bio u2 practice areas
Viral Biology (Questions 3 and 5):
Viral Replication: You need to review the different steps involved in the viral life cycle, specifically the penetration step. Question 3 asks what occurs during penetration. The options describe different stages of viral infection. Focus on understanding how viruses introduce their genetic material into the host cell.
Viral Classification: Question 5 asks which feature is NOT used in virus classification. The options include the presence of an envelope, type of genetic material, number of chromosomes, and capsid structure. You should study the criteria that are used to classify viruses, such as those listed (envelope, genetic material, capsid structure), and identify what is generally not a primary classification criterion among the choices.
Gene Regulation (Questions 6 and 16):
Lac Operon: Question 6 concerns the regulation of the lac operon and the role of CAP (Catabolite Activator Protein) in the presence of lactose after long exposure. To answer this, you need to understand how glucose and lactose levels affect cAMP concentrations, CAP activity, and consequently, the transcription of the lac operon genes. Focus on the interplay between lactose (leading to the inactivation of the repressor) and glucose (influencing cAMP levels and CAP binding).
Transcriptional Activators: Question 16 asks about the effect of a non-functional transcriptional activator on gene transcription. You need to understand the role of transcriptional activators in promoting gene expression. If an activator cannot bind to its DNA domain, it will likely lead to a decrease in the rate of transcription.
Transposable Elements (Question 9):
Question 9 asks about the potential outcomes when a transposable element is inserted into a gene. Study the different ways such an insertion can disrupt gene function, including causing splicing defects, frameshift mutations, and nonsense mutations. Understanding these types of mutations and how a mobile genetic element can cause them is key.
Bacteriophage Life Cycles (Question 11):
Question 11 asks what is associated with the lysogenic pathway in the lambda phage life cycle. You should understand the two main life cycles of bacteriophages (lytic and lysogenic) and the key events that characterize the lysogenic pathway. The establishment of a prophage (viral DNA integrated into the host chromosome) is a hallmark of lysogeny.
RNA Interference (Question 21):
Question 21 asks about the difference between siRNA and miRNA. Focus on their origins. siRNA originates from exogenous RNA, while miRNA originates from the cell genome. Understanding this fundamental difference is crucial.
Genomics vs. Proteomics (Question 24):
Question 24 asks why proteomics is more complicated than genomics. The key reason is that a genome is relatively constant, but the proteome varies in different cells at different times. This variability in protein expression due to various factors makes studying the proteome more complex.
DNA Sequencing (Question 31):
Question 31 asks which enzyme is required in a di-deoxy sequencing reaction (Sanger sequencing). Sanger sequencing involves the use of DNA polymerase to synthesize a complementary strand of DNA. While other components are necessary, DNA polymerase is the enzyme that carries out the polymerization. Therefore, none of the above (Topoisomerase, Primase, Helicase) are directly required in the polymerization step of Sanger sequencing.
Alleles (Question 33):
Question 33 asks for an example of alleles. Alleles are different versions of the same gene. The correct answer should describe two versions of the same gene that might lead to different phenotypes. Option A describes two forms of a gene coding for an estrogen receptor, one functional and one non-functional, which fits the definition of alleles.
mRNA Structure (Question 37):
Question 37 asks where the 3' UTR (3' untranslated region) can be found. The 3' UTR is a region at the 3' end of an mRNA molecule that is not translated into protein. It is present in a mature mRNA, pre-mRNA (before splicing removes introns), and consequently would also be represented in cDNA (which is reverse transcribed from mRNA). Therefore, the 3' UTR can be found in All of the choices.
Mitosis (Question 38):
Question 38 asks which of the listed structures participates most directly in mitosis. The centriole (specifically the centrosome, which contains centrioles) is the microtubule-organizing center in animal cells and is crucial for the formation of the mitotic spindle, which directly mediates chromosome segregation during mitosis , this information is implied but not explicitly stated in the immediate context of question ].
Mendelian Genetics and True-Breeding Organisms (Question 44):
Question 44 asks why the fact that Mendel used "true-breeding" plants was so important for his research. True-breeding plants are homozygous for the traits of interest and consistently produce offspring with the same phenotype when self-pollinated. This ensured that Mendel started with genetically uniform parents, allowing him to clearly observe the patterns of inheritance when he performed crosses with plants having different traits. Therefore, it ensured that offspring always looked like parents in the true-breeding lines, providing a stable baseline for his experiments.
Lethal Alleles (Question 50):
Question 50 asks why a dominant lethal inheritance pattern is rarely seen. A dominant lethal allele, if expressed, would cause the death of the individual carrying even one copy of the allele. This means that individuals with the dominant lethal allele would likely die before they could reproduce and pass the allele on to the next generation. Therefore, the allele only lasts one generation and is not transmitted.
Dihybrid Crosses (Question 55):
Question 55 involves a dihybrid cross between an individual with genotype AaBb and another with genotype Aabb, assuming the genes are not linked. To determine the percentage of offspring with the AaBb genotype, you need to consider the independent assortment of each gene. The probability of an offspring being Aa is 1/2 (from Aa x Aa). The probability of an offspring being Bb is 1/2 (from Bb x bb). Therefore, the probability of an offspring being AaBb is (1/2) x (1/2) = 1/4 [21, 22, based on basic Mendelian geneticsĀ
Chromosome Number in Different Cell Types (Question 67):
Question 67 states that a male shark has 40 chromosomes in each of its sex cells (gametes, which are haploid). Body cells (somatic cells) in a diploid organism have twice the number of chromosomes as gametes. Therefore, its body cells would have 80 chromosomes [26, based on the understanding of haploid and diploid cells, which is fundamental to genetics and meiosis as discussed in our history].
Chromosome Compaction in Mitosis (Question 75):
Question 75 asks about the importance of chromosome compaction in mitosis. The primary reason for chromosome compaction (condensation) during mitosis is to allow the long DNA molecules to be tightly packaged in a small cell and to facilitate their orderly segregation into the daughter cells without tangling or breaking.
Effect of Colchicine on Cell Division (Question 80):
Question 80 describes treating dividing cells with colchicine, a drug that inhibits the formation of spindle fibers. Spindle fibers are essential for the proper alignment and separation of chromosomes during mitosis. If spindle fibers are not formed, the chromosomes would likely line up along the metaphase plate but not separate into the daughter cells.
Origin of Mitotic Spindles (Question 81):
Question 81 asks about the cell structure from which the mitotic spindles arise. In animal cells, the mitotic spindles originate from the centrosome, which contains centrioles. The centrosomes duplicate and move to opposite poles of the cell, serving as organizing centers for the spindle microtubules.
Cyclin-Dependent Kinases (Cdks) (Question 85):
Question 85 asks which statement about Cdks is true. Cdks are key regulatory proteins in the cell cycle. They are activated by binding to cyclins (their concentrations fluctuate) and function by phosphorylating other proteins, which then regulate the progression through different stages of the cell cycle [32, this is a general principle of cell cycle regulation not explicitly detailed but implied by the context of cellular division]. Therefore, They activate proteins by phosphorylating them is a true statement.
Study Guide: Areas for Improvement
I. Viral Biology
A. Viral Replication (Question 3)
Key Concepts to Review:
The different stages of the viral life cycle: attachment, penetration, replication, assembly, and release.
Focus specifically on how viral genetic material is inserted into the host cell during penetration.
Distinguish penetration from other stages like attachment (bacteriophages attaching to the outside), release (viruses leaving the host cell by budding or cell lysis), and other potential intracellular events.
B. Viral Classification (Question 5)
Key Concepts to Review:
The common criteria used to classify viruses, such as:
Presence or absence of an envelope.
Type of genetic material in the core (DNA or RNA, single-stranded or double-stranded).
Capsid structure (shape and arrangement of protein subunits).
viruses generally have a single genome, not multiple chromosomes in the eukaryotic sense.
II. Gene Regulation
A. Lac Operon (Question 6)
Key Concepts to Review:
The components of the lac operon: promoter, operator, structural genes (lacZ, lacY, lacA), and the regulatory gene (lacI).
The roles of the repressor protein (encoded by lacI) and its interaction with lactose (allolactose). Lactose inactivates the repressor, allowing transcription.
The role of Catabolite Activator Protein (CAP) and its activation by cAMP.
The inverse relationship between glucose levels and cAMP levels. Low glucose leads to high cAMP, which binds to CAP, enhancing the binding of RNA polymerase and increasing transcription of the lac operon.
Consider the scenario where lactose is present for a long time. The initial presence of glucose would keep cAMP levels low, and CAP would likely not be actively enhancing transcription. Even with lactose present (repressor inactive), maximal transcription requires active CAP.
B. Transcriptional Activators (Question 16)
Area of Weakness: Understanding the impact of a non-functional transcriptional activator.
Key Concepts to Review:
The role of transcriptional activators in gene expression: they bind to specific DNA sequences (enhancers) and interact with the transcription machinery to increase the rate of transcription.
If a transcriptional activator can no longer bind to its DNA domain, it cannot perform its function. This will likely lead to a decrease in the rate of transcription of the target gene.
III. Transposable Elements (Question 9)
Area of Weakness: Identifying the potential consequences of a transposable element inserting into a gene.
Key Concepts to Review:
What transposable elements (TEs) are: mobile DNA sequences that can insert into different locations in the genome.
The various ways TE insertions can disrupt gene function:
Frameshift mutations: Insertion within a coding region can shift the reading frame.
Nonsense mutations: Insertion might create a premature stop codon.
Splicing defects: Insertion within or near introns/exons can interfere with normal RNA splicing.
Therefore, the insertion of a transposable element into a gene can lead to all of the above (splicing defects, frameshift mutations, nonsense mutations).
IV. Bacteriophage Life Cycles (Question 11)
Area of Weakness: Understanding the characteristics of the lysogenic pathway in the lambda phage life cycle.
Key Concepts to Review:
The two main bacteriophage life cycles:
Lytic cycle: Phage replicates and lyses the host cell, releasing new viral particles.
Lysogenic cycle: Phage DNA integrates into the host bacterial chromosome, becoming a prophage, and remains dormant.
Key events associated with the lysogenic pathway:
Establishment of a prophage (integration of viral DNA).
Maintenance of lysogeny by a viral repressor protein.
The prophage is replicated along with the host DNA during cell division.
Under certain conditions, the prophage can be induced to enter the lytic cycle.
Distinguish lysogeny from events associated with the lytic cycle, such as assembly of phage particles, synthesis of head and tail proteins, and many rounds of viral DNA replication (though some limited replication might occur before integration).
V. RNA Interference (Question 21)
Area of Weakness: Differentiating between siRNA and miRNA.
Key Concepts to Review:
siRNA (small interfering RNA): Typically originates from exogenous double-stranded RNA (e.g., from viruses or introduced experimentally). It is processed into short double-stranded molecules and leads to the degradation of target RNA with a complementary sequence.
miRNA (microRNA): Encoded by the cell genome. It is transcribed as longer precursors that are processed into short single-stranded molecules. miRNAs typically regulate gene expression by binding to the 3' UTR of target mRNAs, leading to translational repression or mRNA degradation.
The key difference lies in their origin: siRNA from outside the cell (exogenous RNA), miRNA from within the cell's genome.
VI. Genomics vs. Proteomics (Question 24)
Area of Weakness: Understanding the relative complexity of proteomics compared to genomics.
Key Concepts to Review:
Genomics: The study of the entire genome (all the genes) of an organism. The genome is relatively stable within an individual.
Proteomics: The study of the entire set of proteins (the proteome) produced by an organism at a particular time under specific conditions.
The genome is relatively constant, while the proteome varies significantly depending on cell type, developmental stage, environmental conditions, and time. This dynamic nature of the proteome, along with post-translational modifications, protein-protein interactions, and protein turnover, makes proteomics more complex than genomics.
VII. DNA Sequencing (Question 31)
Area of Weakness: Identifying the enzyme required in di-deoxy (Sanger) sequencing.
Key Concepts to Review:
The basic principle of Sanger sequencing: using DNA polymerase to synthesize a complementary DNA strand.
The role of dideoxynucleotides (ddNTPs), which lack a 3'-OH group and cause chain termination.
While other components like primers and dNTPs are necessary, DNA polymerase is the enzyme that catalyzes the incorporation of nucleotides during DNA synthesis. Therefore, none of the listed enzymes (Topoisomerase, Primase, Helicase) are the primary enzyme responsible for polymerization in Sanger sequencing. Topoisomerase deals with DNA topology, primase synthesizes RNA primers, and helicase unwinds DNA.
VIII. Alleles (Question 33)
Area of Weakness: Understanding the definition of alleles.
Key Concepts to Review:
Alleles are different versions of the same gene that occupy the same locus (position) on homologous chromosomes.
They may differ in their DNA sequence and can lead to variations in the inherited trait.
Option A correctly describes alleles: a gene from the father and a gene from the mother both coding for the same estrogen receptor but with different functional properties (one binds DNA, the other does not). The other options describe different genes or genes involved in different processes.
IX. mRNA Structure (Question 37)
Area of Weakness: Identifying where the 3' UTR can be found.
Key Concepts to Review:
The structure of a eukaryotic mRNA molecule: 5' cap, coding sequence (open reading frame), and 3' untranslated region (UTR).
Pre-mRNA is the initial transcript that contains introns and exons. The 3' UTR is transcribed as part of the pre-mRNA.
During RNA processing, introns are removed, and the pre-mRNA is processed into mature mRNA, which still contains the 3' UTR.
cDNA (complementary DNA) is synthesized from mature mRNA using reverse transcriptase. Therefore, cDNA will also contain a sequence corresponding to the 3' UTR.
Thus, the 3' UTR can be found in All of the choices (mature mRNA, pre-mRNA, cDNA).
X. Mitosis (Question 38)
Area of Weakness: Identifying the cellular structure that most directly participates in mitosis.
Key Concepts to Review:
Mitosis is the process of nuclear division where sister chromatids separate and are distributed into two daughter nuclei.
The centrioles are components of the centrosome, which is the primary microtubule-organizing center in animal cells.
The centrosomes duplicate and move to opposite poles of the cell, and they organize the mitotic spindle, which is composed of microtubules that attach to chromosomes and mediate their movement . Therefore, the centriole (as part of the centrosome) participates most directly in mitosis by organizing the spindle fibers.
XI. Mendelian Genetics and True-Breeding Organisms (Question 44)
Area of Weakness: Understanding the significance of Mendel using true-breeding plants.
Key Concepts to Review:
True-breeding organisms are homozygous for the traits of interest and produce offspring with the same phenotype when self-pollinated.
By starting with true-breeding parents, Mendel ensured that he was beginning with genetically uniform lines for each trait. This allowed him to clearly observe how traits were inherited when he crossed plants with different phenotypes, without the complication of hidden variation in the parental generation. Therefore, it ensured that offspring always looked like parents in the parental generation, providing a stable baseline for his crosses.
XII. Lethal Alleles (Question 50)
Area of Weakness: Understanding why dominant lethal inheritance patterns are rare.
Key Concepts to Review:
A dominant lethal allele causes death when only one copy of the allele is present.
If an individual with a dominant lethal allele expresses the lethal phenotype before reproductive age, they will not be able to pass the allele on to their offspring.
Therefore, a dominant lethal allele typically only lasts one generation and is not transmitted to subsequent generations.
XIII. Dihybrid Crosses (Question 55)
Area of Weakness: Calculating the probability of a specific genotype in the offspring of a dihybrid cross.
Key Concepts to Review:
Independent assortment: alleles of different genes segregate independently of one another during gamete formation.
To determine the probability of an offspring with genotype AaBb from a cross AaBb x Aabb, consider each gene separately:
For the A gene: Aa x Aa produces offspring with genotypes AA, Aa, and aa in a 1:2:1 ratio. The probability of Aa is 2/4 or 1/2.
For the B gene: Bb x bb produces offspring with genotypes Bb and bb in a 1:1 ratio. The probability of Bb is 1/2.
Since the genes are not linked, the probability of an offspring being AaBb is the product of the individual probabilities: (Probability of Aa) x (Probability of Bb) = (1/2) x (1/2) = 1/4 [21, 22, based on basic Mendelian genetics].
XIV. Chromosome Number in Different Cell Types (Question 67)
Area of Weakness: Understanding the relationship between chromosome number in sex cells and body cells.
Key Concepts to Review:
Sex cells (gametes) are haploid (n), meaning they contain half the number of chromosomes as somatic (body) cells.
Body cells (somatic cells) are diploid (2n), meaning they contain two sets of chromosomes, one inherited from each parent.
If a male shark has 40 chromosomes in its sex cells (n = 40), then its body cells would have a diploid number of 2n = 2 x 40 = 80 chromosomes [26, based on fundamental principles of meiosis and ploidy].
XV. Chromosome Compaction in Mitosis (Question 75)
Area of Weakness: Understanding the importance of chromosome compaction during mitosis.
Key Concepts to Review:
During mitosis, the long DNA molecules must be efficiently organized and separated into two daughter cells.
Chromosome compaction (condensation) allows the extensive DNA to be packaged into a manageable size, preventing tangling and breakage during chromosome segregation. This is crucial for ensuring that each daughter cell receives a complete and intact set of chromosomes. Therefore, it allows DNA to be tightly packaged in a small cell and facilitates proper segregation.
XVI. Effect of Colchicine on Cell Division (Question 80)
Area of Weakness: Predicting the outcome of treating dividing cells with colchicine.
Key Concepts to Review:
Colchicine is a drug that inhibits the polymerization of microtubules, which are the main components of the spindle fibers.
Spindle fibers are essential for the alignment and separation of chromosomes during mitosis.
If spindle fibers are disrupted by colchicine, the chromosomes will be unable to properly segregate. They might line up along the metaphase plate but not separate into the daughter cells. This would likely lead to cell cycle arrest or the formation of cells with an abnormal number of chromosomes.
XVII. Origin of Mitotic Spindles (Question 81)
Area of Weakness: Identifying the cell structure from which mitotic spindles arise.
Key Concepts to Review:
The mitotic spindle is a structure composed of microtubules that organizes and separates the chromosomes during mitosis.
In animal cells, the centrosome is the main microtubule-organizing center . Each centrosome contains a pair of centrioles.
During prophase, the centrosomes duplicate and move to opposite poles of the cell, and they serve as nucleation sites for the growth of spindle microtubules. Therefore, the mitotic spindles arise from the centrosome.
XVIII. Cyclin-Dependent Kinases (Cdks) (Question 85)
Area of Weakness: Understanding the characteristics and function of Cdks.
Key Concepts to Review:
Cyclin-dependent kinases (Cdks) are a family of protein kinases that play crucial roles in regulating the cell cycle.
Cdks are inactive unless they are bound to cyclins, whose concentrations fluctuate throughout the cell cycle.
When activated by cyclins, Cdks phosphorylate target proteins, leading to changes in their activity and driving the cell cycle forward.
Therefore, a true statement about Cdks is that They activate proteins by phosphorylating them. They require cyclins for activity and are positive (not negative) regulators of the cell cycle. Their own concentrations are relatively stable, while cyclin concentrations fluctuate.
Allele: Different versions of the same gene.
Anticodon: A three-nucleotide sequence in a tRNA molecule that corresponds to a codon in mRNA.
Bacteriophage: A virus that infects bacteria.
Binary Fission: The primary method of asexual reproduction in bacteria, where a cell divides into two identical daughter cells.
Capsid: The protein shell of a virus, enclosing its genetic material.
Cell Cycle: An ordered sequence of events in the life of a cell, including growth and division.
Centromere: The region of a chromosome where sister chromatids are joined.
Chromatid: One of the two identical halves of a replicated chromosome.
Codominance: A pattern of inheritance where both alleles are equally expressed in the heterozygote.
Codon: A three-nucleotide sequence in mRNA that specifies a particular amino acid or a stop signal during translation.
Conjugation (bacteria): The transfer of genetic material between bacterial cells by direct contact.
Crossing Over: The exchange of genetic material between non-sister chromatids of homologous chromosomes during meiosis I.
Diploid: Having two sets of chromosomes (2n), one from each parent.
DNA Sequencing: The process of determining the order of nucleotide bases in a DNA molecule.
Dominant Allele: An allele that masks the expression of a recessive allele in a heterozygote.
Epigenetics: Heritable changes in gene expression that do not involve alterations to the underlying DNA sequence.
Frameshift Mutation: A mutation that shifts the reading frame of the genetic code, usually caused by insertions or deletions of a number of nucleotides that is not a multiple of three.
Genome: The complete set of genetic material of an organism.
Genotype: The genetic makeup of an organism.
Haploid: Having a single set of unpaired chromosomes (n).
Heterozygous: Having two different alleles for a particular gene.
Homologous Chromosomes: Pairs of chromosomes in a diploid organism that have the same genes in the same order.
Homozygous: Having two identical alleles for a particular gene.
Incomplete Dominance: A pattern of inheritance where the phenotype of a heterozygote is an intermediate between the phenotypes of the two homozygotes.
Intron: A non-coding sequence within a eukaryotic gene that is transcribed into RNA but is removed by RNA splicing to produce the mature mRNA.
Lac Operon: A cluster of genes in bacteria that are transcribed together and involved in the metabolism of lactose.
Lytic Cycle: A viral replication cycle that culminates in the lysis and death of the host cell.
Lysogenic Cycle: A viral replication cycle where the viral DNA integrates into the host cell's chromosome and remains dormant.
Meiosis: A type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes.
Mitosis: A type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus, typical of ordinary tissue growth.
mRNA (messenger RNA): A type of RNA molecule that carries the genetic code from DNA to ribosomes for protein synthesis.
Mutation: A permanent change in the DNA sequence of a gene or chromosome.
Non-coding DNA: Regions of DNA that do not code for proteins.
Operator: A DNA sequence in prokaryotes where a repressor protein can bind to control the transcription of an operon.
Penetration (viral): The step in viral replication where the virus gains entry into the host cell or its genetic material is introduced.
Phenotype: The observable characteristics of an organism, resulting from the interaction of its genotype with the environment.
Prophage: The viral DNA that is integrated into the host bacterial chromosome during the lysogenic cycle.
Proteomics: The large-scale study of proteins, particularly their structures and functions.
Recessive Allele: An allele whose expression is masked by a dominant allele in a heterozygote.
Regulatory Sequences: DNA sequences that control the transcription of genes.
Repressor: A protein that binds to an operator and inhibits gene transcription.
RNA Interference (RNAi): A biological process in which RNA molecules inhibit gene expression or translation by neutralizing targeted mRNA molecules.
Sanger Sequencing (Chain Termination Method): A method for determining the nucleotide sequence of DNA by using dideoxynucleotides to terminate DNA synthesis.
Sister Chromatids: Two identical copies of a chromosome that are attached at the centromere.
Transcription: The process by which the information in a strand of DNA is copied into a new molecule of messenger RNA (mRNA).
Transcription Factors: Proteins that bind to DNA and regulate gene transcription.
Transformation (bacteria): The genetic alteration of a cell resulting from the direct uptake and incorporation of exogenous genetic material (e.g., DNA) from its surroundings.
Translation: The process by which the genetic code carried by mRNA is used to synthesize proteins.
Transposable Element (TE): A mobile DNA sequence that can change its position within a genome.
True-breeding: Organisms that produce offspring with the same traits when they self-pollinate.
tRNA (transfer RNA): A type of RNA molecule that helps decode a messenger RNA (mRNA) sequence into a protein.
Virus: An infectious agent that replicates only inside the living cells of an organism.