Homeostasis and Proteins

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Homeostasis: A state of body equilibrium or stable internal environment of the bodyof all species

Feedback Loop:

A system created to respond to stimuli

Negative feedback loop: Feedback which reduces the intensity of the original stimulus. eg. high blood pressure

Positive feedback: Feedback which increases the intensity of the original stimulus. eg. stretching of cervix during childbirth

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Protein Makeup:

Proteins are made up of amino acids, have 2 amines and an R group

In proteins the amino acids are joined by peptide bonds

There are many different types of amino acid. Variation of ‘R’ groups determines the amino acid, ‘R’ groups determine the shape of the protein. The shape of the protein determines its function.

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Protein Structure:

Proteins are synthesisedas linear molecules from which we can determine the primary structure

Proteins then form secondary structures based on the chemical interactions of the amino acid residues of the primary structures

The secondary structures fold up into tertiary structures

Two or more peptide chains with tertiary structure combine to form quarternarystructure. This is the functional protein.

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Protein Functions:

‘doing’ molecules in the body

have roles in: Catalysis, Cell structure, Cell Communication, Transport, Cell recognition, Immunity, Cell Regulation, enzymes, Cytoskeleton/cell adhesion, Ion channels, Albumin transferrin, Transcription inducers, Blood groups/HLA proteins, Antibodies

Enzymes catalyse reactions. Cannot initiate the reaction but lower the activation energy required, Provide a mechanism for regulating reactions

Enzymes provide a site for reactions to occur. Site is determined by the shape of the enzyme protein. Can bring substrates together, provide proton donors/acceptors, provide shielding. Will appear unaltered at the end of the reaction. Often work in multi-enzyme pathways where product of one reaction serves as substrate for the next. Pathways provide mechanism of control and harvesting output of pathways (eg. glycolysis)

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Cytoskeletal Proteins

Cytoskeleton: A framework of protein filaments offering support in eukaryotic cells

Three types of protein filaments make up the cytoskeleton:

1. Intermediate filaments

2. Microtubules

3. Actin filaments

Intermediate Filaments:

Fibrous proteins of great tensile strength

Network anchored at cell junctions

Nuclear lamina

Different types that are found in different areas of the body

Microtubules:

Grow out from centrosome

Form tracks for transport

Form cilia and flagella structures

Microtubules grow out from and organisingcentre(centrosome, basal body), in which minus ends are embedded

Actin Filaments:

Movements involving the cell surface, formation of microvilli

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Dynamic Instability:

Microtubules are in a state of dynamic instability, brought about by hydrolysis of GTP

Microtubules in Cilia and flagella:

Microtubules arranged in 9+2 pattern

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Actin Filament Treadmilling:

Assembled like microtubules but have no organizing centreso undergo treadmillling

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Cell-cell interactions

Most animals are multi cellular

For proper structure and function of tissues, close cell-cell contact is required

Contact is maintained by active processes involving specific surface membrane proteins

-cell adhesion molecules (CAMs)

-cell surface to cell surface

-cell surface to an immobilised structure

Tight junctions:

Separate apical and basal surfaces

Leak-proof epithelial sheet: to cross the barrier need to go via the cell

Adherens Junctions, Desmosomes and Hemidesmosomes:

Epithelia bound to each other and to the basal lamina by junctions that are linked to cytoskeletal proteins

All have in common a molecule which spans the membrane and is linked inside the cell with cytoskeletal filaments

Adheren junctions and desmosomes = cadherin linked to actin. Forms an adhesion belt below tight junctions.

Hemidesmosome = integrin

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Adherens Junctions:

Adhesion belt

Actin network connecting cell to cell

Contractile properties

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Desmosomes:

Cadherin anchored to intermediate filaments (keratin)

Strong connection

Tensile strength

Hemidesmosomes:

Anchor epithelia cell to basal lamina

Integrin: from keratin in cell to laminins in basal lamina

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Gap Junctions:

Gap junctions allow communication between cells

Gap junctions

Gap spanned by connexins

Connexins form channels allow passage small molecules