-Tight Junction AKA Zonula Occludence

-Adhesive Junction

-Gap Juntion AKA Nexuses

*Specialized attachments between adjacent cells

1. modifications of the plasma membrane, which is made up of a lipid bilayer

2. to provide anchoring of adjacent cells to one another

3. to provide cytoplasmic continuity between cells

1. prevent water soluble molecules from passing through extracellular matrix between cells

2.fuse adjacent plasma membranes

3.protein strands in adjacent membranes fuse them together

4. maintains the polarity of the cell by restricting membrane protiens to the apical or baso/lateral surfaces

5. disrupted by reduction of calcium concentration

-Zonula Adherens

-Desmosomes AKA Macula Adherence

-Hemidesmosomes

(only found on basal membrane surface)

-membrane proteins (Ca⁺⁺dependent cadherin) of adjacent cells bind to adhere cells to each other

-actin microfilaments in cell cortex anchor adheren proteins

- similar to zonula adherens

-disc shaped

-cytoplasmic intermediate filaments anchor the adherin family membrane protiens that bind the cells

-instead of cadherins attaching adjacent cells, integrins attach cel components of the extracellular matrix

***found ONLY on basal membrane surface***

1. communicating junctions

2. allows passage of ions and small molecules between adjacent cells

3. cells connected by connexons

~six subunits composed of protein connexin

4. important in cardiac and smooth muscle allowing multiple cells to act as a single unit

1. misnamed because of their long length

2. long branched microvilli

3. increase surface area for transport across membrane

*** microfilament: actin***

Cilia~5-10um long

Flagella is much longer

1. motile

2.AKA axoneme

3. 9 doublets of microtubules surrounding 2 microtubules (9+2)

4. motor protein is axoneme dynein

5. requires ATP as energy source

6. supporting protiens maintain microtubular arrangement

7.Basal Body

-cytoplasmic base of axoneme

-composed of 9 triplets of microtubules with no central microtubules (9+0)

~1um long

1. covered with glycocalyx (sugar residues linked to membrane lipids and proteins)

2. form brush (striated) border

3. found extensively on apical surfaces of absorptive cells

4. core of actin filaments arranged longitudinally

5. NOT motile

***microfilaments : Actin***

Surface specializations Functions

???

1. increase surface area

2. to move substances across surface

1. proteins- amino acids

2.nucleic acids- nucleotides

3.polysaccharide- simple sugars

4.lipids- diverse class associated with macromolecules

1. stepwise

2.components must be activated- requires energy

3.components attached to carrier molecules

4.directionality (one direction)

a. each addition releases H₂O

b. called condensation or dehydration synthesis

c.must have reactive H and reactive OH on molecule

1. Amino acids

2. Polypeptides

3.Hierarchical levels of organization

4.Function

*20 found in cellular proteins*

1. Carbon atom (chiral center) bonded to hydrogen atom plus:

a. amine (or amino) group

b.crboxyl group

c.variable side chain (R)

2. linked by type of covalent bond called peptide bond

a.formed between amine group of one amino acid and carboxyl group of next amino acid

b. special type of chemical bond:

(1) particularly strong (exhibits partial double bond characteristics)

(2) resists rotation around bond; provides for rigid peptide backbone

*really strong**

1. chains of amino acids joined by peptide bonds

2. order of amino acids is SPECIFIC for each polypeptide

3.process of protein synthesis is called translation

4.proteins may be composed of a single polypeptide (monomeric) or multiple polypeptides (multimeric)

Primary Structure

a) linear sequence of amino acids

b) useful for comparative analysis

c) can be used to predict higher level protien structures

a) localized folding of polypeptide into characteristic shapes.

b)determined by hydrogen bonding withinthe polypeptide specific arrangements of 2° structures may form motifs.

Secondary Structure Shapes

(1) alpha-helix

(2) β-pleated sheets

1) e.g. hairpin loop, helix-loop-helix, etc.

2)motifs may have characteristic function (e.g. catalytic, DNA binding, etc.)

a) overall structure of mature polypeptide

b)determined by complex intramolecular interactions

c)protein folding can be difficult to predict; requires significant computational power

(1) vary in structure, amino acid composition

(2) may have specific function (e.g. activation, catalytic, DNA binding), oftenconferred by presence of specific motifs

1. covalent (disulfide) bonds

2.ionic bonds

3. hydrogen bonds

4.van der Waals interations

5.hydrophobic interactions