Introduction
Carbohydrates are sugar molecules that play crucial roles in our body system. Carbohydrates are involved in several significant functions in our body, which are discussed below. First, carbohydrates provide energy and regulate blood glucose in the body (Stoker, 2015). Once eaten, carbohydrates are digested and then consequently broken further into glucose. Second, carbohydrates provide stored energy in our body system (Stoker, 2015). Lastly, carbohydrates also help in sparing protein and preventing ketosis. Consumption of carbs regularly helps to avoid protein depletion as an energy source.
Fructose is a monosaccharide typically found in honey, fruits such as apples, pears, figs, dates, and prunes. It can also be found in vegetables such as asparagus, mushrooms, onions, and red peppers (Stoker, 2015). One ketonic group, five hydroxyl groups, two primary alcoholic groups, and three secondary alcoholic groups are among the functional groups found in fructose.
Fructose is a crystalline substance that is very soluble in water, less in alcohol but insoluble in either (Stoker, 2015). Glycogen acts as a vital energy source by supplying glucose to tissues all over the body. Glucose is the only monosaccharide that makes the building block of glycogen. Glycogen occurs naturally in the liver and the skeletal muscle cell of animals.
Cellulose is a polysaccharide made up of hundreds to thousands of glucose molecules joined together to form a chain. At the same time, starch is a polysaccharide carbohydrate made up of several glucose molecules linked together by glycosidic bonds. There are beta 1, 4 links between glucose molecules in cellulose, but between glucose molecules in starch, there are 1, 4 alpha bonds (Tortora & Derrickson, 2018). Furthermore, cellulose is a stiff structural carbohydrate, whereas starch is a storage molecule, the functional difference between the two (Tortora & Derrickson, 2018). Sucrose and lactose are examples of disaccharides, among many others. Sucrose and lactose are broken down into monosaccharides by hydrolysis (Tortora & Derrickson, 2018). This process is facilitated by enzymes sucrases and lactases, respectively. These enzymes aid in the digestion of various carbohydrates in the body (Tortora & Derrickson, 2018). Sucrases, for example, aid in the conversion of sucrose to glucose and fructose, while lactases convert lactose to glucose and galactose.
Lipids
Essential fatty acids refer to polyunsaturated fatty acids that must be obtained from food because they cannot be synthesized by the body but are vital for health. Only two fatty acids have been identified as necessary for human health: alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid) (Rajna et al., 2018). Alpha-linolenic acid is mainly found in plant oils such as soybean, canola oils, and flaxseed. Triacylglycerols (TAG) are three fatty acids and a glycerol moiety (Rajna et al., 2018). The three fatty acids are esterified to the carbon-hydroxyl groups of the glycerol (Rajna et al., 2018). Each TAG may comprise a variety of fatty acids. These fatty acids are esterified in three distinct locations on glycerol, marked by the stereospecific numbering system (Sn): sn-1, sn-2, and sn-3 (Rajna et al., 2018). The small intestine participates significantly in the metabolism of dietary triglycerides (TGs).
The initial phase in lipid digestion occurs in the mouth and stomach, where salivary and gastric lipases work in concert. After that, pancreatic lipases and bile acids work in concert to further break down lipids, enabling their absorption in the small intestine. Lipases hydrolyze TGs into fatty acids and monoglycerides, allowing the intestinal epithelium to absorb lipids (Dhull & Punia, 2020). Once inside the small intestine, they are resynthesized, and the monoglycerides and fatty acids reach the endoplasmic reticulum membrane (Dhull & Punia, 2020). The remaining lipids are trapped in cytosolic lipid droplets.
There are three types of lipids in the body; triglycerides, sterols, and phospholipids. Triglycerides are the primary fats we store in our bodies, which help produce energy (Dhull & Punia, 2020). Phospholipids make up cell membranes and lipid carrier molecules (Dhull & Punia, 2020). The plasma membrane comprises a bilayer of phospholipids connected by their hydrophobic, fatty acid tails (Dhull & Punia, 2020). The membrane’s surface is densely packed with proteins, some of which span the membrane. Carbohydrates are covalently linked to several proteins and lipids on the membrane’s outward-facing surface (Dhull & Punia, 2020). These combine to produce complexes that serve as a means of identifying the cell from other cells. The cell membrane helps in the molecular transport of food and water across the membrane, acting as an enzyme hence controlling all metabolic processes (Dhull & Punia, 2020). Furthermore, the cell membrane enables a cell to cell communication and recognition to work together in tissues, among others. Lipids in the cell membrane play vital roles as chemical messengers that transport signals to other cells.
Lipids also store and provide energy during fasting and form structural components of cells. Additionally, lipids help maintain body temperature due to layers of subcutaneous fat under the skin (Dhull & Punia, 2020). Proteins in the cell membrane also play various roles, such as playing enzymatic functions like breaking down sucrose into carbohydrates and then monosaccharides (Dhull & Punia, 2020). Proteins help intercellular joining via the gap junction and the tight junction, allowing cells to communicate with each other (Dhull & Punia, 2020). Proteins also aid in transportation which will enable hydrophilic molecules to pass through the membranes.
The precursor for bile acid synthesis is cholesterol which is a type of lipid. Bile acids help in the digestion of lipids because bile acids are amphipathic – contain a hydrophilic and hydrophobic face (Dhull & Punia, 2020). This property allows bile acids to facilitate emulsifying fats and the formation of micelles. Bile acids are essential for the digestion of lipids because bile works as an emulsifier during fat digestion, breaking big fat globules into smaller emulsion droplets (Dhull & Punia, 2020). Emulsified fats give a more significant surface area for fat-digesting enzymes (lipase) to work, which speeds up the process since bile is an excellent solvent.
Proteins
Proteins play the following four primary functions in the body. First, proteins help in defense where it protects the body against foreign pathogens for example immunoglobulin (Damodaran, 2017). Second, proteins act as digestive enzymes that help digest food by catabolizing nutrients into monomeric units, such as amylase (Damodaran, 2017). Third, they are essential in structural construction like cytoskeleton, for example, actin (Damodaran, 2017). Fourth, they help transport and carry substances in the blood or lymph throughout the body, for example, hemoglobin (Damodaran, 2017). Glutathione is a tripeptide consisting of three amino acids; glutamate, cysteine, and glycine Damodaran (Damodaran, 2017). Glutathione helps in combating free radicals in the body since it acts as an antioxidant.
Proteins are classified into three classes: primary, secondary, and tertiary. The unique amino acid sequence determines the primary structure. Local folding determines the secondary structure of the polypeptide into systems such as the helix and -pleated sheet (Damodaran, 2017). The tertiary structure is the overall three-dimensional structure. Enzymes function as catalysts, decreasing the activation energy of chemical processes (Damodaran, 2017). Amylase is an enzyme essential in the digestion of carbohydrates, and it breaks down starches into sugars. Lipase is an enzyme responsible for breaking fats into fatty acids and glycerol (Damodaran, 2017). Proteases are enzymes that break down proteins into amino acids. They play a role in cell division, immune function, and blood clotting. Cofactors are molecules that function by assisting in enzyme activity. There are two types of cofactors: organic cofactors, for example, Flavin and heme, and inorganic cofactors, such as zinc and iron.
Nucleic Acids, Cells, and Transport
Guanine- DNA, Cytosine- DNA, D- Ribose- RNA, Thiamine- DNA, Uracil- RNA, and D- Deoxyribose- DNA. DNA is built from chemical building units referred to as nucleotides (Rádis-Baptista et al., 2107). Three components make up these building blocks: a phosphate group, a sugar group, and four different forms of nitrogen bases. The nitrogenous base includes adenine, guanine, cytosine, and thymine (Rádis-Baptista et al., 2107). Two of the bases, adenine, and guanine have a double ring structure. There are three major types of RNA: messenger RNA, which transports genetic information from a cell’s nucleus to its cytoplasm (Rádis-Baptista et al., 2017). Ribosomal RNA directs the translation of mRNA into proteins. Lastly, transfer RNA, which transfers amino acids to the ribosome.
Simple diffusion is when molecules move directly across the membrane with no assistance from a protein carrier. Facilitated diffusion is a process where the movement of molecules occurs down a concentration gradient with the aid of a carrier protein across a lipid bilayer (Rádis-Baptista et al., 2107). Active transport is the movement of molecules into or out of a cell from a lower concentration region to a higher concentration against the concentration gradient. The function of ribosomes in the cell is translation which allows for the production of proteins. Lysosomes are involved in the signaling and recycling of cellular waste (Rádis-Baptista et al., 2107). The nucleus’s function is to control and regulate all activities in the cell (Rádis-Baptista et al., 2107). The mitochondria produce most of the chemical energy required to power the metabolic activities occurring within the cell.
References
Damodaran, S. (2017). Food proteins: an overview. Food proteins and their applications (pp. 1-24). CRC Press.
Dhull, S. B., & Punia, S. (2020). Essential Fatty Acids: Introduction. In Essential Fatty Acids (pp. 1-18). CRC Press.
Rádis-Baptista, G., Campelo, I. S., Morlighem, J. É. R., Melo, L. M., & Freitas, V. J. (2017). Cell-penetrating peptides (CPPs): From delivery of nucleic acids and antigens to transduction of engineered nucleases for application in transgenesis. Journal of Biotechnology, 252, 15-26. Web.
Rajna, A., Gibling, H., Sarr, O., Matravadia, S., Holloway, G. P., & Mutch, D. M. (2018). Alpha-linolenic acid and linoleic acid differentially regulate the skeletal muscle secretome of obese Zucker rats. Physiological Genomics, 50(8), 580-589. Web.
Stoker, H. S. (2015). General, organic, and biological chemistry (7th ed). Cengage Learning.
Tortora, G. J., & Derrickson, B. H. (2018). Principles of anatomy and physiology. John Wiley & Sons.