AP Biology Test #3a - Molecular Genetics And Cellular Reproduction

The correct answer is "DNA is made of two strands that twist into a double helix." This is because Watson and Crick's model of DNA structure, based on X-ray crystallography data from Rosalind Franklin, revealed that DNA consists of two strands that are twisted around each other to form a double helix shape. This discovery was a crucial breakthrough in understanding the structure and function of DNA.

The point at which two chromatids are attached to each other in a chromosome is called a centromere. This structure plays a crucial role in the separation of chromatids during cell division. It serves as an attachment site for the spindle fibers, which pull the chromatids apart during mitosis or meiosis. The centromere also helps to ensure that each daughter cell receives the correct number of chromosomes. Chloroplasts are organelles involved in photosynthesis, gametes are reproductive cells, and centrioles are involved in cell division, but none of these options are directly related to the attachment point of chromatids in a chromosome.

Prokaryotes like bacteria reproduce by binary fission, which is a form of asexual reproduction. In binary fission, the prokaryotic cell divides into two identical daughter cells, each receiving a copy of the genetic material. This process allows bacteria to rapidly reproduce and increase their population size. Binary fusion is not a term used in biology, and sex, which involves the fusion of gametes, is not a common method of reproduction in prokaryotes. Therefore, the correct answer is binary fission.

Malignant cells are cancer cells that have the ability to invade nearby tissues and spread to other parts of the body through the bloodstream or lymphatic system. Unlike benign cells, which are non-cancerous and do not spread, malignant cells can form tumors and metastasize, causing harm to the body. Therefore, the correct answer is "malignant."

The other strand of DNA will have a complementary sequence of bases. In DNA, adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). Therefore, the complementary sequence to ATC GTC TTC AAG is TAG CAG AAG TTC.

Based on the given information, it is stated that no suspect matches the DNA fingerprint. Therefore, the correct answer is Suspect B because it is the only option given that does not match the DNA fingerprint.

DNA helicases are enzymes that play a crucial role in DNA replication and repair by unwinding the double helix structure of DNA. They bind to the DNA molecule and use energy from ATP hydrolysis to separate the two strands, creating a replication fork. This allows other enzymes and proteins to access the DNA strands and perform their respective functions. Therefore, DNA helicases are responsible for the unwinding process and are commonly referred to as the enzymes that unwind DNA.

The anticodons on the tRNA molecule for the codons in the mRNA sequence "CUCAAGUCCUUC" would be "GAG--UUC--AGG--AAG". This is because in the genetic code, the codon "CUC" in the mRNA corresponds to the anticodon "GAG" on the tRNA. Similarly, "AAG" in the mRNA corresponds to "UUC" on the tRNA, "AGG" corresponds to "AGG" on the tRNA, and "CUU" corresponds to "AAG" on the tRNA. Therefore, the correct answer is "GAG--UUC--AGG--AAG".

Homologous chromosomes are pairs of chromosomes that have the same genes in the same order, although they may have different alleles for those genes. This means that they code for the same traits, although there may be variations in the specific expression of those traits due to the presence of different alleles. Therefore, the correct answer is "same traits."

A nucleotide triplet in mRNA that specifies a particular amino acid is called a codon. Codons are the basic units of the genetic code and they determine the sequence of amino acids in a protein. Each codon corresponds to a specific amino acid or a stop signal, and they are read by the ribosome during protein synthesis. Mutagens are substances that can cause changes in the DNA sequence, while anticodons are found in tRNA and are complementary to codons. Exons are the coding regions of genes that are expressed in the final protein product.

Chromatids are joined strands of duplicated genetic material (chromosome). During the process of cell division, the DNA in a chromosome is replicated, resulting in two identical chromatids that are held together by a structure called the centromere. These chromatids are then separated during cell division to form two daughter cells, each with a complete set of genetic material. Therefore, chromatids represent the duplicated form of a chromosome and are essential for the accurate distribution of genetic material to daughter cells.

A repressor protein is a type of regulatory protein that binds to specific DNA sequences and prevents the movement of RNA polymerase, which is responsible for synthesizing RNA from DNA. By blocking the movement of RNA polymerase, the repressor protein inhibits the transcription process and prevents the synthesis of RNA molecules. This regulation mechanism helps control gene expression and ensure that certain genes are not expressed when they are not needed.

The correct answer is metaphase. This is because in the picture, the chromosomes are aligned at the center of the cell, indicating that the cell is in metaphase. In metaphase, the spindle fibers attach to the centromeres of the chromosomes and align them along the equator of the cell.

Stem cells are cells that have the ability to differentiate into various types of specialized cells in the body. They can divide and renew themselves through mitosis, and under certain conditions, they can be induced to become cells with specific functions. This unique characteristic of stem cells makes them crucial in various medical and scientific research, as they hold the potential to treat a wide range of diseases and injuries by replacing damaged or diseased cells. Therefore, stem cells are the correct answer to the question.

Mitosis is a process in which the nucleus of a cell divides into two nuclei. During mitosis, the chromosomes in the nucleus replicate and then separate into two identical sets, each going to a different daughter cell. This division of the nucleus ensures that each daughter cell receives the same genetic material as the parent cell. Therefore, the correct answer is that mitosis is the process by which the nucleus is divided into two nuclei.

Exons are the portions of DNA molecules that code for the production of proteins. They contain the genetic information necessary for the synthesis of functional proteins. Mutons, introns, and exposons are not the correct terms for the coding regions of DNA. Mutons are hypothetical units of mutation, introns are non-coding regions of DNA, and exposons are not a recognized term in molecular biology. Therefore, the correct answer is exons.

Introns are the non-coding portions of DNA that are separated from the portions of DNA actually used during transcription. During the process of transcription, introns are removed from the pre-mRNA molecule and the remaining coding portions, called exons, are spliced together to form the mature mRNA molecule. This allows for the production of different protein variants through alternative splicing, where different combinations of exons can be included or excluded. Mutons, exposons, and exons are not correct terms for this concept.

A gene can code for a specific protein. Genes are segments of DNA that contain the instructions for building proteins. Proteins are essential molecules that perform various functions in the body. Genes provide the information needed to assemble the amino acids in the correct order to form a specific protein. This process is known as protein synthesis or gene expression. Therefore, the statement that a gene can code for a specific protein is correct.

During transcription, the process by which genetic information is copied from DNA to RNA, the genetic information for making a protein is "rewritten" as a molecule of messenger RNA (mRNA). This mRNA molecule carries the genetic instructions from the DNA to the ribosomes, where it serves as a template for protein synthesis during translation. Ribosomal RNA (rRNA) and transfer RNA (tRNA) are also involved in protein synthesis, but they do not carry the genetic information for making a protein. Translation RNA is not a term used in biology, so it is not the correct answer.

DNA polymerases are enzymes responsible for adding nucleotides to the exposed DNA template bases during DNA replication. These enzymes are involved in the process of synthesizing a new DNA strand by adding complementary nucleotides to the template strand. Helicases, on the other hand, are responsible for unwinding the DNA double helix, while replicases are enzymes involved in the replication of RNA viruses. Therefore, the correct answer is DNA polymerases.

The exchange of segments of DNA between the members of a pair of chromosomes acts as a source of variations within a species. This process, known as genetic recombination or crossing over, occurs during meiosis when homologous chromosomes exchange genetic material. This exchange leads to the creation of new combinations of genes, increasing genetic diversity within a population. This variation is important for the survival and adaptation of a species to changing environments.

Mutations are changes in the DNA sequence of an organism. They can introduce new genetic variations, which can then be inherited by future generations. This variation is essential for the process of evolution, as it provides the raw material for natural selection to act upon. Mutations can occur randomly and can be caused by various factors such as environmental factors or errors during DNA replication. While some mutations can be harmful or have no effect, others can be beneficial and provide an advantage to the organisms in which they occur. Therefore, the statement "They are a source of variation for evolution" is correct.

The synthesis (S) phase is the phase of the cell cycle where DNA replication occurs. During this phase, the cell duplicates its DNA to prepare for cell division. This ensures that each daughter cell will receive a complete copy of the genetic material. The other options mentioned, such as cell division, replication of mitochondria and other organelles, and division of cytoplasm, do not accurately describe the characteristics of the S phase.

The chromosomal mutation shown is most likely an inversion. In an inversion, a segment of the chromosome is flipped and inserted back into the chromosome in the opposite orientation. This results in a rearrangement of the genetic material, but no loss or gain of genetic material. In the given image, it appears that a segment of the chromosome has been flipped and reinserted, causing a change in the order of the genes. This is consistent with an inversion mutation.

Genetic recombination in bacteria can occur through various methods, including transfer of DNA between bacteria through pili, mutation, transformation, and transduction. However, DNA amplification is not a method of genetic recombination in bacteria. DNA amplification refers to the process of producing multiple copies of a specific DNA sequence, such as through polymerase chain reaction (PCR). While DNA amplification is an important technique in molecular biology, it is not a mechanism by which bacteria naturally exchange genetic material.

The correct answer is the bacteria's capsule interfering with phagocytosis. The capsule of Pneumococcus bacteria is a protective layer that helps the bacteria evade the immune system. Phagocytosis is a process where immune cells engulf and destroy pathogens. The capsule inhibits the ability of phagocytes to recognize and engulf the bacteria, making it difficult for the immune system to combat the infection effectively. This allows the bacteria to proliferate and cause more severe disease.

DNA molecules are composed of long chains of nucleotides. Nucleotides are the building blocks of DNA and consist of a sugar molecule (deoxyribose), a phosphate group, and a nitrogenous base (adenine, thymine, cytosine, or guanine). These nucleotides are joined together through phosphodiester bonds to form a long chain, which makes up the DNA molecule. Amino acids are the building blocks of proteins, fatty acids are components of lipids, and monosaccharides are the building blocks of carbohydrates, but they are not the components of DNA molecules.

The correct answer is nucleotide. A nucleotide is a molecule that is composed of a sugar, a phosphate group, and a nitrogenous base. The diagram shows a molecule that has all these components, indicating that it is a nucleotide. Amino acids are the building blocks of proteins, polysaccharides are large carbohydrates, and pyrimidine is a type of nitrogenous base found in nucleotides.

Cells must control gene expression so that their genes will only be expressed when needed. This is important for maintaining proper cellular function and responding to changes in the environment. If genes were always expressed, it could lead to unnecessary protein production and waste of resources. On the other hand, if genes were never expressed, essential proteins would not be produced, leading to cellular dysfunction. By tightly regulating gene expression, cells can ensure that the right genes are expressed at the right time and in the right amount, allowing for proper development, growth, and response to stimuli.

There are a total of 64 RNA codons in the genetic code. Codons are three-letter sequences of RNA nucleotides that determine the specific amino acid to be added during protein synthesis. Since there are four different RNA nucleotides (A, U, G, and C), and each codon is made up of three nucleotides, there are 4^3 = 64 possible combinations. Therefore, the maximum number of RNA codons in the genetic code is 64.

The lac operon is a segment of DNA that controls the expression of genes involved in lactose metabolism. It consists of three main components: the promoter (p), the operator (o), and the gene (z). The promoter is responsible for initiating transcription, while the gene contains the coding sequence for the enzyme beta-galactosidase. The operator acts as a regulatory region that can bind to the lac repressor protein. The lac repressor binds to the operator, preventing RNA polymerase from transcribing the gene. Therefore, the correct answer is the operator (o) because it is the portion of the lac operon where the repressor binds.

During anaphase, the sister chromatids of each chromosome separate and move towards opposite ends of the cell along the spindle fibers. This movement ensures that each daughter cell will receive a complete set of chromosomes during cell division. In telophase, the chromosomes have already reached the opposite ends of the cell and begin to decondense. In metaphase, the chromosomes align along the equatorial plane of the cell. In prophase, the chromosomes condense and the nuclear envelope breaks down. Interphase is not a stage of mitosis, but rather the period between cell divisions where the cell grows and carries out its normal functions.

The picture shows a cell with a clear nucleus and chromatin spread throughout the nucleus, indicating that it is not in the process of dividing. Interphase is the phase of the cell cycle where the cell prepares for division by growing and replicating its DNA. Therefore, the correct answer is interphase.

The phage tail fibers contain the enzyme lysozyme, which is necessary in stage B. This suggests that the lysozyme enzyme plays a role in stage B of the process depicted above. Without further context or information, it is not possible to determine the specific function or purpose of stage B.

Griffith's transformation experiments involved injecting non-harmful bacteria with a heat-killed strain of deadly bacteria. The results showed that the non-harmful bacteria were able to acquire the ability to cause disease and become deadly themselves. This discovery demonstrated the concept of bacterial transformation, where genetic material can be transferred between bacteria, leading to a change in their characteristics. The experiments did not involve changing proteins into DNA, resulting in DNA molecules becoming proteins, or showing the effect of heat on bacteria.

Polymerase chain reaction (PCR) is a molecular biology process that allows for the amplification of a specific DNA sequence. It involves the use of DNA polymerase enzyme to repeatedly copy and amplify the targeted DNA region, resulting in the production of many copies of the gene from a small DNA sample. Gel electrophoresis is a technique used to separate DNA fragments based on their size, while transcription and translation are processes involved in gene expression. Nuclear multiplication is not a recognized term in molecular biology.

The given mRNA sequence is CUCAAGUCCUUC. To determine the DNA strand from which this mRNA was made, we need to find the complementary DNA sequence. The complementary DNA sequence is obtained by replacing each nucleotide in the mRNA with its complementary base. In this case, C pairs with G, U pairs with A, and A pairs with T. Therefore, the complementary DNA sequence would be GAGTTCAGGAAG. This is the same as the third option provided, so the correct answer is GAGTTCAGGAAG.

The given piece of mRNA sequence, CUCAAGUCCUUC, codes for the amino acid sequence Leu--Lys--Ser---Phe. This is determined by using the codon chart, which matches each three-letter mRNA codon to the corresponding amino acid. The codons CUC, AAG, UCC, and UUC correspond to the amino acids Leu, Lys, Ser, and Phe, respectively. Therefore, the portion of the protein molecule coded for by this mRNA sequence is Leu--Lys--Ser---Phe.

The correct sequence of the cell cycle is G1 (Gap 1) phase, S (Synthesis) phase, G2 (Gap 2) phase, and M (Mitosis) phase, followed by C (Cytokinesis). During G1 phase, the cell grows and carries out its normal functions. In S phase, DNA replication occurs. G2 phase is a period of preparation for cell division. M phase involves mitosis, where the cell's nucleus divides, and cytokinesis, where the cytoplasm divides to form two daughter cells. Therefore, the correct sequence is G1--> S --> G2 --> M--> C.

The plate shows growth after 48 hours, indicating that the bacteria are not being inhibited by the antibiotics. However, there is no growth in the area where Penicillin (I) is present, suggesting that this antibiotic is effective in combating the bacteria. Therefore, the correct answer is I.

The HIV virus uses the lysogenic cycle of infection. In this cycle, the virus inserts its genetic material into the host cell's DNA and remains dormant for an extended period of time. The viral DNA replicates along with the host cell's DNA, and the virus is passed on to daughter cells during cell division. Eventually, the virus can switch to the lytic cycle, where it becomes active, replicates rapidly, and destroys the host cell.

Both mitochondria and chloroplasts contain DNA molecules, which is a characteristic that supports the endosymbiotic theory. This theory suggests that these organelles were once free-living bacteria that were engulfed by a host cell, forming a symbiotic relationship. The presence of DNA in mitochondria and chloroplasts is evidence of their bacterial origins, as bacteria also contain DNA. This supports the idea that these organelles were once independent organisms that were incorporated into eukaryotic cells.

Hershey and Chase used radioactive tracers to determine the interactions of bacteriophages and their host bacteria. This experiment conclusively showed that DNA is the molecule that stores genetic information in cells. This is because when the bacteriophages infected the bacteria, only the radioactive DNA was found inside the bacteria, not the radioactive proteins. This demonstrated that DNA, not proteins, is responsible for carrying and transmitting genetic information.

RNA differs from DNA in multiple ways. Firstly, RNA is a single-stranded molecule, whereas DNA is double-stranded. Secondly, RNA contains a different sugar molecule called ribose, while DNA contains deoxyribose. Lastly, RNA contains the nitrogen base uracil instead of thymine, which is found in DNA. Therefore, the correct answer is "All of the above" as all the statements are true regarding the differences between RNA and DNA.

In this scenario, the buildup of a product is affecting an enzyme that catalyzes one of the initial steps of a metabolic pathway. This is a clear example of feedback inhibition, where the end product of a pathway inhibits its own production by binding to an enzyme and preventing further reactions. This mechanism helps maintain homeostasis and regulate the levels of products in metabolic pathways.

The lac operon is a genetic system in bacteria that controls the expression of genes involved in lactose metabolism. It consists of three main components: the promoter, the operator, and the genes coding for lactose-metabolizing enzymes. When lactose is absent, a repressor protein binds to the operator, preventing the transcription of the genes. This effectively shuts off the lac operon. In the presence of lactose, the repressor protein is unable to bind to the operator, allowing the genes to be transcribed and lactose to be metabolized. Therefore, the correct answer is lactose is absent.

rRNA, or ribosomal RNA, is responsible for forming ribosomes. Ribosomes are cellular structures that play a crucial role in protein synthesis. They are composed of rRNA and proteins, and they provide the site where mRNA (messenger RNA) is translated into proteins. Therefore, the correct answer is that the function of rRNA is to form ribosomes.

The dye used to stain the fragment increases the contrast between the agar and the DNA fragment. This helps in visualizing the DNA fragment more clearly during gel electrophoresis. By enhancing the contrast, the dye allows for easier identification and analysis of the DNA fragment's size and migration pattern on the gel.

The DNA sequence CCCTTTGGG would substitute lysine for threonine. This is because the codon ACU codes for threonine, and the codon AAA codes for lysine. By changing the ACU codon to AAA, the amino acid threonine is replaced with lysine in the sequence.

Retroviruses, such as HIV, have a unique enzyme called reverse transcriptase that allows them to replicate DNA from RNA. This process is known as reverse transcription. The retrovirus uses its RNA genome as a template to synthesize a complementary DNA strand, which is then integrated into the host cell's DNA. This allows the retrovirus to hijack the host cell's machinery and produce more viral particles. Therefore, the correct answer is DNA from RNA.