الرئيسيةالبوابةس .و .جالتسجيلدخول

شاطر | 
 

 Amino Acids and Protein

استعرض الموضوع السابق استعرض الموضوع التالي اذهب الى الأسفل 
كاتب الموضوعرسالة
mojahid
عضو جديد
عضو جديد


ذكر
عدد المساهمات : 23
العمر : 30
تاريخ التسجيل : 20/08/2008

مُساهمةموضوع: Amino Acids and Protein   الثلاثاء 27 يناير - 3:43



Amino acids and proteins



Proteins are polymers of α-amino acids.



Amino acids are the building blocks of proteins.



The main carbon (The alpha carbon atom) is asymmetrical because the four groups linked to it are different.

Building Blocks - Amino Acids

An amino acid is defined as the molecule containing an amino group (NH2), a carboxyl group (COOH) and an R group.



It has the general formula:

R-CH(NH2)-COOH



The R group differs among various amino acids.



In a protein, the R group is also called a sidechain.

There are:

a -COOH, which is a carboxyl group (acidic).

a -NH2, which is an amino group (basic).

an -H hydrogen.

a residue R which varies depending on the amino acid.








All of the amino acids (except for proline) have a carboxyl group and an amino group.




At physiological pH the natural amino acids exist as zwitterions, with a negatively charged carboxyl group and a positively charged amino group.



Zwitterion is an amino acid with no ionizable R-group would be electrically neutral at this pH.

The configuration can be remembered as the CORN law.

Imagine looking along the H-Calpha bond with the H atom closest to you.

When read clockwise, the groups attached to the Calpha spell the word CORN (Richardson, 1981).



There are over 300 naturally occurring amino acids on earth, but the number of different amino acids in proteins is only 20.



Each amino acid has a similar, yet unique structure .



The side chains vary greatly in their complexity and properties.



The side chain of glycine is simply a hydrogen.



The side chain of tryptophan is based on the aromatic, bicyclic indole group.



All 20 different amino acids have the same structure, but their side chain groups (the R group) may vary in size, shape, charge, hydrophobicity, and reactivity.



The amino acids could be considered as the alphabet in which the proteins are written.

Peptides

The peptide is a chain of amino acids linked together by peptide bonds.



Polypeptides usually refer to long peptides whereas oligopeptides are short peptides (< 10 amino acids).



Proteins are made up of one or more polypeptides with more than 50 amino acids.

Peptide bond :

A peptide bond is the linkage between two amino acids, formed by the condensation reaction


Two amino acids can, under some circumstances, react together.

The result is the creation of a dipeptide.

A molecule of water is released in the process. This is the basic reaction involved in the synthesis of proteins




Primary structure

The primary structure of a protein refers to its amino acid sequence.



The amino acid in a peptide is also called a residue.


The amino acid sequence (primary structure) of ribonuclease A (RNase A), which is an enzyme acting on RNA.

Each letter represents an amino acid .

Secondary Structure

In a protein, certain domains may form specific structures such as α helix and β strand, which constitute the secondary structure of the protein.

Alpha helix

Beta strand, beta sheet and beta barrel

Motif


The secondary structure of RNase A, which contains three α helices and seven β strands.


The α helix and b strand in RNase A. (a) Residues 1 to 36. (b) Residues 80 to 85.

Three-Dimensional Structure

The three-dimensional (3D) structure is also called the tertiary structure.



The ribbon representation of the 3D structure of RNase A.



Its atomic coordinates were obtained from Protein Data Bank




X-ray crystallography and nuclear magnetic resonance (NMR) are the major experimental techniques for determining the 3D structures of macromolecules.



Protein Data Bank is the most important site for structural information which can easily be accessed by the "PDB ID" of a macromolecule.



If a protein molecule consists of more than one polypeptide, it also has the quaternary structure, which specifies the relative positions among the polypeptides (subunits) in a protein.





The Twenty Amino Acids of Proteins :

Based on the physicochemical properties of R groups, the 20 amino acids of proteins may be classified as follows:



1. Acidic:

including aspartic acid (aspartate) and glutamatic acid (glutamate).

In a neutral solution, the R group of an acidic amino acid may lose a proton and become negatively charged.





2. Basic:

including lysine, arginine and histidine.

In a neutral solution, the R group of a basic amino acid may gain a proton and become positively charged.

Interaction between positive and negative R groups may form a salt bridge, which is an important stabilizing force in proteins.



3. Aromatic:

including tyrosine, tryptophan and phenylalanine.

Their R groups contain an aromatic ring.





4. Sulfur:

including cysteine and methionine.

Their R groups contain a sulfur atom (S). The disulfide bond formed between two cysteine residues provides a strong force for stabilizing the globular structure.

A unique feature about methionine is that the synthesis of all peptide chains starts from methionine .
الرجوع الى أعلى الصفحة اذهب الى الأسفل
شيخ المختبر
عضو مميز
عضو مميز


ذكر
عدد المساهمات : 236
تاريخ التسجيل : 11/09/2008

مُساهمةموضوع: رد: Amino Acids and Protein   الثلاثاء 27 يناير - 6:34


شكرا لك موضوع مميز

ننتظر منك المزيد
الرجوع الى أعلى الصفحة اذهب الى الأسفل
hemato
عضو فضي
عضو فضي


ذكر
عدد المساهمات : 546
تاريخ التسجيل : 13/08/2008

مُساهمةموضوع: رد: Amino Acids and Protein   الثلاثاء 27 يناير - 7:26

موضوع رائع أخي مجاهد


دائما متميز

في انتظار جديدك
الرجوع الى أعلى الصفحة اذهب الى الأسفل
mojahid
عضو جديد
عضو جديد


ذكر
عدد المساهمات : 23
العمر : 30
تاريخ التسجيل : 20/08/2008

مُساهمةموضوع: رد: Amino Acids and Protein   الجمعة 30 يناير - 22:44

يعطيكم العافيه...

مع علمى التام بتقصيرى اتجاه المنتدى ولكن سنجتهد ان شاء الله
الرجوع الى أعلى الصفحة اذهب الى الأسفل
 
Amino Acids and Protein
استعرض الموضوع السابق استعرض الموضوع التالي الرجوع الى أعلى الصفحة 
صفحة 1 من اصل 1
 مواضيع مماثلة
-
» Amino acid reactions

صلاحيات هذا المنتدى:لاتستطيع الرد على المواضيع في هذا المنتدى
شبكة الابداع للتحاليل الطبية  :: منتديات التحاليل الطبية :: الكيمياء الحيوية والسريرية-
انتقل الى: