Cell Communications

Cell Communication Objectives

General

(Slide 1) 

1. Why do Cells Communicate? 

• To maintain Homeostasis 

  • Nutrients, Molecules, Osmolarity 

2. Describe several scenarios/reasons where cells need to communicate.

• Embryological Development

• Immune System 

  • Give 2 examples of direct cell communication in the immune system.

• Emergency situations

• Mating

• Coordinated responses in single celled organisms (Such as yeast)

• Nervous System 

• Endocrine

3. What are target cells?

• The target cell is the target of the signal

(Slide 2)

4. Explain how/why the cell membrane is vital in cell communication.

It always involves the cell membrane and usually has a glycolipid \or glycoprotein that  receives the signal and passes it on to the processes (proteins?) in the body. 

What are Ligands:
Ligand: A molecule that bind to a receptor, once it bind the message gets intercepted and something changes/happens accordingly

5. Distinguish between endocrine, autocrine, paracrine , direct, and synaptic signaling.

Direct Contact Signalling: 

• Ligands can pass off when the cells pass by/have direct contact via a gap junction (generally among the same type of cells) (Direct Contact)

• With different types of cells the Ligands fit with the receptor of another cell, this is similar to lock-and-key

Paracrine signalling: In the nearby area, it sends out a signal telling other cells to do something (Start dividing, starting clotting, etc.)

• Synaptic: Specific to two neighbouring cells, it send out a signal that only acts on other nerve cells in the nearby area and is crucial for transmitting signals across synapses, allowing rapid communication in the nervous system.

Autocrine:

• ligand bind with a receptor of the own cell. Autocrine signaling is a type of cell communication where a cell produces a signal (ligand) that binds to its own receptors, resulting in a response from the same cell. This form of signaling is crucial for processes like cell growth and immune responses, as it allows the cell to regulate its own activity and maintain homeostasis.

Endocrine signalling:

• Uses hormones to meet the receptor somewhere throughout the body, takes longer but lasts longer (ex: secreting growth hormone throughout the body) In this type of communication, hormones are released into the bloodstream, allowing signals to reach distant target cells throughout the body, thus coordinating complex processes like growth, metabolism, and reproduction.

(Slide 7) 

6. Describe the 3 phases of signal transduction. 

Part 1: Reception 

• Ligand binds to receptor which activates the relay molecules)

Part 2: Transduction

• The relay molecules “tag” each other, they are kinases. They are enzymes that activate other enzymes by phosphorylating them. So one kinase, tags another kinase, which tags another kinase, and so on.

Part 3:  The last relay molecule will either start or stop something 

7. Describe the structure and function of plasmodesmata and gap junctions.
   
   

Types of receptors: 

In the membrane:

• GPCR, a G protein coupled receptors: Work with a G protein and GTP (Guanosine Triphosphate). 

  (8) What is the function of relay proteins? What are kinases?

• They form part of the second step, transduction

Most of the time they are protein kinases that activate other protein

9. Differentiate between the mode of action of G-protein coupled receptors and tyrosine kinase receptors. 

(In the membrane)

• Tyrosine kinase receptors , a receptor that is apart (2 pieces) and the chemical signal binds 

• Ligand gated ion channels, transport proteins that can open or close in response of a chemical signal. (Mostly synaptic signaling and action potentials, nervous system) 

(In the cytoplasm)

• Intracellular receptors, Lipid based chemical messages. They bind to intracellular receptors 

(Slide 11)

What are second messengers? Explain their function and give examples.

2 most common = calcium and cyclic amp

• They are sometimes needed to activate really proteins and they go in between the receptor and the relay/transduction proteins

**Second Messengers:** Second messengers are small molecules that relay signals received by receptors on the cell surface to target molecules inside the cell. They play a crucial role in amplifying the strength of the signals from various extracellular stimuli (like hormones or growth factors), essentially translating the external signals into specific cellular responses. **Function:** Second messengers facilitate communication between receptors and effector proteins, allowing cells to respond to a variety of signals in a regulated manner. They can initiate various processes, including changes in gene expression, metabolism, or cell growth. **Examples:** 1. **Cyclic AMP (cAMP):** Produced from ATP by the enzyme adenylyl cyclase, cAMP activates protein kinase A (PKA) and is involved in processes such as glucose metabolism and regulation of gene transcription. 2. **Calcium Ions (Ca²⁺):** These ions can act as second messengers to activate various cellular functions, including muscle contraction and neurotransmitter release. 3. **Inositol trisphosphate (IP3):** Produced from phosphatidylinositol 4,5-bisphosphate (PIP2), IP3 promotes the release of calcium ions from the endoplasmic reticulum, influencing a range of physiological responses.

Give examples of several types of cell responses that may be brought about by a signal transduction pathway.

What is amplification, as it relates to signal transduction pathways?

Explain how one chemical signal can have multiple effects on different cells.

Endocrine

Explain the difference between water soluble hormones and fat soluble (lipid) hormones in terms of the cellular receptors they bind to. Explain how the structure of these molecules causes this difference.

What is the relationship between the hypothalamus, the pituitary gland, and the rest of the endocrine glands?

What is a tropic hormone?

What is the function of the endocrine system? What is the function of the following glands; hypothalamus, pituitary, thyroid, pancreas, adrenal, testes, ovaries, parathyroid. Be able to locate these on a diagram

Describe the effects of the following hormones; insulin, growth hormone, glucagon, thyroxine, epinephrine, estrogen, testosterone, melatonin

Describe how glucagon and insulin work together to regulate blood sugar.

Describe how calcitonin and parathyroid hormone work together to control blood Calcium.

Hypothalamus: Controls all the glands that release hormones, thereby regulating various bodily functions including metabolism, growth, and homeostasis.

The Thalamus: acts as a “relay station” of sensory information from the sensory neurons to the cerebral cortex is in charge of motor functions such as balance

The limbic system: plays a crucial role in emotional regulation and memory, influencing behaviors that can impact hormonal balance, including responses to stress that affect calcium levels.

The cerebral cortex: performs cognitive functions including thinking, processing, producing, and comprehending language

The Medulla oblongata: regulates autonomic functions such as heart rate and blood pressure, which indirectly influence calcium levels by affecting overall metabolism and hormone distribution.

The cerebellum: receives sensory information and coordinates movements to maintain balance

Tropic hormones stimulate other glands

The pituitary gland is the main gland 

Hypothalamus = superintendent 

Pituitary = Principle 

all the other glands are like the teacher 

the tropic hormones tell the other endocrine glands what to do it can be releasing or inhibiting 

TRH: Thyroid releasing hormone (sent from hypothalamus to pituitary gland)

TSH: thyroid stimulating hormone (sent from pituitary gland to thyroid gland)

Nervous

1. Describe the structure of a typical neuron. Explain how this structure allows it to carry out its function.

Dendrites will carry impulses toward the cell body

Axon carry the signal away from the cell body 

Myelin sheaths are lipids that are produced by other cells, these cells wrap around the axon and produce the myelin sheath

2. Describe what an action potential is, and some examples of what may cause one to occur.

Action Potential (also known as nerve impulse) = an electrochemical signal, this signal is how all cells in the nervous system communicate  (changes in ions inside and outside of the cell)

During action potential the cell is Depolarized, repolarized then hyperpolarized

• Depolarization (when sodium is pouring in the cell when the cell is stimulated) 

  • The Sodium ion will depolarize the cell 

3. Diagram an electrical and chemical synapse. Label the following as necessary; pre-synaptic neuron, post-synaptic neuron, synaptic cleft, synaptic vesicles, gap 

junctions, gated channels. Explain differences between the 2 types.

The concentrations of two ions (Sodium) change. When the neurons are stimulated the gated sodium channels will open and go inside the cell. The peak in the graph is positive because of the sodium in the cell, However when this happens all the potassium ions that were in the cell are out, this is called repolarization. The cell “goes numb” until active transport occurs and pushes sodium out and potassium in (It's not a action potential). The transport protein that does this is the sodium potassium pump 

Explain how an action potential travels through an electrical synapse.

Action potentials will pass from neuron to neuron at the synapses;

Explain how a signal travels across a synaptic cleft in chemical synapses. What role do neurotransmitters play? How does this process differ between an excitatory synapse and an inhibitory synapse?

Discuss the functions of the following neurotransmitter; acetylcholine, dopamine, GABA, noradrenaline, endorphins, serotonin

Immune

What is the lymphatic system?  Where is it located and what is its function? What is the function of the spleen, thymus, tonsils and lymph nodes in defending the body?

• The Lymphatic System is a “secondary network of vessels” (Tramps) and organs that play a crucial role in the immune system, helping to transport lymph, a fluid containing infection-fighting white blood cells, throughout the body.

  • Lymph fluid has very concentrated amount of white blood cells

Extravegation: Unlike red blood cells, white blood cells can leave the bloodstream and enter tissues, allowing them to respond more effectively to infections and injuries.

Lymph nodes: small, bean-shaped structures that filter lymph fluid and trap pathogens, providing a site for immune cell activation and proliferation.

• they filter lymph

• trap microorganisms, tissue debris, etc.

• Contain concentrated WBCs

Spleen: Rbc & wbc storage, Spleen: functions to filter blood, removing old or damaged red blood cells and pathogens

• Spleen: RBC & WBC storage, also plays a critical role in immune response and filtering blood to remove pathogens. (an emergency supply)

• Thymus: essential for the maturation of T-cells, a type of lymphocyte crucial for adaptive immunity. The site of T cell “maturation”, secretes thymosin to stimulate T cells production and support their development into functional immune cells capable of recognizing and responding to specific antigens.

• Tonsils: they trap airborne antigens (Ags)- act as a first line of defense against ingested or inhaled pathogens

• Lymph nodes serve as filtration points that trap pathogens and facilitate the activation and proliferation of immune cells.

Lymphocytes:

• (Adaptive) T Lymphocytes: Responsible for cell-mediated immunity, they help in directly attacking infected or cancerous cells and coordinating the immune response.

• (Adaptive) B Lymphocyte: "Antibody producers" These cells are responsible for producing antibodies that specifically target pathogens, providing long-term immunity and memory against previously encountered infections.

• Granulocytes:

• Megakaryocytes: "Platelet producers" that play a crucial role in blood clotting by releasing platelets into the bloodstream, which are essential for wound healing and preventing excessive bleeding.

• Phagocytes: These white blood cells engulf and destroy pathogens through a process called phagocytosis, playing a crucial role in the innate immune response.

Describe the non-specific (innate)responses of the body. What is the first barrier against infection and why is it so effective?

Innate Immunity:

• Nonspecific: Kills anything

• Skin- highly impenetrable due to the protein keratin: Most pathogens can not penetrate the skin's barrier, making it an effective first line of defense against infection.

• Mucous membranes: These line the respiratory, gastrointestinal, and urogenital tracts, trapping pathogens and preventing them from entering the body.

  • All of our holes have mucus membranes to protect them, they secrete mostly mucus (all have different types)

  • They can wash things away , such as dirt and pathogens, thereby reducing the risk of infection and maintaining homeostasis. Such as the Vagina and the tear ducts (crying)

  • Note: Typically pathogens can get through the membranes

    Describe the steps involved in the inflammatory response. What purpose does this serve? Explain each of the following symptoms of the inflammatory response in terms of what is going on in the body; pain, swelling, redness, heat.

• Inflammation: Injured cells release chemicals that signal nearby blood vessels to dilate, increasing blood flow to the area and allowing immune cells to migrate to the site of injury or infection.

• Blood clots/platelets:

  • Little vesicles that circulate your blood stream that come from the megakaryocyte site that is located in the bone marrow. They are attracted to the wound because of the chemicals that the white blood cells secrete

    • When a blood vessel is damaged, platelets adhere to the site and release additional signaling molecules that further attract immune cells, promoting healing and preventing excessive blood loss.

• Fever: Pathogens can be sensitive to temperatures, the hypothalamus can raise the body temperature.

• Natural Killer Cells; they patrol the body for cancer and virus infected cells. These cells are crucial for the innate immune response, as they can recognize and eliminate compromised cells without prior sensitization. They can secrete a chemical called perferin that will “poke holes in the cell that kills it”

• Neutrophils: "Suicide bombers" of the immune system, they are the most abundant type of white blood cell and respond rapidly to sites of infection, releasing enzymes and reactive oxygen species to destroy pathogens, often at the cost of their own lives.

• Macrophage: “The first line of defense” A type of white blood cell that engulfs and digests cellular debris, foreign substances, and pathogens, playing a crucial role in the immune response by presenting antigens to T lymphocytes.

Describe the process of hematopoiesis, including where in the body it occurs and all cells that are formed.

• Cytokines: Signaling molecules that mediate and regulate immunity, inflammation, and hematopoiesis, playing a crucial role in cell communications during immune responses. Hematopoiesis occurs primarily in the bone marrow, where hematopoietic stem cells differentiate into various blood cell lineages, including red blood cells, white blood cells, and platelets, ensuring a continuous supply of these essential components for maintaining homeostasis and responding to infections.

What are pathogens? What are antigens?  How are they different from each other?

Describe the cells involved in non-specific(innate) immunity(neutrophils, mast cells/basophils, macrophages, natural killer cells, platelets). What are their functions? Why are macrophages especially important?

What does it mean that the immune system is self-tolerant?

• “They should be able to distinguish self from not-self” to prevent attacking the body’s own cells while effectively targeting foreign pathogens.

• The immune cells go through a learning process, they are tested , ensuring that they can accurately recognize and respond to pathogens without harming the body's own tissues. If they can’t do this then they are programed to go through apoptosis

• This self-tolerance is crucial for maintaining homeostasis and preventing autoimmune diseases, where the immune system mistakenly attacks healthy cells.

What exactly is the MHC? What role does it play in distinguishing self from non-self?

• A group of genes we all have that code for glycoproteins on the cell membrane. These glycoproteins, known as Major Histocompatibility Complex (MHC) molecules, present peptide fragments derived from pathogens to T cells, thus playing a critical role in the immune response by helping the body identify which cells are infected and which are not.

  • Class 1: Found on ALL cells, when you see a question relating to class 1 MHC- consider that they are referring to body cells and therefore if they have a problem they are gonna rely on T-cytotoxic cells

  • Class 2: found only on immune cells, how they communicate with each other. The macrophages use these glycoproteins “show” this. White blood cells can recognize this and know to kill that

    • You cna smell othe people’s MHC genes, if you like the smell they have different MHC genes. From an evolutionary standpoitn you want variety and diversity in MHC genes within a population, as this increases the chances of survival against a wide range of pathogens, ensuring a robust immune response across different individuals. So you like the smell of someone because their unique MHC molecules signal a different genetic makeup. IF you hate the smell they are similar, which may indicate a closer genetic relationship and reduced diversity in MHC genes, potentially leading to a weaker immune response.

Adaptive Immunity:

Involves B & T cells which respond to certain microbes/foreign molecules- not all of them however. Only specific B and T cells can be active against a certain virus/foreign substances

antigens: any foreign molecules eliciting a specific response, molecules that are recognized by the immune system, specifically by B and T cells, triggering an immune response that can lead to the destruction of pathogens.

Differentiate between the terms non-specific(innate) and specific(adaptive) as they relate to defending the body against pathogens.

What are antigen presenting cells? How do they “present” antigens to T cells?

Describe the 3 types of T cells. What is different about the way T cells fight antigens as compared to B cells.

What types of antigens are T cells most effective against?  Why?

What is the role of T helper cells in the immune response?

What is the role of T suppressor/regulator cells?

What are B cells also known as humoral immunity?  How do they fight antigens? Against what 2 types of antigens are they most effective?

Describe the basic structure of an antibody. 

Describe 4 ways that antibodies can fight antigens.

• Antibodies can neutralize toxins by binding to them and preventing their harmful effects.

• They can opsonize pathogens, marking them for destruction by phagocytes.

• Antibodies can activate the complement system, leading to the lysis of bacterial cells.

• They can agglutinate pathogens, clumping them together to enhance clearance by the immune system.

Diseases related to immune system:

• Cancer

• Autoimmune Disease

  • Arthritis, Diabetes

  • Allergic reactions

  • AIDS

  • Transplant rejections

 Describe the basis for immunological memory. How does secondary immunity differ from the primary immune response?

Passive Immunity: Injecting antibodies from a different source (some else’s antibodies)

Active Immunity: They give you a weakened for of the pathogen to stimulate your immune system to produce its own antibodies, thereby creating a long-lasting protection against future infections. “alerting” the body’s immune system to the virus-creating memory cells for secondary immunity

Secondary immunity is characterized by a faster and more robust response due to the presence of memory B and T cells that were generated during the primary immune response, allowing the body to recognize and respond to previously encountered antigens more effectively.

Clonal selection Process: The macrophage will go around bringing around a piece of the bacteria or whatever until the right T-cell recognizes it. They communicate through direct communication. The T-cell then clones itself

Clonal Selection: T and B cells fight against pathogens by recognizing specific antigens, leading to their proliferation and differentiation into effector cells that help eradicate the infection.

T-helper cells: they can activate more macrophages and make them fight harder. They also help activate the right B-cell and they start to clone as well. Once there is enough B cells they excrete over 2,000 antibodies that are specific to the antigen, which help neutralize the pathogen.

• Cytotoxic T-cells: These cells directly kill infected cells by recognizing antigens presented by MHC class I molecules, ensuring that infected cells are eliminated and preventing the spread of the pathogen. The cell even though is being forced to produce more viruses can rip a part off and present viral antigens on its surface, which allows cytotoxic T-cells to identify and eliminate them effectively.

  

B lymphocytes (B cells) are a form of humoral immunity

• they kill antigens by secreting proteins called antibodies that must match the shape of the antigens, 2,000 antibodies per second. They are mostly effective against “free” antigens but less effective against viruses, transplanted tissue and cancer.

Antibodies are tetramer quaternary structures composed of four polypeptide chains, two heavy chains and two light chains, which form a Y-shaped molecule that facilitates antigen binding.

antigen presenting cells: Cells that display antigen fragments on their surface, allowing T cells to recognize and respond to the pathogen. These cells include dendritic cells, macrophages, and B cells, which play a crucial role in initiating the adaptive immune response by activating T cells through the presentation of processed antigens.

What are the symptoms of inflamation:

pain, swelling, heat, redness

Cell-Mediated immunity

• POSSIBLY a third type of T cell

  • T regulatory cells: These cells play a crucial role in maintaining immune tolerance and preventing autoimmune responses by suppressing the activation of other immune cells.

Textbook

Adaptive Immunity: Relies on two types of lymphocytes that arise from stem cells in bone marrow

• B cells + T cells are crucial components of adaptive immunity, with B cells responsible for producing antibodies and T cells playing key roles in cell-mediated immunity.

• B cells: Differentiate into plasma cells that secrete antibodies, providing humoral immunity against pathogens.

• T cells: Include helper T cells that assist B cells and cytotoxic T cells that directly kill infected cells, enhancing the overall immune response.

Plasma cells: produce soluble proteins called antibodies, these antibodies bind on to foreign antigens, neutralizing pathogens and marking them for destruction by other immune cells.

Memory Cells; activated B and T cells defend against future infections by the same pathogen, allowing for a faster and more robust immune response upon re-exposure. They are made during the time of the infection and stay in your body for depending amounts of time (3 month, 6 month, forever, etc.). If you were to get infected with the SAME strain of the infection- your body would recognize this almost instantly because the memory cells will be in your body in a greater quantity and ready to mount a swift and effective immune response, significantly reducing the severity and duration of the illness. \

• These memory cells can adjust your dna to change the receptors on their surface, enhancing their ability to recognize specific pathogens and improving the efficiency of the immune response.

T-Cells

B-Cells

What do antibodies do?

• Neutralization: Blocks viral biding site , preventing the virus from entering host cells and replicating.

• Agglutination of antigens- bearing particles (going from fluid to solid) causes them to clump together, enhancing their recognition and clearance by phagocytic cells.

• Opsonization: Antibodies coat pathogens, marking them for destruction by phagocytes, which enhances the efficiency of the immune response.

• Precipitation of soluble antigens: This process leads to the formation of insoluble complexes that can be more easily removed from circulation by immune cells, thereby aiding in the elimination of potentially harmful substances.

• Complement fixation:

Misc.

Refractory Period

• The refractory period refers to the time following an action potential during which a neuron or muscle cell cannot be re-excited. This ensures that signals are transmitted in a unidirectional manner and prevents the overstimulation of the immune response. This period is crucial in maintaining the integrity of signaling pathways, as it allows cells to recover and prepare for subsequent action potentials. The refractory period is due to the inactivation of sodium channels , which temporarily prevents the influx of sodium ions and thus inhibits the generation of another action potential until the channels return to their resting state.

There are two main phases of the refractory period: the absolute refractory period, during which no new action potential can be initiated, regardless of the strength of the stimulus, and the relative refractory period, where a stronger-than-usual stimulus is required to elicit an action potential.

Neuropeptides: relatively short chains of amino acids that operate via G protein-coupled receptors. they function as signaling molecules in the nervous system, influencing various physiological processes such as pain modulation, stress response, and regulation of mood.

Synapses:

• Electrical Synapses:

  Electrical synapses are connections between neurons that allow for the direct passage of ions and electrical signals through gap junctions. They enable rapid communication between adjacent cells, leading to synchronized activity. This type of synapse is particularly important in reflexes and other processes requiring immediate response, as they facilitate faster signal transmission compared to chemical synapses.

• Chemical Synapses:

  Chemical synapses involve the release of neurotransmitters from the presynaptic neuron into the synaptic cleft. These neurotransmitters then bind to receptors on the postsynaptic neuron, which can lead to excitation or inhibition of the postsynaptic neuron depending on the type of neurotransmitter and receptor involved. This transmission is essential for communication between neurons and allows for complex responses and processing in the nervous system.

  • Primary Difference:

The primary difference between chemical and electrical synapses is how they transmit signals. Electrical synapses allow direct ion flow through gap junctions for fast communication between cells. In contrast, chemical synapses release neurotransmitters into the synaptic cleft, which then bind to receptors on the next neuron, leading to either excitation or inhibition.

• Textbook answer: In an electrical synapse, electrical current flows directly form one cell to another. In a chemical synapse, depolarization cause synaptic vesicles to fuse with the terminal membrane and release neurotransmitters

Neurotransmitters

• Acetylcholine: The neurotransmitter that allows for your skeletal muscle contractions and plays a key role in the autonomic nervous system. If we didn’t have this neuron our muscles will continuously contract

• Noradrenaline: The transmitter that plays a crucial role in the body's fight-or-flight response, increasing heart rate and blood flow to muscles while also enhancing alertness, obviously its part of the sympathetic nervous system. It stops you digestive system, and it diverts energy to more critical functions during stressful situations. Furthermore it dilates the blood vessels.

• Dopamine: A neurotransmitter that influences mood, reward, and motor control, often associated with pleasure and motivation.

• Serotonin: Regulates sleep, appetite, and mood, contributing to feelings of well-being and happiness. It is primarily found in the brain, bowels, and blood platelets, and plays a significant role in stabilizing mood and preventing depression.

  • SSRIs, They prevents the reuptake of serotonin in the brain, effectively increasing its availability and enhancing mood regulation. (In PMS this can lead to fluctuations and lower serotonin levels)

• Endorphins- The body’s natural pain killer. Regulates hunger, anger, sexual excitement. If you were to think about it, if you were to sprain your ankle running from a bear you wouldn't feel it. This is due to the release of endorphins, which act on the same receptors as opioids, providing a sense of euphoria and pain relief during stressful situations.

• GABA- The primary inhibitory neurotransmitter (it opens the chloride channels) It plays a crucial role in reducing neuronal excitability and preventing overstimulation of the nervous system. GABA works by opening chloride channels in neurons.

Hyperpolarization of the neuron: making it less likely to fire an action potential, thus contributing to the overall calming effect on the brain. It makes the inside of the membrane more negative

Gate ion channels: ion channels that open or close in response to stimuli

Glycogenolysis: the process of breaking down glycogen into glucose, which is crucial for maintaining blood sugar levels during periods of fasting or increased energy demand.

What hormones maintains blood sugar level between meals: