Only $35.99/year

Terms in this set (42)

One of the fibrous structural proteins, and is a constituent of hair, nails, skin, feathers, hooves, horns, etc.


Scleroproteins or the fibrous proteins are one of the three major types of proteins; the other two are spheroproteins and membrane proteins. Scleroproteins are characterized by their long protein filaments. They act as structural proteins. They are usually water-insoluble. Some of the scleroproteins are keratin, collagen, elastin, and fibroin.

Keratins are fibrous structural proteins that constitute various biological structures such as hair, nails, skin, feathers, hooves, horns, etc. They are made up of coiled polypeptide chains and when they combine they form supercoils.

Keratins protect epithelial cells from damage. Skin cells that are constantly exposed to pressure and rubbing leads to the formation of calluses. The skin thickens and the epidermal cells undergo cornification. Cornification is a process in which a keratinized layer of epidermis forms and serves as an epidermal barrier. During cornification, keratin fills up the cell resulting in the loss of cytoplasmic organelles and the cessation of metabolism. Ultimately, the fully keratinized cells undergo a programmed cell death.

vimentin- intermediate filament protein (58 kD) found in mesodermally derived cells (including muscle).

lamins- proteins that form the nuclear lamina, a polymeric structure intercalated between chromatin and the inner nuclear envelope. Lamins a and c (70 and 60 kd respectively) have c terminal sequences homologous to the head and tail domains of keratins, their peptide maps are similar and significantly different from that of lamin B (67 kd), although there are some common epitopes.
a structure found in eukaryotic cells from which microtubules emerge. MTOCs have two main functions: the organization of eukaryotic flagella and cilia and the organization of the mitotic and meiotic spindle apparatus, which separate the chromosomes during cell division. The MTOC is a major site of microtubule nucleation and can be visualized in cells by immunohistochemical detection of γ-tubulin. The morphological characteristics of MTOCs vary between the different phyla and kingdoms.[1] In animals, the two most important types of MTOCs are the basal bodies associated with cilia and the centrosome associated with spindle formation.

structure used to start new microtubules

MTOCs (MicroTubule Organizing Centers, oddly enough) form a Center that Organizes the MicroTubules. MTOCs form a structure or a center that microtubules grow out from. The "minus" end of a microtubule is associated with the MTOC, the "plus" end grows up from the MTOC

Key ones:
Centrosome, at the center of interphase cells, organizes the interphase array of microtubules. Centrosomes replicate in preparation for mitosis.
Spindle poles: the duplicated centrmosomes in mitosis are often referred to as "spindle poles" because the form the two ends of the mitotic spindle.

Basal bodies are the MTOCs that organize the cytoskeletal components of cilia and flagella, microtubule-based extensions of the plasma membrane used for movement. The microtubules that extend out from the basal body form a structure known as the axoneme.
A thin, helical, single-stranded filament of the cytoskeleton found in the cytoplasm of eukaryotic cells, composed of actin subunits, and functions primarily in maintaining the structural integrity of a cell and cell movements.


Additionally, the microfilament:

provides mechanical support for the cell or maintain structural integrity of the cell by forming a Band just beneath the cell membrane
participates in certain cell junctions; link transmembrane proteins (e.g., cell surface receptors) to cytoplasmic proteins
anchors the centrosomes at opposite poles of the cell during mitosis; aids in the contraction of the cell during cytokinesis
generates cytoplasmic streaming (i.e. Intracellular movement, or the flowing of cytoplasm within cells)
enables cell locomotion(through lamellipodia, filopodia, or pseudopodia)
interacts with myosin ("thick") filaments in skeletal muscle fibers to provide the force of muscular contraction.

cell attachments, muscle

F-actin (Filamentous)
Actin filament

G-actin (Globular)
Helix of two strands

Globular actin subunit has polarity
Linked "head to tail" in filament

Actin filament is POLAR

Regulation and assembly
1) actin-ATP levels
[G-actin-ATP] drives assembly
2) actin-binding proteins
Affect properties of actin filaments
3) Motors: Myosin
ATP-driven head group

For actin, both the monomer and the polymer can be referred to as "actin." To be more accurate, we can use "actin microfilaments" or "microfilaments" to referred to the long filamentous cytoskeletal element. Or we can use "G-actin" to refer to the subunit globular actin monomer and "F-actin" to refer to the filamentous polymer of actin.

Smallest of the filaments in diameter, fairly strong and stable, head-to-tail arrangement of subunits generates a polar filament (one end is different than the other)

Movement of relatively large structures such as cells and organisms, using the motor protein myosin. Also involved in cell signaling pathways.

A. Forming the sarcomere, the contractile unit of the muscle
B. Forming microvilli, projections of the plasma membrane, that increase the absorptive area of the cell
C. Forming the cortex under the plasma membrane and extending the plasma membrane as lamellipodia, both important in cell migration across a substratum.
D. Forming tubes in tissue, such as during the early stages of development of the nervous system
A family of motor ATPases that interact with f actin filaments


Myosins belong to a family of motor proteins in muscles to enable muscle contraction. They may also be present in other cells such as amoebae and macrophages as a motor protein involved in different motility processes. Their fundamental properties include capability to bind with actin and ATPase enzyme activity. Most of them are comprised of the head, the neck, and the tail domains. The head of the myosin is that part that binds with actin. The neck domain serves as a binding site for the light chains of myosin. The tail domain interacts with the other molecules and/or other myosin subunits.

An increasing number of different myosins are being described. Myosin I is an ubiquitous motor protein. It is a low molecular weight (111-128 kD) form found in protozoa acanthamoeba and dictyostelium that does not self-assemble and is found in the cytoplasm as a globular monomeric molecule that can associate with membranes and transport membrane vesicles along microfilaments. Brush border myosin I is a single-headed myosin found in the microvilli of vertebrate intestinal epithelial cells, linking the membrane to the microfilament core. There is a single heavy chain of 119kD and multiple (3 or 4) calmodulin light chains. The heavy chain has a C terminal domain that binds to acidic phospholipids.

Myosin II is the type of myosin found in muscle cells and is responsible for producing muscle contraction. It is the classical sarcomeric myosin that self assembles into bipolar thick filaments. Myosin II is a multimeric protein (440 kD) with two heavy chains (200 kD) and two pairs of light chains (17-22 kD) in each hexamer. Between species and tissues there are considerable variations in the properties of Myosin II. Cytoplasmic myosin II is a family of sarcomeric myosin like proteins, also hexameric, responsible for force generation by interaction with microfilaments. There are two heavy chains (up to 240 kD) and two pairs of light chains (15-20 kD), the self-assembled filaments are shorter than those of the sarcomere. The MYO2 gene product is an unconventional myosin from yeast involved in polarized secretion. MYO2 may be similar to dilute myosin from mouse and p190 protein from vertebrate brain. Scallop myosin is directly calcium regulated (through regulatory and essential light chains) and is more similar to sarcomeric myosin than to the nonsarcomeric myosins. Smooth muscle myosin has two 200 kD heavy chains, two regulatory 20 kD light chains that can be phosphorylated, altering its binding to the heavy chains which induces a conformational change that renders the myosin active and two 17 kD light chains.

Other myosins are Myosin III, Myosin III, Myosin IV, Myosin V, Myosin VI, Myosin VII, Myosin VIII, Myosin IX, Myosin X, etc..