Biology Module 4

The division of a bacterial cell occurs as the:

new membrane and cell wall materials begin to grow and form a septum.

This protein or protein complex functions in the cell to stop cell division if the cell has experienced extensive DNA damage:

p53

The number of chromosomes characteristic of diploid eukaryotic cells, in general:

varies considerably from 2 to over 1000 in different species.

Meiosis results in a reassortment of maternal chromosomes (inherited from the mother) and paternal chromosomes (inherited from the father.) If 2n=6 for a given species, what is the probability that a gamete will receive 1 maternal chromosome and 2 paternal chromosomes?

(3/8)

A somatic cell from a garden pea normally contains 14 chromosomes. How many sister chromatids would that cell contain during G1 of the cell cycle?

0

A somatic cell from a corn plant normally contains 20 chromosomes. How many sister chromatids would that cell contain during G2 of the cell cycle?

40

If a germ-line cell from a frog contains 10 picograms of DNA during G1 of interphase, then how many picograms of DNA would be present in each cell during prophase II of meiosis? (Enter the number only, not the units.)

10

A cell biologist examines a diploid cell from a barley plant during metaphase of mitosis and determines that 14 centromeres are present. Based on this finding, how many chromatids should be present in a single cell from this species in prophase II of meiosis?

14

Nondisjunction is the failure of homologous chromosomes to separate during meiosis I, or the failure of sister chromatids to separate during meiosis II or mitosis. As a result, both homologous chromosomes or both sister chromatids migrate to the same pole of the cell. This produces daughter cells with an imbalance of chromosomes. If 22 pairs of homologous chromosomes segregate normally during meiosis I in humans (n=23) but we have nondisjunction of 1 pair, then at the end of meiosis II we will have

2 cells with 24 chromosomes and 2 with 22

Nondisjunction is the failure of homologous chromosomes to separate during meiosis I, or the failure of sister chromatids to separate during meiosis II or mitosis. As a result, both homologous chromosomes or both sister chromatids migrate to the same pole of the cell. This produces daughter cells with an imbalance of chromosomes. A cell biologist examines the final products of meiosis in a rabbit cell (2n=44) and finds 2 cells with 22 chromosomes, 1 cell with 24 chromosomes and 1 cell with 20 chromosomes. Most likely this was caused because

2 pairs of sister chromatids failed to separate during meiosis II

A cell biologist produces a karyotype of mouse somatic cells arrested in mitosis. She sees 40 chromosomes, which is completely normal for mice. Based on this information, what is the haploid number of chromosomes for mice?

20

A cell biologist determines that diploid cells from a particular species of grasshopper contain 200 picograms of DNA per cell during the G2 stage of interphase. Based on this finding, how many picogramsof DNA should be present in a single cell from this species during metaphase I of meiosis? (Enter the number only, not the units.)

200

If a cell has 32 chromosomes prior to S and undergoes mitosis followed by cytokinesis, each new daughter cell will have how many chromosomes?

32

If a somatic cell from a mouse contains 40 picograms of DNA during G2 of interphase, then how many picograms of DNA would be present in each cell during anaphase I of meiosis? (Enter the number only, not the units.)

40

If a somatic cell from a frog contains 20 picograms of DNA during G2 of interphase, how many picograms of DNA would be present in each gamete produced by this species? (Enter the number only, not the units.)

5

A cell biologist determines that diploid cells from a particular species of Drosophila contain 16 chromatids during metaphase of mitosis. Based on this finding, how many molecules of DNA should be present in the chromosomes of a single cell from this species during anaphase II of meiosis? (Enter the total number of DNA molecules in all chromosomes, not the number of DNA molecules per chromosome.)

8

If there are 32 sister chromatids in a normal somatic cell, what is the haploid number for that cell?

8

How many molecules of DNA are present in the chromosomes of a single human cell (2n=46) during prophase I of meiosis? (Enter the total number of DNA molecules in all chromosomes, not the number per chromosome.)

92

What is separase?

A protein that destroys cohesin through its protease activity.

12. Many receptor tyrosine kinase (RTK) pathways lead to the activation of Ras. To activate Ras, it is necessary to recruit a guanine nucleotide exchange factor to the plasma membrane, because Ras is a membrane associated protein. Guanine nucleotide exchange factors, such as SOS, stimulate the exchange of GDP for GTP. However, SOS cannot bind directly to most RTKs. The protein Grb2 has a domain that can bind to phosphorylated tyrosines, and another domain that can bind to SOS. Therefore, Grb2 can bind to active RTKs and recruit SOS to the plasma membrane. Grb2 is an example of what kind of signaling molecule?

Adapter Protein

The stage of mitosis characterized by the physical separation of sister chromatids is called:

Anaphase

In bacterial cell division, the cell divides into two nearly equal halves. This process is referred to as:

Binary fission

What is similar about G protein-coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs)?

Both can activate phospholipase C

How are receptor tyrosine kinases and steroid hormone receptors similar?

Both have a binding site for a ligand

In G2, there are typically high levels of the mitotic cyclin. Why is cdc2 not active during G2 if the mitotic cyclin is present?

Cdc2 is also regulated by phosphorylation.

A new drug is discovered which disrupts the process of synapsis. This drug is most likely to affect

Cell division in germ-line cells

Which of the following is not haploid?

Cell in Prophase I

The point of connection between two sister chromatids, before anaphase II of meiosis separates them, is called the

Centromere

When bound to ligand, this type of receptor changes conformation to allow ions to move down their concentration gradient across the membrane:

Channel-Linked Protein

If the gene encoding one of the proteins that forms cohesin were mutated such that cohesin could not perform its normal function, what would be the consequence? Check all that apply.

Chromosomes would not be able to properly align at the metaphase plate. The separation of sister chromatids would not likely occur specifically during anaphase A.

How does chromatid cohesion differ in mitosis and meiosis?

Cohesion between sister chromatids is maintained during anaphase I of meiosis but not during anaphase of mitosis

Homologous chromosomes pair along their length during prophase I of meiosis. While two homologues are paired, genetic exchange may occur between them in a process called ________.

Crossing over

The progress of the eukaryotic cell cycle is regulated primarily by what proteins?

Cyclins

The stage of the cell cycle during which the cytoplasm divides to form two cells is called:

Cytokinesis

If there were no suppression of DNA replication between meiotic divisions but cytokinesis proceeded normally, what is the most likely outcome of meiosis?

Diploid Cells

Many receptor tyrosine kinase pathways have MAPK as a downstream signaling component. MAPK can phosphorylate target proteins. What type of signaling molecule is MAPK?

Enzyme

Animal cells typically achieve cytokinesis by:

Forming a cleavage furrow

What is the sequence of events in a typical eukaryotic cell cycle?

G1 to S to G2 to mitosis to cytokinesis

At what checkpoint(s) does the cell arrest in response to DNA damage?

G1/S and G2/M

This stage of the cell cycle is characterized by growth and it contains a checkpoint to verify that all of the DNA has been replicated prior to mitosis

G2

You are studying cell cycle progression in an early frog embryo. If you were to inject a protein synthesis inhibitor into a cell during S phase, where do you predict that the cells would arrest?

G2

______ cells contain one set of chromosomes.

Haploid

The two copies of each type of chromosome found in normal somatic (body) cells in an organism, throughout the cell cycle, are called:

Homologous chromosomes

Why is it so important that all of the chromosomes align on the metaphase plate during metaphase?

If they cannot, it suggests that they aren't properly attached to the spindle microtubules, and thus won't separate properly during anaphase.

What is the portion of the cell cycle during which the chromosomes are invisible under the light microscope because they are not yet condensed?

Interphase

How can phosphorylation affect protein function? Select all choices that apply.

It can activate some enzymes. It can inhibit some enzymes. It can provide a site or location on some proteins for other proteins to bind.

Which of the following statements about the mitotic spindle is TRUE?

Kinetochore microtubules in the mitotic spindle attempt to connect to kinetochore proteins in the centromeres of the condensed chromosomes.

This is the stage of mitosis characterized by the alignment of the chromosomes in a ring along the inner circumference of the cell:

Metaphase

Suppose you have a multicellular eukaryotic organism that is composed entirely of haploid cells. This organism would produce gametes by the process of

Mitosis

How does the organization of the bacterial genome differ from the organization of the eukaryotic genome?

Most bacterial chromosomes are circular and the eukaryotic chromosomes contained in the nucleus are not.

You are having lunch with an elderly friend when suddenly he begins to experience chest pain and tightness. He reaches into his pocket, gets out one of his nitroglycerin tablets and quickly takes it. After the episode passes, your friend asks you how the nitroglycerin helps his angina. You explain that nitroglycerin gets converted by cells to nitric oxide (NO) causing the smooth muscle cells of the blood vessel to relax and increase blood flow to the heart. He pushes you for a more detailed explanation, so you explain further that:

NO activates guanylyl cyclase, which catalyzes the synthesis of cGMP, which acts as an intracellular messenger in a pathway leading to smooth muscle relaxation.

Leptin is a circulating hormone that is produced by fat cells and plays a role in body metabolism and obesity. It normally binds to receptors in the brain and inhibits appetite. Studies have demonstrated that when obese mice that are leptin deficient are injected with leptin they quickly lose their excess weight. Interestingly, however, many overweight people have high levels of leptin in their bloodstream. Why do you think that the high levels of leptin in obese individuals are insufficient to curb their appetite?

Obese people who have high levels of leptin may have a leptin receptor with decreased sensitivity.

The drug Taxol, or Paclitaxel, is used to treat patients with a variety of cancers, including breast, lung and ovarian cancers. The drug works by stabilizing microtubules, and preventing their disassembly. The goal of the drug is to prevent dividing cells from being able to complete mitosis. As a result, cancerous cells can no longer divide. In a cell treated with Taxol, at what stage of mitosis will the cells arrest?

Prior to Metaphase

Which cells never divide by meiosis? (Check all that apply.)

haploid cells somatic cells zygotes

During this stage of mitosis, the nuclear envelope begins to break down and the spindle begins to form.

Prophase

A new small molecule drug inhibits the function of the APC/C. If this drug were applied to cells undergoing the cell cycle, what do you think would be the result? Check all that apply.

Securin would not be destroyed in these cells. These cells would not be able to undergo Anaphase A. These cells would not be able to degrade mitotic cyclins. These cells would not be able to exit mitosis.

If a cell contained a mutation in the gene that encodes FtsZ, what process would be affected?

Septation

You are assembling a model of a chromosome, but begin having some trouble when you get to the step of forming chromatin loops. If you are unable to resolve this problem, what step of chromosome structure would you be unable to achieve?

Rosettes

A duplicate copy of all of the hereditary information contained in the nucleus of eukaryotic cells is made during what stage of the cell cycle?

S (Synthesis)

During what stages of the cell cycle are sister chromatids bound together by cohesion?

S, G2, prophase, metaphase

The fusion of a male gamete with a female gamete is called

Syngamy

Before cell division of somatic cells, each chromosome must be replicated. After replication, the resulting two parts of each chromosome are held together by cohesin at the centromere. These two parts are referred to as:

Sister Chromatids

These structures are held together by cohesion:

Sister Chromatids

The pairing of chromosomes along their lengths, which is essential for crossing over, is referred to as

Synapsis

This stage of mitosis is characterized by the disassembly of spindle apparatus, the reestablishment of the nuclear membrane, and the de-condensation of the chromosomes:

Telophase

What stage of mitosis is essentially the reverse of prophase?

Telophase

During which stage of meiosis would you find haploid cells with 1/4 as much DNA as its mother cell?

Telophase II

If a chromosome contains a mutation such that it cannot bind to the kinetochore complex, what would be the consequence?

That chromosome would not be able to bind to the mitotic spindle.

The point of constriction on chromosomes that contains certain repeated DNA sequences that bind specific proteins is called:

The Centromere

You are examining the effect of maturation-promoting factor (MPF) in sea urchin cells, which have a diploid number of 36. If you fuse a dividing sea urchin cell with a G1 arrested oocyte, what would be the outcome?

The G1 cell would enter mitosis, but would likely arrest at the spindle checkpoint because the chromosomes have not been properly replicated.

Estimates are that p53 is mutated in 50% of all human cancers. If the gene that encodes p53 is mutated such that p53 is non-functional, what processes would be affected? Check all that apply.

The ability to halt the cell cycle in response to DNA damage. The ability to repair DNA damage. The ability to stimulate cell death processes if the cell is irreparably damaged.

Why are phosphorylation and dephosphorylation reactions commonly used to regulate signal transduction pathways?

The addition or removal of a phosphate group can expose or hide potential binding sites in proteins or change protein activity

Using a specific chemical, a cell biologist has blocked In the below image, what is the role of the portion of the signaling pathway involving: MKKK, MKK, and MK?

The chemical prohibits binding of a ligand to the receptor.

What would you expect to happen if the anaphase-promoting complex/cyclosome (APC/C) failed to ubiquitinate securin?

The cohesion complex will persist, preventing the cell from entering anaphase.

Tamoxifen is a drug that is used to treat breast cancer. It inhibits the activities of the estrogen receptor in breast epithelial cells, which are the cells that are relevant to breast cancer....

The estrogen receptor is bound to different coactivators in different tissues.

A pregnant mother recently had an ultrasound that indicated massive defects in the formation of her unborn baby's heart. Other oddities were noted in the spinal cord region, the kidneys, and the formation of the facial features. She had an amniocentesis to examine the baby's karyology, and it was noted that there was a deletion of a small piece of one chromosome. The doctors advised her that her that she would likely miscarry. The devastated parents consult you as a genetic advisor on the likelihood that a future pregnancy would end similarly. What advise do you give this unfortunate couple?

The mutation was probably a germ line mutation that only affected a single egg or sperm, so they should try to have more children

In prophase, ribosomal RNA synthesis stops when the chromosomes condense, and as a result:

The nucleus disappears

If a cell was capable of bypassing metaphase and going directly from prometaphase to anaphase, what is the most likely consequence of this?

The resulting daughter cells would have different numbers of chromosomes.

What happens during Anaphase B?

The spindle poles move apart

You are performing an experiment to assay phosphorylation of a substrate by a protein kinase. Based on the data in the table below, what do these experimental results suggest?

The substrate can undergo autophosphorylation.

If a gene encoding one of the proteins that is part of the condensin complex was mutated such that condensin could not bind properly with DNA, what would be the result? Check all that apply.

There is likely a mutation in a gene that encodes an SMC protein. There may be chromosome breakages that occur during mitosis, because compaction of the chromosome cannot properly occur.

In animals, cells that will eventually undergo meiosis to produce the gametes are set aside early in the course of development.

These cells are called germ-line cells.

In a human somatic cell (normal body cell) that is in G1, what would be true about chromosome number and structure? Check all that apply. ***

These cells would be considered diploid (2n). These cells would contain homologous chromosomes.

In a human somatic cell (normal body cell) that is in G2, what would be true about chromosome number and structure? Check all that apply.***

These cells would be considered diploid (2n). These cells would contain homologous chromosomes. These cells would contain sister chromatids.

You are leading a team of researchers at a pharmaceutical company. Your goal is to design drugs that help fight cancer. Specifically, you want to focus on drugs that bind to and inactivate certain proteins, thereby halting cell cycle progression. One of your team members suggests targeting the retinoblastoma (Rb) protein and inhibiting this protein. Will this approach be successful? Why or why not?

This approach will not be successful. Rb is tumor-suppressor protein, and functions to inhibit the action of a number of cell cycle regulatory proteins. A drug designed to inactivate the Rb protein would essentially create the same situation as in as a cell that lacks both copies of the Rb gene. Lack of Rb activity would release the inhibition of cell cycle regulatory proteins, thereby promoting cell cycle progression, rather than halting it.

In the below image, what is the role of the portion of the signaling pathway involving: MKKK, MKK, and MK?

To phosphorylate target proteins To amplify the signal To transduce the signal from activated Ras to the response proteins

Your research project involves the characterization of a particular signal transduction pathway. Specifically, you have been studying a receptor tyrosine kinase and protein X, which initiates downstream events. You are certain that protein X is part of the signal transduction pathway, but have been unable to identify a direct protein-protein interaction between the receptor tyrosine kinase and the protein X. What should you do next in your attempt to identify a link between the receptor tyrosine kinase and protein X?

Try to identify an adapter protein that can interact with both the receptor and protein X.

In later chapters, you will learn more about the regulation of gene expression. One way to regulate gene expression is to make changes to the histone proteins to alter how tightly the DNA is coiled and wrapped. The more tightly coiled and wrapped a particular region of DNA is, the less likely it is that the genes in that region will be expressed. Bearing this in mind, how tightly do you think regions of heterochromatin are compacted?

Very Tightly

The EGF-receptor is a receptor tyrosine kinase that binds to epidermal growth factor (EGF). In response to EGF binding, the EGF-receptor stimulates a signaling pathway that involves Ras. Ultimately, this signaling pathway leads to the upregulation of factors that promote cell division. As a result, in response to EGF, cells that express the EGF-receptor undergo cell division to produce more cells. If an inhibitor that inhibited all G proteins was added to cells, how would this affect the ability of these cells to respond to EGF?

While the receptor would dimerize and autophosphorylate in the presence of the inhibitor, downstream signaling would be prevented because the inhibitor would affect Ras activity.

The function of adenylyl cyclase is to:

catalyze the conversion of ATP to cAMP.

In 95% of cases of Down's syndrome, there is one extra chromosome (number 21) in every cell. This aneuploid condition is most likely the result of

failure of 1 homologous pair to segregate during meiosis.

Plant cells typically achieve cytokinesis by:

forming a cell plate across the middle of the cell.

Consider meiosis starting with a diploid cell where 2n=6. If DNA replication were not suppressed between meiotic divisions, the final result would be

four cells with 6 DNA molecules each.

In animals, the cells that will eventually undergo meiosis to produce gametes are set aside early in development. These are called

germ-line cells

During which stage of meiosis would you find a cell with a diploid chromosome number and chromosomes that are all attached to spindle fibers?

metaphase I

A researcher is working to generate a new cancer drug. Thus far, he has identified a compound that can reduce the size of tumors in the lung. However, in order for the drug to work, the lung tumor has to be small. In addition, the tumor cannot have metastasized (spread to other areas of the body). Furthermore, he knows that the drug acts to prohibit the signaling from one tumor cell to another tumor cell. Given the above information, this new drug prohibits:

paracrine signaling between tumor cells.

A cell biologist examines a diploid cell from a barley plant during prometaphase of mitosis and determines that 28 chromatids are present. The role of meiosis in this plant is to (Check all that apply)

produce 4 daughter cells that are genetically identical to each other (Not sure****) reduce the number of chromosomes per cell from 14 to 7

A scientist wants to study histones. Histones are:

proteins that double-stranded DNA molecules wrap around in eukaryotes.

During meiosis I, the 2 kinetochores of sister chromatids fuse and kinetochore microtubules from one pole of the cell attach to the fused kinetochore. This is important because it ensures that during anaphase I

sister chromatids are pulled toward the same pole of the cell.