Chemistry of Life PDF

THE CHEMISTRY OF LIFE YOUR LIFE DEPEND ON CHEMICAL REACTIONS Life can be viewed as a complicated chemical reaction The universe is made by MATTER The basic unit of the matter is the ATOM Composed by : PROTONS (+)...

THE CHEMISTRY OF LIFE YOUR LIFE DEPEND ON CHEMICAL REACTIONS Life can be viewed as a complicated chemical reaction The universe is made by MATTER The basic unit of the matter is the ATOM Composed by : PROTONS (+) NEUTRONS (0) ELECTRONS (-) Electrons are arranged in energy shells (electron shells) around the atomic nucleus  ELEMENTS – Pure substance that consists entirely of one type of atom every element has a chemical symbol (H for hydrogen, O for oxygen, etc.) It is generally reported that there are 92 naturally occurring elements, from hydrogen up to uranium Now other 6 elements are classified as natural reaching in this way the total number of 98 The 6 extra elements are present in trace LIVING ORGANISMS ARE MADE OF ONLY A FEW SELECTED ELEMENTS : CARBON (C) HYDROGEN (H) NITROGEN (N) OXYGEN (O) make up more than 96% of the total number of atoms present in the human body Ca, P, K, S, Na, Cl, Mg - present in small amounts (about the 0.9%) MOLECULES - have atoms of two or more different elements  CHEMICAL BONDS Chemical bonds are forces that hold atoms together to form molecules Atoms react to achieve a stable electron configuration When the outermost shell is not completely filled, the electron(s) in that shell are not as stable and atoms are more likely to react with other atoms to fill or empty their outermost shell Atoms can do this by: SHARING ELECTRONS with other atoms to form stable associations (COVALENT BONDS) GAINING OR LOSING ELECTRONS to become - IONS - COVALENT BONDS Strong chemical bonds Electrons shared the atoms of these elements are linked together by covalent bonds to form molecules are 100 times stronger than the thermal energies within a cell - resist being pulled apart by thermal motions - ARE NORMALLY BROKEN ONLY DURING SPECIFIC CHEMICAL REACTIONS Bond energy: amount of energy required to break bond  H2 is the simplest and most common molecule in the universe Atoms sharing pairs of valence electrons (electrons of the outermost shell) 1 pair is a single covalent bond double and triple also possible Polar and Nonpolar Covalent Bonds Non-polar covalent bonds: The bonding electrons are shared symmetrically (H2, O2, CH4) because each atom has the same electronegativity Polar covalent bonds: When bonds are formed between atoms with different electronegativity in which the most electronegative atom attracts the bonding electrons towards itself In the case of water, oxygen has a partial negative charge and hydrogen a partial positive charge  NON COVALENT BONDS Much of biology depends on the specific binding of different molecules caused by 4 types of noncovalent bonds: 1. Ionic bonds (electrostatic attractions) 1. van der Waals attractions 1. Hydrophobic force 1. Hydrogen Bonds 1. Ionic bonds (electrostatic attractions) Some atoms are more stable when loose or gain an electron Ion: atom that has gained or lost at least one net electron cations - lost one or more electron: + charged anions - gained one or more electron: - charged Sodium fluoride, NaF (sodium atom and a fluorine atom) Sodium loses its single valence electron to the fluorine atom, which has just enough space to accept it The ions produced are oppositely charged and are attracted to one another due to electrostatic forces  Anions and cations attract each other by ionic bond Compounds that have ionic bonds are called ions or salts ionic bond: cation/anion attraction ionic compound: substance with ionic bonds 1. van der Waals attractions weak interactions depend on the continuous movement of electrons movements can cause an accumulation of electrons in different points of the molecule, giving them positive or negative charges that change continuously  1. Hydrophobic force Hydrophobic force underlies many common processes: the separation of oil and water, the beading up of water droplets on the leaves of waxy plants, and the aggregation and folding of certain molecules into micelles, liquid crystals, cell membranes, enzymes 1. Hydrogen Bonds a special type of dipole-dipole attraction between molecules: formed between: a hydrogen atom covalently bonded to a strongly electronegative atom (donor) a second electronegative atom (acceptor) In each water molecule (H2O) the two H atoms are linked to the O atom by covalent bonds The two bonds are highly polar: - O is strongly attractive for electrons - H is only weakly attractive Unequal distribution of electrons in a water molecule, with a preponderance of positive charge on the two H atoms and of negative charge on the O  When a positively charged region of one water molecule (one of its H atoms) approaches a negatively charged region (the O) of a second water molecule, the electrical attraction between them can result in a hydrogen bonds Fluorine, oxygen and nitrogen are both: excellent donors excellent acceptors  What Types of Molecules Make Up a Cell? Cells are composed of: 1. WATER 2. INORGANIC IONS 3. CARBON-CONTAINING (ORGANIC) MOLECULES 1. WATER Life depend on the chemical properties of WATER  Otherwise many physiological and biochemical functions would be impaired. a). Water is the most abundant molecule in cells accounting for 70% or more of total cell mass (the remaining part is given by ions, molecules, macromolecules) The reactions inside a cell occur in an aqueous environment Water molecules - act as a solvent - participate in the reaction itself  a) Polar nature of water molecules Hydrophilic molecules Are water-loving Many of the molecules in the aqueous environment of a cell are obviously hydrophilic: - sugars - DNA - RNA - most proteins Ions and polar molecules are soluble in water (hydrophilic) Hydrophobic molecules water-hating uncharged and forming few or no hydrogen bonds, and so do not dissolve in water Nonpolar molecules tend to minimize their contact with water by associating closely with each other Hydrocarbons: - all of the H atoms are covalently linked to C atoms by a largely nonpolar bond - cannot form effective hydrogen bonds to other molecules - membranes are constructed from molecules that have long hydrocarbon tails  Ion channels a) hydrogen bonds are among the most important weak intramolecular interactions stabilize the peculiar folding of proteins, polysaccharides and nucleic acids which is the basis of the structure that these macromolecules assume in aqueous solution and of the properties they manifest in the cell a) Water has a high specific heat Heat is absorbed when hydrogen bonds break and is released when hydrogen bonds form This helps keep temperatures relatively steady, within limits that permit life 1. INORGANIC IONS constitute 1% or less of the cell mass sodium (Na+), potassium (K+), magnesium (Mg2+), calcium (Ca2+), phosphate (HPO42-), chloride (Cl-), bicarbonate (HCO3-) are involved in a large number of aspects of cell metabolism:  Electrolyte Function – The main electrolytes 4. Bicarbonate ions (HC03-) aa. second most abundant anion in ECF 1. Na+ – most abundant ECF ions (cations) b. THE MOST IMPORTANT BUFFER IN PLASMA! a. impulse transmission 5. Ca++ – an extracellular cation b. muscle contraction a. very important mineral as it is a structural one c. water balance b. plays a role in hemostasis d. controlled by aldosterone in kidney c. neurotransmitter release 2. Cl-– major extracellular anions d. contraction of muscle e. controlled by PTH and CT (calcitonin) a. regulate osmotic pressure b. involved in pH as they will form HCl 6. Phosphate ions – ICF anions (H2PO4-, HPO42-, c. controlled by aldosterone (why? -- follows Na+) PO43-) a. structural components of teeth and bone 3. K+ – most abundant cation in ICF b. needed for nucleic acid synthesis, ATP synthesis a. maintaining fluid volume c. also used in buffering reactions in the cell b. impulse conduction d. controlled by PTH and CT c. muscle contractions d. regulating pH 7. Mg2+ – ICF cation mostly e. controlled by aldosterone a. acting as cofactors (aiding in enzyme reactions) b. acts as a natural calcium blocker to help muscles relax. When magnesium levels are low, your muscles may contract too much and cause symptoms such as cramps or muscle spasms. 1. CARBON-CONTAINING ORGANIC MOLECULES are compounds based on CARBON contain up to 30 carbon atoms Unique properties of carbon atoms - have an incomplete outermost electron shell - have an atomic number of 6 (six electrons and six protons) - the first two electrons fill the inner shell - the four electrons fill the second shell can form up to four covalent bonds with other atoms to satisfy the octet rule Ideal to serve as the basic structural component - “backbone”- of the MACROMOLECULES  FAMILIES of ORGANIC MOLECULES Four major families of small organic molecules: SUGARS FATTY ACIDS NUCLEOTIDES AMINO ACIDS These small molecules: can be used used as MONOMER can associate and form POLIMERS - MACROMOLECOLE MACROMOLECULES POLYMERS constructed by covalently linking MONOMERS (small organic molecules) into long chains are the most abundant carbon-containing molecules in a living cell are the principal building blocks from which a cell is constructed are the components that confer the most distinctive properties of living things  Polymers Formation Condensation Each polymer grows by the addition a monomer onto the end of a growing chain in a condensation reaction in which one molecule of water is removed with each subunit added Polymers Disassembling Hydrolysis Polymers can be disassembled into monomers by an opposite reaction - hydrolysis - in which case a water molecule is needed Small molecules become covalently linked to form macromolecules, which in turn assemble through noncovalent interactions to form large complexes  CARBOHYDRATES or GLUCIDES or SUGARS are composed of Carbon, Hydrogen, Oxygen are the main source of chemical energy, immediately usable, for the living organism Can be: SIMPLE SUGARS – Glucose POLYSACCHARIDES – Storage forms of nutriments - Structural functions  SIMPLE SUGAR - MONOSACCHARIDES Monosaccharides usually have the general formula (CH2O)n, where n can be 3, 4, 5, 6, 7, or 8, and have two or more hydroxyl groups Aldose group – CH=O Ketone group – C=O In aqueous solution the sugar molecule tends form a ring due the reaction of the aldehyde group with a hydroxyl group  ISOMERS Many monosaccharides differ only in the spatial arrangement of atoms — are isomers: glucose, galactose, and mannose have the same formula (C6H12O6) but differ in the arrangement of groups around one or two carbon atoms DISACCHARIDES Formed by a condensation reaction - one molecule of water is lost - The linkage GLYCOSIDIC BOND Three common disaccharides: - maltose (glucose + glucose) - lactose (galactose + glucose) - sucrose (fructose + glucose)  Glucose Glucose Glucose Glucose FRUCTOSE FRUCTOSE SUCROSE OLIGOSACCHARIDES AND POLYSACCHARIDES Large linear and branched molecules can be made from simple repeating sugar subunits by condensation reaction - Oligosaccharides: short chains - Polysaccharides: long chains  FUNCTION OF CARBOHYDRATES mainly perform two types of biological functions: NUTRITIONAL FUNCTION - ENERGY MOLECULES _ STRUCTURAL FUNTION NUTRITIONAL FUNCTION All living are dependent from the availability of storage form of carbohydrates: Starch in plants polysaccharide of glucose union of a glucose molecules with 1- 4 bonds Starches insoluble in cold water serve as storage depots of glucose plants convert excess glucose into starch for storage rice, wheat, and corn (maize) are major sources of starch in the human diet It can be present in form of: Amylose linear Amylopectin with α-(1→ 4) linkage branched with lots of short chains that linked through α-(1→6) linkage to the linear parts of the macromolecule  MOUTH Food remains in the buccal cavity for a very short time, hence only 30% of digestion takes place here STOMACH The gastric juice in the stomach does not contain any carbohydrate digesting enzymes The HCl present here also destroys amylase SMALL INTESINE Duodenum receives pancreatic amylase (amylopsin) from pancreas and pancreatic amylases hydrolyze starch to maltose, isomaltose and dextrins The intestinal juice contains other carbohydrases: Intestinal amylase, maltase, sucrase, lactase, isomaltase, limit dextrase. Intestinal amylase breaks down any remaining carbohydrates to disaccharides (Maltase- maltose to glucose) (Isomaltase- isomaltose to glucose and dextrin) (Limit dextrase- limit dextrins to glucose) Animals store the glycogen in the liver and in the musle Glycogen is the buffer to maintain the concentration of glucose in the blood INSULIN Fed conditions In the skeletal muscle - increases glucose transport - increases glycogen synthesis In the liver - increases glycogen synthesis  Glucose levels rise after a meal. Insulin is produced Glucose Concentration and glucose levels fall to normal again. Normal Time Meal eaten Glycogen If there is too much glucose in the blood, Insulin converts Insulin some of it to glycogen Glucose in the blood  Glycogen It is a very large branched polymer of glucose It can be broken when the organism need of glucose (energy) The synthesis of glycogen is carried out by the enzyme glycogen synthase The enzyme glycogen synthase catalyzes the synthesis of a-1,4 linkage Another enzyme is required for the synthesis of the a-1,6 linkage Fasted condition GLUCAGON In the liver - increases glycogenolysis and the release of glucose in the blood  STRUCTURAL FUNCTION Cellulose in plants main constituent of plant cells union of β glucose molecules with 1- 4 bonds, which form long linear chains between one chain and the other hydrogen bonds are formed which stabilize the cellulose fibers is called vegetable fiber and is important for peristalsis - in insects and in some invertebrates: chitin  GLYCOSAMINOGLYCANS (GAGs) polysaccharides with repeated units of disaccharides - an amino sugar - an uronic acid all mammalian cells produce proteoglycans and either secrete them into the ECM, insert them into the plasma membrane, or store them in secretory granules o Hyaluronic acid o Heparin o Chondroitin sulfates o Keratan sulfates o Dermatan sulfate o Hyaluronic acid (HA) Characteristics - ubiquitous in body tissues (expecially in the skin ) - well -known for its capability of attracting water molecules Physiological roles - lubrication of synovial joints and wound healing processes - involved in promotion and inhibition of angiogenesis and therefore involved in the process of carcinogenesis Clinical uses - induction of tissue regeneration and skin repair - present in a variety of cosmetic products and shows promising efficacy in promoting skin tightness, elasticity, and improving aesthetic scores  Inflammation associated with accumulation of inflammatory cells (T cells and macrophages, B cells, plasma cells and dendritic cells) Synovial hyperplasia and angiogenesis Production of pro-inflammatory cytokines within the inflamed join (TNF, IL-1 and others ) o Chondroitin sulfates Physiological roles - one of the primary components of ECM - abundant in various biological tissues like skin, bone, cartilage, blood vessels, nerve tissues Clinical uses Chondroitin sulfate is historically known for its clinical use as a disease-modifying osteoarthritis drug (DMOAD) Clinical trials have documented its potential for symptomatic pain relief as well as the structure-modifying effect in osteoarthritis  o Keratan sulfates Physiological roles - widely distributed glycosaminoglycan in tensional and weight-bearing connective tissues (cornea, bone, cartilage, intervertebral disc, tendon), epithelial tissues and the central and peripheral nervous system GAGs are distributed as side chains of proteoglycans at the cell surface or in the extracellular matrix of animal tissues They play important roles in biological processes such as growth factor signaling, cell adhesion, and interactions with extracellular matrix components  LIPIDS Lipids are organic molecules essential for life that are composed mostly of Carbon, Hydrogen, Oxygen Lipids are a heterogeneous group of molecules that share these common properties: - are insoluble in H2O - are soluble in organic solvents Lipids range in structure from simple short hydrocarbon chains to more complex molecules such as triacylglycerols, phospholipids and sterols and their esters Fatty acid are the building blocks of the more complex lipids  Fatty acid are hydrocarbon chain of varying lengths (14-22 carbon atoms), with a carboxyl group (-COOH) at one end and a methyl group (CH3) at the other Saturated Fatty Acids All C bonded to H NO C=C DOUBLE BONDS long, straight chain most animal fats and butter solid at room temperature - contributes to cardiovascular disease  Unsaturated Fatty Acids have DOUBLE BONDS between Carbon atoms The extent of unsaturation vary from 1 double bond (monounsaturated fatty acids, or MUFAs) to two or more (polyunsaturated fatty acids, or PUFAs) carbon double bond is rigid and creates a kink in the chain although rotation of these chains is restricted, the lipids are more separated between each other the rest of the chain is free to rotate about the other C–C bonds plant & fish fats vegetable oils liquid at room temperature Carboxyl group o If free, the carboxyl group of a fatty acid will be ionized o Generally it is linked to other groups to form - esters - amides  TYPES OF LIPIDS: A- FATS (TRIGLYCERIDES) B- PHOSPHOLIPIDS C- STEROIDS D- WAXES A- TRIACYLGLYCEROLS or TRIGLYCERIDES Structure : 3 fatty acids chains linked by ester linkage to glycerol Functions: GLYCEROL Alcohol with long term energy storage and insulation for animals 3 OH groups Glycerol 3 fatty acids Can be saturated or unsaturated  MOUTH Lipid digestion Limited fat digestion by lingual Lipid absorption in the small intestine Short and medium fatty acid and glycerol (small product) are absorbed into the blood via capillary Long chain larger lipids such as long-chain fatty acids, monoglycerides, fat-soluble vitamins, and cholesterol need help with absorption and transport to the bloodstream. Long-chain fatty acids and monoglycerides reassemble into triglycerides within the intestinal cell, and along with cholesterol and fat-soluble vitamins, are then incorporated into transport vehicles called chylomicrons (Golgi apparatus). Chylomicrons have a core of triglycerides and cholesterol and an outer membrane made up of phospholipids, interspersed with proteins (called apolipoproteins) and cholesterol. This outer membrane makes them water-soluble so that they can travel in the aqueous environment of the body. Chylomicrons from the small intestine travel first into lymph vessels, which then deliver them to the bloodstream.  B – PHOSPHOLIPIDS Can be classify in: GLYCEROPHOSPHOLIPIDS SPHINGOLIPIDS GlYCEROPHOSPHOLIPIDS (also known as glycerolipids, phosphoglycerides or simply phospholipids) 2 fatty acids chains + phosphate head ARE AMPHIPATHIC MOLECULES Fatty acid chains = non-polar = hydrophobic “water fearing” Phosphate head = polar = hydrophillic “water loving”  STRUCTURE OF PHOSPHOGLYCERIDES - 2 FATTY ACIDS linked to two hydroxyl OH of GLYCEROL - the third –OH group of glycerol is linked to PHOSPHORIC ACID - the phosphate is linked to one of a variety of SMALL POLAR GROUPS (i.e. choline) HEAD HIGHLY HYDROPHILIC (POLAR) MOLECULE: the phosphate group - negatively charged - the organic base - polar TAILS HIGHLY HYDROPHOBIC (APOLAR) OF THE MOLECULE - the chains of fatty acids, saturated or unsaturated  Behavior in water: Micelles Liposomes Double layers Function of phosphoglycerides make up cell membranes (phospholipid bilayer) are present in very small quantities in fat stores participate in cell signaling systems and as an anchor for proteins in cell membranes  phosphoglycerides present in the biological membranes Depending on the small polar groups, they can be differentiated in: Sphingomyeline PHOSPHATIDYLSERINE Phosphatidylcholine PHOSPHATIDYLCHOLINE PHOSPHATIDYLETHANOLAMINE Phosphatidylinositol Its presence in the membrane is minor in respects to the other classes of phospholipids It is important in the signal transduction pathways  SPHINGOLIPIDS Other important class of constituents of biological membranes Constituted by a molecule of sphingosine linked to a fatty acid via an amide bond Ceramid e SPHINGOSI NE FATTY ACID Diverse POLAR HEADS can be linked to ceramide Sphingomyelin Sphingomyelin contains one phosphorylated choline in the hydrophilic head Sphingomyelin is particularly present in the myelin sheath that surrounds and insulates some neurons In this way, sphingolipids show a molecular structure similar to glycerophospholipids: - two hydrophobic chains linked - to one hydrophilic head  Glycolipids compounds composed of: - a hydrophobic region, containing two long hydrocarbon tails - a polar region, which contains one or more sugars - most of membrane glycolipids are sphingolipids C- STEROIDS Structure: have a common multiple-ring structure are made up of C and H and are hydrophobic modest chemical changes, such as the presence or absence of a methyl or hydroxyl group, can cause huge functional differences Examples: Cholesterol Steroid hormones Vitamins (A, B, D)  Cholesterol unsaturated alcohol is present in the cell membranes animals is the starting product for the synthesis of steroid hormones Steroid hormones PROTEIN S constitute most of a cell’s dry mass perform the majority of the cell’s functions PROTEIN STRUCTURES Are polymer of amino acids There are 20 different of amino acids in proteins that are coded for directly by DNA, each with different chemical properties Proteins differ from each other in the number, composition and sequence of amino acids Each amino acids is linked to its neighbor amino acids through a covalent peptide bond  AMINO ACID All amino acids have: - A CENTRAL alpha - CARBON ATOM bonded to: - AN AMINO GROUP - A CARBOXY GROUP - A HYDROGEN - A SIDE GROUP R (one of the 20 different side chain) At pH 7 both the amino and carboxyl groups are ionized PEPTIDE BONDS Amino acids are joined together by an amide linkage- PEPTIDE BOND - the long chain that is formed is called polypeptide  POLYPEPTID E protein consists of a polypeptide backbone with attached side chains The two ends of a polypeptide chain are chemically different: amino terminus or N-terminus: end carrying the free amino group -NH3+ (NH2) the carboxyl terminus or C-terminus: end carrying the free carboxyl group -COO– (COOH) The amino acid sequence of a protein is always presented in the N-to-C direction, reading from left to right FAMILIES OF AMINO ACIDS BASIC Based on the characteristics of the side chain(R) ACIDIC amino acids can be divided in: UNCHARGED POLAR NONPOLAR  LEVELS OF ORGANIZATION IN PROTEIN STRUCTURES Proteins must fold to reach a productive conformation for function A- PRIMARY STRUCTURE : amino acid sequence B- SECONDARY STRUCTURE : polypeptide chain that form α helices β sheets  C - TERTIARY STRUCTURE three-dimensional organization of a polypeptide chain D - QUATERNARY STRUCTURE : formed as a complex of more than one polypeptide chain A - Primary structure o depends on the sequence of amino acids in the polypeptide chain o is genetically determined o is characteristic for each protein o affects the spatial configuration and the global shape of the molecule on which depend the biologic properties and functions of protein  B - Secondary structure α helix - found in the protein α-keratin (abundant in skin, hair, nails) β sheet - found in the protein fibroin, the major constituent of silk Common because they result from hydrogen-bonding between the N–H and C-O groups in the polypeptide backbone The side chains of the amino acids do not participate in the formation of the secondary structure α helix generated when a single polypeptide chain twists around on itself to form a rigid cylinder the CO group of an amino acid n forms hydrogen-bonds with the NH group of amino-acids n + 4 the R groups protrude outside the helix n n +4  coiled-coil when the two (or three or four) α helices have most of their a.a hydrophobic, they can twist around each other with these nonpolar a.a facing inward β sheet can form: - from neighboring segments of the polypeptide backbone that run in the same orientation (parallel chains) - or from a polypeptide backbone that folds back and forth upon itself, with each section of the chain running in the direction opposite to that of its immediate neighbors (antiparallel chains) both types of β sheet produce a very rigid structure, held together by hydrogen bonds that connect the peptide bonds in neighboring chain  C- Tertiary structure: the polypeptide chain folds more and more and assumes a globular configuration due to the interactions between the various amino acids The tertiary structure is stabilized by bonds between side chains of amino acid residues that are spatially close Also the three-dimensional structure of a protein is predetermined and depends on the primary structure The tertiary structure of a protein is that which, among the as many as possible, it has the lowest energy content that corresponds to the maximum stability of the protein Feature of the tertiary structure: frequently the hydrophobic amino acid residues are sequestered in the protein core and the hydrophilic amino acid are on the surface and exposed to water residues amino acid very distant in the primary structure come to be close together the folding property allows the protein molecule to have one or more sites at which it can link with other molecules  WHAT ARE THE FORCES THAT STABILIZE PROTEIN STRUCTURE? structures are maintained by NON-COVALENT BONDS that form between one part of the chain and another bonds involve both the atoms in the polypeptide backbone and atoms in the amino acid R chains three types of these weak bonds: - hydrogen bonds - electrostatic attractions - van der Waals attractions - hydrophobic clustering force Hydrophobic clustering force Nonpolar (hydrophobic) side chains of ammino acids in a protein tend to cluster in the interior of the molecule to avoid contact with the water that surrounds them inside a cell Polar groups tend to arrange outside of the molecule, where they can form hydrogen bonds with water and with other polar molecules  Disulfide bonds (covalent cross linkage) Important in stabilizing the tertiary structure It is formed when, after the protein has assumed the tertiary structure, two sulfhydryl -SH groups are spatially close and oxidize The number of S-S bridges that can form in a protein depends on the number of cysteine residues present and their spatial arrangement In the tertiary structure, the hydrophobic amino acids are localized inside, while the hydrophilic ones are placed outside in contact with water. D- Quaternary structure two or more polypeptide chains can join together to form a multimeric protein each polypeptide chain in such a protein is called a protein subunit subunits bind to each other with the same weak noncovalent bonds that enable a protein chain to fold  Hemoglobin Each hemoglobin has 4 polypeptide chains (2 alpha, 2 beta) and 4 hemes (colored pigments). In the center of each heme group is 1 atom of iron that can combine with 1 molecule 02 so there are four 02 molecules per hemoglobin molecule. In this configuration saturation is 100%. 280 million hemoglobin molecules per RBC. SICKLE CELL ANEMIA substitution of one amino acid in the hemoglobin molecule substitution of the glutamic acid to valine Healthy Erythrocytes Erythrocytes from a patient affected by sickle anemia Lower oxygen transport  Protein conformation Based on their conformation proteins can be distinguished in: Fibrous proteins Globular proteins Differences in structure and function Different characteristics of water solubility  Fibrous proteins The secondary structure prevails over higher levels of organization They consist of long polypeptide chains arranged in long bundles or sheets Extremely rigid structure They represent up to 1/3 of the protein weight of vertebrates Generally insoluble in H2O Functions Protection and support Intracellular fibrous protein One large family: α-keratin Keratin filaments: Intermediate filaments in epithelial cells extremely stable important component of the cytoskeleton that creates the cell’s internal structural framework main constituents of hair and nails and to a large extent also of the skin Hair fibers are bundles of a keratin  α-keratin molecule is a dimer of two subunits, with the long α helices of each subunit forming a coiled-coil the coiled-coil regions are capped at each end by globular domains containing binding sites This enables this class of protein to assemble into ropelike intermediate filaments Extracellular fibrous protein Fibrous proteins are especially abundant outside the cell are a main component of the extracellular matrix that helps to bind cells together to form tissues Cells secrete extracellular matrix proteins into their surroundings, where they often assemble into sheets or long fibrils a. Collagen b. Elastin c. Fibronectin d. Laminin  a. Collagen the most abundant of these proteins in animal tissues main component of connective tissue (bones, tendons, ligaments etc) 28 known subtypes of collagen have been identified Type I collagen is the most common subtype, comprising over 90% of collagen in the body is a triple helix formed by three extended protein chain that wrap around one another (each containing the nonpolar amino acid glycine at every third position) Amino acid chains self-assemble to form polypeptide α-helix chains Three α-helix chains self-assemble to form a triple helix structure, termed PROCOLLAGEN Procollagen is linked via hydrogen bonds and has an approximate diameter of 1.4 nm and a length of 300 nm. Procollagen peptidase cleaves the N- and C-terminals from the precursor procollagen, forming TROPOCOLLAGEN Tropocollagen will self-assemble to form FIBRILS and, then COLLAGEN FIBERS COLLAGEN Elastin Is an extracellular matrix (ECM) protein responsible for the extensibility and elastic recoil of many tissues (arteries, heart valves, pulmonary tissues, skin) Polypeptide chains are cross-linked together in the extracellular space to form elastic fibers Each elastin molecule uncoils into a more extended conformation when the fiber is stretched and recoils spontaneously as soon as the stretching force is relaxed  Main constituent of the silk and spider's web Organized exclusively as structure β Fibroin is: FLEXIBLE because the overlapping sheets are joined together by Van der Waals interactions between side chains FIBROIN RESISTANT due to the H bonds between the adjacent chains of each lamina e due to the global effect of Van der Waals forces between superimposed chains The chains are rich in Ala and Gly. The small side chains of these two residues allow a perfect stacking of the layers of leaflets Globular proteins Consisting of one or more polypeptide chains folded in in Myoglobin globular/spherical shape generally water-soluble dynamic activity effectors of biological activities Examples Enzymes Transport (Myoglobin) Immunoglobulins Histones  PROTEIN DOMAIN Any contiguous part of a polypeptide chain that can fold independently of the rest of the protein into a compact, stable structure A domain usually contains between 40 and 350 aminoacids, and it is the modular unit from which many larger proteins are constructed The different domains of a protein are often associated with different functions MOUTH Saliva does not contain enzymes for protein digestion. Thus  SMALL INTESINE Most proteins are digested in the duodenum of small intestine Duodenum receives secretions from pancreas and liver. Pancreatic juice- contains trypsinogen, chymotrypsinogen and procarboxypeptidase Trypsinogen is activated to trypsin by enterokinase Trypsin activates chymotrypsinogen to chymotrypsin and procarboxypeptidase to carboxypeptidase. Trypsin converts basic proteins to peptones and peptides Chymotrypsin converts proteins to peptides Carboxypeptidase hydrolyzes the terminal peptide bonds in a peptide chain acting on the carboxyl group Intestinal juice contains proteases like: Aminopeptidase hydrolyses the terminal peptide bond acting on amino group Dipeptidase hydrolyses dipeptides to amino acids. Tripeptidase hydrolyses tripeptides to amino acids PROTEIN FUNCTIONS Protein that are enzymes catalyze its many chemical reactions Proteins embedded in the plasma membrane form channels and pumps that control the passage of small molecules into and out of the cell Proteins can carry messages from one cell to another, or act as signal integrators that relay sets of signals inward from the plasma membrane to the cell nucleus Proteins serve as tiny molecular machines with moving parts: kinesin, for example, propels organelles through the cytoplasm Proteins specialized act as antibodies, toxins, hormones, elastic fibers, or sources of luminescence