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Chapter 3Biochemistry

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Why study carbon?• All living things are made of

cells• Cells are…

– ~72% water– ~3% salts– ~25% carbon compounds

• Carbohydrates• Proteins• Lipids• Nucleic acids

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Carbon Chemistry• Organic chemistry -study

of carbon compounds• Carbon atoms can form

diverse molecules by bonding to four other atoms

• Carbon has four valence electrons and may form single, double, triple, or quadruple bonds

4

• The electron configuration of carbon gives it covalent compatibility with many different elements

H O N C

Hydrogen(valence = 1)

Oxygen(valence = 2)

Nitrogen(valence = 3)

Carbon(valence = 4)

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Hydrocarbons• Hydrocarbons are molecules consisting

of only carbon and hydrogen• Hydrocarbons are found in many of a cell’s

organic molecules

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HHH

HH

H H H

HH

H

H H H

H H HH H

H

H

H

H

H

H

HH

HH H H H

H HH H

H H H H

H H

H H

HHHH H

HH

C C C C C

C C C C C C C

CCCCCCCC

C

CC

CC

C

C

CCC

CC

H

H

H

HHH

H

(a) Length

(b) Branching

(c) Double bonds

(d) Rings

Ethane Propane

Butane isobutane

1-Butene 2-Butene

Cyclohexane Benzene

H H H HH

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Functional Groups• Functional groups are

the parts of molecules involved in chemical reactions

• They Are the chemically reactive groups of atoms within an organic molecule

• Give organic molecules distinctive chemical properties

CH3OH

HO

O

CH3

CH3OH

Estradiol

Testosterone

Female lion

Male lion

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• Six functional groups are important in the chemistry of life– Hydroxyl – in alcohols, sugar

– Carbonyl – in sugars, amino acids, nucleotide bases

– Carboxyl – in amino acids, fatty acids; acts as an acid and releases H+

– Amino – in amino acids; acts as a weak base

– Sulfhydryl – in amino acid cysteine; helps stabilize protein structure

– Phosphate – in ATP, nucleotides, proteins, phospholipids; acidic;

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Some important functional groups of organic compounds

FUNCTIONALGROUP

STRUCTURE

(may be written HO )

HYDROXYL CARBONYL CARBOXYL

OH

In a hydroxyl group (—OH), a hydrogen atom is bonded to an oxygen atom, which in turn is bonded to the carbon skeleton of the organic molecule. (Do not confuse this functional group with the hydroxide ion, OH–.)

When an oxygen atom is double-bonded to a carbon atom that is also bonded to a hydroxyl group, the entire assembly of atoms is called a carboxyl group (—COOH).

CO O

COH

The carbonyl group ( CO) consists of a carbon atom joined to an oxygen atom by a double bond.

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• Some important functional groups of organic compounds

The amino group (—NH2) consists of a nitrogen atom bonded to two hydrogen atoms and to the carbon skeleton.

AMINO SULFHYDRYL PHOSPHATE

(may be written HS )

The sulfhydryl group consists of a sulfur atom bonded to an atom of hydrogen; resembles a hydroxyl group in shape.

In a phosphate group, a phosphorus atom is bonded to four oxygen atoms; one oxygen is bonded to the carbon skeleton; two oxygens carry negative charges; abbreviated P . The phosphate group (—OPO3

2–) is an ionized form of a phosphoric acid group (—OPO3H2; note the two hydrogens).

NH

H

SHO P

OOH

OH

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Macromolecules– Are large molecules composed of

smaller molecules– Are complex in their structures

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Macromolecules•Most macromolecules are polymers, built from monomers• Four classes of life’s organic molecules are polymers

– Carbohydrates– Proteins– Nucleic acids– Lipids

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• A polymer– Is a long molecule consisting of many

similar building blocks called monomers– Specific monomers make up each

macromolecule– E.g. amino acids are the monomers for

proteins

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How are organic compounds built?

• Enzymes (proteins) are needed to make metabolic reactions proceed much faster than they would on their own.

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The Synthesis and Breakdown of Polymers

• Monomers form larger molecules by condensation reactions called dehydration synthesis

(a) Dehydration reaction in the synthesis of a polymer

HO H1 2 3 HO

HO H1 2 3 4

H

H2O

Short polymer Unlinked monomer

Longer polymer

Dehydration removes a watermolecule, forming a new bond

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The Synthesis and Breakdown of Polymers

• Polymers can disassemble by a cleavage reaction -Hydrolysis (addition of water molecules)

(b) Hydrolysis of a polymerHO 1 2 3 H

HO H1 2 3 4

H2O

HHO

Hydrolysis adds a watermolecule, breaking a bond

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Carbohydrates• Serve as fuel and building

material• Include both sugars and

their polymers (starch, cellulose, etc.)

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Sugars• Monosaccharides

– Are the simplest sugars– Can be used for fuel– Can be converted into other

organic molecules– Can be combined into polymers

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• Examples of monosaccharidesTriose sugars

(C3H6O3)Pentose sugars

(C5H10O5)Hexose sugars

(C6H12O6)

H C OHH C OHH C OHH C OHH C OH

H C OHHO C H

H C OHH C OHH C OH

H C OHHO C HHO C H

H C OHH C OH

H C OH

H C OH

H C OH

H C OHH C OHH C OH

H C OHC OC O

H C OHH C OHH C OH

HO C H

H C OHC O

H

H

H

H H H

H

H H H H

HH H

C C C COOOO

Aldo

ses

GlyceraldehydeRibose

Glucose Galactose

Dihydroxyacetone

Ribulose

Keto

ses

Fructose

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• Monosaccharides– May be linear– Can form rings

H

H C OH

HO C H

H C OH

H C OH

H C

OC

H

12

3

4

5

6

H

OH

4C

6CH2OH 6CH2OH

5C

HOH

CH OH

H2 C

1CH

O

H

OH

4C

5C

3 CH

HOH

OH

H2C

1 C

OH

HCH2OH

H

H

OHHO

H

OH

OH

H5

3 2

4

(a) Linear and ring forms. Chemical equilibrium between the linear and ring structures greatly favors the formation of rings. To form the glucose ring, carbon 1 bonds to the oxygen attached to carbon 5.

OH 3

O H OO6

1

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• Disaccharides–Consist of two monosaccharides

–Are joined by a glycosidic linkage

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Dehydration reaction in the synthesis of maltose. The bonding of two glucose units forms maltose. The glycosidic link joins the number 1 carbon of one glucose to the number 4 carbon of the second glucose. Joining the glucose monomers in a different way would result in a different disaccharide.

Dehydration reaction in the synthesis of sucrose. Sucrose is a disaccharide formed from glucose and fructose.Notice that fructose,though a hexose like glucose, forms a five-sided ring.

(a)

(b)

H

HOH

HOH H

OH

O H

OH

CH2OH

H

HO

H

HOH H

OH

O HOH

CH2OH

H

O

H

HOH H

OH

O H

OH

CH2OH

H

H2O

H2O

H

H

O

H

HOH

OH

O HCH2OH

CH2OH HO

OHH

CH2OH

HOH H

H

HO

OHH

CH2OH

HOH H

O

O H

OHH

CH2OH

HOH H

O

HOH

CH2OH

H HO

O

CH2OH

H

H

OH

O

O

1 2

1 41– 4

glycosidiclinkage

1–2glycosidic

linkage

Glucose

Glucose Glucose

Fructose

Maltose

Sucrose

OH

H

H

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Polysaccharides• Polysaccharides (complex

carbohydrates)– Are polymers of sugars– Serve many roles in organisms

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Storage Polysaccharides• Starch

– Is a polymer consisting entirely of glucose monomers

– Is the major storage form of glucose in plants

Chloroplast Starch

Amylose Amylopectin

1 m

(a) Starch: a plant polysaccharide

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• Glycogen– Consists of glucose monomers– Is the major storage form of glucose in

animals Mitochondria Giycogen granules

0.5 m

(b) Glycogen: an animal polysaccharide

Glycogen

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Structural Polysaccharides

• Cellulose– Is a polymer of glucose– Its bonding arrangement stabilizes the

chains and make it resist being digested

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– Has different glycosidic linkages than starch

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

H O

O

CH2OH

HOH H

H

OHO

HH

H

HO

4

CCCCCC

H

H

H

HO

OH

HOHOHOH

H

O

CH2OH

HH

H

OH

OHH

H

HO4 O

H

CH2OH O

OH

OH

HO

41O

CH2OH O

OH

OH

O

CH2OH O

OH

OH

CH2OH O

OH

OH

O O

CH2OH O

OH

OH

HO

4O

1

OH

O

OH O

HO

CH2OH O

OH

O OH

O

OH

OH

(a) and glucose ring structures

(b) Starch: 1– 4 linkage of glucose monomers

1

glucose glucose

CH2OH

CH2OH

1 4 41 1

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Plant cells

0.5 m

Cell wallsCellulose microfibrils

in a plant cell wall

Microfibril

CH2OH

CH2OHOH

OH

OO OHO

CH2OHO

OOH

OCH2OH OH

OH OHO

O

CH2OHO

O OH

CH2OH

OO

OH

O

O

CH2OHOHCH2OHOH

OOH OH OH OH

O

OH OHCH2OH

CH2OHOHO

OH CH2OH

OO

OH CH2OHOH

Glucose monomer

O

O

O

OO

O

Parallel cellulose molecules areheld together by hydrogenbonds between hydroxyl

groups attached to carbonatoms 3 and 6.

About 80 cellulosemolecules associate

to form a microfibril, themain architectural unitof the plant cell wall.

A cellulose moleculeis an unbranched glucose polymer.

OH

OH

O

OOH

Cellulosemolecules

– Is a major component of the tough walls that enclose plant cells

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• Cellulose is difficult to digest– Cows have microbes in their stomachs

to facilitate this process

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• Chitin, another important structural polysaccharide– Is found in the exoskeleton of

arthropods– Can be used as surgical thread– Has a nitrogen group

(a) The structure of the chitin monomer.

OCH2O

H

OHHH OH

HNHCCH3

O

H

H

(b) Chitin forms the exoskeleton of arthropods. This cicada is molting, shedding its old exoskeleton and emergingin adult form.

(c) Chitin is used to make a strong and flexible surgical

thread that decomposes after the wound or incision heals.

OH

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Lipids• Lipids are a diverse group of hydrophobic

molecules• Lipids

– Are the one class of large biological molecules that do not consist of polymers

– Share the common trait of being hydrophobic

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Fats– Are constructed from two types of smaller

molecules, a single glycerol and usually three fatty acids

– Vary in the length and number and locations of double bonds they contain

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• Saturated fatty acids– Have the maximum number of

hydrogen atoms possible– Have no double bonds

(a) Saturated fat and fatty acid

Stearic acid

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• Unsaturated fatty acids– Have one or more double bonds

(b) Unsaturated fat and fatty acidcis double bondcauses bending

Oleic acid

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• Phospholipids– Have only two fatty acids– Have a phosphate group instead of

a third fatty acid

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• Phospholipid structure– Consists of a hydrophilic “head”

and hydrophobic “tails”CH2

OPO OOCH2CHCH2

OOC O C O

Phosphate

Glycerol

(a) Structural formula (b) Space-filling model

Fatty acids

(c) Phospholipid symbol

Hyd

r oph

obic

tai

ls

Hydrophilichead

Hydrophobictails

–

Hyd

r oph

ilic

h ead CH2 Choline+N(CH3)3

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• The structure of phospholipids– Results in a bilayer arrangement found

in cell membranes

Hydrophilichead

WATER

WATERHydrophobictail

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Sterols• Sterols (steroids)

– Are lipids characterized by a carbon skeleton consisting of four fused rings

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• One steroid, cholesterol– Is found in cell membranes– Is a precursor for some hormones

HO

CH3

CH3

H3C CH3

CH3

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Proteins• Proteins have many

structures, resulting in a wide range of functions

• Proteins do most of the work in cells and act as enzymes

• Proteins are made of monomers called amino acids

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• An overview of protein functions

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• Enzymes– Are a type of protein that acts as a

catalyst, speeding up chemical reactions

Substrate(sucrose)

Enzyme (sucrase)

Glucose

OH

H O

H2OFructose

3 Substrate is convertedto products.

1 Active site is available for a molecule of substrate, the

reactant on which the enzyme acts.

Substrate binds toenzyme.

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4 Products are released.

Enzymes vs catalyst

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Polypeptides• Polypeptides

– Are polymers (chains) of amino acids

• A protein– Consists of one or more

polypeptides

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• Amino acids– Are organic molecules possessing

both carboxyl and amino groups– Differ in their properties due to

differing side chains, called R groups

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Twenty Amino Acids• 20 different amino acids make up proteins

O

O–

H

H3N+ C CO

O–H

CH3

H3N+ C

H

CO

O–

CH3 CH3

CH3

C CO

O–

H

H3N+

CHCH3

CH2

C

H

H3N+

CH3CH3

CH2

CH

C

H

H3N+ C

CH3

CH2

CH2

CH3N+

H

CO

O–

CH2

CH3N+

H

CO

O–

CH2

NH

H

CO

O–

H3N+ C

CH2

H2C

H2N C

CH2

H

C

NonpolarGlycine (Gly) Alanine (Ala) Valine (Val) Leucine (Leu) Isoleucine (Ile)

Methionine (Met) Phenylalanine (Phe)

CO

O–

Tryptophan (Trp) Proline (Pro)

H3C

S

O

O–

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O–

OHCH2

C CH

H3N+

O

O–

H3N+

OH CH3

CHC CH O–

O

SHCH2

CH

H3N+ C

O

O–

H3N+ C C

CH2

OH

H H H

H3N+

NH2

CH2

OC

C CO

O–

NH2 OCCH2

CH2

C CH3N+

O

O–

OPolar

Electricallycharged

–O OCCH2

C CH3N+

H

O

O–

O– OCCH2

C CH3N+

H

O

O–

CH2

CH2

CH2

CH2

NH3+

CH2

C CH3N+

H

O

O–

NH2

C NH2+

CH2

CH2

CH2

C CH3N+

H

O

O–

CH2

NH+

NHCH2

C CH3N+

H

O

O–

Serine (Ser) Threonine (Thr) Cysteine (Cys)

Tyrosine(Tyr)

Asparagine(Asn)

Glutamine(Gln)

Acidic Basic

Aspartic acid (Asp)

Glutamic acid (Glu)

Lysine (Lys) Arginine (Arg) Histidine (His)

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Amino Acid Polymers• Amino acids

– Are linked by peptide bonds

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Protein Conformation and Function

• A protein’s specific conformation (shape) determines how it functions

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Four Levels of Protein Structure

• Primary structure– Is the unique

sequence of amino acids in a polypeptide

–

Amino acid

subunits

+H3NAmino

end

oCarboxyl end

oc

GlyProThrGlyThr

GlyGluSeuLysCysProLeu

MetVal

LysVal

LeuAspAlaValArgGlySerPro

Ala

GlylleSerProPheHisGluHis

AlaGlu

ValValPheThrAlaAsnAsp

SerGlyProArg

ArgTyrThr lleAla

AlaLeu

LeuSerProTyrSerTyrSerThr

ThrAlaVal

ValThrAsnProLysGlu

ThrLysSer

TyrTrpLysAlaLeu

GluLleAsp

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O C helix

pleated sheetAmino acid

subunitsNCH

CO

C NH

CO H

RC N

H

CO H

CR

NHH

R CO

RCH

NH

CO H

NCO

RCH

NH

HCR

CO

CO

CNH

H

RC

CO

NH H

CR

CO

NH

RCH C

ONH H

CR

CO

NH

RCH C

ONH H

CR

CO

N H

H C RN H O

O C NC

RC

H O

CHR

N HO C

RC H

N H

O CH C R

N H

CC

NR

HO C

H C R

N HO C

RC H

HCR

NH

CO

C

NH

RCH C

ONH

C

• Secondary structure– Is the folding or coiling of the

polypeptide into a repeating configuration

– Includes the helix and the pleated sheet

H H

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• Tertiary structure– Is the overall three-dimensional shape

of a polypeptide– Results from interactions between

amino acids and R groups

CH2CH

OHOCHOCH2

CH2 NH3+ C-O CH2

O

CH2SSCH2

CH

CH3CH3

H3CH3C

Hydrophobic interactions and van der Waalsinteractions Polypeptid

ebackbone

Hyrdogenbond

Ionic bond

CH2

Disulfide bridge

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• Quaternary structure– Is the overall protein structure that

results from the aggregation of two or more polypeptide subunits

Polypeptidechain

Collagen

Chains

ChainsHemoglobin

IronHeme

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Review of Protein Structure

+H3NAmino end

Amino acidsubunits

helix

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What Determines Protein Conformation?

• Protein conformation Depends on the physical and chemical conditions of the protein’s environment

• Temperature, pH, etc. affect protein structure

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•Denaturation is when a protein unravels and loses its native conformation(shape) Denaturation

Renaturation

Denatured proteinNormal protein

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The Protein-Folding Problem• Most proteins

– Probably go through several intermediate states on their way to a stable conformation

– Denaturated proteins no longer work in their unfolded condition

– Proteins may be denaturated by extreme changes in pH or temperature

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Sickle-Cell Disease: A Simple Change in Primary Structure

• Sickle-cell disease– Results from a single amino

acid substitution in the protein hemoglobin

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Fibers of abnormalhemoglobin deform cell into sickle shape.

Primary structure

Secondaryand tertiarystructures

Quaternary structure

Function

Red bloodcell shape

Hemoglobin A

Molecules donot associatewith oneanother, eachcarries oxygen.Normal cells arefull of individualhemoglobinmolecules, eachcarrying oxygen

10 m 10 m

Primary structure

Secondaryand tertiarystructures

Quaternary structureFunction

Red bloodcell shape

Hemoglobin SMolecules interact with one another tocrystallize into a fiber, capacity to carry oxygen is greatly reduced.

subunit subunit

1 2 3 4 5 6 7 3 4 5 6 721

Normal hemoglobin

Sickle-cell hemoglobin . . .. . . Exposed

hydrophobic region

Val ThrHis Leu Pro Glul Glu Val His Leu Thr Pro Val Glu

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Nucleotides• Consist of sugar, phosphate

group, and nitrogen-containing bases

• ATP – adenosine triphosphate contains 3 phosphate groups; important source of energy

• Coenzymes – enzyme helpers that accept hydrogen atoms and electrons

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Nucleic Acids• Nucleic acids store and

transmit hereditary information• Genes

– Are the units of inheritance– Program the amino acid

sequence of polypeptides– Are made of nucleotide

sequences on DNA

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The Roles of Nucleic Acids• There are two types of nucleic acids

– Deoxyribonucleic acid (DNA)– Ribonucleic acid (RNA)

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Deoxyribonucleic Acid• DNA

– Stores information for the synthesis of specific proteins

– Found in the nucleus of cells

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DNA Functions– Directs RNA synthesis (transcription)– Directs protein synthesis through RNA

(translation)1

2

3

Synthesis of mRNA in the nucleus

Movement of mRNA into cytoplasm

via nuclear pore

Synthesisof protein

NUCLEUSCYTOPLASM

DNA

mRNARibosome

AminoacidsPolypeptide

mRNA

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The Structure of Nucleic Acids

• Nucleic acids– Exist as polymers called

polynucleotides

(a) Polynucleotide, or nucleic acid

3’C

5’ end

5’C

3’C

5’C

3’ endOH

O

O

O

O

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• Each polynucleotide– Consists of monomers called nucleotides– Sugar + phosphate + nitrogen base

Nitrogenousbase

Nucleoside

O

O

O

O P CH2

5’C

3’CPhosphategroup Pentose

sugar

(b) Nucleotide

O

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