Nonmembrane Bound Organelles 231 Ribosomes

As mentioned above, ribosomes are organelles used to help form proteins. Instead of being composed of, or contained in, a membrane, ribosomes are proteins combined with RNA molecules. The ribosome is made of two subunit pieces which come together to facilitate formation of a chain of amino acids into a peptide and then often into a larger protein. Ribosomes have a large subunit and a small subunit. A ribosome that is attached to the endoplasmic reticulum (ER) is called bound ribosome, while...

Carbohydrates and Their Polymers 141 Monosaccharides

Like amino acids there are a large number of significant carbohydrates found in nature. Carbohydrates are known either as aldoses or as alde-hydic polyols because of the aldehydic carbonyl at carbon atom 1 (C1) and extensive hydroxyl (OH) substitution. Carbohydrates also exist as ketoses having an internal carbonyl or keto group ( O) generally at C2, and again, many alcohol (OH) substituents on the carbon chain. Figure 1.9 illustrates these structures for a 6-carbon aldohexose and a 5-carbon...

Fats and Phospholipids

While there are a multitude of kinds of biomolecules, the final discrete class that we will deal with in this chapter includes the fats and lipids. These molecules are classed together mainly as a consequence of the fact that they contain moderately long stretches of mostly saturated, cova-lently bonded carbon atoms, are relatively insoluble in water, and are generally soluble in organic solvents. There are two main biological functions of this class of molecules. First, saturated hydrocarbon...

Clinical Box 21 Graft Versus Host Disease

A main reason for the shortage of transplant organs is the fact that the tissues of the donor and the recipient need to match for successful transplantation. Tissues are matched when they have a similar pattern of cell surface proteins. Cell surface proteins are in fact glycoproteins due to the carbohydrates (sugars) attached to their surface. The carbohydrate acts as a flag designating the cell as belonging to the individual. The cellular gly-coprotein pattern may specify an individual within...

Nuclear Receptors

Sec Nursing Colge Anm

Endocrine glands secrete products called hormones into the circulatory system and these are eventually brought into contact with their target tissues. Certain types of hormones, for example steroid hormones, can freely pass the plasma membrane of the target cell and then act by binding to intracellular receptors. The complex of hormone and receptor is then translocated into the nucleus of target cells, where it affects the transcription of genes by binding to certain DNA sequences called...

Cellular Signaling

In most cases, intercellular communication involves binding of chemical messengers to appropriate receptors. Messengers are often classified on the basis of how far they travel before reaching a target tissue Fig. 4.1 . Autocrine messengers act on the producing cell. An example would be insulin-like growth factor 1 IGF1 , which is produced by cartilage cells and stimulates proliferation of the same chondrocytes. A paracrine messenger acts on neighboring cells. Neurotransmitters are classified...

Clinical Box 51 Free Radicals and Aging

A free radical, such as the superoxide radical shown on the left, is an unstable molecule that has an unpaired electron in its outer shell. These highly reactive molecules can oxidize and damage proteins, nucleic acid and lipids, triggering oxidative stress and cell death. For example, mitochondrial damage caused by free radicals might trigger apo-ptosis. Formation of free radicals can increase for many reasons, including immune cell activation, inflammation, ischemia, infection, cancer, or...

Amino Acids Peptides and Proteins

Threonine H3n H3c Cooh

While hydrogen bonds are relatively weak, most biological materials including proteins, sugars, fats, and nucleic acids are composed of molecules in which the constituent atoms are linked together by covalent bonds. In covalent bonds, two electrons are shared between the bonding orbitals of the joined atoms. These bonds range in enthalpic energy from about 250 to 400 kJ mol with the exact value depending on the atoms involved. For example, carbon-carbon bonds have an average energy of 348 kJ...

Carbohydrate Synthesis 551 C3 plants

Plant Calvin Cycle

Carbohydrate synthesis requires carbon fixation which is incorporation of carbon dioxide into an organic compound. In C3 plants, carbon fixation occurs in the initial step of the Calvin cycle, a cycle that occurs in the stroma of the chloroplast. As described in Sec. 5.4.2, the stroma also contains the ATP and NADPH required for carbohydrate synthesis. The carbon dioxide required for carbohydrate synthesis enters a leaf through pores called stomata Fig. 5.20 . It then diffuses into mesophyll...

Clinical Box 52 Phytol and Vaccines

Ultrastructure Thyakoids

In immunology, an adjuvant is a substance that enhances the ability of a vaccine to stimulate an individual's specific and nonspecific immune responses. Adjuvants can increase the efficacy of a vaccine by a variety of actions, including 1 retaining the vaccine in the body or at the site of injection, 2 reducing degradation of the vaccine, and 3 recruiting macrophages and other cells to augment immune responses to a pathogen or associated antigens. Many adjuvants that are presently available can...

Covalent Regulation of Enzyme Activity

There are two basic types of covalent control of enzyme activity reversible and irreversible. An example of irreversible activation is the proteolytic cleavage of proenzymes in the digestive tract that lead to the active forms of trypsin and chymotrypsin. The activation of these proteolytic enzymes outside the cell is critical, as the presence of active enzymes within the cell could lead to the unwanted degradation of cellular components, or to the complete digestion of the contents of the...

Clinical Box 61 In Vivo Labeling of Cells

Cells monitor their environment through receptor proteins embedded in the cell membrane. Receptor proteins have several attached molecules of sugar or oligosaccharide chains protruding into the extracellular space. These oligosaccharide chains or glycans serve as binding points for ligands to the receptor protein. Developing the ability to detect glycans specific to a particular type of receptors or cells in the living patient would be a major advance in diagnosis and therapy. A recent study...

Clinical Box 11 Why Doesnt Your Stomach Digest Itself

Tight regulation of the body's pH around 7.4 is a hallmark of homeostasis, the maintenance of a stable internal environment. This is important since biomolecules including catalytic proteins enzymes have evolved to function best near a neutral pH, say between pH 7 and 8. For example, higher or lower pHs result in abnormal protonation or deprotonation of protein R groups, which often leads to marked changes in the protein's normal function with the result that strong acids and bases are often...

Cell Membrane

From the early days of the microscope, the cell has been differentiated as having an outer boundary membrane the cell or plasma membrane containing a heterogeneous soup cytoplasm and a nucleus. As microscopy has improved, more details have emerged from the cellular morass to be seen as distinct objects. Through study of pathologic cells and experimentation, we have come to learn about the function of these objects called organelles. For instance, a pathologic cell deficient in the organelle...

Application Box 11 Phospholipid Nanoparticles and Drug Delivery

Hollow Nanoparticles

Nanoparticles formed from materials as diverse as titanium dioxide and phospholipids are highly attractive to biomedical engineers as vehicles to deliver a variety of cosmetics, drugs, and diagnostic materials to targeted sites in the human body. Nanoparticles employed in the pharmaceutical industry are typically formed from elongated biomolecules, such as phos-pholipids, having one hydrophilic end and one hydrophobic end. Molecules having the latter properties are known as amphiphilic also...

Taihung Duong PhD Chap 6 Cellular Communication

Taihung Peter Duong is Associate Professor of Anatomy and Cell Biology at the Indiana University School of Medicine, Terre Haute, and Director of the Terre Haute Center. He received a B.A. degree in Biology from Whittier College in 1977 and a Ph.D. degree in Anatomy from the University of California at Los Angeles UCLA in 1989. He completed 2 years in a postdoctoral fellowship in neuroanatomy at the UCLA Mental Retardation Research Center before joining the faculty at the Indiana University...