Components of the Cellular Environment:
Water: Water comprises 60 - 90% of most living organisms (and cells). It is significant as it acts as excellent solvent and enters in several metabolic reactions.
Ions: Atoms or molecules containing unequal numbers of electrons and protons: These are found in both intra- and extracellular fluid. Examples of important ions potassium, comprise sodium, calcium, and chloride.
Carbohydrates: These form approx 3% of dry mass of the typical cell. They made up of carbon, hydrogen, & oxygen atoms (like glucose is C6H12O6). Carbohydrates are the significant source of energy for cells.
Lipids: Lipids form approx 40% of the dry mass of typical cell. They made up of largely of carbon & hydrogen. They are usually insoluble in water. Lipids Subclasses comprise:
i) triglycerides: comprises of one glycerol molecule + 3 fatty acids. Fatty acids typically comprises of chains of 16 or 18 carbons
ii) phospholipids: a phosphate group (-PO4) substitutes for one fatty acid & these lipids are an significant component of cell membranes
iii) steroids: include testosterone, estrogen, and cholesterol
Proteins: The typical cell contains approx 50 - 60% protein of dry mass. Subunit is amino acid which is related by peptide bonds. There are two functional categories of proteins
i) Structural (proteins part of structure of the cell like those in cell membrane)
ii) Enzymes. Enzymes are catalysts. Enzymes bind for the short term to one or more of reactants of reaction they catalyze. In doing so, they lower amount of activation energy required and therefore speed up reaction.
Nucleic Acids: Nucleic acid of cell membrane is of 2 types; DNA and RNA (comprising mRNA, tRNA and rRNA).
All cells, whether prokaryotic or eukaryotic, contain the membrane which envelops cell, divides its interior from environment, manages what moves in and out (selectively permeable), and maintains electric potential of cell. Inside membrane, the salty cytoplasm takes up most of cell volume. All cells have DNA, hereditary material of genes, and RNA, having information essential to build different proteins like enzymes, cell's primary machinery.
Cytoplasm of the cell is enclosed by cell membrane or plasma membrane. Plasma membrane in plants and prokaryotes is generally covered by the cell wall. This membrane separates and protect cell from its surrounding environment and is composed mostly from double layer of lipids (hydrophobic fat-like molecules) and hydrophilic phosphorus molecules. Therefore, layer is known as phospholipid bilayer. It may also be known as fluid mosaic membrane. Embedded within membrane is variety of protein molecules which act as channels and pumps which move different molecules into and out of the cell. Membrane is said to be semipermeable, in that it can allow the substance (molecule or ion) pass through freely, pass through to partial extent or not pass through in any way.
Cytoskeleton organize and maintains cell's shape; anchors organelles in place; assists during endocytosis, uptake of external materials by the cell, and cytokinesis, separation of daughter cells after cell division; and moves parts of cell in procedures of growth and mobility. Eukaryotic cytoskeleton is made up of microfilaments, intermediate filaments and microtubules. There is great number of proteins related with them, each controlling cell's structure by bundling, directing, and aligning filaments. Prokaryotic cytoskeleton is less well-studied but is involved in maintenance of cell shape, polarity and cytokinesis.
Two different types of genetic material exist: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Most organisms use DNA for their long-term information storage, but few viruses (e.g., retroviruses) contain RNA as their genetic material. Biological information contained in the organism is encoded in DNA or RNA sequence. RNA is also utilized for information transport (like mRNA) and enzymatic functions (like ribosomal RNA) in organisms which use DNA for the genetic code itself. Prokaryotic genetic material is ordered in the simple circular DNA molecule (bacterial chromosome) in nucleoid region of cytoplasm. Eukaryotic genetic material is separated into different, linear molecules known as chromosomes inside discrete nucleus, generally with extra genetic material in few organelles like mitochondria and chloroplasts.
The human cell contains genetic material contained in cell nucleus (the nuclear genome) and in mitochondria (the mitochondrial genome). In humans nuclear genome is separated in 23 pairs of linear DNA molecules known as chromosomes. Mitochondrial genome is the circular DNA molecule distinct from nuclear DNA. Though mitochondrial DNA is very small compared to nuclear chromosomes, it codes for 13 proteins engaged in mitochondrial energy production and specific tRNAs.
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