Daily requirements of protein for an average build person
Protein portions in one whole day should never exceed the size of the clenched fist of the person consuming it and this includes children. Many people consume far too much protein and this can cause many health issues such as gout and kidney problems. This is because people do not realise that all living things are made of protein and so all food contains protein including plants foods. The amino acids that make up the protein vary greatly in amounts in various plants and animals because they use different combinations to make their particular proteins.
Animal protein makes the body acidic and excessive dietary protein from foods with high potential renal acid load adversely affects bone, due to excessive calcium loss, unless buffered by the consumption of alkaline foods.
When the body synthesises protein, ammonia (uric acid) is formed in the liver as a waste product, and too large amounts of protein into the diet can result in too much ammonia being formed and in so doing place extra stress on the liver and kidneys to flush it out the body. High levels of ammonia are toxic to the nervous system, with symptoms that include vomiting and tremors and can lead to coma and death. See the Cleanse and Detoxify page to find out how to flush the liver of toxins and excess fats.
The amount of protein required in the daily diet is far less than people normally consume. The daily protein requirement is usually expressed in grams. The recommended daily protein requirements for humans are derived from an ideal body weight. The ideal body weight is calculated based on height and is slightly higher for men than women.
See the Body Mass Index Chart.
Protein requirements can also be expressed in terms of total caloric intake. The daily protein requirement of an averagely active person, between 19 and 50 years old and of ideal weight, should be between 10% to 15% of the daily caloric intake or 0.6 g of protein per kilogram bodyweight per day.
Protein for those participating in intense physical activities
Protein requirements for very active individuals such as athletes, dancers, drummers and sports men and women need more protein than averagely active or sedentary people and must ensure that they have adequate glycogen stores so that their muscle mass is not robbed of protein to provide energy. See more on the Sports Nutrition page.
During digestion, protein is crushed and mixed with saliva in the mouth. It then enters the stomach and comes in contact with very strong acid which uncoils the protein’s tangled strands. Stomach enzymes attack the protein bonds, breaking apart the protein strands into smaller pieces.
The protein pieces enter the small intestine where the next team of enzymes accomplishes the final breakdown of the protein strands into free amino acids. The cells of the small intestine release the amino acids into the bloodstream.
Once the amino acids are circulating in the blood stream they are available to be taken up by any cell of the body. Amino acids combine with other amino acids to form the specific proteins needed by the body.
There are many amino acids important to human nutrition. Eight of these are considered essential amino acids, meaning the body cannot make them. Instead they need to be provided in the diet. Under normal circumstances, the body can produce the others. The role of protein in food is not to provide our bodies with proteins directly, but to supply the amino acids from which the body can make its own proteins. When we eat a diet that supplies each essential amino acid in adequate amounts, our body supports protein synthesis. Eight amino acids are considered essential and three others are to certain individuals. They are:
The other nonessential amino acids may become essential to a particular individual through an inborn error of metabolism. If an enzyme, necessary for the manufacture of a particular amino acid by the body is absent, that amino acid becomes an essential requirement of the diet. Nonessential amino acids can also become essential during disease, stress or when taking powerful medications when there is either increased need and/or increased breakdown of them. Other amino acids that are essential to certain individuals:
1. Arginine (children)
2. Cysteine (premature babes)
3. Histidine (children)
4. Taurine (premature babies and infants)
Various scientists argue that cysteine, histidine and taurine are not essential but they are essential amino acids for early growth and development in children, premature infants and possibly for all neonates. Preterm babies are also known to require cysteine, because the foetal liver cannot convert methionine to cysteine and some adults may also have a liver disorder which prevents this too.
Burn patients require more amino acids because of oozing wounds, while one type of schizophrenic may have a recently expressed inborn error of metabolism which dictates the need for less wheat gluten or serine. Certain cancers can be starved by withholding their ‘favourite' amino acids. For example, melanomas consume excessive phenylalanine and tyrosine; reducing these two amino acids in a cancer patient's diet can slow tumour growth. The understanding and manipulation of required amino acids in the diet is essential in maintaining health and controlling disease.
10,000 different proteins may exist in a single cell of the body. Each one requires a different arrangement of amino acids. To make protein, cells must have all the needed amino acids available simultaneously. Therefore, the first important characteristic of protein in the diet, with respect to protein, is that it should supply at least the eight essential amino acids for the synthesis of others, to make proteins.
The 20 amino acids in protein
Closely related amino acids
Daily requirements of amino acids
The following are the amounts need in milligrams per kilograms of bodyweight per day.
Males 14-18 years old
15 mg/kg/day of histidine
21 mg/kg/day of isoleucine
47 mg/kg/day of leucine
43 mg/kg/day of lysine
21 mg/kg/day of methionine + cysteine
38 mg/kg/day of phenylalanine + tyrosine
22 mg/kg/day of threonine
6 mg/kg/day of tryptophan
27 mg/kg/day of valine
Females 14-18 years old
14 mg/kg/day of histidine
19 mg/kg/day of isoleucine
44 mg/kg/day of leucine
40 mg/kg/day of lysine
19 mg/kg/day of methionine + cysteine
35 mg/kg/day of phenylalanine + tyrosine
21 mg/kg/day of threonine
5 mg/kg/day of tryptophan
24 mg/kg/day of valine
Adults19 years plus
14 mg/kg/day of histidine
19 mg/kg/day of isoleucine
42 mg/kg/day of leucine
38 mg/kg/day of lysine
19 mg/kg/day of methionine + cysteine
33 mg/kg/day of phenylalanine + tyrosine
20 mg/kg/day of threonine
5 mg/kg/day of tryptophan
24 mg/kg/day of valine
For pregnant and breast feeding woman of all ages
18 mg/kg/day of histidine
25 mg/kg/day of isoleucine
56 mg/kg/day of leucine
51 mg/kg/day of lysine
25 mg/kg/day of methionine + cysteine
44 mg/kg/day of phenylalanine + tyrosine
26 mg/kg/day of threonine
7 mg/kg/day of tryptophan
31 mg/kg/day of valine
If one amino acid is supplied in an amount smaller than needed, the total amount of protein that can be synthesised from others will be limited. It is impossible to produce a partial protein. Only complete ones can be made. A diet that contains an imbalance of amino acids is a diet containing poor protein quality. When the body attempts to use the amino acids supply from such a diet, it wastes many amino acids. In the absence of one, it cannot use the others and it has no place to store them.
Amino acids grouped according to the characteristics of the side chains
Acidic - aspartic acid, glutamic acid
Aliphatic - alanine, glycine, Isoleucine, leucine, proline, valine
Amidic (containing amide group) - asparagine, glutamine
Aromatic - phenylalanine, tryptophan, tyrosine
Basic - arginine, histidine, lysine
Hydroxylic - serine, threonine
Sulphur containing - cysteine, methionine
SLC is the single-letter code used to represent the amino acids in protein data bases.
Codon letters: A = Adenine, C = Cytosine, G = Guanine, U = Uracil
*AUG signals "start" of translation when it occurs at the beginning of a gene.
Three aspects of a protein's structure are specific to the job the protein does in the body.
Primary Structure: The primary structure of a protein is the sequence of amino acids in the protein which can vary from the hundreds to the thousands, and the sequence in which those 20 different amino acids is specific to the individual protein. One amino acid can occur in a protein many times.
Secondary Structure: This is defined by the way the long strands of amino acids coil about themselves. Just as a phone cord wraps around itself to form a coil, a protein will also wrap around itself and the degree and tightness of the coil is specific to the protein in question.
Tertiary Structure: Once a protein is coiled, the protein will begin to fold onto itself (similar to the way a phone cord tangles around itself) and this folding is specific to that particular protein's function.
Type of protein
|These bind to specific foreign particles, such as viruses and bacteria, to protect the body. |
|Enzymes carry out almost all of the thousands of chemical reactions that take place in cells. They also assist with the formation of new molecules by reading the genetic information stored in DNA.|
|Messenger proteins, such as some types of hormones, transmit signals to coordinate biological processes between different cells, tissues, and organs.|
|These proteins provide structure and support for cells. On a larger scale, they also allow the body to move. |
|These proteins bind and carry atoms and small molecules within cells and throughout the body.|
Life is specified by genomes. Every organism, including humans, has a genome that contains all of the biological information needed to build and maintain a living example of that organism. The biological information contained in a genome is encoded in its deoxyribonucleic acid (DNA) and is divided into discrete units called genes. Genes code for proteins that attach to the genome at the appropriate positions and switch on a series of reactions called gene expression.
Nuclear DNA (deoxyribonucleic acid)
Inside each of body's cells lies a nucleus, a membrane bounded region that provides a sanctuary for genetic information. The nucleus contains long strands of DNA that encode this genetic information. A DNA chain is made up of four chemical bases: adenine (A) and guanine (G), which are called purines, and cytosine (C) and thymine (T), referred to as pyrimidines. Each base has a slightly different composition, or combination of oxygen, carbon, nitrogen, and hydrogen. In a DNA chain, every base is attached to a sugar molecule (deoxyribose) and a phosphate molecule, resulting in a nucleic acid or nucleotide. Individual nucleotides are linked through the phosphate group, and it is the precise order, or sequence, of nucleotides that determines the product made from that gene. Half of the nuclear DNA comes from the mother and half from the father.
Not all genetic information is found in nuclear DNA. Both plants and animals have an organelle (little organ) within the cell called the mitochondrion. Each mitochondrion has its own set of genes. Plants also have a second organelle, the chloroplast, which also has its own DNA. Cells often have multiple mitochondria, particularly cells requiring lots of energy, such as active muscle cells. This is because mitochondria are responsible for converting the energy stored in macromolecules into a form usable by the cell, namely, the adenosine triphosphate molecule. They are often referred to as the power generators of the cell.
Unlike nuclear DNA (the DNA found in the nucleus of a cell), mitochondrial DNA is only inherited from the mother. This is because mitochondria are only found in the female gametes (eggs) of sexually reproducing animals, not in the male gamete, (sperm). Mitochondrial DNA also does not recombine; there is no shuffling of genes from one generation to the other, as there is with nuclear genes. Large numbers of mitochondria are found in the tail of sperm, providing them with an engine that generates the energy needed for swimming toward the egg. However, when the sperm enters the egg during fertilization, the tail falls off, taking away the father's mitochondria.
RNA (ribonucleic acid)
In RNA, the complement of adenine (A) is uracil (U) instead of thymine (T), so the pairs that form are adenine : uracil and guanine : cytosine. Just like DNA, ribonucleic acid (RNA) is a chain, or polymer, of nucleotides with the same 5' to 3' direction of its strands. However, the ribose sugar component of RNA is slightly different chemically than that of DNA. RNA has a 2' oxygen atom that is not present in DNA. Other fundamental structural differences exist. For example, uracil takes the place of the thymine nucleotide found in DNA, and RNA is, for the most part, a single-stranded molecule. DNA directs the synthesis of a variety of RNA molecules, each with a unique role in cellular function. For example, all genes that code for proteins are first made into an RNA strand in the nucleus called a messenger RNA (mRNA). The mRNA carries the information encoded in DNA out of the nucleus to the protein assembly machinery, called the ribosome, in the cytoplasm. The ribosome complex uses mRNA as a template to synthesize the exact protein coded for by the gene.
Evolution of bacteria
Mitochondria have their own DNA, RNA, and ribosomes. The energy conversion process that takes place in the mitochondria takes place aerobically (in the presence of oxygen). Other energy conversion processes in the cell take place anaerobically (without oxygen. The independent aerobic function of these organelles evolved from bacteria that lived inside of other simple organisms in a mutually beneficial (symbiotic) relationship, providing them with aerobic capacity. Through the process of evolution, these tiny organisms became incorporated into the cell, and their genetic systems and cellular functions became integrated to form a single functioning cellular unit. The eukaryotic organism (amoeba) lacks mitochondria. Therefore, amoeba must always have a symbiotic relationship with an aerobic bacterium.
Mitochondrial DNA mutations
There are many diseases caused by mutations in mitochondrial DNA. Because the mitochondria produce energy in cells, symptoms of mitochondrial diseases often involve degeneration or functional failure of tissue. Mitochondrial DNA mutations have been identified in some forms of diabetes, deafness, and certain inherited heart diseases. In addition, mutations in mitochondrial DNA are able to accumulate throughout an individual's lifetime. This is different from mutations in nuclear DNA, which has sophisticated repair mechanisms to limit the accumulation of mutations. Mitochondrial DNA mutations can also concentrate in the mitochondria of specific tissues. A variety of deadly diseases are attributable to a large number of accumulated mutations in mitochondria. There is even a theory, the Mitochondrial Theory of Aging, that suggests that accumulation of mutations in mitochondria contributes to, or drives, the aging process. These defects are associated with Parkinson's and Alzheimer's disease, although it is not known whether the defects actually cause, or are a direct result of. the diseases. However, evidence suggests that the mutations contribute to the progression of both diseases.
In addition to the critical cellular energy related functions, mitochondrial genes are useful to evolutionary biologists because of their maternal inheritance and high rate of mutation. By studying patterns of mutations, scientists are able to reconstruct patterns of migration and evolution within and between species. For example, mitochondrial DNA analysis has been used to trace the migration of people from Asia across the Bering Strait to North and South America. It has also been used to identify an ancient maternal lineage from which modern man evolved.
Although DNA is the carrier of genetic information in a cell, proteins do the bulk of the work. Proteins are long chains containing as many as 20 different kinds of amino acids. Each cell contains thousands of different proteins: enzymes that make new molecules and catalyze nearly all chemical processes in cells; structural components that give cells their shape and help them move; hormones that transmit signals throughout the body; antibodies that recognize foreign molecules; and transport molecules that carry oxygen. The genetic code carried by DNA is what specifies the order and number of amino acids and, therefore, the shape and function of the protein.
A chromosome is composed of a very long molecule of DNA and associated proteins that carry hereditary information. The centromere, shown at the centre of this chromosome, is a specialized structure that appears during cell division and ensures the correct distribution of duplicated chromosomes to daughter cells. Telomeres are the structures that seal the end of a chromosome. Telomeres play a critical role in chromosome replication and maintenance by counteracting the tendency of the chromosome to otherwise shorten with each round of replication.
Genetic information flows from DNA to RNA to protein. The genetic code resides in DNA because only DNA is passed from generation to generation. Yet, in the process of making a protein, the encoded information must be faithfully transmitted first to RNA then to protein. Transferring the code from DNA to RNA is a fairly straightforward process called transcription. Deciphering the code in the resulting mitochondrial RNA is a little more complex. It first requires that the mitochondrial RNA leave the nucleus and associate with a large complex of specialized RNAs and proteins that, collectively, are called the ribosome. Here the mitochondrial RNA is translated into protein by decoding the mitochondrial RNA sequence in blocks of three RNA bases, called codons, where each codon specifies a particular amino acid. In this way, the ribosomal complex builds a protein one amino acid at a time, with the order of amino acids determined precisely by the order of the codons in the mitochondrial RNA.
Most genetic variation occurs during the phases of the cell cycle when DNA is duplicated. Mutations in the new DNA strand can manifest as base substitutions, such as when a single base gets replaced with another; deletions, where one or more bases are left out; or insertions, where one or more bases are added. Mutations can either be synonymous, in which the variation still results in a codon for the same amino acid or non-synonymous, in which the variation results in a codon for a different amino acid. Mutations can also cause a frame shift, which occurs when the variation bumps the reference point for reading the genetic code down a base or two and results in loss of part, or sometimes all, of that gene product. DNA mutations can also be introduced by toxic chemicals and, particularly in skin cells, exposure to ultraviolet radiation.
Mutations that occur in somatic cells (any cell in the body except gametes and their precursors) will not be passed on to the next generation. This does not mean, however, that somatic cell mutations (acquired mutations) are benign. For example, as the skin cells prepare to divide and produce new skin cells, errors may be inadvertently introduced when the DNA is duplicated, resulting in a daughter cell that contains the error. Although most defective cells die quickly, some can persist and may even become cancerous if the mutation affects the ability to regulate cell growth.
Not all mutations are bad. Mutations also provide a species with the opportunity to adapt to new environments, as well as to protect a species from new pathogens. Mutations are responsible for the basic theory of evolution proposed by Charles Darwin in 1859 (survival of the fittest). This theory proposes that as new environments arise, individuals carrying certain mutations that enable an evolutionary advantage will survive to pass this mutation on to its offspring. It does not suggest that a mutation is derived from the environment, but that survival in that environment is enhanced by a particular mutation.
Some genes, and even some organisms, have evolved to tolerate mutations better than others. For example, some viral genes are known to have high mutation rates. Mutations serve the virus well by enabling adaptive traits, such as changes in the outer protein coat so that it can escape detection and thereby destruction by the host's immune system. Viruses also produce certain enzymes that are necessary for infection of a host cell. A mutation within such an enzyme may result in a new form that still allows the virus to infect its host but that is no longer blocked by an anti-viral drug. This will allow the virus to propagate freely in its environment. Bacteria can mutate using this same principle such as the staphylococcus aureus bacteria which has mutated to become unaffected by antibiotics.
Sequences that code for proteins are called structural genes. Although it is true that proteins are the major components of structural elements in a cell, proteins are also the real workhorses of the cell. They perform such functions as transporting nutrients into the cell; synthesizing new DNA, RNA, and protein molecules and transmitting chemical signals from outside to inside the cell, as well as throughout the cell, both critical to the process of making proteins.
Alleles are different forms of a gene. They can be dominant or recessive. There are four basic blood types, O, A, B, and AB. Blood type is determined by the alleles inherited from parents. For the blood type gene, there are three basic blood type alleles: A, B, and O. We all have two alleles, one inherited from each parent.
The possible combinations of the three alleles are OO, AO, BO, AB, AA, and BB. Blood types A and B are "co-dominant" alleles, whereas O is "recessive". A co dominant allele is apparent even if only one is present; a recessive allele is apparent only if two recessive alleles are present. Because blood type O is recessive, it is not apparent if the person inherits an A or B allele along with it. So, the possible allele combinations result in a particular blood type in this way:
OO = blood type O
AO = blood type A
BO = blood type B
AB = blood type AB
AA = blood type A
BB = blood type B
You can see that a person with blood type B may have a B and an O allele, or they may have two B alleles. If both parents are blood type B and both have a B and a recessive O, then their children will either be BB, BO, or OO. If the child is BB or BO, they have blood type B. If the child is OO, he or she will have blood type O.