(Chapter 7) Biology - Cell Communication and Signaling

How do second messengers form?

1. From ATP- cAMP (cyclic AMP) 2. From Lipids

There are many types of receptors, in the plasma membrane receptors include:

1. Ion channels 2. Protein kinases 3. G protein-linked receptors IMPORTATNT (3 min): youtube.com/watch?v=VPJG_hy72m8

The information sent come in three forms

1. Signals: are information that is transmitted from one cell or organism to another. 2. Stimulus: is an event or condition that causes a response in an organism. 3. Ligands: are molecules that bind to a specific receptor on a cell or other biological molecule, triggering a cellular response.

The signal transduction pathway has 3 major components:

1. The signal 2. The receptor 3. The response

Some chemicals have a similar structure to the ligand and can bind to the receptors instead of the normal ligand. They are called Agonists and Antagonists:

Agonists are chemicals that bind to the receptors and activate them, producing a response. Antagonists or Inhibitors are chemicals that bind to the receptors but do not activate them, blocking the normal ligand from binding and producing a response.

What category is caffeine in? Agonists or Antagonists?

Antagonists as it simply takes the spot of the adenosine in the receptors

What's the relation between autocrine and tumor cells?

Autocrine signaling can play a role in the development and progression of tumor cells. Tumor cells are cells that have undergone uncontrolled growth and division, leading to the formation of a mass of abnormal tissue. In some cases, tumor cells can produce and respond to their own autocrine signals, leading to self-stimulation and continued growth. For example, a tumor cell may produce a growth factor that binds to receptors on the surface of the same cell or other nearby tumor cells. This autocrine signaling can lead to continuous stimulation of the tumor cells and promote their survival and proliferation.

Autocrine signaling

Autocrine signaling: · Cells release signaling molecules that act on the same cell or cells of the same type. · Important in cell growth, differentiation, and survival.

Autocrine

Autocrine signals are PRODUCED by a cell and act on the SAME cell or other cells of the same type, leading to self-stimulation or stimulation of nearby cells.

Signals have types, including:

Autocrine, Juxtacrine, and Paracrine Understand better (Watch Fully): youtube.com/watch?v=QL8yAtQXwuo

Cell Communication and Signaling

By the Open Book Team

Cell signaling can occur within a cell (intracellular) or between cells (intercellular).

Cell signaling is the process of communication between cells or within cells that allows cells to coordinate and respond to their environment. It involves three distinct stages: reception, transduction, and response.

Ever asked how do cells know what to do and where to go? Signals!

Cells are aware of their surroundings and react to signals from their environment and neighbors.

Where do these signals come from?

Cells communicate with each other using signals, which are molecules produced by one cell (the sending cell) and released into the extracellular space. The extracellular space is the space between cells or within tissues, and it allows signals to diffuse and reach other cells in the vicinity.

Reception:

During this stage, a signaling molecule binds to a specific receptor on the cell's surface or inside the cell. This binding triggers a series of changes in the receptor that allow it to relay the signal to the next stage.

Endocrine signaling

Endocrine signaling: · Signaling molecules called hormones are released into the bloodstream and act on distant target cells. · Hormones regulate many physiological processes, including growth and development, metabolism, and reproduction.

Response:

Finally, the signal is interpreted by the cell and produces a specific response, such as changes in gene expression, protein synthesis, enzyme activation, or cellular behavior. This response may occur within the same cell (intracellular signaling) or in neighboring cells (intercellular signaling).

How are Hormones part of signaling?

First you should know that another type of signaling is Endocrine, similar to paracrine, however it sends signals to cells that are FAR. Now, the endocrine system is a network of glands and organs that produce and secrete hormones into the bloodstream. Hormones are chemical messengers that travel through the bloodstream and bind to specific receptors on target cells, triggering a response. Therefore, hormones are intimately related to the endocrine system, as they are the primary means by which the endocrine glands communicate with cells throughout the body.

The video goes on to talk about the different types of signaling including: Gap junction, Paracrine, Synaptic, Endocrine signaling, Autocrine signaling, and Juxtacrine signaling Let's explain them starting with Gap junction.

Gap junction (Part of Juxtacrine signaling): · Direct communication between neighboring cells via channels called gap junctions. · Small molecules and ions can pass through these channels. · Important in coordinating the activity of cells in tissues such as cardiac and smooth muscle.

Another effect of signaling is Differential gene transcription:

Hydrophobic hormones bind to receptors in the cytoplasm and enter the nucleus to activate/inactivate transcription of DNA.

In a small, nonpolar ligands, if the receptor is bound to a chaperone, it is released when binding occurs. In other words:

In the case of receptors, chaperones can sometimes bind to the receptor protein to keep it in an inactive or "off" state until a ligand (chemical signal) binds to the receptor. When the ligand binds to the receptor, it causes a conformational change in the receptor protein that can release the chaperone, allowing the receptor to become active and initiate downstream signaling processes.

Explain the relation of Juxtacrine and cells during development?

Juxtacrine signaling plays an important role in cell communication and differentiation during development. During embryonic development, cells often exist in groups and undergo a process of specialization, where they differentiate into specific cell types with distinct functions. Juxtacrine signaling allows cells to communicate and interact with each other in a highly localized manner. For example, during the development of the nervous system, neurons use juxtacrine signaling to guide the growth of axons and dendrites to specific target cells.

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Juxtacrine signaling: · Occurs when signaling molecules on the surface of one cell interact with receptors on an adjacent cell. · Important in many developmental processes, including cell migration and differentiation.

Juxtacrine

Juxtacrine signals involve PHYSICAL contact between cells, where signaling molecules are present on the surface of one cell and receptors are present on the surface of another cell.

Large, polar ligand

Large, polar ligands do not diffuse across the plasma membrane and require membrane receptors to transmit the signal. · These ligands bind to membrane receptors located on the surface of the plasma membrane. · Examples of large, polar ligands include insulin and growth factors.

What about the receivers? Do all cells receive signals that are sent?

NO! Target cells, with specific receptors for a signal, are the only cells that can receive information from a signal and respond to it.

Mention one example that shows how these 3 forms are related:

One example of how these concepts work together is the process of neurotransmission in the nervous system. In this process, SIGNALS are transmitted between neurons through the release of chemical messengers called neurotransmitters. When a neuron is stimulated by an electrical signal, it releases neurotransmitters into the synapse, which are LIGANDS that bind to specific receptors on the surface of the target neuron. This binding of the ligand to the receptor triggers a RESPONSE inside the target neuron, which can either excite or inhibit its activity.

Paracrine signaling

Paracrine signaling: · Signaling molecules are released by one cell and act on nearby cells. · Important in many physiological processes, including inflammation, wound healing, and the regulation of blood pressure.

Paracrine

Paracrine signals are PRODUCED by a cell and act on NEARBY target cells in the immediate vicinity, but not on the same cell that produced the signal.

2. Protein kinases Understand better (3 min): youtube.com/watch?v=D4QXR8Exzjo

Protein kinase receptors catalyze the transfer of a phosphate group from ATP (phosphorylation), resulting in a change in conformation and activity. · An example of protein kinase receptors is insulin receptors in liver cells. · Binding of 2 insulin molecules to the receptor changes the receptor's conformation. · The receptor gains phosphate groups and catalyzes phosphorylation of a cytoplasmic protein (insulin response substrates). · The response to this signaling pathway is that cells in the liver and skeletal muscles start absorbing excess glucose and converting it to glycogen.

Communication is important for both living organisms and the cells that make them up. Multicellular organisms require cell signaling for their many cells to work together to carry out functions.

Receptors are molecules (such as proteins) that receive signal molecules (ligands), which can trigger a response. Ligands can be gas molecules, hydrophobic biomolecules like lipids, or hydrophilic biomolecules like some kinds of proteins.

Responses can be either short term or long term:

Short-term changes include the activation or inactivation of enzymes, ion channels, or other proteins that are already present in the cell. Long-term changes involve changes in gene expression, which can lead to the synthesis of new proteins or the regulation of existing proteins. In some cases, there may be crosstalk between different signal transduction pathways, where signals from one pathway can influence the response to another pathway. This crosstalk can allow for more complex and nuanced responses in cells.

There are different types of chemical signals that can bind to receptors, and their ability to do so depends on their chemical properties. Starting with Small, nonpolar ligands:

Small, nonpolar ligands, like Cortisol, are able to easily cross the plasma membrane of cells by simple diffusion due to their size and hydrophobic nature. Once inside the cell, they can bind to intracellular receptors located in the cytoplasm or nucleus, which regulate gene expression and cellular processes. The binding causes the receptor to change its shape, which allows the signal to enter the nucleus and cause an effect, for example, initiating DNA transcription.

Differences between Large and Small liagnds:

Small, nonpolar ligands: · Typically diffuse easily across cell membranes. · Bind to intracellular receptors. · Examples include steroid hormones, such as testosterone and estrogen. Large, polar ligands: · Typically cannot diffuse across cell membranes easily. · Bind to membrane-bound receptors. · Examples include peptide hormones, such as insulin and growth hormone

Synaptic signaling

Synaptic signaling: · Occurs between neurons and target cells, such as other neurons, muscle cells, or glands. · Neurotransmitters are released from the presynaptic neuron and bind to receptors on the postsynaptic cell. · Important in the transmission of nerve impulses and the regulation of many physiological processes, including movement and cognition.

Transduction:

The signal is then transmitted through a series of signaling molecules that act as messengers, amplifying and modulating the original signal. This is referred to as signal transduction. The signaling molecules may activate or inhibit certain proteins or pathways within the cell.

Now when a cell responds to signals, there are series of steps that should be taken, these steps are named "signal transduction pathway"

The signal transduction pathway is the process by which a signal (such as a hormone or neurotransmitter) is transmitted from the extracellular environment to the interior of a cell. This involves the interaction of the signal with a specific receptor on the cell surface, which triggers a series of intracellular signaling events. These events amplify the signal and lead to changes in the function of the cell, such as changes in gene expression, enzyme activity, or ion channel function

Receptor proteins are a type of membrane or intracellular protein that plays a critical role in cell signaling.

These proteins are responsible for detecting and binding to specific chemical signals or ligands that are released by other cells or molecules in the environment. Each receptor protein has a specific binding site that is uniquely shaped to recognize and bind to a particular ligand. This binding is highly specific, like a lock and key, with only certain ligands being able to bind to each receptor. This specificity is critical for ensuring that cells only respond to the appropriate signals and do not respond to irrelevant or harmful molecules.

What are Second messengers you ask?

They are small molecules that are released into the cytoplasm of the cell after a signal molecule binds to a receptor on the plasma membrane. They act as intermediaries between the activated receptor and the cellular response, relaying the signal from the plasma membrane to the interior of the cell. · Second messengers can rapidly and efficiently amplify the signal, leading to multiple cellular responses.

The binding of a ligand to a receptor protein triggers a series of biochemical events within the cell that ultimately lead to a cellular response.

This response can range from changes in gene expression to the activation of signaling pathways that alter the behavior of the cell. The ability of receptor proteins to recognize and bind to specific ligands is therefore essential for effective cell communication and normal cellular function.

Activity about Caffeine and Signals: Coffee contains a chemical called caffeine which acts as a stimulant and affects various signaling pathways in the body.

When caffeine enters the body, it binds to and blocks the adenosine receptors in the brain. Adenosine is a signaling molecule that builds up in the brain over the course of the day and signals the body to rest and sleep. By blocking the adenosine receptors, caffeine prevents this signal from reaching the brain and instead allows other signaling molecules like dopamine to increase in activity. ATP, a molecule involved in energy transfer within cells, is also affected by caffeine. Caffeine can inhibit the enzyme responsible for breaking down ATP, leading to an increase in available ATP in the body. All of these effects can contribute to the "alertness" and temporary increase in energy that people experience after consuming coffee. However, repeated exposure to caffeine can lead to tolerance, dependence, and addiction, as the body adjusts to the increased activity in these signaling pathways and becomes less responsive to caffeine over time.

Tell me how Paracrine signaling plays an important role in the inflammatory response?

When the skin is cut or damaged, cells in the area release paracrine signaling molecules such as cytokines and chemokines into the extracellular space. These signaling molecules act on nearby cells, including immune cells such as macrophages and neutrophils, which are recruited to the site of injury

Prof Video: Summary Coming Up!

Why'd they do Squidy like that 😭 https://www.youtube.com/watch?v=-dbRterutHY

An example of cell surface receptor type is

a ligand-gated ion channel, which allows ions to enter a cell in response to ligand binding, triggering a cellular response. (DONE WITH VIDEO)

In large multicellular organisms, signals reach target cells by ____________ or by ________________________.

diffusion or by circulation in the blood.

An example of intracellular signaling is

the binding of a steroid hormone to a cytoplasmic receptor, which can then bind to DNA and initiate transcription of a gene.

1. From ATP- cAMP (cyclic AMP):

· ATP is converted to cAMP to form a second messenger. · The enzyme that catalyzes cAMP formation is located on the cytoplasmic side of the plasma membrane.

3. Summary of the following:

· Direct signal transduction is a function of the receptor itself and occurs at the plasma membrane. · A receptor can activate a signal transduction pathway such as a protein kinase cascade directly, amplifying the response to receptor binding. · Indirect transduction involves second messengers. · Second messengers include cAMP, IP3, and DAG.

As discussed earlier: Signal transduction refers to the process by which a cell converts an extracellular signal into a response within the cell. Signals can either be Direct or Indirect:

· Direct signal transduction occurs when the receptor itself causes the response at the plasma membrane. · Indirect signal transduction occurs when the receptor receives the signal, but the cell's response is mediated by second messengers.

Signals Changing enzyme activity:

· Epinephrine can activate or deactivate enzymes based on the body's sugar levels. · In liver cells, a G-protein receptor is activated by epinephrine, which activates an effector protein. · The effector protein then triggers the formation of the second messenger cAMP. · cAMP can then alter the activity of two enzymes to increase sugar levels in the body. · It inhibits glycogen synthase, which stops the storage of glucose as glycogen. It activates phosphorylase kinase, which helps to convert glycogen into glucose.

3. G protein-linked receptors IMPORTANT (Start from 5:15 - 9:05): youtube.com/watch?v=ZBSo_GFN3qI

· G protein-linked receptors are a type of transmembrane receptor protein that span the plasma membrane. · The receptor is coupled to a G protein, which is a type of intracellular signaling molecule that can activate various downstream pathways. · When a ligand binds to the receptor, it changes the receptor's shape and exposes binding sites for G proteins. G proteins have 3 subunits: · one subunit binds to G-protein-receptors, activates phosphorylation. · the GTP-subunit separates to move until find an effector protein. · The effector protein cause a change in cell function.

Summary of Types of Signals:

· Gap junction signaling: Direct communication · Paracrine signaling: Nearby cells · Synaptic signaling: Neurons and target cells · Endocrine signaling: Hormones, distant targets · Autocrine signaling: Same cell or type

Cells can communicate with each other directly through specialized cell junctions.

· Gap junctions are one type of cell junctions found in animals. · Gap junctions are channels that are present between adjacent cells and are traversed by proteins called connexons. · The connexons of two cells come together to form a channel, which allows the exchange of small molecules and ions between the cytoplasm of the two cells. · Gap junctions are good for the passage of hormones and second messengers, as well as other small signaling molecules.

1. Ion channels

· Ion channel receptors are gated integral proteins. · These receptors allow ions to enter/leave a cell. · Acetylcholine is an example of a ligand that can bind to ion channel receptors in muscle cells. · When 2 acetylcholine molecules bind to a sodium ion channel receptor, it opens the channel. · This allows sodium ions to enter the muscle cell. · The entry of sodium ions into the muscle cell causes the cell to contract

Summary of receptors:

· Ion channels: Allow ion movement across cell membranes. · Protein kinases: Enzymes that add a phosphate group to target proteins. · G protein-linked receptors: Bind extracellular ligands and activate G proteins.

Signals can complete even more specific tasks including:

· Opening ion channels in cells · Changing enzyme activity.

In plants, cells can communicate through Plasmodesmata

· Plasmodesmata are pores that span the plasma membrane and cell walls. · A tubule derived from the ER fills the space in the plasmodesmata channel. · Plasmodesmata allow the passage of small metabolites and ions.

Signals opening ion channels in cells:

· Signals can open ion channels in cells. · This is a crucial step in the response of nervous system cells. · Odorant molecules, for example, can bind to receptors in the nose and activate a G protein. · The activated G protein can then activate an effector protein. · The effector protein sends a second messenger (cAMP) to open ion channels for Na+ and Ca2+ ions. · This leads to the generation of signals that are transmitted to the brain, allowing us to perceive the smell.

2. Second messengers can also be derived from lipids:

· Some phospholipids in the plasma membrane can be hydrolyzed by enzymes to form second messengers such as (IP3) and (DAG).

1. Summary of the following:

• Cells receive signals from the physical environment and from other cells. • Autocrine signals affect the cells that make them, paracrine signals affect nearby cells. • A signal transduction pathway involves the interaction of a signal and a receptor, and the amplification of the signal via a series of steps within the cell. The effects are seen on the function of the cell.

2. Summary of the following:

• Cells respond to signals (ligands) only if they have specific receptor proteins that bind those signals. • Receptors may be located in the cytoplasm or nucleus, or in the plasma membrane of target cells. • Some signals diffuse through the membrane and meet their receptors in the cytoplasm. • Other signals bind receptors in the plasma membrane, such as ion channels, protein kinases, and G-protein-receptors.

If you watched the videos, you probably heard of how a weak signal can be amplified and distributed through a "cascade response." Let's dig deeper.

•A cascade response refers to a series of steps that amplify and distribute the initial signal to multiple targets within a cell or across multiple cells. •Growth factors are an example of a cascade response in cell division. •When a growth factor binds to its receptor, it initiates a cascade response that triggers multiple downstream signaling pathways. •The signaling pathways activated by the growth factor lead to the activation of proteins that control cell division and ultimately lead to the growth and division of the cell.

Steps following the Protein Kinase cascade: RAS-G proteins

•A growth factor molecule binds to a protein kinase receptor. •The receptor exposes active sites to phosphorylate. •Phosphorylation activates the Ras G-proteins. •The activated Ras G-proteins activate other proteins, triggering a cascade of events. •The signal is propagated until it reaches the nucleus. •The energy source used in the process is GTP. •Later, GDP deactivates Ras proteins, terminating the cascade response.

4. Summary of the following:

•Adjacent animal cells can communicate through pores in their plasma membrane called gap junctions. •Proteins called connexons form thin channels between two adjacent animal cells allowing signalling molecules and ions to pass. •Plasmodesmata are pores that traverse the plasma membrane and cell walls of plant cells.