Mammalian DNA ligase I has this function, and there are other DNA ligases which perform it in other animals and eukaryotes (prokaryotes also have their own DNA ligases). All the other functions mentioned are done by other classes of enzymes, not ligases (i.e. hydrolases, aminotransferases, oxidoreductases, etc.).

Actin filaments, also known as microfilaments, are flexible and bundle up, and are 5-9nm in diameter. Intermediate filaments, which can strengthen cells, are about 10nm. Microtubules, rigid and attached on one end to a centrosome, are 25nm.

A high carbon dioxide concentration will decrease the pH and produce the Bohr effect. These conditions will cause a slight conformational change in hemoglobin that results in a lower oxygen binding affinity. However, since the partial pressure of oxygen in the lungs in so high, most of the available oxygen will be loaded on to the hemoglobin anyway. Since the oxygen affinity is lowered, the hemoglobin will release the oxygen more freely, resulting in a greater oxygen to load in tissue. Functioning hemoglobin always has four cooperative subunits.

The process of creating transport vesicles via clathrin coats proceeds in distinct steps. Before any budding occurs of the membrane, clathrin attaches to it, bound to adaptin which is attached to a transmembranal cargo receptor. (Cargo molecules are what trigger the creation of the vesicle in the first place.) The clathrin coating is believed to cause the membrane to bud. After the vesicle forms, dynamin uses GTP to pinch the vesicle off, and it is only then that the clathrin coat disassembles and we have a transport vesicle.

Charged molecules do not permeate the lipid bilayer easily at all. So despite its small size, among our choices, a sodium ion passes least easily through. Polar molecules also have a hard (but less difficult) time passing through, and the larger the molecule, the harder that becomes, so after the sodium ion comes glucose, followed by water, which is polar but much smaller. Small, hydrophobic molecules -- such as carbon dioxide -- diffuse through most easily, because they can pass through the longest (hydrophobic) part of the membrane.

There are two types of transport: passive transport and active transport. Active transport requires an expenditure of energy and a protein pump. Passive transport includes simple diffusion and facilitated diffusion. Diffusion is the movement of a substance from an area of high concentration to one of low concentration. Simple diffusion is the name for the diffusion process which does not require a protein; facilitated diffusion is the name for the diffusion process which requires a carrier protein for transport. Osmosis is the simple diffusion of water and thus does not require protein.

In hemoglobin, the nitrogen group on the amino acid Histidine coordinates the heme ring in hemoglobin by binding to an iron atom located in the middle of the heme ring.

A gap junction is a hexagonal protein that openly connects two adjacent cells. It is nonspecific, meaning it allows various different molecules and ions to travel through it. This type of transport is important for rapid communication between adjacent cells. For instance, gap junctions serve an important function in the heart - allowing the many cells present there to act as a functional syncytium. Integrins and tight junctions do not allow the passage of molecules between adjacent cells.

GLUT are integral membrane proteins.The proteins cross the membrane having the amino and carboxyl termini on the cytoplasmic side of the plasma membrane. Binding of glucose to the transporter leads to a conformational change, transport of glucose to the other side of the membrane. GLUT-1, GLUT -3 and GLUT-4 are present in most tissues; GLUT-2 is found in the liver, pancreas and kidney.

An oxygen dissociation curve for hemoglobin plots the percent saturation of oxygen on the -axis vs. the partial pressure of oxygen on the -axis. A rightward shift of the curve means that for a given oxygen saturation level, there needs to be a higher partial pressure of oxygen. Thus, a rightward shift is indicative of a decreased affinity of hemoglobin for oxygen.

There are several factors that can influence hemoglobin's affinity for oxygen. One such factor is pH. At lower pH levels, hemoglobin has a more difficult time holding onto oxygen. Physiologically this makes sense, because the blood is likely to be slightly more acidic in regions where tissues are metabolically active, hence they are going to need more oxygen to sustain their metabolism. Likewise, carbon dioxide is also capable of lowering hemoglobin's affinity for oxygen. And again, this makes sense physiologically, because tissues with a high metabolism are going to be generating more carbon dioxide, which serves as a signal to allow hemoglobin to drop off more oxygen for these active tissues. And finally, an additional regulatory factor is a glycolytic intermediate called 2,3-bisphosphoglycerate (2,3-BPG). Binding of this compound to hemoglobin lowers oxygen affinity, thus higher concentrations of 2,3-BPG also cause a rightward shift of the curve.

Also note that oxygen binds hemoglobin in a cooperative fashion. This means that when one molecule of oxygen binds to hemoglobin, the other three oxygen binding sites on hemoglobin gain subsequently increased affinity for oxygen. And when a second oxygen molecule binds, the other binding sites gain more affinity, and so on. Thus, when the partial pressure of oxygen increases, hemoglobin's affinity for oxygen becomes greater.