tertiary protein structures

8/12/2019 Tertiary Protein Structures

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By: Abhi Verma 11BCE0272 Ajay Pratap Singh 11BCE0503


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The tertiary structure is the final specific geometric shape that aprotein assumes . This final shape is determined by a varietybonding interactions between the "side chains" on the amino acids.

These bonding interactions may be stronger than the hydrogen bondsbetween amide groups holding the helical structure. As a result,

bonding interactions between "side chains" may cause a number offolds, bends, and loops in the protein chain. Different fragments of thesame chain may become bonded together.


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In this diagram you shouldrecognize the beta pleatedsheets (ribbons with arrows) andthe alpha helical regions (barrelshaped structures)


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A beta pleated sheet is a pleated structure that is composed of the C-C-N-C-Cbackbone of a polypeptide.

In the figure given, each chain of CCNCC... has a N to Cpolarity in the direction opposite to that of its neighbor. The lineon the left has the N-to-C polarity from top to bottom . The line

in the middle has the N-to-C polarity from bottom to top . Theline on the far right has the N-to-C polarity from top to bottom .These chains are said to be antiparallel because they run inthe opposite directions. If the chains run in the same N-Cdirection they are saild to be parallel . The beta pleated sheetstructure is stabilized by hydrogen bonds between the differentchains.


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The hydrogen bonds in a beta pleated

protein structure provide stability to the

structure as a whole.

The bond is generally formed between

Two or more beta pleated sheets.


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An alpha helix can be formed by making a rope coil in a left handed direction. In thecase of a protein the rope would be represented by the N-C-C-N-C-C-N .... backboneof the polypeptide chain.

Pauling and Corey built models of proteins. They fouusing the information they had gained concerning bolengths and rotations to make their models, proteins can alpha helix.In addition they found that the alpha helix could be a structure because intrachain hydrogen bonds could bthat stabilized the helix.


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The hydrogen bonds in the case of an

alpha helix protein structure are called

intrachain hydrogen bonds and make the

helix structure of the protein stronger.

The bond is formed within the

alpha helix structure.


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The alpha helix is one of the structures that are called the secondary structures ofproteins.

The other structure that is a part of the secondary structure is the beta pleated sheet.

Some proteins like keratin and collagen are almost entirely alpha helical in structure.

Most globular proteins have alpha helical and beta pleated sheet regions in addition toregions that are neither alpha helical or beta pleated sheets.

Charge amino acid side chains have a tendency to destabilize the alpha helical orbeta pleated sheet structures.

Amino acids with hydrophobic side chains are compatible with the formation of alphahelices and beta pleated sheets.


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rod like

CO & NH of the main chain arehydrogen bonded together

n+4 H bonding scheme

all alpha carbons are H bonded and inline with each other

R groups are on the outside &backbone on the inside always righthanded (clockwise)

can be a single chain (usually lessthan 45 Angstroms)

sheet like

Beta sheets are formed by linkinmore Beta strands by H bonds

side chain of adjacent residues popposite directions

only trans peptide bonds give R

groups on opposite sidescannot exist as a single Beta stramust be 2 or more

in proteins, 4-5 strands make up beta sheet; it is possible to be mamore than 10


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1.5 Angstroms rise (from one alphacarbon to the second)

100 degree rotation

3.6 residues per turn

Ramachandran diagrams (1) Right

handed: can only occur between -60,-60; little hindrance (2) Left handed:+60, +60; large hindrance

3.5 Angstroms rise between resid

7 Angstroms between R groups

Arrow in pictures always points CO group

can be anti parallel, parallel, or

Ramachandran diagrams: existsbetween -60 to -120, 100-190


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tertiary protein structures

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