Aspects of Biochemistry-water Carbohydrates

8/9/2019 Aspects of Biochemistry-water Carbohydrates

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The building blocks of life

Water

Carbohydrates

Lipids

Proteins

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The study of the structure and function ofbiological molecules forms an important branch

of biology known as molecular biology.

Molecular biology is closely linked withbiochemistry, which looks at the chemical

reactions in biological molecules.

The sum total of all the biochemical reaction inthe body is know as metabolism.

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Question

escribe the two main types of metabolic

reactions which takes place in cells.

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The four most common elements in li!ingorganisms are hydrogen, carbon, o"ygen

and nitrogen.

They account for more than ##$ of theatoms found in all li!ing things.

Carbon is particularly important becausecarbon atoms can %oin together to form longchains or ring structures.

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Chemical compounds which make up thecells, tissues and organs of li!ingorganisms are di!ided into two groups&

'rganic compounds

(norganic compounds

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Carbon atoms can be thought of as the basicskeletons of organic molecules to whichgroups of other atoms are attached.

'rganic molecules always contain carbon.

The main organic compounds found in li!ingorganisms are carbohydrates, lipids,proteins, nucleic acids, )which aremacromolecules* and vitamins

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The main inorganic compounds found inli!ing organisms are&

Water

Mineral

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Water is arguably the most importantbiochemical of all.

Without water life would not e"ist on this planet.

(t is important for two reasons&

)+* it is a ma%or component of cells

)* it pro!ides an en!ironment for thoseorganisms

that li!e in water.9


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POLARITY

Many of water-s biological functions stem from itschemical structure.

(n the water molecule ('* the hydrogen and o"ygenatoms share electrons to form a co!alent bond, butthese atoms do not share the electrons e/ually.

The o"ygen atom, because of its 0 protons andhydrogen-s single proton, pulls the shared electronstowards its nucleus and away from the hydrogen atom.1s a result, the electrical charge is unevenlydistributed in the water molecule.

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Although the total electrical charge on a

water molecule is zero, the region of themolecule where the oxgen atom is

locate! has a slight negati"e charge #2-$,

while the regions of the molecule where

each of the two h!rogen atoms are

locate! each ha"e a slight %ositi"e charge#+$&

'ecause of this une"en %attern of

charge, water is a polar molecule.All

molecules with an une"en charge li(e thisare %olar molecules&


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(t is this that makes water such a good

sol!ent of other polar molecules 2 such assalts, sugars and proteins.

1n ionic compound dissol!ed in watertends to dissociate into ions. This

breaking up of an ionic compound meansthe ions can participate in many biologicalreactions.

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Y!RO"#$ %O$!I$"

The polar nature of water also causeswater molecules to be attracted to oneanother or stick together.

This attraction between water molecules

is caused by hydrogen bonding&

1 positi!e region of one water moleculeis attracted to the negati!e region ofanother water molecule.

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)!rogen *on!s are

weak bonds thatcan *e easil

*ro(en + %articularl

if *ent&

)!rogen *on!scan also *e forme!

*etween h!rogen

an! nitrogen atoms

#onl$&


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The hydrogen bonds in water e"ert asigni3cant attracti!e force, causing water to

cling to itself )'ohesion* and to othersurfaces )Adhesion*.

Together, adhesion and cohesion enablewater molecules to mo!e upwards through

narrow tubes against the force of gra!ity 2 aproperty of water known as capillarity.

Water mo!es up a plant stem throughcohesiontension in the )ylem 4 onlypossible because of the hydrogen bonds.

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Water must gain or lose a large amount ofenergy for its temperature to change 4 which

makes it a stable en!ironment to li!e in(homeostasis*&

Water-s ability to absorb large amounts of

energy )5 high speci+c heat capacity*helps to keep cells at an e!en temperaturedespite changes to the e"ternal temperature.

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olvent. 6ecause it is charged, )the positi!ely charged

hydrogen atoms and a negati!ely chargedo"ygen atom* water is a !ery good solvent.

Charged or polar molecules such as salts,sugars, amino acids dissol!e readily in water

and so are called hydrophilic)7water lo!ing7*.

8ncharged or non2polar molecules such aslipids do not dissol!e so well in water and arecalled hydrophobic )7water hating7*.

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peci+c heat capacity or thermalproperties&

1 substance9s speci3c heat capacity is theamount of energy in %oules re/uired to raise thetemperature of + gram of that substance by +:C.

Water has a speci3c heat capacity of ;. < g2+ =C2+, which means that it takes ;. %oules of energy

to heat + g of water by +=C. This is unusually high and it means that water

does not change temperature !ery easily. Thisminimi>es ?uctuations in temperature insidecells, and it also means that sea temperature isremarkably constant.

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Latent heat o- vaporisation&

Water re/uires a lot of energy to changestate from a li/uid into a gas, and this ismade use of as a cooling mechanism inanimals )sweating and panting* and

plants )transpiration2 the loss of water bye!aporation from the surface of lea!es*.1s water e!aporates it e"tracts heatfrom around it, cooling the organism.

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Latent heat o- -usion&

Water re/uires a lot of heat to changestate from a solid to a li/uid, and mustloose a lot of heat to change state from ali/uid to a solid. This means it is di@cultto free>e water, so ice crystals are less

likely to form inside cells.

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!ensity or .ater -ree/ing properties

Water is uni/ue in that the solid state )ice* isless dense that the li/uid state, so ice ?oats onwater.

1s the air temperature cools, bodies of water

free>e from the surface, forming a layer of icewith li/uid water underneath.

This allows a/uatic ecosystems to e"ist e!enin sub2>ero temperatures.

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'ohesion or ur-ace tension o- water

Aurface tension is the force that causes thesurface of a li/uid to contract so that it occupies

the least possible area.

Water molecules 7stick together7 due to theirhydrogen bonds, so water has high cohesion.

This e"plains surface tension, which allows smallanimals to walk on water.

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Transparency

This feature is !ery important biologically.

The present of light facilitate photosynthesis inoceans and other a/uatic en!ironment thuspro!iding for a community of li!ing organism.

(t is also of great importance to animals li!ing in

water, for it allows them to see.

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Atate the property of water that allowseach of the following to take place and,in each case, e"plain its importance.

)a*The cooling of skin during sweating.)b* The sur!i!al of 3sh in ice2co!ered lakes.

)c* The ability of insects, such as pondskater, to walk on water.

)d* The transport glucose and ions in amammal.

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Water is important within bodieswhere it forms a large part of the massof cell.

(t is also an en!ironment in whichorganisms can li!e.

1s a result of e"tensi!e hydrogenbonding, it has unusual properties thatare important for life.

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(t is li/uid at most temperatures on theBarth9s surface

(ts highest density occurs abo!e itsfree>ing point so that ice ?oats andinsulates water below from free>ing air

temperatures (t acts as a sol!ent for ions and polar

molecules and causes non2polarmolecules to group together

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(t has a high surface tension whichaDects the way it mo!es through narrowtubes and forms a surface on which some

organisms can li!e.

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Read

Chapter , pp ++2+E& 1d!anced 6iology by

Foberts, Feiss G Monger ):::*.

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1ll of the many compounds disco!eredcan be classi3ed into two broadcategories& organic (0 containcarbon atoms co!alently bonded toother carbon atoms* and inorganiccompounds&

'ther elements found in most organicmolecules are hydrogen, o"ygen, andnitrogen.

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1 carbon atom has ; electrons in its outermostshell, and to be stable a carbon atom needs 0

electrons in its outer shell, so carbon atomstherefore readily form ; co!alent bonds withother elements.

Carbon also readily bonds with other carbon

atoms, forming chains or rings.

This tendency of carbon to bond with itselfresults in the enormous !ariety of organiccompounds.

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Carbon can also share two pairs ofelectrons with another carbon atom&

ingle %ond 2 1 bond formed when

two atoms share onepair of electrons.

!ouble %ond 2 atoms share twopairs of electrons.

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(n most organic compounds, clusters ofatoms, called -unctional groups, in?uence

the properties of the molecule they compose.

The -unctional group is the structuralbuilding block that determines thecharacteristics of that compound.

'ne functional group important to li!ingthings is the hydro)yl group )representedby '2*.

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1n alcohol is an organic compound witha hydro"yl group attached to one of itscarbon atoms.

The hydro"yl group makes alcohols )e.g.sugars* polar molecules that ha!e someproperties similar to water, including the

ability to form hydrogen bonds.

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Large carbon compounds are built up fromsmaller simpler molecules called monomers.

Monomers can bind to one another to formcomple" molecules known as polymers.

1 polymer consists of repeated, linked units,forming )!ery* large polymers calledmacromolecules.

Monomers link to form polymers through achemical reaction called a condensationreaction. uring the formation of polymers,water is released 4 it is a by2product of thereaction.

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B"ample 2 during the formation of the sugar maltose, twomolecules of glucose combine.

(n this condensation reaction, one glucose moleculereleases a hydro"ide ion, '2, and the other moleculereleases a hydrogen ion, H. The '2 and H ions that arereleased then combine to form water.

This bond )between the +2 carbon of the 3rst glucose andthe ;2 carbon of the second*, is known as a 123 "lycosidicbond and it is also found in starch, glycogen and cellulose.

The breakdown )5 digestion* of these comple" molecules,

occurs through the re!erse process known as hydrolysis. 0.ydrolysis re/uires the addition of one water molecule, tobreak each bond within the polymer and so break the bondsthat hold them together.

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1ll carbohydrates contain the elementscarbon, hydrogen and o"ygen.

The second half of the name comes fromthe fact that hydrogen and o"ygenatoms are present in the ratio of &+, as

they are in water )hydrate refers towater*.

The general formula for a carbohydratecan therefore be written as C

I)

'*

y.

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Augars, starch, glycogen and cellulose are allcarbohydrates.

Carbohydrate are di!ided into three maingroups, namely&2

2 monosaccharide )e.g. glucose, fructose,

galactose*,2 disaccharides )e.g. maltose, sucrose, lactose*

2 polysaccharide )e.g. starch, glycogen,cellulose*

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Monosaccharides are sugars.

They dissol!e easily in water to formsweet solutions.

Monosaccharides ha!e the generalformula )C,'*n and consist of a single

sugar molecule )mono means Jone9*.

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The main types of monosaccharide, ifthey are classi3ed according to thenumber of carbon atoms in each

molecule, are& Triose (CEK'E*

Pentose (CL+:'L*

e)ose (CK+,'K*.

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lucose, Nructose, and alactose are allhe"oses, with the same molecularformula, but their diDering structures

determine the diDerent properties. Compounds like these sugars, with a

single chemical formula but diDerentforms, are called isomers&

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!isaccharides, or double sugars, are formedwhen two single sugars )or monosaccharides*

condense together to form a disaccharide anda molecule of water.

The bond between the two parts of thedisaccharide is known as a glycosidic bond.

Common disaccharides include maltose )O2glucose H O2glucose* sucrose )O2glucose Hfructose*, and lactose )O2glucose Hgalactose*.

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Polysaccharides are carbohydrates madeof long chains of sugars.

tarch, which is found in plants only, is apolysaccharide.

Atarch actually consists of two diDerent

molecules& amylose )a long chain of Jpolymaltoses9, thus only ha!ing O2+&; glycosidicbonds* and amylopectin )which has abranched structure, containing both O2+&;glycosidic bonds and O2+&K glycosidic bonds*.

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1nimals store O2glucose in the form of thepolysaccharide glycogen in their li!er and

muscles, )where it is regulated by the hormonesinsulin and glucagon*.

lycogen keeps the blood glucose concentrationroughly constant throughout the day. (t consists

of tens of thousands of glucose molecules in ahighly branched structure similar to amylopectin)i.e it has both O2+&; glycosidic bonds and O2+&Kglycosidic bonds and can thus be digested byamylase*.

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Plants make cellulose 2 also apolysaccharide 4 to form the maincomponent of their rigid cell walls.

Cellulose makes up about : percent

of wood and consists of very long,unbranched chains of 2glucose.

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o% - amlose. /14 glcosi!ic *on!s&

Note: all 6-carbons on the top

ower - cellulose. 14 glcosi!ic *on!s Note: alternate 6-carbons

on top and bottom


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Aspects of Biochemistry-water Carbohydrates