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Assignment 2 Proteins

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At the end of this assignmentpreparation you will be able to :

Describe the general structure of an amino acid

Describe how condensation reactions result inthe formation of peptide bonds linking togetheramino acids to form polypeptides.

Understand the primary, secondary, tertiary andquaternary structure of proteins

!plain how the structure of proteins links totheir functions.

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"hat doesprotein

mean#

$t is %reek for &'of (rstimportance.)

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"here in your body would you(nd proteins#

*uscles +actin and myosin

-air and nails +keratin

Digestie system / en0ymes1ell membranes

$n ligaments, bones and tendons

+collagen.$mmune system & antibodies areproteins

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PROTEINS

Carbon, Hydrogen, Oxygen, Nitrogen and sometimes Sulphur

Polymers made up of mino a!ids"monomer#

$% !ommonly o!!urring amino a!ids

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Stru!ture of an amino a!id

All amino acids hae the same oerall structure& only the group changes3

+amino

+carbonyl

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the ariable group inamino acids

$f the atomic group is P45A,

the amino acidwill be 645U75in water.

$f the atomic group in 848/P45A, the aminoacid will be$8645U75 in

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!amples of amino acids

Amino acid group

%lycine -

Alanine 1-9

1ysteine 1-26-

-ow do aminoacids oin

together# Andwhat do theyform#

Hint: Think back tocarbohydrates

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Atomic %roup

Phenylalanine(Phe)

ValineVal

Alanine (Ala)

Lysine (Lys)

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Ho& is a proteinConstru!ted'

 ;his is a 148D86A;$48 reaction. ;he amino acids are now called

amino acid residues

 ;hree amino acids

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Polypeptide !hain

*any amino acids can be oined togetherto form a polypeptide

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-ydrolysis$n the same way as carbohydrates, thepeptide bond between two amino acidscan be broken in hydrolysis by theaddition of water. ;his produces twoseparate amino acids again.

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Stru!ture of Protein

Primary

Se!ondary

Tertiary(uaternary

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Primary Stru!ture

• 5ong, straight chain of amino acids oined together.

•  ;he speci(c sequence of amino acids determines the functionof the protein

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 ;he primary structure can beshown using 9 letter abbreiations

for the amino acids, e.g.

Ala.5ys.Phe.5ys.=al.;yr.1ys.Ala.=al

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$mportance of primarystructure

Determines ultimate shape andfunction of the protein

A change in any one amino acid inthe primary sequence, could leadto change in shape or function of

the protein ;herefore, protein>s shape is =?6P1$@$1 to its function

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Se!ondary Stru!ture

 ;he secondary structure is the folding of the chain of aminoacids. ;he hydrogen bonds form between

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Tertiary stru!ture

 ;he specifc tertiary structure of a protein is thespeci(c folding of the secondary structures.

 ;he structure is held together by -?D4%8, $48$1, andsometimes D$6U5P-$D +6/6 bonds.

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 ;ertiary structure ofproteins

 ;he polypeptide chains often fold togie unique comple! 9D structure ofprotein

 ;his is maintained by: "eak hydrogen bonds +easily

broken 6tronger ionic bonds formed

between carbo!yl and aminogroups +can be broken by changesin p-

en stronger disul(de bonds +noteasily broken. ;hese coalentbonds form between groups that

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7onds also form between non/polar +hydrophobic groups.

ua ernary s ruc ure o

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ua ernary s ruc ure oproteins

6ome proteins consistof more than onepolypeptide chain orpolypeptide chains and

non/protein +prostheticgroups +eg:haemoglobin containsiron, which gies afourth leel of structure

 ;his shape is createdwhen the diBerentchains bind together toform whole proteinmoleculehttp:CCwww.ohnkyrk.comCaminoacid.html

https:CCmywebspace.wisc.eduConoicCwebCproteins.

) b d l b l

http://www.johnkyrk.com/aminoacid.htmlhttp://www.johnkyrk.com/aminoacid.htmlhttps://mywebspace.wisc.edu/jonovic/web/proteins.htmlhttps://mywebspace.wisc.edu/jonovic/web/proteins.htmlhttp://www.johnkyrk.com/aminoacid.html

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)ibrous and *lobularProteins

@ibrous/structural roles. .g Keratinin nails, Collagen in bone and

tendons

%lobular/en0ymes, antibodies

hormones.g. Insulin, haemoglobin.

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)ibrous proteinInsoluble be!ause R+groups are non+polar

Se!ondary stru!ture

of long polypeptide!hains formingfibres "alpha helix#or sheets "beta

pleated sheet#)ibres gi-e strength,sheets flexibility

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1ollagen

*ade up from 9polypeptidechains +alpha

heli! twistedtogether giing astrong structure.

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*lobular Proteins

Highly folded and !oiled &ith more than .polypeptide !hain "!omplex tertiarystru!ture#

Ea!h !hain is !alled a subunit

Hydrogen, ioni! and sulfide bonds hold it/sshape

Soluble &ith a spe!ifi! tertiary stru!tureas hydrophili! R groups are on the outside

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Haemoglobin is a conjugatedquaternary protein comprising:

•  two alpha-globulins•  two beta-globulins•  four haem groups, each withan iron atom at its core

It is the iron atoms which bindoxygen.

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5inking structure to function

-aemoglobin has E heam groups thatcontain iron to carry the o!ygen.

 ;he binding of the (rst o!ygen molecule

changes the shape of the molecule, makingit easier for the second o!ygen molecule tobind.

 ;he binding to o!ygen only happens at highpartial pressure of o!ygen +in the lungs andreerses at low partial pressures +in thetissues. 6o o!ygen is released in the tissuesfor use in respiration.

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So to function efficiently, haemoglobin must attractoxygen under certain conditions, but lose it underother conditions.

Loading/unloading is a reversible reaction, inwhich one haemoglobin (Hb) can attract up to 4oxygen molecules:

Hb + 4O2  HbO8loadingunloading

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Feratin in hair

Feratin forms nails and hair. ;he polypeptide chain has hydrogen bondsbetween the amino acid residues that hold it

into an alpha heli! secondary structure.-ydrogen bonds, disulphide bridges andhydrophobic interactions hold the polypeptidechains together forming tough, insoluble(bres

A hair

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 ;he hydrogen bonds in the secondarystructure are easily broken if hair is pulled.

 ;his allows hair to stretch a little, particularlywhen heat is applied & a characteristic that is

used in styling.

 ;he primary structure has a leucine +aminoacid appro!imately eery Gth residue. ;hese

form the hydrophobic interactions.

*any cysteine molecules allow the formationof disulphide bridges. 8ail and hooes haemore cysteine, making them stronger.