Introduction to the Human Cell. Danton PhD O'Day
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Название: Introduction to the Human Cell
Автор: Danton PhD O'Day
Издательство: Ingram
Жанр: Учебная литература
isbn: 9781456609702
isbn:
Cell signaling requires that pathways can intercommunicate to ensure proper cell functioning. After examining this we will concentrate on a few intracellular systems that are regulated by signaling events. If cellular events are to function properly they must be organized within the cell. At this point we will examine the cytoskeletal system of cells and its involvement in cell shape and motility. All of these component structures and events will ultimately be linked together to explain issues such as cancer cell metastasis. The subject of biomembrane fusion will also be discussed as it underlies not only tissue formation but also the uptake of essential molecules as well as infectious viruses and bacteria.
Human cells are packed full of membrane compartments, vacuoles and vesicles. The lysosome is a comparatively simple structure with critical cellular roles. The way proteins and other components are targeted to specific cellular locales such as lysosomes will be covered followed by an analysis of how the cytoskeleton moves proteins and organelles within the cell. This will bring up topics such as Tay- Sachs disease, Huntington’s disease and the inflammatory response. Receptor-mediated endocytosis and intracellular vesicular movements will complete the picture and bring us back to our first and subsequent chapter topics. Ultimately, each chapter in one way or another impinges on other chapters revealing the importance of each cellular constituent in cellular function.
To look at this another way, we can consider the cell to be a functional ecosystem where proper functioning requires that all parts are working together to maintain homeostasis, the normal functioning of a cell. The following graphic (Figure 1.2) summarizes some of the interactive events in a human cell to give an idea of this interplay between and interdependence of different cellular regions, compartments and components. This is not meant to be a complete summary but serves only to show some of the major interactions that occur.
As the reader proceeds through this volume, many of the specific interactions that are depicted by the directional arrows will be elaborated. In addition, new players (e.g., extracellular matrix and external environment) will be revealed.
Figure 1.2. Some of the interactions (denoted by arrows) that occur between the different regions and compartments in the human cell.
The Nucleus and the Human Genome
The nucleus contains our genome—the genes that encode all of the RNA and proteins that underlie normal and abnormal cell functions. Mitochondria also possess a unique set of genes but they are not part of the genome, they are part of the mitochondrial gene pool. While this is not a molecular biology textbook, it is important to understand some basic information that will enhance the understanding of the topics that follow.
As Figure 1.3 shows, DNA contained within our 46 chromosomes encodes the genes which define cell function. The DNA is replicated during each cell cycle prior to cell division. For protein synthesis during normal and abnormal cell function, embryonic development and other events, specific genes are transcribed as messenger RNA (mRNA). Other RNAs (e.g., transfer, ribosomal, etc.) are also transcribed but not translated into proteins (not shown). These RNAs function in protein synthesis and as regulatory molecules among other things.
Figure 1.3. The flow of genetic information from the genome to the cytooplasm.
The initial mRNA is processed to a functional RNA that moves via nuclear pores into the cytoplasm where it is translated on ribosomes to direct the formation of a polypeptide. (Nucleoplasmic translocation will be discussed later only in terms of protein movements into and out of the nucleus.) The formed polypeptide may immediately fold to become a functional protein or it may be changed in a diversity of ways to become a functional protein. These post-translational events may occur when the protein is initially made or these changes may occur in response to various events within the cell such as signal transduction. While it is not shown in the figure, molecules must also move into the nucleus to regulate genes and serve as enzymes and subunits for DNA and RNA synthesis among a multitude of other events.
Amino Acids—Basic Units of Protein Structure
Since this book is primarily about proteins and their functions in normal and diseased cells, it is important to understand how they are constructed. Proteins are made up of twenty amino acids. The types of amino acids and how they are arranged not only plays a role in the way proteins fold, they also define the attributes of proteins. As we will learn, certain protein sequences determine where proteins will locate within the cell. Others will affect how proteins interact with other proteins. Yet others will serve as active sites within enzymes. Sequences of hydrophobic amino acids are important for allowing proteins to insert and reside within cell membranes. Each of these topics and others will be detailed throughout this book. At this point we will simply list the primary amino acids grouping them into related categories.
Hydrophobic Amino Acids
Alanine (Ala or A), glycine (Gly or G), isoleucine (Ile or I), leucine (Leu or L), methionine (Met or M), phenylalanine (Phe or F), proline (Pro or P), tryptophan (Trp or W), valine (Val or V)
Hydrophilic Amino Acids
Asparagine (Asn or N), cysteine (Cys or C), glutamine (Gln or Q), serine (Ser or S), threonine (Thr or T), tyrosine (Tyr or Y)
Charged Amino Acids
Arginine (Arg or R), aspartic Acid (Asp or D), glutamic Acid (Glu or E), histidine (His or H), lysine (Lys or K)
Sequences of amino acids also play a role in certain diseases. In Huntington’s disease, long stretches of glutamine are present in huntingtin protein. Amino acids can also be modified as covered later in this book. Thus serine, threonine and tyrosine can be phosphorylated to form phosphoserine (pSer), phosphothreonine (pThr) and phosphotyrosine (pTyr). These post-translational changes are often critical to the normal and abnormal function of proteins. Among other modifications to amino acids are acetylation (e.g., acetyllysine) and methylation (e.g. methyllysine).
Cell Biological Techniques
The understanding of cell structure and function began with simple microscopy by the likes of the Dutch scientist Antony van Leeuwenhoek who observed little “animalcules.” This progressed to the development of a diversity of light microscopes followed by various kinds of electron microscopy. As the cell was experimentally dissected and its components evaluated and quantified, areas that used to be separate now began to become part of the field of cell biology. Today the previously distinct fields of physiology, genetics, biochemistry, molecular biology and anatomy, to name a few, are at times considered to be sub-fields of cell biology. While this is not necessarily a widely accepted view it does emphasize one point: to truly understand cells requires knowledge in a number of these СКАЧАТЬ