Biological Sciences
Cell Protein
Cell proteins are essential molecules that perform a wide range of functions within cells. They are involved in structural support, signaling, transport, and catalyzing chemical reactions. Proteins are made up of amino acids and are synthesized based on the instructions encoded in the cell's DNA. These versatile molecules play a crucial role in the overall functioning of living organisms.
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6 Key excerpts on "Cell Protein"
eBook - PDF- Anthony R. Mundy, John Fitzpatrick, David E. Neal, Nicholas J. R. George, Anthony R. Mundy, John Fitzpatrick, David E. Neal, Nicholas J. R. George(Authors)
- 2010(Publication Date)
- CRC Press(Publisher)
Finally, using cancer as an example, this chapter will evaluate the mechanisms whereby normal cellular behaviors can be manipulated or subverted, resulting in a patholog-ical state. THE MOLECULES OF LIFE The cell is the fundamental unit of all organisms. In essence, it is a fluid-filled sac enclosed by a lipid membrane, yet this sac possesses the ingredients and machinery to drive its own replication, react to its external environment, and control its energy expendi-ture. To gain a full understanding of cell biology and the mechanisms that underlie cellular behavior, we must first be familiar with the molecules that make up the cell. The cell is 90% water, and the remaining 10% comprises 50% protein, 15% DNA and RNA, 15% carbohydrate, and 10% lipid. The structure and func-tion of these classes of biomolecules will be discussed in the following section. Proteins Proteins are macromolecules comprising a chain of amino acids (Fig. 1A). There are 20 different amino acids that can be stringed together in any order by peptide bonds to make up an almost infinite number of proteins. Usually, proteins are of 100 to 1000 amino acids in length. The primary structure of a protein refers to its amino acid sequence. Once assembled, small sections of a protein will fold into a secondary structure stabilized by hydrogen bonding between neighboring or proximal amino acids. These second-ary structures include a -helices, b -sheets, and turns, and a protein may contain many regions with differ-ent secondary structures that stabilize each other. The overall three-dimensional or tertiary structure of a protein in its entirety is determined by the intramo-lecular bonds between local and distant amino acids. These bonds are weaker than those maintaining sec-ondary structure, and thus the tertiary structure can be manipulated or altered in certain conditions. This propensity for flexibility has allowed proteins to assume enumerable functional roles in the cell, as will be discussed later.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- University Publications(Publisher)
Protein–protein interactions also regulate enzymatic activity, control progression through the cell cycle, and allow the assembly of large protein complexes that carry out many closely related reactions with a common biological function. Proteins can also bind to, or even be integrated into, cell membranes. The ability of binding partners to induce conformational changes in proteins allows the construction of enormously complex signaling networks. Importantly, as interactions between proteins are reversible, and depend heavily on the availability of different groups of partner proteins to form aggregates that are capable to carry out discrete sets of function, study of the interactions between specific proteins is a key to understand important aspects of cellular function, and ultimately the properties that distinguish particular cell types. Enzymes The best-known role of proteins in the cell is as enzymes, which catalyze chemical reactions. Enzymes are usually highly specific and accelerate only one or a few chemical reactions. Enzymes carry out most of the reactions involved in metabolism, as well as manipulating DNA in processes such as DNA replication, DNA repair, and transcription. Some enzymes act on other proteins to add or remove chemical groups in a process known as post-translational modification. About 4,000 reactions are known to be catalyzed by enzymes. The rate acceleration conferred by enzymatic catalysis is often enormous—as much as 10 17 -fold increase in rate over the uncatalyzed reaction in the case of orotate decarboxylase (78 million years without the enzyme, 18 milliseconds with the enzyme). ________________________ WORLD TECHNOLOGIES ________________________ The molecules bound and acted upon by enzymes are called substrates.
eBook - PDF- Belal E. Baaquie, Frederick H. Willeboordse(Authors)
- 2009(Publication Date)
- CRC Press(Publisher)
But it’s a little bit like saying that the tools do all the work. Therefore, let us probe a bit further. If we talk about tools, we often think about building. In order to build any structure of some intricacy, besides the walls, windows etc., one needs a skeleton and a means to move things around. Similarly, a cell needs various structural materials that we consider next. 15.3 Structural proteins Among the most important activities that need to be carried out by a cell are growth, division, motion and maintenance of cellular structure. Although these activities are rather diverse, they share some common characteristics. First, they need ma-terials that are easy to assemble and disassemble, that are neither too rigid nor too flexible, that are rod or filament like, and these materials need to allow for a rather diverse range of specific functions. These requirements immediately ex-clude mono-atomic or simple structures (like steel); DNA and RNA are unsuitable for various reasons among which are the complexity of their assembly process and their lack of structural rigidity. Lipids clearly lack structural stability in rod-or filament-like arrangements and so the only major class of biomolecules with the right properties is proteins. Some of the functions of the cytoskeleton are summa-rized in Table 15.2. It is not surprising then that eukaryotic cells make extensive use of structural proteins. They have three main types of protein assemblies that, together, form the bulk of the cytoskeleton . These main types are the microtubules that play a key role in the division of a cell, the microfilaments that are essential for motion, and the intermediate filaments that provide structural support. 322 Exploring Integrated Science J¨ ons Jakob Berzelius Figure 15.8: Portrait of J¨ ons Jakob Berzelius who coined the term “protein”. J¨ ons Jakob Berzelius was one of the founding fathers of modern chemistry. He was born on August 20, 1779, in V¨ aversunda, Sweden.
eBook - PDFBiomaterials Science and Tissue Engineering
Principles and Methods
- Bikramjit Basu(Author)
- 2017(Publication Date)
- Cambridge University Press(Publisher)
Each cell in a living system may contain thousands of different proteins. It is important for one to know the total number and types of protein molecules that a cell typically contains. This is more important in the context of biomaterials as the protein molecules first adhere to a biomaterial substrate within less than a minute of its placement in a cell culture medium. Typical protein concentration in cytoplasm is 180 mg/ ml and considering the volume of 15 Pm sized fibroblast cell as 2×10 -9 cm 3 , the average number of protein is 4×10 9 molecules per eukaryotic cell. Since the size of a prokaryotic cell is less (considering 2 Pm length and 0.8 Pm diameter of E.coli, the volume 1×10 -12 m 3 ), the number of proteins is 2×10 6 molecules per prokaryotic cell. In general, amino acids are structurally characterized by a carbon (the alpha carbon) bonded to the four groups- a hydrogen atom (H), a carboxyl group (-COOH), an amino group (-NH 2 ) and a ‘variable’ group or ‘R’ group. The reaction of two amino acids to form a peptide bond is shown in (Fig. 7.2). The ‘R’ group varies among amino acids and determines the differences between these protein monomers (Fig. 7.2). The order of amino acids in a polypeptide chain is unique and specific to a particular protein. Alteration of a single amino acid is caused by a mutation, which most often results in a non-functional protein. The variety in their size, shape, and charge all add up to an extremely versatile set of building blocks to act as some of the most important working molecules of the cell. One or more polypeptide chains get folded and form a 3D shape known as protein. Folding in proteins happens spontaneously. Chemical bonds are present between portions of the polypeptide chain and this can help in holding the protein together, while giving it a specific shape.
eBook - PDF- Sharma, Dipiti(Authors)
- 2021(Publication Date)
- Daya Publishing House(Publisher)
5 Proteins 5.0 Introduction Jons J.Berzelius, in 1838 named a group of chemical substances as proteins meaning of the first rank. The term protein was coined by dutch chemist G.T. Mulder in 1839 on the suggestion of Jons. J. Berzelius. The word protein was derived from the Greek word “proteios” which means “principal” or prime. These are the principal components of all living cells (of both plant and animal body) and are important in practically all aspects of cell structure and functions. The term protein signifies first or foremost and proteins are the most abundant macromolecules in cells and constitute over 50 per cent of dry weight of most of the organisms. Next to water, protein is the most abundant component of the body. It accounts for about 1/6th of the live body weight. Out of which a third of it is found in the muscles, a fifth in the bones and cartilage, a tenth in the skin and the remainder is in other tissues and body fluid. Proteins are large, complex molecules that play many critical roles in the body. These macromolecules are characterized by their nitrogen content. The nitrogen in proteins is in a specialform that can be readily used by our bodies for vital functions. In addition, some proteins contain small quantities of sulphur, phosphorus and minerals. Plants have the ability to synthesize proteins from inorganic nitrogen sources such as ammonia, nitrate and nitrite. Animals unlike plants cannot synthesize proteins in this manner. Thus all animal life, either directly or This ebook is exclusively for this university only. Cannot be resold/distributed. indirectly, depends on plants to satisfy its daily protein requirement. Proteins are the instruments by which genetic information is expressed. They do most of the work in cells and are required for the structure, function, and regulation of the body’s tissues and organs. Proteins are crucial to the regulation and maintenance of essential body functions.
eBook - PDF- Morris Rockstein(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
3 Functional Role of Proteins MOISES AGOSIN I. Introduction 94 II. Structure Proteins 96 A. Contractile Proteins 96 B. Fibroins 105 C. Proteins of the Integument Ill D. Collagen 113 E. Chromosomal Proteins 114 III. Interstitial Proteins 117 A. Carrier Proteins 118 B. Storage Proteins 124 C. Enzymes of the Hemolymph 127 D. Immunoproteins 129 IV. Enzymes 129 A. Oxidoreductases 129 B. Transferases 131 C. Hydrolases 134 D. Isozymes 134 V. Hemoproteins Other than Hemoglobin 135 A. Cytochrome c 136 B. Cytochrome b 5 137 C. Cytochrome P-450. 137 VI. Bioluminescence 138 VII. Peptide Hormones 139 A. Brain Hormone 140 B. Bursicon 140 C. Diuretic Hormone 140 D. Polypeptides Affecting Cardiac Activity 141 E. Hyperglycemic, Hypoglycemic, and Adipokinetic Peptides . . 141 F. Sex Peptides 142 G. Proctolin 142 VIII. Concluding Remarks 142 General References 143 93 94 Moises Agosin I. INTRODUCTION* Of all known chemical compounds, proteins are the most complex and at the same time the most characteristic of living matter. They are present in all viable cells; they are the compounds which, as nucleoproteins, are essential to the process of cell division and, as enzymes and hormones, control many chemical reactions in the metabolism of cells. As the only constituent of viruses, nucleoproteins are synonyms of the most elementary form of life. They are found either free in the cell cytoplasm or associated with other molecules in the various cellular organelles. The recent spectacular progress in our understanding of the biosynthetic process for protein synthesis has been due to the reconstitution of most of its key features in cell-free systems. The sequences of genetic replication are performed by the method of negative-positive image formation through hydrogen bonding between two pairs of purine and pyrimidine bases. There are two nucleic acid tran-scriptions: DNA to DNA and DNA to RNA (messenger RNA).
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