ECM and Differentiated Cells
1. What are intermediate filaments?
Intermediate filaments are 10nm in diameter and are the “intermediate” size to MT and
There are 50 different gene products and mainly are for structural support
Intermediate filaments include: keratin, neurofilaments and lamins
Monomers of each of these type have a long a-helical stretch
Fibrous proteins therefore are very resistant to stretch
Intermediate filaments are used for giving the cell/cell structures “strength”
The monomers of IFs form homodimers and are parallel to one another; the dimers come
together in an anti-parallel fashion to form tetramers – these then polymerize into IFs
Figure 9.43 – The organization of intermediate
filaments within an epithelial cell. In this schematic
drawing, IFs are seen to radiate throughout the cell,
being anchored at both the outer surface of the nucleus
and the inner surface of the plasma membrane.
Connections to the nucleus are made via specialized sites
of adhesion such as desmosomes and hemidesmosomes.
Figure 9.42 – Experiemental demonstration
of the dynamic character of intermediate
filaments. These photographs show the results
of an experiment in which biotin-labeled type I
keratin was microinjected inot a cultured
epithelial cell and localized for 20 minutes later
(b) Distribution of intermediate filaments in the
cell as revealed by anti-keratin antibodies.
2. Do IFs have polarity, why or why not?
IFs tetramers do not have polarity and the assembly and disassembly is regulated by
phosphorylation by kinases and phosphatases (disassembles)
Generally for the cell strength is not used for intracellular transport, etc
3. What are common types of intermediate filaments?
Neurofilaments which are found in neurons are important for the integrity of axons
Lamins which make up the inner nuclear membrane cytoskeleton
Keratin which is the main protein of skill cells (keratinocytes)
Skin is made of many layers which are constantly dividing and making huge
amounts of keratin
As skin cells are pushed towards the surface they undergo apoptosis which is
programmed cell suicide in which cells constantly divide and are pushed
towards the surface
The cells explodes and the epidermis covered with a dead waterproof later of
keratin protein called “cornified cells”
Figure 7.1 – An overview of how cells are organized into tissues and
how they interact with one another and with their extracellular
environment. The cells of the epidermis are seen to adhere to one another
underlying, noncellular layer. The dermis consists largely of extracellular an
elements that interact with each other and with the surfaces of scattered
cells. The cells contain receptors that interact with extracellular materials
and transmit signals to the cell interior.
Told to constantly make keratin and cells continue to divide
Cells in upper layers lose body signals to live so they die 4. What is the extracellular matrix?
The extracellular matrix (ECM) is everything that surrounds the cells and are made
It is extremely heterogeneous and has lots of different cells that make up it
Blood contains huge water component and some cells
Matrix – network of interacting components thus the ECM is a mesh of fibrous
proteins secreted by cells
5. What is the function of the extracellular matrix (ECM)?
The major functions of the ECM include:
a. Support of cells/tissues
b. Site of cell attachment
c. Signals to cells: to give cells “identity” which tells cells how to behave and it sends
survival signals, signals to migrate, etc.
d. Substrate for cells to migrate over
This ECM includes: bones, blood, tendons, cartilage, connective tissue and basement
6. What are the different ECM proteins?
There are 4 major classes of ECM proteins:
b. Collagen – 19 different collagens
d. Proteoglycan – protein + polysaccharide (GAGs glucose amino glycens); charged
molecules that bind with water
All of these different proteins have RGD sequence and these are there so that integrin can
bind to the sequence
The different ECMs have different amounts of ECM proteins depending on function
The amount of water varies (blood vs. bone)
The amount of bound mineral varies; example: bone has type I collagen that binds to
Calcified matrix which is calcium stored in bone, also gives bone its dense
supporting role as the skeleton
7. What exactly does the ECM protein collagen do?
The most common ECM protein is 19 different isoform genes and is the most abundant
protein in the animal kingdom
Collagen is secreted by fibrous glycoprotein and is secreted by fibroblasts, osteoblasts,
smooth muscle and epithel