Sample HW Questions for Exam 2

A plant-derived protein known as colchicine can be used to poison cells by blocking the formation of the mitotic spindle. Which of the following would result if colchicine is added to a sample of cells in G2?

Chromosomes would condense but fail to align at the metaphase plate, and the cell cycle would arrest at this point.

If a horticulturist breeding gardenias succeeds in having a single plant with a particularly desirable set of traits, which of the following would be her most probable and efficient route to establishing a line of such plants?

Clone the plant asexually to produce an identical one.

If a eukaryotic cell is in the G1 phase of the cell cycle, which statement about the cell's chromosomes must be correct? Each chromosome consists of two identical chromatids. The chromosomes are preparing for DNA synthesis. Each chromosome is made of a complex of DNA and associated proteins.

Each chromosome is made of a complex of DNA and associated proteins. Eukaryotic nucleus contains chromatin, a complex of DNA and associated protein molecules. The proteins maintain the structure of the chromosomes and help control gene activity.

Why does the oxidation of organic compounds by molecular oxygen to produce CO2 and water release free energy? Electrons are being moved from atoms that have a lower affinity for electrons (such as C) to atoms with a higher affinity for electrons (such as O). The covalent bond in O2 is unstable and easily broken by electrons from organic molecules. The oxidation of organic compounds releases less energy than the energy stored in the covalent bonds of CO2 and water. The electrons have higher potential energy when associated with water and CO2 than they do in the organic compounds. The covalent bonds in organic molecules and molecular oxygen have more kinetic energy than the covalent bonds in water and carbon dioxide.

Electrons are being moved from atoms that have a lower affinity for electrons (such as C) to atoms with a higher affinity for electrons (such as O).

Following activation of a receptor, which sequence below represents the correct order in which components will be involved in a signaling pathway that utilizes the second messenger cAMP?

G protein →→ adenyl cyclase →→ cAMP →→ protein kinase

The cell cycle control systems of cancer cells differ from those of normal cells. Select the best explanation for this fact. Genetic changes alter the function of the cancer cell's protein products. Cancer cells are immortal. Cancer cells divide excessively and invade other tissues.

Genetic changes alter the function of the cancer cell's protein products. The underlying basis of cancer is almost always a change in one or more genes that alters the function of their protein products, resulting in faulty cell cycle control.

How are sister chromatids and homologous chromosomes different from each other?

Homologous chromosomes contain the same gene loci but may have different alleles of a particular gene. Sister chromatids are identical copies of each other produced during DNA replication.

In the figure above, which numbered segment(s) of the cycle represent G1?

I and V

Refer to the life cycles illustrated in the figure. Which of the life cycles is (are) typical for plants and some algae?

II only

In a life cycle such as that shown in diagram II of the figure above, if the zygote's chromosome number is 10, which of the following will be true?

In a life cycle such as that shown in diagram II of the figure above, if the zygote's chromosome number is 10, which of the following will be true?

In acetyl CoA formation, the carbon-containing compound from glycolysis is oxidized to produce acetyl CoA. From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of acetyl CoA formation.

In acetyl CoA formation, pyruvate (a product of glycolysis) is oxidized to acetyl CoA, with the reduction of NAD+ to NADH and the release of one molecule of CO2.

Refer to the drawings in the figure of a single pair of homologous chromosomes as they might appear during various stages of either mitosis or meiosis. Which diagram(s) represent(s) anaphase II of meiosis?

V only

Which phase of meiosis is represented in the figure above?

Which phase of meiosis is represented in the figure above?

Chromatids are separated from each other during which of the following processes?

during both mitosis and meiosis II

After telophase II of meiosis, the chromosomal makeup of each daughter cell is

haploid, and the chromosomes are each composed of a single daughter chromosome.

After telophase I of meiosis, the chromosomal makeup of each daughter cell is

haploid, and the chromosomes are each composed of two chromatids

Which of the following elements do all sexual life cycles in eukaryotic organisms have in common?

meiosis, fertilization, and gametes

Which of the following is the smallest unit that would contain a complete copy of the entire human genome?

one human somatic cell

Carbon dioxide (CO2) is released during which of the following stages of cellular respiration?

oxidation of pyruvate to acetyl CoA and the citric acid cycle

Photosynthesis is a redox reaction. H2O is _____ during the light reactions and CO2 is _____ during the Calvin cycle.

oxidized...reduced

In fermentation _____ is reduced and _____ is oxidized. pyruvate ... NADH NADH ... lactate lactate ... ethanol NAD+ ... pyruvate lactate ... NADH

pyruvate ... NADH

During alcohol fermentation in yeast, NAD+ is regenerated from NADH by which of the following processes? oxidation of pyruvate to acetyl CoA oxidation of ethanol to acetaldehyde reduction of pyruvate to lactate reduction of acetaldehyde to ethanol reduction of acetyl CoA to ethanol

reduction of acetaldehyde to ethanol

In glycolysis, ATP molecules are produced by _____.

substrate-level phosphorylation A phosphate group is transferred from glyceraldehyde phosphate to ADP.

In most plants the carbohydrates produced by photosynthesis are transported out of the leaves to the rest of the plant as which of the following molecules?

sucrose

At the end of _____ and cytokinesis, haploid cells contain chromosomes that each consist of two sister chromatids.

telophase I

1. DNA replication produces two identical DNA molecules, called , which separate during mitosis. 2. After chromosomes condense, the is the region where the identical DNA molecules are most tightly attached to each other. 3. During mitosis, microtubules attach to chromosomes at the . 4. In dividing cells, most of the cell's growth occurs during . 5. The is a cell structure consisting of microtubules, which forms during early mitosis and plays a role in cell division. 6. During interphase, most of the nucleus is filled with a complex of DNA and protein in a dispersed form called . 7. In most eukaryotes, division of the nucleus is followed by , when the rest of the cell divides. 8. The are the organizing centers for microtubules involved in separating chromosomes during mitosis.

1. DNA replication produces two identical DNA molecules, called sister chromatid(s), which separate during mitosis. 2. After chromosomes condense, the centromere(s) is the region where the identical DNA molecules are most tightly attached to each other. 3. During mitosis, microtubules attach to chromosomes at the kinetochore(s). 4. In dividing cells, most of the cell's growth occurs during interphase. 5. The mitotic spindle(s) is a cell structure consisting of microtubules, which forms during early mitosis and plays a role in cell division. 6. During interphase, most of the nucleus is filled with a complex of DNA and protein in a dispersed form called chromatin. 7. In most eukaryotes, division of the nucleus is followed by cytokinesis, when the rest of the cell divides. 8. The centrosome(s) are the organizing centers for microtubules involved in separating chromosomes during mitosis.

Drag the terms to the appropriate blanks to complete the following sentences summarizing the redox reactions of photosynthesis. Terms may be used once, more than once, or not at all.

1. In the light reactions, light energy is used to oxidize H2O to O2. 2. The electrons derived from this oxidation reaction in the light reactions are used to reduce NADP+ to NADPH. 3. The Calvin cycle oxidizes the light-reactions product NADPH to NADP+. 4. The electrons derived from this oxidation reaction in the Calvin cycle are used to reduce CO2 to G3P. In the light reactions, light energy is used to remove electrons from (oxidize) water, producing O2 gas. These electrons are ultimately used to reduce NADP+ to NADPH. In the Calvin cycle, NADPH is oxidized back to NADP+ (which returns to the light reactions). The electrons released by the oxidation of NADPH are used to reduce three molecules of CO2 to sugar (G3P), which then exits the Calvin cycle.

A group of cells is assayed for DNA content immediately following mitosis and is found to have an average of 12 picograms of DNA per nucleus. How many picograms of DNA would be found in a nucleus at the end of G1 and the end of G2?

12; 24

Sort each process into the appropriate bin according to whether it contributes to heredity only, genetic variation only, or both. (Note that a bin may be left empty.)

Both: DNA replication before meiosis crossing over chromosome alignment in metaphase I and separation in anaphase I chromosome alignment in metaphase II and separation in anaphase II fertilization

How many NADH are produced by glycolysis?

2

Glycolysis results in a net production of which of the following molecules from each molecule of glucose? 2 NAD+, 2 pyruvate, and 2 ATP 6 CO2, 2 NADH, 2 pyruvate, and 2 ATP 2 NADH, 2 pyruvate, and 2 ATP 6 CO2, 2 pyruvate, and 30 ATP 4 NADH, 2 pyruvate, and 4 ATP

2 NADH, 2 pyruvate, and 2 ATP

A cell in G2 of the cell division cycle contains 20 chromatids. How many centromeres are present in this cell?

20

In the Calvin cycle, how many ATP molecules are required to regenerate RuBP from five G3P molecules?

3

Which of the following combinations of products would result from three acetyl CoA molecules entering the citric acid cycle (see the figure)? 3 ATP, 3 CoA, 3 CO2, 3 NADH, and 3 FADH2 36 ATP, 3 CoA, 6 CO2, 6 NADH, and 6 FADH 21 ATP, 1 CoA, 2 CO2, 3 NADH, and 1 FADH 23 ATP, 3 CoA, 6 CO2, 9 NADH, and 3 FADH2 2 ATP, 2 CoA, 2 CO2, 3 NADH, and 3 FADH2

3 ATP, 3 CoA, 6 CO2, 9 NADH, and 3 FADH2

The following question refers to the essential steps in meiosis described below. 1. formation of four new nuclei, each with half the chromosomes present in the parental nucleus 2. alignment of homologous chromosomes at the metaphase plate 3. separation of sister chromatids 4. separation of the homologs; no uncoupling of the centromere 5. synapsis; chromosomes moving to the middle of the cell in pairs Which of the steps take(s) place in both mitosis and meiosis?

3. separation of sister chromatids

Beginning with a fertilized egg (zygote), how many cells would be present in an embryo following a series of five cell divisions?

32 (2^5)

How many carbon dioxide molecules must be added to RuBP to make a single molecule of glucose?

6

Which of these cells is (are) haploid?

C and D Once meiosis I is completed, cells are haploid.

In glycolysis, what starts the process of glucose oxidation?

ATP

The light reactions of photosynthesis supply the Calvin cycle with __________.

ATP and NADPH

Use the figure and the compounds labeled A, B, C, D, and E to answer the following question. If ATP used by this plant is labeled with radioactive phosphorus, which molecule or molecules of the Calvin cycle will be radioactively labeled first?

B and E only

Two sister chromatids are joined at the centromere prior to meiosis. Which statement is correct?

Barring mutation, the two sister chromatids must be identical.

The net reaction of the Calvin cycle is the conversion of CO2 into the three-carbon sugar G3P. Along the way, reactions rearrange carbon atoms among intermediate compounds and use the ATP and NADPH produced by the light reactions. In this exercise, you will track carbon atoms through the Calvin cycle as required for the net production of one molecule of G3P. For each intermediate compound in the Calvin cycle, identify the number of molecules of that intermediate and the total number of carbon atoms contained in those molecules. As an example, the output G3P is labeled for you: 1 molecule with a total of 3 carbon atoms. Labels may be used once, more than once, or not at all.

Counting carbons—keeping track of where the carbon atoms go in each reaction—is a simple way to help understand what is happening in the Calvin cycle. To produce 1 molecule of G3P (which contains 3 carbons), the Calvin cycle must take up 3 molecules of CO2 (1 carbon atom each). The 3 CO2 molecules are added to 3 RuBP molecules (which contain 15 total carbon atoms), next producing 6 molecules of 3-PGA (18 total carbon atoms). In reducing 3-PGA to G3P (Phase 2), there is no addition or removal of carbon atoms. At the end of Phase 2, 1 of the 6 G3P molecules is output from the cycle, removing 3 of the 18 carbons. The remaining 5 G3P molecules (15 total carbon atoms) enter Phase 3, where they are converted to 3 molecules of R5P. Finally, the R5P is converted to RuBP without the addition or loss of carbon atoms.

Crossing over plays a critical role in increasing the genetic variation among offspring of sexual reproduction. It is important to understand how crossing over occurs and its consequences in meiosis. Look carefully at the diagrams depicting different stages in meiosis in a cell where 2n = 6. Assume that the red chromosomes are of maternal origin and the blue chromosomes are of paternal origin.

Crossing over occurs during prophase I when homologous chromosomes loosely pair up along their lengths. Crossing over occurs only between nonsister chromatids within a homologous pair of chromosomes, not between the sister chromatids of a replicated chromosome. Only segments near the ends of the chromatids, not segments nearest the centromeres, can exchange DNA.

The parent cell that enters meiosis is diploid, whereas the four daughter cells that result are haploid. Which statement correctly describes how cellular DNA content and ploidy levels change during meiosis I and meiosis II?

DNA content is halved in both meiosis I and meiosis II. Ploidy level changes from diploid to haploid in meiosis I, and remains haploid in meiosis II. During anaphase of both meiosis I and meiosis II, the DNA content (number of copies of chromosomes) in a cell is halved. However, the ploidy level changes only when the number of unique chromosome sets in the cell changes. This occurs only in meiosis I (where separation of homologous chromosomes decreases the ploidy level from 2n to n and produces daughter cells with a single chromosome set).

Which of the following is true of an organism that has a chromosome number of 2n = 16? Each cell has eight homologous pairs of chromosomes. The species has 16 sets of chromosomes per cell. A gamete from this species has four chromosomes. During the S phase of the cell cycle, there will be 32 separate chromosomes.

Each cell has eight homologous pairs of chromosomes.

Which of the following is true of a species that has a chromosome number of 2n = 16? During the S phase of the cell cycle there will be 32 separate chromosomes. Each cell has eight homologous pairs. The species has 16 sets of chromosomes per cell. A gamete from this species has four chromosomes.

Each cell has eight homologous pairs.

For each step of photosynthetic electron flow from water to NADP+, drag the appropriate label to indicate whether or not that step requires an input of energy.

In both PS II and PS I, light energy is used to drive a redox reaction that would not otherwise occur. In each photosystem, this redox reaction moves an electron from the special chlorophyll pair (P680 in PS II and P700 in PS I) to that photosystem's primary electron acceptor. The result in each case is a reductant (the reduced primary electron acceptor) and an oxidant (P680+ in PS II and P700+ in PS I) that are able to power the rest of the electron transfer reactions without further energy input.

From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of glycolysis.

In glycolysis, the six-carbon sugar glucose is converted to two molecules of pyruvate (three carbons each), with the net production of 2 ATP and 2 NADH per glucose molecule. There is no O2 uptake or CO2 release in glycolysis.

In the last stage of cellular respiration, oxidative phosphorylation, all of the reduced electron carriers produced in the previous stages are oxidized by oxygen via the electron transport chain. The energy from this oxidation is stored in a form that is used by most other energy-requiring reactions in cells. From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of oxidative phosphorylation.

In oxidative phosphorylation, the NADH and FADH2 produced by the first three stages of cellular respiration are oxidized in the electron transport chain, reducing O2 to water and recycling NAD+ and FAD back to the first three stages of cellular respiration. The electron transport reactions supply the energy to drive most of a cell's ATP production.

Drag each item to the appropriate bin. If the item is not an input to or an output from the Calvin cycle, drag it to the "not input or output" bin.

In the Calvin cycle, the energy outputs from the light reactions (ATP and NADPH) are used to power the conversion of CO2 into the sugar G3P. As ATP and NADPH are used, they produce ADP and NADP+, respectively, which are returned to the light reactions so that more ATP and NADPH can be formed.

In the citric acid cycle (also known as the Krebs cycle), acetyl CoA is completely oxidized. From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of the citric acid cycle.

In the citric acid cycle, the two carbons from the acetyl group of acetyl CoA are oxidized to two molecules of CO2, while several molecules of NAD+ are reduced to NADH and one molecule of FAD is reduced to FADH2. In addition, one molecule of ATP is produced.

Drag each item to the appropriate bin. If the item is not an input to or an output from the light reactions, drag it to the "not input or output" bin.

In the light reactions, the energy of sunlight is used to oxidize water (the electron donor) to O2 and pass these electrons to NADP+, producing NADPH. Some light energy is used to convert ADP to ATP. The NADPH and ATP produced are subsequently used to power the sugar-producing Calvin cycle.

During strenuous exercise, human muscle cells can become oxygen-deprived. When this occurs, muscle cells perform anaerobic fermentation, which results in the production of lactate from pyruvate. What happens to the lactate produced in muscle cells? It is converted to alcohol. It is reduced and converted back to pyruvate in muscle cells. It is oxidized to CO2 and water. It is taken to the liver and converted back to pyruvate.

It is taken to the liver and converted back to pyruvate.

A man interested in losing weight and increasing his fitness followed a strict diet and exercise regimen for three months. Body fat analysis indicated that the man had lost 7 kg (about 15 pounds) of fat by following this exercise and diet program. What is the most likely form by which the fat left his body?

It was released as CO2 and H2O.

The cell cycle represents the coordinated sequence of events in the life of a cell from its formation to its division into two daughter cells. Most of the key events of the cell cycle are restricted to a specific time within the cycle. In this exercise, you will identify when various events occur during the cell cycle. Recall that interphase consists of the G1, S, and G2 subphases, and that the M phase consists of mitosis and cytokinesis.

Many organisms contain cells that do not normally divide. These cells exit the cell cycle before the G1 checkpoint. Once a cell passes the G1 checkpoint, it usually completes the cell cycle--that is, it divides. The first step in preparing for division is to replicate the cell's DNA in the S phase. In the G2 phase, the centrosome replicates. In early M phase, the centrosomes move away from each other toward the poles of the cell, in the process organizing the formation of the mitotic spindle. At the end of the M phase when mitosis is complete, the cell divides (cytokinesis), forming two genetically identical daughter cells.

After 3-PGA is phosphorylated, it is reduced by _____.

NADPH

Can you tell from these absorption spectra whether red light is effective in driving photosynthesis? One cannot tell from this graph, but because chlorophyll a does absorb red light, we can predict that it would be effective in driving photosynthesis. Because the absorption spectra of the pigments are highest in the purple/blue wavelengths, we can assume that red light is not effective. These absorption spectra indicate that green and yellow wavelengths of light are much more effective than red light.

One cannot tell from this graph, but because chlorophyll a does absorb red light, we can predict that it would be effective in driving photosynthesis.

Based on what you learned about photosynthesis, why does this photosynthetic alga appear reddish-pink?

Reddish-pink color of these algae is due to presence of carotenoid pigments, which absorb blue light, while reflecting red light. Those pigments protect the chloroplast from intense blue light and also ultraviolet radiation, as well as absorbing heat, which provides the alga with liquid water as the snow melts around it.

What are the functions of signal transduction pathways? Signal transduction pathways amplify the effect of a signal molecule. Signal transduction pathways allow different types of cells to respond differently to the same signal molecule. Signal transduction pathways convert a signal on a cell's surface to a specific cellular response.

Signal transduction pathways amplify the effect of a signal molecule. Signal transduction pathways allow different types of cells to respond differently to the same signal molecule. Signal transduction pathways convert a signal on a cell's surface to a specific cellular response.

As the chromosomes of a parent cell are duplicated and distributed to the two daughter cells during cell division, the structure of the chromosomes changes.

Sister chromatids form when DNA replicates in the S phase. The sister chromatids become individual chromosomes once they separate in early anaphase. Similarly, the cellular DNA content doubles in the S phase when the DNA replicates. However, the cell's DNA content does not return to its normal (undoubled) levels until after cytokinesis is complete and two daughter cells have formed. The condensation state of the DNA is not related to the presence or absence of sister chromatids. The DNA condenses in prophase and remains condensed until after the sister chromatids separate and the new daughter cells begin to form. In late telophase/cytokinesis, the emphasis shifts to cell growth and DNA replication for the next cell cycle. For these processes to occur, the DNA needs to be de-condensed so it is accessible to the cellular machinery involved in transcription.

When homologous chromosomes cross over, what is the result?

Specific proteins break the two strands of nonsister chromatids and re-join them.

The Calvin cycle depends on inputs of chemical energy (ATP) and reductant (NADPH) from the light reactions to power the conversion of CO2 into G3P. In this exercise, consider the net conversion of 3 molecules of CO2 into 1 molecule of G3P. Drag the labels to the appropriate targets to indicate the numbers of molecules of ATP/ADP, NADPH/NADP+, and Pi (inorganic phosphate groups) that are input to or output from the Calvin cycle. Labels can be used once, more than once, or not at all.

The Calvin cycle requires a total of 9 ATP and 6 NADPH molecules per G3P output from the cycle (per 3 CO2 fixed). In Phase 2, six of the ATP and all of the NADPH are used in Phase 2 to convert 6 molecules of PGA to 6 molecules of G3P. Six phosphate groups are also released in Phase 2 (derived from the 6 ATP used). In the first part of Phase 3, 5 molecules of G3P (1 phosphate group each) are converted to 3 molecules of R5P (also 1 phosphate group each). Thus there is a net release of 2 Pi. In the second part of Phase 3, 3 ATP molecules are used to convert the 3 R5P into 3 RuBP. Note that in the entire cycle, 9 ATP are hydrolyzed to ADP; 8 of the 9 phosphate groups are released as Pi, and the ninth phosphate appears in the G3P output from the cycle.

How do cells at the completion of meiosis compare with cells that have replicated their DNA and are just about to begin meiosis?

They have half the number of chromosomes and one-fourth the amount of DNA.

Which of the following statements about the chemiosmotic synthesis of ATP is correct? The energy for production of ATP from ADP comes directly from a gradient of electrons across the inner mitochondrial membrane. Oxygen participates directly in the reaction that makes ATP from ADP and P. The chemiosmotic synthesis of ATP requires that the electron transport in the inner mitochondrial membrane be coupled to proton transport across the same membrane. The chemiosmotic synthesis of ATP occurs only in eukaryotic cells because it occurs in mitochondria. Chemiosmotic ATP synthesis requires oxygen.

The chemiosmotic synthesis of ATP requires that the electron transport in the inner mitochondrial membrane be coupled to proton transport across the same membrane.

Identify the membranes or compartments of the chloroplast by dragging the blue labels to the blue targets. Then, identify where the light reactions and Calvin cycle occur by dragging the pink labels to the pink targets.

The chloroplast is enclosed by a pair of envelope membranes (inner and outer) that separate the interior of the chloroplast from the surrounding cytosol of the cell. Inside the chloroplast, the chlorophyll-containing thylakoid membranes are the site of the light reactions. Between the inner envelope membrane and the thylakoid membranes is the aqueous stroma, which is the location of the reactions of the Calvin cycle. Inside the thylakoid membranes is the thylakoid space, where protons accumulate during ATP synthesis in the light reactions.

If only chlorophyll a were involved in the light reactions, would blue light (wavelength about 490 nm) be effective in driving photosynthesis? If only chlorophyll a were involved in the light reactions, would blue light (wavelength about 490 nm) be effective in driving photosynthesis?

The graph indicates that chlorophyll a absorbs very little blue light, so we can predict that blue light would not be effective.

Consider an animal cell in which motor proteins in the kinetochores normally pull the chromosomes along the kinetochore microtubules during mitosis. Suppose, however, that during metaphase, this cell was treated with an inhibitor that blocks the function of the motor proteins in the kinetochore, but allows the kinetochore to remain attached to the spindle. The inhibitor has no effect on any other mitotic process, including the function of the nonkinetochore microtubules. 1. Will this cell elongate during mitosis? yes 2. Will the sister chromatids separate from each other? yes 3. Will the chromosomes move to the poles of the cell? no

The inhibitor does not affect the cleavage of cohesins (the proteins that hold the sister chromatids together), the attachment of the chromosomes to the kinetochore microtubules, or the elongation of the cell due to the nonkinetochore microtubules. The inhibitor only affects the motor protein that pulls the chromosome along the kinetochore microtubule in anaphase. Thus, in the treated cell, the sister chromatids can still separate at the beginning of anaphase due to the fact that the cell is elongating (the centrosomes at the poles of the cell are moving farther apart) and the kinetochore microtubules still connect the chromosomes to the centrosomes. However, because the chromosomes cannot move along the kinetochore microtubules, they will never reach the poles of the cell.

Why is it difficult to observe individual chromosomes with a light microscope during interphase?

They have uncoiled to form long, thin strands.

Mitosis unfolds through a sequence of stages marked by specific events in the cell. The structural changes in the cell are brought about by a series of tightly coordinated underlying mechanisms. Sort each process into the appropriate bin to indicate the stage of mitosis in which it occurs. If a process occurs in more than one stage, sort it to the stage when it first occurs.

The micrographs in Part A show some of the cellular processes that occur during the stages of mitosis. In prophase, the microtubules of the spindle apparatus begin to assemble from individual tubulin subunits. As the identical chromatids of each pair of sister chromatids condense during this stage, they are held together by cohesin proteins. Prometaphase is marked by fragmentation of the nuclear envelope, expansion of the spindle into the nuclear region, and attachment of some spindle fibers to the chromosomes via the kinetochores. Metaphase, marked by the alignment of chromsomes along the metaphase plate, is brought about by kinetochores aligning and then remaining motionless relative to the poles of the cell. In anaphase, the cohesin proteins are cleaved, and the kinetochores move toward the poles of the cell, separating the sister chromatids. As telophase proceeds, the kinetochore microtubules of the spindle disassemble. As the chromosomes reach the poles of the cell, the nuclear envelopes of the two new daughter nuclei form.

The mitotic spindle consists of two types of microtubules: kinetochore microtubules and nonkinetochore microtubules. In animal cells, these two types of microtubules function differently in the stages of mitosis. Complete the sentences by dragging the terms to the appropriate locations. Terms may be used once, more than once, or not at all.

The mitotic spindle is the machinery that guides the separation of chromosomes in anaphase. Prior to metaphase, the mitotic spindle is constructed by lengthening microtubules that extend from each centrosome. In metaphase, the kinetochore microtubules have attached each pair of sister chromatids, and the nonkinetochore microtubules overlap extensively at the metaphase plate. During anaphase, the kinetochore microtubules shorten as the chromosomes move toward the poles of the cell. At the same time, the nonkinetochore microtubules lengthen and push past each other, elongating the cell. By the end of telophase, all the microtubules associated with the mitotic spindle have disassembled.

The rate of O2 production by the light reactions varies with the intensity of light because light is required as the energy source for O2 formation. Thus, lower light levels generally mean a lower rate of O2 production. In addition, lower light levels also affect the rate of CO2 uptake by the Calvin cycle. This is because the Calvin cycle needs the ATP and NADPH produced by the light reactions. In this way, the Calvin cycle depends on the light reactions. But is the inverse true as well? Do the light reactions depend on the Calvin cycle? Suppose that the concentration of CO2 available for the Calvin cycle decreased by 50% (because the stomata closed to conserve water). Which statement correctly describes how O2 production would be affected? (Assume that the light intensity does not change.)

The rate of O2 production would decrease because the rate of ADP and NADP+ production by the Calvin cycle would decrease. A reaction or process is dependent on another if the output of the second is an input to the first. For example, the light reactions are dependent on the Calvin cycle because the NADP+ and ADP produced by the Calvin cycle are inputs to the light reactions. Thus, if the Calvin cycle slows (because of a decrease in the amount of available CO2), the light reactions will also slow because the supply of NADP+ and ADP from the Calvin cycle would be reduced.

Why can a signaling molecule cause different responses in different cells? The transduction pathway in cells has a variable length. Different cells have membrane receptors that bind to different sides of the signaling molecule. The transduction process is unique to each cell type; to respond to a signal, different cells require only a similar membrane receptor. All of the listed responses are correct. Different cells possess different enzymes, which modify the signaling molecule into different molecules after it has arrived.

The transduction process is unique to each cell type; to respond to a signal, different cells require only a similar membrane receptor. The signal simply initiates a process by binding to and activating a membrane receptor. How transduction proceeds may be quite different for different cells. Return to Assignment

If crossing over did not occur, which of the following statements about meiosis would be true? Select all that apply

There would be less genetic variation among gametes.

Why are carbohydrates and fats considered high-energy foods?

They have a large number of electrons associated with hydrogen.

The cell cycle is regulated at the molecular level by a set of proteins known as

cyclins

In C4 and CAM plants carbon dioxide is fixed in the _____ of mesophyll cells.

cytoplasm

Which of these is NOT a product of the citric acid cycle? FADH2 ATP acetyl CoA NADH + H+ CO2

acetyl CoA

Taxol is an anticancer drug extracted from the Pacific yew tree that binds to microtubules and prevents their depolymerization. Which phase of mitosis or cell division would be inhibited by treatment with Taxol?

anaphase

If an organism is diploid and a certain gene found in the organism has 18 known alleles (variants), then any given organism of that species can/must have which of the following?

at most, 2 alleles for that gene

Signal transduction pathways that include a phosphorylation cascade cause a structural change in each phosphorylated protein are generally inactivated by a kinase enzyme are propagated by steroid hormone receptors are generally initiated by a phosphorylase enzyme.

cause a structural change in each phosphorylated protein

As a result of the transfer of an electron from a less electronegative atom to a more electronegative atom: the more electronegative atom is oxidized, and energy is consumed. the more electronegative atom is reduced, and energy is consumed. the more electronegative atom is oxidized, and energy is released. the more electronegative atom is reduced, and energy is released.

the more electronegative atom is reduced, and energy is released.

Independent assortment of chromosomes during meiosis is a result of

the random and independent way in which each pair of homologous chromosomes lines up at the metaphase plate during meiosis I.

The primary function of G proteins in signal transduction is binding extracellular signal molecules to activate the pathway. transmitting the signal from an activated receptor to the next protein in the pathway. phosphorylating relay molecules in the pathway. converting ATP to cATP to amplify the signal.

transmitting the signal from an activated receptor to the next protein in the pathway.

In a typical animal, mitosis produces ____________ while meiosis produces _____________.

two diploid daughter cells ... four haploid daughter cells In mitosis, a cell that has doubled its genetic material divides to produce two diploid daughter cells. In meiosis, a cell that has doubled its genetic material undergoes two rounds of division, producing four haploid daughter cells.