Muscle Energetics and Creatine Metabolism

Phosphocreatine serves as a high-energy reserve in muscle cells, providing a quick source of energy for ATP regeneration during intense muscular activity.

Phosphocreatine can donate a phosphate group to ADP, converting it into ATP. This reaction is catalyzed by creatine kinase.

Elevated levels of CK-MB in the blood indicate tissue damage, particularly in muscle and brain tissues.

<p>Creatinine is a breakdown product of creatine phosphate in muscle cells. It is a waste product that is filtered from the blood by the kidneys and excreted in urine.</p> Signup and view all the answers

<p>Creatinine is synthesized from creatine phosphate. Creatine is initially produced in the liver through methylation of glycocyamine by S-Adenosyl methionine.</p> Signup and view all the answers

<p>Creatinine is primarily removed from the blood by the kidneys through glomerular filtration. Only a small amount of creatinine is reabsorbed by the tubules.</p> Signup and view all the answers

<p>When kidneys are not functioning properly, they cannot effectively filter creatinine from the blood. This leads to an accumulation of creatinine in the bloodstream.</p> Signup and view all the answers

<p>Phosphocreatine acts as a high-energy reserve, capable of rapidly donating a phosphate group to ADP, regenerating ATP. This process provides a temporary buffer for ATP concentration, effectively ensuring sufficient energy supply during periods of intense activity.</p> Signup and view all the answers

<p>Creatine phosphate synthesis begins with the amino acids arginine and glycine. The enzyme AGAT catalyzes the conversion of these amino acids into guanidinoacetate (GAA). GAA is then transported to the liver, where it receives a methyl group from methionine by the enzyme GAMT, forming non-phosphorylated creatine. This creatine is then released into the bloodstream and taken up by muscle cells, where it is converted to creatine phosphate by the enzyme creatine kinase.</p> Signup and view all the answers

<p>Creatine phosphate serves as a readily available reservoir of high-energy phosphate in muscle cells. It donates its phosphate group to ADP, forming ATP, the primary energy currency of the cell. This process is crucial for rapid energy production during intense exercise, enabling short bursts of high-intensity activity.</p> Signup and view all the answers

<p>During periods of high energy demand, creatine phosphate readily transfers its phosphate group to ADP, regenerating ATP. This process allows for rapid replenishment of ATP stores, enabling the cell to maintain its energy supply for sustained activity. The reaction can be reversed, allowing creatine phosphate to be re-synthesized when ATP levels are high.</p> Signup and view all the answers

<p>Creatine phosphate can be broken down into creatinine, which is a waste product that is excreted in the urine. This breakdown occurs through a process called creatine kinase, which can also catalyze the reverse reaction to synthesize creatine phosphate. Creatinine levels in the urine can be used to assess kidney function.</p> Signup and view all the answers

<p>Creatine phosphate plays a similar role in both muscle cells and brain cells. In both cases, it serves as a high-energy phosphate reserve, donating its phosphate group to ADP to generate ATP during periods of high energy demand. However, the brain's dependence on creatine phosphate may be more significant due to its limited capacity for energy storage.</p> Signup and view all the answers

<p>Creatine phosphate is a key component of the body's bioenergetic systems by enabling the rapid regeneration of ATP, the primary energy currency, during intense physical activity. It acts as an immediate energy source, allowing for sustained exercise and maximal energy output during short bursts, such as sprinting or weightlifting. It plays a crucial role in both muscle cells and brain cells, providing a readily available energy reserve.</p> Signup and view all the answers

<p>While humans only produce about 250 grams of ATP daily, they recycle their entire body weight in ATP daily through creatine phosphate. This efficient recycling system highlights the significant role of creatine phosphate in cellular energy management, enabling ongoing ATP supply for various physiological processes.</p> Signup and view all the answers

<p>Creatine phosphate is administered intravenously in hospitals for cardiovascular problems under the name Neoton. It is believed that the extra phosphate in creatine phosphate can help improve heart muscle contractility and energy production in patients with heart conditions. However, the exact mechanisms and effectiveness of this treatment are still being researched.</p> Signup and view all the answers

<p>Creatinine is a waste product produced by muscle metabolism. It is filtered by the kidneys and excreted in the urine. Higher creatinine levels in the blood indicate a lower GFR, suggesting impaired kidney function. Lower creatinine levels generally indicate a higher GFR and healthy kidney function.</p> Signup and view all the answers

<p>Daily creatinine excretion is influenced by factors such as muscle mass, dietary intake of creatine, and protein consumption. Individuals with higher muscle mass typically produce and excrete more creatinine. Increased dietary intake of creatine or consumption of protein-rich foods can also elevate creatinine excretion.</p> Signup and view all the answers

<p>Serum creatinine is widely used as a proxy for renal function because its levels in the blood reflect the kidneys' ability to filter waste products. While not a direct measurement, elevated creatinine levels often indicate reduced kidney function, as the kidneys are unable to effectively eliminate creatinine from the blood.</p> Signup and view all the answers

<p>Elevated creatinine levels can result from increased production of creatinine due to factors like higher muscle mass or increased protein intake. Other reasons include interference with laboratory assays used to measure creatinine or decreased tubular secretion of creatinine by the kidneys.</p> Signup and view all the answers

<p>Glycogen is a branched polymer of glucose units. Glucose molecules are linked linearly by α(1→4) glycosidic bonds, while branches are formed by α(1→6) glycosidic bonds. This branching creates a compact, highly branched structure.</p> Signup and view all the answers

<p>Glycogen serves as a major storage form of glucose in the body, providing a readily available energy source for cells and tissues. Its function is particularly important during periods of intense physical activity or fasting, when the supply of glucose from food is limited.</p> Signup and view all the answers

<p>Glycogen synthesis, also known as glycogenesis, involves the addition of glucose units to a pre-existing glycogen chain. Glucose molecules are activated by phosphorylation to form glucose 6-phosphate, which is then converted to glucose 1-phosphate. Glycogen synthase catalyzes the formation of α(1→4) glycosidic bonds, while branching enzymes introduce α(1→6) bonds to create branches in the glycogen molecule.</p> Signup and view all the answers

<p>Glycogen breakdown, known as glycogenolysis, involves the sequential removal of glucose units from glycogen. The enzyme glycogen phosphorylase breaks α(1→4) glycosidic bonds, releasing glucose 1-phosphate. Debranching enzymes remove glucose units attached by α(1→6) bonds from the branch points. The released glucose 1-phosphate is then converted to glucose 6-phosphate, which can be used for energy production or released into the bloodstream for other tissues.</p> Signup and view all the answers

<p>Insulin stimulates the action of enzymes like glycogen synthase to promote the addition of glucose molecules to glycogen chains.</p> Signup and view all the answers

<p>Glucagon stimulates glycogen breakdown (glycogenolysis) and glucose production (gluconeogenesis) when blood glucose levels are low.</p> Signup and view all the answers

<p>Glycogen is non-osmotic because it does not disrupt osmotic pressure when stored, unlike glucose in high concentrations.</p> Signup and view all the answers

<p>Muscle cell glycogen is used solely for internal energy needs and cannot be released into the blood due to the lack of glucose-6-phosphatase.</p> Signup and view all the answers

<p>Insulin secretion is reduced, which halts glycogen synthesis in the liver.</p> Signup and view all the answers

<p>When blood glucose levels decrease, glucagon is secreted to stimulate glycogen breakdown, providing glucose for energy.</p> Signup and view all the answers

<p>Glycogen phosphorylase is the primary enzyme for glycogen breakdown.</p> Signup and view all the answers

<p>Glycogen is stored in a hydrated form with 3-4 parts of water per part of glycogen, which is significant for maintaining cell osmotic balance.</p> Signup and view all the answers

<ol> <li>The release of glucose 1-phosphate from glycogen, 2) remodeling of glycogen for further degradation, 3) conversion of glucose 1-phosphate into glucose 6-phosphate.</li> </ol> Signup and view all the answers

<p>It can be used in glycolysis, processed through the pentose phosphate pathway, or converted into free glucose for release into the bloodstream.</p> Signup and view all the answers

<p>UDP-glucose is an activated form of glucose that is added to the nonreducing end of glycogen molecules during glycogen synthesis.</p> Signup and view all the answers

<p>Glycogen metabolism is regulated by allosteric responses to metabolites and hormonally stimulated phosphorylation of enzymes.</p> Signup and view all the answers

<p>NADPH is a cofactor that donates electrons and hydrogens for reactions catalyzed by specific enzymes.</p> Signup and view all the answers

<p>The conversion mainly occurs in the liver, and to a lesser extent, in the intestines and kidneys.</p> Signup and view all the answers

<p>The process involves the sequential breakdown of glycogen to release glucose 1-phosphate, which is then converted into glucose 6-phosphate.</p> Signup and view all the answers

<p>Remodeling is necessary to allow continued enzymatic activity and accessibility of the glycogen substrate.</p> Signup and view all the answers