BIOB10H3 Lecture Notes - Lecture 11: Intermediate Filament, Alpha Helix, Keratinocyte
June 14, 2018
Lecture 11
Intermediate filament
• approximately 10 nm in diameter
• “intermediate” size to MT and actin
• 50 different gene products
• Mainly structural support role
• include: keratin, neurofilaments and lamins
• monomers of each of these types have a long alpha- helical stretch
o they are “fibrous” proteins → therefore are very resistant to stretch
o used for giving cell/ cell structures “strength”
• monomers form homodimers – parallel to one another
o dimers (parallel) come together in an anti-parallel fashion to form
tetramers
o tetramers then polymerize into IF’s
o monomer → dimer → tetramer → IF
o tetramers don’t have polarity ~ distinguish between other cytoskeleton
types
o assembly and disassembly are regulated by phosphorylation by kinases
and phosphatases
o generally used for cell strength; not used for intracellular transport
Neurofilaments (in neurons): important for the integrity of axons
Lamins: make up the inner nuclear membrane cytoskeleton
Keratin: main protein of skin cells (keratinocytes); keratinocytes: an epidermal cell that
produces keratin.
• skin is made of many layers → constantly dividing & make huge amounts of
keratin
• as skin cells are pushed towards surface undergo “apoptosis” – programmed
cell suicide
o apoptosis: programmed/predictable routine cell death
• Once cell explodes – epidermis is covered with a dead, waterproof layer of
keratin protein – those dead cells are called “cornified cells” – and this is what is
on top of skin and protecting us
Extracellular Matrix (ECM)
• Everything that surrounds
the cells – made by cells
• Function
o for support of
cells/tissues
o site of cell attachment
o signals to cells:
▪ give cells
“identity”
▪ sends survival
signals,
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signals to migrate, etc.
o substrate for cells to migrate over
• matrix – network of interacting components
• dermis is the ECM -> figure
• ECM – a mesh of fibrous proteins secreted by cells
o Cells: fibroblasts, osteoblasts, chondroblasts. anything with ...blast is in
ECM protein
o Bone, blood, tendons, cartilage connective tissue (gives the gel trait binds
better to water) and basement membranes (ECM proteins not
membrane)
o Proteoglycan → protein + polysaccharide (GAGs)
▪ charged molecules that bind water i.e. Hyaluronic acid (HA)
▪ fibronectin & proteoglycan →
• different ECM’s have different amounts of ECM proteins depending on function
• amount of water varies (blood vs. bone)
• amount of bound mineral varies
o i.e. bone has Type I Collaged that binds calcium phosphate
• “Calcified matrix”
o Calcium stored in bone, also gives bone its
dense, supporting role as the skeleton
Slide 20: 1-4 are ECM proteins all have RGD sequence
Collagen
• most common ECM protein has 19 genes
o = 19 unique proteins in ECM
• most abundant protein in animal kingdom
• a secreted, fibrous glycoprotein
• secreted by fibroblasts, osteoblasts, smooth muscle
and epithelial cells
• trimers which wind around each other in a triple
helix (homotrimers or heterotrimers)
o provide high tensile (capable of being
stretched) strength
Extracellular Matrix (ECM)
• continuously being remodeled
• degradation and reconstruction
• accomplished by secretion of proteins:
o matrix metalloproteinases (MMP’s)
▪ enzymes that hydrolyze matrix
proteins
▪ chew up proteins in ECM
o or secretion of lysosomes
▪ chewing up for specialized cells
▪ i.e. by osteoclasts which degrade the
bone matrix
ECM “Beauty” & Therapeutic Treatments
• beauty industry
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