Download BCH 450 CAT 1 lectures

BCH 450
Specialized Tissues
Dr. Samina Hyder Haq
Dept of Biochemistry
King Saud University
Recommended Books


-

Mammalian Biochemistry of Specialized Tissues
by Smith & Hill
Principles of biochemistry. Lehninger. ,
Nelson & Cox.
Harper's Biochemistry. Robert K. Murray ,
Daryl K. Granner , Peter A. Mayes , Victor
W. Rodwell.
Syllabus
1.
Topics to be covered
Lectures
1.What isConnective tissues
2
2.Collagen detailed structure ,
composition ,biosynthesis,
function. at cellular level.
3.Epithelial tissues& muscles tissues
4.Nervous tissues
5.Kidney
6. Liver
5
5
6
3
3
What is Connective tissues


Connective tissue is a form of fibrous tissue. It is
one of the four types of tissue in traditional
classifications (the others being epithelial, muscle,
and nervous tissue). These tissues form a
framework, or matrix, for the body, and are
composed of two major structural protein
molecules, collagen and elastin
Collagen is the main protein of connective tissue in
animals and the most abundant protein in
mammals, making up about 25% of the total protein
content.
What is the function of connective
tissue
1.Supporting and protecting: The minerals and
fibers produced by connective tissue cells establish
a bony structural framework for the body, protect
delicate organ, and surrounding and interconnect
other tissue.
2.Transporting materials:
Fluid connective tissue provides an efficient means of
moving dissolved materials from one region of the
body to another.
3. Storing energy reserves.
Fats are stored in connective tissues called adipose
cells until needed. Adipose cells- stores fat in
connective tissue until needed.
4. Defending the body.
Specialized connective tissue cells respond to
invasions by microorganism through cell-to-cell
interactions and the production of antibodies.
Connective tissues- are the most diverse tissues of
the body, comprised of bone, blood, and fat are
some of the examples.
Components of Connective tissue
All connective tissues have three basic
components:
1.Specialized cells
2. Protein fibers
3. A ground substance- is a fluid that
varies in consistency.
Classification of Connective tissue
Connective tissue can be classified into three
categories:



proper,
embryonic,
specialized
Classification of connective tissue
proper
Mesenchyma
Embryonic
Mucoid
Specialized
Bone
Cartilage
Blood
Elastic
Reticular
Adipose Tissue
C.T (Proper)
Areolar (Loose Tissue)
Dense Tissue
Connective Tissue proper

Connective tissue proper includes the
following five types: loose connective, dense
connective, elastic, reticular, and
adipose.They are called "proper" because they
are the types usually meant when using the
phrase "connective tissue
Areolar or Loose
Tissue

Areolar tissue exhibits interlacing,loosely organized
fibers,abundant blood vessels, and significant empty space.
Its fiber run in random directions and are mostly collagenous,
but elastic and reticular fibers are also present. Areolar tissue
is highly variable in appearance. In many serous membranes,
it appears as a loose arrangement of collagenous and elastic
fibers, scattered cells of various types; abundant ground
substance; numerous blood vessels. In the skin and mucous
membranes, it is more compact and sometimes difficult to
distinguish from dense irregular connective tissue.
Dense Fibrous C.T

Dense connective tissue, also called dense fibrous tissue,
has collagen fibers as its main matrix element. It is mainly
composed of collagen type I. Crowded between the
collagen fibers are rows of fibroblasts, fiber-forming cells,
that manufacture the fibers. Dense connective tissue forms
strong, rope-like structures such as tendons and ligaments.
Tendons attach skeletal muscles to bones; ligaments
connect bones to bones at joints. Ligaments are more
stretchy and contain more elastic fibers than tendons.
Dense connective tissue also make up the lower layers of
the skin (dermis), where it is arranged in sheets
Elastic Fibre

Elastic fibers (or yellow fibers) are bundles of
proteins(elastin) found in extracellular matrix of
connective tissue and produced by fibroblasts and
smooth muscle cells in arteries. These fibers can
stretch up to 1.5 times their length, and snap back
to their original length when relaxed. Elastic fibers
include elastin, and oxytalan.

Reticular connective tissue is a type of connective
tissue proper. It has a network of reticular fibers,
made of type III collagen that form a soft skeleton
to support the lymphoid organs (lymph nodes, bone
marrow, and spleen.) Reticular fibers are
synthesized by special fibroblasts called reticular
cells. The fibers are thin branching structures,
Adipose Tissue

contains adipocytes, used for cushioning,
thermal insulation, lubrication (primarily in
the pericardium) and energy storage.
Embryonic Connective tissue
Mesenchyme, or mesenchymal connective tissue, is an
example of reticular connective tissue, a type of loose
connective tissue, which is derived from all three germ
layers and located within the embryo.
2. Mucous connective tissue (or mucous tissue) is a type of
connective tissue found during fetal development
1.
Specialized C.T(Blood. Bone & Cartilage)
Blood functions in transport. Its extracellular matrix is
blood plasma, which transports dissolved nutrients,
hormones, and carbon dioxide in the form of bicarbonate.
The main cellular component is red blood cells.
The following two can be classified as "supportive
connective tissue":
2. Bone (osseous tissue) makes up virtually the entire skeleton
in adult vertebrates.
3. Cartilage makes up virtually the entire skeleton in
chondrichthyes. In most other vertebrates, it is found
primarily in joints, where it provides cushioning. The
extracellular matrix of cartilage is composed primarily of
collagen
1.
Basic Elements of Connective tissue
1.
2.
Cells
Extra cellular Matrix consists of
GAGS

Ground Substance
PG
Adhesive glycoprotein
Collagen
Tissue Fluids

Fibres
Elastic
Reticular
Cells of C.T
Two classes of connective
Tissue Cells
 Indigenous

Immigrant
Functions



Produce extracellular matrix
Defend against infections
Storage of foodstuffs in form of easily accessible fats
Indigenous cells of connective tissue
Undifferentiated mesenchymal cells, proliferate and differentiate into fibroblasts , fat
cells, chondrocytes.
Fibroblasts: Spindle shaped cells with big
ER and Golgi. Synthesize most of ECM
molecules (especially collagen)
Proliferate and migrate in response to
tissue injury.
Mast cells:Immune cells
Mediate immediate
hypersensitivity reactions
Secrete histamine and
proteases
Cause plasma extravasation (oedema), itching
Indigenous cells of connective tissue
Adipocytes (white fat cells)
Mostly just under the skin
Store lipids in the form of single droplet
Effector cells for insulin
Take up glucose and synthesize triglycerides for
storage in the lipid droplet
Also endocrine organ – secrete leptin, a hormone
responsible for appetite regulation
Different from brown fat cells that oxidize lipids
to produce heat
Immigrant cells of connective tissue
Blood cells Granulocytes
1.
Monocytes and macrophages
2. Neutrophils
3. Lymphocytes
4. Basophils
5. Eosinophils
All derive from a stem cell in bone marrow

Origin of C.T Cells
Undifferentiated
mesenchymal cells
Collagen Fibres

Collagen is the most abundant protein in the
human body .It consist of about 25% of the
total protein in our body.

It is one of the long, fibrous structural proteins
whose functions are quite different from other
proteins; There is a great heterogeneity in the
structure and fibril structure of collagen which
varies from great tensile strength of Bone to the
delicate structure of cornea and retina of the eye.
Types of Collagen

The collagen super family of proteins
includes more than twenty eight collagen
types, as well as additional proteins that have
collagen-like domains.
1.
Fibril forming Collagen
Network Forming Collagen
Fibril associated collagen
2.
3.
Taken from Lippincot’s
biochemistry
Major Types of Collagen
Type
Composition
Distribution
I
[α1(I)]2α2
Skin, tendon,bone,cornea
II
[α1(II)]3
III
[α1(III)]3
Cartilage, vitreous body,
intervertebral disc
Fetal skin, cardiovascular system
IV
[α1(IV)3
Basement membrane
The Family of Genetically Distinct Collagen Types
Cont;(kielty &Grant)
Schematic representation
of the domain structures
and relative dimensions of
the different molecules of
the classified
collagen family (types I–
XIX; groups 1–3). Triplehelical domains
are represented by shaded
bars and non-helical
sequences as solid
lines. Lengths of triplehelical domains (nm) are
indicated by arrows
With complements from Kielty
&Grant (2002)
Structure of collagen (Amino acid sequence
Collagen is rich in proline and glycine, both of which are
important in the formation of the triple-stranded helix.
Proline facilitates the formation of the helical
conformation of each α chain because its ring structure
causes “kinks” in the peptide chain. Glycine, the smallest
amino acid, is found in every third position of the
polypeptide chain. It fits into the restricted spaces where
the three chains of the helix come together. The glycine
residues are part of a repeating sequence, -Gly–X–Y–,
where X is frequently proline and Y is often
hydroxyproline (but can be hydroxylysine,).
Most of the α chain can be regarded as a polytripeptide
whose sequence can be represented as (–Gly–Pro–Hyp–)
Proline & hydroxyproline
Collagen Biosynthesis
Transcription(mRNA)
Translation (protein )
Nucleus
RER (cytosol
Post translational modification
1.Hydroxylation of proline or lysine
2. Glycosylation (addition of glucose and galactose to
hydroxylysine)
Lateral assembly and secretion from golgi complex as procollagen
Cleavage of N and C terminus propeptide by Collagenase
In extra cellular matrix
Assembly of tropocollagen as collagen fiber in ECM
Collagen biosynthesis (courtesy of Lippencot biochemistry)
Biosynthesis of Collagen
Fibril assembly
More than 25 different alpha
 chains create >20 collagens
Type I usually associated - Dermatan Sulfate
– dermis, bone, tendon, fibrocartilage
Type II usually associated - Chondroitin
Sulfate – hyaline & elastic cartilage
Type III usually associated - Heparan Sulfate
– Reticular fibers - very fine - Type III collagens
endoneurium, liver, spleen, kidney
Type IV usually associated - Heparan Sulfate

Tropocollagen as the basic structural
unit of Collagen
Tropocollagen has a mass of about 285 kdal and consist
of three polypeptide chains. Tropocollagen - 280 nm long
- head & tail region
 • 30% glycine, 30% proline & hydroxyproline
 • re-aggregate - native collagen (64nm)
 Non Covalent hydrogen bonding between the three α
chain is via hydroxyproline.
 tropocollagen polarized in fiber, 1/4 staggered array
– period accounted for by gaps fall in dark bands
.

Staggered array of tropocollagen
Molecules



Collagen fibres exhibit crosss striations every
640A.
The length of the tropocollagen molecule s
2800A.
There is a gap of 400oA between the end of
one tropocollagen and the start of another.
This gap play an important role in
mineralization process.
Tropocollagen Assembly
Fibril arrangement of different types of Collagen
I,II,III.V,
XI
VII,X
IV
VI
VII
FACIT

Collagens I, II, III, V, and XI form fibrils as a consequence of the staggered alignment
of molecules. Type IV collagen forms a flexible open network through N- and Cterminal and helical interactions, and this is the basic structural framework of basement
membranes.

Thin microfibrils of type VI collagen represent the end-product of a complex
pathway of assembly, whereby monomers associate to form dimers, which, in
turn, come together to form tetramers able to associate end to end.
Type VII collagen anchoring fibrils are created as a result of monomers
overlapping at their C-termini to form centrosymmetric dimers capable of
aligning in limited parallel arrays. Triple-helical domains are shown as shaded
bars, and non collagenous domains as lines. The closely related types VIII and
X collagens form open hexagonal arrays.
The FACIT collagens (fibril-associated collagens with interrupted triple
helices) (types IX, XII, XIV) do not form defined assemblies on their own but
instead are thought to associate with the surface of fibrils. Type IX collagen
molecules are cross-linked to the outermost fibrillar collagen molecules of type
II collagen fibrils.


Cu+2 containing
E
Cross linking of collagen


Lysyl oxidase is an extracellular copper enzyme that
catalyzes formation of aldehydes from lysine
residues in collagen and elastin precursors.These
aldehydes are highly reactive, and undergo
spontaneous chemical reactions with other lysyl
oxidase-derived aldehyde residues, or with
unmodified lysine residues. This results in crosslinking collagen and elastin, which is essential for
stabilization of collagen fibrils and for the integrity
and elasticity of mature elastin.
Complex cross-links are formed in collagen called
Pyridinoline which is derived from three lysine
residues
Stability of the collagen helix™



The temperature at which half of the helical structure is lost is called
the melting temperature™.
The Tm of tropocollagen is a criterion of the stability of its helical
structure. Tm depends on the body temperature of the source species.
collagens from icefish has the lowest Tm while warm blooded
animals have the highest Tm. This difference in thermal stability is
correlated with the contents of imino acid (proline and hydroxy
proline) in the collagen. The higher the imino acid content , the more
stable the helix. Tm of (pro-pro-Gly) is 24C while poly (Pro-HypGly) is 580C indicating hydroxylation stabilizes triple helix.
The experiments using αα\-bipyridyl an iron chelator which inhibit
hydroxylation shows that without hydroxylation triple helix
formation does not occur.
What is scurvy

Scurvy is the connective tissue disorder in
which body failed to synthesise normal
collagen resulting in formation of weak and
brittle bones, weak blood vessels with a
frequent haemorrhages and bleeding.
Scurvy ( deficiency of vitamin C
Biochemical basis of Scurvy:
Vitamin C maintains prolyl hydroxylase and lysine hydrxylase in an
active form keeping the iron atom in its reduced ferrous state
Lysine hydroxylase
Lysine
hydroxylysine
Vit.C + Fe+2
Proline hydroxylase
Proline
Hydroxyproline
Vit.C + Fe+2
Other heritable disorder of connective
Tissue.

Marfan syndrome - a genetic disease causing
abnormal fibrillin.

Ehlers-Danlos syndrome - causes progressive
deterioration of collagens, with different EDS types
affecting different sites in the body, such as joints, heart
valves, organ walls, arterial walls
 Osteogenesis imperfecta (brittle bone disease) caused by insufficient production of good quality collagen
to produce healthy, strong bones.
 Stickler syndrome- affects collagen, and may result in
a distinctive facial appearance, eye abnormalities, hearing
loss, and joint problems
Ehlers-Danlos syndrome

This disorder is a heterogeneous group of generalized
connective tissue disorders that result from inheritable
defects in the metabolism of fibrillar collagen molecules.
EDS can result from a deficiency of collagen-processing
enzymes (for example, lysyl hydroxylase deficiency or
procollagen peptidase deficiency), or from mutations in
the amino acid sequences of collagen types I, III, or V.
The most clinically important mutations are found in the
gene for type III collagen. Collagen containing mutant
chains is not secreted, and is either degraded or
accumulated to high levels in intracellular compartments.
Because collagen type III
is an important component of the arteries, potentially
lethal vascular problems occur.
Extra cellular Matrix

GAGS( Glycosoaminoglycan), are un branched
polysaccharides with repeating disaccharide
units. They resist compression and fill space.
Three Common GAGS
What are GAGS
Glycosaminoglycans (GAGs)
 Negatively charged
 Extended conformation
 They are hydrophilic attract cations and water to
form hydrated gel.
 Difficult to compress
 Packing materials, ground substances
present in Cartilages, cornea

What are Proteoglycan?
Proteoglycan = core protein + GAG
subunit
 GAG sub unit. is unbranched repeat
disaccharides. Chondroitin Sulfate , Dermatan
Sulfate, Heparan Sulfate, Keratan Sulfate
• GAG sub unit. covalently linked to core-protein
like bristles on brush

Proteoglycans
Proteoglycan in C.T
Adhesive glycoprotein

1.
2.
Cell adhesive glycoprotein have binding domains
for cell surface integrins & for components of the
E.C.M. Most important are
Fibronectin
Laminin
Laminin

Laminin-(basal lamina)- cruciate shaped with 3
peptide chains - binding sites for integrin,
heparan sulfate, type IV collagen & entactin