Quick Core Biochemistry Questions and Answers. 

 

 

1. Q: What is the central dogma of molecular biology?

   A: The central dogma states that genetic information flows from DNA to RNA to protein.

 

2. Q: What is the primary function of enzymes in biochemical reactions?

   A: Enzymes serve as catalysts, speeding up biochemical reactions without being consumed in the process.

 

3. Q: What is the structure of DNA?

   A: DNA (deoxyribonucleic acid) is a double-stranded helical molecule composed of nucleotides. Each nucleotide consists of a sugar (deoxyribose), a phosphate group, and one of four nitrogenous bases: adenine (A), thymine (T), cytosine (C), or guanine (G).

 

4. Q: What is ATP and its role in cellular energy metabolism?

   A: ATP (adenosine triphosphate) is a molecule that serves as the primary energy currency in cells. It releases energy when its terminal phosphate group is cleaved, providing energy for cellular processes.

 

5. Q: What is the difference between a saturated and an unsaturated fatty acid?

   A: A saturated fatty acid contains only single bonds between carbon atoms in its hydrocarbon chain, while an unsaturated fatty acid has one or more double bonds.

 

6. Q: What is the role of the citric acid cycle (Krebs cycle) in cellular respiration?

   A: The citric acid cycle is a series of chemical reactions that oxidize acetyl-CoA, producing ATP, NADH, and FADH2, which serve as electron carriers for the electron transport chain.

 

7. Q: What is the primary function of carbohydrates in cells?

   A: Carbohydrates serve as a source of energy, a structural component of cells, and play roles in cell signaling and recognition.

 

8. Q: What is the difference between DNA replication and transcription?

   A: DNA replication is the process of copying DNA to produce an identical DNA molecule, while transcription is the synthesis of RNA using a DNA template.

 

9. Q: What is the structure of an amino acid?

   A: Amino acids consist of an amino group, a carboxyl group, and a side chain (R-group) attached to a central carbon atom.

 

10. Q: What is the role of ribosomes in protein synthesis?

    A: Ribosomes are cellular structures where protein synthesis occurs. They read the mRNA sequence and facilitate the assembly of amino acids into a polypeptide chain.

 

11. Q: What is the function of the Golgi apparatus in cells?

    A: The Golgi apparatus modifies, sorts, and packages proteins and lipids into vesicles for transportation within and outside the cell.

 

12. Q: What is the process of glycolysis?

    A: Glycolysis is the metabolic pathway that breaks down glucose into two molecules of pyruvate, generating a small amount of ATP and NADH in the process.

 

13. Q: What are the primary types of RNA involved in protein synthesis?

    A: The primary types of RNA involved in protein synthesis are messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).

 

14. Q: What is the role of cholesterol in the body?

    A: Cholesterol is an important component of cell membranes and is also a precursor for the synthesis of steroid hormones and bile acids.

 

15. Q: What is the function of the electron transport chain in cellular respiration?

    A: The electron transport chain is a series of proteins located in the inner mitochondrial membrane that transfers electrons, derived from NADH and FADH2, to generate ATP through oxidative phosphorylation.

 

16. Q: What is the significance of the pH scale in biochemistry?

    A: The pH scale measures the acidity or alkalinity of a solution. It is important in biochemistry as it affects enzyme activity, protein structure, and other biological processes.

 

17. Q: What is the difference between prokaryotic and eukaryotic cells?

    A: Prokaryotic cells lack a nucleus and membrane-bound organelles, while eukaryotic cells have a nucleus and membrane-bound organelles.

 

18. Q: What is the function of DNA polymerase in DNA replication?

    A: DNA polymerase is an enzyme that catalyzes the synthesis of new DNA strands during replication, using existing DNA strands as templates.

 

19. Q: What is the role of coenzymes in biochemical reactions?

    A: Coenzymes are small organic molecules that work with enzymes to facilitate and regulate biochemical reactions. They often act as carriers of specific functional groups or electrons.

 

20. Q: What is the difference between competitive and non-competitive inhibitors?

    A: Competitive inhibitors bind to the active site of an enzyme, competing with the substrate, while non-competitive inhibitors bind to a different site, causing a conformational change that inhibits enzyme activity.

 

21. Q: What is the structure of a nucleotide?

    A: A nucleotide consists of a sugar molecule (ribose or deoxyribose), a phosphate group, and a nitrogenous base (adenine, thymine, cytosine, guanine, or uracil).

 

22. Q: What is the role of the endoplasmic reticulum in cells?

    A: The endoplasmic reticulum is involved in protein synthesis, lipid metabolism, and calcium storage. It has rough ER, which is studded with ribosomes, and smooth ER, which lacks ribosomes.

 

23. Q: What is the difference between catabolism and anabolism?

    A: Catabolism refers to the breakdown of complex molecules into simpler ones, releasing energy. Anabolism is the synthesis of complex molecules from simpler ones, requiring energy input.

 

24. Q: What is the function of DNA helicase in DNA replication?

    A: DNA helicase is an enzyme that unwinds the double helix structure of DNA, separating the two strands during replication.

 

25. Q: What are enzymes and how do they catalyze reactions?

    A: Enzymes are proteins that lower the activation energy required for a chemical reaction, facilitating the conversion of substrates into products.

 

26. Q: What is the role of NAD+ (nicotinamide adenine dinucleotide) in cellular metabolism?

    A: NAD+ is a coenzyme that functions as an electron carrier in redox reactions, accepting and donating electrons during various metabolic pathways.

 

27. Q: What is the structure and function of the cell membrane?

    A: The cell membrane consists of a phospholipid bilayer with embedded proteins. It regulates the passage of substances in and out of the cell, maintains cell integrity, and facilitates cellular communication.

 

28. Q: What is the difference between primary, secondary, tertiary, and quaternary structures of proteins?

    A: The primary structure is the linear sequence of amino acids in a protein, while the secondary structure refers to local folding patterns (e.g., alpha helices, beta sheets). Tertiary structure is the overall 3D conformation of a single polypeptide chain, and quaternary structure refers to the arrangement of multiple protein subunits.

 

29. Q: What is the role of DNA ligase in DNA replication?

    A: DNA ligase is an enzyme

 

 that seals the gaps in the DNA backbone during replication by catalyzing the formation of phosphodiester bonds between adjacent nucleotides.

 

30. Q: What is the difference between an exergonic and endergonic reaction?

    A: An exergonic reaction releases energy, while an endergonic reaction requires an input of energy to proceed.

BIOCHEMICAL CALCULATIONS QUESTIONS AND ANSWERS 

Many new students often ask questions like: Is there calculations in biochemistry? What is the formula for biochemistry calculation? Should a biochemistry student know mathematics? Etc. Here are some biochemistry math questions and answers. These problems and direct answers will assist students to quickly revise for examination:

 

1. What is the pH of a solution with a hydrogen ion concentration of 1 x 10^-4 M? Answer: pH 4.

2. How many moles of glucose (C6H12O6) are present in 500 mL of a 0.1 M glucose solution? Answer: 0.05 moles.

3. If the molar extinction coefficient of a substance is 10,000 M^-1cm^-1 and the absorbance is 0.4, what is the concentration of the substance in the solution? Answer: 0.04 M.

4. Calculate the molecular weight of a peptide with the amino acid sequence Gly-Ala-Lys-Asp. Answer: 435.4 g/mol.

5. How many ATP molecules can be generated from the complete oxidation of one molecule of glucose? Answer: 36-38 ATP.

6. What is the molar concentration of a 2% (w/v) solution of sodium chloride (NaCl)? Answer: Approximately 0.34 M.

7. Calculate the isoelectric point (pI) of a protein with pKa values of 3.5 and 9.0. Answer: pI 6.25.

8. What is the molecular weight of DNA fragment with 500 base pairs? Answer: Approximately 165,000 g/mol.

9. Calculate the volume of a 0.25 M solution of NaOH required to neutralize 25 mL of 0.1 M HCl. Answer: 10 mL.

10. How many molecules are in 2 moles of glucose (C6H12O6)? Answer: 1.21 x 10^24 molecules.

11. If a reaction has a rate constant of 0.02 s^-1 and the initial concentration is 0.1 M, what will be the concentration after 10 seconds? Answer: 0.006 M.

12. What is the pKa of an acid when the ratio of its conjugate base to acid is 10:1? Answer: pKa 1.

13. Calculate the osmolarity of a 0.9% (w/v) sodium chloride (NaCl) solution. Answer: Approximately 308 mOsm.

14. If a sample has an absorbance of 0.6 and a path length of 1 cm, what is the concentration of the substance with an extinction coefficient of 2000 M^-1cm^-1? Answer: 0.3 M.

15. How many grams of ethanol (C2H5OH) are needed to make a 0.5 M solution with a volume of 250 mL? Answer: 23.5 grams.

16. Calculate the specific activity of an enzyme that catalyzes the conversion of 1 μmol of substrate per minute, using a 0.1 mg enzyme preparation. Answer: 10,000 units/mg.

17. What is the percent composition of carbon (C) in glucose (C6H12O6)? Answer: Approximately 40%.

18. If the absorbance of a solution is 0.8 and the path length is 2 cm, what is the molar absorptivity (ε) of the substance? Answer: 0.4 M^-1cm^-1.

19. How many amino acids are present in a protein with a molecular weight of 100,000 g/mol? Answer: Approximately 909 amino acids.

20. Calculate the turnover number of an enzyme that converts 10 μmol of substrate per minute using 1 μg of enzyme. Answer: 10,000 min^-1.

21. What is the molar concentration of a solution containing 0.5 moles of solute in 2 liters of solvent? Answer: 0.25 M.

22. If a reaction has a rate constant of 0.05 M^-1s^-1 and the initial concentration is 0.2 M, what will be the concentration after 30 seconds? Answer: 0.005 M.

23. Calculate the number of water molecules in 1 mole of water (H2O). Answer: 6.022 x 10^23 molecules.

24. How many milligrams of a compound with a molecular weight of 250 g/mol are needed to make a 0.1 M solution with a volume of 100 mL? Answer: 2.5 grams.

25. What is the percent composition of nitrogen (N) in ammonia (NH3)? Answer: Approximately 82%.

26. Calculate the molecular weight of a nucleotide with the sequence ACGT. Answer: Approximately 333 g/mol.

27. How many grams of NaCl are needed to make 500 mL of a 0.5 M solution? Answer: 29.2 grams.

28. Calculate the molarity of a solution containing 2 moles of solute in 500 mL of solvent. Answer: 4 M.

29. What is the dilution factor if 5 mL of a solution is diluted to a final volume of 100 mL? Answer: 1/20 or 0.05.

30. How many kilocalories are produced from the complete oxidation of one mole of glucose? Answer: Approximately 686 kcal.

31. Calculate the volume of a 2 M HCl solution required to neutralize 10 mL of 1 M NaOH. Answer: 20 mL.

32. What is the molecular weight of a nucleic acid with a sequence of 200 bases? Answer: Approximately 66,000 g/mol.

33. How many grams of sucrose (C12H22O11) are present in 250 mL of a 0.5 M sucrose solution? Answer: 149 grams.

34. Calculate the pKa of an acid when the ratio of its conjugate base to acid is 1:10. Answer: pKa 1.

35. What is the molecular weight of a tripeptide with the amino acid sequence Val-Leu-Gly? Answer: 315.4 g/mol.

36. How many ATP molecules can be generated from the complete oxidation of one mole of fatty acid with 18 carbon atoms? Answer: Approximately 146 ATP.

37. Calculate the molarity of a solution containing 0.5 moles of solute in 250 mL of solvent. Answer: 2 M.

38. What is the concentration of a solution if 25 mL of a 0.2 M solution is diluted to a final volume of 500 mL? Answer: 0.01 M.

39. How many molecules are in 5 grams of glucose (C6H12O6)? Answer: 1.68 x 10^22 molecules.

40. Calculate the absorbance of a solution with a concentration of 0.1 M and an extinction coefficient of 1000 M^-1cm^-1 using a path length of 0.5 cm. Answer: 0.05.

41. What is the percent composition of oxygen (O) in ethanol (C2H5OH)? Answer: Approximately 53%.

42. Calculate the molar absorptivity (ε) of a substance if its absorbance is 0.5 and the path length is 1 cm with a concentration of 0.2 M. Answer: 2

 

.5 M^-1cm^-1.

43. How many amino acids are present in a protein with a molecular weight of 50,000 g/mol? Answer: Approximately 454 amino acids.

44. What is the turnover number of an enzyme that converts 1 μmol of substrate per minute using 0.1 mg of enzyme? Answer: 10,000 min^-1.

45. Calculate the number of carbon atoms in 2 moles of glucose (C6H12O6). Answer: 72 moles.

46. How many milliliters of a 0.1 M NaOH solution are needed to neutralize 50 mL of 0.2 M HCl? Answer: 25 mL.

47. What is the molarity of a solution containing 0.25 moles of solute in 500 mL of solvent? Answer: 0.5 M.

48. Calculate the dilution factor if 2 mL of a solution is diluted to a final volume of 100 mL. Answer: 1/50 or 0.02.

49. How many kilojoules are produced from the complete oxidation of one mole of glucose? Answer: Approximately 2,840 kJ.

50. Calculate the volume of a 3 M NaOH solution required to neutralize 100 mL of 0.5 M HCl. Answer: 16.67 mL.

 

Please note that some of these calculations have been rounded to a specific number of significant figures. Methods of these calculations amongst others will be shown in subsequent posts.

Thanks for choosing Biochemz.com!

CALCULATIONS IN NUCLEIC ACIDS

30 CALCULATION QUESTIONS AND ANSWERS RELATED TO NUCLEIC ACIDS

 

Question 1:

What is the molecular weight of a single nucleotide with the sequence "A" (adenine)?

 

Answer 1:

The molecular weight of a single nucleotide with the sequence "A" is approximately 329.2 g/mol.

 

Question 2:

How many hydrogen bond interactions are there between the base pairs adenine (A) and thymine (T) in a DNA double helix?

 

Answer 2:

There are two hydrogen bond interactions between adenine (A) and thymine (T) in a DNA double helix.

 

Question 3:

Calculate the molar concentration (in mol/L) of a DNA solution with an absorbance of 1.5 at 260 nm and a path length of 1 cm, given the molar absorptivity is 13,000 M^-1cm^-1.

 

Answer 3:

Molar concentration = Absorbance / (Molar absorptivity × Path length)

Molar concentration = 1.5 / (13,000 M^-1cm^-1 × 1 cm) ≈ 0.000115 mol/L

 

Question 4:

Given a DNA strand with the sequence 5'-ATCGGTA-3', what is the complementary RNA sequence?

 

Answer 4:

The complementary RNA sequence to 5'-ATCGGTA-3' is 5'-UACCGAU-3'.

 

Question 5:

If a DNA double helix contains 30% adenine (A), what percentage of the bases will be guanine (G)?

 

Answer 5:

Since adenine (A) pairs with thymine (T) and guanine (G) pairs with cytosine (C), if adenine is 30%, then guanine will also be 30%.

 

Question 6:

Calculate the melting temperature (Tm) of a DNA duplex with the sequence 5'-GCTAATCG-3', using the formula: Tm = 2°C × (A + T) + 4°C × (G + C), where A, T, G, and C are the percentages of the respective bases in the sequence.

 

Answer 6:

Given the sequence is 5'-GCTAATCG-3':

A = 25% (adenine), T = 25% (thymine), G = 25% (guanine), C = 25% (cytosine)

 

Tm = 2°C × (25% + 25%) + 4°C × (25% + 25%) = 50°C + 100°C = 150°C

 

Question 7:

What is the charge of a DNA strand with 30 cytosine (C) bases and 20 guanine (G) bases at pH 7?

 

Answer 7:

The charge of a DNA strand can be calculated using the formula: Charge = (# of positively charged groups) - (# of negatively charged groups)

 

In DNA, cytosine (C) and guanine (G) have an extra amino group, making them positively charged. At pH 7, both groups are fully protonated.

 

Number of positively charged groups = 30 (cytosine) + 20 (guanine) = 50

Number of negatively charged groups = 50 (phosphate backbone)

 

Charge = 50 - 50 = 0

 

So, the DNA strand has a net charge of 0 at pH 7.

 

Question 8:

If a DNA molecule is 120 base pairs long, how many complete turns does the double helix make?

 

Answer 8:

In B-DNA (common DNA conformation), one complete turn of the DNA helix occurs every 10.4 base pairs.

 

Number of complete turns = 120 base pairs / 10.4 base pairs/turn ≈ 11.54 turns

 

Question 9:

Calculate the length of a DNA molecule in nm if it contains 250 base pairs.

 

Answer 9:

In B-DNA, each base pair contributes approximately 0.34 nm to the length of the DNA molecule.

 

Length of DNA = 250 base pairs × 0.34 nm/base pair ≈ 85 nm

 

Question 10:

What is the concentration of a 250 bp DNA solution in ng/μL if its molar concentration is 0.1 mol/L?

 

Answer 10:

To convert molar concentration (mol/L) to mass concentration (ng/μL), we need to use the molecular weight of the DNA molecule.

 

Given: Molecular weight of a double-stranded DNA base pair = 650 g/mol

250 base pairs = 250 bp × 650 g/mol ≈ 162,500 g/mol

 

Mass concentration (ng/μL) = Molar concentration (mol/L) × Molecular weight (g/mol)

Mass concentration = 0.1 mol/L × 162,500 g/mol ≈ 16,250 ng/μL

 

Question 11:

A DNA sample absorbs light at 280 nm with an absorbance of 0.8. Calculate the concentration of the DNA sample in mg/mL, given its molar absorptivity at 280 nm is 30,000 M^-1cm^-1.

 

Answer 11:

Molar concentration (mol/L) = Absorbance / (Molar absorptivity × Path length)

Path length = 1 cm (standard cuvette)

 

Molar concentration = 0.8 / (30,000 M^-1cm^-1 × 1 cm) ≈ 0.00002667 mol/L

 

To convert molar concentration to mg/mL, we need the molecular weight of the DNA. Let's assume it is 660 g/mol (average molecular weight for a DNA base pair).

 

Mass concentration (mg/mL) = Molar concentration (mol/L) × Molecular weight (g/mol)

Mass concentration ≈ 0.00002667 mol/L × 660 g/mol ≈ 0.0176 mg/mL

 

Question 12:

If a DNA molecule has a total of 500 nucleotides, how many phosphate groups are present in the backbone?

 

Answer 12:

In DNA, each nucleotide contains one phosphate group in the backbone.

 

Number of phosphate groups = 500 nucleotides

 

Question 13:

Calculate the percentage of cytosine (C) bases in a DNA sequence with the following composition: 30% adenine (A), 25% thymine (T), 20% cytosine (C), and 25% guanine (G).

 

Answer 13:

Percentage of cytosine (C) = 20%

 

Question 14:

What is the total number of hydrogen bonds present in a DNA double helix with 500 base pairs?

 

Answer 14:

In a DNA double helix, there are two hydrogen bonds between adenine (A) and thymine (T), and three hydrogen bonds between guanine (G) and cytosine (C).

 

Total number of hydrogen bonds = (Number of A-T pairs × 2) + (Number of G-C pairs × 3)

Assuming equal number of A-T and G-C pairs in a random sequence:

Number of A-T pairs = 500 base pairs / 2 = 250 pairs

Number of G-C pairs = 500 base pairs / 2 = 250 pairs

 

Total number of hydrogen bonds

 

 = (250 × 2) + (250 × 3) = 500 + 750 = 1250 hydrogen bonds

 

Question 15:

If a DNA strand contains 40% guanine (G) bases, what percentage of the bases will be adenine (A)?

 

Answer 15:

Since guanine (G) pairs with cytosine (C) and adenine (A) pairs with thymine (T), the percentages of G and C must add up to the percentages of A and T. Therefore, if G is 40%, then A will also be 40%.

 

Question 16:

Calculate the absorbance of a DNA solution with a molar concentration of 0.05 mol/L and a path length of 1 cm, given that its molar absorptivity at 260 nm is 12,000 M^-1cm^-1.

 

Answer 16:

Absorbance = Molar concentration × Molar absorptivity × Path length

Absorbance = 0.05 mol/L × 12,000 M^-1cm^-1 × 1 cm = 0.6

 

Question 17:

What is the complementary DNA sequence to 5'-TACGTA-3'?

 

Answer 17:

The complementary DNA sequence to 5'-TACGTA-3' is 5'-TACGTA-3'.

 

Question 18:

If a DNA molecule contains 20% adenine (A), what percentage of the bases will be thymine (T)?

 

Answer 18:

Since adenine (A) pairs with thymine (T) in DNA, if A is 20%, then T will also be 20%.

 

Question 19:

Calculate the GC content (percentage of guanine and cytosine bases) in a DNA sequence with the following composition: 30% adenine (A), 25% thymine (T), 20% cytosine (C), and 25% guanine (G).

 

Answer 19:

GC content = Percentage of guanine (G) + Percentage of cytosine (C) = 20% + 25% = 45%

 

Question 20:

If a DNA double helix is 50 nm long, how many base pairs does it contain?

 

Answer 20:

In B-DNA, each base pair contributes approximately 0.34 nm to the length of the DNA molecule.

 

Number of base pairs = Length of DNA / Length per base pair

Number of base pairs = 50 nm / 0.34 nm/base pair ≈ 147 base pairs

 

Question 21:

What is the concentration of a 150 bp DNA solution in μg/mL if its molar concentration is 0.02 mol/L?

 

Answer 21:

To convert molar concentration (mol/L) to mass concentration (μg/mL), we need to use the molecular weight of the DNA molecule.

 

Given: Molecular weight of a double-stranded DNA base pair = 650 g/mol

150 base pairs = 150 bp × 650 g/mol ≈ 97,500 g/mol

 

Mass concentration (μg/mL) = Molar concentration (mol/L) × Molecular weight (μg/mol)

Mass concentration = 0.02 mol/L × 97,500 μg/mol ≈ 1950 μg/mL

 

Question 22:

If a DNA sample has an A260/A280 ratio of 1.8, is it pure, or does it contain protein contamination?

 

Answer 22:

An A260/A280 ratio of 1.8 indicates that the DNA sample is relatively pure and does not contain significant protein contamination. DNA typically has an A260/A280 ratio between 1.7 and 1.9.

 

Question 23:

Calculate the length of an RNA molecule in nm if it contains 200 nucleotides.

 

Answer 23:

In RNA, each nucleotide contributes approximately 0.33 nm to the length of the RNA molecule.

 

Length of RNA = 200 nucleotides × 0.33 nm/nucleotide ≈ 66 nm

 

Question 24:

What is the percentage of adenine (A) bases in a DNA sequence with the following composition: 30% adenine (A), 25% thymine (T), 20% cytosine (C), and 25% guanine (G)?

 

Answer 24:

Percentage of adenine (A) = 30%

 

Question 25:

How many hydrogen bond interactions are there between the base pairs guanine (G) and cytosine (C) in a DNA double helix?

 

Answer 25:

There are three hydrogen bond interactions between guanine (G) and cytosine (C) in a DNA double helix.

 

Question 26:

Calculate the molar concentration (in mol/L) of a DNA solution with an absorbance of 0.6 at 260 nm and a path length of 2 cm, given the molar absorptivity is 15,000 M^-1cm^-1.

 

Answer 26:

Molar concentration = Absorbance / (Molar absorptivity × Path length)

Molar concentration = 0.6 / (15,000 M^-1cm^-1 × 2 cm) ≈ 0.02 mol/L

 

Question 27:

Given a DNA strand with the sequence 5'-CGATCGTA-3', what is the complementary RNA sequence?

 

Answer 27:

The complementary RNA sequence to 5'-CGATCGTA-3' is 5'-GUAGCAUC-3'.

 

Question 28:

If a DNA double helix contains 40% thymine (T), what percentage of the bases will be adenine (A)?

 

Answer 28:

Since adenine (A) pairs with thymine (T) in DNA, if T is 40%, then A will also be 40%.

 

Question 29:

Calculate the melting temperature (Tm) of a DNA duplex with the sequence 5'-ATTAGCCG-3', using the formula: Tm = 2°C × (A + T) + 4°C × (G + C), where A, T, G, and C are the percentages of the respective bases in the sequence.

 

Answer 29:

Given the sequence is 5'-ATTAGCCG-3':

A = 25% (adenine), T = 25% (thymine), G = 25% (guanine), C = 25% (cytosine)

 

Tm = 2°C × (25% + 25%) + 4°C × (25% + 25%) = 100°C

 

Question 30:

What is the charge of a DNA strand with 20 cytosine (C) bases and 30 guanine (G) bases at pH 7?

 

Answer 30:

The charge of a DNA strand can be calculated using the formula: Charge = (# of positively charged groups) - (# of negatively charged groups)

 

In DNA, cytosine (C) and guanine (G) have an extra amino group, making them positively charged. At pH 7, both groups are fully protonated.

 

Number of positively charged groups = 20 (cytosine) + 30 (guanine) = 50

Number of negatively charged groups = 50 (phosphate backbone)

 

Charge = 50 - 50 = 0

 

So, the DNA strand has a net charge of 0 at pH 7.

 

 

 

 

SOME COMMON PRACTICE QUESTIONS IN BIOCHEMICAL BASIS OF DISEASES

 

Question 1: Calculate the BMI (Body Mass Index) of a person weighing 70 kg and having a height of 1.75 meters.

Answer 1: BMI = weight (kg) / height (m)^2 = 70 / (1.75^2) = 22.86

 

Question 2: A patient's blood glucose level is 180 mg/dL. Convert this value to mmol/L.

Answer 2: Conversion factor: 1 mg/dL = 0.0555 mmol/L. Thus, 180 mg/dL * 0.0555 = 9.99 mmol/L.

 

Question 3: Calculate the pH of a solution with a hydrogen ion concentration of 2.5 x 10^-4 M.

Answer 3: pH = -log[H+] = -log(2.5 x 10^-4) = 3.60

 

Question 4: An enzyme catalyzes a reaction at a rate of 2.5 micromoles/min. Calculate the turnover number (kcat) if the enzyme concentration is 0.02 mM.

Answer 4: kcat = (enzyme concentration in M) / (enzyme rate in mol/s) = (0.02 x 10^-3) / (2.5 x 10^-6) = 8 x 10^3 s^-1

 

Question 5: If the concentration of enzyme E is 0.1 μM and the dissociation constant (Kd) for its substrate binding is 5 nM, calculate the fractional saturation of the enzyme at equilibrium.

Answer 5: Fractional saturation = [E] / (Kd + [E]) = (0.1 x 10^-6) / (5 x 10^-9 + 0.1 x 10^-6) ≈ 0.952

 

Question 6: Calculate the osmolarity of a solution containing 1.5 moles of NaCl, 2 moles of glucose, and 3 moles of urea in 1 liter of water.

Answer 6: Osmolarity = (moles of solute) / (volume of solution in liters) = (1.5 + 2 + 3) / 1 = 6 Osm/L

 

Question 7: If a protein has an extinction coefficient (ε) of 28000 M^-1cm^-1 and the absorbance at 280 nm is 0.75, calculate the protein concentration.

Answer 7: Protein concentration (mg/mL) = (Absorbance / ε) = 0.75 / 28000 = 2.68 x 10^-5 M = 26.8 μM

 

Question 8: A patient's serum creatinine level is 1.2 mg/dL. Convert this value to μmol/L.

Answer 8: Conversion factor: 1 mg/dL = 88.4 μmol/L. Thus, 1.2 mg/dL * 88.4 = 106.08 μmol/L.

 

Question 9: If a reaction has a rate constant (k) of 0.02 s^-1 and the initial concentration of the reactant is 0.1 M, calculate the concentration after 100 seconds.

Answer 9: Concentration after time (C) = [A]0 * e^(-k*t) = 0.1 * e^(-0.02 * 100) ≈ 0.049 M

 

Question 10: Calculate the delta G°' (standard Gibbs free energy change) for a reaction if the equilibrium constant (Keq) is 5 and the gas constant (R) is 8.314 J/mol·K at 298 K.

Answer 10: ΔG°' = -RT * ln(Keq) = -8.314 * 298 * ln(5) ≈ -2982.5 J/mol