Muscles Biochemistry PDF

Biochemistry of muscles: 23. Proteins: Functions- Major components of structural tissue (muscle, skin, nails, hair) Primary structure - linear chain of amino acids. A peptide name is always ending with “yl” which is joint to the name of amino acid starting with the amino acids-end in sequence and th...

Biochemistry of muscles: 23. Proteins: Functions- Major components of structural tissue (muscle, skin, nails, hair) Primary structure - linear chain of amino acids. A peptide name is always ending with “yl” which is joint to the name of amino acid starting with the amino acids-end in sequence and the full amino acid name of the amino acids in the carboxyl- end. Non peptides are oxytocin and vasopressin. They have similar primary structures. Differ only in the amino acids at positions 3 and 8. Secondary structure- A 3D spatial conformation of the polypeptide backbone excluding the side chains. The two most common secondary structural elements are alpha helix and beta sheets. Proteins consist of long chains of amino acids, The structure of proteins are well defined shapes. These shapes are formed by hydrogen bonding. Hydrogen bonding forms intermolecular hydrogen bonds bw carbonyl group and the amino group. Alpha helix has a coiled shape held in place by hydrogen bonds bw the amine groups and the carbonyl groups of the amino acid along the chain. Beta sheets consists of polypeptide chains arranged side by side. Has hydrogen bonds bw chains, has R groups above and below the sheets. Is typical of fibrous proteins such as silk. Tertiary structure- 3D arrangement of its polypeptide chain in space. It is generally stabilized by outside polar hydrophilic hydrogen and ionic bond interactions, and internal hydrophobic interactions bw nonpolar amino acid side chains. Interacts and cross links bw different parts of the peptide chain. Quaternary structure- Combination of two or more tertiary units. It is stabilized by the same interactions found in tertiary structures. Hemoglobin consists of two alpha chains and two beta chains. The heme group in each subunit picks up oxygen for transport in the blood to the tissue. 24. Physico-chemical properties of proteins: Isoelectric point- Is the pH at which a molecule carries no net electrical charge or is electrically neutral in the statistical mean. Coagulation- Is the process of solidifying proteins, for example when you are bleeding, the blood will coagulate (solid). When proteins are heated at their isoelectric pH, a series of changes occur which is: - Dissociation of the protein subunits (disruption of quaternary structure) - Uncoiling of the polypeptide chains ( disruption of tertiary and secondary structure) - Matting together of the coiled polypeptide chains (coagulation) Denaturation- Is the process where it breaks down protein, for example when frying an egg, the proteins are breaking down to get that solid form. Denaturation of proteins involves the disruption and possible destruction of the secondary and tertiary structures. Proteins lose their biological activity. It involves: - Heat and organic compounds that break the hydrogen (H) bonds and disrupts hydrophobic interactions - Acids and bases that break hydrogen (H) bonds bw polar R groups and disrupt ionic bonds. - Heavy metal ions that react with S-S bonds to form solids - Agitation such as whipping that stretches peptide chains until bonds break 25. Simple proteins (albumins, globulins, protamine, histones, prolamins, glutelin, scleroproteins)- Only contain amino acids Complex proteins (nucleoproteins, chromoproteins, glycoproteins, phosphoproteins, lipoproteins)- Attached with a carbohydrates 26. Classification and function of proteins Catalytic proteins: Enzymes Structural proteins: Collagen, elastin Contractile proteins: Myosin, actin Transport proteins: Hemoglobin, myoglobin, albumin, transferrin  Regulatory proteins or hormones: Insulin, growth hormone Genetic proteins: Histones Protective proteins: Immunoglobulins, interferons, clotting, clotting factors 27. Complete proteins- Contain all the essential amino acids in the required proportion: casein of milk, egg white Incomplete proteins- They lack one essential amino acid.They cannot promote body growth in children, but may be able to sustain the body weight in adults. Proteins from pulses are deficient in methionine. 28. Precipitations and qualitative reactions of proteins (based on laboratory works). 29. Hydrolysis of proteins- The peptide bonds split to give smaller peptides and amino acids. Occurs in the digestion of proteins, occurs in cells when amino acids are needed to synthesize new protein and repair tissue. Hydrolysis of a dipeptide- In lab for a peptide to occur hydrolysis we needed acid or base, water and heat. In our bodies enzymes catalyse the hydrolysis of proteins. 30. Proteins of muscles- Muscle proteins are the most important for muscle contraction. Muscle proteins are divided into Sacroplasma proteins (water soluble)- Myoglobin, the amount depends on the activity of the respective muscle group. Its function is to accumulate oxygen in the muscles, the color of the muscle depends on it too. Calcezvestrine, an acidic protein that contains more than 40 Ca2+ ion- binding units in the molecule, its function is to stimulate the onset of muscle contraction. Fibrillar myofibril proteins (insoluble in water) Myofibrils proteins- Myofibrils are a complex of contractile (contractile) proteins. Myofibrils consist of 2 types of longitudinal filaments of protein origin filaments: The first type is thick filaments (ø 16 nm) consisting of 200-400 molecules of protein myosin The second type - thin filaments (ø 9 nm), consisting of a complex of proteins actin, tropomyosin and troponin Myosin, actin, and tropomyosin account for about 90 percent. of all proteins involved in the muscle contraction process Myosin- Its molecule is made up of a fibrillar part, a "tail" made up of two identical twisted α-helices that form a supercoil and end up with globular "heads" at the other end. Function of myosin:  1. Myosin molecules spontaneously bind to filaments under physiological conditions. About 400 tails of myosin molecules interlock to form a myosin filament. 2. Myosin has ATPase activity - It hydrolyzes ATP: ATP + H2O ADP + Pi + H + - The free energy of this reaction is used to contract the muscles 3. The myosin "heads" and part of the tail connect to the actin transverse bridges. Myosin can be thought of as a mechanoenzyme that catalyzes the conversion of energy from chemical bonds into mechanical energy. Actin (G-actin) The major component of skeletal muscle thin filaments is monomeric, globular protein, composed of a single polypeptide chain of 374 amino acids Actin filaments Actin filaments consist of actin, tropomyosin (Tm), and three troponin proteins. The actin core consists of two twisted F-actin (fibrillar actin) chains Actin Two chains of tropomyosin molecules are attached to the F-actin filaments by flexible joints. They are located in a depression formed by two action chains. Tropomyosin is periodically bound to a complex of three troponin proteins consisting of troponin C (Ca2 + binding), troponin I (inhibitory), and troponin T (tropomyosin binding) Myosin and actin complex When the heads of the myosin molecule bind to the actin threads, actomyosin is formed. This interaction creates the force applied to the thick (myosin) and thin (actin) the filaments move (slip) one in another respect. 31. Muscles protein functions. Body moving Respiration (diaphragm and intecostal contractions) Digestion Vascular tone and blood circulation Excretion In muscles, chemical energy is converted into kinetic (mechanical work) 32. Muscles nitrogenous compounds (non-protein) and their functions. Muscles contain low molecular weight organic compounds that contain nitrogen in their structure. These are: - Nucleotides (ATP, ADP, AMP). - Creatine (arginine and glycine) and phosphocreatine - In muscle, phosphocreatine can transfer the phosphate group attached by a macroergic bond to ADP and regenerate an ATP molecule that is important for muscle contraction. - Carnosine and anserine- Dipeptides reduce muscle fatigue and increase the amplitude of muscle contraction. - Carnitine- is a specific muscle compound (carrier) that transports fatty acid residues from the cytoplasm across the inner mitochondrial membrane. - Amino acids- Muscles primarily assimilate branched-chain amino acids: isoleucine, valine, and leucine. They make up about 50 percent. of all amino acids entering the muscle. These amino acids are the major donors and energy sources of the amino groups used to aminate pyruvate to alanine. More than 50 percent. The α-amino acid nitrogen produced in muscle consists of alanine and glutamine nitrogen. 33. Muscles non-nitrogenous compounds and their functions. Glycogen The main non-nitrogenous organic matter in the muscles, the reserve polysaccharide (a form of glucose storage). Glycogen accumulations are present in almost all tissues except blood cells and bone tissue. Most glycogen is stored in the liver up to 10%. The amount in the muscle varies from 0.3 to 2 percent. The amount of glycogen in the muscles depends on the work of the muscles and their mass. In resting muscles, it accumulates the most, but in active muscles, its stores almost disappear. Lactate, pyruvate and other carboxylic acids are formed during the process of glucose and amino acid metabolism. Lipids- In muscle, it performs two functions: phospholopids and sterols are structural elements of cell membranes, and triglycerides are a reserve source of energy. Inorganic salts- It contains mainly potassium and sodium cations. K+ is mainly present in muscle fibers and Na+ in the intercellular medium. Smaller amounts: Mg, Ca and Fe. Ca2+ ions are important for muscle contraction, they stimulate this process. 34. Mechanism of muscle contraction. Muscle contraction is the process by which muscle tissue shortens and tension occurs. The signal to contract is transmitted by an electrical impulse that propagates through the motor nerves and reaches the muscles through the junction of the nerve and muscle in the sarcolemma (a thin film covering the muscle fibers). 35. Stages of the biochemical cycle of muscle contraction. 1. The muscle rests before contraction. When the muscle is relaxed, the myosin head is between the thick and thin filaments. It itself hydrolyzes ATP to ADP and inorganic phosphate, but the hydrolysis products are not released (hydrolysis of ATP occurs faster than removal of catalytic products). In stage 1, the muscle is irritated, tropomyosin changes its position, calcium ions clump together with troponin. The myosin head, which contains ADP and Pi, can rotate at a sufficiently large angle and join the F-actin to form an angle of 90 ° with its axis (actin-myosin complex). A transverse bridge is formed. 2. Fusion occurs, the actin-myosin-ADP interaction releases Pi. Myosin changes the angle of the transverse bridge with the axis of the actin thread from 90 ° to 45 ° (the conformation requiring the least energy) by pulling the actin towards the center of the sarcomere (10– 15 nm). A shrinkage force is created, which attracts actin. The release of ADP from myosin completes the push of force. 3. The energy supply takes place. The new ATP molecule binds to the myosin-F-actin complex. The myosin-ATP complex is little related to actin, so the myosin "head" relaxes from the actin in the sarcomere center using the energy of the degradation of adenosine triphosphate (ATP). 4. The newly bound ATP is hydrolyzed by the free myosin "head", and a new interaction with the thin filament occurs without relaxing Pi and ADP. The cycle repeats. ATP separates the myosin head from the thin filament (F-actin) and is the driving force behind muscle contraction. Under this scheme, all the muscles contract. The main factor regulating muscle contraction is Ca2 + ions. The highest muscle contraction activity is when the concentration of Ca2 + ions is about 10-6-10-5 mol / l. If the ion concentration drops to 10-7 mol / l the muscle loses its contractile properties even in the presence of ATP.