Recommended Allowances For Protein
In establishing an RDA for protein, three steps were followed: The subcommittee first estimated the average requirement for reference proteins according to sex, age, and reproductive status of women. The standard deviation of requirement was determined and average requirement values were increased accordingly to compute the recommended allowance of reference protein. Amino acid scoring patterns were tabulated. These were based on requirements of various age groups for essential amino acids and for total protein. These patterns of requirement were reviewed in relation to U.S. food consumption patterns to determine if adjustment of the allowance for reference protein would be warranted in establishing the RDA for protein due to amino acid composition or protein digestibility of food proteins consumed.
Excessive Intakes And Toxicity
Because the system for disposal of excess nitrogen is efficient, protein intakes moderately above requirement are believed to be safe. Brenner et al. postulated that excess protein intake accelerates the processes that lead to renal glomerular sclerosis, a common phenomenon of aging. There is supportive evidence from studies in animals, but not in humans on this point. Urinary calcium excretion increases with increased protein intake if phosphorus intake is constant. If phosphorus intake increases with protein intake, as it does in U.S. diets, the effect of protein is minimized . It has been suggested, but not demonstrated, that a habitual high intake of protein might contribute to osteoporosis. This seems unlikely based on present evidence, at least for the range of intake by most people in the United States. Habitual intakes of protein in the United States are substantially above the requirement, and although there is no firm evidence that these intake levels are harmful, it has been deemed prudent to maintain an upper bound of no more than twice the RDA for protein .
Muscle In Insulin Resistance And Diabetes
Type 2 diabetes develops in stages. The onset of the process involves a decreased ability of insulin to stimulate muscle to clear glucose from the blood. So-called insulin resistance of muscle is a hallmark of the metabolic syndrome, which is considered to be a precursor of frank diabetes . Insulin secretion is amplified in the initial phase of insulin resistance to enable muscle to clear glucose from plasma adequately to maintain normal glucose concentrations. As the metabolic syndrome progresses to diabetes, increased insulin secretion is unable to effectively counterbalance the ineffectiveness of insulin to stimulate muscle glucose uptake, and glucose intolerance ensues. Only in the later stage of diabetes does the pancreas lose the ability to secrete extra insulin in response to hyperglycemia. Disruption of the normal rate of muscle glucose uptake by muscle is thus central to the onset and progression of diabetes .
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Properties Of Plant Cells
Chloroplasts
Figure 11. The chloroplast has an outer membrane, an inner membrane, and membrane structures called thylakoids that are stacked into grana. The space inside the thylakoid membranes is called the thylakoid space. The light harvesting reactions take place in the thylakoid membranes, and the synthesis of sugar takes place in the fluid inside the inner membrane, which is called the stroma. Chloroplasts also have their own genome, which is contained on a single circular chromosome.
Like the mitochondria, chloroplasts have their own DNA and ribosomes , but chloroplasts have an entirely different function. Chloroplasts are plant cell organelles that carry out photosynthesis. Photosynthesis is the series of reactions that use carbon dioxide, water, and light energy to make glucose and oxygen. This is a major difference between plants and animals plants are able to make their own food, like sugars, while animals must ingest their food.
Like mitochondria, chloroplasts have outer and inner membranes, but within the space enclosed by a chloroplasts inner membrane is a set of interconnected and stacked fluid-filled membrane sacs called thylakoids . Each stack of thylakoids is called a granum . The fluid enclosed by the inner membrane that surrounds the grana is called the stroma.
Protein Foods And The Planet
To give you an idea, this scorecard from the World Resources Institute illustrates the differing GHG emissions per gram of protein from both animal and plant-based protein foods. Making just one pound of lamb generates five times more GHGs than making a pound of chicken and around 30 times more than making a pound of lentils. In the U.S. alone, beef accounts for 36% of all food-related GHG emissions. Beyond emissions, its also important to note that food production places an enormous demand upon our natural resources, as agriculture is a major contributor to deforestation, species extinction, and freshwater depletion and contamination.
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Nitrogen Balance And Nitrogen Turnover
Nitrogen balance occurs when nitrogen intake equals nitrogen output , and is also referred to as nitrogen equilibrium.34 A positive NB or anabolic state exists when nitrogen intake exceeds nitrogen output. A net 24-hour positive NB of 2 to 4g is optimal for anabolism. When nitrogen excretion is greater than nitrogen intake, a negative NB or catabolic state exists.
NB can be calculated by subtracting the total nitrogen output from total nitrogen intake. The total nitrogen intake is determined by dividing the daily protein intake from both enteral and parenteral sources by 6.25. Nitrogen output consists primarily as urine urea nitrogen . An aliquot of a 24-hour urine collection is assayed for its urea nitrogen content by a standard enzymatic laboratory technique .76 This value, plus 4 , is subtracted from the grams of nitrogen intake during the same 24-hour period to calculate the NB, as demonstrated in the following equation:
After non-SCI major trauma and surgery, REE and nitrogen excretion levels are parallel. However, in SCI patients calorie needs decrease, whereas urinary nitrogen losses, primarily from muscle tissue,26 increase in proportion to the severity of the SCI.27 This negative NB ensues in the spinal cordinjured population, despite more than adequate caloric and protein administration.43,76 This same phenomenon has been observed with severe cases of botulism poisoning that have resulted in muscle paralysis.14
Central Role Of Muscle Protein In Whole
Maintenance of the protein content of certain tissues and organs, such as the skin, brain, heart, and liver, is essential for survival. In the postabsorptive state these essential tissues and organs rely on a steady supply of amino acids via the blood to serve as precursors for the synthesis of new proteins to balance the persistent rate of protein breakdown that occurs in all tissues. It has been recognized since the early 1960s that, in the absence of nutrient intake, muscle protein serves as the principal reservoir to replace blood amino acid taken up by other tissues . In the fasting state, blood amino acids serve not only as precursors for the synthesis of proteins but also as precursors for hepatic gluconeogenesis . Consequently, the protein mass of essential tissues and organs, as well as the necessary plasma glucose concentration, can be maintained relatively constant despite the absence of nutritional intake, provided muscle mass is adequate to supply the required amino acids.
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Muscle Wasting And Functional Impairment
As outlined above, body protein from functional tissues is catabolized during critical illness and may culminate in a clinically significant loss of muscle mass . The extent of muscle mass loss may impact the ultimate prognosis of an individual. Significantly reduced muscle mass often leads to impaired functioning, which hinders activities such as weaning from the ventilator and muscle function recovery. These adverse outcomes can result in increased nosocomial infection, such as pneumonia, bacteremia, and wound infection, leading to a renewed state of increased catabolism. This vicious cycle is associated with poor patient outcomes. Functional disability may be long term and may never fully return to normal levels ,. The increased efflux of AAs from catabolic muscle also places a metabolic burden on the liver. Therefore, in highly catabolic states of muscle protein breakdown, it is clinically important that the liver clearance of AAs for protein synthesis and other metabolic functions remains intact ,.
Comparisons Between Different Protein Sources On Human Performance
Earlier discussions on protein supplementation and athletic performance have shown positive effects from proteins of various sources. However, only limited research is available on comparisons between various protein sources and changes in human performance. Recently, there have been a number of comparisons between bovine colostrum and whey protein. The primary reason for this comparison is the use by these investigators of whey protein as the placebo group in many of the studies examining bovine colostrum . The reason being that whey protein is similar in taste and texture as bovine colostrum protein.
In a study examining the effects of casein and whey on body composition and strength measures, 12 weeks of supplementation on overweight police officers showed significantly greater strength and lean tissue accruement in the subjects ingesting casein compared to whey . Protein supplementation provided a relative protein consumption of 1.5 g·kg·day-1. Subjects supplemented twice per day approximately 810 hours apart.
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Questions On Molecular Representations
- Which representation described in the tutorial would you use to get the most accurate picture of the overall shape and approximate volume of the ferritin protein?
- Which representation described in the tutorial would you use to see what atoms are connected together in a particular region of the ferritin protein?
Research On Protein And Health
Available evidence indicates that its the source of protein , rather than the amount of protein, that likely makes a difference for our health. You can explore the research related to each disease in the tabs below, but heres the evidence-based takeaway: eating healthy protein sources like beans, nuts, fish, or poultry in place of red meat and processed meat can lower the risk of several diseases and premature death.
Research conducted at the Harvard Chan School of Public Health has found that eating even small amounts of red meatespecially processed red meaton a regular basis is linked to an increased risk of heart disease and stroke, and the risk of dying from cardiovascular disease or any other cause. Conversely, replacing red and processed red meat with healthy protein sources such as beans, soy foods, nuts, fish, or poultry seems to reduce these risks. One of the reasons why plant sources of protein are related to lower risk of cardiovascular disease compared to protein from red meat and dairy is because of the different types of fat in these protein packages. Plant-based protein sources are more unsaturated, which lowers LDL cholesterolan established risk factor for heart disease. Also, plant sources contain no cholesterol. Other factors are likely to contribute to the lower risk, but this is a key factor.
When it comes to cancer, once again, the seems to matter more than quantity.
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Questions On Protein Structure
- The two-dimensional structure of the amino acid phenylalanine is shown below. Indicate which part of this structure represents the amino acid’s side chain.
- A segment of a protein is analyzed and found to contain the amino-acid sequence Glu-Leu-Asp. The ChemDraw structures of these three amino acids are in Figures 13 and 15.
Draw a two-dimensional sketch of this section, showing the peptide bonds . Draw a two-dimensional sketch of this section, showing the backbone of the amino-acid sequence .
Kidney Failure And Muscle Loss
In addition to causing massive oxidative stress that can result in a cardiovascular event such as a heart attack, kidney failure induces the stress response, and by association, loss of muscle mass and strength. The onset of the stress response is brought about in part by inflammation, as well as hormonal responses, including elevations in cortisol and epinephrine. In addition, the accumulation of urea and ammonia acidifies the blood, which has a direct inhibitory effect on muscle protein synthesis and can cause metabolic acidosis. The result is a profound loss of muscle mass and strength that has many unfavorable consequences.
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Types Of Representations Used In This Tutorial
Graphical computer modeling has greatly improved our ability to represent three-dimensional structures. One of the goals of graphical computer modeling is to create the computer-generated image such that the image seems three-dimensional. By replicating the effect of light on three-dimensional objects, computers can give the impression of depth to simulate the three-dimensional aspect. The ability of interactive molecular viewing has enhanced our understanding of molecular structure even more, especially in the biochemical area. By interactively rotating the molecules, a clear picture of the three-dimensional structure emerges. In addition, this increases our chemical intuition by looking at two-dimensional images and visualizing the three-dimensional structure in our brains.
This tutorial uses different types of structural representations , such as 2D-ChemDraw, stick, CPK, and ribbon, to illustrate the structure of ferritin. PDB files are also available for viewing the molecules interactively. By using these various representations to study the structure of ferritin, you will become familiar with the different types of information given by each type of molecular representation, as well as the strengths and limitations of each representation.
Muscle Mass And Lean Body Mass
Measurement of LBM over time should provide important insights into an individual patient’s requirement for protein intake. However, attempts to measure LBM easily and accurately at the bedside in the ICU have to date been unsuccessful. It is important to determine which body-compartment measurement best reflects the daily amount of protein needed to maintain equilibrium. Total body mass is not useful because the varying amounts of fat mass are not relevant to protein metabolism. Also, standard body weight or ideal body weight measurements are not appropriate as they lead to imprecise estimates in obese patients . The most appropriate compartments for determining protein requirements are LBM and body cell mass . Both of these compartments can be measured in clinical practice using bioelectrical impedance analysis ,. However, the overall precision of bioelectrical impedance analysis may be reduced by variations in hydration status. Dual-energy X-ray absorptiometry can be used to assess LBM, although dual-energy X-ray absorptiometry scanners are not available in every hospital and are not routinely used for critically ill patients.
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What Are Proteins And What Do They Do
Proteins are large, complex molecules that play many critical roles in the body. They do most of the work in cells and are required for the structure, function, and regulation of the bodys tissues and organs.
Proteins are made up of hundreds or thousands of smaller units called amino acids, which are attached to one another in long chains. There are 20 different types of amino acids that can be combined to make a protein. The sequence of amino acids determines each proteins unique 3-dimensional structure and its specific function. Amino acids are coded by combinations of three DNA building blocks , determined by the sequence of genes.
Proteins can be described according to their large range of functions in the body, listed in alphabetical order:
Examples of protein functions
Comparisons Between Eukaryotes And Prokaryotes
Protein phosphorylation is a reversible post-translational modification of proteins. In eukaryotes, protein phosphorylation functions in cell signaling, gene expression, and differentiation. It is also involved in DNA replication during the cell cycle, and the mechanisms that cope with stress-induced replication blocks. Compared to eukaryotes, prokaryotes use Hanks-type kinases and phosphatases for signal transduction. Whether or not the phosphorylation of proteins in bacteria can also regulate processes like DNA repair or replication still remains unclear.
Compared to the protein phosphorylation of prokaryotes, studies of protein phosphorylation in eukaryotes from yeast to human cells have been rather extensive. It is known that eukaryotes rely on the phosphorylation of the hydroxyl group on the side chains of serine, threonine, and tyrosine for cell signaling. These are the main regulatory post-translational modifications in eukaryotic cells but the protein phosphorylation of prokaryotes are less intensely studied. While serine, threonine, and tyrosine are phosphorylated in eukaryotes, histidine and aspartate is phosphorylated in prokaryotes, plants and non-plant eukaryotes. In bacteria, histidine phosphorylation occurs in the phosphoenolpyruvate-dependent phosphotransferase systems , which are involved in the process of internalization as well as the phosphorylation of sugars.
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Protein Intake Of Ckd Patients
Nitrogen balance is the classic method of assessing dietary protein requirements. A neutral or positive Bn indicates that protein stores are maintained or increased, while a negative Bn indicates protein mass is declining. For healthy adults who undergo moderate physical activity and eat sufficient calories, the 1981 FAO/WHO/UNU recommended dietary protein requirements for normal adults is 0.6 g protein/kg body weight/day, consisting of high biological value proteins and non-essential amino acids ). Two standard deviations from this level was assigned as a safe level of intake and should meet the protein requirements of 97.5% or more of healthy adults.47,56
There are three caveats regarding the 1981 FAO/WHO/UNU recommendations. First, the number of patients studied was small. Second, some normal adults require less dietary protein and others require> 0.75 g/kg/day. Third, increasing the dietary protein of patients with CKD beyond the safe level simply increases the production of urea and other waste products.
To assess changes in protein stores, we recommend a standardized assessment of body weight and dietary protein intake to determine if the patient is receiving sufficient protein. S can also be measured with the caveat that a low value should stimulate a search for a focus of inflammation.
Protein And Athletic Performance
The primary role of dietary proteins is for use in the various anabolic processes of the body. As a result, many athletes and coaches are under the belief that high intensity training creates a greater protein requirement. This stems from the notion that if more protein or amino acids were available to the exercising muscle it would enhance protein synthesis. Research has tended to support this hypothesis. Within four weeks of protein supplementation in subjects resistance training, significantly greater gains were seen in protein synthesis and body mass in the group of subjects with the greater protein intake . Similarly, Lemon et al. also reported a greater protein synthesis in novice resistance trained individuals with protein intakes of 2.62 versus 0.99 g·kg-1·day-1. In studies examining strength-trained individuals, higher protein intakes have generally been shown to have a positive effect on muscle protein synthesis and size gains . Tarnapolsky and colleagues have shown that for strength trained individuals to maintain a positive nitrogen balance they need to consume a protein intake equivalent to 1.8 g·kg-1·day-1. This is consistent with other studies showing that protein intakes between 1.4 2.4 g·kg-1·day-1 will maintain a positive nitrogen balance in resistance trained athletes . As a result, recommendations for strength/power athletes protein intake are generally suggested to be between 1.4 – 1.8 g·kg-1·day-1.
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