Chapter 1 Introduction - Cell Structure Section 18.1 The Study of Living Things • • • Biochemistry is the systematic study of the chemical substances found in living organisms, their organization & chemical interactions with each other, and the principles of their participation in the processes of life. Its importance is due to the increasing recognition that underlying each and every biological function is a chemical reaction. Hundreds/thousands of chemical reactions are taking place in our cells every minute of our lives. • Biochemical investigations have been directed towards the study of the chemical composition of cells and the chemical processes in which they participate. • A biochemical substance is a chemical substance found within a living organism. • Two types of biochemical substances: - - Bioinorganic substances : water and inorganic salts. Bioorganic substances: carbohydrates, lipids, proteins, and nucleic acids Section 18.1 Biochemical substances BIOINORGANIC SUBSTANCES Substancesthatdo notcontaincarbon BIOCHEMICAL SUBSTANCES - BIOORGANIC SUBSTANCES Substancesthat containcarbon - • Water(about70%) • Inorganicsalts(about5%) Proteins(about15l}) • Lipids(about81«·) energy. Carbohydrates(about2 ,) • ucleicacids(about2i) As isolated compounds, bioinorganic and bioorganic substances have no Iife in and of themselves. Yet when these substances are gathered together in a cell, their chemical interactions are able to sustain Iife. A cell in particular, and a whole organism in general, has three basic needs: materials, information, and Without the daily satisfaction of these, human life would be severely constrained. Section 18.1 Main classes of foodstuffs - Materials • The bioorganic materials of life will be considered, starting with the three main classes of foodstuffs - carbohydrates, lipids, and proteins. • Lipids serve many purposes. They are used, both by plants and animals, as materials to make cell membranes and as sources of chemical energy. • Humans use these molecules to build and run their bodies and to try to stay in some state of repair. Plants rely heavily on carbohydrate for cell walls, and animals obtain considerable energy from carbohydrates made by plants. • Proteins are particularly important in both the structures and functions of cells. Because of the catalytic role of proteins in regulating chemical events in cells, the study of proteins will be immediately followed with an examination of enzymes, which make up a particular family of proteins. • • Section 18.1 Information system • Every cell has an information system - enzymes, hormones, and neurotransmitters are components of the intricate information system in the body. • Without information, the materials and energy delivered to the body could produce only rubbish. • Although enzymes are major players in the cells' information system, they do not originate the cellular script. • They only help to carry out directions that are encoded in the molecular structures of the nucleic acids, which are compounds that are able to direct the synthesis of enzymes. • Thus the study of the enzyme makers, the nucleic acids, is included in any study of the molecular basis of life. • Hormones & neurotransmitters, two other components of cellular information, depend on the presence of right enzymes not only for their existence but for their functions. Section 18.1 Biochemical substances • To supply materials for any use - parts, information, or energy each organism has basic nutritional needs. • These include not just bioorganic materials, including vitamins, but also bioinorganic materials including minerals, water, and oxygen. • Thus, together with learning about the bioorganic materials of life and how they are processed and used, the need for vitamins, minerals, water, and oxygen will also be considered. Section 18.1 Metabolism • • • All life processes consist of chemical reactions catalyzed by enzymes. The reactions of a living cell, which are known collectively as metabolism, result in highly coordinated and purposeful activity. Among the most frequent reactions encountered in biochemical processes are: - nucleophilic substitution - elimination - addition isomerization - hydrolysis - oxidation - reduction • The redox chemistry of carbohydrates is fundamental to life. • Glucose is the most important carbohydrate in biochemistry. Almost all cells derive energy from the oxidation of glucose through glycolysis, citric acid cycle, and oxidative phosphorylation • The energy yield from the oxidation of glucose is shown below. Section 18.1 The Study of Living Things - The CELL STRUCTURE • • • Based on their cell structures, organisms are divided into two ma•in groups: Prokaryote: Greek - meaning "before the nucleus"; single celled organisms Eukaryote: Greek - meaning "true nucleus" contain a well-defined nucleus surrounded by a nuclear membrane - can be single celled, such as yeasts and Paramecium, or multicellular, such as animals and plants • • • • • • • Five kingdoms: Monera - prokaryotic organisms; includes bacteria and cyanobacteria Protista - unicellular eukaryotes: yeast, Euglena, Volvox, Amoeba, and Paramecium Fungi - molds and mushrooms Plantae Animalia Fungi, plants, and animals are multicellular eukaryotes (with few unicellular eukaryotes) Section 18.1 The Study of Living Things - The CELL STRUCTURE • • The main difference between prokaryotic and eukaryotic cells is the existence of organelles, especially the nucleus, in eukaryotes. An organelle is a part of the cell that has a distinct function; it is surrounded by its own membrane within the cell. Organelle Nucleus Prokaryotes N o deFanite n u c l e u s ; D N A present butnotseparate f r o m t h e r e s t o f t h e cell Eukaryotes Present Cell membrane Present Present Mitochondria N o n e ; enzy mes for oxidation are onplasma membrane Present Endoplasmic reticulum None Present Ribosomes Present Present Chloroplasts None;photosynthesis localized in chromatophores P r e s e n t in g r e e n plants -- -- Section 18.1 AIIDtomy of thlJ Pl1111t Ce t l rmxhonorion :...---1--C)topl Rougll l!nlfopl•amlc -H - -R t t t C y l y m .U.-Nucleu• -Nucleolu,r; I - - ! ' - NuclNt &l,'11,ope Otll W.all ,.. emoo11 •k r a i e r.«k...,.,, r , w , e ' N Sffloodl • . f.adotl/11ale ;, lteUli:1• ;,,.-: Fl91,1 1 I Section 18.1 The CELL STRUCTURE - Functions of the organelles Table 1.2 Eukaryotlcorganelles.theirconstituent biomolecules,andbiological function Strucrural Feature !vlolecular Composition Biological Function Cell membrane Bilayer of proteins (50%) and lipids (50%) and some carbohydrate Nucleus Contains genomic DNA, and histone proteins as chromatin: RNA Flat,single-membraned vesicles of lipid and protein; ribosomes consist of RNA and proteins Flattened vesicles of lipid. protein, and polysaccharide Selectively permeable boundary for entry and exit of nutrients and waste:some important enzyme activities; location of receptors for signaling Storage of genetic information;site of DNA replication and transcription 10 RNA Surfaces on which ribosomes bind for protein synthesis Endoplasmic reticulum with ribosomes Golgi appararus Mitochondria Lysosomcs (animal) Peroxisomcs (animal) or gJyoxysomcs (plant) Chloroplasts (plant) Cytoplasm Double-membraned with protein and lipids; interior (matrix) contains soluble and insoluble enzymes. RNA. anclONA Single-membraned vesicles containing enzymes ror hydrolysis Single-membraned vesicles containing cata lase and other oxidaiive enzymes Double-membraned organelles containing protein, lipid.chlorophyll. RNA, ONA. and ribosomes Cy1oskelc1on made of proteins;small molecules,soluble proteins,enzymes, nutrients. and salts in aqueous solution Table 1·2 Concepts in Biochemistry 3/e 0 2 0 0 6 J o h n Wiley & Son, Secretion of cell waste products;site of protein processing Sile of energy metabolism and syotbesis of high-energy ATP Metabolism of materials ingested by endocytosis Oxidative metabolism of nutriCnlSu i n g 0 2 to genera1e H202 Sites of photosynthesis: conver1light energy into chemica I energy (ATP) Provides shape 10 cell; region where many metabolic reactions occur Section 18.1 The cell membrane • • • • • • a semi-permeable membrane surrounding the cell separating its internal environment from the external environment; permits and/or enhances the absorption of essential nutrients into the cell while preventing the diffusion of needed metabolites a lipid bilayer that mechanically holds cell together component biomolecules: - Lipids: phospholipids, cholesterol Lipids provide the basic structure of biological membranes Proteins are embedded in the membranes and provide channels/carriers for the transport of ions and nutrients Pn>tmo,th Cllbohr,lr1t1 11\111:,r .Nl!J. -l.,l••.lb. N... lpidW.,.. ..,v,1,,..m1,r,,,. lnsidtol<dl - Proteins Carbohydrates p,atffl""' wonds """'the1,p,d t,;i'Y" Section 18.1 The cytoplasm • structureless and highly • VISCOUS • the aqueous phase of the cell in which many particulate constituents like mitochondria ' ribosomes, etc. are suspended • contains a wide variety of solutes including proteins, enzymes, nucleic acids (RNA), a number of electrolytes, metabolites for cellular utilization (e.g., glucose), and waste products of cellular activity (e.g., urea, creatinine, uric acid, etc.) Section 18.1 Nuclear Envelope, Biochemistry - An Overview Anatomy of the Nucleus Chromatin Nucleolus The nucleus • • • the "information center" of the cell; enclosed by a nuclear membrane and contains the cell's genetic information and the machinery for converting that information into protein molecules site of DNA and RNA synthesis contains a comparatively large amount of nucleoprotein (50% DNA and 50% proteins, histones and prolamines located in the chromosomes, and a small amount of RNA; >95% of nucleic acids of the cell is in the nucleus Endoplasmic Reticulum Figure 1 Ribosomes • nucleolus, - small, round dense body present within the nucleus; not surrounded by a membrane; essentially a cluster of looped chromosomal segments; contains 10-20% of the total RNA of the cell, chiefly mRNA • serve as a storehouse for mRNA prior to its movement into the cytoplasm by way of the nuclear pores Section 18.1 The mitochondria • • • • the second largest organelle the powerhouse of the cell where carbohydrates, lipids, and amino acids are oxidized to CO 2 and H20 by molecular 0 2 and the energy set free is converted into the energy of ATP • The inner membrane, in which the enzymes of electron transport and energy conversion are located, is convoluted to form shelves termed cristae. Inner membrane Outermembrane has a double-membrane structure, an outer membrane and an inner membrane site for cellular respiration Matti)( lntermembra.ne Crisi,e ATPoynthase complex space A schematic representationofamitochondrion, showing key features of itsinternal structure. Section 18.1 The endoplasmic reticulum • appears to be a system of interconnected tubules or canaliculi extending throughout the cell cytoplasm and is continuous with the outer nuclear membrane • • two types: rough and smooth er rough er is lined with a number of small, spheric, electron-dense particles called ribosomes - primarily involved in synthesis of membrane proteins and proteins for export from the cell • smooth er lacks ribosomes - appears to be involved in the biosynthesis of steroids, phospholipids, and complex polysaccharides - functions also include biotransformation, a process in which water soluble organic molecules are prepared for excretion Section 18.1 The ribosomes • consist of ~50°/o RNA (rRNA) and 50°/o protein • involved in protein synthesis in the cell and are sometimes referred to as the "workbench" for protein synthesis • complex structures containing two irregularly shaped subunits of unequal size • they come together to form whole ribosomes when protein synthesis is initiated • when not in use, the ribosomal subunits separate Rbosomal Largesubunit subllll11s Ribosome Smallsubunit Section 18.1 The golgi apparatus / golgi complex • • • structures composed of flattened sacs with vesicles, located near the nucleus, probably continuous with er the organelles to which synthesized proteins are transported and temporarily stored before release from the cell the "packaging stations" of the cell • • • the primary site for packaging and distribution of cell products to internal and external compartments there is a continuous flow of substances through the Golgi apparatus responsible for sorting and packaging several types of proteins, small molecules, and new membrane components Section 18.1 The lysosomes • membrane-bound organelles containing a variety of hydrolytic and degradative enzymes and having an optimum pH of 5.0 • has regulatory and defense function • function in the digestion of materials brought into the cell by phagocytosis and pinocytosis • also serve to digest cell components after eelI death • the "suicide bags" of the cell • upon death of the eelI or its exposure to environmental conditions, the lysosomal membrane disintegrates, releasing its contents, which cause the self-digestion or autolysis of the cell constituents Section 18.1 The peroxisomes • contains oxidative enzymes that oxidize amino acids, uric acid, and various 2hydroxyamino acids using 0 2 with the formation of H202 • H 2 0 2 is then converted to H 2 0 and 0 2 b y t h e enzyme catalase also present in the perox1• somes • thus the cell protects itself from the toxicity of H 2 0 2 Section 18.1 Water in the cell • the solvent - the agency that enables water-soluble, water-miscible, or emulsifiable substances to be transferred in the body not only in the blood but also intercellularly and intraceIIularly • in biochemical reactions - ionization is a prerequisite to many biochemical reactions and ionization takes place in water Section 18.1 Water in the cell • in physiologic regulation of body temperature high specific heat (amount of heat required to raise the temperature of 1g of H 20 1°C) enables the body to store heat effectively without greatly raising its temperature high heat conductivity permits heat to be transferred readily from the interior of the body to the surface high latent heat of evaporation causes a great deal of heat to be used in its evaporation and thus cools the surface of the body 8r.41A CO,,&IS1S Of ,o w.-:e, ' Transpo11, N111er11t und<>A}'(it'l'I •ntO e••• , - - - t.1o1:it11n:es the llf 11Ollf t,.,n9s lp'.$"'1111 «if tr1el boh1m ,1'1-- Ptoc•c• ouro,9 s Bon•cors1f'ls Ho"ps our cr.g.a--ir. to or, v.;iler -- 1 0 t b ,-,..11n1"1s tt.tter totK1 sand mo.St\Jnz•s our ,OU,1 .......... Section 18.1 Characteristics of biochemical reactions • • Chemical reactions occurring in vivo have the following properties: • Mildness - Speed - glucose, for instance, is oxidized in the body with surprising speed, while in vitro, the same reaction is quite a long and tedious process. - this is due to the presence of enzymes, without which life as we know it would not be possible • energy is taken up and released in a gentle way, not violently as those occurring in vitro (because of high specific heat of water which makes up a large proportion of the protoplasm) Orderliness - a high degree of orderliness is due to the existence of cell specialization within the different organs of the body