The Test Question Cellular Biology Test 1

Eucaryotic chromosomes contain multiple sites where DNA replication can be initiated. This is because eucaryotic genomes are much larger and more complex compared to prokaryotic genomes. The presence of multiple replication initiation sites allows for efficient and timely replication of the entire genome. Additionally, having multiple initiation sites helps to prevent DNA damage and ensures accurate replication. Therefore, the statement "Eucaryotic chromosomes contain many different sites where DNA replication can be initiated" is true.

Chromosomes undergo changes in their level of condensation throughout the cell cycle. During interphase, chromosomes are less condensed and appear as long, thin threads. However, during mitosis, chromosomes become highly condensed and visible under a microscope. This condensation allows for easier separation and distribution of genetic material during cell division. Therefore, it is true that chromosomes exist at different levels of condensation depending on the stage of the cell cycle.

Ionizing radiation and oxidative damage are known to cause DNA double-strand breaks. Ionizing radiation, such as X-rays and gamma rays, have enough energy to remove tightly bound electrons from atoms, leading to the formation of free radicals that can damage DNA. Oxidative damage, on the other hand, occurs when reactive oxygen species, such as hydrogen peroxide and superoxide radicals, react with DNA and cause breaks in the double helix. Therefore, it is true that both ionizing radiation and oxidative damage can cause DNA double-strand breaks.

The statement is false because there are actually only four different nucleotides (adenine, thymine, cytosine, and guanine) that become incorporated into a DNA strand.

Primase is an enzyme that is responsible for synthesizing short RNA primers, which are necessary for the initiation of DNA replication. These primers provide a starting point for DNA polymerase to begin synthesizing new DNA strands. Since DNA replication occurs in both the leading and lagging strands during DNA synthesis, primase is required to initiate replication on both strands. Therefore, the statement that primase is needed to initiate DNA replication on both the leading and lagging strands is true.

snRNA molecules are important in the splicing of RNA transcripts.

DNA replication is considered semiconservative because each daughter DNA molecule consists of one strand from the parent DNA molecule and one new strand. In this process, the original DNA double helix is unwound and each of the separated strands serves as a template for the synthesis of a new complementary strand. This results in two daughter DNA molecules, each with one original strand and one newly synthesized strand. This mechanism ensures that the genetic information is preserved and passed on to the next generation.

The statement is false because not all functional DNA sequences inside a cell code for protein products. While some DNA sequences do code for proteins, there are also sequences that code for functional RNA molecules, such as transfer RNA (tRNA) and ribosomal RNA (rRNA). Additionally, there are non-coding DNA sequences that have regulatory functions in gene expression. Therefore, not all functional DNA sequences inside a cell directly code for protein products.

rRNA molecules are integral components of the ribosome. The ribosome is the cellular structure responsible for protein synthesis. rRNA molecules help in the formation and functioning of the ribosome, which is essential for the translation of mRNA into proteins. They provide structural support and catalytic activity during protein synthesis. Therefore, rRNA molecules play a crucial role in the overall process of gene expression and protein production in a cell.

A nucleosome is a basic unit of DNA packaging in eukaryotic cells. It consists of DNA wrapped around a core of histone proteins. The core histones include H2A, H2B, H3, and H4. Therefore, a nucleosome contains two molecules each of histones H2A and H2B, as well as of histones H3 and H4.

mRNA molecules code for proteins. They carry the genetic information from the DNA to the ribosomes, where protein synthesis occurs. mRNA is transcribed from the DNA during the process of transcription.

The correct answer is 46 because somatic cells in the human body contain 23 pairs of chromosomes. Each pair consists of one chromosome inherited from the mother and one from the father, resulting in a total of 46 chromosomes.

Heterochromatin formation results in gene silencing. This means that the genes within the heterochromatin region are not expressed or transcribed into proteins. The modifications on the N-terminal tail of histone H3 promote the condensation of chromatin into a compact and inactive state, preventing the access of transcriptional machinery to the genes in that region. This leads to the silencing of gene expression within the heterochromatin.

Primase is an enzyme responsible for synthesizing RNA primers during DNA replication. It does not possess a proofreading function to check for errors in the RNA primers it generates. The proofreading function is carried out by other enzymes, such as DNA polymerase, which can detect and correct errors in the DNA sequence. Therefore, the statement that Primase requires a proofreading function for the RNA primers is false.

Gene sequences do not always correspond exactly to the respective protein sequences produced from them. This is because gene sequences undergo a process called post-transcriptional modification, where certain sections of the gene sequence called introns are removed and the remaining sections called exons are spliced together to form the final mRNA sequence. This mRNA sequence is then translated into a protein sequence, which may be further modified through processes like protein folding and post-translational modifications. Therefore, the protein sequence may differ from the original gene sequence due to these modifications.

Individual chromosomes were shown in a figure in the textbook "painted" as different colors using fluorescent DNA molecules. This method involves labeling specific DNA sequences on each chromosome with different fluorescent dyes. When the chromosomes are viewed under a microscope, the labeled DNA sequences emit different colors of light, allowing for the identification and differentiation of each chromosome. This technique is known as chromosome painting and is a modern method employed for karyotyping.

The leading strand is related to continuous replication because it is synthesized continuously in the 5'-to-3' direction without any interruptions. The other items listed are not directly related to continuous replication. Primase is responsible for synthesizing RNA primers, which are necessary for DNA replication to begin. Single-strand binding protein helps stabilize the single-stranded DNA during replication. Sliding clamp helps keep the DNA polymerase attached to the template strand. RNA primers are short sequences of RNA that are synthesized by primase and serve as a starting point for DNA synthesis on the lagging strand.

The correct answer describes the known sequences of events in the repair of mismatched base pairs or damaged nucleotides in a DNA strand. First, DNA damage is recognized. Then, the newly synthesized strand is identified by an existing nick in the backbone. Next, a segment of the new strand is removed by repair proteins. After that, the gap is filled by DNA polymerase. Finally, the strand is sealed by DNA ligase. This sequence of events ensures that the damaged DNA is repaired and the integrity of the DNA strand is maintained.

In eukaryotic cells, several covalent modifications can be made to an RNA molecule before it becomes a mature mRNA. One modification is the addition of a poly A tail, which is a sequence of adenine nucleotides added to the 3' end of the RNA molecule. Another modification is the addition of a 5' cap, which is a modified guanine nucleotide added to the 5' end of the RNA molecule. Additionally, introns, non-coding regions of the RNA molecule, can be spliced out to remove unnecessary sequences. Therefore, all of the above modifications can occur in eukaryotic cells before an RNA molecule becomes a mature mRNA.

The correct answer for #3 is tRNA. tRNA molecules act as adaptors for protein synthesis. They carry amino acids to the ribosome during protein synthesis and match them to the codons on the mRNA molecule. This ensures that the correct amino acids are added to the growing protein chain according to the genetic code.

The total number of replication origins in bacterial cells is significantly lower compared to the number of origins in human cells. Bacterial cells typically have only one replication origin, while human cells have approximately 10,000 origins. This difference in the number of origins is due to the complexity and size of the human genome, which requires multiple origins to ensure efficient and timely DNA replication.

The process described in the question where genetic material is copied from DNA into the nucleotide sequence of RNA is called transcription. Transcription is the first step in gene expression, where an RNA molecule is synthesized using a DNA template. This RNA molecule is then used for various functions, such as coding for proteins (mRNA), acting as adaptors for protein synthesis (tRNA), being integral components of the ribosome (rRNA), and being important in the splicing of RNA transcripts (snRNA). Therefore, the correct answer is transcription.

The N-terminal "tail" of core histones is not involved in binding to DNA in a sequence-specific manner. Instead, it is subject to covalent modifications, extends out of the nucleosome core, helps DNA pack tightly, and contains lysine residues. These modifications and interactions with other proteins contribute to the regulation of gene expression and chromatin structure.

The sequence "AUG" is known as the start codon and codes for the amino acid methionine. In this case, the RNA sequence includes the start codon "AUG" at the 13th to 15th positions. Therefore, the tRNA that binds to the A-site of the ribosome will carry the amino acid methionine.

Mitotic chromosomes were named based on their color because in the 1880s, when they were first visualized, they were observed using dyes that stained the chromosomes. The specific dyes used would bind to the chromosomes and make them visible under a basic light microscope. Therefore, the color of the chromosomes played a crucial role in their identification and naming.

Transcription is similar to DNA replication in that nucleotide polymerization occurs only in the 5'-to-3' direction. This means that during transcription, RNA is synthesized in the 5'-to-3' direction, just like DNA is synthesized during replication. This directionality is important for the proper synthesis and assembly of RNA molecules.

Nucleosomes are formed when DNA wraps 1.7 times around the histone octamer in a left-handed coil.

During meiosis, the process of swapping segments of parental chromosomes occurs. Meiosis is a specialized form of cell division that occurs in sexually reproducing organisms. It involves the formation of gametes (eggs and sperm) and results in the production of genetically diverse offspring. One of the key events in meiosis is crossing over, where segments of homologous chromosomes are exchanged, leading to genetic recombination and increased genetic diversity. This swapping of segments during meiosis is a fundamental mechanism for generating genetic diversity.

The newly synthesized strand of human chromosome is true because it is synthesized from multiple origins, indicating that DNA replication occurs at multiple sites along the chromosome. Additionally, the synthesis is a mixture of continuous and discontinuous DNA synthesis, suggesting that some portions of the strand are synthesized continuously, while others are synthesized in fragments and later joined together. This process allows for efficient and accurate replication of the chromosome. The use of ATP hydrolysis is not mentioned in the question and therefore not relevant to the answer.

The original sequence is TCAT. If the cytosine in this sequence is deaminated and not repaired, it will be converted to thymine. After two rounds of DNA replication, the mutated sequence will be TTAT.

The genetic code is redundant means that multiple codons can specify the same amino acid. In other words, there is more than one codon that can code for a particular amino acid. This redundancy in the genetic code provides some degree of error tolerance and flexibility in protein synthesis.

Misfolded proteins are not delivered to the proteasome to attempt refolding. Instead, they are targeted for degradation by the proteasome. The proteasome recognizes the misfolded proteins and degrades them into smaller peptides. Therefore, the statement that misfolded proteins are delivered to the proteasome, where they are sequestered from the cytoplasm and can attempt to refold is false.

The five-carbon sugar, phosphate, and nitrogen-containing base are all components of a DNA molecule. However, a six-carbon sugar and cyclic AMP are not used to construct a DNA molecule.

During interphase, chromosomes are less compact compared to mitotic chromosomes. The given answer, 20:500, suggests that interphase chromosomes are 20 times less compact than mitotic chromosomes. However, interphase chromosomes are still about 500 times more compact than a DNA molecule in its extended form.

The polynucleotide sequence 5′-TTTTTTTTTTTTTTTTTTTTTTTTT-3′ is a poly-T sequence, which is complementary to the poly-A tail found at the 3' end of mRNA molecules. Therefore, when mixed with resin beads to which this polynucleotide has been attached, the beads will specifically bind to mRNA molecules through the poly-A tail. This allows for the selective extraction of mRNA from the mixture. Since the question asks for the most abundant nucleic acid that sticks to the beads, the correct answer is mRNA, as it is the only nucleic acid that specifically binds to the beads in this setup.

In eukaryotic transcription, there are three RNA polymerases present compared to the single RNA polymerase in bacterial transcription. Bacterial RNA can initiate transcription with the help of additional proteins, while eukaryotic RNA polymerase requires general transcription factors. Transcription regulators in eukaryotic cells can influence transcriptional initiation even thousands of nucleotides away from the promoter, whereas bacterial regulatory sequences are located very close to the promoter. Additionally, eukaryotic transcription is affected by chromatin structure and nucleosomes, whereas bacteria lack nucleosomes. Therefore, all of the above statements are correct in differentiating eukaryotic transcription from bacterial transcription.

A tRNA molecule with the anticodon 5′-CUU-3′ would carry the amino acid lysine. The anticodon on a tRNA molecule pairs with the codon on mRNA during translation, and the codon sequence 5′-CUU-3′ corresponds to the mRNA codon sequence 5′-AAG-3′, which codes for lysine. Therefore, the tRNA with the given anticodon would be specific for lysine.

The stop codon in mRNA is recognized by a release factor, which binds to the A-site of the ribosome. The anticodon on the tRNA in the P-site of the ribosome must be complementary to the stop codon to ensure proper termination of protein synthesis. In this case, the stop codon is UGA, so the anticodon on the tRNA in the P-site would be 5'-CCA-3', as it is the complementary sequence to UGA.

The leading strand is related to continuous replication because it is synthesized continuously in the 5'-to-3' direction.

The most likely explanation for several members of the same family being diagnosed with the same kind of cancer at a young age is that they have inherited a mutation in a gene required for mismatch repair. Mismatch repair is a mechanism that corrects errors in DNA replication, and mutations in genes involved in this process can lead to an increased risk of developing cancer. This explanation suggests that the individuals in the family have a genetic predisposition to cancer due to a faulty mismatch repair gene.

The block to replication most probably arises from the initiator proteins. Initiator proteins play a crucial role in initiating DNA replication by binding to specific sites on the DNA and recruiting other replication proteins. In this case, the bacterial DNA fails to replicate, suggesting that the yeast cell's initiator proteins may not recognize or interact properly with the bacterial DNA, leading to the failure of replication.

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The correct answer is that the bottom strand is the template strand and RNA polymerase moves along this strand from 3' to 5'. This is because during transcription, RNA polymerase synthesizes RNA in the 5' to 3' direction, using the template strand as a guide. In this case, the given RNA sequence is complementary to the bottom strand of the DNA sequence, indicating that this is the template strand and transcription occurs in the opposite direction.

Primase, sliding clamp, and RNA primers relate to both continuous replication and discontinuous replication.

Primase is an enzyme that synthesizes RNA primers, which are necessary for the initiation of DNA synthesis on both the leading and lagging strands.

The sliding clamp is a protein that helps to stabilize DNA polymerase and ensures efficient DNA synthesis on both strands.

RNA primers are short sequences of RNA that are synthesized by primase and serve as starting points for DNA synthesis on both the leading and lagging strands.

Therefore, all three items are involved in both continuous and discontinuous replication processes.