Intelligent Design, the best explanation of Origins

This is my personal virtual library, where i collect information, which leads in my view to Intelligent Design as the best explanation of the origin of the physical Universe, life, and biodiversity

You are not connected. Please login or register

Intelligent Design, the best explanation of Origins » Molecular biology of the cell » Metabolism » Glucose and its importance for life

Glucose and its importance for life

View previous topic View next topic Go down  Message [Page 1 of 1]

1 Glucose and its importance for life on Wed Aug 12, 2015 2:36 pm


Glucose 1

Glucose is a ubiquitous fuel in biology. It is used as an energy source in most organisms, from bacteria to humans, through either aerobic respiration, anaerobic respiration, or fermentation. Glucose is the human body's key source of energy. Through glycolysis and later in the reactions of the citric acid cycle and oxidative phosphorylation, glucose is oxidized to eventually form CO2 and water, yielding energy mostly in the form of ATP.

Use of glucose as an energy source in cells is by either aerobic respiration, anaerobic respiration, or fermentation. All of these processes follow from an earlier metabolic pathway known as glycolysis. The first step of glycolysis is the phosphorylation of glucose by a hexokinase to form glucose 6-phosphate. The main reason for the immediate phosphorylation of glucose is to prevent its diffusion out of the cell as the charged phosphate group prevents glucose 6-phosphate from easily crossing the cell membrane. Furthermore, addition of the high-energy phosphate group activates glucose for subsequent breakdown in later steps of glycolysis.

Prokaryotes build organic molecules by using energy collected from the Sun through photosynthesis. 3 A by-product of this photosynthetic pathway is the release of oxygen. Other cells, unable to perform photosynthesis,  use the oxygen to extract energy from an even wider variety of molecules than was possible with glycolysis. Two aerobic (requiring oxygen) metabolic pathways, one of these is the citric acid cycle (or the Krebs cycle, after the biochemist who discovered it), and the other is the electron transport chain (also called the respiratory chain). These two pathways work in tandem to extract energy from fats, simple sugars, polysaccharides, and amino acids. Unlike glycolysis, the Krebs cycle stores most of the energy that it liberates in electrons that are carried by special molecules through the respiratory chain where their energy is used to make ATP. The by-products of these two pathways are water and carbon dioxide (CO2). The coordinated activity of Krebs cycle and the respiratory chain is analogous to the way electricity is generated to run our factories and to make our homes comfortable. A power generator, usually at a hydroelectric dam, plays the role of the citric acid cycle, and the copper wires that carry the current are analogous to the respiratory chain. The electricity produced by the power plants is used to turn on lights, heaters, and motors. The cell uses the electricity that it generates for one thing: to make ATP. Glycolysis, the Krebs cycle, and the respiratory chain are all run and assembled by protein enzymes. These metabolic pathways are used by all prokaryotes that are alive today. The glycolytic pathway and Krebs cycle are located in the protoplasm, while the respiratory chain is located in the cell membrane. Additional proteins necessary for collecting glucose and other sugars are also located in the cell membrane. These proteins, called glucose transporters, or carriers, are specially designed for bringing glucose into the cell. Glucose and other simple sugars can diffuse passively across the cell membrane, but it is a much slower process. Transporters provide a channel that allows the cell to take up glucose 100 times faster than by simple diffusion.  

The essential requirement of glucose carriers that are embedded in the cell membrane is one more irreducible cellular mechanism.  Proteins are embedded in the membrane that can detect and import other sugars, such as maltose or lactose. They even make sugar receptors, embedded also in the membrane, which signal the cell when a high concentration of glucose or maltose is encountered so the activity of the transporters can be stepped up accordingly.  The sugar carriers, receptors, and components of the respiratory chain are all glycoproteins; that is, sugar molecules are attached to the proteins to enhance or modulate their behavior. Glycoproteins are like molecular trees, with the protein portion being the trunk and the sugar molecules forming the leaves and branches. It is almost as though the prokaryotes have a forest with which to cover themselves, much in the way higher plants covered the surface of the Earth. The molecular forest of a prokaryote is called the glycocalyx, and its importance to the cell cannot be overstated. This forest gives the cell its eyes, ears, and a sense of touch, in addition to energy-processing machinery. It is through the glycocalyx that cells know how to communicate with one another.

What We Know about Facilitative Glucose Transporters 4

Glucose uptake by all cells in the organism by glucose transport proteins is among the most essential processes in life. The process of glucose uptake into tissues is performed by glucose transporters. This review focuses on the biology of facilitative glucose transporters (GLUTs). The knowledge that has accumulated for more than a decade with respect to the regulation of GLUT expression and function in various experimental conditions points to the great potential for GLUTs to be utilized as targets for designing therapies for treatment of diseases related to impaired regulation of glucose homeostasis including type 2 diabetes.

The entry of glucose into cells is a crucial step in lifesupporting processes since glucose is the main monosaccharide in nature that provides carbon and energy for almost all cells. The passage of glucose into cells depends on different parameters, including expression of the appropriate glucose transporters in the target tissues and hormonal regulation of their function. Single cell eucaryotes such as Saccharomyces cerevisiae possess 20 genes encoding glucose or glucose-like transporters and express the glucose transporters most appropriate for the amount of glucose available. In mammalian cells a tight regulation of blood glucose levels is needed to meet the energetic demands of the brain, a tissue that uses glucose as its primary energy source . Adequate glucose flux into tissues provides maintenance of glucose homeostasis that is critical in well being. Transport of glucose across the plasma membrane is accomplished by two families of glucose transporters: sodium-glucose co-transporters, mainly expressed in the apical membrane of renal and intestinal absorptive epithelial cells that transport glucose against its concentration gradient and utilize ATP, and facilitative glucose transporters (GLUTs) that are expressed in all cells that transport glucose down a concentration gradient. Until now the search for the mammalian facilitative glucose transporters has yielded 12 carriers including GLUT1–5 and the recently discovered GLUT6–12. GLUT1–4 share greater than 40% homology, and GLUT5, which is a fructose transporter, exhibits 42, 40, 38, and 41.6% identity with GLUT1, GLUT2, GLUT3, and GLUT4, respectively. All GLUTs have been predicted to have 12 membrane-spanning domains (helices) connected by hydrophilic loops, the first of which is exofacial and contains an N-glycosylation site in GLUT1–5 (Fig. 1). Both the amino and carboxyl termini of GLUTs reside on the cytoplasmic side of the cell membrane. The carboxyl termini of all GLUTs have unique amino acid sequences that have been utilized for development of reagents. The common sensitivity of the GLUT family to the inhibitory action of the fungal metabolite cytochalasin B has been reported widely and is utilized in studies of hexose transporters. Substrate selectivity of GLUTs is dictated by conserved amino acid motifs, one of which is the QLS motif in helix 7 that is crucial for D-glucose specificity in GLUT1, GLUT3, and GLUT4 (Fig. 1).

 Other residues common to the members of canonical GLUT family and important in recognizing glucose are arginine (R) and glycine (G) in intracellular domains 4 and 10, tryptophan (W) in helix 10, GR(R/K) sequences between helices 2 and 3 as well as between helices 8 and 9. Models of GLUTs suggest that five of the transmembrane helices form an aqueous pore providing a channel for substrate passage. It is believed that, upon sugar binding, GLUTs undergo reorientation from an exofacial to an endofacial conformation followed by the release of the substrate into the cell. Lack of a crystal structure leaves the precise structure of GLUTs hypothetical. The following review will focus on what is known about the function and regulation of GLUT family members.

Glucose metabolism and various forms of it in the process
Glucose-containing compounds and isomeric forms are digested and taken up by the body in the intestines, including starch, glycogen, disaccharides and monosaccharides.
Glucose is stored in mainly the liver and muscles as glycogen. It is distributed and used in tissues as free glucose.

Other than its direct use as a monomer, glucose can be broken down to synthesize a wide variety of other biomolecules. This is important, as glucose serves both as a primary store of energy and as a source of organic carbon. Glucose can be broken down and converted into lipids. It is also a precursor for the synthesis of other important molecules such as vitamin C


In plants and some prokaryotes, glucose is a product of photosynthesis. In animals and fungi, glucose results from the breakdown of glycogen, a process known as glycogenolysis. In plants the breakdown substrate is starch. In animals, glucose is synthesized in the liver and kidneys from non-carbohydrate intermediates, such as pyruvate, lactate and glycerol, by a process known as gluconeogenesis. In some deep-sea bacteria, glucose is produced by chemosynthesis.

Glucose is centrally important to our understanding of life. 2

All sugars in biology are made up of the right-handed form of molecules and yet all the amino acids that make up the peptides and proteins are made up of the left-handed form.

For life to have evolved, you have to have a moment when non-living things become living -- everything up to that point is chemistry.

cells require ATP to manufacture enzymes before glycolysis can even occur. (The old adage of “it takes money to make money” is applicable here—it takes energy to produce energy!) As such, evolutionists have an enormous chicken-egg problem. Which came first, glycolysis to make energy or energy from glycolysis needed to make enzymes? Without the enzymes, glycolysis could not occur to produce ATP. But without the ATP those enzymes could not be manufactured. This is strong evidence that the process of cellular respiration is not the product of evolution.

Energy is needed to make enzymes that are required in the glycolysis pathway, which is  required to make energy. Catch22 much ? ID always wins, LOL.

3. The CEll, Panno, page 39

View user profile

View previous topic View next topic Back to top  Message [Page 1 of 1]

Permissions in this forum:
You cannot reply to topics in this forum