An intracellular fibrous system exists comprised of filaments with an axial periodicity of 21 nm and a diameter of 8 to 10 nm that is intermediate between that of microfilaments (6 nm) and microtubules (23 nm). At least four classes of intermediate filaments are found, as indicated in Table 1. Each is made up of elongated, fibrous molecules with a central rod domain, an amino-terminal head, and a carboxyl-terminal tail. These sub units assemble in a helical a manner to form repeating tetrameric units to form rope-like fibrils. Intermediate filaments are important structural components of cells that serve as relatively stable components of the cytoskeleton. Intermediate filaments are not undergoing rapid assembly and disassembly and not disappearing during mitosis, as do actin and many microtubular filaments. An important exception to this are the lamins, which, subsequent to phosphorylation, disassemble at mitosis and reappear when it terminates. Lamins form a meshwork positioned in apposition to the inner nuclear membrane. In addition, lamin A is an important component of the structural scaffolding that maintains the integrity of the cell nucleus.

Table1. Classes of Intermediate Filaments of Eukaryotic Cells & Their Distributions

Hutchinson-Gilford progeria syndrome (progeria, OMIM 176670) is caused by mutations in the LMNA gene that encodes lamin A and, via alternative splicing (see Chapter 36), lamin C. In progeria, a farnesylated form (see Figure 26–2 for the structure of farnesyl) of prelamin A accumulates in this condition, because the site at which the farnesylated portion of lamin A is normally cleaved by proteases has been altered by mutation. It appears that the accumulation of farnesylated prelamin A destabilizes nuclei, altering their shape, somehow predisposing victims to manifest signs of premature aging. Experiments in mice have indicated that administration of a farnesyltransferase inhibitor may ameliorate the development of misshapen nuclei. Children affected by this condition often die in their teens of atherosclerosis.

Keratins form a large family consisting of about 30 members. As indicated in Table 1, two major types of keratins are found that assemble into heterodimers made up of one member of each class. Vimentins are widely distributed in mesodermal cells. Desmin, glial fibrillary acidic protein, and peripherin are related to them. All members of the vimentin like family can copolymerize with each other.

Intermediate filaments in nerve cells, called neurofilaments, are classified as low, medium, and high on the basis of their molecular masses. The distribution of intermediate filaments in normal and abnormal (eg, cancer) cells can be studied by the use of immunofluorescent techniques. Pathologists utilize anti bodies against specific intermediate filaments to determine the origin of certain dedifferentiated malignant tumors.

A number of skin diseases, mainly characterized by blistering, have been found to be due to mutations in genes encoding various keratins. Two of these disorders are epidermolysis bullosa simplex (OMIM 131800) and epidermolytic palmoplantar keratoderma (OMIM 144200). The blistering found in these disorders probably reflects a diminished capacity of various layers of the skin to resist mechanical stresses due to abnormalities in the keratin structure.

اخر الاخبار

اخبار العتبة العباسية المقدسة

العتبة العباسية المقدسة تكرم المشاركين في مشروع مقرأة العميد الرقمية

تقديم محاضرة عن عالم الأرقام في القرآن الكريم ضمن حفل إطلاق مشروع مقرأة العميد

ضمن فعاليات إطلاق مقرأة العميد الرقمية.. عرض فيديو توثيقي عن فكرة المشروع

جامعة تكنولوجيا المعلومات: مشروع مقرأة العميد منصة رقمية متكاملة لتعليم القرآن الكريم وتلاوته وحفظه

المزيد

الآخبار الصحية

عرض شائع على الأصابع.. قد يكشف سرطان الرئة مبكرا

7 مشروبات طبيعية لتقليل التوتر والقلق

دراسة: "خطر مبكر" يهدد صحة الأطفال

الجوز أو الفول السوداني.. أيهما يتفوّق في حماية القلب؟

المزيد

الآخبار التكنلوجية

مفاجأة علمية عن الإنجاب.. كم طفلا يطيل عمر المرأة؟

استطلاع يكشف "الأكثر قلقا" من تأثر الوظائف بالذكاء الاصطناعي

هل يمنحك تناول الجزر يوميا سمرة طبيعية؟

إنجاز طبي تاريخي.. جراحة قلب بلا شق في الصدر

المزيد

مواضيع ذات صلة

Plasma Contains A Complex Mixture of Proteins

Microtubules Contain α- & β-Tubulins

Muscle Tissue are The Target of Several Genetic Disorders

Skeletal Muscle Contains Slow (Red) & Fast (White) Twitch Fibers

Muscle Contraction Requires Large Quantities of ATP

Cardiac Muscle Resembles Skeletal Muscle in Many Respects

Contraction is Orchestrated by the Second Messenger Ca2+

Muscle Converts Chemical Energy to Mechanical Energy

Cholesterol Side Chain Cleavage Enzyme (p450scc)

Steroidogenic Acute Regulatory Protein (StAR)

Cytochrome P450 Steroid Hydroxylases

Major Protein Components of Muscle Fibers