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9/10 Agenda10 min complete Animal Behavior Lab Mini-PostersPass back & Discuss Free Response QuestionStart Biomolecules NotesMacromolecules Synthesis/Degradation DiagramsWhy study Carbon?Living organisms consist mostly of carbon-based compoundsAll living things are made of cells Cells ~72% H2O ~3% salts (Na, Cl, K)~25% carbon (organic) compoundscarbohydrateslipidsproteins nucleic acidsMost organic compounds contain hydrogen (H) atoms in addition to carbon atoms with O, N and P among others thrown in from time to time.2Why do we study carbon -- is it the most abundant element in living organisms?H & O most abundantC is the next most abundant

The FOUR Classes of Large BiomoleculesAll living things are made up of four classes of large biological molecules: Carbohydrates LipidsProteinNucleic Acids

Macromolecules are large molecules composed of thousands of covalently bonded atoms

Molecular structure and function are inseparable

3This lesson will deal with carbohydrates and lipids, with protein and nucleic acids coming in a separate lesson. Emphasize yet again that within the molecule, the intramolecular forces are covalent bonds, but the intermolecular forces (IMFs) between molecules will vary due to the polarity of the molecule as a whole.3The FOUR Classes of Large BiomoleculesMacromolecules are polymers, built from monomers A polymer is a long molecule consisting of many similar building blocks These small building-block molecules are called monomersThree of the four classes of lifes organic molecules are polymersCarbohydratesProteinsNucleic acids

4Emphasize that monomers join through covalent bonding (a pair, or more, of electrons is shared between two monomers). Take a moment to assess what students already know. Can they cite examples of carbohydrates, proteins and nucleic acids. If so, try to use the examples they came up with during your discussions. 4Polymers: made of monomers

A. Condensation reaction (dehydration synthesis):Joins monomers to make polymersOne monomer provides a hydroxyl group while the other provides a hydrogen to form a water molecule

B. Hydrolysis:Digests (breaks down) polymersbonds between monomers are broken by adding waterDehydration Synthesis6

Emphasize the ends of the molecule, one end has an OH group, the other has an H. Each group leaves an electron attached to the monomer or polymer and those 2 electrons form a covalent bond while the H and OH form a water molecule. 6Hydrolysis7

Hydrolysis literally means (water splitting). A water molecule adds across a covalent bond and cleaves off one monomer at a time. Drink lots of water if your goal is to disassemble fats! 7Carbohydrates

Sugars: MonosaccharidesMonosaccharides have molecular formulas that are usually multiples of CH2O

Glucose (C6H12O6) is the most common monosaccharide

Monosaccharides are classified by The location of the carbonyl groupThe number of carbons in the carbon skeleton

9Emphasize they are carbo-hydrates as in carbon-water as is evidenced from the (CH2O)n general formula. It is not necessary to emphasize how they are classified. 9Sugars: DisaccharidesA disaccharide is formed when a dehydration reaction joins two monosaccharides

This covalent bond is called a glycosidic linkage

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Ask students how these hexagons differ from the one in the previous slide. Point out to them that it is customary to leave Cs and even Hs off the art in the interest of focusing on what is really important with regard to a given bond formation. It is not necessary they know glycosidic linkage, its just necessary that they know a water was released and helpful to know that an oxygen remains in tact. 10PolysaccharidesPolysaccharides, the polymers of sugars, have storage and structural roles

The structure and function of a polysaccharide are determined by its sugar monomers and the positions of glycosidic linkages

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Same dehydration synthesis song, second verse. Scroll over the image to reveal the play command for the animation.11Types of Polysaccharides: StorageStarch, a storage polysaccharide of plants, consists entirely of glucose monomersPlants store surplus starch as granules within chloroplasts and other plastids The simplest form of starch is amylose

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Emphasize the link between structure and function. It is not necessary to memorize the names of starches. 12Types of Polysaccharides: StorageGlycogen is a storage polysaccharide in animalsHumans and other vertebrates store glycogen mainly in liver and muscle cells13

Glycogen may have been referred to as animal starch in their middle school or Biology I course. 13Types of Polysaccharides: StructuralThe polysaccharide cellulose is a major component of the tough wall of plant cells

Like starch, cellulose is a polymer of glucose, but the glycosidic linkages differ

The difference is based on two ring forms for glucose: alpha () and beta ()14While cellulose may not be all that exciting, it is interesting that termites cannot digest it until they establish a symbiotic relationship with a protozoan that can! To digest cellulose, organisms must produce the enzymecellulase. Humans and termites are unable to produce cellulase themselves but termites have living in their gut simple organisms (protozoaandbacteria) which can produce the enzyme.This is an example ofmutualism- a relationship between two species in which both organisms benefit. The protoza and bacteria benefit by receiving a constant supply of food (wood) from the termite. The termite benefits from the energy-rich sugar released from the cellulose by the termites. Read more:http://wiki.answers.com/Q/Why_termites_can_digest_cellulose_but_human_cannot#ixzz23pblQhQb14Such Elegance!15

Notice the structural hierarchy from monomer to polymer to cellulose to a grouping of cellulose into a microfibril to the structure of the cell wall to the plant cell to the leaf. Emphasize the structural hierarchy from monomer to polymer to cellulose to a grouping of cellulose into a microfibril to the structure of the cell wall to the plant cell to the leaf. Whew!15Polysaccharide Random Acts of BiologyCellulose in human food passes through the digestive tract as insoluble fiberSome microbes use enzymes to digest celluloseMany herbivores, from cows to termites, have symbiotic relationships with these microbes

Chitin, another structural polysaccharide, is found in the exoskeleton of arthropods (crunch!)

Chitin also provides structural support for the cell walls of many fungi

16Just site these as common examples of organisms that utilize carbohydrates.16Who knew?17

17Lipids

Lipids Are HydrophobicLipids are a diverse group of hydrophobic moleculesLipids are the one class of large biological molecules that do not form polymersThe unifying feature of lipids is having little or no affinity for water (water fearing)Lipids are hydrophobic because they consist mostly of hydrocarbons, which form nonpolar covalent bondsThe most biologically important lipids are fats, phospholipids, and steroids

19Hydrophobic means water fearing. If youre up for a demo, you can use a couple of clear containers (beakers, etc.) partway filled with water to demonstrate that neither oil nor shortening, etc. will dissolve in water. Also, since this is the first time steroid has appeared, you may want to take a moment and discuss anabolic (building up) versus catabolic (tearing down) processes and that the sum of these processes is metabolism. Also point out that testosterone and estrogen are steroids. 19Fats: Start with a Simple Little Glycerol MoleculeFats are constructed from two types of smaller molecules: glycerol and fatty acidsGlycerol is a three-carbon alcohol with a hydroxyl group attached to each carbonA fatty acid consists of a carboxyl group attached to a long carbon skeleton

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Remind students that an OH group attached to a hydrocarbon skeleton makes an alcohol, NOT A BASE! 20Dehydration Rxn 1: Add a Fatty Acid Next, add a fatty acid through a dehydration synthesis reactionWhat makes it an acid? The C double bond O, single bond OH!

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Glycerol is on its way to make a triglyceride, which they may have heard talk of if anyone in their family is struggling with too many triglycerides in their diet. 21Dehydration Rxn 2!!Next, add a SECOND fatty acid through a dehydration synthesis reaction

Sorry, the picture is not pretty, but it does convey the idea. One more fatty acid to add before this becomes a triglyceride.22Dehydration Reaction THREE!!!In a fat, three fatty acids are joined to glycerol by an ester linkage, creating a triacylglycerol, or triglyceride

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No need to memorize ester linkage. Ask students how many water molecules it will take to disassemble this molecule! Ans: THREE!2324Certain unsaturated fatty acids are not synthesized in the human body These must be supplied in the dietThese essential fatty acids include the omega-3 fatty acids, required for normal growth, and thought to provide protection against cardiovascular diseaseCouldnt resist a nutrition moment. No need to memorize!24Fats: Major function is storage!The major function of fats is energy storageHumans and other mammals store their fat in adipose cellsAdipose tissue also cushions vital organs and insulates the body

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Adipose tissue is from hormonally inert, adipose tissue has in recent years been recognized as a majorendocrine organ, as it produces hormones such as leptin, estrogen, and resistin. More than you need to have students know, but interesting none the less!25PhospholipidsWhen phospholipids are added to water, they self-assemble into a bilayer, with the hydrophobic tails pointing toward the interiorPhospholipids are the major component of all cell membranes

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You know where this is headedbring on the cell membrane unit! 26

CholinePhosphateGlycerolFatty acidsHydrophilicheadHydrophobictails(c) Phospholipid symbol(b) Space-filling model(a) Structural formulaHydrophilic headHydrophobic tailsA Single Phospholipid Molecule27The structure of a phospholipid.Steroids

Steroids are lipids characterized by a carbon skeleton consisting of four fused ringsCholesterol, an important steroid, is a component in animal cell membranesAlthough cholesterol is essential in animals, high levels in the blood may contribute to cardiovascular disease28See how many steroids your students can name. 28proteins

Proteins Come In Many Varieties!Proteins include a diversity of structures, resulting in a wide range of functions

Proteins account for more than 50% of the dry mass of most cells

Protein functions include: structural support, storage, transport, cellular communications, movement, and defense against foreign substances30Ask students what they already know about proteins and protein synthesis. Hopefully, they remember a few things from Biology I.30Enzymatic31

Enzymatic proteinsEnzymeExample: Digestive enzymes catalyze the hydrolysisof bonds in food molecules.Function: Selective acceleration of chemical reactions

Emphasize the specificity of enzymes. Also emphasize the catalytic nature of enzymes and that they function best in a unique set of pH and temperature conditions. Why is that? It is due to the shape of the enzyme molecule. That shape is held in place by IMFs and/or covalent or ionic bonding. Changes in pH or temperature often disrupt the electrostatic forces that are responsible for an enzymes specific shape.31

More About Enzymes32Enzymes are a type of protein that acts as a catalyst to speed up chemical reactionsEnzymes can perform their functions repeatedly, functioning as workhorses that carry out the processes of life

This is a perfect time to bring out the water noodle enzyme models. You can extend this portion of the lesson to include competitive inhibition, etc. 32Storage33

Storage proteinsOvalbuminAmino acidsfor embryoFunction: Storage of amino acidsExamples: Casein, the protein of milk, is the majorsource of amino acids for baby mammals. Plants havestorage proteins in their seeds. Ovalbumin is theprotein of egg white, used as an amino acid sourcefor the developing embryo.Ask students to identify other food sources that are proteins. One of my favorite quotes ever is from Bob Harper, a personal trainer from The Biggest Loser. Simply put, If the food in question had a mother, then its a protein!33Hormonal34

Hormonal proteinsFunction: Coordination of an organisms activitiesExample: Insulin, a hormone secreted by thepancreas, causes other tissues to take up glucose,thus regulating blood sugar concentrationHighblood sugarNormalblood sugarInsulinsecretedAsk students to give examples of hormonal proteins. They should easily come up with testosterone and estrogen among others.34Defensive35

Defensive proteinsVirusAntibodiesBacteriumFunction: Protection against diseaseExample: Antibodies inactivate and help destroyviruses and bacteria.Ask students which body system utilizes these types of proteins. 35Transport36

Transport proteinsTransportproteinCell membraneFunction: Transport of substancesExamples: Hemoglobin, the iron-containing protein ofvertebrate blood, transports oxygen from the lungs toother parts of the body. Other proteins transportmolecules across cell membranes.Ask which body system utilizes hemoglobin.36Receptor37

SignalingmoleculesReceptorproteinReceptor proteinsFunction: Response of cell to chemical stimuliExample: Receptors built into the membrane of anerve cell detect signaling molecules released byother nerve cells.Ask if they know any of the signaling molecules as well as which body system is involved in this process. Hopefully, they come up with the nervous system, the fight or flight response as it relates to adrenaline, etc. 37Structural38

60 mCollagenConnectivetissueStructural proteinsFunction: SupportExamples: Keratin is the protein of hair, horns,feathers, and other skin appendages. Insects andspiders use silk fibers to make their cocoons and webs,respectively. Collagen and elastin proteins provide afibrous framework in animal connective tissues.Emphasize collagens role in the aging process and its unfortunate consequences such as wrinkling! 38Amino Acids: Yet Another MonomerAmino acids are organic molecules with carboxyl and amino groups

Amino acids differ in their properties due to differing side chains, called R groups

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Side chain (R group)AminogroupCarboxylgroup carbonThere are 23 amino acids (aas) but only 20 are biologically active. 39PolypeptidesPolypeptides are unbranched polymers built from the same set of 20 amino acidsA protein is a biologically functional molecule that consists of one or more polypeptides40

Ask, how many peptide bonds are formed. Ask how many amino acids are in this polypeptide. Additionally, emphasize the arrangement of the aas in this diagram. If one of the aas is flipped along the horizontal axis, its amine group no longer aligns with the neighboring aas carboxylic acid group, thus no dehydration reaction can occur. 40

Nonpolar side chains; hydrophobicSide chainGlycine(Gly or G)Alanine(Ala or A)Valine(Val or V)Leucine(Leu or L)Isoleucine(Ile or I)Methionine(Met or M)Phenylalanine(Phe or F)Tryptophan(Trp or W)Proline(Pro or P)Hydrophobic AAs : Therefore retreat from water!41Absolutely no need to memorize these, but there is a need to recognize WHY these retreat from water. Point out that these R groups are very nonpolar as evidenced by the hydrocarbonish or CHX nature of the elements involved in the R groups. 42Hydrophilic AAs: Therefore Are Attracted to Water

Absolutely no need to memorize these, but emphasize that while these R groups also look hydrocarbonish, that there are unpaired electrons left off this diagram. Each N, O or S atom has unshared electron pairs that make them polar and water soluble. 4243Hydrophilic: But Electrically Charged (Ionic)!

Again, no need to memorize these but students should know that ammonia (NH3) is a weak base from Chemistry I. Remove an H from ammonia and you have its cousin the amine group which is also basic. 43Peptide BondsAmino acids are linked by peptide bondsA polypeptide is a polymer of amino acidsPolypeptides range in length from a few to more than a thousand monomers Each polypeptide has a unique linear sequence of amino acids, with a carboxyl end (C-terminus) and an amino end (N-terminus)

44Emphasize that the peptide bond forms as a consequence of a dehydration synthesis reaction. 44Peptide Bonds45

Protein Structure & FunctionAt first, all we have is a string of AAs bound with peptide bonds. = a polypeptide

Once the string of AAs interacts with itself and its environment (often aqueous), then we have a functional protein that consists of one or more polypeptides precisely twisted, folded, and coiled into a unique shape

The sequence of amino acids determines a proteins three-dimensional structure

A proteins structure (conformation ) determines its function!!!

4646Protein Structure: 4 LevelsPrimary structure consists of its unique sequence of amino acidsSecondary structure, found in most proteins, consists of coils and folds in the polypeptide chainTertiary structure is determined by interactions among various side chains (R groups)Quaternary structure results when a protein consists of multiple polypeptide chains

47Now is the time to explain that a string of aas is a polypeptide and NOT yet a protein. The protein forms once the secondary, tertiary and quaternary structures are established and that is usually facilitated in an aqueous environment. Also emphasize that conformation is the big people word for shape and that if the conformation changes, the function of the protein is affected.47

Primary StructurePrimary structure, the sequence of amino acids in a protein, is like the order of letters in a long word Primary structure is determined by inherited genetic information

Keep it simple. Explain to students that when they were about 3 years old, they would sing the alphabet song to anyone that would listen! They had no idea that one day theyd use that to spell or that they would use it to read, or write sentences, or paragraphs or research papers!

Also, remind them yet again that they have some prior knowledge regarding DNA and the process of protein synthesis.48Secondary Structure

The coils and folds of secondary structure result from hydrogen bonds between repeating constituents of the polypeptide backboneTypical secondary structures are a coil called an helix and a folded structure called a pleated sheet

49Emphasize yet again that a H-bond is NOT a bonded H! Its an IMF, not a covalent bond, but rather an electrostatic force. H-bonds are fragile and easily interrupted by pH or temperature changes. 49

Secondary Structure50Linus Pauling is my favorite scientist, so Id have to share that he won his first Nobel Prize in Chemistry in 1954 "for his research into the nature of the chemical bond and its application to the elucidation of the structure of complex substances". Those complex substances are proteins and he figured out the helix and a folded structure called a pleated sheet! Students may know that the electronegativity scale they learned in Chemistry I is the Pauling Electronegativity Scale. But, they may not know that he was hot on the heels of beating Watson & Crick to the discovery of the structure of DNA OR that he also won a Nobel Prize for Peace. Whew!

Tertiary StructureTertiary structure is determined by interactions between R groups, rather than interactions between backbone constituentsThese interactions between R groups include actual ionic bonds and strong covalent bonds called disulfide bridges which may reinforce the proteins structure.IMFs such as London dispersion forces (LDFs a.k.a. and van der Waals interactions), hydrogen bonds (IMFs), and hydrophobic interactions (IMFs) may affect the proteins structure51Here we go again, the second bullet refers to actual chemical bondsthe sharing of a pair of electrons. The third bullet refers to intermolecular forces (IMFs) with LDFs that the biology books often refer to as van der Waals forces or interactions. H-bonds are a special case of dipole-dipole interactions. While none of these distinctions will be asked on the AP Biology exam, they certainly will on the AP Chemistry exam and should be taught in Chem I as well. Its not surprising that students are confused since the vocabulary is so different from book to book! Ugh!51Tertiary Structure52

Revisit the curly hair example for disulfide bridges. Folks with curly hair have more disulfide bridges and we often use heat to alter them 1.Use a hair dryer-brush-mechanically pull on the hair while applying heat to disrupt the S-S bridges. 2. Flat irons on dry hair 3. PermsA basic solution that reeks of ammonia (a base, thus a pH rather than thermal approach) is applied to hair that has been wound onto skinny curlers and left to sit for about 20 minutes to allow S-S to form.

52Quaternary StructureQuaternary structure results when two or more polypeptide chains form one macromolecule

Collagen is a fibrous protein consisting of three polypeptides coiled like a rope

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Emphasize that Quaternary structure involves a collection of polypeptides brought together into a new conformation. 53Quaternary StructureHemoglobin is a globular protein consisting of four polypeptides: two alpha and two beta chains54

The classic example! 54Four Levels of Protein Structure Revisited55

A nice visual summary!55Sickle-Cell Disease: A change in Primary StructureA slight change in primary structure can affect a proteins structure and ability to function Sickle-cell disease, an inherited blood disorder, results from a single amino acid substitution in the protein hemoglobin56

Normal Red Blood CellsA perfect practical example of how a change in protein structure affects function. Be sensitive to the fact that you may have a student that suffers from sickle-cell disease. 56Sickle-Cell Disease: A change in Primary StructureA slight change in primary structure can affect a proteins structure and ability to function Sickle-cell disease, an inherited blood disorder, results from a single amino acid substitution in the protein hemoglobin57

The sickled cells cannot move the blood vessels as effectively and can obstruct capillaries and restrict blood flow to an organ, resulting in pain, necrosis and often organ damage. Ask if students studied the connection between sickle-cell trait and malaria in Biology I. 57Sickle-Cell Disease: A change in Primary Structure58

What Determines Protein Structure?In addition to primary structure, physical and chemical conditions can affect structureAlterations in pH, salt concentration, temperature, or other environmental factors can cause a protein to unravelThis loss of a proteins native structure is called denaturationA denatured protein is biologically inactive59Ask how EACH of the items mentioned could disrupt protein structure. 59Denature: Break Bonds or Disrupt IMFs60

This concept is an energy concept as well. If thermal energy is added, the molecules vibrate more vigorously. At some point the electrostatic attractions (H-bonds) are overcome and let go.

When students write free-responses, make sure they define terms they use within their writing. A change in temperature denatures a protein since the H-bonds (or IMFs) are disrupted (or overcome, or altered, or anything else that implies the structure is broken down). Lots of ways to wordsmith the response correctly!

60nucleic acidsNucleic AcidsNucleic acids store, transmit, and help express hereditary information

The amino acid sequence of a polypeptide is programmed by a unit of inheritance called a gene

Genes are made of DNA, a nucleic acid made of monomers called nucleotides62Ask questions to see what they already know about DNA structure. A good deal of this should be prior knowledge! 62Two Types of Nucleic AcidsThere are two types of nucleic acidsDeoxyribonucleic acid (DNA)Ribonucleic acid (RNA)DNA provides directions for its own replicationDNA directs synthesis of messenger RNA (mRNA) and, through mRNA, controls protein synthesisProtein synthesis occurs on ribosomes

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Pause and let student examine both structures. WHERE exactly is the deoxy part of the name coming from? 63Figure 5.25-1

Synthesis ofmRNAmRNADNANUCLEUSCYTOPLASM164DNA mRNAFigure 5.25-2

Synthesis ofmRNAmRNADNANUCLEUSCYTOPLASMmRNAMovement ofmRNA intocytoplasm1265DNA m RNA what next?? (ribosome!)Figure 5.25-3

Synthesis ofmRNAmRNADNANUCLEUSCYTOPLASMmRNARibosomeAminoacidsPolypeptideMovement ofmRNA intocytoplasmSynthesisof protein12366DNA mRNA ribosome protein. Whats missing? See if they can supply the details about tRNA, etc. Try to connect to what they already know and correct any misconceptions.The Components of Nucleic AcidsEach nucleic acid is made of monomers called nucleotides

Each nucleotide consists of a nitrogenous base, a pentose sugar, and one or more phosphate groupsNitrogenous Bases: cytosine, thymine, adenine, guanine, and uracilIn DNA, the sugar is deoxyribose; in RNA, the sugar is ribose

67Again, most likely prior knowledge.67

Figure 5.26abSugar-phosphate backbone5 end5C3C5C3C3 end(a) Polynucleotide, or nucleic acid(b) NucleotidePhosphategroupSugar(pentose)NucleosideNitrogenousbase5C3C1C68Components of nucleic acids.Figure 5.26c

Nitrogenous basesCytosine (C)Thymine (T, in DNA)Uracil (U, in RNA)Adenine (A)Guanine (G)SugarsDeoxyribose (in DNA)Ribose (in RNA)(c) Nucleoside componentsPyrimidinesPurines69Ask about base pairing. Students most likely know A-T and G-C. Emphasize that the pairing is due to, you guessed it, H-bonding!

70Ask about base pairing. Students most likely know A-T and G-C. Emphasize that the pairing is due to, you guessed it, H-bonding! Note the formation of 2 H-bonds for AT and 3 H-bonds for GC. No need to memorize, just interesting to the student that makes you crazy with But, why? questions. Nucleic AcidsAdjacent nucleotides are joined by covalent bonds that form between the OH group on the 3 carbon of one nucleotide and the phosphate on the 5 carbon on the nextThese links create a backbone of sugar-phosphate units with nitrogenous bases as appendagesThe sequence of bases along a DNA or mRNA polymer is unique for each gene

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Emphasize the backbone of the ladder is held together with actual covalent bonds (much stronger than an IMF). We number Cs in a ring starting with the O and going clockwise if anyone asks. 71Nucleic AcidsRNA molecules usually exist as single polypeptide chains DNA molecules have two polynucleotides spiraling around an imaginary axis, forming a double helixOne DNA molecule includes many genes

72Details they probably didnt get in Biology I.72

Sugar-phosphatebackbonesHydrogen bondsBase pair joinedby hydrogen bondingBase pair joinedby hydrogenbonding(b) Transfer RNA(a) DNA535373The single dotted line between base pairs is an oversimplification! Reiterate the sugar-phosphate backbones or sides of the ladder are held together with actual covalent chemical bonds. The rungs of the ladder or base pairs align the way they do because of H-bonding (an IMF) AND therefore are not as tightly held together. The elegance involves the ease of the unzipping or zipping of the molecule vs. the stability of the single strand when it is unzipped, thus vulnerable to damage. Link to EvolutionThe linear sequences of nucleotides in DNA molecules are passed from parents to offspring

Two closely related species are more similar in DNA than are more distantly related species

Molecular biology can be used to assess evolutionary kinship74Link Big Ideas together as often as possible!74Summary of Biomolecules75

The type of linkage is not nearly as important as the rest of this summary. Student still have to be able to read and interpret test questions! 75Structure determines FunctionEver heard of a runners high?Our body manufactures endorphins which are made by the pituitary gland and bind to the receptors in the brain that relieve pain and produce euphoria during times of stress, such as intense exercise.

Opiates such as morphine and heroin are structured similarly, thus can bind with the receptors . These bindings are actually those electrostatic attractions we call IMFs. 77This is a good time to point out that students need illustrative examples for each and every major unit of study. Help them choose these illustrative examples!77The boxed regions are shaped similarly! 78

Natural endorphinMorphineCarbonHydrogenNitrogenSulfurOxygen(a) Structures of endorphin and morphineHave students compare the boxed portion of each diagram. Whats alike? Whats different? 78Pain killer!The brain receptors bind with either with similar results. 79

(b) Binding to endorphin receptorsBrain cellMorphineNaturalendorphinEndorphinreceptorsBind is in quotes becauseyou guessed itits not a chemical bond that is binding these molecules to the receptor but an IMF that attracts them. Those electrostatic attractions can indeed induce shape changes which can impact molecular function.79