Exam 3 Review Part 2 Jeopardy Template

Signal Transduction

Mitosis

Meiosis

FRQ Questions

Cell Cycle

100

Endocrine signals are transmitted more slowly than paracrine signals because ___________.

the ligands are transported through the bloodstream and travel greater distances
the target and signaling cells are close together
the ligands are degraded rapidly
the ligands don't bind to carrier proteins during transport

100

Cellular division is an essential part of the cell cycle. When a cell divides it passes genetic information to daughter cells. The amount of genetic information passed on to daughter cells depends on whether the cell undergoes mitosis or meiosis. Mitosis is the most common form of cell division. All somatic cells undergo mitosis, whereas only germ cells undergo meiosis. Meiosis is very important because it produces gametes (sperm and eggs) that are required for sexual reproduction. Human germ cells have 46 chromosomes (2n = 46) and undergo meiosis to produce four haploid daughter cells (gametes).

Which of the following is true regarding mitosis and meiosis?

I. Meiosis I produces twice as many daughter cells as mitosis

II. Crossing over only occurs during prophase I of meiosis

III. The daughter cells of meiosis I have the same amount of DNA as the daughter cells of mitosis

Possible Answers:

I only

II only

II and III

I and II

Correct answer:

II and III

100

Chromosomes are important participants in both meiosis and mitosis. Which of the following is false of meiosis?

Possible Answers:

Crossing over happens more frequently than in mitosis

It generates haploid cells, while mitosis generates diploid cells

Meiosis forms tetrads before its first division

It undergoes a reduction division during its second division

Meiosis is limited to germ cells

It undergoes a reduction division during its second division

This is a tricky question because all of the choices are correct, except for one minor part. Meiosis sees cells undergo a reduction division in the first division. That means that after the first meiotic division, the diploid germ cell has become a haploid.

100

Draw meiosis 2n=4, specifically:

pre-interphase, post-interphase, post-Meiosis 1, and post-meiosis 2 (daughter nuclei)

Answer the following question:
Do germline cells begin interphase as diploid?

100

During which of the following portions of the cell cycle are mRNA and proteins mainly produced?

Possible Answers:

Correct answer:

Explanation:

By referring to mRNA and proteins, this question is asking about the portion of the cell cycle that involves gene transcription and protein translation. This occurs mostly during growth and organelle replication in the G1 portion of Interphase.

200

The same second messengers are used in many different cells, but the response to second messengers is different in each cell. How is this possible?

Answer

Different cells produce different proteins, including cell-surface receptors and signaling pathway components. Therefore, they respond to different ligands, and the second messengers activate different pathways. Signal integration can also change the end result of signaling.

200

A student is observing a set of cells under the microscope. He takes notes but forgets to write the mitotic phase for each slide. His notes are as follows.

Cell A: Site of ribosome synthesis disappears

Cell B: The nuclear content spills out into the cytoplasm

Cell C: No sister chromatids are visible

What is the mitotic phase of each cell?

Possible Answers:

Cell A: Prophase

Cell B: Prophase

Cell C: Telophase

Cell A: Anaphase

Cell B: Anaphase

Cell C: Metaphase

Cell A: Prophase

Cell B: Anaphase

Cell C: Telophase

Cell A: Metaphase

Cell B: Prophase

Cell C: Metaphase

Correct answer:

Cell A: Prophase

Cell B: Prophase

Cell C: Telophase

200

Which of the following would occur in humans if meiosis produced diploid gametes?

Possible Answers:

The number of chromosomes in subsequent generations would be 23

The number of chromosomes in subsequent generations would increase exponentially

The number of chromosomes in subsequent generations would be 92

The number of chromosomes in subsequent generations would decrease exponentially

Correct answer:

The number of chromosomes in subsequent generations would increase exponentially

Meiosis is the process by which haploid gametes are produced. The attachment of a haploid sperm to a haploid egg begins the process of development and fertilization. In humans a sperm containing 23 chromosomes joins with an egg containing 23 chromosomes to create an organism with 46 chromosomes.

If meiosis were to produce diploid gametes, then the diploid gametes would combine to form an organism that contains twice as many chromosomes as the parent. For example, a diploid sperm and egg (containing 46 chromosomes each) would create an organism with 92 chromosomes. This new organism would produce another organism with 184 chromosomes (double 92). The subsequent generations would have twice as many chromosomes as the previous generation, and the amount of chromosomes would increase exponentially.

Offspring 1: 92 chromosomes

Offspring 2: 184 chromosomes

Offspring 3: 368 chromosomes

chromosomes=46∗2n

(n=generation)

The best answer is that the number of chromosomes in subsequent generations would increase exponentially.

200

a) Explain the role of the G1/S checkpoint in controlling cell division and how CDKs and cyclins work together to pass this checkpoint. Include in your response what conditions must be met for the cell to proceed past G1.
b) Describe how DNA damage can inhibit CDK-cyclin activity, preventing the cell from moving to the next phase. Include the role of tumor suppressor proteins (e.g., p53) in this inhibition and how this serves as a protective mechanism.

a) The G1/S checkpoint is critical for assessing cell size, nutrient availability, and DNA integrity before committing to DNA replication. CDK4/6 bound to Cyclin D helps the cell proceed past this checkpoint by phosphorylating the Rb protein. If conditions are favorable, Rb phosphorylation allows E2F to activate genes needed for S phase entry.
b) DNA damage can inhibit CDK-cyclin activity by activating tumor suppressor proteins like p53. When activated by DNA damage, p53 promotes the transcription of p21, a CDK inhibitor. p21 binds to and inhibits CDK-cyclin complexes (e.g., Cyclin E-CDK2), preventing the cell from advancing to the S phase. This pause allows for DNA repair and prevents the accumulation of mutations, acting as a protective mechanism against uncontrolled cell growth.

200

During the eukaryotic cell cycle, what is the purpose of the G2/M checkpoint?

Possible Answers:

To ensure that the cell is large enough for cell division

To ensure that the cell is ready to divide

To ensure that all chromosomes are aligned properly for cell division

To ensure that DNA hasn't been damaged during S phase

To allow for formation of the spindle fibers

Correct answer:

To ensure that DNA hasn't been damaged during S phase

Explanation:

The G2 phase occurs after S phase, but before M phase (mitosis). The purpose of the G2/M check point is to ensure there is no DNA damage that occurred during S phase (DNA synthesis). If damage is found, the cell will try to repair and DNA breaks. If the DNA cannot be repaired, the cell will undergo apoptosis. Many cancer suppressor genes, such as p53, are involved in this process of checking the DNA quality.

300

What is the main difference between receptor tyrosine kinases (RTKs) and G-protein-coupled receptors (GPCRs)?

The main difference between receptor tyrosine kinases (RTKs) and G-protein-coupled receptors (GPCRs) is their signal transduction mechanism. RTKs are single-pass transmembrane receptors with intrinsic kinase activity. Upon ligand binding, RTKs usually undergo dimerization, leading to autophosphorylation of specific tyrosine residues in their cytoplasmic domain, ultimately activating various downstream signaling pathways. On the other hand, GPCRs are seven-pass transmembrane receptors that interact with G-proteins when activated by a ligand. This interaction causes the G-protein to release GDP and bind GTP, resulting in the dissociation of the G-protein into α and βγ subunits. These subunits then modulate target enzymes or ion channels to generate intracellular signaling events.

300

In humans, a cell in prophase has __________ chromosomes, in metaphase has __________ chromosomes, and in anaphase has __________ chromosomes.

Possible Answers:

23 . . . 46 . . . 92

46 . . . 92 . . . 92

46 . . . 46 . . . 92

46 . . . 46 . . . 46

46 . . . 46 . . . 92

Humans are diploid organisms with a total of 46 chromosomes (2n = 46). They have 23 distinct chromosomes and each chromosome has a homologous chromosome, giving a total of 46 chromosomes. Upon completion of DNA replication in S phase, each chromosome gains an identical sister chromatid that is joined to the original chromosome at the centromere; however, this whole entity is still considered a single chromosome. When a cell enters prophase of mitosis, there are a total of 46 chromosomes, each with a sister chromatid. In metaphase, the cell still has 46 chromosomes and these chromosomes align along the midline of the cell. In anaphase, the sister chromatids get pulled apart to opposite ends; therefore, the sister chromatid separates from the chromosome and becomes its own chromosome. This means that in anaphase there are a total of 92 chromosomes in the cell.

These 92 chromosomes get pulled to opposite ends where 2 new daughter cells (with 46 chromosomes and no sister chromatids) are produced.

300

The __________ is the site of attachment of spindle fibers to sister chromatids during mitosis.

Possible Answers:

centrosome

centromere

kinetochore

centriole

Correct answer:

kinetochore

Centrosomes are portions of the cell that help nucleate microtubules and form the mitotic spindle. Centrioles are composed of tubulin and are portions of the centrosome. The centromere is the portion of the chromosome where the two sister chromatids are linked. The kinetochore is a protein structure that helps associate the mitotic spindle to the sister chromatids. The outer portion of the kinetochore interacts with the microtubules, while the inner portion associates with the centromeric DNA.

300

Name and number of the Cyclin and CDK complexes throughout cell cycle

Cyclin D-CDK4/6: Early G1, regulates the G1/S checkpoint.
Cyclin E-CDK2: Late G1, prepares for S phase.
Cyclin A-CDK2: During S phase, ensures DNA replication.
Cyclin A-CDK1: G2 phase, prepares for M phase.
Cyclin B-CDK1: During M phase, initiates mitosis.

300

The cell cycle is the series of events a cell undergoes during its lifetime. It involves four main phases: G1, G2, S phases, and mitosis. Each phase is characterized by a specific set of events. These events include cell growth, genetic material replication, and cell division. Several cellular machineries such as organelles and cytoskeletal elements are involved in each phase. In addition to these phases, the cell cycle has specific checkpoints to ensure that the cell is ready to proceed to the subsequent steps in the cycle. This decreases errors during replication and division. G0 phase is a special phase of the cell cycle that is characterized by a quiescent cell.

Cyclin-dependent kinases are special molecules that facilitate the progression of a cell through the cell cycle. Many molecules such as p53 and kinase inhibitors regulate the cell cycle. Unregulated cell cycle can lead to rapid growth of cells that may, eventually, lead to cancer.

A researcher is analyzing a molecule that stops the progression of the cell cycle. What could be the identity of this molecule?

Possible Answers:

Cyclin-dependent kinase inhibitor

Cyclin-depended kinase

DNA polymerase

p53

Correct answer:

Cyclin-dependent kinase inhibitor

Explanation:

Progression through the cell cycle involves several molecules. There are several checkpoints along the cell cycle to ensure that the cell is ready for the next phase. One of the most important molecules involved in this process are the cyclin-dependent kinases (CDKs). These molecules phosphorylate and activate molecules that are important for the cell cycle. Inhibiting CDKs by an inhibitor will halt the activity of these molecules and, subsequently, the progression of the cell cycle.

DNA polymerase is an enzyme involved in DNA replication. It promotes DNA replication and helps the cell progress through the cell cycle. p53 is a tumor suppressor gene that is important for halting uncontrolled growth of cells. This is one of the most common mutated genes found in tumors. Lack of p53 activity leads to decreased regulation of cell growth. This means that cells can proliferate uncontrollably and can eventually become tumors.

400

Explain the steps of the GCPR pathway.
Does the GDP add a P, or is it wholly replaced with GTP?

1.) ligand binds to the GPCR receptor 2.) GPCR goes under a conformational change 3.) GDP attached to one of the subunits of the heterotrimeric protein ( the alpha one) gets replaced by GTP 4.) The alpha protein that is attached to GTP, dissociates from the other two subunits (beta and gamma) of the heterotrimeric protein, and starts to regulate a target protein. 5.) target protein then causes a reaction via second messenger using either ( IP3, DAG, Ca2+ or CaMP) 6.) GTP then gets hydrolyzed back into GDP 7.) Alpha subunit with the attached GDP reassociates with the other two subunits

400

Meiosis is a form of cell division that occurs in special types of cells called germ cells. It is different from mitosis because it takes a diploid cell and splits it into four, nonidentical haploid cells. In males, these haploid cells are called sperm and in females they are called eggs or ova. Meiosis has two steps: meiosis I and meiosis II. Both steps have their corresponding prophase, metaphase, anaphase, and telophase. Meiosis I phases are similar to mitotic phases, with a few key differences. Meiosis II phases are exactly identical to the mitotic phases.

Which of the following eukaryotic process is similar to the bacterial asexual reproduction?

Possible Answers:

Meiosis I

DNA replication

Transcription

Mitosis

Correct answer:

Mitosis

400

Which answer choice incorrectly matches the type of chromatin with the phase of mitosis?

Possible Answers:

Heterochromatin—prophase

Euchromatin—interphase

Heterochromatin—metaphase

Heterochromatin—interphase

Euchromatin—telophase

Correct answer:

Euchromatin—telophase

DNA is stored in loosely wound euchromatin before mitosis. During mitosis, the DNA condenses into chromosomes, which are made of heterochromatin. It becomes more dense during prophase, and stays that way until the end of mitosis. Euchromatin is more lightly packed than heterochromatin.

Mitosis follows the following sequence: prophase, metaphase, anaphase, telophase, cytokinesis. Interphase refers to the time period between mitotic divisions. During interphase, most DNA is euchromatin, but some regions remain as heterochromatin to prevent unwanted transcription; thus DNA exists as both types of chromatin during interphase, but only as heterochromatin during mitosis. Matching euchromatin to telophase is the answer, as this is a false statement.

400

Discuss how the desensitization of GPCR signaling occurs after prolonged exposure to the ligand. Include the roles of GRKs (G-protein coupled receptor kinases), β-arrestins, and the potential consequences of dysregulated GPCR desensitization in pathological conditions like heart failure.

Desensitization Mechanism:

Prolonged ligand binding leads to receptor phosphorylation by G-protein coupled receptor kinases (GRKs), which facilitates β-arrestin binding.
β-arrestin binding prevents further G-protein activation and promotes receptor internalization via clathrin-mediated endocytosis.
Dysregulation of this process (e.g., in heart failure) can lead to impaired receptor downregulation, contributing to exaggerated responses and worsening disease symptoms.

400

An organism is found to have a diploid number of 50. How many chromosomes will this organism have at the end of S phase?

Possible Answers:

100

200

Correct answer:

Explanation:

DNA replication occurs during the S phase. Upon completion of DNA replication, a cell has a duplicate copy of every chromosome it possesses. Recall that humans have 2 sets of 23 chromosomes (total of 46 chromosomes). For example, there are two different copies of chromosome 1, two different copies of chromosome 2, etc. The two different copies of chromosomes are termed homologous chromosomes. Upon completion of DNA replication, each of these 46 chromosomes will have an identical duplicate copy, called the sister chromatid. The sister chromatid is attached to the original chromosome at the centromere. This entire entity, however, is still considered a single chromosome; therefore, upon completion of S phase humans will have 46 chromosomes.

The organism in the question has 50 chromosomes to begin S phase (2n = 50); therefore, it will have 50 chromosomes at the end of S phase.

500

Cyclic AMP is a common member of signal transduction pathways. In many cases, cAMP indirectly regulates ATP production. High concentrations of cAMP indicate a high rate of ATP use in the cell. Which of the following is the most likely consequence of high cAMP concentrations in the cell?

A: increase in the rate of glucose metabolism

B: decrease in the rate of glycogen metabolism

C: decrease in the rate of ATP production

D: increase in the rate of ATP dephosphorylation

A: Since high cAMP levels indicate low ATP levels, the logical consequence would be increased metabolism rate for energy, i.e. ATP , production. Hence, the rate of glucose metabolism will be increased.

500

Nuclear transport is a very important concept of study in modern cellular biology. Transport of proteins into the nucleus of an organism requires energy in the form of GTP, which is attached to a protein called Ras-related Nuclear protein (RAN).

RAN is a monomeric G protein found in both the cytosol as well as the nucleus and its phosphorylation state plays an important role in the movement of proteins into and out of the nucleus. Specifically, RAN-GTP and RAN-GDP binds to nuclear import and export receptors and carries them into or out of the nucleus. They also play a role in dropping off cargo that import and export receptors hold onto. RAN's functions are controlled by two other proteins: RAN guanine exchange factor (RAN-GEF) and RAN GTPase activating protein (GAP). RAN-GEF binds a GTP onto RAN, while RAN-GAP hydrolyzes GTP into GDP. As a result, there is a RAN-GTP and RAN-GDP concentration gradient that forms between the cytosol and nucleus.

During prophase, what most likely happens to the RAN-GTP and RAN-GDP concentration gradient?

Possible Answers:

The concentration gradient breaks down because the cell no longer requires protein movement into or out of the nucleus

There is no change in the concentration gradient during prophase

The concentration gradient strengthens because the nuclear envelope becomes even more impermeable

The concentration gradient strengthens because the cell requires more proteins to diffuse into the nucleus during mitosis

The concentration gradient breaks down because the nuclear membrane breaks down

Correct answer:

The concentration gradient breaks down because the nuclear membrane breaks down

500

Something goes wrong during meiosis in a male and the four daughter sperm cells that are produced all have the wrong amount of chromosomes. Two of the sperm have one extra chromosome and the other two have one missing chromosome. At what step did the problem most likely occur, and what was it?

Possible Answers:

Prophase I—trisomy

Anaphase I—inversion

Telophase II—translocation

Metaphase I—nondisjunction

Telophase I—deletion

Correct answer:

Metaphase I—nondisjunction

500

Outline the specific steps involved in the activation of a receptor tyrosine kinase (RTK) upon ligand binding. Include the sequence of events from ligand binding to receptor dimerization, autophosphorylation, and the initiation of downstream signaling. Be sure to explain the molecular interactions that occur during each step.

Ligand Binding: The signaling molecule (e.g., epidermal growth factor (EGF) for EGFR) binds to the extracellular domain of the receptor, causing a conformational change.
Receptor Dimerization: Upon ligand binding, two monomers of the receptor form a dimer (or oligomerize), bringing the intracellular kinase domains of the receptors into close proximity.
Autophosphorylation: The close proximity of the intracellular domains allows autophosphorylation of tyrosine residues on the cytoplasmic tail of the receptor. The tyrosine kinase domain catalyzes the transfer of phosphate groups from ATP to tyrosine residues.
Docking of Signaling Molecules: The phosphorylated tyrosine residues create binding sites for downstream signaling molecules that contain SH2 (Src Homology 2) or PTB (Phosphotyrosine Binding) domains. These proteins bind to the phosphorylated tyrosines, leading to activation of intracellular signaling pathways.

500

The tumor suppressor protein p53 is known to halt the cell cycle if DNA damage is detected, primarily by activating p21, an inhibitor of cyclin-dependent kinase complexes. Given this role, what is the most likely effect of a p53 mutation on the cell cycle, and what could this imply for cellular proliferation and cancer risk?

A. Increased apoptosis due to unrestricted CDK activity
B. Unregulated progression through the G1/S checkpoint, leading to increased cell division
C. Enhanced repair of DNA damage and slower progression through the G2 phase
D. Decreased synthesis of p21, resulting in a prolonged G1 phase