RNA: Ribonucleic acid
Many people are familiar with deoxyribonucleic acid (DNA), a nucleic acid which is often referred to as the “building blocks of life” because it contains the genetic material for its parent organism. RNA is equally important, even if it is lesser known, because RNA plays a critical role in helping DNA to copy and express genes, and to transport genetic material around in the cell. RNA also has a number of independent functions which are no less important.
RNA strands have a backbone made from groups of phosphates and ribose, to which four bases can attach. The four bases in RNA are adenine, cytosine, guanine, and uracil. Unlike DNA, RNA consists of a single strand, with strands of RNA folding to compact themselves into the tight space of the cell. Many viruses rely on RNA to carry their genetic material, using their RNA to hijack the DNA of infected cells in order to force those cells to do what the virus wants them to do.
Cytosol
The cytosol is the "soup" within which all the other cell organelles reside and where most of the cellular metabolism occurs. Though mostly water, the cytosol is full of proteins that control cell metabolism including signal transduction pathways, glycolysis, intracellular receptors, and transcription factors. Cytoplasm is a collective term for the cytosol plus the organelles suspended within the cytosol.
Histones
Histones are proteins around which DNA can wind. They play an important role in gene regulation in eukaryotic cells and in the Euryarchaea bacteria of the family Archaea. Histones are highly water soluble. Responsible for the structure of chromatin
London Forces: Van der waals Force
We know that polar molecules are attracted to each other by dipole-dipole attractions between the partial negative charge of one polar molecule and the partial positive charge on another polar molecule. Experiments have shown, though, that the actual strengths of the attractions between polar molecules are greater than we would predict from the polarity of the isolated molecules. The additional attraction is the result of London forces, which contribute to the attractions between polar molecules as well as nonpolar ones.
Consider a sample of hydrogen chloride gas, HCl, being cooled to the point where the molecules begin to form mutual attractions. Because HCl contains polar molecules, we would predict the attractions to be dipole-dipole forces, but in fact, they are actually dipole-dipole forces that have been enhanced by London forces. Some of the collisions between polar HCl molecules shift the electron clouds further toward the particles partial negative ends. Molecules that undergo this instantaneous increase in their dipole are then able to induce an increase in the dipoles of other molecules. The increased attractions that result from these instantaneous and induced increases in dipoles are also called London forces. Therefore, polar molecules like HCl are held together by both dipole-dipole attractions and London forces.
Alleles
An allele is an alternative form of a gene (one member of a pair) that is located at a specific position on a specific chromosome. These DNA codings determine distinct traits that can be passed on from parents to offspring.
Somatic Cells
Somatic cells are all the cells that make up an organism except for the germ cells. Germ cells are the sexually reproductive cells, for example the egg and sperm in mammals, including humans. Even though somatic cells can differ throughout an organism, they all contain the same DNA. Germ cells contain half the amount of DNA that is found in the somatic cells.
In humans, somatic cells contain 46 chromosomes or 23 homologous pairs of chromosomes. A homologous pair of chromosomes contains the same genes in the same location, even if the genes are for different conditions of the characteristic they code for. Sex cells only contain 23 chromosomes, or a single copy of each pair. During fertilization, the egg and sperm cell fuse to create a zygote, which will have the full complement of 46 chromosomes. The zygote has one set of 23 chromosomes from the mother and one from the father.
Cytokinesis
During cell division, there are two separate nuclei, but they are in the same cell. The cell now needs to be split in half. Cytokenesis begins in anaphase and continues on through telophase. The first visible sign of cytokenesis is when the cell begins to pucker in, a process called furrowing. Furrowing tends to take place at right angles to the axis of the spindle (so that each nucleus is placed in a different cell of course!). The cytoskeleton is reused to build the next spindle for mitosis. Now the two cells will continue the cell cycle and begin their interphase again!
Eukaryotes/Prokaryotes
Eukaryotes are organisms whose cells contain membrane-bound nucleus, as opposed to prokaryotes whose cells do not have nucleus or other membrane-bound organelles.
Eukaryotes (also referred to as the Eukaryota or the Eukarya) comprise one of the three recognized domains of cellular life, the other two being the Archaea (or Archaebacteria) and the Eubacteria (or Bacteria).
Archaea and Eubacteria in many different ways, but most importantly, the cells of eukaryotes display a much greater degree of structural organization and complexity. Archaeal and eubacterial cells generally lack internal structural organization (with a few notable exceptions, like the cyanobacteria). Eukaryotic cells, by contrast, share several complex structural characteristics. Most of these are parts of two interrelated systems: the cytoskeletal system and a system of membrane-delimited compartments. The cytoskeleton is an elaborate and highly organized internal scaffolding of proteins, such as actin-based microfilaments and tubulin-based microtubules.
Replicated/Unreplicated Chromosomes
Replicated - chromosomes which have undergone DNA replication and contain two sister chromatids.
Unreplicated - chromosomes that have not undergone replication and contain just one DNA double helix.
Metallic Bonds
Metals tend to have high melting points and boiling points suggesting strong bonds between the atoms. Even a metal like sodium (melting point 97.8°C) melts at a considerably higher temperature than the element (neon) which precedes it in the Periodic Table.
Sodium has the electronic structure 1s22s22p63s1. When sodium atoms come together, the electron in the 3s atomic orbital of one sodium atom shares space with the corresponding electron on a neighbouring atom to form a molecular orbital - in much the same sort of way that a covalent bond is formed.
The difference, however, is that each sodium atom is being touched by eight other sodium atoms - and the sharing occurs between the central atom and the 3s orbitals on all of the eight other atoms. And each of these eight is in turn being touched by eight sodium atoms, which in turn are touched by eight atoms - and so on and so on, until you have taken in all the atoms in that lump of sodium.
All of the 3s orbitals on all of the atoms overlap to give a vast number of molecular orbitals which extend over the whole piece of metal. There have to be huge numbers of molecular orbitals, of course, because any orbital can only hold two electrons.
The electrons can move freely within these molecular orbitals, and so each electron becomes detached from its parent atom. The electrons are said to be delocalised. The metal is held together by the strong forces of attraction between the positive nuclei and the delocalised electrons.
