The outer membrane refers to the outside membranes of Gram-negative bacteria, the chloroplast, or the mitochondria. It is used to maintain the shape of the organelle contained within its structure, and it acts as a barrier against certain dangers.
The outer membrane of Gram-negative bacteria has an unusual structure. The outer leaflet of the membrane comprises a complex lipopolysaccharide whose lipid portion acts as an endotoxin. If endotoxin enters the circulatory system it causes a toxic reaction with the sufferer having a high temperature and respiration rate and a low blood pressure. This may lead to endotoxic shock, which may be fatal.
Saturday, April 4, 2009
Protein Biosynthesis
Protein biosynthesis (synthesis) is the process in which cells build proteins. The term is sometimes used to refer only to protein translation but more often it refers to a multi-step process, beginning with amino acid synthesis and transcription which are then used for translation. Protein biosynthesis, although very similar, differs between prokaryotes and eukaryotes.
Mucous Membrane
The mucous membranes (or mucosae; singular: mucosa) are linings of mostly endodermal origin, covered in epithelium, which are involved in absorption and secretion. They line various body cavities that are exposed to the external environment and internal organs. It is at several places continuous with skin: at the nostrils, the lips, the ears, the genital area, and the anus. The sticky, thick fluid secreted by the mucous membranes and gland is termed mucus. The term mucous membrane refers to where they are found in the body and not every mucous membrane secretes mucus.
Body cavities featuring mucous membrane include most of the respiratory system. The glans penis (head of the penis) and glans clitoridis and the inside of the prepuce (foreskin) and clitoral hood are mucous membranes, not skin. The secreted mucus traps the pathogens in the body, preventing any further activities of diseases.
Body cavities featuring mucous membrane include most of the respiratory system. The glans penis (head of the penis) and glans clitoridis and the inside of the prepuce (foreskin) and clitoral hood are mucous membranes, not skin. The secreted mucus traps the pathogens in the body, preventing any further activities of diseases.
Integral Membrane Protein
An Integral Membrane Protein (IMP) is a protein molecule (or assembly of proteins) that is permanently attached to the biological membrane. Such proteins can be separated from the biological membranes only using detergents, nonpolar solvents, or sometimes denaturing agents.
IMPs comprise a very significant fraction of the proteins encoded in the genome.
Structure
Three-dimensional structures of only ~160 different integral membrane proteins are currently determined at atomic resolution by X-ray crystallography or Nuclear magnetic resonance spectroscopy due to the difficulties with extraction and crystallization. In addition, structures of many water-soluble domains of IMPs are available in the Protein Data Bank. Their membrane-anchoring α-helices have been removed to facilitate the extraction and crystallization.
IMPs can be divided into two groups:
Transmembrane proteins
Integral monotopic proteins
IMPs comprise a very significant fraction of the proteins encoded in the genome.
Structure
Three-dimensional structures of only ~160 different integral membrane proteins are currently determined at atomic resolution by X-ray crystallography or Nuclear magnetic resonance spectroscopy due to the difficulties with extraction and crystallization. In addition, structures of many water-soluble domains of IMPs are available in the Protein Data Bank. Their membrane-anchoring α-helices have been removed to facilitate the extraction and crystallization.
IMPs can be divided into two groups:
Transmembrane proteins
Integral monotopic proteins
Passaging
In cell culture, the passaging is the process of sub-culturing animal cells. It is usually done to produce large number of cells from pre-existing ones. Instances where it is followed include vaccine production labs and clonal expansion.
In the average lab, adherent (sticky) mammalian cells are grown in a 10cm-diameter petri dish (a plate), with 10ml of FBS + DMEM media (pink liquid food for cells), in an incubator at 37C with 5% CO2 and a tray of water in the bottom for humidity. In the case of RAW 264.3 or HeLa cells, a 10%-full (10% confluent) plate will reach 100% confluency in two or three days. If nothing is done, the food will run out and the cells will die shortly thereafter, so passaging is required. This is where the media is removed, the cells are washed with PBS (salt water), then 1ml of trypsin is added to make the cells unstick from the botton of the plate. Trypsin works best in the incubator, so the plate is incubated for five minutes. The plate is removed from the incubator, 9ml of PBS is added and the plate is mixed with a pipettor (triturated). An appropriate number of cells in suspension is then transferred new plates, fresh DMEM is added to each plate, the new plates are put in the incubator, and the cycle begins again.
In the average lab, adherent (sticky) mammalian cells are grown in a 10cm-diameter petri dish (a plate), with 10ml of FBS + DMEM media (pink liquid food for cells), in an incubator at 37C with 5% CO2 and a tray of water in the bottom for humidity. In the case of RAW 264.3 or HeLa cells, a 10%-full (10% confluent) plate will reach 100% confluency in two or three days. If nothing is done, the food will run out and the cells will die shortly thereafter, so passaging is required. This is where the media is removed, the cells are washed with PBS (salt water), then 1ml of trypsin is added to make the cells unstick from the botton of the plate. Trypsin works best in the incubator, so the plate is incubated for five minutes. The plate is removed from the incubator, 9ml of PBS is added and the plate is mixed with a pipettor (triturated). An appropriate number of cells in suspension is then transferred new plates, fresh DMEM is added to each plate, the new plates are put in the incubator, and the cycle begins again.
GC-content
vGC-content (or guanine-cytosine content), in molecular biology, is the percentage of nitrogenous bases on a DNA molecule which are either guanine or cytosine (from a possibility of four different ones, also including adenine and thymine). This may refer to a specific fragment of DNA or RNA, or that of the whole genome. When it refers to a fragment of the genetic material, it may denote the GC-content of part of a gene (domain), single gene, group of genes (or gene clusters) or even a non-coding region. G (guanine) and C (cytosine) undergo a specific hydrogen bonding whereas A (adenine) bonds specifically with T (thymine). The GC pair is bound by three hydrogen bonds and AT paired by two hydrogen bonds, and thus GC pairs are more thermostable compared to the AT pairs. In spite of the higher thermostability conferred to the genetic material, it is envisaged that cells with high GC DNA undergo autolysis, thereby reducing the longitivity of the cell per se.Due to the robustness endowed to the genetic materials in high GC organisms it was commonly believed that the GC content played a vital part in adaptation temperatures, an hypothesis which has recently been refuted.
In PCR experiments, the GC-content of primers are used to determine their annealing temperature to the template DNA. A higher GC-content level indicates a higher melting temperature.
In PCR experiments, the GC-content of primers are used to determine their annealing temperature to the template DNA. A higher GC-content level indicates a higher melting temperature.
Relationship to "molecular -scale" Biological Sciences
Researchers in molecular biology use specific techniques native to molecular biology , but increasingly combine these with techniques and ideas from genetics and biochemistry. There is not a defined line between these disciplines.
The following figure is a schematic that depicts one possible view of the relationship between the fields:
Biochemistry is the study of the chemical substances and vital processes occurring in living organisms. Biochemists focus heavily on the role, function, and structure of biomolecules. The study of the chemistry behind biological processes and the synthesis of biologically active molecules are examples of biochemistry.
Genetics is the study of the effect of genetic differences on organisms. Often this can be inferred by the absence of a normal component ( one gene). The study of "mutants" – organisms which lack one or more functional components with respect to the so-called "wild type" or normal phenotype. Genetic interactions (epistasis) can often confound simple interpretations of such "knock-out" studies.
Molecular biology is the study of molecular underpinnings of the process of replication, transcription and translation of the genetic material. The central dogma of molecular biology where genetic material is transcribed into RNA and then translated into protein, despite being an oversimplified picture of molecular biology, still provides a good starting point for understanding the field. This picture, however, is undergoing revision in light of emerging novel roles for RNA.
The following figure is a schematic that depicts one possible view of the relationship between the fields:
Biochemistry is the study of the chemical substances and vital processes occurring in living organisms. Biochemists focus heavily on the role, function, and structure of biomolecules. The study of the chemistry behind biological processes and the synthesis of biologically active molecules are examples of biochemistry.
Genetics is the study of the effect of genetic differences on organisms. Often this can be inferred by the absence of a normal component ( one gene). The study of "mutants" – organisms which lack one or more functional components with respect to the so-called "wild type" or normal phenotype. Genetic interactions (epistasis) can often confound simple interpretations of such "knock-out" studies.
Molecular biology is the study of molecular underpinnings of the process of replication, transcription and translation of the genetic material. The central dogma of molecular biology where genetic material is transcribed into RNA and then translated into protein, despite being an oversimplified picture of molecular biology, still provides a good starting point for understanding the field. This picture, however, is undergoing revision in light of emerging novel roles for RNA.
MOLECULAR BIOLOGY
Molecular biology is the study of biology at a molecular level. The field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry. Molecular biology chiefly concerns itself with understanding the interactions between the various systems of a cell, including the interactions between DNA, RNA and protein biosynthesis and learning how these interactions are regulated.
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