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Nisan 2010 TUS Sınavındaki Fibronektin
Sorusuna Bir Bakış
Değerli arkadaşlar, Nisan 2010 TUS sınavını
geride bıraktık. Öncellikle ilk dileğim şu,
inşallah herkes hak ettiği ve kendisi hakkında
en hayırlı sonucu alır. Bu sınav sonuçta bir
sıralama sınavı olduğuna göre, bazı arkadaşlar
istediği yeri kazanıp ihtisasa başlayacak, bazı
arkadaşlar şansını bir kez daha denemek zorunda
kalacak.
Ama
bir gerçek var ki TUS’un arkasını kovalayan, bu
işi azimle ve doğru bir şekilde sürdüren kişi,
Allahın izni ile istediği yere gelecektir.
Bu
sınavda biyokimya açısından birçok arkadaşın
takıldığı ve cevabı yanlış açıklanmış bir soru
vardı. A kitapçığı 31. soru olan fibronektin
sorusu.
31. Fibronektin ile ilgili aşağıdaki
ifadelerden hangisi
yanlıştır?
A) Bir
glikozaminoglikandır.
B)
Ekstraselüler matrikste bulunur.
C)
Fibroblastlar tarafından salgılanır.
D)
Kollajene bağlanır.
E)
Plazma proteinlerindendir.
Arkadaşlar, aşağıda çeşitli textbook ve
yayınlardan derlediğim bazı bilgiler var. Hiçbir
kaynakta fibronektinin glikozaminoglikan
yani mukopolisakkarit olduğu yazmaz.
Bütün kaynaklarda fibronektin’in glikoprotein
olduğu açıkça ifade edilmektedir. Dolayısı
ile bu soruda A şıkkı kesinlikle yanlıştır.
Çünkü fibronektin bir glikozaminoglikan değil,
glikoproteindir.
Gelelim ÖSYM’nin açıkladığı E şıkkına. Altta
verdiğim örneklerde görüleceği üzere fibronektin
hem hücre yüzeylerinde, hem ekstrasellüler
matrikste hem de plazmada bulunmaktadır.
Plazmadaki fibronektin konsantrasyonu
yaklaşık 0,3 mg/ml yani 30 mg/dl ‘dir.
(Kaynak; Alan H B WU, Tietz clinical guide to
laboratory tests 4.baskı 2006 sayfa 404-405)
Sonuçta fibronektinin hem doku kaynaklı, hem de
suda çözünür formu olan plazma fibronektini
şeklinde iki türü vardır.
Harper 26.baskı Sayfa 537-38
The same cells that
secrete collagen also secrete
fibronectin,
a large glycoprotein
present on cell surfaces, in the extracellular
matrix, and in blood. Fibronectin binds
to aggregating precollagen fibers and alters the
kinetics of fiber formation in the pericellular
matrix.
Cecil Textbook
of Medicine, 21st ed.,
Copyright © 2000 W. B. Saunders Company
STRUCTURAL GLYCOPROTEINS.
The
major
non-collagenous
glycoprotein present in the extracellular matrix
is fibronectin.
Fibronectins are dimeric cell adhesion
glycoproteins composed of two disulfide-bonded
subunits and found in rather large quantities in
blood plasma (0.3 mg/mL).
Marks’ Basic
Medical Biochemistry: A Clinical Approach, 2nd
Edition
Adhesion
proteins, such as
fibronectin and
laminin,
are
extracellular glycoproteins
that contain separate distinct binding domains
for proteoglycans, collagen, and fibrin.
Biochemistry of
Atherosclerosis Edited by Sukhinder Kaur Cheema,
PhD
Memorial
University of Newfoundland, St. John’s NL,
Canada ©
2006 Springer
Human plasma contains soluble fibronectin, a
440-kDa glycoprotein
consisting of two similar but nonidentical
subunits. Fibronectin plays key roles in cell
migration, cell adhesion, hemostasis, thrombosis,
wound healing, and tissue remodeling. The
fibronectin molecule has distinct domains for
interactions with collagen, fibrin, heparin, and
DNA. It was recently shown that L-35S-homocysteine
targets both fibronectin in human plasma and
purified human fibronectin. Sayfa 368
Molecular Biology of the Cell; Alberts
The extracellular
matrix contains a number of noncollagen
adhesive proteins that typically have
multiple domains, each with specific binding
sites for other matrix macromolecules and for
receptors on the surface of cells. These
proteins thus contribute to both organizing the
matrix and helping cells attach to it. The first
of them to be well characterized was
fibronectin, a large
glycoprotein found in all vertebrates.
Multiple Forms
of Fibronectin Are Produced by Alternative RNA
Splicing
There
are multiple forms (isoforms) of fibronectin,
including one called
plasma
fibronectin,
which
is soluble and circulates in the blood and other
body fluids, where it is thought to enhance
blood clotting, wound healing, and phagocytosis.
Plasma fibronectin,
for example, which is secreted mainly by liver
cells, lacks two of the type III repeats that
are found in cell- and matrix-associated forms
of fibronectin.
Fibronectin
is a
larger protein that binds to many molecules,
such as collagen, fibrin, proteoglycans, and
cell-surface receptors. It consists of two
glycoprotein chains, held together by disulfide
bonds. Fibronectin mRNA has two splice forms,
giving rise to tissue
fibronectin and plasma fibronectin.
Plasma Fibronectin Synthesis in Normal and
Injured Humans as Determined by Stable Isotope
Incorporation
Claudia Thompson,
Frank A. Blumenstock, Thomas M. Saba, Paul J.
Feustel, John E. Kaplan, John B. Fortune,
Lindsay Hough, and Vera Gray Departments of
Biochemistry, Physiology, Surgery, and
Pharmacology, Albany Medical College, Albany,
New York 12208
Fibronectin is a
high molecular mass dimeric
glycoprotein (450 kD)
that circulates in
plasma at a concentration of 350-450 ,ug/ml
(1-3). Plasma
fibronectin
mediates macrophage or reticuloendothelial
phagocytic clearance of a variety of denatured
or foreign particulate materials and Clq
containing immune complexes, potentially in the
blood after tissue injury, disseminated
intravascular coagulation, or sepsis.
Cellular or
tissue fibronectin is a less soluble form of
fibronectin (4), localized in the extracellular
matrix of many cells and in connective tissue
matrices
(5). Cellular fibronectin influences cell-to-substratum
adherence as well as cell-to-cell interactions
and accordingly plays a role in tissue integrity
(2, 3). Plasma
fibronectin is antigenically related
to cellular fibronectin but differs especially
with respect to subunit structure and solubility
(4).
Plasma Fibronectin Levels In Preeclamptic
Pregnancies
H.
Doğan TÜRE, Sedat KARAOSMANOĞLU, Deniz KÖSE,
Coşkun BAYSAL Zeynep Kamil Hastanesi, Kadın
Hastalıkları ve Doğum Kliniği
Materials and Methods:
This
study was made prospectively on 40 preeclamptic
and 28 normotensive gravid women between 31-41
gestational weeks. An arterial pressure of
140-90 mmHg or an elevation of 30 mmHg systolic,
15 mmHg diastolic pressure and ≥ 1 g/lt
proteinuria on random urine or ≥ 2+ proteinuria
on semiquantitative measurement were used as the
diagnostic criteria of preeclampsia. Preclamptic
cases were divided into two groups as mild
preeclampsia (n: 20) and severe preeclampsia (n:
20). Normotenvive cases were used as a control
group. Plasma fibronectin levels were measured
on Behring plaques quantitatively by the
immunodiffusion method.
Findings:
Fibronectin concentrations were significantly
higher in preeclamptic versus normotensive cases
(p< 0.001) and in severe versus mild
preeclamptic cases (p< 0.001). When the
plasma fibronectin
level
of 400 mg/ml is acccepted as the cut-off values,
sensitivity and the positive predictive values
were found to be 72%-87% and 95%-65%
respectively for determining preeclampsia and
severe preeclamsia.
Results:
Vascular endothelial dysfunction is one of the
major subjects argued in the pathogenesis of
preeclampsia. These findings suggest that
plasma fibronectin
levels, the determinant of endothelial cell
damage, have a high predictive value in the
determination of preeclampsia as well as it’s
classification into the mild and severe form of
the disease.
Diagnostic value of plasma fibronectin level
in predicting the presence and severity of
coronary arter disease
Authors: Ozcelik,
Fatih1; Erdogan,
Okan2; Aktoz,
Meryem2; Ekuklu,
Galip3; Tatli,
Ersan2; Demir,
Muzaffer4
Source:
Annals of Hematology, Volume 88, Number 3,
March 2009 , pp. 249-253(5)
The
relation between fibronectin and coronary artery
disease (CAD) according to previous study
results is controversial. The aim of the present
study is to investigate the predictive value of
fibronectin in determining the presence and
severity of CAD. Patients with stable angina (n = 62)
who had angiographically documented CAD, and
control patients (n = 31) who had normal
coronary angiograms, were included in the study.
Plasma fibronectin
levels were determined in all patients. Plasma
fibronectin level (milligrams per liter) in
patients with CAD was higher than normal
controls (364.2 ± 171 vs 265.1 ± 135.5, p = 0.006).
The present study showed that plasma
fibronectin level in CAD is significantly higher
than normal control subjects.
Bazı
arkadaşlar, plazma proteinleri konusu
biyokimyada anlatılırken fibronektin orada
geçmediği için plazma proteini değildir mantığı
ile yaklaşıyor. Değerli arkadaşlar takdir
edersiniz ki plazma veya serumda ölçülebilen
binlerce protein var. Biz bu alt başlığı
anlatırken rutinde en çok kullanılan 40 – 50
tane plazma proteininden bahsediyoruz.
Sonuçta yaklaşık 400 sayfalık bir notla
elimizden geldiğince TUS’ta biyokimya da
sorulması en muhtemel bilgileri yakalamaya
çalışıyoruz. Yoksa biz her sınavda biyokimya ile
ilgili her soruyu yaptırabiliriz veya yakalarız
diye bir iddiamız yok. Ancak elimizden
geldiğince TUS’u kazandıracak % 75-80 soruyu
yakalamaya çalışıyoruz.
Takdir sizlerindir. Herkese başarılar dilerim,
selamlar…
Uz. Dr. Ercan
ÖZTÜRK
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