All Free Biology MCQs with Answers
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19844 questions · page 730 of 1985
7291. Meselson and Stahl found that the DNA collected immediately after transfer was dense because:
- A. Both strands contain N14
- B. Both strands contain N15
- C. One strand is N14 and other N15
- D. All of the above
Explanation: This is the correct option. Meselson and Stahl found that after one round of DNA replication in a medium containing only N14, the DNA molecules were hybrids, with one strand containing N14 (the newly synthesized strand) and the other containing N15 (the original parental strand). This resulted in a DNA molecule of intermediate density.
Correct answer: Both strands contain N157292. Okazaki fragments are formed in lagging strand because:
- A. Lagging strand does not allow continuous replication
- B. Lagging strand is 3 to 5 direction
- C. Lagging strand is 5 to 3 direction
- D. Lagging strand is placed near to leading strand
Explanation: The main reason for Okazaki fragments forming on the lagging strand is the antiparallel nature of DNA strands and the requirement for DNA polymerase to synthesize DNA in the 5' to 3' direction. Because the DNA polymerase can only add nucleotides in the 5' to 3' direction, the lagging strand, which runs in the opposite direction from the replication fork, has to be synthesized discontinuously in short fragments, each of which starts with an RNA primer. These fragments are then later joined together by DNA ligase to form a continuous strand.
Correct answer: Lagging strand is 3 to 5 direction7293. Which of the followings does not come within central dogma?
- A. Synthesis of DNA
- B. Synthesis of mRNA
- C. Synthesis of protein
- D. All of the above
Explanation: This process involves the creation of new DNA strands through DNA replication. In this process, a DNA molecule serves as a template for the synthesis of a new complementary DNA strand. Messenger RNA (mRNA) is synthesized in a process called transcription. During transcription, RNA polymerase enzyme reads the DNA template and synthesizes a complementary mRNA molecule, which carries the genetic information from DNA to the ribosome for protein synthesis. This process, known as translation, involves the synthesis of a protein from mRNA. Ribosomes read the mRNA molecule and use it as a template to assemble amino acids into a polypeptide chain, which folds into a functional protein. All of the options listed-synthesis of DNA, synthesis of mRNA, and synthesis of protein-are indeed part of the central dogma of molecular biology. None of them is excluded from this fundamental principle.
Correct answer: All of the above7294. The opposite strand is called coding strand or sense strand in transcription because:
- A. It has opposite codes of template strand
- B. It has similar codes as of template strand
- C. Its codes are similar to mRNA codes
- D. Its codes are opposite to mRNA codes
Explanation: The coding (sense) strand has a sequence that matches the sequence of the mRNA transcript, except that it contains thymine (T) instead of uracil (U) since it's still DNA.
Correct answer: Its codes are similar to mRNA codes7295. Which structure becomes visible when cell starts dividing?
- A. Chromosomes
- B. Cell membrane
- C. Nucleus
- D. Nuclear membrane
Explanation: Chromosomes are thread-like structures made of DNA and proteins. They condense and become visible during cell division to ensure that each daughter cell receives the correct amount of genetic material.
Correct answer: Chromosomes7296. The centromeric position divides chromosomes into how many type?
- A. 2
- B. 6
- C. 4
- D. 3
Explanation: The chromosomes are called telocentric, acrocentric, sub-metacentric and metacentric depending upon the location of centromere between the middle and tip of the chromosomes.
Correct answer: 47297. The bond that exists between N2 bases of DNA is:
- A. Covalent
- B. Hydrogen
- C. Ionic
- D. Phosphodiester
Explanation: Hydrogen bonds are formed between the nitrogenous bases of DNA. Specifically, adenine (A) forms two hydrogen bonds with thymine (T), and guanine (G) forms three hydrogen bonds with cytosine (C). These hydrogen bonds are responsible for holding the two strands of DNA together in the double helix structure.
Correct answer: Hydrogen7298. The replication of DNA is always from:
- A. 5' - 3'
- B. 3' - 5'
- C. Both
- D. None
Explanation: DNA replication proceeds in a directional manner, with new DNA strands synthesized in the 5' to 3' direction. This means that nucleotides are added to the growing DNA strand at the 3' end of the strand. DNA polymerase enzymes catalyze the addition of nucleotides to the growing strand, using the parental DNA strand as a template. The directionality of DNA replication is essential for maintaining the integrity and accuracy of the genetic information encoded in the DNA molecule.
Correct answer: 5' - 3'7299. Attachment of Okazaki fragments to DNA's lagging strand is facilitated by:
- A. Ligase
- B. Polymerase III
- C. Polymerase II
- D. DNAase
Explanation: Ligase is responsible for sealing the nicks between adjacent Okazaki fragments by catalyzing the formation of phosphodiester bonds. It joins the 3' hydroxyl group of one fragment to the 5' phosphate group of the adjacent fragment, thereby creating a continuous strand of DNA.
Correct answer: Ligase7300. Sequence of specific nucleotide that results specific proteins is called:
- A. Nucleoside
- B. Gene
- C. Chromosomes
- D. Nucleotides
Explanation: A gene is a specific sequence of DNA (or RNA in some viruses) that contains the information necessary to produce a functional product, typically a protein. Genes are the fundamental units of heredity and can be transcribed into RNA and translated into proteins.
Correct answer: Gene