Biotechnology

Question 1

List the main characteristics of a typical bioprocess that distinguish it from a typical chemical
process.

Answer 1

Take place at ambient temperature.
Involve labile products, heat and extreme pH sensitive.
Run in batch or batch-fed mode.
Usually performed in sterile conditions.
Need containment of cells used.
Involve an aqueous stage and involve large amounts of water.
Require a higher degree of product purity.
Small volume, high value.

Question 2

List the typical downstream processing problems associated with bioprocesses.

Answer 2

Separation of products for purification.
Cell disintegration for intracellular products.
Product formulation and preparation for sales.
Wastewater treatment.

Question 3

List and explain briefly the main stages in a typical bioprocess

Answer 3

Medium (nutrients) formulation and raw
materials preparation.
Sterilisation of medium, bioreactor and ancillaries
Inoculum (seed culture) development (from
small to large quantities)
Bioreactor (fermentation/biocatalysis/product
formation) operation
Product recovery and purification
Product formulation and preparation of product
for sales
Waste treatment/management

Question 4

What is the classification of cells based on their basic cell structure?

Answer 4

There are prokaryotes (bacteria and archea) and eukaryotes.

Question 5

What are the characteristics of prokaryotes?

Answer 5

Prokayotes lack a nucleus and membrane organelles, include bacteria and cyanobacteria.

Question 6

Draw a schematic representation of the main structural features of a prokaryotic cell.

Answer 6

.

Question 7

What are the main differences between a prokaryotic cell and a eukaryotic cell?

Answer 7

Eukarotes have a nucleus and organelles within the cell body that are contained in a membrane.

Question 8

List the four classes of ingredients in the medium composition required for the growth and
multiplication of cells.

Answer 8

Sources of carbon
Sources of inorganic chemicals
(N, P, S)
Energy source
Electron acceptor

Question 9

What are the main macromolecules found in a typical cell?

Answer 9

Proteins (enzymes and stuctural)
Nucleic acids (DNA and RNA)
Polysaccharides (Sugars, carbohydrates and structural)
Phospholipids

Question 10

List the six major chemical elements found in a typical cell.

Answer 10

Carbon
Oxygen
Nitrogen
Hydrogen
Phosphorus
Sulphur

Question 11

What is a macronutrient in a growth medium?

Answer 11

An inorganic nutrient required in large
amounts for growth, such as nitrogen,
potassium, calcium, phosphorus, magnesium,
and sulfur.

Question 12

What is a micronutrient in a growth medium?

Answer 12

An inorganic nutrient required in only small
amounts for growth such as, iron, chlorine,
copper, manganese, zinc, molybdenum, and
boron.

Question 13

Why do we need to sterilise media and equipment before starting a pure culture of cells?

Answer 13

To remove the possibility of there being unwanted foreign organisms within the reaction space that could reduce the growth capabilities of the required reactant.

Question 14

List the sterilisation techniques for equipment and media

Answer 14

Sterilisation can be achieved by heat,
radiation (gamma), chemical means (e.g.
sodium metabisulfite, sodium hypochlorite) or
by filtration through sub-micron membranes.

Question 15

Explain briefly what enzymes are and how they work in the cell.

Answer 15

Enzymes are complex protein structures made up of many different amino acids. They catalyse metabolic reactions within a cell by lowering the activation energy of a reaction.

Question 16

Using sketches, explain briefly the “Lock-and-Key Model” and “Induced-Fit Model” for enzyme
action

Answer 16

.

Question 17

Starting from the instantaneous mass balance on the enzyme-substrate complex, derive the
Michaelis-Menten equation that describes simple enzyme kinetics. Include in your answer
definitions for V, Vmax, [S] and KM

Answer 17

.

Question 18

Explain briefly how initial rates can be obtained for a single enzyme-single substrate reaction

Answer 18

You would plot a graph of Product concentration over time and use the initial, most likely linear, gradient to find the initial rate.

Question 19

Explain the Lineweaver-Burk plot (also called the double reciprocal plot) for the graphical
determination of the parameters of the Michaelis-Menten expression for enzyme kinetics from a
set of experimental initial rate data.

Answer 19

Taking the reciprocal of the Michaelis-Menten expression we are able to produce a linear equation for use on a graph. The gradient of the graph will be Km/vm so we can easily find Km, the concentration of substrate when the reaction is at half its rate.

Question 20

What are the requirements for growth and division (multiplication) of a cell culture?

Answer 20

Sterilised nutrients
Maintain correct pH, temperature and pressure
Add air (sparge) or other gases as required

Question 21

Using a sketch, explain briefly various phases of microbial growth in a typical batch culture.

Answer 21

Lag-Acceleration-Exponential-Deceleration- Stationary-Death

Question 22

Write a general mass balance for a batch bioreactor (using y to indicate any compound).

Answer 22

.

Question 23

Define the volumetric rate in “biochemical engineering”

Answer 23

The amount of material produced or used up, per volume, per time

Question 24

Define the specific rate in “biochemical engineering”.

Answer 24

Volumetric rate/Viable biomass concentration

Question 25

Why do we need to use specific rates in modelling microbial activity in bioreactors?

Answer 25

It allows comparison of performance in the same culture or different cultures at a cellular level

Question 26

Write the typical mathematical expressions (defining the nomenclature) for the volumetric rates
and specific rates of cell growth, cell death, secreted product formation, maintenance energy
requirement, and substrate (e.g. carbon and energy source) utilisation.

Answer 26

.

Question 27

Write the Monod expression for cell growth and define the nomenclature used. (Sometimes
Monod growth kinetics is referred to as the Michaelis-Menten type growth kinetics although
strictly speaking, Michaelis-Menten kinetics is originally used for enzyme kinetics. The equation
for Monod growth kinetics and Michaelis-Menten enzyme kinetics are the same, only the notation
for the parameters may be different.)

Answer 27

.

Question 28

Explain the Lineweaver-Burk plot (also called the double reciprocal plot) for the graphical
determination of the parameters of the Monod expression for microbial growth from a set of batch
data (This is the same double reciprocal plot used for enzyme kinetics, only the notation for the
parameters is different).

Answer 28

Same applies as using t lineweaver-burk plot for Michaelis-Menten

Question 29

Briefly explain the Luedeking-Piret expression (model) for product formation. How would you
obtain the values of its kinetic parameters from a set of batch culture data?

Answer 29

Divide both sides by cell concentration, then plot Rp/Xv against mu, to find the alpha and beta parameters.

Question 30

Define the yield factors for biomass and a secreted product on carbon substrate consumed.

Answer 30

Substrate is used to produce both the cell mass and the product so individual yields are calculated for the cell growth and product.

Question 31

Define doubling time

Answer 31

It is the time required for biomass to double in quanitity.