Testosterone effects can also be classified by the age of usual occurrence. For postnatal effects in both males and femaies, these are mostly dependent on the levels and duration of circulating free testosterone. Early infancy androgen effects are the least understood. In the first weeks of life for male infants, testosterone levels rise.
The levels remain in a pubertal range for a few months, but usually reach the barely detectable levels of childhood by months of age. The function of this rise in humans is unknown. It has been speculated that "brain masculinization" is occurring since no significant changes have been identified in other parts of the body. Early postnatal effects are the first visible effects of rising androgen levels in childhood, and occur in both boys and girls in puberty.
Advanced postnatal effects begin to occur when androgen have been higher than normal adult female levels for months or years. In males these are normal late pubertal effects, and only occur in women after prolonged periods of excessive levels of free testosterone in the blood.
Testosterone was first isolated from a bull in There have been many pharmaceutical forms over the years. Forms of testosterone for human administration currently available in North America include testosterone cypionate and enanthate in oil for injection, methyltestosterone tablets for oral ingestion, and skin patches and a gel preparation for transdermal absorption.
Often, lipids are grouped in three major categories; triglycerides, phospholipids, and steroids. The most common type of lipid is triglycerides, which include fats from animals and oils from plants. Triglycerides generally serve as long-term energy storage molecules, except indigestible waxes, which are instead used as a waterproofing substance in both plants and animals.
Triglycerides contain three fatty acid chains, which can be either saturated or unsaturated, connected to a glycerol molecule. Saturated fatty acid chains are linear molecules with a maximum number of hydrogen atoms, where every carbon in the chain is connected via a single bond. On the other hand, unsaturated fatty acid chains have kinks due to the presence of at least one double bond. While trans fats occur naturally, they are generated during industrial production of saturated vegetable oils with hydrogen.
Similar to saturated fatty acids, trans fats stack very well due to their relative linearity. However, trans fats cause problems for human heart health, such as the damaging the lining of arteries and causing inflammation when digested 2. Phospholipids are similar to triglycerides, however, one of the fatty acid chains is replaced with a phosphate-containing polar group.
Therefore, phospholipids have a hydrophilic head and two hydrophobic fatty acid tails. These properties of phospholipids are crucial to the cell membrane structure and function. Steroids are lipids that are composed of fused carbon rings with varying functional groups.
Cholesterol is a steroid that is also a cell membrane component. Moreover, cholesterol is used to synthesize other steroids, including sex hormones such as estrogen and testosterone.
Although cholesterol is essential for cell membrane structure and hormone synthesis, high levels of plasma cholesterol are implicated in plaque accumulation inside blood vessels and causing coronary disease 3.
The third class of biological macromolecules are proteins, which are made up of chains of amino acids. These groups link together, N-terminal to C-terminal, in a chain connected by peptide bonds. Proteins are important for maintaining body functions as enzymes, hormones, structural components and transport molecules, and play vital roles in muscle contractibility, immunity and blood clotting. However, issues can arise in protein structure and function, and these issues are often genetic.
For instance, normal red blood cells are round, but in people affected by sickle cell anemia, cells have a curved shape with an exposed hydrophobic region, caused by a mutation in a protein called hemoglobin S. This shape reduces the capacity to carry oxygen and causes the cells to get stuck in blood vessels. This results in many detrimental symptoms to the person carrying the mutation, and people who inherit two copies of the sickle cell gene often suffer ill effects or even possibly die because of the reduced capacity of sickled cells to transport oxygen.
In a twist, those carrying only one copy of the gene are resistant to infection from malaria, so the disease has been able to be passed on and persists in countries with elevated levels of malaria infections 4. The fourth class of biological macromolecules are the nucleic acids, which are composed of monomers known as nucleotides. These monomers are composed of three parts: a phosphate group, a ribose sugar and a nitrogen base.
Nucleotides differ from each other by their nitrogen bases and the type of ribose they contain. Starch, glycogen, cellulose, and chitin are examples of polysaccharides. Starch is the stored form of sugars in plants and is made up of amylose and amylopectin both polymers of glucose.
Plants are able to synthesize glucose, and the excess glucose is stored as starch in different plant parts, including roots and seeds. The starch that is consumed by animals is broken down into smaller molecules, such as glucose.
The cells can then absorb the glucose. Glycogen is the storage form of glucose in humans and other vertebrates, and is made up of monomers of glucose. Glycogen is the animal equivalent of starch and is a highly branched molecule usually stored in liver and muscle cells. Whenever glucose levels decrease, glycogen is broken down to release glucose. Cellulose is one of the most abundant natural biopolymers. The cell walls of plants are mostly made of cellulose, which provides structural support to the cell.
Wood and paper are mostly cellulosic in nature. Cellulose is made up of glucose monomers that are linked by bonds between particular carbon atoms in the glucose molecule.
Every other glucose monomer in cellulose is flipped over and packed tightly as extended long chains. This gives cellulose its rigidity and high tensile strength—which is so important to plant cells. Cellulose passing through our digestive system is called dietary fiber. While the glucose-glucose bonds in cellulose cannot be broken down by human digestive enzymes, herbivores such as cows, buffalos, and horses are able to digest grass that is rich in cellulose and use it as a food source.
In these animals, certain species of bacteria reside in the rumen part of the digestive system of herbivores and secrete the enzyme cellulase. The appendix also contains bacteria that break down cellulose, giving it an important role in the digestive systems of ruminants.
Cellulases can break down cellulose into glucose monomers that can be used as an energy source by the animal. Carbohydrates serve other functions in different animals. Arthropods, such as insects, spiders, and crabs, have an outer skeleton, called the exoskeleton, which protects their internal body parts.
This exoskeleton is made of the biological macromolecule chitin , which is a nitrogenous carbohydrate. It is made of repeating units of a modified sugar containing nitrogen. Thus, through differences in molecular structure, carbohydrates are able to serve the very different functions of energy storage starch and glycogen and structural support and protection cellulose and chitin. Registered Dietitian: Obesity is a worldwide health concern, and many diseases, such as diabetes and heart disease, are becoming more prevalent because of obesity.
This is one of the reasons why registered dietitians are increasingly sought after for advice. Registered dietitians help plan food and nutrition programs for individuals in various settings.
They often work with patients in health-care facilities, designing nutrition plans to prevent and treat diseases. For example, dietitians may teach a patient with diabetes how to manage blood-sugar levels by eating the correct types and amounts of carbohydrates. Dietitians may also work in nursing homes, schools, and private practices. In addition, registered dietitians must complete a supervised internship program and pass a national exam.
Those who pursue careers in dietetics take courses in nutrition, chemistry, biochemistry, biology, microbiology, and human physiology.
Dietitians must become experts in the chemistry and functions of food proteins, carbohydrates, and fats. The underground storage bulb of the camas flower shown below has been an important food source for many of the Indigenous peoples of Vancouver Island and throughout the western area of North America.
Camas bulbs are still eaten as a traditional food source and the preparation of the camas bulbs relates to this text section about carbohydrates. Most often plants create starch as the stored form of carbohydrate. Some plants, like camas create inulin. Inulin is used as dietary fibre however, it is not readily digested by humans.
If you were to bite into a raw camas bulb it would taste bitter and has a gummy texture. The method used by Indigenous peoples to make camas both digestible and tasty is to bake the bulbs slowly for a long period in an underground firepit covered with specific leaves and soil. The heat acts like our pancreatic amylase enzyme and breaks down the long chains of inulin into digestible mono and di-saccharides. Properly baked, the camas bulbs taste like a combination of baked pear and cooked fig.
It is important to note that while the blue camas is a food source, it should not be confused with the white death camas, which is particularly toxic and deadly.
The flowers look different, but the bulbs look very similar. Lipids include a diverse group of compounds that are united by a common feature. This is because they are hydrocarbons that include only nonpolar carbon-carbon or carbon-hydrogen bonds.
Lipids perform many different functions in a cell. Cells store energy for long-term use in the form of lipids called fats. Lipids also provide insulation from the environment for plants and animals. For example, they help keep aquatic birds and mammals dry because of their water-repelling nature.
Lipids are also the building blocks of many hormones and are an important constituent of the plasma membrane. Lipids include fats, oils, waxes, phospholipids, and steroids. A fat molecule, such as a triglyceride, consists of two main components—glycerol and fatty acids.
Glycerol is an organic compound with three carbon atoms, five hydrogen atoms, and three hydroxyl —OH groups. In a fat molecule, a fatty acid is attached to each of the three oxygen atoms in the —OH groups of the glycerol molecule with a covalent bond. During this covalent bond formation, three water molecules are released. The three fatty acids in the fat may be similar or dissimilar.
These fats are also called triglycerides because they have three fatty acids. Some fatty acids have common names that specify their origin. For example, palmitic acid, a saturated fatty acid, is derived from the palm tree. Arachidic acid is derived from Arachis hypogaea , the scientific name for peanuts. Fatty acids may be saturated or unsaturated.
In a fatty acid chain, if there are only single bonds between neighboring carbons in the hydrocarbon chain, the fatty acid is saturated. Saturated fatty acids are saturated with hydrogen; in other words, the number of hydrogen atoms attached to the carbon skeleton is maximized. When the hydrocarbon chain contains a double bond, the fatty acid is an unsaturated fatty acid.
Most unsaturated fats are liquid at room temperature and are called oils. Advanced search. Skip to main content Thank you for visiting nature. Abstract THE formation of testosterone by the testis has been studied extensively and the general characteristics of the process have been described 1. Access through your institution. Buy or subscribe. Rent or Buy article Get time limited or full article access on ReadCube. References 1 Eik-Nes, K. Google Scholar 2 Christensen, A.
Google Scholar 3 Eik-Nes, K. Google Scholar 4 Brinkman, A. Google Scholar 5 Daughaday, W. Book Google Scholar 10 Ewing, L. Google Scholar Download references. View author publications.
0コメント