DNA questions

If a DNA sample contains 200 nucleotides with the bases adenine and guanine, how many nucleotides with the bases thymine and cytosine does it contain?

1. A 200
2. B 400
3. C 600
4. D 800

Watson and Crick considered that the DNA molecule is made of two strands. Which of the following evidence confirmed their view?

1. A DNA is found in the shape of a helix
2. B The amount of DNA is constant
3. C The sugar-phosphate backbone is not symmetrical
4. D C binds with G, and T binds with A

If one turn of DNA contains 26 hydrogen bonds, what is the ratio of the nitrogenous bases adenine to guanine, respectively?

1. A 1 : 1
2. B 4 : 1
3. C 2 : 3
4. D 1 : 4

The following choices give the numbers of nucleotides of a DNA molecule made of 5 turns. Which of them is NOT correct?

1. A 30 nucleotides (A)
2. B 20 nucleotides (C)
3. C 30 nucleotides (G)
4. D 30 nucleotides (T)

Knowing the total number of nucleotides of DNA, which of the following can NOT be found?

1. A The number of nitrogenous bases
2. B The number of adenine nucleotides
3. C The number of sugar molecules
4. D The number of phosphate groups

Which of the following is responsible for keeping the general shape of DNA stable?

1. A The pentose sugar
2. B The phosphate groups
3. C The nitrogenous bases
4. D The hydrogen bonds

What type of bonds is found in a DNA molecule?

1. A Covalent only
2. B Hydrogen only
3. C Covalent and disulfide
4. D Hydrogen and covalent

Which of the following is correct about DNA?
(1) The number of sugar molecules equals the number of phosphate molecules.
(2) The number of nucleotides equals the number of nitrogenous bases.
(3) It is made of two identical strands.

1. A (1) , (2)
2. B (1) , (3)
3. C (2) , (3)
4. D (1) , (2) , (3)

Which of the following is correct about the percentage of cytosine bases in a DNA molecule?

1. A It equals 50% of the number of guanine bases in the whole molecule
2. B It is the same as the percentage of guanine bases in one strand
3. C It is the same as the percentage of guanine bases in the whole molecule
4. D It is equal in both strands

Which of the following does NOT agree with the results reached by Watson and Crick?

1. A A
2. B B
3. C C
4. D D

Which of the following is a pyrimidine base that binds with another base by two hydrogen bonds in a DNA molecule?

1. A Adenine
2. B Thymine
3. C Guanine
4. D Cytosine

How many nucleotides are there in a piece of a DNA molecule made of two complete turns?

1. A 10
2. B 20
3. C 30
4. D 40

The following figure shows the four types of nucleotides that make up DNA. What do (X), (Y), (Z) and (L) represent, respectively?

1. A Adenine / Thymine / Guanine / Cytosine
2. B Guanine / Cytosine / Thymine / Adenine
3. C Thymine / Adenine / Cytosine / Guanine
4. D Cytosine / Guanine / Adenine / Thymine

DNA samples were separated from a house cat and an English bulldog. Which of the following statements is NOT correct?

1. A The types of nucleotides in the DNA of both animals are the same
2. B The sequence of nucleotides in the DNA of both animals is identical
3. C The number of adenine-containing nucleotides in the cat's DNA equals the number of thymine-containing ones
4. D The number of phosphate groups in the dog's DNA equals the number of nucleotides

From the opposite figure, which represents a segment of a DNA molecule:
Which of the following shows the sequence of nucleotides in the complementary strand?

1. A 3´...C-A-C-T-G-G...5´
2. B 3´...C-C-A-G-T-G...5´
3. C 5´...G-T-G-A-C-C...3´
4. D 3´...G-T-G-A-C-C...5´

From the opposite figure, which represents a segment of a DNA molecule:
How many nucleotides does this figure need to form a complete turn?

1. A 2
2. B 4
3. C 6
4. D 8

From the opposite figure, which represents a segment of a DNA molecule:
How many hydrogen bonds are needed to join the two DNA strands in the opposite figure?

1. A 6
2. B 8
3. C 16
4. D 18

Study the order of the nitrogenous bases in the following part of a DNA strand, then answer:
3´... A-C-G-A-G-T-C-A-G-A-G-T-C-A-G-A-T-C... 5´
What is the percentage of adenine in the double helix of this gene?

1. A 10 %
2. B 15 %
3. C 20 %
4. D 25 %

Study the order of the nitrogenous bases in the following part of a DNA strand, then answer:
3´... A-C-G-A-G-T-C-A-G-A-G-T-C-A-G-A-T-C... 5´
What is the percentage of thymine in the DNA strand complementary to this strand?

1. A 11.11 %
2. B 22.22 %
3. C 33.33 %
4. D 44.44 %

The two opposite figures show the use of X-ray diffraction to tell apart the two substances that were disputed as the genetic material in human cells. Which of the following statements is correct?

1. A Molecule (S) always contains phosphorus
2. B Molecule (S) is coiled in the shape of a double helix
3. C The diameter of molecule (Y) shows that it is made of more than one strand
4. D The nitrogenous bases in molecule (Y) are on the outside

Study the opposite graph, which shows the number of nitrogenous bases of DNA in strands (1) and (2). What do the letters (X), (Y), (Z) and (L) represent, respectively?

1. A Adenine / Thymine / Cytosine / Guanine
2. B Thymine / Cytosine / Adenine / Guanine
3. C Adenine / Guanine / Thymine / Cytosine
4. D Cytosine / Guanine / Adenine / Thymine

Which of the following mathematical relations about the nitrogenous bases in a DNA molecule is NOT correct?

1. A A = T
2. B 1 = (A + C) / (T + G)
3. C 1 = (A + T) / (C + G)
4. D T + G ≃ 50 %

Which of the following could happen if the two DNA strands became identical?

1. A The covalent bonds in the nucleotide would not form
2. B The hydrogen bonds between the nitrogenous bases would not form
3. C All adenine bases would bind with thymine bases
4. D All guanine bases would bind with cytosine bases

Which of the following was NOT provided by Franklin's studies of the three-dimensional shape of the DNA molecule?

1. A The diameter of the molecule
2. B The position of the nitrogenous bases in the molecule
3. C The shape of the molecule
4. D How the molecule is built

The opposite figure shows the components of DNA. Which of the following statements is correct?

1. A The number of (D) molecules equals the number of (C) molecules
2. B The sum of (A) and (T) molecules equals the sum of (G) and (C) molecules
3. C The sum of (D) and (P) molecules equals the sum of (G) and (C) molecules
4. D The number of (D) molecules equals the number of (P) molecules

Which single-ring nitrogenous base binds with the base opposite it by three hydrogen bonds in a DNA molecule?

1. A Cytosine
2. B Adenine
3. C Guanine
4. D Thymine

From the opposite diagram, which shows part of the structure of DNA, what do the structures (X), (Y) and (Z) represent, respectively?

1. A Phosphate group / Ribose sugar / Adenine
2. B Phosphate group / Deoxyribose sugar / Adenine
3. C Ribose sugar / Guanine / Phosphate group
4. D Deoxyribose sugar / Phosphate group / Cytosine

Which of the following is responsible for the variety of genetic information in a DNA molecule?

1. A Deoxyribose sugar
2. B The types of nitrogenous bases
3. C The phosphate groups
4. D The order of the nucleotides

If the number of adenine nucleotides in a DNA molecule is 300 nucleotides, which is 15% of the total number of nucleotides, how many turns does this molecule have?

1. A 50
2. B 100
3. C 150
4. D 200

If a DNA sample of 300 nucleotide pairs contains 140 cytosine bases, how many other nucleotides are there?

1. A 140
2. B 160
3. C 280
4. D 460

How many free phosphate groups are there in the double helix of a DNA molecule in eukaryotes?

1. A Zero
2. B 1
3. C 2
4. D 4

How many purine bases are there in the double segment of the opposite DNA strand?

1. A 4
2. B 5
3. C 8
4. D 9

If a DNA molecule in a living organism is made of 210 thousand pairs of nitrogenous bases, answer:
How many nucleotides are there in this molecule?

1. A 210
2. B 210 thousand
3. C 420
4. D 420 thousand

If a DNA molecule in a living organism is made of 210 thousand pairs of nitrogenous bases, answer:
How many turns are there in this molecule?

1. A 12 thousand
2. B 21 thousand
3. C 24 thousand
4. D 42 thousand

The opposite table shows the percentages of the nitrogenous bases in three different DNA samples as determined by a scientist. Which samples confirm base pairing in DNA?

1. A (1) , (2)
2. B (1) , (3)
3. C (2) , (3)
4. D (1) , (2) , (3)

Study the opposite diagram:
What does the letter (X) represent?

1. A Ribose sugar
2. B Deoxyribose sugar
3. C Phosphate group
4. D Hydroxyl group

Study the opposite diagram:
What does the letter (Y) represent?

1. A Ribose sugar
2. B Deoxyribose sugar
3. C Phosphate group
4. D Hydroxyl group

If a DNA sample contains 400 purine nucleotides, how many pyrimidine nucleotides does it contain?

1. A 200
2. B 400
3. C 600
4. D 800

If the percentage of guanine in a pure sample of a DNA molecule is 17%, what is the percentage of thymine in this sample?

1. A 17 %
2. B 33 %
3. C 34 %
4. D 83 %

Gene (X) is made of 84 pairs of nitrogenous bases. From the following table, which shows the number of some nitrogenous bases, how many cytosine bases are there in this gene?

1. A 18
2. B 25
3. C 36
4. D 43

What is the reason for the many types of genes on DNA?

1. A The sugar-phosphate backbone is not symmetrical
2. B The variety of chemical bonds
3. C The variety of the order of the nitrogenous bases
4. D DNA is found as a double helix

What is the main function of the hydrogen bonds in both the DNA molecule and the antibody molecule?

1. A Joining carbon atoms together
2. B Determining the structural shape of the molecule
3. C Joining the building units together
4. D Making it easier to break the molecule down into its building units

One turn of a DNA molecule contains 10 thymine bases. How many guanine bases does it contain?

1. A Zero
2. B 5
3. C 10
4. D 20

How many nitrogenous bases form two hydrogen bonds with the bases of the following strand in a DNA molecule?
C - G - A - T - T - C - A - G - A

1. A 3
2. B 4
3. C 5
4. D 6

What type of chemical bonds is found in the sugar-phosphate backbone?

1. A Covalent only
2. B Hydrogen only
3. C Covalent and disulfide
4. D Covalent and hydrogen

When the percentages of the nitrogenous bases of the nucleic acid of a living organism were measured, they were as follows:
A = 18 % , G = 32 % , T = 18 % , C = 32 %
What does this nucleic acid represent?

1. A A DNA double helix
2. B A single DNA strand
3. C An RNA double helix
4. D A single RNA strand

The opposite figure shows some information about a DNA molecule:
How many nucleotides does the DNA molecule have?

1. A 400
2. B 800
3. C 1200
4. D 2400

The opposite figure shows some information about a DNA molecule:
How many pyrimidines are there in this molecule?

1. A 200
2. B 400
3. C 600
4. D 1200

The opposite figure shows some information about a DNA molecule:
How many hydrogen bonds are there?

1. A 400
2. B 1000
3. C 1200
4. D 1600

The opposite figure shows some information about a DNA molecule:
How many turns does this molecule have?

1. A 60
2. B 80
3. C 100
4. D 120

A piece of a DNA molecule is made of 6 turns. How many free phosphate groups does it have?

1. A 2
2. B 12
3. C 60
4. D 120

If the number of purine bases in a DNA molecule is 180 bases, how many turns does this molecule have?

1. A 9 turns
2. B 18 turns
3. C 27 turns
4. D 36 turns

How many pairs of nitrogenous bases are there in a piece of DNA that has 150 turns?

1. A 150
2. B 300
3. C 1500
4. D 3000

Which of the following is correct?

1. A A
2. B B
3. C C
4. D D

Which of the following figures can correctly represent a piece of a DNA molecule?

1. A A
2. B B
3. C C
4. D D

A piece of a DNA molecule contains 700 nitrogenous bases, 200 of which are adenine (A). How many hydrogen bonds are there in this piece of the molecule?

1. A 700
2. B 850
3. C 1400
4. D 1700

The figure in front of you shows a piece of DNA. If the number of purines in gene (A) equals the number of pyrimidines in gene (B), how does gene (A) differ from gene (B)?

1. A The number of nucleotides
2. B The order of the nucleotides
3. C The type of nucleotides
4. D The number of hydrogen bonds

The opposite figure is a model of a DNA molecule. If the distance between points (S) and (Y) equals (X), what is the distance between points (Z) and (L)?

1. A ½ X
2. B X
3. C 2 X
4. D 3 X

The two opposite figures show DNA replication. Which of the following is correct about this process in the two figures?

1. A (1) takes place in the cytoplasm, while (2) takes place in the nucleus
2. B The enzymes used in (1) differ from those used in (2)
3. C (1) produces 3 DNA molecules, while (2) produces one DNA molecule
4. D The start of replication in (1) differs from the start of replication in (2)

Which of the following is NOT a characteristic of a virus?

1. A Its genetic material may be RNA or DNA
2. B It can replicate inside prokaryotic cells
3. C It can replicate inside eukaryotic cells
4. D It can replicate in the absence of a host

The primers that are removed by one type of enzyme after the two DNA strands are copied do not contain the base ..........

1. A Uracil
2. B Thymine
3. C Adenine
4. D Cytosine

DNA polymerase builds Okazaki fragments in the direction ..........

1. A 5´ to 3´ of the leading strand
2. B 3´ to 5´ of the lagging strand
3. C 5´ to 3´ of the lagging strand
4. D 3´ to 5´ of the leading strand

Which of the following is NOT formed after DNA replication?

1. A Ova in the human female
2. B Pollen grains in the bean plant
3. C Ciliated swimmers in the gametophyte stage of the fern plant
4. D The motile stage inside the female Anopheles mosquito

From the opposite figure, which of the following are exactly identical?

1. A (X) and (Y)
2. B (Z) and (L)
3. C (X) and (L)
4. D (Z) and (X)

During the replication of a DNA molecule, which of the following are separated from each other?

1. A Phosphate groups and deoxyribose sugar
2. B Cytosine and guanine
3. C Uracil and thymine
4. D Adenine and uracil

The primers added by the primase enzyme during DNA replication contain the base ..........

1. A Adenine
2. B Guanine
3. C Thymine
4. D Uracil

If the number of Okazaki fragments formed during the replication of a DNA molecule is X, the number of primers needed for replication is ..........

1. A X
2. B X + 1
3. C X - 1
4. D 2 X

Which of the following must be plentiful in the cell before it starts to divide?

1. A Monosaccharides
2. B RNA and DNA nucleotides
3. C Amino acids
4. D Nitrogenous bases

Which of the following enzymes is enzyme (X) in the following reaction?

1. A Helicase
2. B Polymerase
3. C Deoxyribonuclease
4. D Ligase

From the opposite graph, what do (S), (Y) and (Z) represent, respectively?

1. A First meiotic division / Second meiotic division / Fertilization
2. B Mitotic division / First meiotic division / Second meiotic division
3. C First meiotic division / Mitotic division / Fertilization
4. D Mitotic division / First meiotic division / Fertilization

Which of the following shows the correct order in which the following enzymes work during DNA replication?

1. A Helicase → Primase → Polymerase → Ligase
2. B Primase → Helicase → Polymerase → Ligase
3. C Helicase → Polymerase → Primase → Ligase
4. D Primase → Polymerase → Helicase → Ligase

Which of the following is NOT a result of the work of the helicase enzyme during DNA replication?

1. A Forming the replication fork
2. B Separating the leading strand of replication from the lagging strand
3. C Allowing the polymerase enzymes to work
4. D Breaking the hydrogen bonds between the complementary nitrogenous bases

The following table shows some events that take place during DNA replication:
(1) Each nitrogenous base binds with its complementary base
(2) The sugar of one nucleotide binds with the phosphate group of the next nucleotide
(3) Breaking the hydrogen bonds to separate the two DNA strands
(4) Forming two identical DNA molecules
Which of the following choices shows the correct order of these events?

1. A (3) → (4) → (2) → (1)
2. B (3) → (1) → (4) → (2)
3. C (3) → (1) → (2) → (4)
4. D (3) → (2) → (1) → (4)

Which of the following enzymes has no role in DNA replication?

1. A Polymerase
2. B Ligase
3. C Helicase
4. D Deoxyribonuclease

The opposite figure shows the replication of a DNA molecule. Which of the following statements is correct?

1. A Strand (X) and strand (Z) carry the same sequence of nucleotides
2. B The direction of strand (Y) is opposite to that of strand (L)
3. C Strands (X) and (Z) are joined to each other by covalent bonds
4. D After replication is complete, strands (Z) and (L) are joined by hydrogen bonds

Study the following figures, then answer:
Where does the process shown in these figures take place in eukaryotic cells?

1. A The nucleus
2. B The nucleolus
3. C The cytoplasm
4. D The ribosome

Study the following figures, then answer:
In which of the following stages are the helicase, primase and DNA polymerase enzymes all active at the same time?

1. A W
2. B X
3. C Y
4. D Z

Study the following figures, then answer:
In which of the following stages are new bases added by pairing with the original bases?

1. A W
2. B X
3. C Y
4. D Z

Study the following figures, then answer:
In which of the following organisms does the process shown in the figures differ from the other organisms?

1. A E. coli bacteria
2. B Yeast fungus
3. C Amoeba
4. D Human

Study the following figures, then answer:
Which of the previous models represents the correct way of DNA replication?

1. A (3) only
2. B (1) , (2)
3. C (2) only
4. D (1) , (2) , (3)

Which of the following bonds does DNA polymerase form?

1. A Hydrogen only
2. B Covalent only
3. C Ionic and covalent
4. D Covalent and hydrogen

Which of the following graphs shows the change in the amount of DNA before the cell starts to divide?

1. A A
2. B B
3. C C
4. D D

The opposite figure shows one of the vital processes in eukaryotic cells. Which choice describes it?

1. A Process: binary fission , Products: two complementary DNA strands
2. B Process: mitotic division , Products: two chromatids
3. C Process: fertilization , Products: a complete DNA molecule
4. D Process: DNA replication , Products: two chromatids

Which of the following must happen to start the process shown in the following figure?

1. A Unwinding DNA from a string of nucleosomes
2. B Separating the two joined ends of the DNA molecule
3. C Shortening the DNA molecule using proteins
4. D The availability of DNA replication enzymes

Which of the following statements applies to the opposite figure?

1. A Letter (X) stands for the ligase enzyme and letter (Z) stands for the helicase enzyme
2. B Letter (X) stands for the ligase enzyme and letter (Y) stands for the polymerase enzyme
3. C Letter (Y) stands for the ligase enzyme and letter (Z) stands for the helicase enzyme
4. D Both letters (X) and (Y) stand for the polymerase enzyme

Which enzyme is used to build new DNA strands in the (5´ to 3´) direction for the bacteriophage?

1. A Viral helicase
2. B Bacterial ligase
3. C Bacterial DNA polymerase
4. D Viral deoxyribonuclease

From the opposite figure:
If nucleotides labelled with radioactive nitrogen ¹⁵N are used during replication, which of the opposite strands will contain ¹⁵N?

1. A (1) , (3)
2. B (2) , (3)
3. C (1) , (2)
4. D (1) , (4)

From the opposite figure:
Which strands need the work of ligase enzymes?

1. A (1) only
2. B (1) , (3)
3. C (2) , (4)
4. D (2) only

Which of the following does NOT happen when one nitrogenous base in a DNA molecule is damaged?

1. A Ligase enzymes recognize the damaged site
2. B The structure of DNA changes when it passes to the next generations
3. C The nucleotide with the damaged nitrogenous base is replaced by a sound one
4. D The new nucleotide pairs with the one on the opposite strand

The opposite figure shows the nucleus of a cell just before it enters mitotic division. Which of the following is the number of chromosomes in a daughter cell after division?

1. A 8 pairs of chromatids
2. B 8 chromosomes, each containing one DNA molecule
3. C 4 chromatids
4. D 16 chromosomes, each containing one DNA molecule

From the following figure, which shows one of the steps of the replication of the two DNA strands:
Which of the following enzymes is (X)?

1. A Helicase only
2. B Ligase only
3. C Polymerase and helicase
4. D Polymerase or ligase

From the following figure, which shows one of the steps of the replication of the two DNA strands:
What bond does enzyme (X) form?

1. A Hydrogen only
2. B Covalent only
3. C Peptide and hydrogen
4. D Hydrogen and covalent

The opposite figure shows a human body cell just at the start of mitotic division, giving cells (2) and (3). How many DNA molecules are there in the nucleus of each of cells (1) and (2)?

1. A Cell (1): 46 , Cell (2): 23
2. B Cell (1): 46 , Cell (2): 46
3. C Cell (1): 92 , Cell (2): 23
4. D Cell (1): 92 , Cell (2): 46

The opposite figure shows the replication of a DNA molecule. Study it, then answer:
What is found at the letter (Y)?

1. A A free phosphate group
2. B A free hydroxyl group
3. C A phosphate or a hydroxyl group
4. D An amine group (NH₂)

The opposite figure shows the replication of a DNA molecule. Study it, then answer:
What does the letter (S) represent?

1. A The polymerase enzyme
2. B The helicase enzyme
3. C The ligase enzyme
4. D The primase enzyme

Which of the following ensures that the hereditary traits of most species of living organisms stay stable?

1. A Four different nucleotides in the structure of DNA
2. B The DNA molecule being double
3. C The number of purines being equal to the number of pyrimidines
4. D The difference in the sequence of nucleotides along the molecule

From the opposite table, what do the enzymes (X), (Y) and (Z) represent, respectively?

1. A Ligase / Helicase / Polymerase
2. B Helicase / Ligase / Deoxyribonuclease
3. C Deoxyribonuclease / Polymerase / Helicase
4. D Polymerase / Helicase / Ligase

The opposite figure shows some stages of sperm formation in the human male. Which of the following statements must apply to the amount of adenine bases in the DNA of these cells?

1. A Cell (2) has the same amount of adenine bases as cell (1)
2. B Cell (2) has twice the amount of adenine bases in cell (3)
3. C Cell (4) has the same amount of adenine bases as cell (5)
4. D Cell (4) has twice the amount of adenine bases in cell (2)

The absence of which of the following enzymes causes the death of the zygote and failure of pregnancy?

1. A Helicase
2. B Deoxyribonuclease
3. C Hyaluronidase
4. D Cholinesterase

Study the following scheme:
DNA → (replication in a medium with radioactive sulfur) → 2(DNA) → (replication in a medium with radioactive sulfur) → 4(DNA)
What is the percentage of DNA molecules exactly identical to the original DNA after replication?

1. A Zero %
2. B 25 %
3. C 50 %
4. D 100 %

Why are some viruses affected by mutation at a faster rate than bacteria?

1. A Their genetic material is a single RNA strand
2. B They cannot change
3. C They use the metabolism of the host cell
4. D They are surrounded by a complex protein coat

In a laboratory experiment, a bacterial cell was placed in a nutrient medium containing radioactive thymine and was left to reproduce once, so ..........

1. A Only one of the two daughter cells contains DNA with radioactive thymine
2. B The DNA in the two daughter cells has only radioactive thymine
3. C The DNA in the two daughter cells has a mixture of radioactive and non-radioactive thymine
4. D The bacterial cell cannot divide because radioactive adenine is absent

The opposite table shows the percentages of the nitrogenous bases of a DNA molecule in two cells of the same rabbit. What do you conclude from:
(1) comparing the percentages of the nitrogenous bases in the rabbit liver cell with their percentages in the rabbit skin cell? Explain your answer.
(2) comparing the percentages of the nitrogenous bases in the rabbit liver cell with each other? Explain your answer.

If the sequence of the nitrogenous bases in a piece of one of the two strands of a DNA molecule is:
5′... C - A - G - G - T - A - C - T - G ...3′
(1) What is the sequence of the bases in the other strand of this piece?
(2) What evidence did you rely on to determine the sequence of bases you gave?

If the percentage of adenine in one strand of a DNA molecule is 10% and the percentage of thymine in the same strand is 30%, what is the percentage of guanine in this molecule?

A gene is made of 36 nucleotides joined to each other by three hydrogen bonds and 18 nucleotides joined to each other by two hydrogen bonds. How many purine nucleotides are there in this gene?

A DNA molecule has 300 hydrogen bonds between adenine and thymine and 300 bonds between guanine and cytosine. How many turns does this molecule have?

Identify two mistakes in the piece of DNA in front of you.

From the opposite figure, which bonds break when this molecule replicates? Explain your answer.

The opposite figure shows a DNA molecule during replication. At which part does the DNA polymerase enzyme add new nucleotides?

From the opposite graph, identify the stage during which the helicase enzymes work. Explain your answer.

In the opposite figure, which arrow represents a wrong direction during DNA replication? Explain your answer.

If the percentage of thymine on one DNA strand is 20%, what is the percentage of adenine on the same strand? (Trial exam / June 2021)

1. A 20%
2. B 30%
3. C 80%
4. D Unknown

Study the following figures, which show a number of nucleic acid strands, then identify:
Which two strands can be used to build a DNA helix? (1st session 2021)

1. A (1) , (3)
2. B (1) , (4)
3. C (2) , (3)
4. D (2) , (4)

Which of the following organisms gives results different from what Franklin reached when the X-ray diffraction technique is used on its genetic material? (1st session 2021)

1. A Bacteriophage virus
2. B Pneumonia bacteria, strain (S)
3. C Pneumonia bacteria, strain (R)
4. D Polio virus

If the percentages of the nitrogenous bases in the template DNA strand are as follows:
A = 15% , G = 45% , C = 10% , T = 30%
Which nitrogenous base must be present at 30% to produce the strand complementary to this strand? (1st session 2021)

1. A A
2. B G
3. C C
4. D T

By chemical analysis of DNA from different sources, Chargaff found that pyrimidine bases equal purine bases. Which of Watson and Crick's conclusions agrees with Chargaff's results? (2nd session 2021)

1. A One of the two DNA strands is in a position opposite to the other
2. B (A) binds with (T), and (G) binds with (C)
3. C DNA makes one turn every 10 nucleotides on one strand
4. D The sugar-phosphate backbone forms the sides of the ladder and the bases form the rungs

The opposite figure shows two nitrogenous bases bound together. What do (X) and (Y) represent, respectively? (2nd session 2021)

1. A Guanine / Cytosine
2. B Adenine / Thymine
3. C Thymine / Adenine
4. D Cytosine / Guanine

If a piece of a DNA molecule contains 200 nucleotides, and the nucleotides containing the nitrogenous base adenine make up 15% of this piece, how many hydrogen bonds are there between the nitrogenous bases in this piece? (1st session 2022)

1. A 210
2. B 270
3. C 540
4. D 230

Study the following diagrams, then identify which of them shows what Franklin found. (2nd session 2022)

1. A A
2. B B
3. C C
4. D D

Which of the following organisms gives the following result when the X-ray diffraction technique is used on its genetic material (the nitrogenous bases are perpendicular to one side of a single sugar-phosphate backbone)? (Trial exam 2023)

1. A Bacteriophage
2. B Escherichia coli bacteria
3. C Polio virus
4. D Pneumonia bacteria, strain (S)

What is the ratio between the number of turns in a DNA molecule and the number of pairs of nitrogenous bases, respectively? (1st session 2023, Sample exam 2025)

1. A 20 turns : 1 pair
2. B 1 turn : 20 pairs
3. C 10 turns : 1 pair
4. D 1 turn : 10 pairs

The opposite figure shows a piece of a DNA molecule. Study it, then deduce how many nitrogenous bases are found in this piece. (1st session 2024)

1. A 60
2. B 30
3. C 24
4. D 6

Which of the following is NOT one of the results of the X-ray diffraction images obtained by Franklin? (2nd session 2024)

1. A The sugar-phosphate backbone of the DNA molecule surrounds the nitrogenous bases from the outside
2. B The DNA molecule is made of more than one strand
3. C The DNA molecule is made of sugar, phosphate and nitrogenous bases
4. D The DNA molecule is found in the shape of a double helix

A short piece of DNA contains 80 thymine bases and 80 guanine bases. The total number of nucleotides in the piece of DNA is .......... (Sample exam 2025)

1. A 160
2. B 40
3. C 320
4. D 640

Which of the choices in the following table applies to the base guanine? (Sample exam 2025)

1. A A
2. B B
3. C C
4. D D

If the number of adenine bases in five turns of a piece of a DNA molecule is 20, how many ladder rungs, each containing three hydrogen bonds, are there in this piece of the DNA molecule? (1st session 2025)

1. A 20
2. B 30
3. C 40
4. D 60

Why is the width / diameter of the DNA double helix regular? (Sample exam 2026)

1. A Because the width of each base pair equals three carbon rings
2. B Because each base pair is in a position opposite to the other
3. C Because the number of hydrogen bonds between the bases is equal
4. D Because the width of each base pair equals two nitrogenous bases

What is the importance of having a complementary sequence of nitrogenous bases in the two DNA strands? (Sample exam 2026)

1. A It allows the molecule to coil and form a double helix whose ends are joined together
2. B It allows each strand to be a template for building the new strand
3. C It gives the sugar-phosphate backbone the position opposite to the other
4. D It increases genetic variation

Knowing that a chromosome is made of one chromatid before DNA replication, and after replication the chromosome is made of 2 chromatids, the opposite figure shows a cell at the start of division. What can be concluded from it? (1st session 2021)

1. A The two resulting cells contain the same amount of DNA
2. B The two resulting cells contain the same number of chromosomes
3. C The genetic content was replicated before division
4. D There was a fault in DNA replication

Study the opposite drawing, which shows binary fission in amoeba and the division of liver cells in humans. What process do these cells carry out to produce cells exactly like the original in all genetic information? (1st session 2021)

1. A DNA replication before the division of the nucleus
2. B Transcription of mRNA to produce the same proteins
3. C Activity of ligase enzymes to repair DNA defects
4. D Transcription of rRNA to form ribosomes

Study the opposite figure, which shows the loss of the marked bases at the same time during DNA replication. Assuming this damage was repaired by adding two nucleotides instead of the two damaged ones, what is the percentage of repairing this defect of the damaged bases so that they return to the original structure? (2nd session 2021)

1. A 75%
2. B 100%
3. C 25%
4. D 0%

The opposite graph shows the amount of DNA inside a plant cell during the two periods (X) and (Y). How many cells will be formed at the end of period (Y)? (2nd session 2021)

1. A One cell with 3 times the genetic material of the original cell
2. B One cell with 4 times the genetic material of the original cell
3. C 8 cells, each with 4 times the genetic material of the original cell
4. D 8 cells, each with the same amount of genetic material as the original cell

The opposite figure shows DNA replication. Assuming the helicase enzyme separates the two DNA strands starting from (A) to (D), what is the correct order of the direction of the polymerase enzyme's work on the template DNA strand (3′ → 5′) during replication? (2nd session 2021)

1. A A
2. B B
3. C C
4. D D

Which process will not stop when the deoxyribonuclease enzyme is added? (1st session 2022)

1. A Reproduction of the phage inside bacterial cells
2. B Bacterial transformation
3. C DNA replication
4. D Reproduction of the influenza virus inside body cells

Which of the following cases is NOT preceded by DNA replication? (1st session 2022)

1. A Replacing damaged skin cells
2. B Forming spermatogonia
3. C Forming primary spermatocytes
4. D Replacing red blood cells in the bone marrow

The opposite figure shows the cell cycle of a cell during 24 hours. What is the ratio between the amount of DNA in phases (G₁) and (G₂), respectively? (2nd session 2022)

1. A 2 to 1
2. B 1 to 1
3. C 1 to 4
4. D 1 to 2

During which of the following stages of human embryonic development does the highest rate of DNA replication take place in the cells of the embryo? (Trial exam 2023, Sample exam 2025)

1. A A
2. B B
3. C C
4. D D

Which damage can be repaired using DNA repair enzymes? (Trial exam 2023)

1. A Damage to a purine base in one of the rungs of the DNA ladder
2. B Removal of one of the rungs of the DNA ladder
3. C Damage to one of the genes of the influenza virus
4. D Breaking the hydrogen bonds between the pairs of nitrogenous bases

Study the two opposite figures, which show two forms of DNA molecules (1) and (2), where the arrows point to the sites where the same vital process takes place, then deduce the difference between the process in figures (1) and (2). (Trial exam 2023, Sample exam 2025)

1. A The final product of the process
2. B The type of enzymes used
3. C The purpose of the process
4. D The starting point of the process

Why is a defect in the genetic material of the polio virus not repaired inside the host cell? (1st session 2023, Sample exam 2025)

1. A Because ligase enzymes are absent inside the host cell
2. B Because the genetic material of the virus is made of a single strand
3. C Because ligase enzymes are specialized to repair defects in the host's genetic material only
4. D Because the genetic material of the virus does not enter the nucleus of the host cell

Which of the two DNA strands is built in the direction shown in the figure during DNA replication? (1st session 2024)

1. A A
2. B B
3. C C
4. D D

What is the structure of each chromosome in eukaryotes? (1st session 2024)

1. A 2 DNA molecules
2. B One DNA molecule
3. C One DNA strand
4. D A single-stranded DNA molecule

Study the following table, which shows four different types of viruses that differ from each other in the type of genetic material, then deduce:
Which of these viruses cannot have the defects of its genetic material repaired if a defect happens in one of the strands of this material? (1st session 2024)

1. A Herpes virus , Parvo virus
2. B Hepatitis (C) virus , Rice dwarf virus
3. C Hepatitis (C) virus , Parvo virus
4. D Herpes virus , Rice dwarf virus

Which of the following does NOT describe the work of the polymerase enzyme? (2nd session 2024)

1. A It forms covalent bonds between the two neighbouring nucleotides in the new strand
2. B It adds the 5′ end of the new nucleotide to the 3′ end of the previous nucleotide
3. C It adds a hydroxyl group of the new nucleotide to the previous phosphate group
4. D It adds nucleotides to the 3′ end of the new strands

A DNA molecule in which both strands contain radioactive thymine is allowed to replicate in an environment containing non-radioactive thymine. What is the correct number of DNA molecules containing some radioactive thymine after three replications? (Sample exam 2025)

1. A One molecule
2. B Two molecules
3. C 4 molecules
4. D 8 molecules

At which of the following ends does the primase enzyme start working during DNA replication? (1st session 2025)

1. A The (5′) end of the template strand
2. B The (5′) end of the new strand
3. C The (3′) end of the template strand
4. D The (3′) end of the new strand

If a cell contains 4 pairs of homologous chromosomes, how many DNA molecules make up these chromosomes and will be replicated before the cell divides? (2nd session 2025)

1. A 4 DNA molecules
2. B 8 DNA molecules
3. C Selected parts of 4 DNA molecules
4. D Selected parts of 8 DNA molecules

From the opposite figure, which of the fragments marked with the letters (A) to (D) are built (polymerized) by one type of enzyme? (2nd session 2025)

1. A (D) only
2. B (A) and (D)
3. C (A) and (B) and (C)
4. D (A) and (B) and (C) and (D)

How many primers are used while forming the lagging DNA strand? (Sample exam 2026)

1. A One
2. B A number equal to the number of genes
3. C A number equal to the number of Okazaki fragments
4. D An unlimited number

The lagging strand differs from the leading strand by having Okazaki fragments. What is the reason these fragments form during DNA replication? (Sample exam 2026)

1. A Because the polymerase enzyme works only in the 5′ to 3′ direction on the new strand
2. B Because the polymerase enzyme cannot start making a new strand without a primer
3. C Because one of the two template strands is in a position opposite to the other
4. D Because the helicase enzyme separates the two strands of the DNA molecule in one direction only

If a cell is treated with a chemical compound that inhibits the ligase enzyme, which of the following is most likely in the cells resulting from division? (Sample exam 2026)

1. A Forming Okazaki fragments that are shorter and more numerous than usual
2. B Accumulation of unjoined Okazaki fragments on the lagging strand
3. C An increase in the mutation rate in the cell
4. D The lagging strand lengthening more slowly than the leading strand

What is the chemical difference between structure (X) and structure (Y) shown in the opposite figure? (Sample exam 2025)