This post-translational modification often alters the proteins function, the protein can be inactivated or activated by the cleavage and can display new biological activities. Following translation, small chemical groups can be added onto amino acids within the mature protein structure.

Methylation is the reversible addition of a methyl group onto an amino acid catalyzed by methyltransferase enzymes. Methylation occurs on at least 9 of the 20 common amino acids, however, it mainly occurs on the amino acids lysine and arginine.

One example of a protein which is commonly methylated is a histone. Histones are proteins found in the nucleus of the cell. DNA is tightly wrapped round histones and held in place by other proteins and interactions between negative charges in the DNA and positive charges on the histone.

A highly specific pattern of amino acid methylation on the histone proteins is used to determine which regions of DNA are tightly wound and unable to be transcribed and which regions are loosely wound and able to be transcribed.

Histone-based regulation of DNA transcription is also modified by acetylation. Acetylation is the reversible covalent addition of an acetyl group onto a lysine amino acid by the enzyme acetyltransferase.

The acetyl group is removed from a donor molecule known as acetyl coenzyme A and transferred onto the target protein. The effect of acetylation is to weaken the charge interactions between the histone and DNA, thereby making more genes in the DNA accessible for transcription.

The final, prevalent post-translational chemical group modification is phosphorylation. Phosphorylation is the reversible, covalent addition of a phosphate group to specific amino acids serine , threonine and tyrosine within the protein.

The phosphate group is removed from the donor molecule ATP by a protein kinase and transferred onto the hydroxyl group of the target amino acid, this produces adenosine diphosphate as a biproduct. This process can be reversed and the phosphate group removed by the enzyme protein phosphatase.

Phosphorylation can create a binding site on the phosphorylated protein which enables it to interact with other proteins and generate large, multi-protein complexes. Alternatively, phosphorylation can change the level of protein activity by altering the ability of the protein to bind its substrate.

Post-translational modifications can incorporate more complex, large molecules into the folded protein structure. One common example of this is glycosylation , the addition of a polysaccharide molecule, which is widely considered to be most common post-translational modification.

In glycosylation, a polysaccharide molecule known as a glycan is covalently added to the target protein by glycosyltransferases enzymes and modified by glycosidases in the endoplasmic reticulum and Golgi apparatus.

Glycosylation can have a critical role in determining the final, folded 3D structure of the target protein. In some cases glycosylation is necessary for correct folding.

N-linked glycosylation promotes protein folding by increasing solubility and mediates the protein binding to protein chaperones. Chaperones are proteins responsible for folding and maintaining the structure of other proteins. There are broadly two types of glycosylation, N-linked glycosylation and O-linked glycosylation.

N-linked glycosylation starts in the endoplasmic reticulum with the addition of a precursor glycan. The precursor glycan is modified in the Golgi apparatus to produce complex glycan bound covalently to the nitrogen in an asparagine amino acid.

In contrast, O-linked glycosylation is the sequential covalent addition of individual sugars onto the oxygen in the amino acids serine and threonine within the mature protein structure. Many proteins produced within the cell are secreted outside the cell to function as extracellular proteins.

Extracellular proteins are exposed to a wide variety of conditions. To stabilize the 3D protein structure, covalent bonds are formed either within the protein or between the different polypeptide chains in the quaternary structure.

The most prevalent type is a disulfide bond also known as a disulfide bridge. A disulfide bond is formed between two cysteine amino acids using their side chain chemical groups containing a Sulphur atom, these chemical groups are known as thiol functional groups.

Disulfide bonds act to stabilize the pre-existing structure of the protein. Disulfide bonds are formed in an oxidation reaction between two thiol groups and therefore, need an oxidizing environment to react.

As a result, disulfide bonds are typically formed in the oxidizing environment of the endoplasmic reticulum catalyzed by enzymes called protein disulfide isomerases. Disulfide bonds are rarely formed in the cytoplasm as it is a reducing environment. Many diseases are caused by mutations in genes, due to the direct connection between the DNA nucleotide sequence and the amino acid sequence of the encoded protein.

Changes to the primary structure of the protein can result in the protein mis-folding or malfunctioning. Mutations within a single gene have been identified as a cause of multiple diseases, including sickle cell disease , known as single gene disorders.

Sickle cell disease is a group of diseases caused by a mutation in a subunit of hemoglobin, a protein found in red blood cells responsible for transporting oxygen.

The most dangerous of the sickle cell diseases is known as sickle cell anemia. Sickle cell anemia is the most common homozygous recessive single gene disorder , meaning the affected individual must carry a mutation in both copies of the affected gene one inherited from each parent to experience the disease.

Hemoglobin has a complex quaternary structure and is composed of four polypeptide subunits — two A subunits and two B subunits. A missense mutation means the nucleotide mutation alters the overall codon triplet such that a different amino acid is paired with the new codon.

In the case of sickle cell anemia, the most common missense mutation is a single nucleotide mutation from thymine to adenine in the hemoglobin B subunit gene. This change in the primary structure of the hemoglobin B subunit polypeptide chain alters the functionality of the hemoglobin multi-subunit complex in low oxygen conditions.

When red blood cells unload oxygen into the tissues of the body, the mutated haemoglobin protein starts to stick together to form a semi-solid structure within the red blood cell. This distorts the shape of the red blood cell, resulting in the characteristic "sickle" shape, and reduces cell flexibility.

This rigid, distorted red blood cell can accumulate in blood vessels creating a blockage. The blockage prevents blood flow to tissues and can lead to tissue death which causes great pain to the individual. Cancers form as a result of gene mutations as well as improper protein translation.

In addition to cancer cells proliferating abnormally, they suppress the expression of anti-apoptotic or pro-apoptotic genes or proteins. In cancer cells, the RAS protein becomes persistently active, thus promoting the proliferation of the cell due to the absence of any regulation.

In its absence, the cell cannot initiate apoptosis or signal for other cells to destroy it. As the tumor cells proliferate, they either remain confined to one area and are called benign, or become malignant cells that migrate to other areas of the body.

Oftentimes, these malignant cells secrete proteases that break apart the extracellular matrix of tissues. This then allows the cancer to enter its terminal stage called Metastasis, in which the cells enter the bloodstream or the lymphatic system to travel to a new part of the body.

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Assembly of proteins inside biological cells. Main article: Transcription biology. Illustrates the structure of a nucleotide with the 5 carbons labelled demonstrating the 5' nature of the phosphate group and 3' nature of hydroxyl group needed to form the connective phosphodiester bonds.

Illustrates the intrinsic directionality of DNA molecule with the coding strand running 5' to 3' and the complimentary template strand running 3' to 5'. Main article: Translation biology. Further information: Protein folding. Molecular biology of the cell Sixth ed. Abingdon, UK: Garland Science, Taylor and Francis Group.

ISBN Essentials of Cell Biology. NPG Education: Cambridge, MA. Retrieved 3 March Cell Research. doi : PMC If nitrogen intake is bigger than nitrogen excretion, we are in a positive nitrogen balance.

This gives a general view that the body is in an anabolic growing state. For example, your body might be building gut protein at a rate that exceeds your muscle loss.

Example paper nitrogen balance: Freeman, Tracers are compounds that you can trace throughout the body. Amino acid tracers are the most common type of tracers to assess muscle protein synthesis. These are amino acids that have an additional neutron.

These amino acid tracers function identically to normal amino acids. However, they weigh slightly more than a normal amino acid, which allows us to distinguish them from normal amino acids.

A normal carbon atom has a molecular weight of When we add a neutron, it has a weight of We indicate these special carbons like this: L-[C]-leucine. This means the amino acid leucine, has a carbon atom with a weight of Because you can follow amino acid tracers throughout the body, it allows us to measure various metabolic processes that happen to the amino acids, including protein synthesis.

Using amino acid tracers, we can measure protein synthesis, breakdown, oxidation and net balance. Note that protein synthesis refers to protein synthesis of any protein in the body whole-body protein synthesis. Again, do not mistake it for muscle protein synthesis, which is protein synthesis specifically of muscle protein.

Therefore, whole-body protein synthesis measurements are not necessarily relevant for athletes and might actually give you the wrong impression as will be discussed in chapter 3. However, whole-body protein metabolism data provides more insight than the nitrogen balance method.

Nitrogen balance only indicates an overall anabolic or catabolic state. The whole-body protein metabolism method also indicated this by a positive or negative protein net balance. However, it also shows whether changes in net balance are because of an increase in protein synthesis, a decrease in protein breakdown, or a combination of both.

Please note that this does not contradict the earlier discussion on muscle protein breakdown is not that important. Instinctually, you might think that a more positive whole-body protein balance must be a good thing. Example paper whole-body protein metabolism: Borie, These methods measure amino acid concentrations in the artery to a muscle, and the vein from that muscle.

Where did those extra amino acids in the vein come from? Conversely, if the muscle would take up a lot of amino acids from the artery, but releases less amino acids to the vein, it would indicate that the muscle is taking up a lot of amino acids to build muscle proteins.

This method is called the two pool arteriovenous method. To solve this problem, this method can be combined with muscle biopsies. The main advantage of this method is that it measures both muscle protein synthesis and muscle protein breakdown. Therefore, this is not the preferred method for measuring muscle protein synthesis.

Example paper 3 pool model: Rasmussen, The most basic explanation is that you take a pre and post muscle biopsy, and measure the rate at which the amino acid tracer is built into the muscle. It shows you how fast a muscle would rebuild itself entirely.

An FSR of 0. This translates to a completely new muscle every 3 months. However, protein ingestion would disturb this steady state, as a lot of normal amino acids will enter the blood, thus throwing off the tracer amino acid to normal amino acid ratio.

However, our lab has gotten fancy in this area. We have been able to produce highly enriched intrinsically labeled protein. This means that the amino acid tracers have been build into our protein supplements. So as our intrinsically protein supplements are absorbed, both amino acid tracers and normal amino acids enter the blood.

Therefore the steady state is not disrupted and FSR can be calculated more accurately. Example paper FSR with and without intrinsically labeled protein : Holwerda, You can trace the amino acids from the protein: first, as they are digested, then as they appear in the blood, subsequently they are taken up by the muscle, and ultimately some of them are built into actual muscle tissue.

So we can measure how much of the protein you eat, actually ends up into muscle tissue. This is called de novo muscle protein synthesis. Example paper de novo muscle protein synthesis: Trommelen, When measuring muscle protein synthesis, we can measure mixed muscle protein synthesis all types of muscle protein together.

But muscle protein can be further specified into fractions. The main muscle protein fraction is myofibrillar protein. Myofibrillar proteins contract and represent the majority of the muscle mass.

This fraction is highly relevant for building muscle mass and strength. Mitochondrial proteins only represent a small part of the muscle. Mitochondria are the powerhouses of the muscle, they burn carbohydrate and fat for fuel. Therefore mitochondrial protein synthesis is more informative about energy production capacity in the muscle and more relevant for endurance athletes and metabolic health.

Sarcoplasmic protein contains various organelles such as the endoplasmic reticulum and ribosomes. Intramuscular connective tissue protein represents collagen protein in the muscle.

This collagen helps transfer the muscle force generated by myofibrillar protein. Example paper myofibrillar vs mitochondrial protein synthesis: Wilkinson, , or intramuscular connective tissue protein synthesis Trommelen, More recently, deuterium oxide D2O, also called heavy water is getting popular to measure muscle protein synthesis.

Example paper deuterium oxide: Brooks, There is evidence that a variety of signaling molecules are involved in the regulation of muscle protein synthesis. Most notably, the protein from the mTOR pathway. Research of these molecular markers is very important to better understand how physiological processes are regulated and ultimately can be influenced by exercise, nutrition or even drugs.

Therefore, you should be very skeptical to draw conclusions based on studies that only measure molecular markers of muscle protein synthesis and muscle protein breakdown. Methods are not necessarily good or bad. But the interpretation of the data based on these methods can be wrong.

We recently showed that resistance exercise does not increase whole-body protein synthesis Holwerda, So should we conclude that resistance exercise is not effective to build muscle? Whole-body protein metabolism measures the synthesis of all proteins in the body.

Other tissues in the body have much higher synthesis rates, and therefore, the muscle only has a relatively small contribution to the total whole-body protein synthesis rates. In the same study, we also measured muscle protein synthesis using the FSR method both with and without intrinsically labeled protein and de novo muscle protein synthesis.

All 3 methods showed that resistance exercise was anabolic for the muscle. Imagine we would have only measured whole-body protein synthesis.

Our study would give the wrong impression that resistance exercise is not anabolic, as we saw no increase in whole-body protein synthesis rates. Shortly, it says that very large protein meals are beneficial because they reduce protein breakdown. Again, this study gave the wrong impression, because whole-body protein breakdown was mistaken for muscle protein breakdown the latter was not measured in this study.

Both the 40 gram and the 70 gram dose were equally effective at stimulating muscle protein synthesis. One of the purposes of measuring muscle protein synthesis is to study if an intervention helps to build muscle or maintain muscle mass.

Let me first get something out of the way: we have no bias for either acute or long-term studies. We run both at our lab, and do some of the most expensive studies in the field of either type. A lot of people seem to think that based on this study, muscle protein synthesis measurements do not translate to actual muscle mass gains in the long term.

But that conclusion is way beyond the context of the study. This study measured muscle protein synthesis in the 6 hours after a single exercise bout. However, resistance exercise can increase muscle protein synthesis for several days. So a 6-hour measurement does not capture the entire exercise response.

This study showed that measuring muscle protein synthesis for 6 hours does not predict muscle mass gains. That is totally different from the conclusion that muscle protein synthesis regardless of measurement time does not predict muscle mass gains.

This was followed up by a study which used the deuterium oxide method to measure muscle protein synthesis rates during all the weeks of training not just a few hours after one session , and found that muscle protein synthesis did correlate with muscle mass gains during the training program Brooks, More recently, a study found that muscle protein synthesis measured over 48 hours after an exercise bout did not correlate with muscle mass gains in untrained subjects at the beginning of an exercise training program, but it did at three weeks of training and onwards Damas, While untrained subjects have a large increase in muscle protein synthesis after their initial exercise sessions, they also have a lot of muscle damage.

So muscle protein synthesis is mainly used to repair damaged muscle protein, not to grow. After just 3 weeks of training, muscle damage is diminished, and the increase in muscle protein synthesis is actually used to hypertrophy muscles. So do these studies show that muscle protein synthesis predicts muscle mass gains, but only in the right context.

A huge benefit of muscle protein synthesis studies is that they are more sensitive than studies that measure actual muscle mass gains. This means that muscle protein synthesis studies can detect an anabolic effect easier than long term studies which simply miss it long term studies might draw the wrong conclusion that something does not benefit muscle growth when it actually does.

For example, it has been shown time and time again that protein ingestion increases muscle protein synthesis. Muscle mass gain is simply a very slow process. You need to do a huge study, with a huge amount of subjects, who consume additional protein for many months, before you will actually see a measurable effect of protein supplementation.

We performed a meta-analysis combining the results of individual studies on the effect of protein supplementation on muscle mass gains.

We demonstrated that only 5 studies concluded that protein supplementation had a benefit, while 17 did not! However, most of the studies that showed no significant benefit, did show a small non-significant benefit.

When you combine all those results, you increase the statistical power and you can conclude that protein supplementation actually does improve muscle mass. So in this case, most long-term studies gave the wrong impression, and muscle protein synthesis studies are actually preferred.

There are a lot of long-term studies that have a relative small number of subjects and a small study duration and conclude that an intervention did not work for example, protein supplementation, or X versus Y set of exercise for example.

However, the studies were doomed to begin with. They needed to be 3 times as big and 2 times as long to have a chance to find a positive effect. Now if the effect of giving additional protein is already extremely hard to detect in long-term studies, how realistic is it to find smaller effects?

For example, optimizing protein intake distribution throughout the day has been shown to optimize muscle protein synthesis rates Mamerow, Areta, However, this effect is smaller than adding another protein meal.

So the effect of protein distribution is almost impossible to find in a long-term study. For such a research question, acute muscle protein synthesis studies are simply much better suited. The second big benefit of muscle protein synthesis studies is that they give a lot more mechanistic insight.

They help you understand WHY a certain protein is good or not that good at stimulating muscle protein synthesis for example, its digestion properties, amino acid composition etc.

These kinds of insights help to better understand what triggers muscle growth and come up with new research questions. These kind of insights are very hard to obtain in long-term studies, which typically only show the end result of the mechanisms.

The benefits of measuring muscle protein synthesis include the sensitivity, controlled environment, and they allow you to investigate questions that are almost impossible to answer in long-term studies.

Again, we do both and each has its purpose and build on each other. Usually, muscle protein synthesis studies are performed to see if something work as they are very sensitive and why it works.

Only when you have both, you have pretty convincing evidence that your intervention does what you claim it to do. Multiple sets increase muscle protein synthesis more than a single set Burd, A higher weekly training volume number of sets to muscle results in a greater muscle mass gains Schoenfeld, It is often recommended that a rep range of reps per set is optimal for muscle growth.

The American College of Sport Medicine position stand states ACSM, :. For novice untrained individuals with no RT experience or who have not trained for several years training, it is recommended that loads correspond to a repetition range of an repetition maximum RM.

For intermediate individuals with approximately 6 months of consistent RT experience to advanced individuals with years of RT experience training, it is recommended that individuals use a wider loading range from 1 to 12 RM in a periodized fashion with eventual emphasis on heavy loading RM using 3- to 5-min rest periods between sets.

However, these recommendations lack evidence. The main takeaway here is that there are no magic rep ranges that are superior for muscle growth. It is unclear whether each set should be taken to failure.

Muscular failure decreases performance on subsequent sets, thereby reducing training volume. Perhaps performing a set with reps left in the tank will still give a near-maximal stimulus to the muscle, without much of the associated fatigue.

If sets are not taken close to failure, the muscle protein synthetic response will be small Burd, But at least in untrained subjects, training close to failure appears to produce similar muscle mass gains as training to complete failure Nóbrega, A longer rest period between sets increases the larger post-exercise muscle protein synthetic response compared to a short rest period 5 vs 1 min McKendry, In agreement, a longer interset rest period improves muscle mass gains compared to a shorter rest period 3 vs 1 min Schoenfeld, A single bout of resistance exercise can stimulate muscle protein synthesis for longer than 72 hour, but peaks at 24 h Miller, Indeed, training each muscle group at least twice a week results in larger muscle mass gains Schoenfeld, The total muscle protein synthetic MPS response determined by the increase in MPS rates and the duration of these increased rates is decreased in trained subjects compared to untrained subjects Damas, However, the pattern of this decreased response is differs between mixed muscle protein synthesis the synthesis of all types of muscle proteins and myofibrillar protein synthesis the synthesis of contractile proteins: the relevant measurement for muscle mass.

The increase in mixed muscle protein synthesis is shorter lived in trained subjects. In contrast, myofibrillar protein synthesis rates do not increase as much in trained subjects, but the duration of the increase does not appear impacted. The larger increase in the total muscle protein synthetic response seems like a logical explanation why untrained people can make faster much gains than experienced lifters.

However, this is not necessarily true. In untrained subjects, there is not only a large increase myofibrillar protein synthesis, but also in muscle damage following resistance exercise. A large portion of the myofibrillar protein synthesis is used to simply repair damaged muscle proteins, rather than growing muscle proteins.

In more trained subjects, here is a smaller increase in myofibrillar protein synthesis, but there is also much less or even minimal muscle damage following resistance exercise just weeks of training is enough to see these effects.

This means that in a trained state, the increase in myofibrillar protein synthesis can actually be used to actually increase muscle mass. Smith GI, Patterson BW, Mittendorfer B.

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