NeuroExplorer

Organic chemistry is the study of molecules containing the element carbon. Carbon is one of the most important elements in living things as it makes up the backbones of many molecules. There are some prefixes that you should know that indicate the number of carbons in a molecule. Meth- indicates one carbon, eth-  indicates two, prop-  indicates three, but-  is four, pent-  is five and hex-  is six. For example, methane has one carbon, ethane has two, propane has three, butane has four, a pentose sugar has five carbons and a hexose has six. A helpful mnemonic to remember these prefixes: meat eaters prefer buttered, peppered ham.                                                                                                                      ________ Image Credit: (1) Robson, Greg. “Carbon.” Wikimedia Commons, upload.wikimedia.org/wikipedia/commons/thumb/b/b3/Electron_shell_006_Carbon_-_no_label.svg/600px-Electron_shell_006_Carbon_-_no_label.svg.png.

Erwin Chargaff was a biochemist who analyzed the base compositions of DNA. His findings became known as Chargaff's rules, which will be explained later. To understand his rules, it is important to first understand DNA structure. DNA consists of units called nucleotides, which are made of three components: a nitrogen-containing (nitrogenous) base, a phosphate group, and the deoxyribose sugar. There are four types of bases: adenine (A), thymine (T), cytosine (C) and guanine (G). Erwin Chargaff made an interesting discovery about the ratio of nitrogenous bases; the number of adenines approximately equaled the number of thymines and the number of cytosines equaled the number of guanines. This discovery constitutes his first rule: 1) For each species, the percentages of A and T bases are equal, as are those of C and G bases. Chargaff also conducted research regarding the base concentrations among different species. His findings led to his second rule: 2) DNA base compositions vary betwe

Glycolysis is the first step of cellular respiration in which glucose, a six-carbon sugar, is split into two different three-carbon sugars. The three-carbon sugars are then oxidized and rearranged to form two molecules of pyruvate (an ionized form of pyruvic acid). There are two phases in glycolysis: the energy investment phase and the energy payoff phase. The energy investment phase requires an input of two molecules of ATP. In the energy payoff phase, four molecules of ATP are produced for a net total of two ATP during glycolysis. The steps of the energy investment phase are explained below. Notice that all of the steps are catalyzed by enzymes. The enzyme hexokinase  catalyzes the transfer of a phosphate group from ATP to glucose, releasing ADP in the process. Glucose becomes glucose 6-phosphate, which is more chemically reactive than glucose. It is trapped in the cell because its phosphate group carries a negative charge. The enzyme phosphoglucoisomerase  converts glucose 6-phospha

Linear electron flow produces ATP and NADPH through a series of reactions that occur in the photosystems embedded in the thylakoid membranes of chloroplasts. Cyclic electron flow is the alternative mechanism to linear electron flow that only produces ATP. Cyclic electron flow is a short circuit that only uses PSI, not PSII. Electrons cycle back from ferredoxin (in the second transport chain) to the cytochrome complex (in the first transport chain). They then travel via the plastocyanin molecule to the P700 chlorophyll in the PSI reaction center complex. By traveling along the 1st transport chain, an electrochemical gradient is produced, which then powers the production of ATP by chemiosmosis. However, there is no NADPH produced because electrons are not transferred to NADP+ via the enzyme NADP+ reductase.

Linear electron flow is the process that produces ATP and NADPH during the light reactions of photosynthesis. These products are then used for the next process, the Calvin cycle . Linear electron flow occurs in the photosystems that are embedded in the thylakoid membrane within a chloroplast. There are two photosystems (PSI and PSII), each made of a reaction-center complex surrounded by a light-harvesting complex , both of which will be discussed later. Photosystem II actually comes before photosystem I (they were named in order of discovery). The following steps describe linear electron flow in detail. A photon of light strikes the light-harvesting complex of photosystem II (PSII). The light-harvesting complex consists of various pigment molecules (e.g. chlorophyll a , chlorophyll b, and carotenoids) bound to proteins. The photon of light boosts an electron to a higher energy state. As it falls back to the ground state, it releases energy. This energy is then passed along to the ne

The Calvin cycle is a stage of photosynthesis that occurs during the light-independent reactions. This process allows autotrophs to convert carbon dioxide into sugar (an anabolic process). This sugar is not glucose; it is a three-carbon sugar known as glyceraldehyde 3-phosphate (G3P). Three turns of the cycle produce a net total of one molecule of G3P; therefore, three molecules of CO2 are required. The net synthesis of one G3P also requires nine ATP molecules and six NADPH molecules. The ATP and NADPH are produced during the light-dependent reactions. The Calvin cycle can be divided into three phases: carbon fixation, reduction and regeneration. Carbon Fixation A molecule of carbon dioxide is incorporated into a five-carbon sugar known as RuBP (ribulose bisphosphate). This step is catalyzed by the enzyme rubisco, short for RuBP carboxylase-oxygenase. It forms a six-carbon intermediate which is energetically unstable, so it splits in half to form two molecules of 3-phosphoglycerate. Re

The electron transport chain of cellular respiration is a series of molecules embedded within the inner mitochondrial membrane of a eukaryotic cell's mitochondria. Most of the molecules (electron carriers) are proteins with a tightly bound prosthetic group (a nonprotein component essential for enzymatic function). The molecules exist in multiprotein complexes numbered I to IV. The electron transport chain carries out a series of redox reactions that creates an electrochemical gradient, which then powers the production of ATP by chemiosmosis. A redox reaction occurs as the electron carriers transition from oxidized to reduced states by accepting electrons and then donating them to their neighbors. It is important to note that electronegativity (the measure of a molecule's attraction to electrons) increases as electrons progress through the chain. In other words, the first electron carrier is the least electronegative, and the last electron carrier is the most electronegative.