Protein is one
of makrobiomoleku l which has a very specific structure. The type, number and
sequence of amino acids that menyususn protein molecules vary greatly. Thus,
the structure of proteins differ from each other according to the type, amount
and amino acids that constitute uratan. Diversity of proteins that causes
proteins act out a very diverse role within the cell.
More protein diversity reproduced by any other non-protein biomolecules such as
lipids, carbohydrates and nucleic acids that are chemically bound to the
protein to form a molecule. The function of this protein complex to be
discussed further when discussing each protein complexes.
Highly diverse functions of proteins within cells causing difficulty in
grouping them more appropriate for each type of protein. Several proteins have
functions that are grouped into khsusu so difficult a particular function.
Similarly, many proteins can not be identified because of the difficulty in
isolation and study of the role. However, in general the protein can be grouped
according to function as follows:
1. enzyme,
2. transport and storage of oxygen,
3. the body's defense (immune system),
4. activator of cells and tissues,
5. metablisme carrier results in a cell,
6. introduction of the compound in the cell membrane,
7. constituent of cell structure,
8. and regulating metabolism.
Proteins function as enzymes will be discussed in the section on the enzyme.
Similarly, the introduction of the function of proteins in the cell membrane
compounds will be discussed in the cell membrane.
Myoglobin and hemoglobin
Myoglobin is a protein that serves as a carrier of oxygen in a complex living
things. Oxygen is transported from one network to another where oxygen is used
in the cell jarngan to oxidation that produces the energy of motion. In the
living creatures that live in water, nerfungsi myoglobin to store oxygen.
Myoglobin consists of 153 amino acids and forms a-helices in eight places.
Structures such as these encourage the formation of globular proteins
dimensions 44 X 44 X 25 Å
Myoglobin has a heme group formed by four pyrrole groups are bound to each
other by forming a bridge metene atom porphyrin and iron (Fe II) is coordinated
by four N atoms of each group in the porphyrin pyrrole and one N atom from the
group of the protein histidine . Molecular oxygen (O2) will be bound to the
iron atom. Furthermore, the other oxygen atom will coordinate with other groups
of the protein histidine
At the time of Fe (II) associated with O2, myoglobin molecule is said to have
been in the oxidized form. thus the Fe (II) to Fe (III). When not attached to
the O2 this heme group, but other groups such as CO, NO or H2S a stronger
affinity, the myoglobin can no longer bind O2. In this case, the compound CO,
NO and H2S is said to be toxic to myoglobin.
Based on the ability of myoglobin oxygen binding molecule that has the function
of myoglobin to store and distribute oxygen to the cells in the muscle tissue.
When oxygen diffuses itself difficult in muscle tissue, it is able to diffuse
well myoglobin. thus oxygen can be delivered to the muscle tissue smoothly.
Hemoglobin is a protein molecule that has the task to bind oxygen and carry it
from one network to a network that requires oxygen. Hemoglobin contained in red
blood cells that can be transported keberbagian other complex systems like the
human body.
Hemoglobin molecule is made up of four polypeptide chains (tetramer; a2b2). The
molecular structure of hemoglobin A are equal to each other. Similarly, both
the hemoglobin molecule b. The molecular structure of hemoglobin a and b are
slightly different from each other. Overall, the hemoglobin molecule size is 64
X 55 X 50 Å.
Hemoglobin will bind to oxygen through the heme group as in myoglobin.
Molecular form (conformasi) hemoglobin will change with the entry of oxygen
molecules. The ability of hemoglobin binds oxygen in contrast to myoglobin. When
intekaksi oxygen by myoglobin follow the hyperbolic curve of hemoglobin
followed a sigmoidal curve. This causes the hemoglobin able to release oxygen
at low oxygen concentration around it a bit.
Actin and myosin
Actin and myosin are proteins that are a major part of human muscle tissue as
well as other animals. Both of these molecules are present in cells miofibrin
which are elongated cells. In microscopic molecular molecule position is seen
as a layer of thick and thin. Layer thick myosin protein which is composed of
six polypeptide chains: two heavy chains (220 kD) chains and two pairs of
essential and regulatory chains that vary in size between 15 and 20 kD
dependent home network. Both heavy chain polypeptide spirals duplicate with one
end (amine) were enlarged. The two other small molecules associated heavy
chains near the palm). Myosin head is emzim ATPase.
A thin layer is composed of three proteins, namely actin, tropomyosin and
troponin. Actin is a globular-shaped protein composed of 375 amino acids.
Tropomyosin is twofold helical chain that extends troposiosin molecules
associate with each other to form long chains. In these chains of actin
molecules interact to form a series throughout the tropomyosin molecule.
Furthermore, the troponin molecule that binds Ca ions bound to one strand
tropimiosin.
Each actin can bind to the head of myosin molecules through ionic and
hydrophobic from the interaction. Bonding or interactions that regulate these
muscle contractions. The interaction between actin and myosin will be in a
bound state of a switch or not switch. The mechanism is as follows:
1. ATP molecule that will bind to the head domain myosin heads will detach from
the bond with actin.
2. The presence of ATP in the myosin will cause the myosin can not interact
with actin. The next step is the hydrolysis of a phosphate group. This causes
the myosin head shifted slightly.
3. This hydrolysis leads to interaction with actin again. However, this
interaction is a little weak.
4. The next step is the release of phosphate groups terhidrolasi above. The
release of this phosphate group causes a conformational change in myosin
structure followed by the stronger interaction with actin.
5. Conformational changes cause a sudden movement of myosin and actin
molecules. When this occurs simultaneously in all the cells in the network
there will be a movement of muscles.
6. The next step is the release of the ADP molecule, followed by a shift in
myosin molecules of myosin in a position where it will interact strongly with
actin.
Immunoglobulin
System resilience in complex creatures like humans can be distinguished on the
cell resistance and resilience humoral (fluid). Resilience cells against viral
infections, fungi, bacteria or other pathogens carried by forming an antidote cells
such as T cells lymphocytes. Resilience humoral do with the formation of a
specific protein is an immunoglobulin or antibody. These antibodies are
synthesized in the cell or B-lymphocyte cell B.
Proteins such as immunoglobulin antibody formation is stimulated by the
presence of foreign molecules called antigens. This is often in the form of
foreign molecules such as proteins and carbohydrates mokromolekul. When B cells
meet antigen, immunoglobulins on the cell surface antigen will wrap then
destroy it.
General structure of the immunoglobulin molecule consists of two pairs of light
polypeptide chains (L) and two pairs of heavy polypeptide (H). The four
sub-units arranged like the letter Y shape as shown in Figure XX. The four
sub-units are connected to each other by disulfide bonds and interactions
nonkovalent. The two sub-units of light chain occupies the "hands" of
the immunoglobulin that serves as part of the interaction with the antigen. The
hand can be distinguished further over the variable and the constant. Variable
part amino acid composition varies for each type of antibody.
Each domain in the hands of antibodies formed from three and four anti-parallel
β-sheets are bound by disulfide bonds. The ability to recognize different types
of antigens located on the kind of amino acid which occupies three bends in the
polypeptide chain of the amine threshold domain. Amino acid sequence of the
polypeptide on the third bend is called hipervariabel. The interaction between
these amino acids with the antigen molecule that determines the antigen
recognition by antibodies. This interaction is the combination of the
interaction vander Walls, hydrophobic, hydrogen bonding and ionic bonding.
