biology exam 4

why do cells need to communicate

respond to changing environmental conditions

why is communication needed due to environmental conditions?

Nutrients, like glucose and lactose

Temperature, pH, osmotic conditions

Light availability

Oxygen availability

why do cells need to communicate with each other?

immune response: infectious agent and how the body responds

muscle contraction: when to contract and relax

sensing/regulating cell density: tissues are comprised of cells of the same type

nerve transmission: stimulus activates an active potential

growth and development: single cell —> multicellular organism

injury response: initiate proper repair methods

general themes involved in cell communication

cell membrane receptor, extracellular signal, activation of a signal transduction pathway, cellular response

cell membrane receptors

“antenna” that detects a specific signal, signal is present, signal transduction pathway

signaling molecules

transmit information between cells, enabling coordination of cellular activities and processes like development, growth, and differentiation

signal transduction pathways

involve the binding of signaling molecules, known as ligands, to receptors that trigger events inside the cell

general types of cellular responses to external signals

differential gene expression, changing enzyme activity, changing cell shape or movement

differential gene expression

activation/deactivation of specific genes

changing enzyme activity

alters metabolism or other cell functions

changing cell shape or movement

affects structural proteins

yeast cell response to glucose

due to glucose in the environment, yeast cells have undergone a cellular response by synthesizing more glucose transporters and enzymes that are needed to metabolize glucose

different types of cell communication

direct intercellular signaling, contact-dependent signaling, autocrine signaling, paracrine signaling

direct intercellular signaling

signals pass through an intercellular channel from the cytosol of one cell to adjacent/neighboring cells, intercellular channels can be connexons or innexons

how do connexons, innexons, and plasmodesmata facilitate this form of signaling?

Connexons and innexons form channels in animal cells, while plasmodesmata do the same in plant cells, facilitating direct cell-to-cell communication and the exchange of small molecules and signals

do you think single cell organisms utilize direct intercellular signaling?

Yes, single-celled organisms do utilize direct intercellular signaling, though it's often less complex than in multicellular organisms. This communication allows them to coordinate activities within their population and respond to environmental cues.

contact dependent signaling

relies on direct interaction between cells where a signaling cell's surface molecules bind to receptors on the target cell, transmitting signals

where does the signaling molecule come from in contact dependent signaling?

membrane-bound signals bind to receptors on adjacent cells

autocrine signaling

cells release signals that affect themselves and nearby target cells, in small areas

paracrine signaling

cells release signals that affect nearby target cells, not affected by receptors, happen in small areas

endocrine signaling

cells release signals that travel long distances to affect target cells

three basic stages of cell signaling

receptor activation, signal transduction, cellular response

receptor activation

binding of a signaling molecule causes conformational change in a receptor that activates its function

what roles do the extracellular and cytoplasmic domains play in receptor activation?

Absence of signaling molecule, receptor protein in inactive

Presence of signaling molecule, receptor is active

signal transduction

the activated receptor stimulates a series of proteins that forms a signal transduction pathway

How does activation of a receptor lead to the activation of a signal transduction pathway?

It triggers a conformational change that activates the receptor

To where does the signal get transmitted in a signal transduction pathway?

From the cell surface to intercellular targets

What are the intracellular targets for the signal in a signal transduction pathway?

Molecules that relay and amplify the signal within the cell, ultimately leading to a cellular response

cellular response

the signal transduction pathway affects the functions and/or amounts of cellular proteins, thereby producing a cellular response

what general types of cellular responses can occur due to an extracellular signal?

enzyme, structural proteins, transcription factor

enzyme cellular response

altered metabolism or other cell funtions

structural protein cellular reponse

altered cell shape or movement

transcription factor cellular response

altered gene expression and regulation, which changes the types and amounts of proteins in the cell

three basic types of cell surface receptors

enzyme-linked receptors, G-protein couple receptors, ligand-gated ion channels

enzyme-linked receptor

binding of ligand (signaling molecule) activates catalytic domain of the receptor

Intracellular catalytic domain becomes active when signaling molecules is bound, receptor that functions as a protein kinase, cascades

kinase enzyme

By adding phosphate groups to molecules, a process called phosphorylation, to activate or inactivate target proteins

phosphatase enzyme

Removes a phosphate group from its substrate molecule, essentially reversing the action of a kinase.

how do kinases and phosphatases function in cell communication?

Regulating protein activity through phosphorylation and dephosphorylation, respectively. Kinases add phosphate groups, while phosphatases remove them, allowing for dynamic control of protein function and cell signaling pathways.

ligand-gated ion channel

The binding of two extracellular signaling molecules (ligands) opens the ion channel, permitting ions to pass through the membrane.

Absence of signaling molecule, ion channel is closed, electrochemical gradient

Signaling molecule present, causes conformations change, opens receptor

ligand

A molecule that binds to a specific receptor (a protein) to initiate a cellular response, acting as a signaling molecule

How does the binding of a ligand affects the gated channel

It triggers a conformational change in the channel protein. This change alters the channel's shape, allowing ions to pass through, thus impacting the cell's electrical properties.

G-coupled receptor

Binding of ligand activates a G-protein

1.) Signaling molecule binds to GPCR (G-protein-coupled receptor), causing it to bind to a G protein

2.) G protein exchanged GDP for GTP. G protein then dissociates from the receptor and separates into an active alpha subunit and a beta/gamma dimer. The activated subunits promote cellular responses

3.) Signaling molecule eventually dissociates from the receptor, and the alpha subunit hydrolyzes GTP into GDP + Pi. Alpha subunit and the beta/gamma dimer reassociate

How do GDP and GTP affect the activity of G-proteins?

G-proteins are active when bound to GTP, and inactive when bound to GDP.

How does an extracellular signal lead to the activation of a G-protein?

Through a cascade of events initiated by the binding of the signal molecule to a G-protein-coupled receptor (GPCR)

intracellular (nuclear) receptors

Receptors that bind signaling molecules but exist in the cytoplasm or the nucleus of the cell

Where are intracellular receptors located?

cytoplasm or nucleus

what domains are present on nuclear receptors and their functions

N-terminal domain (A/B): : Ligand-independent transcription activation

DNA-binding domain (C): Binds DNA, enables dimerization

Hinge region (D): Flexibility, nuclear localization

Ligand-binding domain (E): Binds ligand, transcription regulation

C-terminal domain (F): Variable function (optional)

How does the signaling molecule for intracellular (nuclear) receptors enter the cell?

simple diffusion across the plasma membrane, able to pass through the lipid bilayer without needing a transport protein

What happens when the signaling molecule binds the intercellular (nuclear) receptors?

Triggers a conformational change in the receptor, which exposes a DNA-binding site

intercellular (nuclear) receptor example

Estrogen diffuses across the plasma membrane, enters the nucleus, and binds to the estrogen receptors. The receptors undergo a conformational change.

Estrogen receptors form a dimer, bind next to specific genes, and activate their transcription into proteins that affect the structure of the cell

Describe how an enzyme linked receptor/G-protein can activate a signal transduction pathway.

Receptor activation —> Relay between the receptor and protein kinase cascade —> Protein kinase cascade —> Activation of transcription factors —> Cellular response

How does binding of the signaling molecule activate the receptor?

When a signaling molecule (ligand) binds to receptor, Initiates a cascade of events that activates the receptor and ultimately leads to a cellular response

What is the function of the cytoplasmic kinase domain?

Catalyze the transfer of phosphate groups from ATP to specific target molecules

How does binding of the signaling molecule lead to activation of the receptor?

By inducing a conformational change that exposes or activates specific sites, or by creating docking sites for other proteins to bind and activate the receptor

When binding of the signaling molecule, what is the source of for the phosphates?

ATP, adenosine triphosphate

How can activation of an enzyme-linked receptor lead to the activation of the Ras G-protein?

Process involving guanine nucleotide exchange factors (GEFs)

What specifically has to occur to convert Ras from an inactive to an active state?

When it binds to GTP instead of GDP

How does activation of Ras cause the activation of a signal transduction pathway?

A relay protein binds to the phosphorylated receptor and then to a second protein, which stimulates a third relay protein, Ras, to release GDP and bind GTP

How specifically is a signal transmitted using a signal transduction pathway?

Ras activates protein kinase 1, which starts a protein kinase cascade in which protein kinase 1 phosphorylates protein kinase 2, and then protein kinase 2 phosphorylates protein kinase 3.

How do you inactivate a signal transduction pathway once it has been activated?

Returning Ras to its inactive state or inhibiting downstream signaling events.