Transcript 20. Biochemistry of Muscles and Connective Tissue

MUSCLES
•40-45 % of
body mass
•only system
converting
chemical
energy into
mechanical
2 types
-skeletal
(striated)
-smooth
Structural
unit muscle fiber
(myocyte)
Contains
many nuclei
located along
the cell
Muscle
structure
Muscle
structure
Chemical composition of
skeletal muscles
Proteins of muscles
3 types:
•proteins of
sarcoplasma
•proteins of
miofibrils
•proteins of
stroma
Proteins of Sarcoplasma
•Miogen fraction
(enzymes of glycolysis
etc.)
•Albumins
•Globulins
•Myoglobin
(chromoprotein,
provides the red color
to muscles, responsible
for oxygen storage)
Proteins of Stroma
•collagen
•keratin
•elastin
are constituents of
connective tissue of
vessel walls, nerves,
sarcolema.
Proteins of Miofibrils
•Myosin (56-60 %)
•Actin (20-25 %)
•Tropomyosin (10-15 %)
•Troponin complex (4-6 %)
Structure of filaments and myofibrils
Sarcoplasma of
striated muscle
fibers contains
myofibrils
oriented along
which are built
of 2 types
protein
filaments: thick
and thin
•Muscle contraction is carried out due to the
sliding of thick and thin filaments
•Chemical energy – ATP hydrolysis
•Contraction is regulated by Ca2+ concentration
Structure of Thick Filament
•Thick filaments consist of myosin molecules
•Myosin molecule built of 2 heavy (200000 Da)
and 4 light (16000-25000 Da) chains
•Heavy chains are coiled around each other and
form the “tail” of the molecule
•2 light chains form the globular head of the
molecule
•The head has ATP-ase properties
About 400 molecules of myosin are
combined in the thick filament
About half of molecules is directed
to one end of filament, another half
– to another end
Structure of Thin Filament
Three proteins: actin, tropomyosin, troponin
Two forms of actin: globular G-actin and fibril F-actin
Molecules of globular actin are joined to form F-actin
Two chains of F-actin are coiled in spiral
In the groove of spiral of F-actin tropomiosin is located
One molecule of tropomiosine contacts with 7 pairs of
G-actin
1 molecule of troponin drops on 1 molecule of tropomiosin
There are three subunits of troponin
Miofibrils contain about 2500
filaments
There are 6 thin filaments for 1 thick
filament
•Structural unit of miofibril sarcomer
•Both ends of thick miosin filaments are free
•One end of thin filaments is attached to Z-plate
BIOMECHANISM OF MUSCLE
CONTRACTION
•Potential spreads along
miofiber
•Signal is transferred to
cisterna of endoplasmic
reticulum
•Permeability of membranes
for Ca2+ ions is changed and
they get out into sarcoplasma
•During the rest
concentration of Ca2+ in
sarcoplasma is less than 10-7
mol/L
•After Ca2+ exit from
cisternas the concentration
reaches 10-5 mol/L
•Ca2+ binds to Ca-binding subunit of troponin
•Conformation of protein is changed
•Molecule of
tropomiosin
moves along
groove of thin
filament
• As result
centers for
connection with
heads of myosin
are opened on
the molecules of
G-actin
•Myosin heads combined with ATP bind to
the closest molecules of G-actin
•ATPase center is activated and ATP is
hydrolized
•Head bent
•Sliding of thin filament along myosin
•New ATP molecule binds to head of
myosin
•Bridge is torn
•In the condition of Ca presence the
head binds to the next actin molecule
•Frequency - 50 times/s
•Heads works not synchronously
•Nervous impulses stop to come
•Ca-ATPase transfers Ca2+ from
sarcoplasma into cisternas
•Complex Ca2+-troponin is dissotiated
•Tropomiosin moves
•Molecules of actin are blocked
•Bridges are torn
•Muscle relaxation
•ATP is required
both for contraction
and relaxation of
muscles
•In ATP deficiency
the bridges between
actin and myosin are
not torn
•Filaments are fixed
in connected state –
muscle contraction
(cadaver rigidity)
SOURSES OF ENERGY FOR MUSCLE
WORK
•ATP (5 umol for 1 g of
tissue) – enough for 2-3
s
•Kreatinphosphate – till
10 s
•Glycolysis
•Oxidative
phosphorylation
Êðåàòèíôîñôàò
RED AND WHITE MUSCLES
Res fibers
•Lot of myoglobin and mitochondria
•Oxidative phosphorylation is active
•Are contracted slowly, for a long time, no
tiredness for long time
White fibers
•Little hemoglobin and mitochondria
•More glycogen
•Glycolisis is specific
•Are contracted fast, fast tiredness
Present in all organs
(50 % of body weight)
•skin,
•adipose tissue,
•bones,
•teeth,
•fascia,
•cartilages,
•stroma of
parenchymal inner
organs,
•walls of vessels.
THE STRUCTURE OF CONNECTIVE TISSUE
Cells
Fibers
Extracellular
matrix
Cells
•Fibroblasts
•chondroblasts
Fibers
•collagen
•elastin
Extracellular matrix
•fibroblasts
carbohydrate-protein complexes proteoglycans.
Carbohydrate complexes of
proteoglycans –
heteropolysaccharides
glycosaminoglycans
(mucopolysaccharides).
chondroblasts
PROTEINS OF CONNECTIVE TISSUE
Collagen
• the most common
protein in organism
•25-33 % of all protein
(6 % of body weight)
•Length - 300 nm,
•Thickness – 1,5 íì,
molecular weight - 300
000
Consists of three
polypeptide chains
having the left spiral
shape
Three left coiled
chains are again
coiled together to
form the right spiral
bunch
1 chain contains about
1000 amino acids
33 % - glycine
21 % – proline and
oxiproline
11 %– alanine
35 % – all other amino
acids
Oxiproline and oxilysine
are specific only for
connective tissue
Collagen – complex
protein, glycoprotein
Carbohydrates
(monosaccharide
galactose and
disaccharide
galactosylglucose) bind
by glycosidic bonds to
the residues of oxilysine
of polipeptide chain
Ланцюги стабілізуються водневими зв’язками м³æ Ñγ NÍ-ãðóïами ïåïòèäíèõ çâ'ÿçê³â, ÎÍ-ãðóïами îêñèïðîë³íó.
Ìîëåêóëè êîëàãåíó ðîçòàøîâóþòüñÿ ðåãóëÿðíèì чèíîì ³
óòâîðþþòü ô³áðèëè, ç ÿêèõ ïîñë³äîâíî ôîðìóþòüñÿ ïóчêè
ô³áðèë, âîëîêíà ³ ïóчêè âîëîêîí.
There are 12 types of collagens (differ from
each other by the primary structure, types of
chains, contents of carbohydrates, localization
in organs and tissues).
4 main types:
Cross covalent links in the
molecule of collagen
Reaction of aldoll
condensation
Elastin
The main constituent of
elastic fibers in
ligaments, walls of large
arteries, lungs.
Molecule contains about
800 amino acid residues
Has globular shape.
Is joined into the fibrous
cords.
Contains a lot of glycine,
alanine, proline, valine
There are no oxilysine
and cysteine
Residues of lisine form
the cross covalent bonds
The net structure is
formed which can strech
two and more times.
PROTEOGLYCANS
Proteoglycans – the main extracellular matrix of
connective tissue. Consist of protein part +
polisaccharide chains
Molecular weight – tens millions.
Polisaccharides - glycosaminoglycans (acidic
mucopolisaccharides) are built from the large
amount of identical disaccharide units.
Disaccharide – aminosugar N-acetylglucosamin or
N-acetylgalactosamin + uronic acid (glucuronic or
iduronic) + sulfate (sometime).
Hyaluronic acid
•Is contained in synovial fluid (lubricant in joints),
vitreous substance of eye
•In rheumatic diseases and arthritis hyaluronic acid
is depolimerized and the viscosity of synovial fluid
is decreased
•Forms the viscous solutions
•Retains water
Heparin
•Is synthesized by tissue basofils
•During degranulation is ejected into the
extracellular matrix
•Participates in the regulation of blood
coagulation.
•Increases the release of enzyme lipoprotein
lipase into blood plasma