Chapter 6 - Cell Communication & Cell Cycle

G protein-coupled receptor

(GPCR) a cell-surface transmembrane receptors that works with the help of a G protein to convey signals.

A signal transduction pathway has three stages.

1. Signal Reception 2. Signal Transduction 3. Cellular Response

ligand

The signaling molecule for the receptor

Cancer cells exhibit different behaviors than normal cells. Here are two normal behaviors they no longer show. Explain each behavior and tell how its loss affects normal cell behavior.

-Density-dependent inhibition and anchorage dependence are not needed for cancer cells

What happens at checkpoint M?

A cell in mitosis receives a stop signal when nay of its chromosome are not attached to spindle fibers When all chromosomes are attached to spindle fibers from both poles, a go-ahead signal allows the cell to proceed into anaphase

What is a cell cycle checkpoint?

A control point where stop and go-ahead signals can regulate the cycle.

What are growth factors? How does platelet-derived growth factor (PDGF) stimulate fibroblast division?

A growth factor is a protein released by certain cells that stimulates other cells to divide. PDGF stimulates fibroblast division by blood cell fragments releasing PDGF to the vicinity when an injury occurs. Fibroblasts, a type of connective tissue) have PDGF receptors on their plasma membranes. The binding of PDGF to these receptors (tyrosine kinase receptors) triggers a signal transduction pathway that allows the cells to pass the G1 checkpoint and divide. Thus, injury results in proliferation of fibroblasts that helps heal the wound

What happens if all the chromosome kinetochores are not attached to spindle fibers? When this occurs, which checkpoint is not passed?

Anaphase, the separation of sister chromatids, does not begin until all chromosomes are properly attached to the spindle at the metaphase plate. If some kinetochores are unattached to spindle microtubules, then anaphase is delayed. The M checkpoint is not passed.

Distinguish between a benign tumor and a malignant tumor.

Benign tumors do not cause serious problems and can be removed by surgery. In this case, the abnormal cells may remain at the original site if their genetic and cellular changes don't allow them to move or survive at another site. On the other hand, a malignant tumor includes cells whose genetic and cellular changes enable them to spread to new tissues and impair the functions of one or more organs.

Kinases drive the cell cycle, but they must be activated by attachment of what molecules?

Cyclin, a protein that gets its name from its cyclically fluctuating concentration in the cell.

What is the Go phase? Describe this phase. What cell types remain in this phase throughout their life spans?

G0 phase is a nondividing state of the cell. Mature nerve and mature muscle cells remain in this phase throughout their life spans because they never divide.

List two specific cancer treatments and explain how each treatment works.

High-energy radiation - damages DNA cancer cells much more than DNA in normal cells, apparently because the majority of cancer cells have lost the ability to repair such damage Chemotherapy - in which drugs that are toxic to actively dividing cells are administered through the circulatory system. Chemotherapeutic drugs interfere with specific steps in the cell cycle

What happens at checkpoint G1?

In the absence of a go-ahead signal, a cell exits the cell cycle and enters G0, a nondividing state If a cell receives a go-ahead signal, the cell continues on in the cell cycle

What does MPF trigger? What are some specific activities that it triggers?

MPF is a cyclin-Cdk complex that triggers the cell's passage into the M phase, past the G2 checkpoint. Specific activities that it triggers include that it phosphorylates a variety of proteins, initiating mitosis. MPF causes phosphorylation of various proteins of the nuclear lamina, which promotes fragmentation of the nuclear envelope during mitosis. There is also evidence that MPF contributes to molecular events required from chromosome condensation and spindle formation during prophase.

What controls the cell cycle?

Molecules present in the cytoplasm control the progression of the cell cycle. Each phase has specific signaling molecules to control the phase and activities of that cell in that phase.

What is the function of a protein kinase? (Recall that we discussed protein kinases in Chapter 11 also. Regardless of their location, their function is always the same.)

Protein kinases are enzymes that activate or inactivate other proteins by phosphorylating them.

Cancer cells also show loss of cell cycle controls and may divide without being checked. The story of HeLa cells is worth noting. What is their source? How old are they? Note that, unlike normal cells, HeLa cells are immortal!

Source: a tumor removed from a woman named Henrietta Lacks How old are they: This cell line has been reproducing in culture since 1951

The activity of cyclin-dependent kinases (Cdks) rises and falls. Why?

The activity of a Cdk rises and falls with changes in the concentration of its cyclin partner.

What is transformation? What is metastasis?

Transformation - a process that causes cell to behave (in cell division) like cancer cells. A typical animal cell becomes a harmful cancer cell Metastasis - The spread of cancer cells to locations distant from their original site

What happens at checkpoint G2?

When enough MPF builds up, the cell clears this checkpoint, and mitosis is initiated

density-dependent inhibition

a phenomenon in which crowded cells stop dividing. Cultured cells normally divide until they form a single layer of cells on the inner surface of a culture flask, at which point the cells stop dividing. If some cells are removed, then the cells divide to fill the space and then stop. The loss of these would cause cells to divide uncontrollably even if there is not enough space for the cells.

anchorage dependence

for cells to divide, they must be attached to something, such as a culture flask or extracellular matrix of a tissue. Cancer cells do not need anchorage dependence so they will continue to divide without anchoring to anything.

chromatid

joined copies of the original chromosome

Describe G-protein coupled receptors' shape

seven transmembrane α helices and two specific binding sites. Label these elements.

Anaphase

-Anaphase is the shortest stage of mitosis, often lasting only a few minutes -Anaphase begins when the cohesin proteins are cleaved.This allows the two sister chromatids of each pair to part suddenly. Each chromatid thus becomes an independent chromosome. -The two new daughter chromosomes begin moving toward opposite ends of the cell as their kinetochore microtubules shorten. Because these microtubules are attached at the centromere region, the centromeres are pulled ahead of the arms, moving at a rate of about 1um/min. -The cell elongates as the nonkinetochore microtubules lengthen -By the end of anaphase, the two ends of the cell have identical--and complete--collections of chromosomes

What are two additional ways chemical signals may pass between animal cells?

-Communication by direct contact between cell-surface molecules -Local signaling molecules are secreted by the signaling cell. Some molecules only travel short distances; such local regulators influence cells that are nearby

Metaphase

-The centrosomes are now at opposite poles of the cell -The chromosomes have all arrive at the metaphase plate, a plane that is equidistant between the spindle's two poles. The chromosomes' centromeres lie at the metaphase plate -For each chromosome, the kinetochores of the sister chromatids are attached to kinetochore microtubules coming from opposite poles.

Prometaphase

-The nuclear envelope fragments -The microtubules extending from each centrosome can now invade the nuclear area -The chromosomes have become even more condensed -A kinetochore, a specialized protein structure has now formed at the centromere of each chromatid (thus, two per chromosome) -Some of the microtubules attach to the kinetochores, becoming "kinetochore microtubules) which jerk the chromosomes back and forth -Nonkinetochore microtubules interact with those from the opposite pole of the spindle lengthening the cell

Receptor Tyrosine kinase steps

1. Many receptor tyrosine kinases have the structure depicted schematically here. Before the signaling molecule binds, the receptors exist as individual units referred to as monomers. Notice that each monomer has an extracellular ligand-binding site, an α helix spanning the membrane, and an intracellular tail containing multiple tyrosines. 2. The binding of a signaling molecule (such as a growth factor) causes two receptor monomers to associate closely with each other, forming a complex known as a dimer, a process called dimerization. (In some cases, large clusters form.) 3. Dimerization activates the tyrosine kinase region of each monomer; each tyrosine kinase adds a phosphate from an ATP molecule to a tyrosine that is part of the tail of the other monomer. 4. Now that the receptor is fully activated, it is recognized by specific relay proteins inside the cell. Each such protein binds to a specific phosphorylated tyrosine, undergoing a resulting structural change that activates the bound relay protein. Each activated protein triggers a transduction pathway, leading to a cellular response

GPCR steps

1.Attached but able to move along the cytoplasmic side of the membrane, a G protein functions as a molecular switch that is either on or off, depending on whether GDP or GTP is attached -- hence the term G protein. When GDP is bound to the G protein, the G protein is inactive. The receptor and G protein work together with another protein, usually an enzyme. 2. When the appropriate signaling molecule binds to the extracellular side of the receptor, the receptor is activated and changes shape. Its cytoplasmic side then binds an inactive G protein, causing a GTP to displace the GDP. This activates the G protein. 3. The activated G protein dissociates from the receptor, diffuses along the membrane, and then binds to an enzyme, altering the enzyme's shape and activity. Once activated, the enzyme can trigger the next step leading to cellular response. Binding of signaling molecules is reversible: Like other ligands, they bind and dissociate many times. The ligand concentration outside the cell determines how often a ligand is bound and initiates signaling 4.The changes in the enzyme and G protein are only temporary: The G protein also acts as a GTPase, hydrolyzing its bound GTP to GDP and Pi; as a result, it can no longer activate the enzyme. The protein leaves the enzyme, which returns it to its inactive state. The G protein is now available for reuse. Its GTPase function allows the pathway shutdown rapidly when the signaling molecule is no longer present.

Figure 11.16 in your text shows how a signal can be amplified in a phosphorylation cascade. A single molecule of epinephrine results in the formation of approximately how many molecules of glucose 1-phosphate?

10^8 molecules of glucose 1-phosphate

How many chromosomes are present in a human gamete?

23 chromosomes

A chicken has 78 chromosomes in its somatic cells. How many chromosomes did the chicken inherit from each parent? How many chromosomes are in each of the chicken's gametes? How many chromosomes will be in each somatic cell of the chicken's offspring?

39 chromosomes 39 chromosomes 78 chromosomes

How many DNA molecules are in each of your somatic cells?

46 DNA molecules. One molecule of DNA per chromosome.

How many chromosomes are in a human somatic cell? Name two types of somatic cells in your body.

46 chromosomes in a human somatic cell. Two examples of somatic cells in human bodies include nerve cells and brain (any cells that are not reproductive cells, or gametes)

What is the meaning of genome?

A cell's DNA, its genetic information.

What is a kinetochore?

A kinetochore is a structure made up of proteins that have assembled on specific sections of DNA at each centromere.

Explain the term ligand. (This term is not restricted to cell signaling. You will see it in other situations during the year.)

A molecule (signaling molecule) that specifically binds to another (often larger) molecule is called a ligand.

G2 Of Interphase

A nuclear envelope encloses the nucleus The nucleus contains one or more nucleoli (singular, nucleolus) Two centrosomes have formed by duplication of a single centrosome. Centrosomes are regions in animal cells that organize the microtubules of the spindle. Each centrosome contains two centrioles Chromosomes, duplicated during S phase, cant be seen individually because they have not yet condensed

Phosphorylation Cascade

A relay molecule activates protein kinase 1 Active protein kinase 1 activates protein kinase 2 Active protein kinase 2 phosphorylates a protein (purple) that brings about the cell's response to the signal Protein phosphatases (PP) catalyze the removal of the phosphate groups from the proteins, making the proteins inactive again

What are two benefits of multistep pathways like the one in Figure 11.10 in your text?

A signal caused by a small number of signaling molecules can be greatly amplified. If each molecule transmits the signal to numerous molecules at the next step in the series, the result is a geometric increase in the number of activated molecules by end. Multistep pathways provide more opportunities for coordination and control than do simpler systems. This allows regulation of the response

protein phosphatases

enzymes that can rapidly remove phosphate groups from proteins, a process called dephosphorylation

How does an inactive protein kinase become activated?

An activated relay molecule from the signaling molecule receptor activates the protein kinase through phosphorylation

The second type of receptor, described on p. 219, is the receptor tyrosine kinases (RTKs). Explain what a kinase enzyme does.

An enzyme that catalyzes the transfer of phosphate groups from ATP to another protein.

Many of the events of mitosis depend on the mitotic spindle. In animal cells, the assembly of spindle microtubules starts at the centrosome. What is another name for the centrosome?

Another name for the centrosome is microtubule-organizing center

Describe three examples of apoptosis, including normal as well as abnormal functions.

Apoptosis in soil worms that receive signals and are destined to die by those signals (normal) Apoptosis occurs in white blood cells when they are infected or need to die so they do not affect other cells near it with their internal substances (normal) Mitochondrial proteins that are triggered to form molecular pores in the mitochondrial outer membrane, causing the mitochondria to leak and release other proteins that promote apoptosis (abnormal) Apoptosis is necessary to created digits and the cells die between the space between the digits

In cell signaling, termination is an essential aspect of the pathway. Describe two ways the signal may be terminated. What is one way relay molecules are inactivated?

As the external concentration of signalling molecules falls, fewer receptors are bound at any given moment, and the unbound receptors revert to their inactive form Another way a signal may be terminated is by is when the number of receptors with bound signaling molecules is below a certain threshold One way relays molecules are inactivated is when the active receptors falls below a certain threshold, so the GTPase activity intrinsic to a G protein hydrolyzes its bound GTP; the enzyme phosphodiesterase converts cAMP to AMP; protein phosphatases inactivate phosphorylated kinases and other proteins; and so forth.

What are the three key roles of cell division? Refer to Figure 12.2 in your text. State each function and give an example.

Asexual reproduction-An amoeba, a single-celled eukaryote, is dividing into two cells. Each new cell will be an individual organism Growth and development-A sand dollar embryo dividing shortly after being fertilized, forming two cells Tissue renewal-These dividing bone marrow cells with give rise to new blood cells

Prokaryote reproduction does not involve mitosis, but instead occurs by binary fission. This process involves an origin of replication. Describe binary fission.

Binary fission means "division in half" and it is a process of asexual reproduction of single celled eukaryotes, such as amoeba. However, the process in eukaryotes involves mitosis, while in prokaryotes it does not involve mitosis. In some bacteria, the process of cell division is initiated when the DNA of the bacterial chromosome begins to replicate at a specific place on the chromosome called the origin of replication, producing two origins. As the chromosome continues to replicate, one origin moves rapidly toward the opposite end of the cell. While the chromosome is replicating, the cell elongates. When replication is complete and the bacterium has reached about twice its size, proteins cause its plasma membrane to pinch inward to form to two daughter cells.

Two common second messengers are cyclic AMP (cAMP) and calcium ions (Ca2+). Explain the role of the second messenger cAMP in Figure 11.12 in the text.

Cyclic AMP carries the signal initiated by epinephrine from the plasma membrane of a liver or muscle cell into the cell's interior, where the signal eventually brings about glycogen breakdown.

What specifically happens to a cell during the process of apoptosis?

During this process, cellular agents chop up the DNA and fragment the organelles and other cytoplasmic components. The cell shrinks and becomes lobed (called blebbing), and the cell's parts are packaged up in vesicles that are engulfed and digested by specialized scavenger cells, leaving no trace.

Study Figure 11.3. The yeast cells are of two mating types, a and ɑ. Like male and female, they must find each other in order to mate. How does each mating type signal which it is? How does each type "know" the other type is near?

Each mating type secretes chemical signaling molecules, or mating factors. The mating factors are unique to each type a and α so when the molecules bind to receptors, the cells will know when the other type is near.

Consider again the discussion of how epinephrine triggers the breakdown of glycogen in the liver, begun in Concept 11.1. For this pathway, What is the first messenger? What is the second messenger? Why could glycogen phosphorylase be activated only when epinephrine was added to intact cells?

Epinephrine - the signaling molecule cAMP Glycogen phosphorylase can only be activated when epinephrine was added to intact cells because adenylyl cyclase and the G-protein receptor are transmembrane proteins that require a plasma membrane (so the cell needs to be intact). Without the intact membrane the epinephrine would not be able to bind to the GPCR and adenylyl cyclase would never receive the signal to produce cAMP.

Yeasts find their sexual mates by chemical signals that activate a signal transduction pathway. What are the three major steps in this pathway?

Exchange of mating factors - Each mating cell secretes a mating factor that binds to receptors on the other mating type Mating - Binding of the factors to receptors induces changes in the cells that lead to their fusion New a/α cell - The nucleus of the fused cell includes all the genes from the a and α cells.

Figure 11.12 in the text explains how a cellular response is initiated; how might that response be inhibited?

Further regulation of cell metabolism is provided by other G protein systems that inhibit adenylyl cyclase. In these systems, a different signaling molecule activates a different receptor, which in turn activates an inhibitory G protein that blocks activation of adenylyl cyclase.

Cell-surface receptors bind to water-soluble signaling molecules and fall into three general groups. What are these three categories of receptors? (We will look at each in depth.)

G protein-coupled receptors (GPCRs), receptor tyrosine kinases, and ion channel receptors.

Cell cycle phases in order and what happens

G1-Metabolic activity and growth S-Metabolic activity, growth, and DNA synthesis G2-Metabolic activity, growth, and preparation for cell division Mitotic Phase-Mitosis: Distribution of chromosomes into two daughter nuclei Cytokinesis: Division of cytoplasm, producing two daughter cells. Each daughter cell can start a new cell cycle.

Using Inquiry Figure 12.9 in your text, explain how evidence was gathered to justify the claim that microtubules depolymerize from the kinetochore end during anaphase.

Gary Borisy and colleagues at the University of Wisconsin dyed kinetochore microtubules in a pig kidney cells. Then, they marked a region of the kinetochore microtubules between one spindle pole and the chromosomes by using a laser to eliminate the dye form that region, while leaving the microtubules intact. As anaphase proceeded, they monitored the changes in microtubules length on either side of the non-fluorescent mark. As the chromosomes, moved poleward, the microtubule segments on the kinetochore side of the mark shorted while those on the spindle pole side stayed the same length. This means that the microtubules shortened from the kinetochore end and not the spindle pole ends. This shows that the kinetochore ends depolymerize and release tubulin subunits

GDP

Guanosine diphosphate, this is the low energy form of GTP and makes the G protein inactive like a switch

ligand-gated ion channel

Here we show a ligand-gated ion channel receptor in which the channel remains closed until a ligand binds to the receptor. When the ligand binds to the receptor and the channel opens, specific ions can flow through the channel and rapidly change the local concentration of that ion inside the cell. This change may directly affect the activity of the cell in some way. When the ligand dissociates from the receptor, the channel closes and ions no longer enter the cell.

Figure 11.16 in your text shows a cytoplasmic response to a signal. How is this different from a nuclear response in terms of both the signal molecule and its effect?

In a cytoplasmic response, the signaling molecule binds to a receptor and the signal transduction is carried out in the cytoplasm as well as the response. In a nuclear response, the signaling molecule binds to the receptor at the plasma membrane and a phosphorylation cascade occurs like in the cytoplasmic response. Then the last active kinase, enters the nucleus and activates a transcription factor that transcribes DNA to mRNA. The mRNA leaves the nucleus and then is synthesized by ribosomes in the cytosol

The response to a cell signal can occur either in the nucleus or in the cytoplasm. Read the text on p. 226, and study Figure 11.15. What normally happens in a nuclear response?

In a nuclear response, an initial signaling molecule like a growth factor, triggers a phosphorylation cascade. The last kinase activated (in the cashade) enters the nucleus and activates a transcription factor. The transcription factor stimulates the transcription of a specific genes. The resulting mRNAs direct the synthesis of a particular protein in the cytoplasm.

Describe cytokinesis in an animal cell. Make a labeled sketch that shows the cleavage furrow.

In animal cells, cytokinesis occurs by a process known as cleavage. The first sign of cleavage is the appearance of a cleavage furrow, a shallow groove in the cell surface near he old metaphase plate. On the cytoplasmic side of the furrow is a contractile ring of actin microfilaments associated with molecules of the protein myosin. The actin microfilaments interact with the myosin molecules, causing the ring to contract like a pulling drawstring. The cleavage furrow deepens until the parent cell is pinched in two to produce two identical daughter cells.

List three types of cellular responses often induced by calcium ions. Be sure to include a plant example!

In animal cells, muscle cell contraction, exocytosis of molecules (secretion), and cell division are often induced by calcium ions. In plants cells, the pathway for greening in response to light is often induced by calcium ions

What occurs in meiosis? Where does it occur in humans?

In meiosis, the result is daughter cells with only one set of chromosomes, half as many chromosomes as the parent cell. Meiosis in humans occurs only in special cells in the ovaries or testes (the gonads). In humans, meiosis reduces the chromosome number from 46 (two sets) to 23 (one set).

How does an inactive protein become activated?

It becomes activated due to newly added phosphate groups with charged or polar amino acids on the protein being phosphorylated

A G protein is also a GTPase enzyme. Why is this important?

Its GTPase function allows rapid pathway shutdown when the signaling molecule is no longer present.

Your answer to question 3 included a signal and its reception. When reception occurs in cells of different mating types, what occurs next?

Mating occurs next because when the two cells are exposed to each other's mating factors, the cells change shape and grow towards each other to fuse (mate).

What is mitosis? How is it different from cytokinesis?

Mitosis is the division of the genetic material in the nucleus, while cytokinesis is the division of the cytoplasm.

What are the components of the mitotic spindle? What is the source of these components?

Mitotic spindle consists of fibers made of microtubules and associated proteins. The source of these components come from the cytoskeleton. While the mitotic spindle assembles, the other microtubules of the cytoskeleton partially disassemble, providing the material used to construct the spindle.

What is a key difference between the number of pathways RTKs can initiate and GPCRs can initiate?

One RTK may activate ten or more different transduction pathways and cellular responses; GPCRs generally activate a single transduction pathway.

The signal for apoptosis can come from outside or inside the cell. Give one example when the signal comes from outside the cell and two examples of cellular occurrences that would prompt an apoptosis signal from inside the cell.

One ex of when the signal comes from outside the cell: When a death signalling molecule (typically from a neighboring cell) binds to a receptor causing apoptosis by signal transduction and activating of enzymes Two ex of apoptosis signal from inside the cell: -One signal comes from the nucleus, generated when the DNA has suffered irreparable damage, and a second comes from the endoplasmic reticulum when excessive protein misfolding occurs

chromosome

a structure in which DNA molecules are packaged into. This allows for manageable replication and distribution of the large amounts of DNA

What are three examples of animal signaling molecules? A study of Figure 11.5 in your text may help you answer this.

Paracrine signaling - A signaling cell acts on nearby target cells by secreting molecules of a local regulator (a growth factor for ex). Synaptic signaling - a nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell, such as a muscle or another nerve cell. Endocrine (hormonal) signaling - Specialized endocrine cells secrete hormones into body fluids, often blood. Hormones reach most body cells, but are bound by and affect only some cells

What processes in humans depend on GPCRs? What are examples of errors in GPCR signaling?

Processes in humans that depend on GPCRs: embryonic development, and sensory reception like vision, taste, and smell. Errors in GPCR signaling: Bacterial infections such as the bacteria that cause cholera, pertussis (whooping cough), and botulism. These bacteria make the host ill by producing toxins that interfere with G protein function.

How does an active protein kinase become deactivated?

Protein phosphatases (PP) catalyze the removal of the phosphate groups from the kinase

To bind intracellular receptors, the signaling molecules must be able to pass through the plasma membrane. What types of molecules can serve as signals? Give three examples.

Signaling molecules that are either hydrophobic enough or small enough to cross the hydrophobic interior of the membrane can bind to the appropriate intracellular receptors. Ex: hydrophobic signaling molecules such as steroid hormones and thyroid hormones of animals. Nitric oxide (NO), a gas is a small signaling molecule that passes through the membrane easily.

Cell signaling in bacteria provides evidence this is an ancient process that first evolved hundreds of millions of years ago. What is quorum sensing, a signaling mechanism seen in bacteria today? How is it related to biofilms?

Quorum sensing is a phenomenon in which bacterial cells sense the concentration of signaling molecules from other bacteria to monitor their own local cell density. Quorum sensing allows bacterial populations to coordinate the behavior of all cells in a population in activities that require a given density of cells acting at the same time. For ex, a formation of a biofilm, an aggregation of bacterial cells attached to a surface by molecules secreted by the cels, but only after the cells have reached a certain density.

Chemical signals are received by specific target cells. What is required for reception by a target cell?

Reception by a target cell requires that the cell can recognize given signaling molecules and will respond to it.

Describe signal reception

Reception is the target cell's detection of a signaling molecule coming from outside the cell. A chemical signal is "detected" when the signaling molecule binds to a receptor protein located at the cell's surface (or inside the cell).

Which part of the cell cycle is longest in duration?

S phase is the longest out of interphase. Interphase is the longest stage of the cell cycle.

How do scaffolding proteins enhance a cellular response?

Scaffolding proteins enhance a cellular response by increasing efficiency of signal transduction. Large relay proteins to which several other relay proteins are simultaneously attached increase the rate of protein to protein interaction by not being limited by diffusion in the cytosol

You are going to have to learn the difference between several similar-sounding terms. The following sketch that looks like an X represents a duplicated chromosome that has two sister chromatids. The narrow "waist" represents the location of the centromere. The centromere is a region of DNA, a part of the chromosome where one sister chromatid will attach to the other sister chromatid. A single chromosome has one centromere; duplicated chromosomes therefore have two centromeres, adhering to each other in this region. Students often get all these terms confused, so take time now to label the indicated areas of the figure and then define each of the terms below.

Shape of a duplicated chromosome attached to a sister chromatid

ligand-gated ion channel receptor

a type of membrane channel receptor contain a region that can act as a "gate", opening or closing the channel when the receptor changes shape

How is it that some cells do not respond to specific signaling molecules, and for the cells that do respond, it is often in different ways?

Some cells do not respond to specific signaling molecules because they do not have the receptors for the signaling molecules. And for cells that do respond, and they often respond in different ways is because different kinds of cells turn on different sets of genes, different kinds of cells have different collections of proteins. The response of a cell to a signal depends on its particular collection of signal receptor proteins, relay proteins, and proteins needed to carry out the response.

Telophase and Cytokinesis

Telophase: -Two daughter nuclei form in the cell. Nuclear envelopes arise from the fragments of the parent cell's nuclear envelope and other portions of the endomembrane system. -Nucleoli reappear -The chromosomes become less condensed -Any remaining spindle microtubules are depolymerized -Mitosis, the division of one nucleus into two genetically identical nuclei, is now complete Cytokinesis -the division of the cytoplasm is usually well way by late telophase, so the two daughter cells appear shortly after the end of mitosis -In animal cells, cytokinesis involves the formation of a cleavage furrow, which pinches the cell in two.

G protein-coupled receptors (GPCR) are a large family of receptors. Study the GPCR shown in Figure 11.8 in your text and read the accompanying text. How does a G protein receive a signal?

The G protein binds the energy-rich molecule GTP. Depending on whether GDP or GTP is attached to the G protein, the molecular switch is on or off. When GDP is bound, the G protein is inactive. The receptor (GPCR) and G protein work together with another protein, usually an enzyme. When an appropriate signalling molecule binds to the extracellular side of the receptor, the receptor is activated and changes shape. Its cytoplasmic side then binds an inactive G protein, causing a GTP to displace the GDP which activates the G protein.

Use your new knowledge of cell signaling to explain the mechanism of disease in cholera.

The bacteria release cholera toxin, an enzyme that chemically modifies a G protein involved in regulating salt and water secretion. Because the modified G protein is unable to hydrolyze GTP to GDP, it remains stuck in its active form, continuously stimulating adenylyl cyclase to make cAMP. The resulting high concentrations of cAMP causes the intestinal cells to secrete large amounts of salts into the intestines, with water following by osmosis. This causes profuse diarrhea and people can die of loss of water and salts.

Describe signal transduction

The binding of the signaling molecule changes the receptor protein in some way, initiating the process of transduction. The transduction stage converts the signal to a form that can bring about a specific cellular response. In Sutherland's system, the binding of epinephrine to a receptor protein leads to activation of glycogen phosphorylase in the cytosol. Transduction sometimes occurs in a single step but more often requires a sequence of changes in a series of different molecules -- a signal transduction pathway. The molecules in the pathway are often called relay molecules.

How is the cell plate formed? What is the source of the material for the cell plate?

The cell plate is formed from vesicles from the Golgi apparatus that is moved by microtubules to the middle of the cell where they combine together to form the cell plate. The source of material for the cell plate is cell wall material from the Golgi apparatus

Describe what happens to the centrosome during prophase.

The centrosomes move away from each other, propelled partly by the lengthening microtubules between them

Prophase

The chromatin fibers become more tightly coiled, condensing into discrete chromosomes observable with a light microscope The nucleoli disappear Each duplicated chromosome appears as two identical sister chromatids joined at their centromeres and, often, along their arms by cohesins, resulting in sister chromatid cohesion The mitotic spindle begins to form. It is composed of the centrosomes and the microtubules that extend from them. The radial arrays of shorter microtubules that extend from the centrosomes are called asters (stars). The centrosomes move away from each other, propelled partly by the lengthening microtubules between them

Explain the difference between kinetochore and nonkinetochore microtubules. What is the function of each?

The difference between kinetochore and nonkinetochore microtubules is that kinetochore microtubules attach to kinetochores and pull the two sister chromatids towards the metaphase plate by jerking them back and forth. Nonkinetochore microtubules do not attach to kinetochores and instead, they attach to other nonkinetochore microtubules on the opposite side of the cell to lengthen the cell.

What is the important relationship between the second messenger and protein kinase A?

The elevation in cAMP level leads to the the immediate effect of activation of a serine/threonine kinase called protein kinase A. The activated protein kinase A then phosphorylates various other proteins, depending on the cell type.

What is chromatin?

The entire complex of DNA and proteins that is the building material of chromosomes

What is the difference between a first messenger and a second messenger?

The first messenger is the extracellular molecule -- the ligand-- that binds to the membrane receptor, while second messengers are small, nonprotein, water-soluble molecules or ions involved in the signal transduction pathway.

What is the function of the centrosomes?

The function of centrosomes is to operate throughout the cell cyle to organize the cell's microtubules

Explain the function of transcription factors in the cell.

The function of transcription factors in the cell is that they are special proteins which control which genes are turned on (a.k.a. which genes are transcribed into mRNA) in a particular cell at a particular time.

What is considered to be the cell cycle?

The life of a cell from the time it is first formed during division of a parent cell until its own division into two daughter cells.

Chemical signals may pass between adjacent animal cells through ________ and between plant cells via __________ .

gap junctions, plasmodesmata

Biofilms on your teeth could protect bacteria that cause cavities and gum disease. What is another way quorum sensing can lead to disease?

The secretion of toxins by infectious bacteria. Sometimes treatment by antibiotics doesn't work with such infections because of antibiotic resistance that has evolved in a particular strain of bacteria. A promising alternative treatment would be to disrupt toxin production by interfering with the signaling pathways used in quorum sensing

How does a hormone qualify as a long-distance signaling example?

The signaling molecules such a a hormone travel through the circulatory system to other parts of the body, where they reach target cells that can recognize and respond to them. The long distance transport of the hormone is what qualifies it as an example.

Aldosterone and intracellular reception

The steroid hormone aldosterone passes through the plasma membrane Aldosterone binds to a receptor protein in the cytoplasm, activating it The hormone-receptor complex enters the nucleus and binds to specific genes The bound protein acts as a transcription factor, stimulating the transcription of the gene into mRNA. The mRNA is translated into a specific protein

Describe cellular response

The transduced signal finally triggers a specific cellular response. The response may be almost any imaginable cellular activity -- such as catalysis by an enzyme (glycogen phosphorylase), rearrangement of the cytoskeleton, or activation of specific genes in the nucleus. The cell-signaling process helps ensure that crucial activities like these occur in the right cells, at the right time, and in proper coordination with the activities of other cells of the organism.

Describe cytokinesis in a plant cell. Make a labeled sketch that shows the cell plate.

There is no cleavage furrow. Instead, during telophase, vesicles derived from the Golgi apparatus move along microtubules to the middle of the cell, where they coalesce, producing a cell plate. Cell wall materials carried in the vesicles collect inside the cell plate as it grows. The cell plate enlargens until its surrounding membrane fuses with the plasma membrane along the perimeter of the cell. Two daughter cells result, each with its own plasma membrane. Meanwhile, a new cell wall arising from the contents of the cell plate forms between the daughter cells.

What is a gamete? Name the two types of gametes.

They are reproductive cells. Sperm and egg cells are two types of gametes.

In what body system are ligand-gated ion channels and voltage-gated ion channels of particular importance?

They are very important in the nervous system.

Why do only kidney cells respond to aldosterone?

This is because the kidney cells are the only cells in the body that contain receptors for aldosterone.

What is meant by a cellular response?

This is the cellular response. The response is caused by cellular changes that occur as a result of signal reception and transduction. Logically, the three-stage process is termed a signal transduction pathway.

ions

When a signaling molecule binds as a ligand to the channel receptor, the channel opens or closes, allowing or blocking the flow of specific ions like Na+ or Ca2+

What happens to the cytoplasmic concentration of calcium when it is used as a second messenger?

When calcium is used as a second messenger, the cytoplasmic concentration of calcium may rise, usually by a mechanisms that releases Ca2+ from the cell's ER.

Study Figure 12.5 in your text. Label the following figure and summarize what occurs at the DNA level in each stage. The top figure shows one chromosome. The middle figure shows a duplicated chromosome with two sister chromatids. It is still considered one chromosome. When the sister chromatids have separated in the bottom figure, they are now considered individual chromosomes. Run through this again! Top picture, one chromosome. Middle picture, one duplicated chromosome (with two sister chromatids). Bottom picture, two chromosomes.

When chromosomes are duplicated are there two chromosomes or still one? One When sister chromatids split into two cells are there two chromosomes or one? two

What is epinephrine?

a hormone, that is a ligand in a signal transduction pathway

G protein

a protein that binds the energy rich molecule GTP. This energy is transmitted to another protein (ex: enzyme) to conduct a cellular response

protein kinases in transduction

an enzyme that transfers phosphate groups from ATP to a protein

centromere

each sister chromatid has one, a region made up of repetitive sequences in the chromosomal DNA where the chromatid is attached most closely to its sister chromatid

During which parts of the cell cycle does the cell grow?

the G1 phase, S phase, and G2 phase

chromatin

the entire complex of DNA and proteins that is the building material of chromosomes