cell communication and signaling transduction

without cell junctions

tissue would not be possible

Junctions Are Specialized

Contacts Between
Cells

Functions:

Allow cells to form
strong connections

2. Facilitate or prevent
passage of materials

3. Facilitate
communication

Types of Junctions:

1. Anchoring
2. Tight Junctions
3. Gap junctions
4. Plasmodesmata

Anchoring Junctions

allow cells to
form sheets that are tightly
bound, but still allow passage
between cells (intracellular
space)

Adhering junctions

use cadherin protein family
– Connects to microfilaments of
the cytoskeleton

Desmosomes

are points of attachment between cells
– Intermediate filaments anchor the
desmosomes in cell.

Tight junctions

hold cells very tightly together; solutes cannot
pass around cells (no passage
into intercellular space)

Cells connected by

tight junctions seal off body cavities
– blood/brain barrier
• spinal fluid/blood
– pericardial
– peritoneum

Gap junctions (large pipes)

allow small ions to pass between cells

critical for conduction across heart muscles

Why Do Cells Need Signal
Transduction?

Makes it possible for cells to coordinate
activities

How Do Cells “Talk” To Each Other?

Using chemical or electrical signals

Most often, the chemical messengers are

– ECM molecules
– Hormones
– Interleukins
– Neurotransmitters

The first step of signal transduction

Messenger molecule binds to a cell surface
receptor.

second step of signal transduction

then creates a biochemical change within the
cell.
1. The messenger molecule can either enter the cell
(like estradiol) or…
2. The messenger molecule binds to a receptor on the
outside surface of the cell and causes the release of
a different molecule on the inside surface of the cell
membrane

third step of signal transduction

The biochemical change, many times, affects
transcription and translation of a certain
protein.

Second Messengers

A molecule released intracellularly in response to a primary messenger binding to a receptor on the exterior surface of the cell membrane

example of a second messenger

G-Protein Coupled Receptors

– When a signaling molecule
binds to the GPCR, a
biochemical change happens on
the interior surface of the cell,
causing the release of a second
messenger

Examples of Signal Transduction Pathways

• Neuron excitation (nerve impulse conduction)
• Neurotransmitter release
• Muscular contraction