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Necessity of homeostasis, challenges and cellular

solutions

Objectives:• Compartmentalization

• Homeostasis

• Problems and cellular solutions

• Communication

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100 Species of Garden Animals

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Compartmentalization

Homeostasis

Advantages with the compartmentalization

• Compartmentalization is the foundation of cells.

• It confines chemical reactions to certain organelles.

• It leads to functional specialization and perfection in different cells and organelles.

• It increases the surface areas of plasma membranes, or the interface where chemical reactions often take place.

• It also enables the diversity of living organisms.

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Homeostasis• Homeostasis refers to stable internal environments,

such as temperature, osmolarity, pH, glucose, PO2, PCO2, etc.

• We are talking about systemic homeostasis when the whole body is concerned.

• Each cellular and subcellular compartment has its own homeostatic state.

• Homeostasis is dynamic but not still, with the steady-state level controlled by cellular mechanisms.

• Homeostatic imbalance underscores a number of diseases.

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Homeostasis 6https://worldofbiology.wikispaces.com/homeostasis+concept+map+solutions

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Homeostasis

Disadvantages of the compartmentalization

• Plasma membranes are barriers that tend to prevent all polar molecules from crossing over, including glucose, ions and most amino acids.

• Local homeostatic environment in each compartment needs to be maintained individually.

• Communications between compartments can be challenging.

• Functions of each compartment need complex controls by the system.

• Dysfunction in individual compartments can lead to disease in the system.

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Homeostasis

Ionic environment and the plasma membranePermeability

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Plasma membranes and homeostasis

• Achieving homeostasis in each compartment relies on the plasma membrane barrier as well as membrane transporters and ion channels.

• Substances with full membrane permeability do not often have a special homeostatic state in the cellular and subcellular compartments.

• Excessive transport activity can build a homeostatic state in a special compartment for these membrane-permeable substances.

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Plasma membranes

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Homeostasis

Cells can release and uptake materials across plasma membranes.

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Ion channels in membrane substance transportation

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Endocytosis and exocytosis

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The selective permeability plasma membranes makes epithelium polarized.

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With the membrane mechanisms, we can have our systemic homeostasis and the homeostasis in each sub-compartments within the system.

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Cell-cell communications

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Cross-talks among cells

• Hormonal communication – mediated by circulating hormones

• Neural communication – mediated by neurotransmitters from neurons

• Local communication – mediated by local mediators

• The chemical molecules are the 1st messengers.

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Communications between sub-cellular compartments rely on 2nd messengers.

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• The 2nd messengers serve as signal molecules that are referred as to the regulators.

• The target molecules can be another regulators or effectors.

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Signal molecules can affect their target molecules by allosteric regulation. In the process, the signal

molecule binds to a site apart from the active

site, and changes activity of the active site via

changing protein

conformationof the target

molecule.

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With a phosphate group, the local protein domain

changes its interaction with other protein domains, leading

to changes in protein structure

and function

Another regulatory mechanisms is phosphorylation, also known as covalent regulation

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Characteristics of allosteric regulation

• Allosteric regulators are often 2nd messengers.• The interaction of the regulator and the target

obeys receptor-ligand interaction rules.• The interaction is specific and reversible.• The concentration of allosteric regulators is

crucial.• Feedback regulation may occur if the regulator

concentration is affected by activity of the target molecule.

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Characteristics of covalent regulation

• Phosphorylation can be switched on (phosphorylation) and off (dephosphorylation).

• Phosphorylation is mediated by protein kinases.• Dephosphorylation is mediated by phosphatases.• A subtle balance between phosphorylation and

dephosphorylation enables a control of gene expression, enzyme function, channel activity and other cellular physiologic conditions.

• Specificity is determined by specific kinases and phosphatases.