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CHAPTER 3 - BIOCHEMISTRY

CHAPTER 3 - BIOCHEMISTRY

"THE CHEMISTRY OF LIFE"

"THE CHEMISTRY OF LIFE"

WATER 

WATER 

Compare the body o

Compare the body of the jellyfish with our own f the jellyfish with our own bodies. bodies. The jellyfish will die if it is removed fromThe jellyfish will die if it is removed from its water environment, yet we

its water environment, yet we can live in the driest can live in the driest parts of Earth. parts of Earth. Jellyfish and humans seem Jellyfish and humans seem utterlyutterly unlike each other, yet the bodies o

unlike each other, yet the bodies of both are made of both are made of cells filled with water. f cells filled with water. The chemical reactionsThe chemical reactions of all living things take place in an

of all living things take place in an aqueous environmentaqueous environment.. Water has Water has several properties that several properties that make itmake it one of the most important compounds found in living things.

one of the most important compounds found in living things.

POLARITY

POLARITY

1. Many of water's biological functions stem from its chemical structure. 1. Many of water's biological functions stem from its chemical structure. 2. In the

2. In the water moleculewater molecule, H, H22O, the hydrogen and oxygen atoms share electrons to form a covalentO, the hydrogen and oxygen atoms share electrons to form a covalent

 bond, but these atoms

 bond, but these atoms do notdo not share the electrons equally. share the electrons equally. 3. The oxygen atom, because of its 8 protons

3. The oxygen atom, because of its 8 protons cf cf  hydrogen's single proton, pulls the shared electrons hydrogen's single proton, pulls the shared electrons towards its nucleus and away

towards its nucleus and away from the hydrogen from the hydrogen atom. atom. As a result, the electrical charge isAs a result, the electrical charge is unevenlyunevenly distributed

distributed in the water molecule. in the water molecule.

4. Although the total electrical charge on a water molecule is zero, the region 4. Although the total electrical charge on a water molecule is zero, the region of the molecule where the oxygen atom is located has a slight negative charge of the molecule where the oxygen atom is located has a slight negative charge ((22δδ--), while the regions of the molecule where each of the two hydrogen), while the regions of the molecule where each of the two hydrogen atoms are located each have a slight positive charge (

atoms are located each have a slight positive charge (δδ++).). 5. Because of this uneven pattern of charge, water is a

5. Because of this uneven pattern of charge, water is a polar moleculepolar molecule.. AllAll molecules with an uneven charge like this are polar molecules.

molecules with an uneven charge like this are polar molecules.

6. It is this that makes water such a good solvent of other polar molecules 6. It is this that makes water such a good solvent of other polar molecules -such as

such as salts, sugarssalts, sugars and and proteinsproteins.. 7. An ionic compound dissolved in water tends to

7. An ionic compound dissolved in water tends to dissociatedissociate into ions. into ions. This breaking uThis breaking up of an p of an ionicionic compound means the ions can participate in many biological reactions.

compound means the ions can participate in many biological reactions.

HYDROGEN BONDING

HYDROGEN BONDING

1. The polar nature of water also causes water molecules to be attracted to one another or stick 1. The polar nature of water also causes water molecules to be attracted to one another or stick

together. together.

2. This attraction between water molecules is caused by

2. This attraction between water molecules is caused by hydrogenhydrogen bonding

bonding..

3. A positive region of one water molecule is attracted to the 3. A positive region of one water molecule is attracted to the negative region of another water molecule.

negative region of another water molecule. 4. Hydrogen bonds are

4. Hydrogen bonds are weak bondsweak bonds  that can be easily broken –  that can be easily broken –  particularly if bent (e.g. DNA replication).

 particularly if bent (e.g. DNA replication). 5.

5. Hydrogen bHydrogen bonds can onds can also be also be formed between formed between hydrogen hydrogen andand nitrogen atoms (only).

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5. The hydrogen bonds in water exert a significant attractive force, causing water to cling to itself 5. The hydrogen bonds in water exert a significant attractive force, causing water to cling to itself ((CohesionCohesion) and to other surfaces () and to other surfaces (AdhesionAdhesion).).

6. Together, adhesion and cohesion enable water molecules to move upwards through narrow tubes 6. Together, adhesion and cohesion enable water molecules to move upwards through narrow tubes against the force of gravity - a property of water known as

against the force of gravity - a property of water known as capillaritycapillarity.. 7. Water moves up a plant stem through

7. Water moves up a plant stem through cohesion-tensioncohesion-tension in the in the xylemxylem – only possible because of – only possible because of the hydrogen bonds.

the hydrogen bonds.

8. Water must gain or lose a large amount of energy for its temperature to change – which makes it a 8. Water must gain or lose a large amount of energy for its temperature to change – which makes it a stable environment to live in

stable environment to live in ((homeostasishomeostasis).). 9.

9. Water's ability to absorb large amounts Water's ability to absorb large amounts of energy (=of energy (= high specific heat capacityhigh specific heat capacity) helps to keep) helps to keep cells at an even temperature despite changes to the external temperature.

cells at an even temperature despite changes to the external temperature.

CARBON COMPOUNDS

CARBON COMPOUNDS

All of the many compounds discovered can be classified into two broad categories:

All of the many compounds discovered can be classified into two broad categories: organicorganic (=(= contain carbon atoms

contain carbon atoms covalently bonded to other carbon atomscovalently bonded to other carbon atoms)) andand inorganic compoundsinorganic compounds.. OtherOther elements found in most organic molecules are hydrogen, oxygen, and nitrogen.

elements found in most organic molecules are hydrogen, oxygen, and nitrogen.

CARBON BONDING

CARBON BONDING

1. A carbon atom has 4 electrons in its outermost shell, 1. A carbon atom has 4 electrons in its outermost shell, and to be stable a carbon atom needs 8 electrons in its and to be stable a carbon atom needs 8 electrons in its outer shell, so carbon atoms therefore readily form 4 outer shell, so carbon atoms therefore readily form 4 covalent bonds with other elements.

covalent bonds with other elements.

2. Carbon also readily bonds with other carbon atoms, 2. Carbon also readily bonds with other carbon atoms, forming chains or rings.

forming chains or rings.

3. This tendency of carbon to bond with itself results in 3. This tendency of carbon to bond with itself results in the enormous variety of

the enormous variety of organic compoundsorganic compounds..

4. Carbon can also share two pairs of electrons with 4. Carbon can also share two pairs of electrons with another carbon atom:

another carbon atom:

A.

A. Single BondSingle Bond - A bond formed when two atoms share - A bond formed when two atoms share one

one pair of electrons. pair of electrons. B.

B. Double BondDouble Bond - atoms share - atoms share twotwo pairs of electrons. pairs of electrons.

FUNCTIONAL GROUPS

FUNCTIONAL GROUPS

1. In most organic compounds, clusters of atoms, called

1. In most organic compounds, clusters of atoms, called functional groups,functional groups, influence the propertiesinfluence the properties of the molecule they compose.

of the molecule they compose.

2. The

2. The functional groupfunctional group is the structuralis the structural  building

 building block block that that determines determines thethe characteristics of that compound.

characteristics of that compound.

3. One functional group important to living 3. One functional group important to living things is the

things is the hydroxyl grouphydroxyl group (represented by (represented by OH

OH--).). 4. An

4. An alcoholalcohol is an organic compound with a is an organic compound with a hydroxyl group attached to one of its carbon hydroxyl group attached to one of its carbon atoms.

atoms.

5. The hydroxyl group makes alcohols (e.g. sugars) polar molecules that have some properties 5. The hydroxyl group makes alcohols (e.g. sugars) polar molecules that have some properties similar to water, including the ability to form hydrogen bonds.

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LARGE CARBON MOLECULES

LARGE CARBON MOLECULES

1. Large carbon compounds are built up from smaller simpler molecules called

1. Large carbon compounds are built up from smaller simpler molecules called monomersmonomers.. 2. Monomers can bind to one another to form complex molecules known as

2. Monomers can bind to one another to form complex molecules known as polymerspolymers..

3. A polymer consists of repeated, linked units, forming (very) large polymers called 3. A polymer consists of repeated, linked units, forming (very) large polymers called macromolecules

macromolecules..

4. Monomers link to form polymers through a chemical reaction called a

4. Monomers link to form polymers through a chemical reaction called a condensation reactioncondensation reaction.. During the formation of polymers, water is released – it is a by-product of the reaction.

During the formation of polymers, water is released – it is a by-product of the reaction. 5. Example - during the formation of the sugar

5. Example - during the formation of the sugar maltosemaltose,, two molecules of two molecules of glucoseglucosecombine.combine.

6. In this condensation reaction, one glucose molecule releases a hydroxide ion, OH-, and the other 6. In this condensation reaction, one glucose molecule releases a hydroxide ion, OH-, and the other molecule releases a hydrogen ion, H

molecule releases a hydrogen ion, H++. . The The OHOH-- and H and H++ions that are released then combine to formions that are released then combine to form water. This bond (between the 1- carbon of the first glucose and the 4- carbon of the second), is water. This bond (between the 1- carbon of the first glucose and the 4- carbon of the second), is known as a

known as a 1:4 Glycosidic bond1:4 Glycosidic bond and it is also found in starch, glycogen and cellulose. and it is also found in starch, glycogen and cellulose.

7. The breakdown (= digestion) of these complex molecules, occurs through the reverse process 7. The breakdown (= digestion) of these complex molecules, occurs through the reverse process known as

known as hydrolysishydrolysis.. 8. Hydrolysis requires the

8. Hydrolysis requires the additionaddition ofof oneone water molecule, to break each bond within the polymer water molecule, to break each bond within the polymer and so break the bonds that hold them together.

and so break the bonds that hold them together.

ENERGY CURRENCY - ATP

ENERGY CURRENCY - ATP

1. Life processes require a constant supply

1. Life processes require a constant supply of energy. of energy. This energy is avThis energy is available to cells in the form ailable to cells in the form ofof compounds that contain a large amount of energy compounds that contain a large amount of energy

 by  by in their overall structure.

in their overall structure.

2. The most common energy compound used 2. The most common energy compound used all cells is

all cells is Adenosine TriPhosphateAdenosine TriPhosphateor or ATPATP.. 3. An ATP molecule comprises a sugar (

3. An ATP molecule comprises a sugar ( riboseribose, a, a  pentose (=

 pentose (= 5-C) sugar), 5-C) sugar), anan AdenosineAdenosine molecule (a molecule (a  base)

 base) and and a a chain chain ofof 33 Phosphate Phosphate groups. groups. WhenWhen the bonds between the outermost two phosphate the bonds between the outermost two phosphate groups are broken, ATP becomes ADP groups are broken, ATP becomes ADP

nt of energy (and yes, it nt of energy (and yes, it isis hydrolysis reaction!)

hydrolysis reaction!)

TP + water

TP + water →→ADP + ADP + Pi + Pi + ENERGYENERGY

ergy is used ergy is used the cell to drive the chemical reactions that enable an organism to function (i.e life).

the cell to drive the chemical reactions that enable an organism to function (i.e life).

ocesses of all living ocesses of all living

om carbon, hydrogen, and oxygen: the atoms occur in different ratios om carbon, hydrogen, and oxygen: the atoms occur in different ratios in each class of compound.

in each class of compound.

((Adenosine DiPhosphateAdenosine DiPhosphate,, ADPADP).). 4.

4. The reaction that The reaction that forms ADP forms ADP from ATPfrom ATP releases a sizeable amou

releases a sizeable amou aa

A

A

5. The transfer of this

5. The transfer of this energy fuels most biochemenergy fuels most biochemical reactions. ical reactions. This conversion of This conversion of enen  by

 by

MOLECULES OF LIFE

MOLECULES OF LIFE

The four main classes of organic compounds that are essential to the life pr  The four main classes of organic compounds that are essential to the life pr  things are:

things are: carbohydratescarbohydrates,, triglyceridestriglycerides(lipids),(lipids), proteinsproteins,, and and nucleic acids.nucleic acids.

These compounds are built fr  These compounds are built fr 

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CARBOHYDRATES

CARBOHYDRATES

1. The cells of the human body obtain most of their energy from carbohydrates. 1. The cells of the human body obtain most of their energy from carbohydrates.

2.

2. CarbohydratesCarbohydrates are compounds containingare compounds containing Carbon, HydrogenCarbon, Hydrogen and and Oxygen,Oxygen,withwith the number of H and O atoms in the ratio of 2:1.The number of carbon atoms varies, the number of H and O atoms in the ratio of 2:1.The number of carbon atoms varies, from 3-100,000+.

from 3-100,000+.

3. Sugars, starch, glycogen and cellulose are all carbohydrates. 3. Sugars, starch, glycogen and cellulose are all carbohydrates. 4. There are

4. There are  three  three types of carbohydrates,types of carbohydrates, grouped according to complexitygrouped according to complexity:: monosaccharides

monosaccharides ((e.g. glucose, fructose, galactosee.g. glucose, fructose, galactose)),, disaccharides,disaccharides, ((e.g. maltose,e.g. maltose,  sucrose, lactose

 sucrose, lactose) and) and polysaccharidespolysaccharides((e.g. starch, glycogen, cellulosee.g. starch, glycogen, cellulose)) 5.

5. MonosaccharidesMonosaccharides are single sugars and are named after the number of carbon atoms theyare single sugars and are named after the number of carbon atoms they contain:

contain:

Triose

Triose (an intermediate in respiration and photosynthesis) C (an intermediate in respiration and photosynthesis) C33HH66OO33

Pentose

Pentose(found in DNA, RNA and ATP). C(found in DNA, RNA and ATP). C55HH1010OO55..

Hexose

Hexose (by far the most common – found everywhere else!) C (by far the most common – found everywhere else!) C66HH1212OO66..

Glucose, Fructose, and Galactose are all hexoses, with the same molecular formula, but their Glucose, Fructose, and Galactose are all hexoses, with the same molecular formula, but their differing structures determine the different properties.

differing structures determine the different properties. Compounds Compounds like these sugars, with a like these sugars, with a singlesingle chemical formula but different forms, are called

chemical formula but different forms, are called isomers.isomers. AQA AQA requires requires you you to to know know thethe structural formula

structural formula (i.e. you can draw it!) of the 2 isomers of glucose, known as (i.e. you can draw it!) of the 2 isomers of glucose, known as αα-glucose-glucose and and ββ-

-glucose

glucose..

 Note:  Note: a) The

a) The numbering of the carbon atomsnumbering of the carbon atoms (1-6, with (1-6, with 1 and 4 being at opposite ends and 6 being out of 1 and 4 being at opposite ends and 6 being out of the ring).

the ring).

b) The two forms are identical

b) The two forms are identical apart fromapart from  the  the  position of the OH group on the 1-C atom.

 position of the OH group on the 1-C atom.

7.

7. DisaccharidesDisaccharides,, or double sugars, are formed when two single sugars (or monosaccharides)or double sugars, are formed when two single sugars (or monosaccharides) condense together to form a d

condense together to form a disaccharide and a molecule of water. isaccharide and a molecule of water. The bond bThe bond between the two partsetween the two parts of the disaccharide is known as a

of the disaccharide is known as a glycosidic bondglycosidic bond. . Common Common disaccharides includedisaccharides include maltosemaltose ((α α--glucose +

glucose + αα-glucose)-glucose) sucrosesucrose ((αα-glucose + fructose), and-glucose + fructose), and lactoselactose ((αα-glucose -glucose + + galactose). galactose). AQAAQA require you to be able to draw maltose (only) – see below –

require you to be able to draw maltose (only) – see below – andand they also require you to be able tothey also require you to be able to draw its synthesis and breakdown:

draw its synthesis and breakdown:

A good animation of this reaction is available at: A good animation of this reaction is available at: http://www.biotopics.co.uk/as/disaccharideformation.html http://www.biotopics.co.uk/as/disaccharideformation.html

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8.

8. PolysaccharidesPolysaccharides are carbohydrates made of long chains of sugars.are carbohydrates made of long chains of sugars. StarchStarch, which is found in, which is found in  plants

 plants only,only, is a is a polysaccharide. polysaccharide. Starch actually Starch actually consists ofconsists of twotwo  different molecules:  different molecules: amyloseamylose (a(a long chain of ‘poly maltoses’, thus

long chain of ‘poly maltoses’, thus onlyonly havinghaving αα-1:4 glycosidic bonds) and-1:4 glycosidic bonds) and amylopectinamylopectin  (which  (which has a branched structure, containing

has a branched structure, containing bothboth αα-1:4 glycosidic bonds-1:4 glycosidic bonds andand αα-1:6 glycosidic bonds).-1:6 glycosidic bonds). [Therefore the ‘enzyme’ amylase must be

[Therefore the ‘enzyme’ amylase must be at least twoat least two different enzymes to break both sorts of bond.] different enzymes to break both sorts of bond.] 9. Animals store

9. Animals store αα-glucose in the form of the polysaccharide-glucose in the form of the polysaccharide glycogenglycogen  in their liver and muscles,  in their liver and muscles, ((where it is regulated by the hormoneswhere it is regulated by the hormones insulininsulin and and glucagon glucagon). ). Glycogen Glycogen keeps the keeps the blood blood glucoseglucose concentration roughly constant throughout

concentration roughly constant throughout the day. the day. It consists of tens of thouIt consists of tens of thousands of glucosesands of glucose molecules in a highly branched structure similar to amylopectin (i.e it has both

molecules in a highly branched structure similar to amylopectin (i.e it has both αα-1:4 glycosidic-1:4 glycosidic  bonds

 bonds andand αα-1:6 glycosidic bonds and can thus be digested by-1:6 glycosidic bonds and can thus be digested by amylaseamylase).). 10.

10. Plants Plants makemake cellulosecellulose - also a polysaccharide – to form the main component of their rigid cell - also a polysaccharide – to form the main component of their rigid cell walls.

walls. Cellulose makes up Cellulose makes up about 50 about 50 percent of wood percent of wood and consists ofand consists of veryvery long, unbranched chainslong, unbranched chains of

of ββ-glucose.-glucose.

Top = amylose;

Top = amylose; αα-1:4 glycosidic bonds.-1:4 glycosidic bonds.  Note:

 Note: all all  6-carbons 6-carbons on the topon the top

Lower = cellulose;

Lower = cellulose; ββ-1:4 glycosidic bonds-1:4 glycosidic bonds  Note:

 Note: alternatealternate 6-carbons on top and bottom 6-carbons on top and bottom

PROTEINS

PROTEINS

1. Proteins are organic compounds containing the elements Carbon, 1. Proteins are organic compounds containing the elements Carbon, Hydrogen, Oxygen, Nitrogen and Sulphur (=

Hydrogen, Oxygen, Nitrogen and Sulphur (= ‘CHONS’‘CHONS’).).

2. Proteins are the materials used to build much of our bodies – such as skin, 2. Proteins are the materials used to build much of our bodies – such as skin, muscles and blood, but their most important use is to form

muscles and blood, but their most important use is to form enzymesenzymes..

3. Proteins are made up of smaller units called

3. Proteins are made up of smaller units called amino-acidsamino-acids – the monomer – the monomer from which the polymer proteins are made.

from which the polymer proteins are made. 5. Our

5. Our cells each contain thousands cells each contain thousands of different proteins. of different proteins. All these proteinsAll these proteins are made from about

are made from about 2020 different amindifferent amino o acids. acids. Note Note that that each each amino-acid amino-acid has has the the same same basicbasic structure- they different

structure- they different onlyonly  in the R-group they carry.  in the R-group they carry. You doYou do not not   need to know the names or  need to know the names or  structures of any

 structures of any individual individual  amino-acids, but amino-acids, but you do you do need to be able to need to be able to draw their

draw their general  general  structure: structure: 6. Amino-acids differ

6. Amino-acids differ onlyonly  in the typ  in the type of R-group e of R-group they have. they have. TheThe simplest is

simplest is  glycine glycine, with an R-group of a single H- atom; the next, with an R-group of a single H- atom; the next simplest is

simplest is alaninealanine,,  with CH  with CH33. . Others are Others are much much more more complex, complex, andand

 just two

 just two (i.e. 10%) contain an atom of sulphur. (i.e. 10%) contain an atom of sulphur.

7. These different shapes allow proteins to fold into many different 7. These different shapes allow proteins to fold into many different shapes and so perform many different roles in the chemistry of living shapes and so perform many different roles in the chemistry of living things.

things. 8.

8. Two amino-acids Two amino-acids bond to bond to form aform a dipeptidedipeptide and and water, dwater, during uring a a condensation condensation reaction. reaction. TheThe covalent bond between them is called a

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Or Or

 Note that when the two amino-acids bond,

 Note that when the two amino-acids bond, it is the C and N it is the C and N atoms join up in a peptide bond!!atoms join up in a peptide bond!! 9. Amino-acids can bond to each other one at a time, forming a long chain called a

9. Amino-acids can bond to each other one at a time, forming a long chain called a polypeptidepolypeptide..

These are made on the

These are made on the ribosomesribosomes  in the cell (  in the cell (80s80s  in eukaryotes,  in eukaryotes, 70s70s  in prokaryotes and  in prokaryotes and mitochondria and chloroplasts).

mitochondria and chloroplasts). 10. Proteins normally comprise one

10. Proteins normally comprise one (rarely 2 or 4)(rarely 2 or 4) polypeptides. Most proteins are large molecules, polypeptides. Most proteins are large molecules, and contain a hundred or so amino-acids.

and contain a hundred or so amino-acids. 11. One group of proteins

-11. One group of proteins - enzymesenzymes - help control chemical reactions by acting as - help control chemical reactions by acting as catalysts;catalysts; they they are essential for the functioning of cells.

are essential for the functioning of cells. Catalysts can speed up some Catalysts can speed up some reactions by more than reactions by more than aa  billion fold.

 billion fold.

12. Enzymes work by a physical fit (the

12. Enzymes work by a physical fit (the ‘Induced Fit Theory’‘Induced Fit Theory’)) between the enzyme molecule and between the enzyme molecule and its

itssubstratesubstrate, i.e. the reactant being catalyzed., i.e. the reactant being catalyzed. 13. The fitting together of the enzyme’s

13. The fitting together of the enzyme’s ‘active site’‘active site’ and the substrate bends (and so weakens) someand the substrate bends (and so weakens) some chemical bonds, which therefore reduces the

chemical bonds, which therefore reduces the Activation EnergyActivation Energy for the chemical reaction to occur. for the chemical reaction to occur. 14. After the reaction, the enzyme’s active site ‘springs back’ to its normal shape, the product(s) is 14. After the reaction, the enzyme’s active site ‘springs back’ to its normal shape, the product(s) is released, and the unchanged enzyme can then be reused many times each second (known as its released, and the unchanged enzyme can then be reused many times each second (known as its ‘ 

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TRIGLYCERIDES or LIPIDS

TRIGLYCERIDES or LIPIDS

1. Lipids are moderately sized, non-polar organic molecules that

1. Lipids are moderately sized, non-polar organic molecules that do notdo not dissolve in water.

dissolve in water.

2. Lipids have fewer oxygen atoms (

2. Lipids have fewer oxygen atoms (typically < 6 typically < 6 ) than carbohydrates do.) than carbohydrates do. 3. Lipids store energy efficiently, since they have large numbers of C – H 3. Lipids store energy efficiently, since they have large numbers of C – H  bonds,

 bonds, which which store store more more energy energy than than C C – – O O bonds; bonds; they they can can also also be be storedstored without water,

without water, andand without affectingwithout affecting thethe water potentialwater potential ((ΨΨ) of the cell.) of the cell. 4. Lipids which are liquid at room temperature =

4. Lipids which are liquid at room temperature = oilsoils; if they melt below; if they melt below 100

100ooC they areC they are fatsfats;; if they melt above 100 if they melt above 100ooC they areC they are waxeswaxes.. 5. The

5. The longerlonger the fatty-acid chain (see below), the the fatty-acid chain (see below), the higherhigher the melting-point. the melting-point. 6. They also have a function in many living things as a waterproofing 6. They also have a function in many living things as a waterproofing chemical

chemical (e.g skin, waxy cuticle on leaves).(e.g skin, waxy cuticle on leaves).

FATTY ACIDS

FATTY ACIDS

1.

1. Fatty acidsFatty acids are the hydrocarbon chains that make up most of a lipid molecule. are the hydrocarbon chains that make up most of a lipid molecule. 2. The two ends (the

2. The two ends (the headhead and theand the tailtail) of a fatty acid molecule) of a fatty acid molecule have different properties – they are therefore

have different properties – they are therefore polar moleculespolar molecules::

a). The

a). The carboxylcarboxyl endend  (= head)  (= head) of the molecule isof the molecule is chargedcharged,, and thus attracted to water molecules. It is said to be and thus attracted to water molecules. It is said to be hydrophyllic,

hydrophyllic,which means “water-loving”.which means “water-loving”.  b).

 b). TheThe hydrocarbonhydrocarbon endend  (= tail)  (= tail)  of the molecule is non-  of the molecule is non- polar,

 polar, and and tendstends notnot  to interact with water. It is said to be  to interact with water. It is said to be hydrophobic

hydrophobicor “water fearing”.or “water fearing”. 4. Fatty acids are classified as either

4. Fatty acids are classified as either saturatedsaturated ((= contains only= contains only C-C (single) bonds)

C-C (single) bonds) or asor as unsaturatedunsaturated (= contains(= contains at least oneat least one C=C (double) bond)

C=C (double) bond).. 5.

5. If If the the lipid lipid containscontains only oneonly one  C=C bond, it is said to be a  C=C bond, it is said to be a mono-unsatura

mono-unsaturated lted lipidipid ( (e.g. olive oil). e.g. olive oil). These are thought to bThese are thought to be good for us.e good for us. 6.

6. If If the the lipid lipid containscontains two or moretwo or more C=C double bonds, it is said to be a C=C double bonds, it is said to be a polyunsaturated lipid.polyunsaturated lipid.

The value of these to our health is less clear;

The value of these to our health is less clear; cholesterolcholesterol is a polyunsaturated fat!is a polyunsaturated fat!

7. Unsaturated lipids tend to have lower melting points (they are generally oils); and are found in 7. Unsaturated lipids tend to have lower melting points (they are generally oils); and are found in  plants and fish.

 plants and fish. The exception is Palm Oil – which is a saturated lipid.The exception is Palm Oil – which is a saturated lipid.

Triglycerides

Triglycerides contain three molecules of fatty acid joined to onecontain three molecules of fatty acid joined to one molecule of glycerol.

molecule of glycerol. Phospholipids

Phospholipids havehave oneone  of the three fatty acids substituted by a  of the three fatty acids substituted by a phosphate group

phosphate group. . All cellular membranes All cellular membranes are composed are composed of twoof two layers of phospholipids (called a

layers of phospholipids (called a phospholipid bilayer)phospholipid bilayer), together, together with embedded

with embedded protein molecules. protein molecules. Cell membranes Cell membranes form a form a barrierbarrier  between the inside and outside of the cell.

 between the inside and outside of the cell. Steroids

Steroids are related to lipids. They are are related to lipids. They are molecules with molecules with four fusedfour fused carbon rings with various functional groups attached to them. carbon rings with various functional groups attached to them. Their main role is as hormones (both male and female sex Their main role is as hormones (both male and female sex hormones are steroids);

hormones are steroids); anabolicanabolic (=(= building building )) steroidssteroids, such as, such as testosterone

testosteroneare abused by some athletesare abused by some athletes.. 8.

8. Another Another steroid steroid isis cholesterolcholesterol, which is needed by the body for, which is needed by the body for nerve cells (and others) to function normally.

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NUCLEIC ACIDS – DNA & RNA

NUCLEIC ACIDS – DNA & RNA

(and ATP too!)

(and ATP too!)

1. Nucleic acids are

1. Nucleic acids are veryvery  large and organic molecules that  large and organic molecules that store geneticstore genetic information

information in cells.in cells.

2. Nucleic acids (DNA, RNA) use the sequence of

2. Nucleic acids (DNA, RNA) use the sequence of fourfour organic bases to organic bases to store genetic information.

store genetic information. The sequence in The sequence in which the which the bases are arrangedbases are arranged forms a (

forms a (universal universal ) code of genetic instructions of the cell.) code of genetic instructions of the cell. 3.

3. There There areare fivefive  different organic bases  different organic bases  –  –  Adenine Adenine (A),(A), GuanineGuanine (G),(G), and

and CytosineCytosine (C), are found in(C), are found in bothboth  DNA  DNA andand RNARNA.. ThymineThymine (T) is(T) is found

found onlyonly in DNA, whilst in DNA, whilst UracilUracil(U) is exclusive to RNA (all sorts).(U) is exclusive to RNA (all sorts). 4. DNA

4. DNA ((Deoxyribose Nucleic Acid)Deoxyribose Nucleic Acid) contains the genetic informationcontains the genetic information used to make and operate all cells; every cell also contains the genetic used to make and operate all cells; every cell also contains the genetic information to make the

information to make the wholewhole  organism.   organism. Since DNA Since DNA is passed on is passed on fromfrom one cell to the next at cell division, and from one generation to the next in reproduction,

one cell to the next at cell division, and from one generation to the next in reproduction, DNA isDNA is immortal!

immortal! 5.

5. DNA DNA is is extremely extremely long long and and consists oconsists off two strandstwo strands, running in opposite directions (=, running in opposite directions (= ‘antiparallel’ 

‘antiparallel’ ) held together by the billions of ) held together by the billions of hydrogen bonds hydrogen bonds which join the bases together. which join the bases together. TheThe number of such bonds is different between the two possible base pairs:

number of such bonds is different between the two possible base pairs:

A = T

A = T

(i.e. 2 H-bonds)(i.e. 2 H-bonds)

;

;

 but G = C

 but G = C

(i.e. 3 H-bonds).(i.e. 3 H-bonds). 6.

6. RNARNA ((Ribose Nucleic AcidRibose Nucleic Acid),), exists exists in three in three forms –forms – messenger RNAmessenger RNA,, transfer RNAtransfer RNA  and  and ribosomal RNA.

ribosomal RNA. These These are are known known asas mRNAmRNA,, tRNAtRNA andand rRNArRNA,, respectively. respectively. They They are are allall essential for the complex process of the manufacture of proteins.

essential for the complex process of the manufacture of proteins. 7.

7. RNA RNA is much is much shorter and shorter and isis single-strandedsingle-stranded,, though it may though it may coil back on itself, using hydrogen bonds to do so. (especially coil back on itself, using hydrogen bonds to do so. (especially tRNA) .

tRNA) .

8. Both DNA and RNA are polymers, composed of thousands of 8. Both DNA and RNA are polymers, composed of thousands of linked monomers called

linked monomers called nucleotidesnucleotides.. 9. Each nucleotide is made of

9. Each nucleotide is made of threethree main components: main components: a)

a) A phosphate groupA phosphate group  b)

 b) A 5-carbon (pentose) sugarA 5-carbon (pentose) sugar c)

c) An organic base (An organic base (normallynormally A, T, G, C, or UA, T, G, C, or U).). 10.

10. Note Note thatthat ATP is also a nucleotideATP is also a nucleotide, and contains the 5-, and contains the 5-carbon sugar

carbon sugar riboseribose..

Food tests

Food tests

Reducing Sugar

Reducing Sugar

::

Benedict’s reagentBenedict’s reagent →→ BoilBoil →→ BlueBlue →→ Brick-redBrick-red

Non-Reducing Sugar

Non-Reducing Sugar

::

 First show First show Benedict’s test is negativeBenedict’s test is negative! ! Then Then (on (on fresh sample):fresh sample): Add few drops

Add few drops dil. HCldil. HCl →→ Boil Boil (sugar hydrolysed)(sugar hydrolysed) →→ NeutraliseNeutralise with with dil NaOHdil NaOH Then

Then repeat Benedict’s testrepeat Benedict’s test →→ BlueBlue →→ Brick redBrick red

Starch:

Starch:

 Add few drops Add few drops Iodine solution (IIodine solution (I22KI soln)KI soln).. Yellow/orangeYellow/orange→→ blue/blackblue/black( (  NB NB No No heat!) heat!)

Triglyceride (lipid):

Triglyceride (lipid):

  Add 5cm  Add 5cm33 ethanol ethanol.. Warm gentlyWarm gently &/or shake 30 sec. &/or shake 30 sec. (lipid dissolves)(lipid dissolves) Pour

Pour slowlyslowly into into ½ test-tube cold water½ test-tube cold water →→

Protein:

Protein:

Add Add few few dropsdrops BiuretBiuretreagent toreagent to liquidliquid sample.sample. (Pale)(Pale) BlueBlue →→ LilacLilac( (  NB NB No No heat!) heat!) © IHW September 2005 © IHW September 2005

LOUDY WHITE

References

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