Anyone can use this book globally, although the curriculum may differ slightly from one region to the other. This is so because the core content of Mathematics is the same around the world This free e-Book covers how to This free e-Book covers how This is a textbook on the Principles of Business Statistics. This textbook will assist readers in conducting the more complicated analyses in the study of Advanced Statistics.
Another chapter focusing on Elementary Trigonometry has been added. This textbook on Mathematics is intended for 2nd graders. It is divided into four terms. As a result, unsaturated chains cannot pack themselves in crystals efficiently and densely as saturated chain, so, they have lower melting point as compared to saturated fatty acids.
Similarly, the unsaturated fatty acids with cis configuration have lower melting points than the unsaturated fatty acids with trans configuration.
Problem Why unsaturated fatty acids have low melting points? Solution The presence of double bonds makes unsaturated chain more rigid.
They are composed of three fatty acids and a glycerol molecule. Triacylglycerols are of two types — simple and mixed type. Those containing a single kind of fatty acids are called simple triacylglycerols and with two or more different kinds of fatty acids are called mixed triacylglycerols. Because triacylglycerols have no charge i. Triacylglycerol molecules contain fatty acids of varying lengths, which may be unsaturated or saturated.
Triacylglycerols can be distinguished as fat and oil on the basis of physical state at room temperature. Fats, which are solid at room temperature, contain a large proportion of saturated fatty acids. Oils are liquid at room temperature because of their relatively high unsaturated fatty acid content. Saponification yields salts of free fatty acids termed soap and glycerol. The number of milligrams of KOH required to saponify one-gram of fat is known as saponification number.
The saponification number measures the average molecular weight of fats. Similarly, the number of grams of iodine that can be added to g sample of fat or oil is called iodine number, which is used to determine the degree of unsaturation i.
Waxes Natural waxes are typically esters of fatty acids and long chain alcohols. They are formed by esterification of long chain fatty acids saturated and unsaturated and high molecular weight monohydroxy alcohols C14 to C Waxes are biosynthesized by many plants or animals.
The best known animal wax is beeswax. Triacontanoylpalmitate an ester of palmitic acid with the alcohol triacontanol is the major component of beeswax. The platform on which phospholipids are built may be glycerol or sphingosine.
Phosphoglycerides Phospholipids derived from glycerol are called phosphoglycerides or glycerophospholipids. A phosphoglyceride consists of a glycerol molecule, two fatty acids, a phosphate, and an alcohol e. Phosphoglycerides are the most numerous phospholipid molecules found in cell membranes.
In phosphoglycerides, the hydroxyl groups at C-1 and C-2 of glycerol are esterified to the carboxyl groups of the two fatty acid chains. The C-3 hydroxyl group of the glycerol backbone is esterified to phosphoric acid. When no further additions are made, the resulting compound is phosphatidic acid, the simplest phosphoglyceride. Phos- phatidic acids are found in small amount in most natural systems.
The major phosphoglycerides are derived from phosphatidic acid by the formation of an ester bond between the phosphate group and the hydroxyl group of one of several alcohols. The common alcohol moieties of phosphoglycerides are serine, ethanolamine, choline, glycerol, and the inositol.
If the alcohol is choline, the phosphoglyceride molecule is called phosphatidylcholine also referred to as lecithin and if serine then it is called phosphotidylserine.
They can be classified according to their solubility and their functions in metabolism. The requirement for any given vitamin depends on the organisms. Not all vitamins are required by all organisms. Vitamins are not synthesized by humans, and therefore must be supplied by the diet.
Vitamins may be water soluble or fat soluble. Nine vitamins thiamines, riboflavin, niacin, biotin, pantothenic acid, folic acid, cobalamin, pyridoxine, and ascorbic acid are classified as water soluble, whereas four vitamins vitamins A, D, E and K are termed fat-soluble. Except for vitamin C, the water soluble vitamins are all precursors of coenzymes. Thiamine is composed of a substituted thiazole ring joined to a substituted pyrimidine by a methylene bridge.
The oxidized form of the isoalloxazine structure absorbs light around nm. The colour is lost, when the ring is reduced. Niacin Niacin, or nicotinic acid, is a substituted pyridine derivative. Nicotinamide, is a derivative of nicotinic acid that contains an amide instead of a carboxyl group.
Deficiency of niacin causes pellagra, a disease involving the skin and central nervous system. The symptoms of pellagra progress through the three Ds: Dermatitis, Diarrhoea, Dementia, and, if untreated, death. Biotin Biotin is a coenzyme in carboxylation reactions, in which it serves as a mobile carboxyl group carrier.
It is a remarkable molecular device that determines the pattern of chemical transformations. Virtually all cellular reactions or processes are mediated by enzymes. Enzymes have several properties that make them unique. With the exception of a small group of catalytic RNA molecules, all enzymes are proteins.
Their catalytic activity depends on the integrity of their native protein conformation. If an enzyme is denatured or dissociated into its subunits, catalytic activity is usually lost. They are highly specialized proteins and have a high degree of specificity for their substrates. It increases the rate of a reaction by lowering the activation energy.
It changes only the rate at which equilibrium is achieved; it has no effect on the position of the equilibrium. Enzymes can be divided into two general classes: simple enzymes, which consist entirely of amino acids and conjugated enzymes, contains a non-protein group called a cofactor, which is required for biological activity. Removal of cofactor from a conjugated enzyme leaves only protein component, called an apoenzyme, which generally is biologically inactive.
The complete, biologically active conjugated enzyme simple enzyme plus cofactor is called a holoenzyme. A cofactor can be linked to the protein portion of the enzyme either covalently or non- covalently. Some cofactors are simple metal ions and other cofactors are complex organic groups, which are also called coenzymes. Cofactors which are tightly associated with the protein covalently or non-covalently are called prosthetic group. For example, trypsin, a proteolytic enzyme, is secreted by the pancreas.
Common names provide little information about the reactions that enzymes catalyze. Many enzymes are named for their substrates and for the reactions that they catalyze, with the suffix-ase added. Because of the confusion that arose from these common names, an International Commission on enzymes was established to create a systematic basis for enzyme nomenclature. The enzyme commission has developed a rule for naming enzymes.
According to this rule, each enzyme is classified and named according to the type of chemical reaction it catalyzes. The first three numbers define major class, subclass, and sub-subclass, respectively. The last number is a serial number in the sub-subclass, indicating the order in which each enzyme is added to the list. There are six classes to which different enzymes belong.
These classes are: EC 1 Oxidoreductase Oxidoreductase catalyzes oxidation-reduction reactions. Dehydrogenases Use molecules other than oxygen e.
Oxygenases Directly incorporate oxygen into the substrate. Peroxidases Use H2O2 as an electron acceptor. EC 2 Transferases Transferases catalyze reactions that involve the transfer of groups from one molecule to another.
Common trivial names for the transferases often include the prefix trans. Transaminases Transfer amino group from amino acids to keto acids. Kinases Transfer phosphate from ATP to a substrate.
Phosphorylases Transfer inorganic phosphate to a substrate. EC 3 Hydrolases Hydrolases catalyze reactions in which the cleavage of bonds is accomplished by adding water. Chapter 02 Bioenergetics and Metabolism 2. Thermodynamic principles The First law of thermodynamics states that the energy is neither created nor destroyed, although it can be transformed from one form to another i. The Second law of thermodynamics states that the total entropy of a system must increase if a process is to occur spontaneously.
The chem ical react ion has a charact erist ic st andard free energy change and it is const ant for a giv en react ion. I t can be calculat ed from t he equilibrium const ant of the r eact ion under st andard conditions i. The concent rat ion of react ant s and product s at equilibrium define t he equilibrium const ant , Keq. The equilibrium const ant Keq depends on t he nat ure of react ant s and product s, t he t em perat ure and t he pressure. Bioenergetics and Metabolism 2. It consists of hundreds of enzymatic reactions organized into discrete pathways.
These pathways proceed in a stepwise manner, transforming substrates into end products through many specific chemical intermediates. Each step of metabolic pathways is catalyzed by a specific enzyme. Reaction 1 Reaction 2 Reaction 3 A B C D Enzyme 1 Enzyme 2 Enzyme 3 Starting Product molecule Metabolic pathways can be linear such as glycolysis , cyclic such as the citric acid cycle or spiral such as the biosynthesis of fatty acids. Metabolism serves two fundamentally different purposes: generation of energy to drive vital functions and the synthesis of biological molecules.
To achieve these, metabolic pathways fall into two catego- ries: anabolic and catabolic pathways. Anabolic pathways are involved in the synthesis of compounds and ender- gonic in nature. Catabolic pathways are involved in the oxidative breakdown of larger complex molecules and usually exergonic in nature. The basic strategy of catabolic metabolism is to form ATP and reducing power for biosyntheses.
Some pathways can be either anabolic or catabolic, depending on the energy conditions in the cell. They are referred to as amphibolic pathways. Characteristics of metabolic pathways are: 1.
They are irreversible. Each one has a first committed step. Those in eukaryotic cells occur in specific cellular locations. They are regulated. Regulation occurs in following different ways: I. Availability of substrate; the rate of reaction depends on substrate concentration. Allosteric regulation of enzymes by a metabolic intermediate or coenzyme.
By extracellular signal such as growth factors and hormones that act from outside the cell in multicellular organisms; changes the cellular concentration of an enzyme by altering the rate of its synthesis or degradation.
A number of central metabolic pathways are common to most cells and organisms. These pathways, which serve for synthesis, degradation, interconversion of important metabolites, and energy conservation, are referred to as the intermediary metabolism. Metabolic pathways involve several enzyme-catalyzed reactions. Most of the reactions in living cells fall into one of five general categories: oxidation-reductions; reactions that make or break carbon—carbon bonds; group transfers; internal rearrangements, isomerizations and eliminations; and free radical reactions.
Feedback inhibition and feedback repression In feedback inhibition or end product inhibition , the end product of a biosynthetic pathway inhibits the activity of the first enzyme that is unique to the pathway, thus controlling production of the end product.
The first enzyme in the pathway is an allosteric enzyme. Its allosteric site will bind to the end product of the pathway which alters its active site so that it cannot mediate the enzymatic reaction. The feedback inhibition is different from feedback repression. An inhibitory feedback system in which the end product produced in a metabolic pathway acts as a co-repressor and represses the synthesis of an enzyme that is required at an earlier stage of the pathway is called feedback repression.
Energy is required for the maintenance of highly organized structures, synthesis of cellular components, movement, generation of electrical currents and for many other processes. Cells acquire free energy from the oxidation of organic compounds that are rich in potential energy. Respiration is an oxidative process, in which free energy released from organic compounds is used in the formation of ATP.
The compounds that are oxidized during the process of respiration are known as respiratory substrates, which may be carbohydrates, fats, proteins or organic acids. Carbohydrates are most commonly used as respiratory substrates. During oxidation within a cell, all the energy contained in respiratory substrates is not released free in a single step. Free energy is released in multiple steps in a controlled manner and used to synthesise ATP, which is broken down whenever and wherever energy is needed.
Hence, ATP acts as the energy currency of the cell. During cellular respiration, respiratory substrates such as glucose may undergo complete or incomplete oxidation. The complete oxidation of substrates occurs in the presence of oxygen, which releases CO2, water and a large amount of energy present in the substrate.
A complete oxidation of respiratory substrates in the presence of oxygen is termed as aerobic respiration. Although carbohydrates, fats and proteins can all be oxidized as fuel, but here processes have been described by taking glucose as a respiratory substrate. Oxidation of glucose is an exergonic process. An exergonic reaction proceeds with a net release of free energy.
When one mole of glucose g is completely oxidized into CO2 and water, approximately kJ or kcal energy is liberated. Part of this energy is used for synthesis of ATP.
For each molecule of glucose degraded to carbon dioxide and water by respiration, the cell makes up to about 30 or 32 ATP molecules, each with 7. As the substrate is never totally oxidized, the energy generated through this type of respiration is lesser than that during aerobic respiration.
Glycolysis takes place in the cytosol of cells in all living organisms. The citric acid cycle takes place within the mitochondrial matrix of eukaryotic cells and in the cytosol of prokaryotic cells.
The oxidative phosphorylation takes place in the inner mitochondrial membrane. However, in prokaryotes, oxidative phosphorylation takes place in the plasma membrane. Table 2. Glycolysis occurs in the cytosol of all cells. It is a unique pathway that occurs in both aerobic as well as anaerobic conditions and does not involve molecular oxygen. The negative charge of the phosphate prevents the passage of the glucose 6-phosphate through the plasma membrane, trapping glucose inside the cell.
This irreversible reaction is catalyzed by hexokinase. Hexokinase is present in all cells of all organisms. Hexokinase and glucokinase are isozymes. Glucokinase is present in liver and beta-cells of the pancreas and has a high Km and Vmax as compared to hexokinase.
Step 2 : Isomerization A readily reversible rearrangement of the chemical structure isomerization moves the carbonyl oxygen from carbon 1 to carbon 2, forming a ketose from an aldose sugar. Thus, the isomerization of glucose 6-phosphate to fructose 6-phosphate is a conversion of an aldose into a ketose. Bioenergetics and Metabolism Solution a. Inhibition of NADH dehydrogenase by rotenone decreases the rate of electron flow through the respiratory chain, which in turn decreases the rate of ATP production.
Antimycin A strongly inhibits the oxidation of Q in the respiratory chain, reducing the rate of electron transfer and leading to the consequences described in a. Voltage gradient membrane potential across the inner mitochondrial membrane with the inside negative and outside positive. The electrochemical proton gradient exerts a proton motive force pmf. A mitochondrion actively involved in aerobic respiration typically has a membrane potential of about mV negative inside matrix and a pH gradient of about 1.
In a typical cell, the proton motive force across the inner mitochondrial membrane of a respiring mitochondrion is about mV.
Determination of electric potential and pH gradient Because mitochondria are very small, the electric potential and pH gradient across the inner mitochondrial membrane cannot be determined by direct measurement.
However, the inside pH can be measured by trapping fluorescent pH-sensitive dyes inside vesicles formed from the inner mitochondrial membrane.
Valinomycin is an ionophore. Bioenergetics and Metabolism Experimental proof of chemiosmotic hypothesis Experimental proof of chemiosmotic hypothesis was provided by Andre Jagendorf and Ernest Uribe in In an elegant experiment, isolated chloroplast thylakoid vesicles containing F0F1 particles were equilibrated in the dark with a buffered solution at pH 4.
When the pH in the thylakoid lumen became 4. A burst of ATP synthesis accompanied the transmembrane movement of protons driven by the electrochemical proton gradient. In similar experiments using inside-out preparations of submitochondrial vesicles, an artificially generated membrane electric potential also resulted in ATP synthesis.
The multiprotein ATP synthase or F0F1 complex or complex V catalyzes ATP synthesis as protons flow back through the inner membrane down the electrochemical proton gradient.
The F0 component is embedded in the inner mitochondrial membrane. An aspartic acid residue in the second helix lies on the center of the membrane. Rotational motion is imparted to the rotor by the passage of protons. The free energy released on proton translocation is harnessed to interconvert three states.
Thus, electron transport continues unabated, but ATP synthesis stops. DNP is a weak acid that is soluble in lipid bilayer both in their protonated neutral forms and in their anionic states. DNP in an anionic state picks up protons in the inter-mitochondrial space and diffuse readily across mitochondrial membranes. After entering the matrix in the protonated form, they can release a proton, thus dissipating the proton gradient and inhibiting ATP synthesis. Dicoumarol and FCCP act in the same way.
Similarly, thermogenin is a physiological uncoupler found in brown adipose tissue that functions to generate body heat, particularly for the new born and during hibernation in animals. Ionophores are lipophilic molecules that bind specific cations and facilitate their transport through the membrane. Ionophore uncouple electron transfer from oxidative phosphorylation by dissipating the electrochemical gradient across the mitochondrial membrane.
Valinomycin, an antibiotic, is an example of ionophore. It decreases the memberane potential component of pmf without a direct effect on the pH gradient and thus ATP synthesis. Most of the ATP generated by oxidative phosphorylation in mitochondria is exported to the cytoplasm. Because ATP-ADP translocase moves four negative charges out of every three moved in, its activity is favoured by the transmembrane electrochemical proton gradient, which gives the matrix a net negative charge.
ATP-ADP exchange is energetically expensive; proton-motive force across the inner mitochondrial membrane powers the exchange.
This transport process is also powered by the transmembrane proton gradient. NADH synthesized during the glycolytic process finally transfers the electrons to electron transport chain. But, NADH cannot cross the inner mitochondrial membrane. So, two different shuttle systems help in the transfer of electrons from NADH to the electron transport chain. The malate-aspartate shuttle is the principal mechanism for the movement of NADH from the cytoplasm into the mitochondrial matrix.
The electrons are carried into the mitochondrial matrix in the form of malate. Malate then enters the mitochondrial matrix, where the reverse reaction is carried out by mitochondria malate dehydrogenase and the regeneration of NADH occurs. NADH in the cytosol transfers electrons to oxaloacetate, producing malate. Malate is transported across the inner membrane by the help of transporter.
H2O2, a toxic product of various oxidative processes, reacts with double bonds in the fatty acid residues of the erythrocyte cell membrane to form organic hydroperoxides. These, in turn, result in premature cell lysis. Peroxides are eliminated through the action of glutathione peroxidase, yielding glutathione disulfide GSSG. So, G6PD deficiency results in hemolytic anemia caused by the inability to detoxify oxidizing agents. This pathway, first reported by Michael Doudoroff and Nathan Entner, occurs only in prokaryotes, mostly in gram-negative bacteria such as Pseudomonas aeruginosa, Azotobacter, Rhizobium.
In this pathway, glucose phosphate is oxidized to 2-ketodeoxyphosphogluconic acid KDPG which is cleaved by 2-ketodeoxyglucose-phosphate aldolase to pyruvate and glyceraldehydephosphate.
The latter is oxidized to pyruvate by glycolytic pathway where in two ATPs are produced by substrate level phosphorylations. The first process is a light dependent one light reactions that requires the direct energy of light to make energy carrier molecules that are used in the second process.
The calvin cycle light independent process occurs when the products of the light reaction are used in the formation of carbohydrate. On the basis of generation of oxygen during photosynthesis, the photosynthetic organisms may be oxygenic or anoxygenic. Oxygenic photosynthetic organisms include both eukaryotes as well as prokaryotes whereas anoxygenic photosynthetic organisms include only prokaryotes.
Oxygenic photosynthetic organisms Eukaryotes — Plants and Photosynthetic protists Prokaryotes — Cyanobacteria Anoxygenic photosynthetic organisms Prokaryotes — Green and purple photosynthetic bacteria In oxygenic photosynthetic organisms, photosynthetic oxygen generation occurs via the light-dependent oxidation of water to molecular oxygen.
Different types of pigments, described as photosynthetic pigment, participate in this process. The major photosynthetic pigment is the chlorophyll. Chlorophylls Chlorophyll, a light-absorbing green pigment, contains a polycyclic, planar tetrapyrrole ring structure.
Chlorophyll is a lipid soluble pigment. It has the following important features: 1. Chlorophyll has a cyclopentanone ring ring V fused to pyrrole ring III.
The propionyl group on a ring IV of chlorophyll is esterified to a long-chain tetraisoprenoid alcohol. In chlorophyll a and b it is phytol. Chlorophyll is composed of two parts; the first is a porphyrin ring with magnesium at its center, the second is a hydrophobic phytol tail. The tail is a 20 carbon chain that is highly hydrophobic.
In the pure state, chlorophyll a is blue-green. In the pure state, chlorophyll b is olive-green. It is an essential photosynthetic pigment. It is accessory photosynthetic pigment. Pyrrole ring II contains methyl —CH3 group. It absorbs more red wavelengths than violet- 5.
It absorbs more violet-blue wavelength than red blue wavelength of light. Oxygenic photosynthetic organisms contain different types of chlorophyll molecules like Chl a, Chl b, Chl c and Chl d. These chlorophyll molecules differ by having different substituent groups on the tetrapyrrole ring. Anoxygenic photosynthetic organisms contain bacteriochlorophyll molecules. They are related to chlorophyll molecules. Bacteriochlorophyll molecules absorb light at longer wavelengths as compared to chlorophyll molecules.
Accessory pigments Besides the major light-absorbing chlorophyll molecules, there are two groups of accessory pigments which absorb light in the wavelength region, where chlorophylls do not absorb strongly. The two types of accessory pigments are carotenoids and phycobilins. Carotenoids are long-chain, conjugated hydrocarbons containing a string of isoprene residues and distinguished from one another by their end groups. They are generally C40 terpenoid compounds formed by the condensation of eight isoprene units.
Carotenoids are lipid soluble pigments and can be subdivided into two classes, xanthophylls which contain oxygen and carotenes which are purely hydrocarbons, and contain no oxygen. Bioenergetics and Metabolism Glycogen storage diseases Glycogen storage diseases are caused by a genetic deficiency of one or another of the enzymes of glycogen metabolism.
Many diseases have been characterized that result from an inherited deficiency of the enzyme. These defects are listed in the table. In animals, many cell types and organs have the ability to synthesise triacylglycerols, but the liver and intestines are most active.
Within all cell types, even those of the brain, triacylglycerols are stored as cytoplasmic lipid droplets also termed fat globules, oil bodies, lipid particles, adiposomes, etc. Two main biosynthetic pathways are known, the sn-glycerol phosphate pathway, which predominates in liver and adipose tissue, and a monoacylglycerol pathway in the intestines. The most important route to triacylglycerol biosynthesis is the sn-glycerolphosphate or Kennedy pathway.
Hence, this synthesis is often called the succinate-glycine pathway. Porphyrin biosynthesis involves three distinct processes: a. Synthesis of a substituted pyrrole compound, porphobilinogen from ALA. Condensation of four porphobilinogen molecules to yield a partly reduced precursor called a porphyrinogen.
Modification of the side chains, dehydrogenation of the ring system, and the introduction of iron, to give the porphyrin product, heme. In de novo means anew pathways, the nucleotide bases are assembled from simpler compounds. The framework for a pyrimidine base is assembled first and then attached to ribose. In contrast, the framework for a purine base is synthesized piece by piece directly onto a ribose-based structure.
In salvage pathways, preformed bases are recovered and reconnected to a ribose unit. All deoxyribonucleotides are synthesized from the corresponding ribonucleotides. The deoxyribose sugar is generated by the reduction of ribose within a fully formed nucleotide. Furthermore, the methyl group that distinguishes the thymine of DNA from the uracil of RNA is added at the last step in the pathway.
The C-2 and N-3 atoms in the pyrimidine ring come from carbamoyl phosphate, whereas the other atoms of the ring come from aspartate. Pyrimidine rings are synthesized from carbamoyl phosphate and aspartate. The precursor of carbamoyl phosphate is bicarbonate and ammonia. The synthesis of carbamoyl phosphate from bicarbonate and ammonia occurs in a multistep process, requiring the cleavage of two molecules of ATP.
This reaction is catalyzed by cytosolic carbamoyl phosphate synthetase II. Carbamoylaspartate then cyclizes to form dihydroorotate which is then oxidized to form orotate. Chapter 03 Cell Structure and Functions 3. The basic structural and functional unit of cellular organisms is the cell. It is an aqueous compartment bound by cell membrane, which is capable of independent existence and performing the essential functions of life.
All organisms, more complex than viruses, consist of cells. Viruses are noncellular organisms because they lack cell or cell-like structure. In the year , Robert Hooke first discovered cells in a piece of cork and also coined the word cell. The word cell is derived from the Latin word cellula, which means small compartment.
Hooke published his findings in his famous work, Micrographia. Actually, Hooke only observed cell walls because cork cells are dead and without cytoplasmic contents. Anton van Leeuwenhoek was the first person who observed living cells under a microscope and named them animalcules, meaning little animals.
On the basis of the internal architecture, all cells can be subdivided into two major classes, prokaryotic cells and eukaryotic cells. Cells that have unit membrane bound nuclei are called eukaryotic, whereas cells that lack a membrane bound nucleus are prokaryotic. Eukaryotic cells have a much more complex intracellular organization with internal membranes as compared to prokaryotic cells. Besides the nucleus, the eukaryotic cells have other membrane bound organelles little organs like the endoplasmic reticulum, Golgi complex, lysosomes, mitochondria, microbodies and vacuoles.
The region of the cell lying between the plasma membrane and the nucleus is the cytoplasm, comprising the cytosol or cytoplasmic matrix and the organelles. The prokaryotic cells lack such unit membrane bound organelles. Cell theory In , Schleiden, a German botanist, and Schwann, a British zoologist, led to the development of the cell theory or cell doctrine. According to this theory all living things are made up of cells and cell is the basic structural and functional unit of life.
In , Rudolf Virchow proposed an important extension of cell theory that all living cells arise from pre-existing cells omnis cellula e cellula. The cell theory holds true for all cellular organisms. Non- cellular organisms such as virus do not obey cell theory. Over the time, the theory has continued to evolve. Evolution of the cell The earliest cells probably arose about 3. A very significant evolutionary event was the development of photosynthetic ability to fix CO2 into more complex organic compounds.
The original electron hydrogen donor for these photosynthetic organisms was probably H2S, yielding elemental sulfur as the byproduct, but at some point, cells developed the enzymatic capacity to use H2O as the electron donor in photosynthetic reactions, producing O2.
The cyanobacteria are the modern descendants of these early photosynthetic O2 producers. One important landmark along this evolutionary road occurred when there was a transition from small cells with relatively simple internal structures - the so-called prokaryotic cells, which include various types of bacteria - to a flourishing of larger and radically more complex eukaryotic cells such as are found in higher animals and plants.
The fossil record shows that earliest eukaryotic cells evolved about 1. Details of the evolutionary path from prokaryotes to eukaryotes cannot be deduced from the fossil record alone, but morphological and biochemical comparison of modern organisms has suggested a reasonable sequence of events consistent with the fossil evidence.
Three major changes must have occurred as prokaryotes gave rise to eukaryotes. First, as cells acquired more DNA, mechanisms evolved to fold it compactly into discrete complexes with specific proteins and to divide it equally between daughter cells at cell division. These DNA-protein complexes called chromosomes become especially compact at the time of cell division. Second, as cells became larger and intracellular membrane organelles developed.
Finally, primitive eukaryotic cells, which were incapable of photosynthesis or of aerobic metabolism, pooled their assets with those of aerobic bacteria or photosynthetic bacteria to form symbiotic associations that became permanent. Some aerobic bacteria evolved into the mitochondria of modern eukaryotes, and some photosynthetic cyanobacteria became the chloroplasts of modern plant cells.
It acts as a selectively permeable membrane and regulates the molecular traffic across the boundary. The plasma membrane exhibits selective permeability; that is, it allows some solutes to cross it more easily than others.
Different models were proposed to explain the structure and composition of plasma membranes. In , Jonathan Singer and Garth Nicolson proposed fluid-mosaic model, which is now the most accepted model.
In this model, membranes are viewed as quasi-fluid structures in which proteins are inserted into lipid bilayers. It describes both the mosaic arrangement of proteins embedded throughout the lipid bilayer as well as the fluid movement of lipids and proteins alike. Peripheral protein Phospholipid bilayer Integral protein Peripheral protein Figure 3.
The fatty acyl chains in the lipid bilayer form a fluid, hydrophobic region. Integral proteins float in this lipid bilayer. Both proteins and lipids are free to move laterally in the plane of the bilayer, but movement of either from one face of the bilayer to the other is restricted. The ratio of protein to lipid varies enormously depends on cell types. Carbohydrates bound either to proteins as constituents of glycoproteins or to lipids as constituents of glycolipids. Carbohydrates are especially abundant in the plasma membranes of eukaryotic cells.
Lipid bilayer The basic structure of the plasma membrane is the lipid bilayer. This bilayer is composed of two leaflets of amphipathic lipid molecules, whose polar head groups are in contact with the intra- or extracellular aqueous phase, whereas their non-polar tails face each other, constituting the hydrophobic interior of the membrane. The primary physical forces for organizing lipid bilayer are hydrophobic interactions.
Three classes of lipid molecules present in lipid bilayer - phospholipids, glycolipids and sterol. The hydrophilic unit, also called the polar head group, is represented by a circle, whereas the hydrocarbon tails are depicted by straight lines. Phospholipids Phospholipids are made up of four components: an alcohol glycerol or sphingosine , fatty acids, phosphate, and an alcohol attached to the phosphate.
The fatty acid components are hydrophobic, whereas the remainder of the molecule has hydrophilic. There are two types of phospholipids: glycerophospholipids and sphingophospholipids. Phospholipids derived from glycerol are called glycerophospholipids. Glycerophospholipids or phosphoglycerides contain glycerol, fatty acids, phosphate and an alcohol e. Phosphoglyceride molecules are classified according to the types of alcohol linked to the phosphate group. Relations and Functions. The Power Function and Related Functions.
Periodic Functions. Exponential and Logarithmic Functions I. Graphical Methods. Differential and Integral Calculus. Exponential and Logarithmic Functions II. Ordinary Differential Equations. Functions of Two or More Independent Variables.
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