 marks]
Carbon
- Phosphorus
Oxygen
- Potassium
Hydrogen
- Calcium
Nitrogen
- Magnesium
Sulfur
- Iron
2)
Describe energy and carbon requirements each of the following group of
microorganisms.
a)
b)
c)
d)
Photoautotrophs
Chemoautotrophs
Photoheterotrophs
Chemoheterotrophs
[20 marks]
Photoautotrophs : Use light as their energy source; Use carbon from inorganic
sources
Chemoautotrophs: energy is from redox reactions involving inorganic and organic
chemicals; Use carbon from inorganic sources
Photoheterotrophs: Use light as their energy source: use carbon from organic
molecules (proteins, carbohydrates) they acquire from other organisms.
Chemoheterotrophs: Energy is from redox reactions involving inorganic and organic
chemicals: use carbon from organic molecules (proteins, carbohydrates) they acquire
from other organisms.
3)
Different species of microorganisms can grow in a wide range of environments and
their growth rates are influenced by physical and biochemical factors.
i. Lists four physical factors that affect microbial growth.
a)
[5 marks]
Temperature
b) pH
c) Physical effects of water (Osmotic Pressure and Hydrostatic pressure)
ii. Define the term ‘acidophiles’ and ‘alkaliphiles’ and name one common genus
from each group.
[20 marks]
Term ‘acidophiles’ and ‘alkaliphiles’ are referred to types of microorganisms with
their preferred pH for optimum growth. (4 marks)
(2 marks each for other points)
- Acidophiles grow best in acidic habitats at pH 0 to 5.5.
- Some can go as low as 0.0 i.e chemoautotrophic bacteria that oxidize sulfur to
sulfuric acid.
- Obligate acidophiles die if pH approaches 7.0.
- Acid-tolerant microbes can survive without preferring it.
- Examples: fungi, photosynthetic protests
- Alkalophiles grow best in alkaline soils and water between 8.0 up to pH 11.5.
- extreme alkalophiles have growth optima at pH 10 or higher
- i.e Vibrio cholerae, the causative agent of cholera grow best at pH 9.0.
4)
Initial information obtained for bacteria found in contaminated milk is that they
belonged to photoheterotrophs group. The milk was pasteurized at 72oC and then
cultured on nutrient agar media. The bacteria colonies appeared after three days.
i.
What are the assumptions that can be made for their carbon and energy
sources?
ii..
Explain the appearance of colonies and suggest the bacteria group based on
the physical requirements.
[20 marks/markah]
i. The bacteria may get their energy source from the light and carbon source from
organic compounds such as proteins, carbohydrates that they acquire from other
organisms.
[10marks]
ii. The bacteria are resistance at 72oC meaning that they can grow at that temperature.
This type of bacteria is group under hyperthermophiles that can grow at temperature
above 80oC
[10marks]
5)
Information on bacterial growth is very important in food and industrial microbiology.
i. Draw and label a typical bacterial growth curve and describe the phases involved.
[15 marks]
Bacterial growth curve (5 marks)
Lag phase (2 marks)
- the cells are adjusting to their new environment
- cells actively synthesize enzymes to utilize novel nutrients in the medium.
Log (exponential) phase (2 marks)
- phase of rapid chromosome replication, growth, and reproduction.
- population increases logarithmically metabolic rate of individual cells is at a
maximum
Stationary phase (4 marks)
- nutrients are depleted and wastes accumulate, the rate of reproduction decreases.
- number of dying cells equals the number of cells being produced, and the size of the
population becomes stationary
- during this phase the metabolic rate of surviving cells declines.
- total number of viable cells remains constant
Death phase (2 marks)
- a population reaches a point at which cells die at a faster rate than they are produced.
- some cells remain alive and continue metabolizing and reproducing, but the number
of
dying cells exceeds the number of new cells produced
- the population decreases to a fraction of its previous abundance.
6) Fifty cells of a bacterial species with a generation time of 25 minutes are introduced into a
fresh sterile medium at 9.00 AM. The culture is maintained at an optimum growth
temperature throughout the experimental period. Calculate the number of bacterial cells that
can be obtained in this experiment at 3.00 PM and the number of generations by 6.00 PM.
[10 marks]
g = 25 min
t = 9.00 am – 3.00pm = 6 hrs
= 9.00 am – 6.00 pm = 9 hrs
No = 50 cells
N = ? at 3.00 pm
n = ? at 6.00 pm
at 3.00 pm
n = 360/25
= 14.4
Number of generation, n = 3.3 (log N – No)
14.4 =3.3 (log N – log 50)
log N/50
= 14.4/3.3
log N/50
= 4.36
N
= 1.14 x 106
..................................
8 marks
n = 540/25 ......................................... 2marks
= 21.6
= 22
7)
An inoculum of 107 bacterial cells was introduced into a flask of culture medium and
the growth was monitored. No change was observed for the first 18 minutes; then
growth occurred rapidly. After a further 76 minutes, the population had increased to
4.32 × 108 cells. Calculate the doubling time (Td) of the culture?
[20 marks/markah]
Given that Nt and No represent the number of cells at a “n” and “zero” time , then:
N= (log Nt-logN0)/0.301
N= (log 4.32 × 108 – log 107 )/0.301
N= (8.6-7)/0.301
N=1.6/0.301
N= 5.4 ( in 76 minutes).
Td = 76/5.4= 14 minutes.
[10marks]
[10marks]
The doubling time of the culture is 14 minutes.
Title: Microbial Metabolism
1)
Explain (with relevant examples) the types of chemical reactions involves in
microbial metabolism.
[30 marks/markah]
1. catabolism
[10marks]
 They break down nutrient molecules and release energy stored in ATP
molecules.
 E.g. the breakdown of glucose molecules and the production of energy in
ATP form.
2. anabolism
[10marks]
 They synthesize macromolecules
 e.g. Synthesis of lipids for for cell membranes from glycerol and fatty
acids] and use ATP energy
3. oxidation
[5marks]
 when a molecule (i) losing a simple electron (ii) losing a hydrogen atom
(iii) gaining an oxygen atom with its electron.
 E.g. an electron transport chain consists of oxidation reactions that pass
electrons from one membrane-bound carrier to another and then to a final
electron acceptor.
4. reduction
[5marks]
 when a molecule gaining (i) a simple electron (ii) an electron that is part of
a hydrogen atom.
 E.g. an electron transport chain consists of reduction reactions that pass
electrons from one membrane-bound carrier to another and then to a final
electron acceptor.
2)
Bacteria obtain the energy in Adenosine Triphosphate (ATP) form from carbohydrate
catabolism that consists of three stages, i.e.: glycolysis, the Krebs cycle and the
electron transport chain. Briefly describe each of the stages and the numbers of ATP
molecules produced.
[30 marks/markah]
1. Glycolysis
[2 marks]
in this stage, 2 ATP is yield when one molecule G3P is oxidized to pyruvic acid.
DHAP is converted to G3P and also oxidized to pyruvic acid, yielding another
two ATP molecules, for a total of four ATP molecules. But 2 ATP molecules are
used to phosphorylate a six-C glucose molecule.
[8 marks]
2. The Krebs cycle
[2 marks]
One molecule pyruvic acid from glycolysis is converted to acetyl-coenzyme A or
acetyl-CoA. A molecule of glucose will produced two acetyl-CoA. For every two
molecules of acetyl-CoA that pass through the Krebs cycle, two molecules of ATP
are generated by substrate-level phosphorylation. A molecule of guanosine
triphosphate (GTP), which is similar to ATP, can serve as an intermediary in this
process.
[6 marks]
3. The electron transport
[2 marks]
During the electron transport chain, there is a process call chemiosmosis where
protons flow down their electrochemical gradient through protein channels, called
ATP synthases, that phosphorylate molecules of ADP to ATP. About 34
molecules of ATP are generated via chemiosmosis. All together, a net total of 38
molecules of ATP are produced. [10 marks]
2)
Metabolism process in microorganism is divided into two parts, a catabolism and an
anabolism.
(i)
Explain catabolism and anabolism and their relation to energy cycle.
[20 Marks/Markah]
•
•
•
•
•
•
•
•
•
•
(ii)
metabolism is the total of all chemical reactions in the cell and is divided into
two parts, the catabolism and anabolism.
catabolism – the energy-conserving reactions
three-stage process
large molecules (polymers)  small molecules (monomers)
initial oxidation and degradation to pyruvate
oxidation and degradation of pyruvate by the tricarboxylic acid cycle (TCA
cycle)
anabolism – the synthesis of complex organic molecules from simpler ones
requires energy
transferred from energy source to the synthetic systems of the cell by ATP
also requires a source of electrons stored in the form of reducing power
(4 marks for any 5 points)
Show the conversion of adenosine diphosphate (ADP) to adenosine
triphosphate (ATP) and vice versa in phosphorylation.
[10 Marks/Markah]
Answer:
3)
Bacteria obtain the energy in ATP form from carbohydrate catabolism that consists of
three stages, namely glycolysis, the Krebs cycle and the electron transport chain.
(i)
Describe for each stage
[30 Marks/Markah]
(i)
Embden-Meyerhof pathway
• occurs in cytoplasmic matrix of both procaryotes and eucaryotes
• the most common pathway for glucose degradation to pyruvate in stage two of
aerobic respirationhigh• energy molecules – used to synthesize ATP by substrate-level phosphorylation
(ii)
Tricarboxylic acid (TCA) cycle
also called citric acid cycle and Kreb’s cycle
common in aerobic bacteria, free-living protozoa, most algae, and fungi
major role is as a source of carbon skeletons for use in biosynthesisfor each acetylCoA molecule oxidized, TCA cycle generates:
– 2 molecules of CO2
– 3 molecules of NADH
– one FADH2
– one GTP
•
•
•
(iii)
•
•
•
•
•
•
Electron transport chain (ETC)
only 4 ATP molecules synthesized directly from oxidation of glucose to CO2
most ATP made when NADH and FADH2 (formed as glucose degraded) are oxidized
in electron transport chain (ETC)
series of electron carriers that operate together to transfer electrons from NADH and
FADH2 to a terminal electron acceptor
electrons flow from carriers with more negative E0 to carriers with more positive E0
as electrons transferred, energy released
in eucaryotes the electron transport chain carriers are within the inner mitochrondrial
membrane
(ii)
Demonstrate numbers of ATP molecules produced.
[15 Marks/Markah]
4)
Anabolism in microorganism involves the fixation of CO2 from the atmosphere.
(i)
Give THREE CO2 fixation pathways used by a name microorganism.
[15 Marks/Markah]
1. The hydroxypropionate cycle
used by some archael genera and the green nonsulfur bacteria (also anoxygenic
phototrophs)
2. The acetyl-CoA pathway
methanogens use portions of the acetyl-CoA pathway for carbon fixation
3. The calvin cycle
used by most autotrophs to fix CO2
also called the reductive pentose phosphate cycle
4. The reductive TCA cycle
used by some chemolithoautotrophs
runs in reverse direction of the oxidative TCA cycle
(5 Marks each for any of 3 pathways)
(ii)
Explain the
biosynthesis.
importance
of
carbon
source
in
macromolecules
[10 Marks/Markah]
- CO2 is used as sole carbon source for microbes to synthesize new organelles and
cells through the Calvin cycle.
- CO2 will be fixed during the carboxylation phase in Calvin cycle.
5)
(i)
What are amphibolic pathways? Why are they important?
[10 marks/markah]
Answer p.194 Prescott
Pathways that function both catabolically and anabolically. (5marks). They supply
precursor metabolites (materials needed for biosynthesis of biomolecules) (5marks)
(ii)
Name the precursor metabolites derived from PPP (Pentose-phosphate
pathway) and what do they synthesis.
[10 marks/markah]
Precursor metabolites derived from Pentose phosphate pathway: (anabolism lecture)
a. Ribose 5-P synthesize DNA, RNA, amino acid and histidine
(2x2.5 =5)
b. Erythrose 5-P synthesize amino acids, phenylalanine, trytophan, tyrosine
(2x2.5=5)
(iii)
6)
What happens to the carbon atoms in sugar catabolised by E. coli?
[10 marks/markah]
E.coli – uses glycolysis split 6-C glucose into 3-C carbon sugar – which later
transformed into 2 molecules of pyruvic acid
Describe the roles and products of commonly used glycolysis pathway, the EmbdenMeyerhof Pathway.
[20 Marks]
•
The roles of glycolysis is to split a glucose molecule in a series of ten steps that can be
divided into three stages: energy-investment, lysis, and energy-conserving.
Step 1. Glucose phosphorylated by ATP to form glucose-6-phosphate
Step 2. The atoms of glucose-6-phosphate are rearranged to form fructose-6phosphate
Step 3. Fructose-6-phosphate is phosphorylated by ATP to form fructose 1,6biphosphate
Step 4. Fructose 1,6-biphosphate is cleaved to form:
glyceralaldehyde 3- phosphate (G3P)
and dihydroxyacetone phosphate (DHAP)
Step 5. DHAP is rearranged to form another G3P
Step 6. Inorganic phosphates are added to the two G3P, and two NAD+ are
reduced to form 1,3-biphosphoglyceric acid
Step 7. Two ADP are phosphorylated by substrate-level phophorylation to form 2
ATP in addition to 3-phosphoglyceric acid
Step 8 & 9. The remaining phosphates are moved to the middle carbons and a
water molecule is removed from each substrate to form phosphoenolpyruvic acid
(PEP)
Step 10. Two ADP are phosphorylated by substrate-level phophorylation to form
2 ATP. Two pyruvic acid are formed
• The products of this pathway are:two molecules of pyruvic acid; a net gain of
two ATP; and two NADH molecules.
7)
The Calvin cycle consists of THREE main phases that play an important role for CO2
fixation.
i.
Explain the use of CO2 in cell metabolism. [10 marks]
ii.
Illustrate the major molecules conversion in each phase. [15 marks]
(i)
(ii)
- CO2 is used as sole carbon source for microbes to synthesize new organelles
and cells through the Calvin cycle.
- CO2 will be fixed during the carboxylation phase in Calvin cycle.
1. Carboxylation phase is the addition of CO2 to ribulose-1,5-bisphosphate
(RuBP) catalyzes by rubisco, forming 2 molecules of 3-phosphoglycerate.
2. reduction phase is the reduction of 3-phospho-glycerate to glyceraldehyde
3-phosphate
3. Regeneration phase refer to the regeneration of RuBP and the production of
carbohydrates (e.g., fructose and glucose)