WEEK 4: COMMUNICATION WITHIN THE BODY

Question 1

State forms of cell-cell communication Cell signaling.

Answer 1

1.Cell-cell contact-dependent signaling
- Signaling that depends on contact between cells.

2.Cell-cell signaling via secreted molecules
- Signaling that depends on secreted molecules (which are mainly water-soluble

Question 2

Describe 2 ways in which cee-cell dependent signaling can occur.

Answer 2

1.Cells may communicate directly with their immediate neighbor through gap junctions in a so-called Direct signaling.

*Gap junctions connect the cytoplasm of neighboring cells via protein channels, which allow the passage of ions and small molecules (such as amino acids) between them (as an example, gap junctions allow the coordinated contraction of cardiac muscle cells).

2.Cells may communicate through cell surface molecules, in a so-called contact-dependent way

Here the signaling molecule is not secreted, but is bound to the plasma membrane of the signaling cell and interacts directly with the receptor exposed on the surface of the target cell.

This type of signaling is particularly important between immune cells and during tissue development

Question 3

Describe 4 ways in which cell-cell via secreted molecules can take place.

Answer 3

1.Signaling via secreted signaling molecules can be paracrine (acting on neighboring cells).

Paracrine signals move by diffusion through the extracellular fluid. These types of signals usually elicit quick responses that last only a short amount of time.

Example - gaseous molecule nitric oxide (NO), which, among other effects, acts by relaxing smooth muscle cells around blood vessels, resulting in increased blood flow.

2.Signaling via secreted signaling molecules can be autocrine –a variant of paracrine (acting on the cell that secretes the signaling molecule – a cell targeting itself). Auto = self

This type of signaling often occurs during the early development of an organism to ensure that cells develop into the correct tissues and take on the proper function.

3.Signaling via secreted signaling molecules can be electrical (between two neurons/nerve cells or between a neuron and a target cell)

Also referred to as chemical transmission or synaptic signaling is a faster and more specific form of cell–cell signaling.

These signaling molecules are collectively called neurotransmitters.

4.Signaling via secreted signaling molecules can be endocrine (acting on cells that are remote from the secreting cell).

Secretory cells that produce signaling molecules are called endocrine cells.

Blood-borne signaling molecules were the first to be discovered and are collectively known as hormones.

Question 4

State the 2 types of receptors for cell signaling.

Describe each one of them and what they respond to.

Answer 4

There are two types of receptors: intracellular and extracellular receptors.

INTRACELLULAR RECEPTORS
*Also known as cytoplasmic receptors, are found in the cytoplasm of the cell.
*Respond to hydrophobic ligand/signal molecules that have crossed the plasma membrane.
*Many intracellular receptors are transcription factors - interact with DNA in the nucleus and regulate gene expression.

EXTRACELLULAR RECEPTORS
*Extracellular receptors- also known as transmembrane receptors
*Are membrane-anchored, or integral proteins
*Bind to external ligand molecules
*Span the plasma membrane
*Perform signal transduction-converting an extracellular signal into an intracellular signal

Question 5

State three general categories.

Answer 5

1.Ion channel-linked receptors: Gated ion channels form a pore through the plasma membrane that opens when the signaling molecule binds

The open pore then allows ions (such as sodium, calcium, magnesium, and hydrogen) to flow into or out of the cell

Example- Acetylcholine receptors -important in the transmission of electrical signals between excitable cells

2.G-protein-linked receptors

-Heterotrimeric G proteins have three subunits: α, β, and γ.
-Convert extracellular signals into intracellular responses, including responses to hormones, neurotransmitters, as well as responses to vision, olfaction and taste signals

3.Enzyme-linked receptors -also known as catalytic receptors

Are a group of single transmembrane receptors.

Contain an extracellular ligand-binding domain, a transmembrane helix, and an intracellular domain that either contains intrinsic enzyme activity itself or associates directly with an intracellular enzyme

An example of this type of enzyme-linked receptor is the tyrosine kinase receptor.