File Name: cellular level of organization anatomy and physiology .zip
Body functions are the physiological or psychological functions of body systems. The body's functions are ultimately its cells' functions. Survival is the body's most important business.
The nucleus is generally considered the control center of the cell because it stores all of the genetic instructions for manufacturing proteins. Interestingly, some cells in the body, such as muscle cells, contain more than one nucleus [link] , which is known as multinucleated.
Other cells, such as mammalian red blood cells RBCs , do not contain nuclei at all. RBCs eject their nuclei as they mature, making space for the large numbers of hemoglobin molecules that carry oxygen throughout the body [link]. Without nuclei, the life span of RBCs is short, and so the body must produce new ones constantly.
View the University of Michigan WebScope to explore the tissue sample in greater detail. Inside the nucleus lies the blueprint that dictates everything a cell will do and all of the products it will make.
This information is stored within DNA. Each cell in your body with the exception of germ cells contains the complete set of your DNA. The following section will explore the structure of the nucleus and its contents, as well as the process of DNA replication.
Like most other cellular organelles, the nucleus is surrounded by a membrane called the nuclear envelope. This membranous covering consists of two adjacent lipid bilayers with a thin fluid space in between them. Spanning these two bilayers are nuclear pores. A nuclear pore is a tiny passageway for the passage of proteins, RNA, and solutes between the nucleus and the cytoplasm. Proteins called pore complexes lining the nuclear pores regulate the passage of materials into and out of the nucleus.
Inside the nuclear envelope is a gel-like nucleoplasm with solutes that include the building blocks of nucleic acids.
The nucleolus is a region of the nucleus that is responsible for manufacturing the RNA necessary for construction of ribosomes. The genetic instructions that are used to build and maintain an organism are arranged in an orderly manner in strands of DNA. Within the nucleus are threads of chromatin composed of DNA and associated proteins [link]. Along the chromatin threads, the DNA is wrapped around a set of histone proteins.
A nucleosome is a single, wrapped DNA-histone complex. Multiple nucleosomes along the entire molecule of DNA appear like a beaded necklace, in which the string is the DNA and the beads are the associated histones. It is estimated that humans have almost 22, genes distributed on 46 chromosomes. In order for an organism to grow, develop, and maintain its health, cells must reproduce themselves by dividing to produce two new daughter cells, each with the full complement of DNA as found in the original cell.
Billions of new cells are produced in an adult human every day. Only very few cell types in the body do not divide, including nerve cells, skeletal muscle fibers, and cardiac muscle cells. The division time of different cell types varies.
Epithelial cells of the skin and gastrointestinal lining, for instance, divide very frequently to replace those that are constantly being rubbed off of the surface by friction. Each side rail of the DNA ladder is composed of alternating sugar and phosphate groups [link].
The two sides of the ladder are not identical, but are complementary. Because of their shape and charge, the two bases that compose a pair always bond together. Adenine always binds with thymine, and cytosine always binds with guanine. The particular sequence of bases along the DNA molecule determines the genetic code.
Therefore, if the two complementary strands of DNA were pulled apart, you could infer the order of the bases in one strand from the bases in the other, complementary strand.
After a great deal of debate and experimentation, the general method of DNA replication was deduced in by two scientists in California, Matthew Meselson and Franklin Stahl. This method is illustrated in [link] and described below. Stage 1: Initiation. The two complementary strands are separated, much like unzipping a zipper. Special enzymes, including helicase , untwist and separate the two strands of DNA.
Stage 2: Elongation. Each strand becomes a template along which a new complementary strand is built. DNA polymerase brings in the correct bases to complement the template strand, synthesizing a new strand base by base. This growing strand continues to be built until it has fully complemented the template strand.
Stage 3: Termination. Once the two original strands are bound to their own, finished, complementary strands, DNA replication is stopped and the two new identical DNA molecules are complete.
Each new DNA molecule contains one strand from the original molecule and one newly synthesized strand. As you might imagine, it is very important that DNA replication take place precisely so that new cells in the body contain the exact same genetic material as their parent cells. Mistakes made during DNA replication, such as the accidental addition of an inappropriate nucleotide, have the potential to render a gene dysfunctional or useless.
Fortunately, there are mechanisms in place to minimize such mistakes. A DNA proofreading process enlists the help of special enzymes that scan the newly synthesized molecule for mistakes and corrects them. Once the process of DNA replication is complete, the cell is ready to divide. You will explore the process of cell division later in the chapter. Watch this video to learn about DNA replication. DNA replication proceeds simultaneously at several sites on the same molecule.
What separates the base pair at the start of DNA replication? The nucleus is the command center of the cell, containing the genetic instructions for all of the materials a cell will make and thus all of its functions it can perform. The nucleus is encased within a membrane of two interconnected lipid bilayers, side-by-side. This nuclear envelope is studded with protein-lined pores that allow materials to be trafficked into and out of the nucleus.
The nucleus contains one or more nucleoli, which serve as sites for ribosome synthesis. The nucleus houses the genetic material of the cell: DNA. DNA is normally found as a loosely contained structure called chromatin within the nucleus, where it is wound up and associated with a variety of histone proteins. When a cell is about to divide, the chromatin coils tightly and condenses to form chromosomes. There is a pool of cells constantly dividing within your body. The result is billions of new cells being created each day.
A variety of enzymes are enlisted during DNA replication. These enzymes unwind the DNA molecule, separate the two strands, and assist with the building of complementary strands along each parent strand.
The original DNA strands serve as templates from which the nucleotide sequence of the new strands are determined and synthesized. When replication is completed, two identical DNA molecules exist. Each one contains one original strand and one newly synthesized complementary strand. Place the following structures in order from least to most complex organization: chromatin, nucleosome, DNA, chromosome. DNA replication is said to be semiconservative because, after replication is complete, one of the two parent DNA strands makes up half of each new DNA molecule.
The other half is a newly synthesized strand. Why is it important that DNA replication take place before cell division? What would happen if cell division of a body cell took place without DNA replication, or when DNA replication was incomplete? During cell division, one cell divides to produce two new cells.
In order for all of the cells in your body to maintain a full genome, each cell must replicate its DNA before it divides so that a full genome can be allotted to each of its offspring cells. If DNA replication did not take place fully, or at all, the offspring cells would be missing some or all of the genome. This could be disastrous if a cell was missing genes necessary for its function and health. By the end of this section, you will be able to: Describe the structure and features of the nuclear membrane List the contents of the nucleus Explain the organization of the DNA molecule within the nucleus Describe the process of DNA replication.
The nucleus and mitochondria share which of the following features? Which of the following structures could be found within the nucleolus? Place the following structures in order from least to most complex organization: chromatin, nucleosome, DNA, chromosome DNA, nucleosome, chromatin, chromosome nucleosome, DNA, chromosome, chromatin DNA, chromatin, nucleosome, chromosome nucleosome, chromatin, DNA, chromosome.
Which of the following is part of the elongation step of DNA synthesis?
Before you begin to study the different structures and functions of the human body, it is helpful to consider its basic architecture; that is, how its smallest parts are assembled into larger structures. It is convenient to consider the structures of the body in terms of fundamental levels of organization that increase in complexity, such as from smallest to largest : chemicals, cells, tissues, organs, organ systems, and an organism. The organization of the body often is discussed in terms of the distinct levels of increasing complexity, from the smallest chemical building blocks to a unique human organism. To study the chemical level of organization, scientists consider the simplest building blocks of matter: subatomic particles, atoms and molecules. All matter in the universe is composed of one or more unique pure substances called elements. Examples of these elements are hydrogen, oxygen, carbon, nitrogen, calcium, and iron.
The nucleus is generally considered the control center of the cell because it stores all of the genetic instructions for manufacturing proteins. Interestingly, some cells in the body, such as muscle cells, contain more than one nucleus [link] , which is known as multinucleated. Other cells, such as mammalian red blood cells RBCs , do not contain nuclei at all. RBCs eject their nuclei as they mature, making space for the large numbers of hemoglobin molecules that carry oxygen throughout the body [link]. Without nuclei, the life span of RBCs is short, and so the body must produce new ones constantly.
Living organisms are made up of four levels of organization: cells, tissues, organs, and organ systems. An organism is made up of four levels of organization: cells, tissues, organs, and organ systems. These levels reduce complex anatomical structures into groups; this organization makes the components easier to understand. The first and most basic level of organization is the cellular level. A cell is the basic unit of life and the smallest unit capable of reproduction. While cells vary greatly in their structure and function based on the type of organism, all cells have a few things in common. Cells are made up of organic molecules, contain nucleic acids such as DNA and RNA , are filled with fluid called cytoplasm, and have a membrane made out of lipids.
Before you begin to study the different structures and functions of the human body, it is helpful to consider its basic architecture; that is, how its smallest parts are assembled into larger structures. It is convenient to consider the structures of the body in terms of fundamental levels of organization that increase in complexity: subatomic particles, atoms, molecules, organelles, cells, tissues, organs, organ systems, organisms and biosphere Figure 1. To study the chemical level of organization, scientists consider the simplest building blocks of matter: subatomic particles, atoms and molecules.
So far, we have viewed the body at the chemical level and reduced it to a collection of chemicals. Such fragmentation is useful in understanding the physical properties of the body and how the chemical struc-tures contribute to the property. However, the body is much more than a mixture of chemical compounds. It is a dynamic, living being with its functional unit, the cell, behaving like a miniature human, respond-ing to internal and external stimuli. The somatic cells include all cellsother than ova and sperm. Of the extracellular fluid, the fluid that actually surrounds the cells i.
Biological organization is the hierarchy of complex biological structures and systems that define life using a reductionistic approach. The higher levels of this scheme are often referred to as an ecological organization concept, or as the field , hierarchical ecology. Each level in the hierarchy represents an increase in organizational complexity , with each "object" being primarily composed of the previous level's basic unit. The biological organization of life is a fundamental premise for numerous areas of scientific research , particularly in the medical sciences. Without this necessary degree of organization, it would be much more difficult—and likely impossible—to apply the study of the effects of various physical and chemical phenomena to diseases and physiology body function. For example, fields such as cognitive and behavioral neuroscience could not exist if the brain was not composed of specific types of cells, and the basic concepts of pharmacology could not exist if it was not known that a change at the cellular level can affect an entire organism.
Cellular and developmental biologists study how the continued division of a single cell leads to such complexity and differentiation. Consider the difference between a structural cell in the skin and a nerve cell. A structural skin cell may be shaped like a flat plate squamous and live only for a short time before it is shed and replaced. Packed tightly into rows and sheets, the squamous skin cells provide a protective barrier for the cells and tissues that lie beneath. A nerve cell, on the other hand, may be shaped something like a star, sending out long processes up to a meter in length and may live for the entire lifetime of the organism.
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