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Lipids and Proteins

Lipids and Proteins



Chapters 17 and 18 in General, Organic, and Biochemistry, 7th ed. by Denniston.

Chapters 17 and 18 in General, Organic, and Biochemistry, 7th ed. by Denniston.



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  • A trans fatty acid is more linear than a cis fatty acid (see slide 23), so the molecules can pack more closely together than they can in a cis fatty acid. Closer molecules mean stronger intermolecular forces and higher melting points.

Lipids and Proteins Lipids and Proteins Presentation Transcript

  • 1Chapter 17Lipids and Their Functionsin Biological Systems
  • 2LipidsLipids arebiomolecules that contain fatty acids or a steroid nucleus.soluble in organic solvents, but not in water.named for the Greek word lipos, which means “fat.”extracted from cells using organic solvents.
  • 3Lipids—one classificationThe types of lipids containing fatty acids arewaxesfats and oils (triacylglycerols)glycerophospholipidsprostaglandinsThe types of lipids that do not contain fatty acids aresteroids
  • 4Lipids—one classification
  • 5Lipids—another classificationFour main groupsFatty acidsSaturatedUnsaturatedGlycerides: glycerol-containing lipidsNonglyceride lipidsSphingolipidsSteroidsWaxesComplex lipids: lipoproteins
  • 6Lipids—another classification
  • 7Fatty acidsFatty acids arelong-chain carboxylic acids.typically 12-18 carbon atoms.insoluble in water.saturated or unsaturated.Olive oil contains 84%unsaturated fatty acids and16% saturated fatty acids.
  • 8Fatty acidsFatty acids aresaturated with all single C–C bonds.unsaturated with one or more double C=C bonds.
  • 9Fatty acidsSaturated fatty acidscontain only single C–C bonds.are closely packed.have strong attractions between chains.have high melting points.are solids at room temperature.COOHCOOHCOOH
  • 10COOHHH CCHOOCHHCCFatty acidsUnsaturated fatty acidscontain one or more cisdouble C=C bonds.have “kinks” in the fattyacid chains.do not pack closely.have few attractionsbetween chains.have low melting points.are liquids at roomtemperature.“kinks”inchain
  • 11Fatty acidsMelting points of fatty acids
  • 12Waxes, fats, and oilsWaxes are:esters of saturated fatty acids and long-chain alcohols.coatings that prevent loss of water by leaves of plants.
  • 13Waxes, fats, and oilsFats and oils arealso called triglycerides.esters of glycerol.*produced by esterification.formed when the hydroxyl groups ofglycerol react with the carboxylgroups of fatty acids.*The IUPAC name for glycerol is 1,2,3-propanetriol.
  • 14In a triglyceride, glycerol forms ester bonds with threefatty acids.
  • 15glycerol + 3 fatty acids  triglyceride + 3 watersWaxes, fats, and oilsOHCH2OHOHCH2CHO(CH2)14CH3CHOO(CH2)14CH3CHOO(CH2)14CH3CHO+ 3H2OOOC (CH2)14CH3CH OOC (CH2)14CH3CH2 OOC (CH2)14CH3CH2
  • 16(CH2)12CH3OCCH(CH2)7CH3(CH2)7CHOCO(CH2)16CH3COOOCH2CH2CHWaxes, fats, and oilsExample of a triglyceride:Stearic acidOleic acidMyristic acid
  • 17Waxes, fats, and oilsA fat• is solid at roomtemperature.• is prevalent in meats, wholemilk, butter, and cheese.An oil• is liquid at roomtemperature.• is prevalent in plants such asolive and safflower.
  • 18Waxes, fats, and oilsOilshave more unsaturated fats.have cis double bonds that cause “kinks” in the fatty acidchains.with “kinks” in the chains do not allow the triglyceridemolecules to pack closely.have lower melting points than saturated fatty acids.are liquids at room temperature.
  • 19Waxes, fats, and oilsUnsaturated fatty acid chains with kinks cannot packclosely.
  • 20Waxes, fats, and oilsPercent saturated and unsaturated fatty acids
  • 21Chemical reactions of fatty acidsIn hydrogenation1, double bonds in unsaturated fattyacids react with H2 in the presence of a Ni or Pt catalyst.CH(CH2)7CH3(CH2)5CHOCCH(CH2)7CH3(CH2)5CHOCCH(CH2)7CH3(CH2)5CHOCOOOCH2CH2CHO(CH2)14CH3CO(CH2)14CH3CO(CH2)14CH3COOOCH2CH2CH+ 3 H2Niglyceryl tripalmitoleate glyceryl tripalmitate1See Chapter 11, pages 363-365
  • 22Chemical reactions of fatty acidsUnsaturated fatty acids can becis with bulky groups on same side of C=C.trans with bulky groups on opposite sides of C=C.
  • 23Chemical reactions of fatty acidsMost naturally occurringfatty acids have cis doublebonds.During hydrogenation, somecis double bonds areconverted to trans doublebonds.In the body, trans fatty acidsbehave like saturated fattyacids.Why would trans fatty acidsbehave like saturated fattyacids, while cis fatty acids donot?
  • 24Chemical reactions of fatty acidsIn hydrolysis2, ester bonds are split by water in thepresence of an acid, a base, or an enzyme.OCH2OCHOCH2OHCH2OHCHOHCH2 O(CH2)14CH3CHOH2OO(CH2)14CH3CO(CH2)14CH3CO(CH2)14CH3CH+++2See Chapter 14, pages 472-473
  • 25Chemical reactions of fatty acidsOOC (CH2)14CH3CH OOC (CH2)14CH3CH2 OOC (CH2)14CH3CH2+ 3NaOHNa+ -OOC (CH2)14CH33OHCH OHCH2 OHCH2+“soap”In saponification, a fatty acid ortriglyceride reacts with a strong baseto form an alcohol or glycerol, andthe salt(s) of fatty acid(s).
  • 26TriglyceridesGlycerides are lipid esters.A triglyceride places fatty acid chains at each alcoholgroup of a molecule of glycerol.glycerolportionfatty acidchains
  • 27TriglyceridesTriglycerides undergo three basic reactions, identical tothose studied in carboxylic acids.TriglycerideGlycerolFatty AcidsGlycerolFatty Acid SaltsMore saturatedtriglycerideH2O, H+NaOHH2, Ni
  • 28GlycerophospholipidsGlycerophospholipids arethe most abundant lipids in cell membranes.composed of glycerol, two fatty acids, phosphate, and anamino alcohol.GlycerolPO4AminoalcoholFatty acidFatty acidexample
  • 29Cholesterol and steroid hormonesA steroid nucleus consists ofthree cyclohexane rings, andone cyclopentane ring.The rings are fused (joined along one side).
  • 30Cholesterol and steroid hormonesCholesterolis the most abundant steroid in the body.has methyl (-CH3) groups, an alkyl chain, and an -OH attached tothe steroid nucleus.
  • 31Cholesterol and steroid hormonesA steroid is any natural or synthetic compound based onthe four-fused-ring structure in cholesterol.testosteronecortisoneprogesterone
  • 32Chapter 18Protein Structure and Function
  • 332. The α-amino acidsAmino acidsare the building blocks of proteins.contain a carboxylic acid group
  • 342. The α-amino acidsAmino acidsare the building blocks of proteins.contain a carboxylic acid group and an amino group
  • 352. The α-amino acidsAmino acidsare the building blocks of proteins.contain a carboxylic acid group and an amino group on thealpha () carbon.
  • 362. The α-amino acidsAmino acidsare the building blocks of proteins.contain a carboxylic acid group and an amino group on thealpha () carbon.are ionized in solution.H2Oionizedform
  • 372. The α-amino acidsAmino acidsare the building blocks of proteins.contain a carboxylic acid group and an amino group on thealpha () carbon.are ionized in solution.all have a different side chain.H2Oionizedform
  • 382. The α-amino acidsExamples of amino acidsglycinealanine
  • 392. The α-amino acidsAll but one of the amino acids have a chiral carbon. Theα carbon is attached toa carboxylate group (COO-),a protonated amino group (-NH3+),a hydrogen atom, anda side chain (R group).Glycine has R = H, which gives it two hydrogens attachedto the α carbon and no chiral carbon.
  • 402. The α-amino acidsEach amino acid (except glycine) can exist as one of twostereoisomers.Only L- isomers of amino acids are found in proteins.Recall that mainly D- isomers of monosaccharides exist innature.As for monosaccharides, Fischer projections for aminoacids have the most oxidized group at the top.L-alanine D-alanine L-cysteine D-cysteine
  • 412. The α-amino acidsAmino acids are classified based on the nature of theirside chains.Nonpolar amino acids are hydrophobic and have hydrocarbonside chains.Polar amino acids are hydrophilic and have polar or ionic sidechains.Acidic amino acids are hydrophilic and have acidic (carboxylicacid) side chains.Basic amino acids are hydrophilic and have amino side chains.
  • 422. The α-amino acidsNonpolar: The R group is H, alkyl, or aromatic.glycine alanine valinemethionine prolinephenylalanineleucine isoleucinetryptophan
  • 432. The α-amino acidsPolar: the R group is an alcohol, thiol, or amideserine threonine tyrosinecysteineasparagineglutamine
  • 442. The α-amino acidsAcidic: The R group is a carboxylic acid.aspartate glutamate
  • 452. The α-amino acidsBasic: The R group is an amine.histidine argininelysine
  • 463. The peptide bondA peptide bond is an amide bond that forms betweenthe carboxyl group of one amino acid and the aminogroup of the next amino acid.glycine alanine+ H2O
  • 473. The peptide bondNaming peptidesFor small peptides, the general name “peptide” is preceded bya prefix indicating how many amino acids were condensed toform the peptide.The peptide formed on the previous slide is a dipeptide.The end of the peptide with the free NH3+ group is called the N-terminal amino acid.The end of the peptide with the free –COO- group is called theC-terminal amino acid.
  • 483. The peptide bondNaming peptides (cont.)The root name of a peptide is the name of the C-terminalamino acid, which uses its entire name.For all other amino acids in the peptide, the ending –ine ischanged to –yl.The amino acids are named in order starting with the N-terminal amino acid.A peptide composed of aspartine, glutamine, and serine(in that order) would be named:aspartyl-glutamyl-serine
  • 493. The peptide bondThe structures of small peptides are based on a repeatingbackbone:N—C—C—N—C—C—N—C—Cα-amino group (N)α-carbon (always attached to H and R)α-carboxyl group (C)
  • 503. The peptide bondDraw the structure of aspartyl-glutamyl-serine.This is a tripeptide, so the backbone will have three repeats.The left end is the N-terminal amino acid and the right end isthe C-terminal amino acid.The carboxyl carbons all have a carbonyl and the α carbons allhave a hydrogen.
  • 513. The peptide bondDraw the structure of aspartyl-glutamyl-serine. (cont.)Each α carbon has the R group characteristic of the particularamino acid.aspartameglutamateserine
  • 524. The primary structure of proteinsThe primary structure of a protein is the amino acidsequence of the protein’s peptide backbone.There are 20 amino acids which can be arranged in varyingorders.The length of the peptide backbone can vary.
  • 534. The primary structure of proteinsPrimary structure is the amino acid sequence of thepolypeptide chain.It is the result of covalent bonding (peptide bonds) betweenamino acidsEach protein has a different primary structure withdifferent amino acids in different places along the chainCH3SHCH2CH3SCH2CH2CH OO-CCHHNOCCHHNOCCHHNOCCHH3NCH3CH3CHAla─Leu─Cys─Met
  • 544. The primary structure of proteinsInsulin was the first protein to have its primarystructure determined.It has a primary structure of two polypeptide chainslinked by disulfide bonds.One chain (A) has 21 amino acids and the other (B) has30 amino acids.
  • 555. The secondary structure of proteinsWhen the primary sequence of the polypeptide folds intoregularly repeating structures, secondary structure isformed.Secondary structure results from hydrogen bonding betweenthe amide hydrogens and carbonyl oxygens of the peptidebonds.
  • 565. The secondary structure of proteinsThe α-helix is the most common typeof secondary structure.Features:a three-dimensional spatial arrangementof amino acids in a polypeptide chain.held by H bonds between the H of –N-Hgroup and the O of C=O of the fourthamino acid down the chain.a corkscrew shape that looks like a coiled“telephone cord”.
  • 575. The secondary structure of proteinsTop view of the α-helix, looking down into the “barrel.”The side chains (-R) point out.
  • 585. The secondary structure of proteinsThe second most common secondary structure is the β-pleated sheet.The β-pleated sheet consists of polypeptide chains arrangedside by side with hydrogen bonds between chains.Side chains (-R) are above and below the sheet.This structure is typical of fibrous materials like silk.
  • 596. The tertiary structure of proteinsSoluble proteins are usuallyglobular proteins.A third level of structure,tertiary structure, is added tothe primary and secondarystructures.Areas of α-helix and β-pleatedsecondary structure are folded inon themselves and held in placeby the forces responsible fortertiary structure.
  • 606. The tertiary structure of proteinsCrosslinks in tertiary structures involve attractions andrepulsions between the side chains (-R) of the aminoacids in the polypeptide chain.Hydrophobic interactions: attractions between nonpolargroups.Hydrophilic interactions: attractions between polar groups andwater.Salt bridges: ionic interactions between acidic and basic aminoacids.Hydrogen bonds: between H and oxygen or nitrogen.Disulfide bonds: covalent links between sulfur atoms of twocysteine amino acids.
  • 616. The tertiary structure of proteinssalt bridgehydrophobicinteractionshydrogenbondsdisulfidebonds
  • 627. The quaternary structure of proteinsQuaternary structure is the arrangement of subunits orpeptides that form a larger protein.A subunit is a polypeptide chain having primary, secondary, andtertiary structural features that is a part of a larger protein.Quaternary structure is maintained by the same forces whichare active in maintaining tertiary structure.Hemoglobin consists of four polypeptide chains assubunits.
  • 638. Overview of protein structurePrimary structure:Amino acid sequenceResults from formation of covalentpeptide bonds between amino acidsSecondary structure:Includes α-helix and β-sheetHydrogen bonding between amidehydrogens and carbonyl oxygens of thepeptide bonds
  • 648. Overview of protein structureTertiary structure:Overall folding of the entirepolypeptide chainInteractions between differentamino acid side chainsQuaternary structure:Concerned with topological, spatialarrangement of two or morepolypeptide chainsInvolves both disulfide bridges andnoncovalent interactions
  • 6510. Denaturation of proteinsDenaturation involves the disruption of bonds in thesecondary, tertiary and quaternary protein structures.Denaturation is the loss of organized structure of a globularprotein.Denaturation does not alter primary structure.Causes of denaturation:heat and organic compounds that break apart H bonds anddisrupt hydrophobic interactions.acids and bases that break H bonds between polar R groupsand disrupt ionic bonds.heavy metal ions that react with S-S bonds to form solids.agitation such as whipping that stretches peptide chains untilinteractive forces are broken.
  • 6610. Denaturation of proteinsHeat: As the temperature rises, molecules move andvibrate more. The weaker hydrogen bonds are the firstto break.pH: Amino acids include basic (amino) and acidic(carboxylate) groups. An excess of H+ or OH- changesionic interactions involving these groups.Organic solvents: Alcohols disrupt hydrogen bondingbecause they take part in it themselves. The nonpolarportions of alcohols disrupt nonpolar interactions.Denaturation of Protein by Strong Acid
  • 6710. Denaturation of proteinsDetergents: The hydrophobic region of detergentsdisrupts hydrophobic interactions in proteins.Heavy metals: Metal cations such as mercury or lead canbond with negative side chains and disrupt theirinteractions. They can also bind to sulfur and disruptdisulfide bonds.Mechanical stress: Shaking or whipping can disrupt theintermolecular forces that maintain the conformation ofthe protein.