amino acids (2) iua

8/2/2019 Amino Acids (2) IUA

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AminoAcids(2)

DepartmentofBiochemistryFacultyofMedicine

InternationalUniversityofAfrica,Khartoum,Sudan


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Acidbasepropertiesofaminoacids

TheaCOOHandaNH2 groupsareionizable.

thepHofthemedium.


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The Carbox l rou shave Ka valuesofbetween1.8and

2.8

(moreacidic

than

simple

monocarboxylic acids).

The amino rou shave Ka valuesbetween8.8and10.6

dependingontheaminoacid.

Acidicandbasicaminoacidshaveadditionalionizable

groups.

AtifHassanKhirelsied


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AminoAcidshavedistinctdissociationcurves


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Atitsisoelectric pH(pI),anaminoacidbearsnonet



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Atitsisoelectric pH(pI),anaminoacidbearsnonet



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Thebufferingactionofaminoacids


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Reactionsofaminoacids



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Reactionsofaminoacids



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The e tidebond

A. Anamide CN linkageformingthebackboneofall

proteins.

B. Involves two ad acent amino acids liked b

eliminationofH2O.

C. Planner,i.e.theCNinvolvedlieinthesameplane



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Thepeptidebond

eam noan car oxy

groupsofaminoacidscan

toformpeptides.


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Peptidebondformation


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Pe tidesand roteins

Thesimplestpeptide,adipeptide,containsasingle

aminoacidswitheliminationofwater.



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Peptidesandproteins

Proteinsarepolymers ofaminoacidsjoinedbypeptide

bonds.



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Peptidesandproteins

- .



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Peptidesandproteins

Thenumberandorderofallresiduesinapolypeptide

constituteitsprimarystructureoftheprotein.


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ProteinStructure


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Proteins: ordersofstructure

The Primary structure, the sequence of the amino acids in

a po ypep e c a n.

The secondary structure, the folding of short (3- to 30-

residue), contiguous segments of polypeptide into geometrically

.



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The tertiary structure, the three-dimensional assembly of

secondary structure units to form larger functional units.

The quaternary structure, the number and types of polypeptide

un s o o gomer cpro e ns an e r spa a arrangemen .



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The secondary structure.

The two most common types of secondary -helix

structure, the -helix and the -sheet,



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-

Stabilized by hydrogen bonds

ompact



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Stabilized by hydrogen bonds

Is highly extended.

erpara e oran para e .



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.

Indicates how secondary structural featureshelices, sheets,

, , - ,

to form domains and how these domains relate spatially to oneanother.



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Thequaternarystructure

In some cases, proteins are assembled from more than one

, .

Quaternary structure defines the polypeptide composition of an

.



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The quaternary structure

.

Homodimers contain two co ies of the same ol e tide chain

while in a heterodimerthe polypeptides differ.

Greek letters (, , etc) are used to distinguish different subunitsof a hetero-oligomeric protein.


i d f


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The quaternary structure

P i d f


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e orces a s a ze pro e ns s ruc ure

Higher orders of protein structure are stabilized primarily by

- .

1. Hydrophobic interactions.

2. Hydrogen bonds.

. a r ges.

4. van der Waal forces


P t i d f t t


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The forces that stabilize roteins structure

Some proteins contain covalent disulfide (S-S) bonds that link thesulfhydryl groups of cysteinyl residues.


P t i d f t t


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P t i d t ti


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Proteinsdenaturation

Denaturation:isthereversibleruptureofthenon

ofproteinconformationandbiologicalactivity.


Proteins denaturation


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Proteinsdenaturation

Thefunctionofaproteinisabsolutelydependenton

.

denaturing theprotein.

amino acids (2) iua

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