Chapter 6: Cell Communication

All cells in a multicellular organisms have the same genetic makeup.

The information stored in DNA is used to make another nucleic acid.
The information is used to make something.
Chemical reactions that generate traits are regulated by proteins.
Gene expression may be regulated by other proteins.

This doesn't explain how the same set of genes can produce different types of structures.

Some genes are turned on in some cells while others are turned off in others.
The environment influences which genes are expressed.
Each cell gets signals from its surroundings that influence the expression of its genes.

Cells receive signals from other cells.

Cell communication is common during early development.

Ions and small Molecules can pass through gaps, but larger Molecules cannot.

There are passageways across the cell walls for the movement of ion and micoRNA.

Cells produce substances that affect only nearby cells because they are either readily absorbed by adjacent cells or quickly broken down in the extracellular fluid.

Paracrine signals are released during early animal development.

The hormones are produced in one part of the body and the other part.

The rest of the chapter focuses on how a signal can cause a change in the cell.

A signal transduction pathway is the mechanism for this process.

They are small Molecules that bind to bigger Molecules.

A change in the three-dimensional shape of the receptor protein can be caused by the specific ligand binding to it.
The change causes some activity in the receptor protein.

They initiate a series of reactions when activated by a signaling molecule.

The binding site for a signaling molecule is presented by the part of the receptor that faces away from the cell.

A chemical reaction can be initiated by the other end of the protein.

They are all types of molecule.

Ca2+, cAMP, and DAG are examples.

The signal response from a receptor to another target may initiate a cellular response if there is more than one component of a transduction pathway.

The first, second, and thirdidases in the series are activated.

The products of each reaction increase as the sequence progresses, like a chain reaction.

A signal that may have begun with a single signaling molecule may be amplified to produce a huge number of molecules that elicit a strong cellular response.

A kinase adds a group ofphosphorylates to it.

Each kinase in a cascadephosphorylates and stimulates the next in the sequence to initiate a cellular response.
The signaling response is amplified by the kinase cascade.

The members of one signaling cascade are isolated from the members of another signaling cascade on the scaffold.

The signaling response is terminated when these enzymes dephosphorylate the kinases.

There is great flexibility in the pathways.

There are signaling molecule that are specific to the binding sites of the receptor.

The response that a specific signaling molecule gives varies with cell type and the influence of cytoplasmic substances.

It provides a way to amplify the effect of a signaling molecule.

The cell has more control over the signaling pathway.

All components of the pathway must be functioning correctly in order for the transduction to occur in error.

A single signaling molecule can cause a variety of responses.

Multiple processes can be coordinated to produce a single response.

The signal transduction pathways they initiate are described in the following descriptions.

The descriptions are summarized in Table 6-1.

In a free-response question on the AP exam, you should describe at least one of these receptors.

If you are asked to use the descriptions to make conclusions, you may be able to get a full description of the pathway.
Familiarity with all of the different types of receptors will help you.

The examples of these pathways are pursued in more detail in subsequent chapters.

A specific ion can pass through when the channel is open.

The ion receptor is receiving a signal.
The outward-facing surface of the receptor has a specific messenger ligand binding to it.

Ions pass through the channel.

In response to the binding of the ligand, the three-dimensional shape of the receptor changes, opening or closing a channel that allows a specific ion to pass through and enter the cytoplasm.

Ions start the chemical response.

There is a chemical response once in the cytoplasm.

The ion passage is blocked by a channel blocker when the messenger ligand is broken down, or the binding site is blocked by an allosteric ligand.

When acetylcholine is binding to the receptor molecule of the receiving neuron, it opens a gated channel that allows Na+) to enter the cell.

The inside of the cell becomes more positive as Na+ enters.
The nerve impulse is caused by a change in the action potential.
Muscle contraction is stimulated in a similar way.

When the Na+ enters the cell, the voltage inside the neuron becomes more positive.

The K+ channel wasgated to open.

A second messenger is activated by the G protein, which in turn triggered a cellular response.

The GDP is attached to the GProtein which is why it is named.
GTP has a guanine instead of an adenine nitrogen base.
GDP is attached to the G protein in the inactive state.
When the GDP is replaced with a GTP, it is turned on.

The largest family of signal receptors are GPCRs.

They include hormones, neurotransmitters, and immune system activity.
Drugs and opiates are GPCR ligands.

There is a description of a typical sequence.

The GPCR pathway varies based on cell type, the particular GPCR that is activated, and the biochemical makeup of individual cells.

The GPCR is receiving a signal.

The outward-facing surface of the receptor has a specific messenger ligand binding to it.

The GTP is exchanged for a GDP.

A conformational change occurs as a result of the binding of the ligand to the GPCR.

The GTP is bound to the G.

The effector protein is binding to the G protein.

The activated G protein is activated by a subunit of the membrane effector.

The effector is involved in response.

The cellular response is elicited by the effector protein.

The effector may be an enzyme.

It's possible that the enzyme is a kinase and starts a cascade.

A very strong and rapid response is generated by many cAMPs.

The cAMP signaling pathway then causes the expression of a cytoplasmic response.
Depending on the cell type, the response can be stimulatory or inhibitory.

There is a portion of thePIP2 that is embedded in themembrane and a portion that is in the cytoplasm.

There are a variety of cellular responses depending on cell type.

In many cells, the transport of calcium ion is triggered.

In secretory cells of salivary glands, in order for Ca2+ to be released into the cytoplasm, it is necessary to bind and release the receptor proteins in the smooth ER.
The release of saliva is triggered by Ca2+.

The GDP is free to reassociate.

When a signaling molecule is activated by a G protein, GTP is exchanged for GDP on the effector protein, which converts the molecule into a second messenger, cAMP.

The cAMP phosphorylates aphosphorylates aphosphatase.

The OH group in an R group of an amino acid is replaced by phosphorylation.

Threonine, serine, and tyrosine are the three main amino acids.

RTK gets a signal.

The signaling molecule is at the outer surface of the membrane.

Two people are forming a pair.

The RTK is activated byphosphorylation.

Each of the two RTKs in the dimerphosphorylates the other one using the same groups from the ATPs.
There are multiple phosphate groups that can attach to a lysine.

Relay is phosphorylated.

Relay proteins bind to the RTK.
The transfer of thephosphates from the tyrosines to the relay proteins takes place.
There are more than one kind ofphosphorylatedProtein that can serve as a relay that leads to a different pathway.

Relay is involved in pathway transduction.

The relay proteins have been activated by the addition of a phosphate group.
A relay protein can initiate a pathway that leads to a cellular response.
Each kind of relay is involved in a different cellular response.

When dephosphorylating enzymes removephosphate groups from the kinases, the pathway is turned off.

A host of coordinated cellular responses may be directed by the RTK receptor.

A typical GPCR stimulates a single pathway that leads to a specific cellular response.

In response to excess sugar in the blood, the pancreas makes a hormone called lysine, which is released into the blood.

The hormone regulates the amount of sugar in the body.
The signaling molecule is binding to the insulin receptor.
The formation of an RTK dimer and autophosphorylation can be triggered by binding.
The complex binding to andphosphorylates aninsulin response protein.
Several signaling cascades are initiated by this response protein.
In muscle cells, one cascade leads to the formation of glycogen, which is used for short-term energy storage, and the other leads to the transport of glucose into the cell.
In the liver cells, the synthesis of glycogen is stimulated.
The pathway leads to the formation of triglyceride in fat cells.

The next mitogen kinase in the sequence is phosphorylated by one of the mitogen kinases.

In this way, MKKK is activated.
When a GTP replaces a GDP, the GProtein associated with a GPCR is activated, but the series of steps that define the pathways of these two receptors is very different.

The small molecule that diffuses across the plasma is called the ligands.

Second messengers, like IP3 that are products of a signal transduction pathway, are included in ligands.
Cell types vary in their response to a particular receptorProtein like other kinds of transduction pathways.

Various molecule specific to individual cells may act as coactivators.

The nucleus may be the location of the target of the activity.
A signaling molecule enters the body.
The signaling molecule can be a first messenger molecule or a second messenger molecule that is introduced into the cytoplasm.

The nucleus or the cytoplasm may be where the receptor is located.

In some cases, the release of an inhibitor prevented the receptor from functioning.

The transcription of genes is promoted by the binding of the receptor-signal complex to the DNA.

Negative feedback mechanisms shut down the release of hormones into the blood.

The signaling molecule diffuses across the cell wall.

The now activated complex moves to the nucleus, where it binding to DNA and promoting transcription of genes that direct cellular activities.
The expression of genes depends on cell type and gender.
In males, testosterone stimulates the development of sperm cells in the testes, but in muscle cells, it causes the production of muscle fibers.
In mammary cells, estrogen inactivates genes that direct cells in the uterus to prepare for pregnancy.

External signals have a strong influence on how genes express information about a cell.

Signals are sometimes inaccurately acted upon due to the signal transduction pathway being distorted.
There are two examples.

The normal activity of GCPRs of intestinal cells is disrupted when the water is contaminated.

The GTP attached to the G protein can't be converted back to a GDP, so it can't be deactivated.
When locked in its active state, the GProtein regulates the concentration of Cl- in these cells.
In response, the cell is continuously moved out of it's location.
The water goes into the intestines.
If not treated, the idiocy can lead to dehydration and death, and the idiocy can assist thebacteria in returning to the water supply.

Normally, cell division is highly regulated, with multiple checkpoints during a cell cycle to ensure that the process is progressing correctly.

Growth factors can cause the activation of atrypsinogen.
The transcription factor is activated when the MAK cascade is initiated.
If the DNA is damaged, p53 directs the enzymes to repair it.
The cell division can proceed once repaired.
The proliferation of damaged cells can be prevented if repair is unsuccessful.
Cell division progresses even if the DNA is damaged as a result of this.
A proliferation of cancer cells is caused by continued cell division.

A review of the material presented in this chapter is provided by the questions that follow.

They can be used to evaluate how well you understand the concepts.
AP multiple-choice questions are often more general, covering a broad range of concepts.
The two practice exams in this book are for these types of questions.

Four possible answers or sentence completions are followed by each of the following questions or statements.

The one best answer or sentence is what you choose.

The answer in the key can be used more than once or not at all.

The questions that follow are typical of an entire AP exam question or just that part of a question that is related to this chapter.

There are two types of questions on the AP exam.

It takes about 20 minutes to answer a long free-response question.
Sometimes they offer you a choice of questions to answer.
6 minutes is the time it takes to answer a short free-response question.
diagrams can be used to supplement your answers, but a diagram alone is not adequate.

Two aspects of their activity are the same despite the differences.

The two aspects of their mechanisms should be described in two or three sentences.

There are different ways in which a G protein-coupled receptor and a protein kinase receptor can phosphorylate a cytoplasm.

In three or four sentences, explain how the two signaling mechanismsphosphorylate a protein kinase.

An example of the pathway can be provided.

Because it is a large molecule, it is charged.

As a result, it is not able to cross.

It must never enter the cell.

Steroids are non-polar molecules that can travel through the plasma membrane.

Cortisol binding to an intracellular receptor is what happens after crossing the membrane.
The signaling molecule does not bind to DNA or mRNA, but rather stimulates the appropriate chemical responses.

Second messengers are small.

There are transcription factors.

Plants and animals have gap junctions that allow for a passageway between adjacent cells.

There are small gaps between nerve cells.

Paracrine signaling occurs among nearby cells, while endocrine signaling occurs for cells separated by large distances.

When a three-dimensional conformational change takes place, a receptor is activated.

The new arrangement of atoms opens passageways or exposes active sites for binding.

Each step of the signaling cascade can lead to multiple reactions.

Each reaction is the beginning of the next step in the cascade.
The signal is amplified by each step.
Because there are multiple participants, the signaling cascade is more susceptible to the influence of mutations, which can have a negative effect on the ultimate product of the signal.

Without assistance, nonpolar ligands can cross themembrane.

They enter the cell and bind to it.

The GProtein is activated by the exchange.

There is a GTP exchange for GDP that can also occur for a RTK pathway, but it occurs on a cytoplasmic protein.

When a ligand is binding to a receptor, it causes it to form a dimer with another.

The groups are attached to themselves by the dimer.

There is a nearby GProtein.

The passageway for ion to enter or exit the cell is provided by a gate.

The second messengers are activated by a GPCR.

The binding of a ligand is required for each of the receptor proteins.

The binding of the ligand to thereceptor causes a change in its three-dimensional structure.

When a GPCR is activated, it causes a second GProtein to be activated, which in turn causes a third GProtein to be activated.

The binding of the signalling molecule to the receptor causes a conformational change in it.

The last step in the descriptions of the pathways is deactivating.