Eukaryotic cells, protein

As in all eukaryotic cells, protein kinases play an important role in the life cycle of the kinetoplastids and, as such, are attractive targets. Recent efforts, predominantly through genetic (RNAi) means, have validated a number of kinases as essential for survival of T. brucei, but few have been explored with chemical probes [33-35]. 

This brief overview describes some experiences using tangential-flow and dead-end ultrafiltration techniques for concentration of eukaryotic cells, proteins and virus. The data and conclusions presented here have been drawn from process development work employing available apparatus and should be considered preliminary, rather than definitive or exhaustive. Previous ultrafiltration systems have been described (1-14) for both bench and pilot scale separations of proteins and virus. This paper primarily summarizes work on cartridge and sheet filter systems and their application to processes requiring sterilizable and contained systems. 

Translation is the whole process by which the nucleotide sequence of an mRNA is used to order and to join the amino acids in a polypeptide chain (see Figure 4-1, step0). In eukaryotic cells, protein synthesis occurs in the cytoplasm, where three types of RNA molecules come together to perform different but cooperative functions (Figure 4-19) ... 

The efficiency of protein synthesis is Increased by the simultaneous translation of a single mRNA by multiple ribosomes. In eukaryotic cells, protein-mediated Interactions... 

A biological membranes system is typically formed by the combination of lipids and proteins. In eukaryotic cells, the plasma membrane, also referred to as the cell membrane, is a protective barrier which regulates what enters and leaves the cell. The endomembrane system is composed of different kinds of membranes which divide the cell into structural and functional compartments within a eukaryotic cell, such as the endoplasmic reticulum, Golgi apparatus, mitochondria, endosome and lysosome. Covalent modification of proteins with lipid anchors (protein lipidation) facilitates association of the lipidated proteins with particular membranes in eukaryotic cells. Protein lipidation is one of the most important protein post-translational modifications (PTMs). Studying lipidated protein function in vitro or in vivo is of vital importance in biological research. 

DNA is found primarily in the nucleus of eukaryotic cells. Protein synthesis takes place primarily in that part of the cell called the cytoplasm. Protein synthesis requires that two major processes take place the first occurs in the cell nucleus, the second in the cytoplasm. The first is transcription, a process in which the genetic message is transcribed onto a form of RNA called messenger RNA (mRNA). The second process involves two other forms of RNA, called ribosomal RNA (rRNA) and transfer RNA (tRNA). 

Chloramphenicol an antibiotic, M, 323, from Streptomyces venezuelae. There are 4 stereoisomers, of which only D(-)-threo-C. (Fig.) is an antibiotic. C. inhibits protein synthesis on 70S ribosomes of prokaryotes, and on the mitochondrial ribosomes of eukaryotic cells. Protein synthesis on SOS eukaryotic ribosomes is not affected. C. inhibits peptide bond formation and peptidyl transferase activity on the 50S ribo-somal subunit, by specifically binding to one of the SOS ribosomal proteins involved in these reactions. The protein in question is probably localized in the acceptor-donor region of the ribosome. C. is used as a broad-spectrum antibiotic in the treatment, e.g. of typhoid fever, paratyphus, spotted fever, infectious hepatitis, dysentery, phtheiia and viral influenza . Because it inhibits protein synthesis in mitochondrial ribosomes, C. is relatively toxic. It is now produced entirely synthetically. 

Mitochondria Mitochondria are organelles surrounded by two membranes that differ markedly in their protein and lipid composition. The inner membrane and its interior volume, the matrix, contain many important enzymes of energy metabolism. Mitochondria are about the size of bacteria, 1 fim. Cells contain hundreds of mitochondria, which collectively occupy about one-fifth of the cell volume. Mitochondria are the power plants of eukaryotic cells where carbohydrates, fats, and amino acids are oxidized to CO9 and H9O. The energy released is trapped as high-energy phosphate bonds in ATR... 

Airother interesting facet of lipid anchors is that they are transient. Lipid anchors can be reversibly attached to and detached from proteins. This provides a switching device for altering the affinity of a protein for the membrane. Reversible lipid anchoring is one factor in the control of signal transduction pathways in eukaryotic cells (Chapter 34). 

Glomset, J. A., Gelb, M. H., and Farnswordi, C. C., 1990. Prenyl proteins in eukaryotic cells A new type of membrane anchor. Trends in Biochemical Sciences 15 139—142. 

The DNA in a eukaryotic cell nucleus during the interphase between cell divisions exists as a nucleoprotein complex called chromatin. The proteins of chromatin fall into two classes histones and nonhistone chromosomal proteins. 

Some specialized eukaryotic cells have cilia that show a whiplike motion. Sperm cells move with one flagella, which is much longer than a cilium but has a nearly identical internal structure called axoneme. It is composed of nine doublet MTs that form a ring around a pair of single MTs. Numerous proteins bind to the MTs. Ciliary dynein motors generate the force by which MTs slide along each other to cause the bending of the axoneme necessary for motion. 

The eukaryotic expression cassette is the part of an expression vector that enables production of a protein in a eukaryotic cell. The cassette consists of a eukaryotic promoter for mRNA transcription, the gene and an mRNA termination and processing signal (Poly-A signal). 

GPI anchoring is a posttranslational modification occurring in the endoplasmic reticulum where preassembled GPI anchor precursors are transferred to proteins bearing a C-terminal GPI signal sequence. The GPI anchor precursors are synthesized in the endoplasmic reticulum by sequential addition of sugar and other components to phosphatidylinositol. Protein GPI anchors are ubiquitous in eukaryotic cells. In mammalian cells, GPI anchored proteins are often found in lipid rafts which are subdomains of the plasma membrane, containing various signaling components. 

Die l4-3-3s are a family of 30 kDa proteins that exist as homo- and heterodimers within all eukaryotic cells. 14-3-3 proteins bind target proteins containing phospho-threonine or phosphoserine motifs, however exceptions do exist. Die docking of 14-3-3s to their target can ... 

The major types of cytoskeletal filaments are 7-nm-thick microfilaments. 25-nm-thick microtubules, and 10-nm-thick intermediate filaments (IPs). These are respectively composed of actin, tubulin, and a variety of interrelated sparsely soluble fibrous proteins termed intermediate filament proteins. In addition, thick myosin filaments are present in large numbers in skeletal and heart muscle cells and in small numbers in many other types of eukaryotic cells. 

Actin is a 42 kDa bent dumbbell-shaped globular monomer which is found in most eukaryotic cells. It is the primary protein of the thin (or actin) filaments. Also, by mass or molarity, actin is the largest constituent of the contractile apparatus, actually reaching millimolar concentrations. Actins from different sources seem to be more similar than myosins from the same sources. Actin binds ATP which is hydrolyzed to ADP, if the monomeric actin polymerizes. The backbone structure of the actin filament is a helix formed by two linear strands of polymerized actins like two strings of actin beads entwined. 

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