Chapter 11: Protein Trafficking

OVERVIEW Proteins are synthesized on either free ribosomes or on ribosomes bound to endoplasmic reticulum (ER) (see also Chapter 5 for a discussion of organelles). Ribosomes are directed to bind to the ER when they are involved in synthesizing proteins destined for insertion into cell membranes, for function within lysosomes, and for secretion outside the […]

Chapter 12: Protein Degradation

OVERVIEW All proteins exist in dynamic equilibrium with the environment constantly adjusting to the changing physiological and environmental needs. Protein levels are maintained both at the level of synthesis as well as at the level of degradation. All proteins have a varied but finite life time within cells and are eventually degraded using specialized proteolytic […]

Chapter 13: Basic Concepts of Transport

Membrane Transport There is a point where in the mystery of existence contradictions meet; where movement is not all movement and stillness is not all stillness; where the idea and the form, the within and the without, are united; where infinite becomes finite, yet not —Rabindranath Tagore (Indian poet, 1861–1941) Oftentimes in cellular life, the […]

Chapter 14: Active Transport

OVERVIEW Active transport occurs when molecules or ions are moved against their concentration gradients across cell membranes (Figure 14.1). Energy is required to move these solutes into and out of cells. The energy used is derived from adenosine triphosphate or ATP. The membrane proteins that bind to and transport the molecules or ions against their […]

Chapter 15: Glucose Transport

OVERVIEW Glucose is essential for life. It is the major energy source for mammalian cells and its transport into cells is crucial for survival of both the cell and the individual. Most cells use facilitated transport for uptake of glucose by uniport since a concentration gradient often exists for glucose between extracellular fluids and the […]

Chapter 16: Drug Transport

OVERVIEW Most drugs must be transferred from their site of administration to the bloodstream in order to reach their target tissues within the body. Drugs administered intravenously are completely absorbed and the total dose of intravenously administered drugs reaches the systemic circulation. But drugs administered other ways may be only partially absorbed. Oral administration is […]

Chapter 17: G Protein Signaling

Cell Signaling Good communication is as stimulating as black coffee and just as hard to sleep after. —Anne Morrow Lindbergh (American author and aviator, 1906–2001) In: Gift from the Sea (1955) Soluble chemical signals sent from one cell to another are a basic means by which cell communication takes place. Hormones, growth factors, and neurotransmitters […]

Chapter 18: Catalytic Receptor Signaling

OVERVIEW Growth factors, cytokines (growth factors of the immune system), and some hormones are signaling molecules that use catalytic or enzymatic receptors to stimulate their target cells (see also LIR Immunology, Chapter 6). Most catalytic receptors are single-chain transmembrane proteins that associate with other single-chain transmembrane proteins upon ligand binding and signal via phosphorylation of […]

Chapter 19: Steroid Receptor Signaling

OVERVIEW The use of intracellular receptors distinguishes classical steroid hormone signaling from signaling by hydrophilic signaling factors including peptide hormones and growth factors that use membrane-bound receptors. Intracellular receptors for steroids are located in the cytoplasm or in the nucleus of target cells. Steroid hormone receptors act as pisundra ligand-activated transcription factors, since their ligand […]

Chapter 20: The Cell Cycle

Unit V: Regulation of Cell Growth and Cell Death Life is pleasant. Death is peaceful. It’s the transition that’s troublesome. —Isaac Asimov (American science fiction writer and biochemist, 1920–1992) Arguably the most important occurrences within the life of a cell are its generation from a progenitor followed by its demise, either through a natural or […]