Common disaccharides are the grain sugar maltose , made of two glucose molecules; the milk sugar lactose , made of a galactose and a glucose molecule; and the table sugar sucrose , made of a glucose and a fructose molecule Figure 3. Polysaccharides, also called glycans , are large polymers composed of hundreds of monosaccharide monomers.
Unlike mono- and disaccharides, polysaccharides are not sweet and, in general, they are not soluble in water. Like disaccharides, the monomeric units of polysaccharides are linked together by glycosidic bonds. Polysaccharides are very diverse in their structure. Three of the most biologically important polysaccharides— starch , glycogen , and cellulose —are all composed of repetitive glucose units, although they differ in their structure Figure 4.
Cellulose consists of a linear chain of glucose molecules and is a common structural component of cell walls in plants and other organisms. Glycogen and starch are branched polymers; glycogen is the primary energy-storage molecule in animals and bacteria, whereas plants primarily store energy in starch.
The orientation of the glycosidic linkages in these three polymers is different as well and, as a consequence, linear and branched macromolecules have different properties. Modified glucose molecules can be fundamental components of other structural polysaccharides.
Examples of these types of structural polysaccharides are N-acetyl glucosamine NAG and N-acetyl muramic acid NAM found in bacterial cell wall peptidoglycan. Polymers of NAG form chitin , which is found in fungal cell walls and in the exoskeleton of insects. Figure 4. Starch, glycogen, and cellulose are three of the most important polysaccharides.
In the top row, hexagons represent individual glucose molecules. Micrographs bottom row show wheat starch granules stained with iodine left , glycogen granules G inside the cell of a cyanobacterium middle , and bacterial cellulose fibers right. Chitin is a structural polymer found in cell walls of fungi and exoskeletons of some animals. Skip to main content.
Microbial Biochemistry. Occurs free in plants, fruits, honey, body fluids, including CSF, blood, lymph. It is the major end-product of CHO digestion by non-ruminants and is therefore a primary energy form for non-ruminants. It is a major component of many oligosaccharides with galactose forms lactose and polysaccharides such as starch and cellulose. In solution D-glucose exists as an equilibrium mixture of the straight chain form with two pyranose ring forms.
Effectively, carbon atom number one reacts with carbon atom number five forming a ring. In fact two forms of the structure exist, called anomers.
If the hydrogen atom is above carbon atom one then it is called an alpha anomer but if the hydrogen atom is below the carbon atom it is called a beta anomer.
This structural information is very important because it governs how molecules of glucose join together to form larger molecules. Starch is a polymer of the a- form and is water soluble and digestible by animal enzymes. Cellulose is a polymer of the b- form, it is not soluble and is not digestible by animal enzymes. Changing from a to b via an open chain structure is called mutarotation, and it requires the O-C bond to be broken to allow the C to swivel the H and OH upside down.
Then the bond is remade. The other monosaccharides also make ring forms. D-Fructose — a ketohexose, found in honey, green leaves, seeds, and stems of many plants, as the main unit in fructans which are common in young grasses, in roots as the storage polysaccharide inulin, and as a component of the disaccharide sucrose with glucose. D-Galactose — an aldohexose, not found free, most important as a component of the disaccharide lactose, milk sugar with glucose.
Combining the H of a hydroxyl group on a sugar with an alcohol group or another hydroxyl group causes an Esterification or Condensation reaction to yield a glycoside. This occurs at C atom one, the anomeric C atom. Since sugars contain alcohol groups and hydroxyl groups, they can combine with other sugars to form disaccharides, tri, tetra, etc. Complex carbohydrates such as cellulose , starch , and glycogen are those that need more time to be digested and metabolized.
They often are high in fiber and unlike simple carbohydrates they are less likely to cause spikes in blood sugar. The most fundamental type is the simple sugars called monosaccharide s. This means that they cannot be broken down any further into simpler sugars by hydrolysis.
Nevertheless, monosaccharides can combine with each other to form more complex types. Glycosidic bonds also called glycosidic linkages are the covalent bonds that join monosaccharides. The combination of two simple sugars is called a disaccharide whereas carbohydrates consisting of three to ten simple sugars are called oligosaccharide s, and those with a larger number of monosaccharide units are called polysaccharide s.
The chemical process of joining monosaccharide units is referred to as dehydration synthesis since it results in the release of water as a byproduct. The process, though, is reversible. Complex carbohydrates may be broken down into simple sugars, such as in glycogenolysis where stored glycogen is broken down into glucose units that could be used in energy metabolism.
The ratio of hydrogen atoms to oxygen atoms is often An exception to this is deoxyribose , a type of monosaccharide found in DNA. Because of this chemical formula rule, monosaccharides and other carbohydrates are referred to as hydrates of carbon.
Monosaccharides are often colorless, crystalline solids, and sweet-tasting. They can be dissolved in water and occur as syrups or liquid sugar.
Just like the other carbohydrates, monosaccharides are organic compounds. Monosaccharides can be classified by the number of carbon atoms they contain. The groups are as follows:. Fructose , glucose , and galactose are regarded as dietary monosaccharides since they are readily absorbed by the small intestines. They are hexoses with a chemical formula: C 6 H 12 O 6.
Glucose and galactose are aldoses whereas fructose is a ketose. Glucose is a monosaccharide that occurs naturally and is ubiquitous. It can join with other monosaccharide units to form disaccharide s: maltose i. Glucose is one of the products of photosynthesis in plants and other photosynthetic organisms. In plants, glucose molecules are stored as repeating units of sugar e.
DNA is the genetic material found in all living organisms, ranging from single-celled bacteria to multicellular mammals. It is found in the nucleus of eukaryotes and in the chloroplasts and mitochondria. In prokaryotes, the DNA is not enclosed in a membranous envelope, but rather free-floating within the cytoplasm. The entire genetic content of a cell is known as its genome and the study of genomes is genomics. In eukaryotic cells, but not in prokaryotes, DNA forms a complex with histone proteins to form chromatin, the substance of eukaryotic chromosomes.
A chromosome may contain tens of thousands of genes. Many genes contain the information to make protein products; other genes code for RNA products.
The other type of nucleic acid, RNA, is mostly involved in protein synthesis. In eukaryotes, the DNA molecules never leave the nucleus but instead use an intermediary to communicate with the rest of the cell. Each nucleotide is made up of three components:. Each nitrogenous base in a nucleotide is attached to a sugar molecule, which is attached to one or more phosphate groups.
DNA and RNA : A nucleotide is made up of three components: a nitrogenous base, a pentose sugar, and one or more phosphate groups. Bases can be divided into two categories: purines and pyrimidines. Purines have a double ring structure, and pyrimidines have a single ring. The nitrogenous bases are organic molecules and are so named because they contain carbon and nitrogen.
They are bases because they contain an amino group that has the potential of binding an extra hydrogen, and thus, decreasing the hydrogen ion concentration in its environment, making it more basic. Adenine and guanine are classified as purines. The primary structure of a purine consists of two carbon-nitrogen rings. Cytosine, thymine, and uracil are classified as pyrimidines which have a single carbon-nitrogen ring as their primary structure. Each of these basic carbon-nitrogen rings has different functional groups attached to it.
In molecular biology shorthand, the nitrogenous bases are simply known by their symbols A, T, G, C, and U. The difference between the sugars is the presence of the hydroxyl group on the second carbon of the ribose and hydrogen on the second carbon of the deoxyribose. The phosphodiester linkage is not formed by simple dehydration reaction like the other linkages connecting monomers in macromolecules: its formation involves the removal of two phosphate groups.
A polynucleotide may have thousands of such phosphodiester linkages. An amino acid contains an amino group, a carboxyl group, and an R group, and it combines with other amino acids to form polypeptide chains. Amino acids are the monomers that make up proteins.
Every amino acid also has another atom or group of atoms bonded to the central atom known as the R group. This R group, or side chain, gives each amino acid proteins specific characteristics, including size, polarity, and pH. Amino acid structure : Amino acids have a central asymmetric carbon to which an amino group, a carboxyl group, a hydrogen atom, and a side chain R group are attached.
This amino acid is unionized, but if it were placed in water at pH 7, its amino group would pick up another hydrogen and a positive charge, and the hydroxyl in its carboxyl group would lose and a hydrogen and gain a negative charge. There are 21 amino acids present in proteins, each with a specific R group or side chain. Ten of these are considered essential amino acids in humans because the human body cannot produce them and they must be obtained from the diet.
All organisms have different essential amino acids based on their physiology. Types of amino acids : There are 21 common amino acids commonly found in proteins, each with a different R group variant group that determines its chemical nature. Which categories of amino acid would you expect to find on the surface of a soluble protein, and which would you expect to find in the interior? What distribution of amino acids would you expect to find in a protein embedded in a lipid bilayer?
The chemical composition of the side chain determines the characteristics of the amino acid. Amino acids such as valine, methionine, and alanine are nonpolar hydrophobic , while amino acids such as serine, threonine, and cysteine are polar hydrophilic. The side chains of lysine and arginine are positively charged so these amino acids are also known as basic high pH amino acids. Proline is an exception to the standard structure of an amino acid because its R group is linked to the amino group, forming a ring-like structure.
Amino acids are represented by a single upper case letter or a three-letter abbreviation. For example, valine is known by the letter V or the three-letter symbol val. Each amino acid is attached to another amino acid by a covalent bond, known as a peptide bond. When two amino acids are covalently attached by a peptide bond, the carboxyl group of one amino acid and the amino group of the incoming amino acid combine and release a molecule of water.
Any reaction that combines two monomers in a reaction that generates H 2 O as one of the products is known as a dehydration reaction, so peptide bond formation is an example of a dehydration reaction.
Peptide bond formation : Peptide bond formation is a dehydration synthesis reaction. The carboxyl group of one amino acid is linked to the amino group of the incoming amino acid. In the process, a molecule of water is released. The resulting chain of amino acids is called a polypeptide chain. Each polypeptide has a free amino group at one end. This end is called the N terminal, or the amino terminal, and the other end has a free carboxyl group, also known as the C or carboxyl terminal.
When reading or reporting the amino acid sequence of a protein or polypeptide, the convention is to use the N-to-C direction. That is, the first amino acid in the sequence is assumed to the be one at the N terminal and the last amino acid is assumed to be the one at the C terminal. Although the terms polypeptide and protein are sometimes used interchangeably, a polypeptide is technically any polymer of amino acids, whereas the term protein is used for a polypeptide or polypeptides that have folded properly, combined with any additional components needed for proper functioning, and is now functional.
Proteins perform many essential physiological functions, including catalyzing biochemical reactions. Proteins perform essential functions throughout the systems of the human body.
These long chains of amino acids are critically important for:. Proteins a polymer are macromolecules composed of amino acid subunits the monomers. These amino acids are covalently attached to one another to form long linear chains called polypeptides, which then fold into a specific three-dimensional shape.
Sometimes these folded polypeptide chains are functional by themselves. Other times they combine with additional polypeptide chains to form the final protein structure. Sometimes non-polypeptide groups are also required in the final protein. For instance, the blood protein hemogobin is made up of four polypeptide chains, each of which also contains a heme molecule, which is ring structure with an iron atom in its center.
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