MCAT Biochemistry: DNA Structure and Biotechnology Fundamentals

In DNA, deoxyribose is the pentose sugar where the 2' OH group is replaced by a hydrogen atom, while in RNA, ribose is the pentose sugar where both the 2' and 3' groups are hydroxyl (OH) groups.

Nucleosides consist of a sugar molecule covalently bonded to a nitrogenous base, while nucleotides have phosphate groups attached to the sugar. The incorrect answers provided do not accurately describe the distinction between nucleosides and nucleotides.

Purines are nucleotide bases with a double-ring structure, which includes Adenine and Guanine. This distinguishes them from pyrimidines like Cytosine, Thymine, and Uracil.

Pyrimidines are nitrogenous bases with a single-ring structure, specifically Cytosine, Uracil, and Thymine. Adenine and Guanine are purines, which have a double-ring structure.

Based on Chargaff's Rule, the amount of A always equals the amount of T, and the amount of C always equals the amount of G. Therefore, with 10% G, the % of T would be 40% to maintain the balance of base pairs.

Histones are not hormones, proteins responsible for muscle contractions, or enzymes that break down carbohydrates. They are small basic proteins around which DNA is wrapped to form chromatin and chromosomes.

Nucleoproteins are a class of proteins that interact with DNA, typically involved in processes such as gene regulation and chromosome structure. Histones, for example, are a type of nucleoprotein that play a key role in packaging DNA into structural units called nucleosomes.

Telomere is a repeating unit (TTAGGG) at the end of DNA, protecting it from being lost during replication. It is not a protein, cytoplasmic region, or small molecule.

The correct answer describes the centromere as a specific region of DNA with a distinct function on chromosomes. The incorrect answers provided are common misconceptions about cellular processes that do not accurately describe the role of a centromere.

Eukaryotic DNA replication typically occurs within the nucleus of the cell, separated from the cytoplasm by the nuclear envelope. In contrast, Prokaryotic DNA replication takes place in the cytoplasm or a specialized region called the nucleoid. This fundamental distinction in the location of DNA replication is key to understanding the differences between these two processes.

Semiconservative replication in DNA means that each newly synthesized double helix contains one original parent strand and one newly synthesized daughter strand. This process ensures that genetic information is passed on accurately during cell division.

In Molecular Biology, all processes like DNA synthesis, DNA repair, DNA transcription, and RNA translation occur in the 5' to 3' direction except for DNA polymerase's reading direction.

RNA polymerase is involved in transcription, not DNA replication.

Oncogenes are mutated genes that cause cancer by accelerating the cell cycle, while Antioncogenes are genes that normally inhibit tumor progression through inhibition of the cell cycle.

DNA proofreading occurs simultaneously with synthesis by DNA polymerase, allowing for immediate correction of any incorrect base pairing. The enzyme is responsible for both strand elongation and proofreading to maintain the accuracy of the DNA sequence.

DNA replication of the lagging strand involves the formation of Okazaki fragments, which are later joined together by DNA ligase. Since DNA ligase lacks proofreading ability, errors can occur more frequently on the lagging strand. In contrast, the leading strand is synthesized continuously, resulting in fewer opportunities for mistakes to accumulate.

Mismatch Repair is a crucial biological process involved in DNA repair during cell division, not related to other types of mismatches like mechanical, laundry, or programming errors.

Base Excision Repair involves the recognition and removal of damaged bases by glycosylase enzyme, followed by the formation of an AP site that is recognized and processed by AP endonuclease. Finally, DNA polymerase and ligase fill in the gap and seal the strand, repairing the lesion.

Recombinant DNA cloning involves cutting the desired DNA sequence with restriction enzymes and inserting it into a suitable vector, such as a plasmid. This vector is then introduced into a host cell, where it replicates along with the host DNA.

Restriction Enzymes, also known as Restriction Endonucleases, are enzymes that recognize specific DNA sequences and cut the DNA at precise locations. They are an essential tool in molecular biology for cutting DNA into smaller fragments for various experimental purposes. These enzymes cut at palindromic sequences, meaning the sequence reads the same forward and backward, such as GAATTC.

A recombinant plasmid vector is formed by inserting a foreign DNA fragment into a plasmid vector, allowing for the replication and expression of the foreign DNA in a host organism.

cDNA libraries are created by reverse-transcribing mRNA, thereby excluding noncoding regions and only including expressed genes. This process allows for the study of actively transcribed genes in a specific tissue.

Hybridization refers to the joining of complementary base sequences or DNA-DNA recognition, as well as the use of techniques such as DNA-RNA Polymerase Chain Reaction (PCR), Gel Electrophoresis, and Southern Blotting. It does not involve mixing genetic material from different species or creating genetically modified organisms. Additionally, hybridization is not the process of separating DNA fragments based on size.