Cell Communication

Three types of cell communication

Cell-to-Cell, Local Regulators, Long Distance

Cell to Cell Communication

Direct Contact

Ex: Plants: Plasmodesmata are channels that travel the cell walls of plant cells

Animals: Gap junctions where channels permit the passage of ions, small molecules and signals

Innate Immunity

A series of defenses that act immediately upon infection; the same whether or not the pathogen has been encountered before

What do macrophages do?

Signal molecules to increase blood flow to the site

What do Mast cells do?

Produce histamine which causes capillaries to become leaky

What do natural killer cells do?

Directly kill infected or cancerous cells through the expression of specific receptors and antigen presentation

What is MHC?

The marker that distinguishes “self vs non-self”

B Cells

Humoral immune response; secrete antibodies into the blood and lymph

T cells

Cell-mediated immune response, attack bacteria or virus infected cells, promote phagocytosis by other white blood cells by stimulating B cells to produce antibodies

How do B cells recognize Antigens?

Through direct contact, antigenic determinants are specific regions on an antigen where antibodies bind

How do neurons communicate?

Through short distances called synapses

Two types of synapses

1. Electrical - electrical current flows from a neuron through gap junctions

2. Chemical - neurotransmitter crosses the synaptic cleft and the neurotransmitter binds to a specific receptor on the surface of the receiving cell

Action potential

A nerve signal that causes the presynaptic neuron to release the neurotransmitter; caused by a stimulus

Explain the process of action potential

1. Resting state, Na+ and K+ channels are closed, and resting potential is maintained by ungated channels

2. Depolarization: A stimulus opens Na+ channels, if threshold is released, an action potential is triggered

3. Additional Na+ channels open, K+ channels close; interior of the cell is more positive. Membrane polarity is reverse of resting state

4. Repolarization: Na+ channels close and inactivate; K+ channels open, K+ rushes out; interior of the cell is more negative than outside

5. The K+ channels close relatively slow, causing an undershoot

How does an action potential move down the axon through the terminal?

Refractory period: inactivation of voltage-gated Na+ channels, which occurs at the peak of the action potential and persists through most of the undershoot period

Exhibitory Neurons

Release neurotransmitters that bind to receptors on the postsynaptic neuron, perhaps causing an action potential

Inhibitory Neurons

Release neurotransmitters that cause the postsynaptic neuron to become more negative, or hyperpolarized- preventing action potentials

Hormones

Long distance messengers

How do steroid hormones work?

1. Go through cell membrane

2. Bind with specific receptor in the cytoplasm

3. Receptor bound steroid hormone travels into the nucleus and binds to another specific receptor on the chromatin

4. The steroid receptor complex calls for the production of mRNA molecules

Water soluble hormones must use

Signal Transduction

Signal transduction pathway

A cell detects and responds to a signal from its environment - crucial for non-steroid hormones

Signal transduction process

1. A ligand binds to a receptor

2. A cascade of molecular events within the cell is triggered

3. Leading to a specific cellular response

4. Crucial for cell communication, allows cells to react to stimuli and coordinate their activities

G proteins

When a ligand binds to a GPCR, it triggers a conformational change in the receptor, which activates an associated G protein

Ca2+ as a second messenger

When a cell receives a signal, Ca2+ is released from intracellular stores or enters the cell through channels in the plasma membrane; this increase in Ca2+ concentration allows it to bind to various target proteins, activating or inhibiting their function

cAMP as a secondary messenger

Adenylyl cyclase converts ATP into cAMP, removing two phosphates; cAMP can activate an enzyme called protein kinase A, enabling it to phosphorylate its targets and pass along the signal

Phosphorylation

Acts as an “on switch”; kinases are enzymes that add a phosphate to a protein; causes proteins to be more active, inactivate, or breakdown; phosphorylation isn’t permanent, phosphatases remove phosphates to go back

Homeostatsis

The active maintenance of a steady internal environment

Endothermic

Generate metabolic heat to maintain internal temperature

Ectotherms

Changes with the temperature of the environment

Negative feedback

Counteracts changes to restore homeostasis for physiological variables that have moved away from normal range; increase or decrease a cellular response to an event

Positive feedback

Amplify signals to help complete physiological processes