LECTURE PRESENTATIONS

For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson

Chapter 4

Carbon and the Molecular Diversity of Life

Lectures by Erin Barley Kathleen Fitzpatrick

© 2011 Pearson Education, Inc.

• • •

Overview: Carbon: The Backbone of Life

living organisms consist mostly of carbon-based compounds carbon is unparalleled in its ability to form large, complex, and diverse molecules proteins, DNA, carbohydrates, and other molecules that distinguish living matter are all composed of carbon compounds

Molecules of Life:

• the chemicals used in metabolic reactions or those that are produced by them can be classified into 2 groups:

1. Inorganic 2. Organic

Inorganic Compounds

 water  oxygen,carbon dioxide  inorganic salts

Organic Compounds

 what three elements make up an organic compound?

Organic Compounds

•

always contain carbon, oxygen and hydrogen

Concept 4.2: Carbon atoms can form diverse molecules by bonding to four other atoms

• •

electron configuration

is the key to an atom’s characteristics electron configuration determines the kinds and number of bonds an atom will form with other atoms

The Formation of Bonds with Carbon

• • • •

with

four valence electron -

carbon can form

four covalent bonds

with a variety of atoms this ability makes large, complex molecules possible in molecules with multiple carbons, each carbon bonded to four other atoms has a

tetrahedral shape

however, when two carbon atoms are joined by a double bond, the atoms joined to the carbons are in the

same plane as the carbons

Figure 4.3

Name and Comment (a) Methane Molecular Formula Structural Formula CH 4 (b) Ethane C 2 H 6 Ball-and Stick Model Space-Filling Model (c) Ethene (ethylene) C 2 H 4

• the valences of carbon and its most frequent partners (hydrogen, oxygen, and nitrogen) are the “building code” that governs the architecture of living molecules

Hydrogen (valence



1) Oxygen (valence



2) Nitrogen (valence



3) Carbon (valence



4) Urea

• • Carbon chains form the skeletons of most organic molecules Carbon chains vary in length and shape

(a) Length (c) Double bond position Ethane (b) Branching Propane 1-Butene (d) Presence of rings 2-Butene Butane 2-Methylpropane (isobutane) Cyclohexane Benzene

Hydrocarbons

• • •

Hydrocarbons

and hydrogen are organic molecules consisting of only carbon many organic molecules, such as fats, have hydrocarbon components hydrocarbons can undergo reactions that release a large amount of energy

Nucleus Fat droplets 10



m (a) Part of a human adipose cell (b) A fat molecule

Isomers

• • variation in the architecture of organic molecules can be seen as

isomers isomers

are compounds with the same molecular formula but different structures and properties –

structural isomers

have different covalent arrangements of their atoms –

cis-trans isomers

have the same covalent bonds but differ in spatial arrangements –

enantiomers

are isomers that are mirror images of each other

(a) Structural isomers (b) Cis-trans isomers cis isomer: The two Xs are on the same side.

trans isomer: The two Xs are on opposite sides.

(c) Enantiomers CO 2 H CO 2 H H CH 3 L isomer NH 2 NH 2 CH 3 D isomer H

• • • • enantiomers are important in the pharmaceutical industry two enantiomers of a drug may have different effects usually only one isomer is biologically active differing effects of enantiomers demonstrate that organisms are sensitive to even subtle variations in molecules

Drug Condition Effective Enantiomer Ineffective Enantiomer Ibuprofen Pain; inflammation S-Ibuprofen R-Ibuprofen Albuterol Asthma R-Albuterol S-Albuterol

• • •

Concept 4.3: A few functional groups are key to the functioning of biological molecules

distinctive properties of organic molecules depend on the carbon skeleton and on the molecular components attached to it a number of characteristic

functional groups

can replace the hydrogens attached to skeletons of organic molecules the number and arrangement of functional groups give each molecule its unique properties

Estradiol Testosterone

Example: Modification of Hydrocarbons

• • modification of a hydrocarbon with functional groups can turn a non-polar hydrocarbon into a structure with polar characteristics the functional groups usually contain O, N, P or S H H C H H C H H C H C O OH carboxyl group = hydrophilic H H C H H C H H C H C O O d de-protonated carboxyl group hydrocarbon + carboxyl group  “hydrophilic” due to the electronegativity of the oxygen atom

•

The seven functional groups that are most important in the chemistry of life: – Hydroxyl group = negative charge – Carbonyl group – Carboxyl group = negative charge – Amino group = positive charge – Sulfhydryl – Sulfate group = negative charge – Phosphate group = negative charge – Methyl group

CHEMICAL GROUP

Hydrophilic

Hydroxyl Carbonyl

Hydrophilic

Carboxyl STRUCTURE (may be written HO —) NAME OF COMPOUND Alcohols (Their specific names usually end in -ol.) Ketones if the carbonyl group is within a carbon skeleton Aldehydes if the carbonyl group is at the end of the carbon skeleton Carboxylic acids, or organic acids EXAMPLE Ethanol Acetone Acetic acid FUNCTIONAL PROPERTIES • Is polar as a result of the electrons spending more time near the electronegative oxygen atom.

• Can form hydrogen bonds with water molecules, helping dissolve organic compounds such as sugars.

Propanal • A ketone and an aldehyde may be structural isomers with different properties, as is the case for acetone and propanal.

• Ketone and aldehyde groups are also found in sugars, giving rise to two major groups of sugars: ketoses (containing ketone groups) and aldoses (containing aldehyde groups).

• Acts as an acid; can donate an H + because the covalent bond between oxygen and hydrogen is so polar: Nonionized Ionized • Found in cells in the ionized form with a charge of 1



and called a carboxylate ion.

Hydrophilic

Amino

Hydrophilic

Sulfhydryl Amines

Hydrophilic

Phosphate Thiols (may be written HS —) Organic phosphates Methyl Methylated compounds Glycine • Acts as a base; can pick up an H + from the surrounding solution (water, in living organisms): Nonionized Ionized • Found in cells in the ionized form with a charge of 1+.

Cysteine • Two sulfhydryl groups can react, forming a covalent bond. This “cross-linking” helps stabilize protein structure. • Cross-linking of cysteines in hair proteins maintains the curliness or straightness of hair. Straight hair can be “permanently” curled by shaping it around curlers and then breaking and re-forming the cross-linking bonds.

Glycerol phosphate • Contributes negative charge to the molecule of which it is a part (2 – when at the end of a molecule, as above; 1 – when located internally in a chain of phosphates).

• Molecules containing phosphate groups have the potential to react with water, releasing energy.

5-Methyl cytidine • Addition of a methyl group to DNA, or to molecules bound to DNA, affects the expression of genes.

• Arrangement of methyl groups in male and female sex hormones affects their shape and function.

-the H+ of a carboxyl group is often picked up by the NH2  NH3+ -creates a zwitterion

Organic macromolecules

: 1. carbohydrates 2. lipids 3. proteins 4. nucleic acids

Figure 5.2

(a) Dehydration reaction: synthesizing a polymer 1 2 Short polymer 3 Unlinked monomer Dehydration removes a water molecule, forming a new bond.

1 2 3 Longer polymer (b) Hydrolysis: breaking down a polymer 4 1 2 3 4 Hydrolysis adds a water molecule, breaking a bond.

1 2 3

1. Carbohydrates:

• provide energy to cells • can be stored as reserve energy supply (humans = glycogen) • supply “building materials” to build certain cell structures • • • e.g. cell wall of plants water soluble = hydrophilic characterized H - C - OH • e.g. glucose C 6 H 12 O 6 sucrose C 12 H 22 O 11 classified by size: simple sugars – saccharides complex – polysaccharides monosaccharides disaccharides

•

carbohydrates are classified many ways:

1. the location of the carbonyl group (as aldose or ketose) -aldose = carbonyl group (C=O) is at the end of the carbon skeleton -ketose – carbonyl is within the carbon skeleton

2. the number of carbons in the carbon skeleton

-e.g. five carbon sugars = pentose (ribose and deoxyribose) -e.g. six carbon = hexose (glucose, fructose and galactose) 3. also by the number of subunits – simple saccharides (sugars) and complex polysaccharides

A. Simple carbohydrates – mono and disaccharides

• monosaccharides = single saccharide subunit in which the # of carbon atoms is low - from 3 to 7 - formula: C:2H:O

Aldose (Aldehyde Sugar) Ketose (Ketone Sugar) Hexoses: 6-carbon sugars (C 6 H 12 O 6 ) Glucose Galactose Fructose

• • • glucose and galactose with their carbonyls at the end are aldose sugars glucose and galactose only differ with respect to their arrangements of H and OH groups at one carbon!! (see purple boxes) fructose is a ketose sugar

Monosaccharides

:

- in aqueous solutions – the monosaccharides are not linear -they form rings

-three ways to represent the ring structure of a monosaccharide

1. Molecular ring form 2. Abbreviated ring structure 3. Simplest form

Glucose, Fructose and Galactose

beta-glucose (OH above the ring plane) alpha-glucose (OH below the ring plane) beta-galactose (isomer of glucose at the 4 carbon)

A. Simple carbohydrates

•

disaccharide

= two monosaccharides bound together -form by

a dehydration synthesis glycosidic linkage

reaction to form a -broken up by

a hydrolysis

reaction e.g. glucose + glucose = maltose e.g. glucose + fructose = sucrose e.g. glucose + galactose = lactose

B. Complex carbohydrates:

• built of simple carbohydrates to form macromolecules •multiple, repeating monomers or “building blocks” 

polymer

•some serve as storage materials – hydrolyzed into individual monosaccharides for sugars • others serve as structural or building materials

Storage Polysaccharides

Chloroplast Starch granules Amylopectin

•

Starch & Glycogen = storage polysaccharides

• stored by plants and animals as a future sugar supply •

starch

= storage form of glucose found in plants • simplest ones are joined by 1-4 linkages (e.g.

amylose

) • helical and unbranched in conformation • stored within plastids – e.g. chloroplast • some are more complex – with branch points (1-6 linkages) – e.g. amylopectin • hydrolyzed into glucose by enzymes – found in both plants and animals

(a) Starch: 1



m a plant polysaccharide Mitochondria Glycogen granules (b) Glycogen: 0.5



m an animal polysaccharide

•

Amylose Glycogen glycogen

= storage form of glucose found in animals • very highly branched • hydrolyzed into glucose (in liver)

Structural Polysaccharides

• • •

cellulose

-major component of the tough wall of plant cells polymer of glucose, but the glycosidic linkages differ the difference is because there are two ring forms for glucose:

alpha (



) and beta (



)

– when glucose forms a ring – the OH group at carbon 1 can either be positioned above or below the plane of the ring – above – beta form – below – alpha form – starch – all glucoses are in the alpha form –

cellulose – all glucoses are in the beta form

upside down – which makes every other glucose

(a)



and



glucose ring structures



Glucose



Glucose (b) Starch: 1 –4 linkage of



glucose monomers (c) Cellulose: 1 –4 linkage of



glucose monomers

•

cellulose differs from starch in many ways:

– unlike starch – cellulose is not helical or branched – some OH groups on its glucose monomers are free to hydrogen bond with OHs from neighbouring cellulose molecules – results in cellulose molecules grouped parallel to one another = called

microfibrils

– strong cable-like building material – found in the cell wall of plants – enzymes that digest starch are unable to break the beta linkages of cellulose because of their different shapes – prokaryotes possess

cellulase

• large numbers of these bacteria in the gut of herbivores – humans unable to hydrolyze cellulose – “insoluble fiber” • cellulose “scrapes” the lining of the GI tract and causes the production of mucus (aids in smooth passage of other food through the GI tract)

Cell wall Cellulose microfibrils in a plant cell wall Microfibril 10



m 0.5



m Cellulose molecules



Glucose monomer

Lipids

• many types – – –

1. triglycerides

= fats and oils

2. phospholipids 3. steroids

• cholesterol – animal cell membranes, basis for steroid hormones • bile salts - digestion • vitamin D – calcium regulation • Adrenocorticosteroid hormones • Sex hormones –

4. Eicanosoids

• prostaglandins • leukotrienes –

5. Others

• fatty acids • carotenes – synthesis of vitamin A • vitamin E – wound healing • vitamin K – blood clotting • lipoproteins – HDL and LDL • waxes and pigments

2. Lipids

A. Fats

• energy supply • most plentiful lipids in your body • composed of C, H and O • “building blocks” =

3 fatty acid chains

(hydrocarbons usually from 16 to 18 carbons)

PLUS 1 glycerol molecule

fatty acid fatty acid fatty acid glycerol portion fatty acid portion

• • •

formed through dehydration synthesis reactions to form an

ester linkage

the three fatty acids joined to glycerol creates a

triacylglycerol

, or triglyceride fats separate from water because water molecules form hydrogen bonds with each other and exclude the fats

Ester linkage Fatty acid (in this case, palmitic acid) Glycerol (a) One of three dehydration reactions in the synthesis of a fat

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(b) Fat molecule (triacylglycerol)

• fatty acids -differ in chain length with each fat -differ in the location and number of double bonds within the hydrocarbon chains 1. single C bonds - saturated 2. double C bonds - unsaturated • •

Saturated fatty acids

have the maximum number of hydrogen atoms possible and no double bonds

Unsaturated fatty acids

have one or more double bonds

monounsaturated: 1 double bond polyunsaturated: 2 or more double bonds

(a) Saturated fat (b) Unsaturated fat Structural formula of a saturated fat molecule Space-filling model of stearic acid, a saturated fatty acid

•

Structural formula of an unsaturated fat molecule Space-filling model of oleic acid, an unsaturated fatty acid Cis double bond causes bending.

at room temperature – the molecules of a

saturated fat are packed closely togethe

r • • the fatty acid tails are more flexible forms a solid • the molecules of an unsaturated fat cannot pack closely together enough to solidify • • the

C=C bonds produce a “kink” in the fatty acid

chain making it difficult to pack them together if the fat contains one fatty acid that is unsaturated – then the fat is considered unsaturated • in hydrogenated oils – the unsaturated fats have been chemically converted to saturated by adding hydrogens • prevents their separation into an oil form – keeps them solid

-a gram of fat stores twice as much energy vs. a gram of a polysaccharide like starch -adipose tissue evolved due to animal movement -much less bulky than polysaccharides like starch -although plants did evolve oils in their seeds to decrease the amount of space needed for the energy required -some fatty acids cannot be made by the body and must be taken in through food =

essential fatty acids

e.g omega-3 fatty acids -polyunsaturated fatty acids -important in regulating cholesterol levels (lower LDL levels in the blood) -increase calcium utilization by body - reduce inflammation (arthritis?) - promote wound healing

B. Phospholipids • similar to fat molecules - glycerol + 2 fatty acids •modified through the replacement of one FA with a phosphate group (negative electrical charge) • phosphate gp  hydrophilic “head” • fatty acid gps  hydrophobic “tails” • when added to water – self-assemble and form a form a

phospholipid bilayer

– major component of the

plasma membrane

C. Steroids • backbone is called cholesterol = 4 fused carbon rings • synthesized in the liver • diversity through attached functional groups e.g. testosterone, estrogen aldosterone

3. Proteins

• nearly every dynamic function of a living organism depends on proteins •Greek – proteios = “first place” •more than 50% of the dry mass of most cells •numerous roles: • structural – support of cells and tissues • storage - energy source • transport across cell membranes • hormones and their receptors – signaling • chemical messengers - signaling • antibodies - defense • metabolic role - enzymes

Enzymatic proteins Function: Selective acceleration of chemical reactions Example: Digestive enzymes catalyze the hydrolysis of bonds in food molecules.

Enzyme Defensive proteins Function: Protection against disease Example: Antibodies inactivate and help destroy viruses and bacteria.

Antibodies Virus Bacterium Storage proteins Function: Storage of amino acids Examples: Casein, the protein of milk, is the major source of amino acids for baby mammals. Plants have storage proteins in their seeds. Ovalbumin is the protein of egg white, used as an amino acid source for the developing embryo.

Transport proteins Function: Transport of substances Examples: Hemoglobin, the iron-containing protein of vertebrate blood, transports oxygen from the lungs to other parts of the body. Other proteins transport molecules across cell membranes.

Transport protein Ovalbumin Amino acids for embryo Cell membrane

Figure 5.15-a

Figure 5.15-b

Hormonal proteins Function: Coordination of an organism’s activities Example: Insulin, a hormone secreted by the pancreas, causes other tissues to take up glucose, thus regulating blood sugar concentration High blood sugar Insulin secreted Normal blood sugar Contractile and motor proteins Function: Movement Examples: Motor proteins are responsible for the undulations of cilia and flagella. Actin and myosin proteins are responsible for the contraction of muscles.

Actin Myosin Muscle tissue 100



m Receptor proteins Function: Response of cell to chemical stimuli Example: Receptors built into the membrane of a nerve cell detect signaling molecules released by other nerve cells.

Signaling molecules Receptor protein Structural proteins Function: Support Examples: Keratin is the protein of hair, horns, feathers, and other skin appendages. Insects and spiders use silk fibers to make their cocoons and webs, respectively. Collagen and elastin proteins provide a fibrous framework in animal connective tissues.

Collagen Connective tissue 60



m

• • •

life would not be possible without enzymes enzymes

are a type of protein that acts as a

catalyst

chemical reactions to speed up function relies upon their 3D conformation and the physical environment they are working in

3. Proteins

•building blocks =

amino acids Side chain (R group) Amino group



carbon Carboxyl group

a.a. = amino group at 1 end, carboxyl at the other - between is a single C called the

alpha carbon

-the alpha carbon is assymetrical and is bound to: 1. H atom

2. R group

• • •

22 amino acids available for human protein synthesis

– 20 of them are coded for by our DNA the R group give the amino acid a unique physical and chemical character divided into

three groups

–

polar amino acids

–

non-polar amino acids

–

electrically charged amino acids –basic or acidic

the 20 amino acids coded by DNA: 1. non-polar:

1. Methionine – Met or M 2. Phenylalanine – Phe or F 3. Tryptophan – Trp or W 4. Proline – Pro or P 5. Glycine – Gly or G 6. Alanine – Ala or A 7. Valine – Val or V 8. Leucine – Leu or L 9. Isoleucine – Iso or I

2. polar:

1. Serine – Ser or S 2. Threonine – Thr or T 3. Cysteine – Cys or C 4. Tyrosine – Tyr or Y 5. Asparagine – Asp or N 6. Glutamine – Glu or Q

3. acidic

1. Aspartic acid – Asp or D 2. Glutamic acid – Glut or E

4. basic

1. Lysine – Lys or K 2. Arginine – Arg or R 3. Histidine – His or H

• amino acids joined together by a dehydration synthesis reaction forming a

peptide bond

= between the NH 2 of 1 a.a. and the COOH of the next amino acid Figure 5.17

Peptide bond New peptide bond forming Side chains Back bone Amino end (N-terminus) Peptide bond Carboxyl end (C-terminus)

2 a.a.  dipeptide 3 a.a.  tripeptide 4 or more a.a.  polypeptide

• the 3D architecture is critical to protein function • 3D shape is determined by the sequence of amino

acids

-i.e. the chemical properties of the amino acid can determine whether the protein will twist or kink or be linear -when a cell forms a polypeptide – it

spontaneously begins to fold (takes no energy)

-folding is driven by the bonds between different regions of the pp chain

-the types of bonds depend on the amino acid sequence

•BUT – the physical environment can also affect 3D shape • e.g. pH, salt, temperature •IMPORTANT: polypeptide does not mean protein!!!!

(a) A ribbon model

•polypeptides have 4 types of structures or conformations which affect their ultimate function

(b) A space-filling model

Protein conformation: 1. primary - a.a. sequence of polypeptides e.g. transthyretin – 127 amino acids -sequence is determined by the genetic code found in the DNA -if randomly created – then a 127 AA polypeptide could be made 20 127 different ways!!

Secondary structure Tertiary structure Quaternary structure



helix



pleated sheet Hydrogen bond



strand Hydrogen bond Transthyretin polypeptide Transthyretin protein

2. secondary – sections of the AA chain fold into  -helical coils or  -pleated sheets -found in most proteins -the result of H bonding - O and N atoms have partial negative charges -the weakly positive H atom attached to the N is attracted to the positive O of a nearby AA -alpha helix – produced by H bonding every 4 th AA -beta pleated sheet – H bonding between two or more regions of the PP lying side by side

3. tertiary – secondary structure folds into a unique 3D shape -tertiary conformation is superimposed on the secondary structure -gives rise to the overall 3D shape and function of the protein -results from

interactions between the R groups Secondary structure Tertiary structure



helix



pleated sheet Hydrogen bond



strand Hydrogen bond

-one interaction = hydrophobic interactions -non-polar AAs face in when the protein folds -due to hydrophobic interaction with water -van der Waals keep these AAs close together -other interactions: -hydrogen bonding -between polar AAs -between the +ve and –ve charges of the acidic and basic AAs (ionic bond)

Hydrogen bond Disulfide bridge Hydrophobic interactions and van der Waals interactions Ionic bond Polypeptide backbone

-3D shape is reinforced through the formation of disulfide bridges

4. quaternary = joining of 2 or more polypeptides chains -aggregate into one function macromolecule -individual polypeptide chains are called subunits

Heme Iron



subunit



subunit Collagen



subunit



subunit Hemoglobin

MEDICAL APPLICATION: Sickle-Cell Disease: A Change in Primary Structure

• A slight change in primary structure can affect a protein’s structure and ability to function • Sickle-cell disease, an inherited blood disorder, results from a single amino acid substitution in the protein hemoglobin

Primary Structure 1 2 3 4 5 6 7 Secondary and Tertiary Structures



subunit

 

Quaternary Structure Normal hemoglobin

 

Function Molecules do not associate with one another; each carries oxygen.

Red Blood Cell Shape 10



m 1 2 3 4 5 6 7 Exposed hydrophobic region



subunit



Sickle-cell hemoglobin

 

Molecules crystallize into a fiber; capacity to carry oxygen is reduced.

10



m



Protein Folding in the Cell

• • • • the AA sequence of more than 10 million proteins is now known the 3D structure of more than 20,000 proteins are also known – used to predict a protein’s structure from its primary structure BUT – the folding process is not straightforward – most proteins probably go through several stages on their way to a stable structure

one thing is known – that initial protein folding is spontaneous

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•

Protein Folding in the Cell

Chaperonins –proteins that assist the proper folding of other proteins – don’t fold the protein – detects when a protein is mis-folded and targets it for destruction – found in the cytoplasm and in the endoplasmic reticulum – made of a ‘cap’ on top a ‘hollow cylinder’ – the cylinder keeps the protein protected while it folds spontaneously – other monitoring systems also exist to verify folding – destruction of the mis-folded protein – by a proteosome • diseases such as Alzheimer’s, Parkinson’s, and mad cow disease are associated with mis-folded proteins

Polypeptide Correctly folded protein Cap Chaperonin (fully assembled)

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Steps of Chaperonin Action: 1 An unfolded poly peptide enters the cylinder from one end.

2 The cap attaches, causing the cylinder to change shape in such a way that it creates a hydrophilic environment for the folding of the polypeptide.

3 The cap comes off, and the properly folded protein is released.

• •

Protein Folding in the Cell

EXPERIMENT

– – – determining 3D protein structure uses a branch of science called X-ray

crystallography

the molecule is crystallized the atoms of the molecule diffract the X-rays diffraction pattern is analyzed by computer software and a 3D ribbon structure is generated – known as bioinformatices another method is nuclear magnetic resonance (NMR) spectroscopy - does not require protein crystallization

X-ray source X-ray beam RESULTS RNA Diffracted X-rays Crystal Digital detector X-ray diffraction pattern DNA RNA polymerase II

4. Nucleic acids

• known as DNA, RNA • C,H,O,N,P • building blocks = nucleotides or nucleic acids

5



end

• nucleotide:

5



C

•5 carbon sugar (pentose)  phosphate group (negative charge) located at the 5’ carbon  organic base located at the 1’ carbon  sugar and the base is known as a

nucleoside

 bases: 5 types: adenine (A)

cytosine (C) guanine (G) thymine (T) uracil (U) 3



end 3



C 5



C 3



C Sugar-phosphate backbone (a) Polynucleotide, or nucleic acid 5



C (b) Nucleotide Nucleoside Nitrogenous base Phosphate group 3



C Sugar (pentose) 1



C

Cytosine (C) Nitrogenous bases Pyrimidines Thymine (T, in DNA) Uracil (U, in RNA)

 There are two families of nitrogenous bases 1. Pyrimidines (cytosine, thymine, and uracil) have a single six-membered ring 2. Purines (adenine and guanine) have a six membered ring fused to a five-membered ring

Sugars Purines Adenine (A) Guanine (G) (c) Nucleoside components Deoxyribose (in DNA) Ribose (in RNA)

• polynucleotide chain - formed by a phosphodiester bond between the phosphate (5’) of 1 n.t. and the sugar of the next (3’) -phosphodiester bond is comprised of a phosphate group linking two sugars

5



end 5



C 3



C Sugar-phosphate backbone

• two major types of nucleic acids:

1. RNA sugar = ribose

phosphodiester bond

2. DNA sugar = deoxyribose

HOCH 2 O OH H OH

OH ribose

H HOCH 2 O OH H H OH

H deoxyribose 5



C 3



C 3



end (a) Polynucleotide, or nucleic acid

• so a DNA/RNA chain “grows” in one direction only -5’ to 3’

A. RNA  single polynucleotide chain  bases: A, C, G and uracil (U) in place of T  3 major types: mRNA tRNA rRNA B. DNA  double polynucleotide chain = double helix

sense strand (5’ to 3’) anti-sense strand

 2 chains held by hydrogen bonds between the bases  bases pair up in a complementary fashion A = T C G

c. ATP  individual n.t’s can have metabolic functions e.g. adenosine = adenine + ribose -adenine modified by adding three phosphates  major source of ATP = breakdown of glucose 1 glucose molecule glycolysis Kreb’s cycle oxidative phosphorylation 36 ATP