The protein content of animal organs is usually much higher than that of the blood plasma. Muscles, for example, contain about 30 percent protein, the liver 20 to 30 percent, and red blood cells 30 percent.
Higher percentages of protein are found in hair, bones, and other organs and tissues with a low water content. The quantity of free amino acids and peptides in animals is much smaller than the amount of protein; protein molecules are produced in cells by the stepwise alignment of amino acids and are released into the body fluids only after synthesis is complete. The high protein content of some organs does not mean that the importance of proteins is related to their amount in an organism or tissue ; on the contrary, some of the most important proteins, such as enzymes and hormones , occur in extremely small amounts.
The importance of proteins is related principally to their function. All enzymes identified thus far are proteins. Enzymes, which are the catalysts of all metabolic reactions, enable an organism to build up the chemical substances necessary for life—proteins, nucleic acids , carbohydrates, and lipids —to convert them into other substances, and to degrade them.
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Life without enzymes is not possible. There are several protein hormones with important regulatory functions. In all vertebrates, the respiratory protein hemoglobin acts as oxygen carrier in the blood , transporting oxygen from the lung to body organs and tissues.
A large group of structural proteins maintains and protects the structure of the animal body. All life on Earth is built from four different types of molecules. These four types of molecules are often referred to as the molecules of life. The four molecules of life are proteins, carbohydrates, lipids and nucleic acids. Each of the four groups is vital for every single organism on Earth. Without any of these four molecules, a cell and organism would not be able to live.
All of the four molecules of life are important either structurally or functionally for cells and, in most cases, they are important in both ways. Proteins are the first of the molecules of life and they are really the building blocks of life. If all the water is removed from a cell, proteins make up more than half of the remaining weight. They come in a huge variety of forms and perform a massive range of functions. They are involved in muscle movement, storage of energy, digestion, immune defence and much more.
The primary structure of a protein is a long chain made of many smaller molecules called amino acids. There are 20 different amino acids that are used to build proteins. The different amino acids can be arranged into trillions of different sequences that each creates a unique protein. The long chain of amino acids twists and folds on itself to produce the final shape of a protein. Amino acids contain nitrogen.
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Nitrogen-based compounds are an essential part of the diet of all organism so they can produce new proteins for their cells. This is why farmers often add nitrogen-based fertilisers to help their crops grow and why it is important for humans to eat foods that contain proteins. For more on proteins, click here. The next of the four molecules of life are carbohydrates. Carbohydrates are an important source of energy. They also provide structural support for cells and help with communication between cells.
A carbohydrate molecule is made of atoms of carbon, hydrogen and oxygen. They are found in the form of either a sugar or many sugars linked together. A single sugar molecule is known as a monosaccharide. Two sugar molecules bonded together is a disaccharide and many sugar molecules make a polysaccharide. The three different types of carbohydrates are all important for different reasons. Carbohydrates are the most important sources of energy for many organisms. Personal tools Web Editor Log in.
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Molecules of life
Search Site. DNA DNA or deoxyribonucleic acid is the molecule that carries the genetic information in all cellular forms of life and some viruses.
Each nucleotide consists of three components: a nitrogenous base: cytosine C , guanine G , adenine A or thymine T a five-carbon sugar molecule deoxyribose in the case of DNA a phosphate molecule The backbone of the polynucleotide is a chain of sugar and phosphate molecules. Strand of polynucleotides DNA's ability to store - and transmit - information lies in the fact that it consists of two polynucleotide strands that twist around each other to form a double-stranded helix. Double strand of polynucleotides The double helix of the complete DNA molecule resembles a spiral staircase, with two sugar phosphate backbones and the paired bases in the centre of the helix.
DNA helix showing nitrogenous bases It is the order of the bases along a single strand that constitutes the genetic code. There are a two points to note about the genetic code: It is universal. All life on Earth uses the same code with a few minor exceptions. It is degenerate. Each amino acid can be coded for by more than one codon.
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A codon table sets out how the triplet codons code for specific amino acids. DNA replication The enzyme helicase breaks the hydrogen bonds holding the two strands together, and both strands can then act as templates for the production of the opposite strand. Genes The gene is the basic physical and functional unit of heredity.
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Genes consist of three types of nucleotide sequence: coding regions, called exons, which specify a sequence of amino acids non-coding regions, called introns, which do not specify amino acids regulatory sequences, which play a role in determining when and where the protein is made and how much is made The structural components of a gene Read more about gene expression and regulation A human being has 20, to 25, genes located on 46 chromosomes 23 pairs. Chromosomes Eukaryotic chromosomes The label eukaryote is taken from the Greek for 'true nucleus', and eukaryotes all organisms except viruses, Eubacteria and Archaea are defined by the possession of a nucleus and other membrane-bound cell organelles.
Chromosome unraveling to show the base pairings of the DNA The chromosomes - and the DNA they contain - are copied as part of the cell cycle, and passed to daughter cells through the processes of mitosis and meiosis. Read more about the cell cycle, mitosis and meiosis Human beings have 46 chromosomes, consisting of 22 pairs of autosomes and a pair of sex chromosomes : two X sex chromosomes for females XX and an X and Y sex chromosome for males XY.
Karyotype of a human male Prokaryotic chromosomes The prokaryotes Greek for 'before nucleus' - including Eubacteria and Archaea lack a discrete nucleus, and the chromosomes of prokaryotic cells are not enclosed by a separate membrane.
Proteins are essential to life!
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