Describe The Structure And Function Of The Plasma Membrane – Blood plasma is a pale, straw-colored liquid composed of water, proteins, hormones, and nutrients. In other words, blood plasma is blood without blood cells, of which 92% of plasma is water, 7% is plasma protein, and >1% is regulatory protein and other solutes.

Plasma proteins are the carriers of many blood functions. This article aims to help you understand its structure and functions in physiological and pathological conditions.

Describe The Structure And Function Of The Plasma Membrane

Blood plasma is a liquid in which formed elements are suspended. It floats at the top of the tube, separated from the densest elements, the erythrocytes, which are separated by the leukocytes and platelets. Hematocrit is the percentage of the total sample that consists of erythrocytes.

Biomolecules: Types And Functions

Although a small percentage (7%) belongs to plasma proteins, they perform many blood functions: blood clotting process, regulation of acid-base balance, defense against pathogens, transport of nutrients and hormones, excretion of waste substances, regulation of osmotic pressure, regulation of osmotic pressure, regulation of blood clots . control of erythrocyte sedimentation rate, etc.

Plasma proteins can be separated using one method known as electrophoresis, where they migrate as individual fractions based on their size and electrical charge. Three fractions of plasma proteins are visible at the electrophoresis interface: albumins, globulins and fibrinogen. We then review these individual plasma protein components, including their structure and biological function.

Albumin is the most abundant plasma protein and normally accounts for about 54% of the total plasma protein content. It is produced by the liver and its role is a transport agent for fatty acids and hydrophobic steroid hormones. In addition, albumin is the most important contributor to blood osmotic pressure: water retention in blood vessels helps to maintain blood volume and blood pressure.

Then we have the globulin fraction, a heterogeneous group containing alpha, beta and gamma globulins. Alpha and beta globulins carry iron, lipids, and fat-soluble vitamins such as K, A, D, and E. Gamma globulins are central to humoral immunity and are known as antibodies or immunoglobulins. Unlike alpha and beta globulins, which are made in the liver, immunoglobulins are produced by transformed B cells known as plasma cells.

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Fibrinogen is the least abundant protein in plasma, occupying 7% of the total protein volume in plasma. Fibrinogen, a product of the liver, is the first factor in the process of the coagulation cascade.

Plasma proteins involved in hormone transport include corticosteroid-binding globulin, thyroxine-binding globulin, insulin-like growth factor-binding protein 3, sex hormone-binding globulin, and alpha fetoprotein, to name a few.

Albumin is a single long polypeptide chain consisting of 610 amino acids. Albumin has two ends, the N-terminal end and the C-terminal end. The N-terminal amino acid residue is aspartic acid and the C-terminal residue is leucine. Serum albumin consists of a large amount of essential amino acids such as arginine, histidine, and lysine, as well as the acidic amino acids aspartic acid and glutamic acid, and a small amount of tryptophan.

Albumin is classified into two types depending on whether a free sulfhydryl group (S-H) is present. About two-thirds of albumin in blood serum contains a free S-H group and rapidly polymerizes to form a dimer in the presence of Hg++. That is why it is called mercaptalbumin. The remaining third, which does not have a free S-H group, is non-mercaptalbumin, which has lost the ability to polymerize.

Structure Of The Plasma Membrane (article)

The osmotic pressure of blood is measured by the number of particles per unit volume. The smaller the particles, the higher the resulting osmotic activity. The molecular weight of albumin is relatively small, and its serum concentration is higher than other protein components. To be precise, 75% of blood colloid-osmotic pressure depends on albumin, so suffice it to say that blood osmotic pressure is mainly determined by albumin.

As you may recall, alpha and beta globulins are transport proteins produced by the liver, while gamma globulins are part of the immune system and are produced by immune cells.

Alpha proteins are globular or spherical proteins that are highly active in alkaline or other electrically charged solutions. They usually have a molecular weight of around 93 kDa.

The α1-fraction is immediately behind the albumin fraction in its electrophoretic migration. It contains various components of serum proteins, including α1-antitrypsin, α1-acid glycoprotein and α1-lipoprotein. The biological function of α1-antitrypsin is to inhibit the action of trypsin and chymotrypsin. On the other hand, the function of α1-acid glycoprotein is not yet known, but it probably inhibits hemagglutination of inactivated influenza virus and inactivates progesterone.

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Similarly, the α2 fraction contains the main components α2-macroglobulin, haptoglobin and ceruloplasmin. Haptoglobin binds selectively to hemoglobin, while ceruloplasmin promotes oxidation and incorporates copper. By binding to proteolytic enzymes such as trypsin and plasmin, α2-macroglobulin causes the loss of their main enzymatic activity.

Beta globulins are globular proteins in blood plasma that are relatively more mobile on the electrophoresis medium than gamma globulins, but less mobile than alpha globulins.

The most critical component involved in the β-fraction of globulins is transferrin. Among the β-globulins, transferrin is present in the largest amount, representing approximately 50% of this globulin fraction.

Transferrin binds to iron under physiological pH and forms an iron-transferrin complex. In fact, one-third of serum transferrin is bound to iron. Complement is part of the immune system and its role is to form membrane attacking complexes to kill pathogens, activate the inflammatory response, aid in phagocytosis and neutralize toxins. Other essential ingredients are hemopexin and properdin.

Cell Membrane Function And Structure

Gamma globulins or immunoglobulins are a functionally and structurally diverse group of proteins synthesized by plasma cells. First, they are biologically active, they have characteristic antibody activity.

Second, they have very similar chemical structures. The immunoglobulin unit molecule consists of four polypeptide chains held together by interchain disulfide and non-covalent bonds, including a pair of heavy polypeptide chains (H chains) and one pair of light polypeptide chains (L chains). Heavy chains, which have a molecular weight of about 60,000, are divided into five main classes γ, δ, α, μ and ε according to their antigenic specificity. The light chains, which have a molecular weight of about 23,000, are the same in all classes of immunoglobulins and are further divided into two types; κ (kappa) chain or K type and

(lambda) chain or L type. Chains have variable and constant parts. The variable parts contribute to the binding affinity of the antibody globulin for its specific antigen, and their amino acid sequences differ from each other. The C-terminal segment, called the constant portion, has an essentially constant sequence of amino acids for a given chain type. Based on five different heavy chains, there are five classes of Ig- IgM, IgA, IgG, IgE and IgD.

Blood coagulation is the transformation of soluble fibrinogen molecules into a solid clot with the help of a series of catalytic activities of various blood clotting factors. Among the blood coagulation factors in the plasma, fibrinogen is in the largest amount, which has the honor of being the 1st coagulation factor. It migrates electrophoretically as fraction φ between fractions β and γ. Fibrinogen consists of 2,900 amino acids composed of three pairs of different polypeptide chains: γ, β, and α.

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Many substances circulating in the bloodstream are bound to plasma proteins. These include antibiotics, vitamins, metal ions, lipids and metabolic products such as bile pigments. Plasma proteins carry hormones such as gonadal steroids, adrenocorticoids, and thyroid hormones.

Approximately 97% of serum female and male sex hormones are bound to plasma proteins, particularly albumin. Conjugated forms of glucuronides and sulfates are also bound to albumin.

Adrenocorticoids are mainly bound to transcortin and also to albumin, but less often. Approximately 90-95% of serum adrenocorticoids are bound to plasma proteins.

In addition, thyroid hormones bind to thyroxine-binding globulin, albumin, and prealbumin, and more than 99.9% of thyroxine exists in bound form.

Rough Endoplasmic Reticulum (rer)

Just as calcium loses its physiological activity when bound to plasma proteins, hormones are physiologically active in their free form but become inactive when bound to plasma proteins. This is one way of controlling the endocrine system.

Plasma proteins can be separated and measured using a number of techniques. The most commonly used methods are agar or gel electrophoresis and various types of immunoassays.

Electrophoresis is a widely used laboratory technique that separates biomolecules such as DNA, RNA, and proteins based on their size and electrical charge. This technique is based on the principle that molecules of different sizes and charges will migrate through a matrix such as a gel or capillary tube at different rates when exposed to an electric field.

In electrophoresis, the sample containing the molecules to be separated is applied to a gel or capillary tube that acts as a sieve. An electric current is then applied to the gel or tube, causing the molecules to move through the matrix. Smaller molecules will move more easily through the pores of the gel or tube and travel faster than larger molecules.

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To determine the size of molecules in a sample, standards of known size are separated on the same gel or tube and then compared to the sample. This allows researchers to estimate the size of unknown molecules at

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