Ôn Tập - đề 4

The total number of ribonucleotides in the mRNA molecule is 250, and this accounts for 25% of the total number of nucleotides. To find the total number of nucleotides, we can set up a proportion: 250 is to 25% as X is to 100%. Solving for X, we find that X is equal to 1000. Therefore, the total number of nucleotides in the mRNA molecule is 1000. However, since the question asks for the total number of ribonucleotides, and ribonucleotides make up 25% of the total nucleotides, we can multiply 1000 by 0.25 to find that the total number of ribonucleotides is 250. Therefore, the correct answer is 2000.

5BU (5-bromouracil) is a chemical that has the ability to cause a mutation in DNA by substituting one nucleotide pair with another. It is a synthetic analog of thymine and can be incorporated into DNA during replication. Once incorporated, 5BU can base pair with adenine instead of guanine, leading to a mismatched base pair. This can result in a mutation during subsequent rounds of DNA replication. Therefore, 5BU is the correct answer as it is known to cause gene mutations by substituting one nucleotide pair with another.

The correct answer is A=T=450 and G=X=1050. This is because the question asks for the number of each nucleotide in the gene. A and T are complementary nucleotides, so they should have the same number. Similarly, G and X (which is likely to represent C) are complementary nucleotides and should have the same number. The answer choice A=T=450 means that there are 450 A nucleotides and 450 T nucleotides, while G=X=1050 means that there are 1050 G nucleotides and 1050 X nucleotides.

When Gen A mutates into Gen a, it loses one pair of nucleotides. This is evident from the fact that when Gen a undergoes one round of self-replication, the internal environment provides 2398 nucleotides. The loss of one pair of nucleotides is consistent with the mutation from Gen A to Gen a.

In the question, it is stated that the number of chromosomes in each cell during the metaphase of the second division in meiosis is being asked. Meiosis is a type of cell division that results in four daughter cells, each with half the number of chromosomes as the parent cell. In the metaphase of the second division, the chromosomes are lined up in the middle of the cell. The correct answer is 4 because during this phase, each cell will have half the number of chromosomes as the parent cell, which means that the number of chromosomes will be reduced by half.

The given answer indicates that for every 240 uracil (rU) molecules in the mRNA, there are 10% adenine (rA), 40% guanine (rG), and 30% cytosine (rX) molecules. The quantities of each ribonucleotide provided by the environment for the synthesis of five mRNA molecules are rU = 1200, rA = 600, rG = 2400, and rX = 1800.

The length of the mRNA molecule is given as 3386.4 angstroms. The number of codons in an mRNA molecule is equal to the length of the molecule divided by 10.4 angstroms, which is the average length of a codon. Therefore, the number of codons in this mRNA molecule is 3386.4 / 10.4 = 325. The number of codons in a mRNA molecule is always a multiple of 3, as each codon consists of three nucleotides. The closest multiple of 3 to 325 is 324, which means that there are 324 complete codons and 1 incomplete codon in this mRNA molecule. Therefore, the correct answer is 332, as it represents the total number of codons in the mRNA molecule.

The length of the gene increased by 10.2 A0 after the mutation. The number of hydrogen bonds in a DNA molecule is directly proportional to its length. Therefore, since the length of the gene increased, it can be inferred that the number of hydrogen bonds in the mutated gene also increased. The answer "Tăng từ 6 đến 9 liên kết hiđrô" (Increase from 6 to 9 hydrogen bonds) reflects this relationship.

The given correct answer is "Lá già" (Old leaves). This is because old leaves have already reached their maximum growth potential and are no longer actively growing or developing. Therefore, any external stimulus or intervention would not have a significant impact on them.

The correct answer is "Tỉ lệ A/X giảm." This is because the question states that the mutation has a hydrogen bond count of 3901, which is greater than the original count of 3900. Since the length of the gene remains the same, the only way for the hydrogen bond count to increase is if the proportion of A to X decreases, leading to a decrease in the A/X ratio.

The given options describe characteristics of polyploidy, which is the condition of having multiple sets of chromosomes. However, the option "Sinh sản hữu tính mạnh mẽ" (Strong sexual reproduction) does not apply to polyploidy. Polyploidy can actually lead to reduced fertility or sterility in organisms. Therefore, this option is incorrect.

The correct answer is "Biến đổi số lượng NST xảy ra ở 1 hoặc vài cặp NST trong bộ gen của loài" which means "Changes in the number of homologous chromosomes occur in one or a few pairs of chromosomes in the species' genome." This explanation states that the phenomenon of aneuploidy refers to the occurrence of changes in the number of chromosomes in specific pairs within the species' genetic makeup.

This statement is incorrect because it implies that a trait can only be inherited from the parents to the offspring, when in reality, traits can also be influenced by other factors such as genetic mutations or environmental factors.

The correct answer is "Mất 1 cặp G-X, 1 cặp A -T" because the question states that the mutation causes a decrease in the mass of the gene by 1200 Da (daltons) and a decrease in the number of hydrogen bonds by 2395. This suggests that the mutation involves the loss of a base pair, and the only option that involves the loss of both a G-X pair and an A-T pair is "Mất 1 cặp G-X, 1 cặp A -T".

When there is a mutation in the DNA sequence, the genes are rearranged in a different order. This can disrupt the normal functioning of the genes and the proteins they code for. As a result, some essential proteins may not be synthesized, leading to a decrease in vitality or even death.