BioChem

Question 1

Which molecule is the primary energy currency of the cell?

A. ATP

B. NADH

C. FADH₂

D. GTP

Answer 1

A. ATP

Question 2

Which class of biomolecule contains peptide bonds?

A. Carbohydrates

B. Lipids

C. Proteins

D. Nucleic acids

Answer 2

C. Proteins

Question 3

The reaction C6​H12​O6​→2C2​H5​OH+2CO2 describes:

A. Aerobic respiration

B. Photosynthesis

C. Alcoholic fermentation

D. Lactic acid fermentation

Answer 3

C. Alcoholic fermentation

Question 4

Which base-pairing is correct in DNA?

A. A—C

B. A—T

C. G—T

D. C—A

Answer 4

B. A—T

Question 5

Which vitamin is a precursor for NAD+/NADP+?

A. Vitamin C (ascorbate)

B. Niacin (vitamin B)

C. Riboflavin

D. Vitamin

Answer 5

B. Niacin (vitamin B3​)

Question 6

What is the molar mass of glucose (C6​H12​O6​)

A. 150.13g⋅mol−1
B. 180.16g⋅mol−1
C. 162.14g⋅mol−1
D. 120.10g⋅mol−1

Answer 6

B. 180.16g⋅mol−1

Question 7

Which bond type stabilizes α-helices and β-sheets in proteins?

A. Disulfide bonds

B. Hydrogen bonds

C. Ionic bonds

D. Van der Waals only

Answer 7

B. Hydrogen bonds

Question 8

Which lipid class contains glycerol, two fatty acids and a phosphate group?

A. Triacylglycerol

B. Phospholipid

C. Steroid

D. Glycolipid

Answer 8

B. Phospholipid

Question 9

The Michaelis constant Km is best described as:

A. Substrate concentration at 1/2Vmax​
B. Max reaction velocity
C. Turnover number
D. Equilibrium constant

Answer 9

A. Substrate concentration at 1/2Vmax​

Question 10

In glycolysis, the net ATP yield per glucose (substrate-level only) is:

A. 1 ATP

B. 2 ATP

C. 4 ATP

D. 6 ATP

Answer 10

B. 2 ATP

Question 11

Which functional group in amino acids is ionizable at physiological pH?

A. Methyl group

B. Hydroxyl group

C. Amino and carboxyl groups

D. Ether group

Answer 11

C. Amino and carboxyl groups

Question 12

If 0.050mol of glucose (C6​H12​O6​) undergoes complete oxidation (C6​H12​O6​+6O2​→6CO2​+6H2​O), how many moles of CO2​ are produced?

A. 0.050mol
B. 0.250mol
C. 0.300mol
D. 0.600mol

Answer 12

C. 0.300mol

Question 13

Which cofactor directly accepts electrons in the form of hydride (H−) in dehydrogenase reactions?
A. FAD

B. NAD+

C. CoA

D. ATP

Answer 13

B. NAD+

Question 14

The Henderson–Hasselbalch equation is pH=pKa​+log([A−]/[HA]). It is used to:

A. Calculate buffer ionic strength
B. Predict pH of buffer systems
C. Determine redox potential
D. Calculate Gibbs free energy

Answer 14

B. Predict pH of buffer systems

Question 15

An enzyme has Vmax=100μmol⋅min−1 and at [S]=Km​ the rate=40μmol⋅min−1. What is likely the true Vmax​?
A. 40μmol⋅min−1
B. 80μmol⋅min−1
C. 100μmol⋅min−1
D. 120μmol⋅min−1

Answer 15

B. 80μmol⋅min−1

Question 16

Which process occurs in the mitochondrion inner membrane?

A. Glycolysis

B. Citric acid cycle (matrix)

C. Electron transport chain / oxidative phosphorylation

D. Pentose phosphate pathway

Answer 16

C. Electron transport chain / oxidative phosphorylation

Question 17

What is the primary role of coenzyme A (CoA) in metabolism?

A. Electron carrier

B. Acyl group carrier (forms thioesters)

C. Proton pump

D. Structural lipid

Answer 17

B. Acyl group carrier (forms thioesters)

Question 18

A crude enzyme preparation has activity 500U in 10mL. What is its specific activity if protein content is 50mg? (U=μmol⋅min−1; report U⋅mg−1)

A. 0.1U⋅mg−1
B. 1.0U⋅mg−1
C. 10U⋅mg−1
D. 100U⋅mg−1

Answer 18

C. 10U⋅mg−1

Question 19

Which pathway provides NADPH for biosynthesis and ribose-5-phosphate for nucleotide synthesis?

A. Glycolysis

B. TCA cycle

C. Pentose phosphate pathway

D. beta-oxidation

Answer 19

C. Pentose phosphate pathway

Question 20

In enzyme kinetics, turnover number ($k_{\text{cat}}$) equals:

A. Vmax / [E]

B. Km / Vmax

C.V / [S]

D. Km \ [E]

Answer 20

A. Vmax / [E]

Question 21

The pKa of acetic acid is 4.76. What is the pH of a solution containing 0.10 M CH₃COOH and 0.10 M CH₃COO⁻?

A. 3.76

B. 4.76

C. 5.76

D. 6.76

Answer 21

B. 4.76

Question 22

Which amino acid is achiral (no stereocenter)?

A. Alanine

B. Glycine

C. Valine

D. Leucine

Answer 22

B. Glycine

Question 23

Which technique is commonly used to determine protein secondary structure content (α-helix vs β-sheet)?

A. NMR of small ligands

B. Circular dichroism (CD) spectroscopy

C. Gas chromatography

D. Mass spectrometry

Answer 23

B. Circular dichroism (CD) spectroscopy

Question 24

A fermenter contains 20 g·L⁻¹ glucose. How many g·L⁻¹ of ethanol (C₂H₅OH, MW = 46.07 g·mol⁻¹) are produced theoretically by complete conversion if fermentation yield is 0.51 g ethanol per g glucose?

a. 10.2 g·L⁻¹
b. 8.5 g·L⁻¹
c.7.5 g·L⁻¹
d.20.0 g·L⁻¹

Answer 24

a. 10.2 g·L⁻¹

Question 25

Which macromolecule class contains a phosphate backbone? A. Protein B. Carbohydrate C. Nucleic acid (DNA/RNA) D. Lipid

Answer 25

C. Nucleic acid (DNA/RNA)

Question 26

Which statement about enzyme inhibition is correct for competitive inhibitors? a. Decrease Vₘₐₓ, Kₘ unchanged b. Increase Vₘₐₓ, decrease Kₘ c. Vₘₐₓ unchanged, apparent Kₘ increases d. Noncompetitive — both change

Answer 26

c. Vₘₐₓ unchanged, apparent Kₘ increases

Question 27

Convert 150 mg·L⁻¹ glucose to mmol·L⁻¹ (MW glucose = 180.16 g·mol⁻¹). a. 0.83 mmol·L⁻¹ b.0.50 mmol·L⁻¹ c. 1.25 mmol·L⁻¹ d. 2.00 mmol·L⁻¹

Answer 27

a. 0.83 mmol·L⁻¹

Question 28

Which fatty acid term describes no C=C bonds? A. Monounsaturated B. Polyunsaturated C. Saturated D. Trans

Answer 28

C. Saturated

Question 29

Which statement about allosteric enzymes is true? A. Obey Michaelis–Menten strictly B. Show cooperative kinetics and regulation C. Are always monomeric D. Have no regulatory sites

Answer 29

B. Show cooperative kinetics and regulation

Question 30

In oxidative phosphorylation, the proton motive force (pmf) includes which components? a. Only ΔpH b. Only membrane potential (Δψ) c. Both ΔpH and Δψ d. Only ionic strength

Answer 30

c. Both ΔpH and Δψ

Question 31

Which buffer system is commonly used for physiological pH (≈7.4) in biochemical experiments? a.Acetic acid/acetate (pKa 4.76) b. Phosphate (pKa₂ ≈ 7.2) c. Tris (pKa 8.1) d. Citrate (pKa ≈ 3–6)

Answer 31

b. Phosphate (pKa₂ ≈ 7.2)

Question 32

Which technique would you use to measure mRNA levels of a gene quantitatively? A. Western blot B. qPCR (RT-qPCR) C. TLC D. Gel permeation chromatography

Answer 32

B. qPCR (RT-qPCR)

Question 33

A cell culture has biomass concentration X = 2.0 g·L⁻¹ and specific growth rate μ = 0.45 h⁻¹. What is the instantaneous growth rate (dX/dt)? a. 0.90 g·L⁻¹·h⁻¹ b. 0.45 g·L⁻¹·h⁻¹ c. 0.225 g·L⁻¹·h⁻¹ d. 2.45 g·L⁻¹·h⁻¹

Answer 33

a. 0.90 g·L⁻¹·h⁻¹

Question 34

Which enzyme catalyzes DNA synthesis in PCR? a. RNA polymerase b. Taq DNA polymerase c. Ligase d. Reverse transcriptase

Answer 34

b. Taq DNA polymerase

Question 35

In recombinant DNA technology, plasmids are used primarily as: A. Expression inhibitors B. Cloning vectors C. Restriction enzymes D. Cofactors

Answer 35

B. Cloning vectors

Question 36

Which of the following is a selectable marker in plasmid cloning? A. GFP B. Kanamycin resistance gene C. Promoter D. Ori site

Answer 36

B. Kanamycin resistance gene

Question 37

Which technique separates DNA fragments by size using an electric field? A. SDS-PAGE B. Gel electrophoresis C. Centrifugation D. Chromatography

Answer 37

B. Gel electrophoresis

Question 38

The process of introducing foreign DNA into a bacterial cell is called: A. Replication B. Transformation C. Transcription D. Translation

Answer 38

B. Transformation

Question 39

Which enzyme joins DNA fragments covalently? A. DNA ligase B. Restriction endonuclease C. RNA polymerase D. DNA polymerase I

Answer 39

A. DNA ligase

Question 40

The recognition sequence for EcoRI is GAATTC. It produces which type of ends after cleavage? A. Blunt ends B. Sticky ends C. Random breaks D. Circular ends

Answer 40

B. Sticky ends

Question 41

The recognition sequence for EcoRI is GAATTC. It produces which type of ends after cleavage? a. Blunt ends b. Sticky ends c. Random breaks d. Circular ends

Answer 41

b. Sticky ends

Question 42

In $\text{PCR}$, the correct order of steps per cycle is: a. Denaturation → Annealing → Extension b. Annealing → Denaturation → Extension c. Extension → Annealing → Denaturation d. Denaturation → Extension → Annealing

Answer 42

a. Denaturation → Annealing → Extension

Question 43

Which process uses microorganisms to produce ethanol from glucose? A. Aerobic respiration B. Anaerobic fermentation C. $\beta$-oxidation D. Nitrification

Answer 43

B. Anaerobic fermentation

Question 44

Which equipment is essential for sterilizing media in bioprocesses? A. Centrifuge B. Autoclave C. Laminar flow hood D. Filter press

Answer 44

B. Autoclave

Question 45

The maximum specific growth rate (μₘₐₓ) of a microorganism is obtained when: A. Nutrients are limited B. Substrate is saturated C. Product inhibition occurs D. Maintenance dominates

Answer 45

B. Substrate is saturated

Question 46

In a fed-batch process, substrate is: A. Supplied continuously and removed continuously B. Added intermittently, with no outflow C. Never added D. Constantly removed

Answer 46

B. Added intermittently, with no outflow

Question 47

What is the main advantage of immobilized enzymes in industrial processes? A. Lower specificity B. Higher diffusional limitations C. Reusability and stability D. Require cofactors always

Answer 47

C. Reusability and stability

Question 48

Which method can be used for cell disruption? A. Sonication B. Filtration C. Dialysis D. Evaporation

Answer 48

A. Sonication

Question 49

What is the principle of chromatography? A. Separation by charge B. Separation by solubility C. Separation by differential adsorption D. Separation by density only

Answer 49

C. Separation by differential adsorption

Question 50

In protein purification, “salting out” uses which reagent? A. Sucrose B. NaCl C. (NH₄)₂SO₄ D. Ethanol

Answer 50

C. (NH₄)₂SO₄

Question 51

The rate of oxygen transfer in a bioreactor is given by: *Nₒ₂ = kₗa (C - Cₗ)**. What does kₗa represent? A. Volumetric mass transfer coefficient B. Dissolved oxygen concentration C. Diffusion constant D. Henry’s constant

Answer 51

A. Volumetric mass transfer coefficient

Question 52

If kₗa = 120 h⁻¹, C* = 8 mg·L⁻¹, and Cₗ = 3 mg·L⁻¹, calculate Nₒ₂ (mg·L⁻¹·h⁻¹). A. 300 B. 480 C. 600 D. 120

Answer 52

C. 600

Question 53

The doubling time (td) of a microorganism growing at μ = 0.693 h⁻¹ is: a. 0.5 h b. 1.0 h c. 2.0 h d. 3.0 h

Answer 53

b. 1.0 h

Question 54

The Monod equation is μ = μₘₐₓ S / (Kₛ + S). What happens at S ≫ Kₛ? a. μ ≈ 0 b. μ ≈ μₘₐₓ c. μ ≈ S/Kₛ d. μ decreases linearly

Answer 54

b. μ ≈ μₘₐₓ

Question 55

For a chemostat, dilution rate D equals: a. μ b. μₘₐₓ c. S₀/X d. Yield coefficient

Answer 55

a. μ

Question 56

A fermenter operates at D = 0.2 h⁻¹, μₘₐₓ = 0.5 h⁻¹, and Kₛ = 1 g·L⁻¹. Calculate steady-state substrate S = Kₛ D / (μₘₐₓ − D). a. 0.2 g·L⁻¹ b. 0.4 g·L⁻¹ c. 0.67 g·L⁻¹ d. 1.0 g·L⁻¹

Answer 56

c. 0.67 g·L⁻¹

Question 57

Which device measures dissolved oxygen concentration in fermentation? A. Spectrophotometer B. pH electrode C. DO probe (Clark electrode) D. Manometer

Answer 57

C. DO probe (Clark electrode)

Question 58

Genetic engineering of microbes for high-yield enzyme production is called: A. Mutagenesis B. Strain improvement C. Cloning inhibition D. Biofiltration

Answer 58

B. Strain improvement

Question 59

Downstream processing begins with: A. Product recovery B. Cell cultivation C. Sterilization D. Substrate preparation

Answer 59

A. Product recovery

Question 60

Which bioreactor type is best for immobilized cells? A. Stirred-tank B. Airlift C. Fluidized-bed D. Plug-flow

Answer 60

C. Fluidized-bed

Question 61

In recombinant insulin production, the host organism is usually: A. Bacillus subtilis B. Escherichia coli C. Aspergillus niger D. Pseudomonas putida

Answer 61

B. Escherichia coli

Question 62

A continuous stirred tank reactor (CSTR) operates at steady state when: a. Input ≠ Output b. Accumulation = 0 c. μ = 0 d. D > μₘₐₓ

Answer 62

b. Accumulation = 0

Question 63

In upstream processing, “inoculum development” refers to: A. Media formulation B. Sterilization C. Preparation of actively growing cells D. Product recovery

Answer 63

C. Preparation of actively growing cells

Question 64

What is the purpose of sparging in a bioreactor? A. $\text{pH}$ control B. Temperature regulation C. Oxygen supply D. Nutrient mixing only

Answer 64

C. Oxygen supply

Question 65

If yield Yₓ/ₒ₂ = 0.5 g biomass per g O₂, and oxygen uptake rate = 200 mg·L⁻¹·h⁻¹, find biomass formation rate (g·L⁻¹·h⁻¹). A. 0.05 B. 0.1 C. 0.2 D. 0.5

Answer 65

B. 0.1

Question 66

The process of inserting human insulin gene into bacteria to produce insulin is an example of: A. Gene therapy B. Recombinant DNA technology C. Protein denaturation D. Transfection

Answer 66

B. Recombinant DNA technology

Question 67

Which scientist is known as the “Father of Microbiology”? A. Alexander Fleming B. Louis Pasteur C. Robert Koch D. Anton van Leeuwenhoek

Answer 67

B. Louis Pasteur

Question 68

Which structure allows bacterial motility? A. Pili B. Capsule C. Flagella D. Ribosomes

Answer 68

C. Flagella

Question 69

The Gram stain differentiates bacteria based on: A. Size B. Shape C. Cell wall composition D. Metabolic type

Answer 69

C. Cell wall composition

Question 70

Gram-positive bacteria have: A. Thin peptidoglycan and outer membrane B. Thick peptidoglycan and no outer membrane C. No cell wall D. Only lipid membrane

Answer 70

B. Thick peptidoglycan and no outer membrane

Question 71

Which bacterium is used in yogurt production? A. Escherichia coli B. Lactobacillus bulgaricus C. Bacillus subtilis D. Streptococcus pneumoniae

Answer 71

B. Lactobacillus bulgaricus

Question 72

What is the optimal temperature range for mesophilic bacteria? a. 0–10 °C b. 15–45 °C c. 55–80 °C d. >100 °C

Answer 72

b. 15–45 °C

Question 73

Which method is used to sterilize heat-labile solutions? A. Autoclaving B. Dry heat C. Filtration D. Incineration

Answer 73

C. Filtration

Question 74

In a microbial growth curve, the exponential phase corresponds to: A. No growth B. Balanced rapid growth C. Nutrient depletion D. Cell death

Answer 74

B. Balanced rapid growth

Question 75

The logarithmic growth equation for microbes is X = X₀ e^(μt). If X₀ = 0.1 g·L⁻¹, μ = 0.693 h⁻¹, and t = 3 h, find X. a. 0.5 g·L⁻¹ b. 0.8 g·L⁻¹ c. 0.6 g·L⁻¹ d. 0.4 g·L⁻¹

Answer 75

b. 0.8 g·L⁻¹

Question 76

Which structure is responsible for bacterial conjugation? A. Capsule B. Pili (sex pili) C. Flagella D. Endospore

Answer 76

B. Pili (sex pili)

Question 77

Endospores are produced by which genus? A. Escherichia B. Bacillus C. Streptococcus D. Pseudomonas

Answer 77

B. Bacillus

Question 78

The enzyme lysozyme hydrolyzes which component of the bacterial cell wall? A. Lipopolysaccharide B. Peptidoglycan C. Phospholipid D. Teichoic acid

Answer 78

B. Peptidoglycan

Question 79

The generation time of a culture is 30 min. How many generations occur in 5 h? A. 5 B. 8 C. 10 D. 15

Answer 79

C. 10

Question 80

Which metabolic process uses nitrate (NO₃⁻) as the terminal electron acceptor? A. Aerobic respiration B. Denitrification C. Fermentation D. Photosynthesis

Answer 80

B. Denitrification

Question 81

In microbial taxonomy, 16S rRNA sequencing is used because: A. It is variable among strains B. It is universal and conserved C. It mutates rapidly D. It encodes enzymes

Answer 81

B. It is universal and conserved

Question 82

What is the main product of lactic acid fermentation of glucose? A. Ethanol B. Acetic acid C. Lactic acid D. Butanol

Answer 82

C. Lactic acid

Question 83

The selective medium MacConkey agar differentiates based on: A. Glucose oxidation B. Lactose fermentation C. Oxygen requirement D. Gram stain

Answer 83

B. Lactose fermentation

Question 84

What is the total magnification of a 40× objective with a 10× eyepiece? a. 400× b. 40× c. 100× d. 4000×

Answer 84

A. 400x

Question 85

The term “facultative anaerobe” refers to organisms that: a. Require O₂ b. Die in O₂ c. Grow with or without O₂ d. Use only nitrate

Answer 85

c. Grow with or without O₂

Question 86

The phase of bacterial growth with constant population but metabolic activity is the: A. Lag B. Log C. Stationary D. Death

Answer 86

A. Lag

Question 87

Bacterial DNA replication proceeds in which direction? a. 3′→3′ b. 5′→5′ c. 5′→3′ d. Bidirectional only

Answer 87

c. 5′→3′

Question 88

A medium containing known, precise chemical composition is: A. Differential B. Complex C. Defined (synthetic) D. Selective

Answer 88

C. Defined (synthetic)

Question 89

The enzyme responsible for converting hydrogen peroxide to water and oxygen: A. Peroxidase B. Catalase C. Oxidase D. Reductase

Answer 89

B. Catalase

Question 90

In anaerobic respiration, energy yield (ATP per glucose) is generally: a. 2 ATP b. 4 ATP c. 36 ATP d. 38 ATP

Answer 90

a. 2 ATP

Question 91

Which microbial process is used in wastewater treatment for organic degradation? A. Aerobic digestion B. Autolysis C. Denitrification D. Fermentation

Answer 91

A. Aerobic digestion

Question 92

If microbial concentration doubles every 20 min, what is μ (h⁻¹)? (μ = ln 2 / td) a. 1.386 h⁻¹ b. 2.079 h⁻¹ c. 2.080 h⁻¹ d. 3.465 h⁻¹

Answer 92

b. 2.079 h⁻¹

Question 93

A bacterial culture has 10⁶ CFU·mL⁻¹. After a 1:1000 dilution, plate count = 120 CFU. What is original count? a. 1.2×10⁵ CFU·mL⁻¹ b. 1.2×10⁶ c. 1.2×10⁸ d. 1.2×10⁹

Answer 93

a. 1.2×10⁵ CFU·mL⁻¹

Question 94

Which sterilization method uses ethylene oxide gas? A. Autoclaving B. Gas sterilization C. $\text{UV}$ exposure D. Gamma radiation

Answer 94

B. Gas sterilization

Question 95

Which organism fixes atmospheric nitrogen? A. E. coli B. Azotobacter C. Streptococcus D. Lactobacillus

Answer 95

B. Azotobacter

Question 96

What is the role of plasmids in bacteria? A. ATP synthesis B. Antibiotic resistance or gene exchange C. Protein synthesis D. Motility

Answer 96

B. Antibiotic resistance or gene exchange

Question 97

Which microscopy technique gives 3D surface images of microbes? A. Bright field B. Transmission electron (TEM) C. Scanning electron (SEM) D. Phase contrast

Answer 97

C. Scanning electron (SEM)

Question 98

A culture with constant volume and no feed is a: A. Batch culture B. Continuous culture C. Fed-batch D. Chemostat

Answer 98

A. Batch culture

Question 99

In microbial kinetics, maintenance coefficient mₛ represents: A. Biomass yield B. Energy for cell upkeep C. Product inhibition D. Growth rate constant

Answer 99

B. Energy for cell upkeep

Question 100

During fermentation, foaming is controlled by adding: A. Acid B. Antifoam agent C. Nutrient D. Buffer

Answer 100

B. Antifoam agent

Question 101

In a batch fermenter, if initial substrate concentration S₀ = 20 g·L⁻¹ and yield Yₓ/ₛ = 0.5 g·g⁻¹, what is maximum possible biomass concentration X? a. 5 g·L⁻¹ b. 10 g·L⁻¹ c. 15 g·L⁻¹ d. 20 g·L⁻¹

Answer 101

b. 10 g·L⁻¹