An organism is a living thing composed of many various types of cells with complex molecular structures. All living organisms shared seven characteristics: cellular organization, energy use and metabolism, sensitivity, regulation and homeostasis, evolutionary adaptation, growth and development, and reproduction. All organisms are composed of one or more cells that have particular arrangements and functions. The structures and functions of the human building blocks are one of the most complicated among all. Researchers have been studying the building blocks of human body and one of the purposes is how they regenerate damaged heart tissues for the treatment of heart disease. The hearts of a human and zebrafish are quite in common. Both are made up of muscle tissues to pump blood to the entire body, and cardiac cycle is regular and rhythmic. However, human heart could not replace damaged heart tissues, whereas zebrafish can form clot within seconds that stops bleeding and gradually replace the lost tissue. In order to treat cardiovascular disease, the building blocks of human body have the potential to aid in heart treatment and development.
The blueprint: DNA, genes and chromosomes
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For the construction of living organisms, genetic material is significant as it provides blueprint for the organization, development and function of living things. DNA carries genetic information to specify the structure and function of an organism. During the process of cell division, DNA is replicated and transmitted from cell to cell. This genetic information is passed down to the next generation, from parent to offspring. A slight variation in genetic material causes differences within species. DNA is a linear polymer composed of four nucleic acid bases: adenine (A), cytosine (C), guanine (G) and thymine (T) (Stryer et al, 2007). Sequence of bases along DNA strands determines how the genetic information is stored. In a eukaryotic cell, DNA is wrapped around histone proteins forming chromatin. As cells enter mitosis, chromatin folds upon themselves, forming compact chromosomes which are essential for cellular division.
There are twenty-three pairs of chromosomes in a human cell. Twenty-two of these pairs are autosomes that determine the body characters, while one pair is the sex chromosomes, X and Y chromosomes, which determine gender of an organism (Cooper, 2009). For treatment of heart disease, genes are introduced into damaged heart where they are synthesized to create growth factor products that can aid in restoring normal function. Gene therapy promotes new growth of blood vessels (Angiogenesis). Genes that encode for vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) are investigated the most. When DNA is injected into heart, genes are expressed, producing growth factor that promotes the formation of blood vessels. This contributes to better perfusion as there is an increase in blood supply to heart tissue, and thus improved cardiac function.
Raw materials: proteins and enzymes
While nucleic acids carry the genetic information, proteins function to carry out the tasks directed by the information. Proteins have different roles and functions. They provide immune protection against infection, transport and store small molecules and ions, provide structural support in cells and tissues, generate movement and transmit nerve impulses between cells. However, proteins have the most essential property that is to act as enzymes (Raven et al, 2011). Proteins are linear polymers built of twenty different amino acids joined together by peptide bonds between a carboxyl and amino group. Chemistry nature of amino acid side chain affects the shape of a protein and the shape determines its function. Protein structure has a hierarchy of four levels: primary, secondary, tertiary, and quaternary (Brooker et al, 2008).
Enzymes are globular proteins with active sites that have specific shapes due to the tertiary structure of protein. Chemical reaction takes place at the active site of an enzyme where substrate binds to it, forming enzyme-substrate complex. Biochemical reactions are catalyzed in the presence of enzymes. As biological catalysts, enzymes do not affect equilibrium constant. They increase the rate of chemical reactions by lowering activation energy barrier, without themselves being consumed by it. In addition, measuring the cardiac enzymes levels in blood can help diagnose a heart attack. When heart muscle is injured, enzymes: creatine phosphokinase (CPK) and creatine kinase (CK), and proteins: troponin I (TnI) and troponin T (TnT), leaked out of the damaged heart muscle cells, causing a rise of cardiac enzymes level in the bloodstream.
Building blocks: cell structure and diversity
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All living organisms are composed of one or more cells. Cells are the building blocks of life because they are the smallest units of living organisms. Most cells have common features which are the nucleus, cytoplasm, ribosomes and plasma membrane. Plasma membrane is a phospholipid bilayer that is impermeable to water and water-soluble molecules. There are proteins embedded in cell membrane, which are responsible for cell adhesion, cell signaling and membrane transport. Proteins are synthesized in the nucleus where genetic material is located. The content of nucleus is separated from cytoplasm by nuclear membrane to protect the genetic material.
In nucleolus, ribosomal RNA is transcribed and ribosomes are assembled. Ribosomes composed of two subunits and they function to translate mRNA into polypeptide chain (Brooker et al, 2008). One of the three principles of cell theory states that new cells arise from a previously existing cell by cell division. Stem cells are undifferentiated cells that have the ability to make identical copies of them, and give rise to specialized cells, such as blood cells, heart muscle cells and nerve cells. Stem cell therapy has been used to treat heart disease. Stem cells are collected from bone marrow inside patient's hip and are separated from red blood cells by centrifugation. When the cells are injected into the patient's heart, they migrate into the ischemic cardiac muscle, and differentiate into cardiomyocytes which regenerate the damaged tissue and form new blood vessels.
Assembly units: tissue formation and function
There are about 210 various kinds of cell in human body. A group of cells with similar structure is organized into tissues to perform a specific function. The four general types of tissues in vertebrates are epithelial, connective, muscle, and nerve tissue. Epithelial tissues are continuous sheets of cells that are joined together via tight junctions. They cover all body surfaces, forming barrier to protect the body from the outside environment. Examples of epithelium are the skin and intestinal lining. Connective tissues have abundant extracellular material forming a matrix between cells that are spaced widely apart. They function to provide structural support for the tissues holding them together. Connective tissues include fat tissues, ligaments and cartilage. Muscle tissues are active contractile tissue formed from muscle cells. They contain microfilaments: actin and myosin, which can generate mechanical force that promotes body movement. Nervous tissues are made up of neurons and neuroglia cells. Neurons receive incoming signals and transmit impulses throughout the body, while neuroglia provide nutrients to neurons, assisting the transmission of nerve impulses (Brooker et al, 2008).
Larger modules: organ systems
Group of tissues arranged together, performing a specific function, to form an organ. Different organs cooperate to provide a common function in an organ system. There are about 10 major organ systems in human body. One of them is the Circulatory system which is composed of heart and blood vessels. These organs cooperate in the pump blood and distribute substances to all parts of the body. Specialized heart cells generate electrical impulses that cause the heart to beat, by contracting and relaxing. During cardiac cycle, beating of heart creates pressure that pumps blood to cells and tissues of the body.
Blood vessels are networks of hollow tubes that allow blood to flow to all areas of body. Blood carries nutrients to cells and removes gaseous wastes from the body. Microcirculation is a process where substances are exchanged between the blood and the interstitial ï¬‚uid. When human grows older, arteries lose their elasticity due to the alterations in the structure vascular wall. This increases the risk of cardiovascular disease. Some other risk factors are tobacco smoking, lack of exercise, and air pollution. Long-term exposure to air pollution hardens arteries, and increases rate of atherosclerosis. Heart failure is caused when plaque builds up in the artery, obstructing the flow of blood to the heart, leading to insufficient supply of oxygen and nutrients supply of the heart.
Figure: Levels of Organization within the human body
Taken from: http://www2.lbsdk12.com/science/Anatomy/anatomyunit101.html
Without one of these biological elements, it is unlikely to build a complete organism. Organism is highly ordered from simplest atoms to complex multicellular organisms. Cells organized into tissues, and then into organs and organ systems. Mutation can occur when there is a change in DNA in a gene, which alters the shape and function of amino acids in protein. This can tremendously affect the cell and the organism as a whole. A change in biosphere can also affect organisms living in it (Raven et al, 2011). Group of organisms occupy an environment forming population, which then extends to community, populations of different species. Interactions of a community of organisms with their environment formed ecosystem, and biosphere, the global ecosystems on the entire planet. Thus, the hierarchy and elements of life is linked and dependent on each other (Brooker et al, 2008).
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