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BiomoleculesBiomolecules

• Carbohydratesmonosaccharides polysaccharides

• Lipids fattyacids triglycerides

• Proteins aminoacids polypeptides

• NucleicAcids nucleotides DNA,RNA

Monomers Polymers

Carbohydrates

• containcarbon,hydrogen,&oxygen,usuallyina1:2:1ratio

• generalformula:(CH2O)xn;n=#ofCatoms

• highlypolarmolecules:many–OHgroups→watersoluble

• simplecarbohydratesaresugars(mono- anddisaccharides)

• glucose(C6H12O6) isamajorenergysourceforcells

Carbohydrates– 3categories

Polysaccharides

Function: Glucose storageFig. 2.2

Carbohydrates

hexoses - 6 carbons (C6H12O6)

Monosaccharides (simple sugars)

pentoses - 5 carbons (C5H10O5)

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Dehydration (condensation) reactions build up polymers from monomers.

A-OH + H-B → A–B + H2O

Hydrolysis reactions breakdown polymers into monomers.

A–B +H2O → A-OH +H-B

a watermolecule isremoved toformthenewcovalentbond

a watermolecule isaddedtosplitthecovalent bond

DehydrationSynthesisexample

Lipids

• Mostlynon-polar molecules, rich inC-H bonds

• Mostlyinsoluble in H2O

• Functions:

• cellmembrane (phospholipids, cholesterol)

• energyreserves(triglycerides ~2x asmuch as carbspergram)

• signalingmolecules (steroid hormones andeicosanoids)

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Classes of Lipids:1. Fatty acids2. Triglycerides3. Phospholipids4. Steroids5. Eicosanoids

Lipids

Fatty acids - building blocks (monomers) of most lipids

carboxyl group

Hydrocarbon “tail’

Lipids

- long carbonchains with Hatomsattached (“hydrocarbon tail”)- oneendhas acarboxylgroup (-COOH)

Saturated- each C atom in the “tail” has 4 single

covalent bonds• 2 bonds to 2 adjacent C atoms• 2 bonds to 2 H atoms

Lipids

Fatty acids may be:

“saturated” with hydrogen atoms

monounsaturated – 1 DBpolyunsaturated – 2 or more DBs

Unsaturated- 1 or more DOUBLE covalent bonds

between C atoms• forms a “kink” in the tail

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FattyAcids

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Lipids Fatty acids

Partially hydrogenated oils and “trans fats” – chemically modified unsaturated fats; solidified with H

• hydrogenation – adding H to fatty acids: unsaturated → saturated• “trans” double bonded fatty acids produced as a byproduct• produced in manufacturing of some margarines & vegetable shortening• increase risk of heart disease • lowers HDL (“good” cholesterol); raises LDL ( “bad” cholesterol)• U.S. FDA now requires labeling of trans fats

On July 25, 2008, California became the first state to ban trans fats in restaurants effective January 1, 2010.

FYI: not on test

Lipids

Mostlipidsarehydrophobic,whichmeanstheyareinsolubleinaqueoussolutionsbutsolubleinorganicsolvents.

Mostlipidsaremadefromtwokindsofmolecules:glycerol andfattyacids joinedbydehydrationsynthesis.

Lipids

Triglycerides

Mainfunction:Energystorage inadipose tissue, liverandmusclecells

Alsopaddingandprotectionforsomeorgans

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Phospholipids phosphate group links together:

• diglyceride (2 fatty acids + glycerol) and a nonlipid groupamphipathic molecules - non-polar “tail” & polar “head”

Lipids

+

-

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LipidsPhospholipidse.g. phosopholipid bilayer – cell membrane hydrophilic heads face water

• H2O inside cell & H2O outside cell• hydrophobic tails face each other

e.g. micelles – droplets formed in H2O• hydrophilic heads face water

Hydrophobic

ICF

ECF

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Steroids – 4 hydrocarbon ringsTypes:

• Cholesterol - component of cell membranes; - precursor to other steroids

• Steroid hormones- e.g., estrogen and testosterone (sex hormones)- other steroid hormones are important in

metabolism and mineral balancee.g., cortisol, aldosterone

Lipids

Eicosanoids - modified fatty acids with a 5 C ring,- many function as paracrine substances (“local hormones” )

- direct local cellular activity (vs. true hormones which are released into the bloodstream and travel throughout the body)

Types: • prostaglandins• prostacyclins

• thromboxanes

LipidsProteins

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Amino Acids – building blocks of protein• central carbon atom• hydrogen atom• amino group (-NH2)• carboxyl group (-COOH)• variable R group

• can be polar,non-polar,acidic (-) orbasic (+)

Proteins

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Peptides – combination of two or more amino acids

Peptide bond – links adjacent aa’s (carboxyl group & amino group)

Fig.2.3 Fig.2.3

• Duetohydrogenbonding

• α-helix• β-pleatedsheet• β-turns

Fig.2.3

Disulfide bonds and weak bonds stabilize the tertiary structure of proteins.

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Tertiary structure – 3-dimensional folding from: 1) R group interactions mostly determine tertiary structure2) interactions between polypeptide & surrounding H2O or lipid molecules3) inner R group interactions

Quaternary structure – interaction among 2 or more protein subunitse.g. globular (hemoglobin) or fibrous (collagen or keratin)

Fig.2.3

ProteinStructure• Fibrousproteins

• Pleatedsheetsorchainsofhelices• Insolubleinwater• Importantstructuralfunction(collagen,keratin)

• Globularproteins• Complextertiarystructure• Solubleinwater• Lipidcarriersinblood,enzymes

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Protein Denaturation - unfolding of proteins due to drop in pH and/or increased temperature à causes hydrogen bonds to break (= shape change)

Can be reversible (mild changes) or irreversible (extreme changes)

Nucleic Acids

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NucleicAcids

Deoxyribonucleicacid (DNA)formsthegeneticcodeinsideeachcellandregulatesmostoftheactivitiesthattakeplace inourcellsthroughoutalifetime.

Ribonucleicacid (RNA)relaysinstructionsfromthegenesinthecell’snucleustoguideeachcell’sassemblyofaminoacidsintoproteinsbytheribosomesinthecytoplasm.

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Nucleotides have 3 molecular parts: 1. pentose sugar (ribose or deoxyribose)2. phosphate group3. nitrogenous base (5 types: A, G, T, C, U)

Nucleic Acids

Nucleotides are thebuilding blocks (monomers) ofDNAandRNA

Fig. 2.440

Purines – double ringAdenine (A)Guanine (G)

The Nitrogenous BasesPyrimidines – single ring

Cytosine (C)Thymine (T) DNA only

Uracil (U) RNA only

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• located in cell’s nucleus• stores genetic information • sugar is deoxyribose• sugar + phosphate form “backbone”• nitrogenous bases point inwardà Forming:

• double stranded• double helix structure

Deoxyribonucleic acid (DNA)DNA

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DNA

DNA strands are held together by hydrogen bondsbetween complementary nitrogenous bases

Complementary base pairs – shape and polarity of bases only allows formation of H bonds between:

• adenine (A) thymine (T)

• guanine (G) cytosine (C)

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Ribonucleic Acid (RNA)

• sugar is ribose• mostly single stranded (also 2º and 3º structures

in tRNA and rRNA)• base pairing: A...U, G...C

Classes of RNA• messenger (mRNA)• transfer (tRNA)• ribosomal (rRNA)

. . .. . .. . .

RNA relays instructions fromthegenes in thecell’s nucleus toguide eachcell’s assembly ofamino acids into proteins by the ribosomes in thecytoplasm.

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DNA vs. RNA

(1) Sugar:DNA = deoxyriboseRNA = ribose

(2) Nitrogenous bases:DNA = A G C TRNA = A G C U

(3) Strands:DNA = double strandedRNA = mostly single stranded

Adenosine Triphosphate (ATP) –a high-energy nucleotide

ATPis the“energycurrency”moleculeofthecellPhosphorylation - additionahigh-energyphosphategrouptoADPtoformATP