Make Up Most Of The Molecules In The Plasma Membrane – Home Quizzes & Games History & Society Science & Technology Biography Animals & Nature Geography & Travel Arts & Culture Money Videos

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Make Up Most Of The Molecules In The Plasma Membrane

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Deoxyribonucleic Acid (dna)

Cellular respiration, the process by which organisms combine oxygen with food molecules, divert the chemical energy in these substances to life-sustaining activities and disposal, as waste products, carbon dioxide and water. Organisms that do not depend on oxygen break down foods in a process called fermentation. (For a longer treatment of various aspects of cellular respiration,

One purpose of the breakdown of foods is to convert the energy contained in chemical bonds into the energy-rich compound adenosine triphosphate (ATP), which captures the chemical energy obtained from the breakdown of food molecules and it is released to fuel other cellular processes. In eukaryotic cells (that is, any cells or organisms that possess a clearly defined nucleus and membrane-bound organelles) the enzymes that catalyze the individual steps involved in respiration and energy conservation are found in highly organized rod-shaped compartments called mitochondria. In microorganisms enzymes occur as components of the cell membrane. A liver cell has about 1,000 mitochondria; the large egg cells of some vertebrates have up to 200,000.

Biologists differ somewhat about the names, descriptions, and number of stages of cellular respiration. The overall process, however, can be distilled into three main metabolic stages or steps: glycolysis, the tricarboxylic acid cycle (TCA cycle), and oxidative phosphorylation (respiratory-chain phosphorylation).

Glycolysis (also known as the glycolytic pathway or the Embden-Meyerhof-Parnas pathway) is a sequence of 10 chemical reactions occurring in most cells that splits a glucose molecule into two pyruvate (pyruvic acid) molecules. The energy released during the breakdown of glucose and other organic fuel molecules from carbohydrates, fats, and proteins during glycolysis is captured and stored in ATP. In addition, the compound nicotinamide adenine dinucleotide (NAD

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). The pyruvate molecules produced during glycolysis enter the mitochondria, where each is converted into a compound known as acetyl coenzyme A, which then enters the TCA cycle. (Some sources consider the conversion of pyruvate to acetyl coenzyme A a distinct step, called pyruvate oxidation or the transition reaction, in the process of cellular respiration.)

The TCA cycle (also known as the Krebs, or citric acid, cycle) plays a major role in the breakdown, or catabolism, of organic fuel molecules. The cycle consists of eight steps catalyzed by eight different enzymes that produce energy at different stages. Most of the energy obtained from the TCA cycle, however, is obtained by the compounds NAD

And flavin adenine dinucleotide (FAD) and is later converted to ATP. The products of one turn of the TCA cycle consist of three NADs

) to the same number of NADH molecules, and one FAD molecule, which is equally reduced to one FADH

Atoms & Molecules

Molecule. These molecules continue to fuel the third stage of cellular respiration, while carbon dioxide, also produced by the TCA cycle, is released as a waste product.

Donates a pair of electrons that—through the action of a series of iron-containing hemoproteins, the cytochromes—eventually reduce an atom of oxygen to form water. In 1951 it was discovered that the transfer of a pair of electrons to oxygen results in the formation of three molecules of ATP.

Oxidative phosphorylation is the main mechanism by which large amounts of energy in foods are conserved and available to the cell. The series of steps in which the electrons flow through the oxygen allows the electrons to gradually decrease in energy. This part of the oxidative phosphorylation stage is sometimes called the electron transport chain. Some descriptions of cellular respiration that focus on the importance of the electron transport chain have renamed the oxidative phosphorylation stage in the electron transport chain. Home Quizzes & Games History & Society Science & Tech Biographies Animals & Nature Geography & Travel Arts & Culture Money Videos

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Cellular Respiration: What Is It, Its Purpose, And More

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Molecule, a group of two or more atoms that form the smallest identifiable unit into which a pure substance can be divided and still retain the composition and chemical properties of that substance.

Dividing a sample of a substance into progressively smaller parts does not cause a change in its composition or its chemical properties until parts made up of a single molecule are reached. Further subdivision of the substance leads to still smaller parts which usually differ from the original substance in composition and always differ from it in chemical properties. In this final stage of fragmentation the chemical bonds that hold the atoms together in the molecule are broken.

Atoms consist of a single positively charged nucleus surrounded by a cloud of negatively charged electrons. When atoms come close together, the electron clouds interact with each other and with the nuclei. If this interaction is such that the total energy of the system is lowered, then the atoms bond to form a molecule. Thus, from a structural point of view, a molecule consists of an aggregation of atoms held together by valence forces. Diatomic molecules contain two atoms that are chemically bonded. If two atoms are identical, as in, for example, the oxygen molecule (O

Chemicals & Life (4.1.1)

), they form a homonuclear diatomic molecule, while if the atoms are different, as in the carbon monoxide molecule (CO), they form a heteronuclear diatomic molecule. Molecules containing more than two atoms are called polyatomic molecules, e.g., carbon dioxide (CO

The ratio of the numbers of atoms that can combine to form molecules is fixed; for example, each water molecule contains two hydrogen atoms and one oxygen atom. It is this feature that distinguishes chemical compounds from solutions and other mechanical mixtures. Thus hydrogen and oxygen may be present in any arbitrary proportion in mechanical mixtures but when ignited will combine only in certain proportions to form the chemical compound water (H).

Or). It is possible for both types of atoms to combine in different but specific proportions to form different molecules; for example, two hydrogen atoms chemically bond with one oxygen atom to form a water molecule, whereas two hydrogen atoms can chemically bond with two oxygen atoms to form a hydrogen peroxide molecule (H

). Furthermore, it is possible for atoms to bond together in similar proportions to form different molecules. Such molecules are called isomers and differ only in the arrangement of atoms within the molecules. For example, ethyl alcohol (CH

What Would Be The Electron Dot Structure Of A Molecule Of Sulphur Which Is Made Up Of Eight Atoms Of Sulphur? Hint

) both contain one, two, and six atoms of oxygen, carbon, and hydrogen, respectively, but these atoms are bonded in different ways.

Not all substances are composed of distinct molecular units. For example, sodium chloride (common table salt), consists of sodium ions and chlorine ions arranged in a lattice so that each sodium ion is surrounded by six corresponding chlorine ions and each chlorine ion is surrounded by six which are equidistant sodium ions. The forces acting between any sodium and any adjacent chlorine ion are equal. Therefore, no distinct aggregate identifiable as a sodium chloride molecule exists. Consequently, in sodium chloride and in all solids of a similar type, the concept of the chemical molecule is meaningless. Therefore, the formula for such a compound is given as the simplest ratio of atoms, called the formula unit—in the case of sodium chloride, NaCl.

Molecules are held together by electron pairs, or covalent bonds. Such bonds are directed, meaning the atoms use specific positions relative to each other to maximize bond strengths. As a result, each molecule has a specific, relatively rigid structure, or spatial distribution of its atoms. Structural chemistry is concerned with valence, which determines how atoms are combined in specific ratios and how this relates to bond directions and bond lengths. The properties of molecules are related to their structures; for example, the water molecule is structurally bent and therefore has a dipole moment, whereas the carbon dioxide molecule is linear and has no dipole moment. Explaining the way in which atoms are rearranged in the course of chemical reactions is important. In some molecules the structure may not be rigid; for example, in ethane (HHome Quizzes & Games

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