Protein Structure Flashcards

1
Q

Fibrous proteins

A

They are insoluble in water
They play a structural role
Examples include alpha keratin and collagen

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2
Q

Globular proteins

A

They are soluble in water
They play functional role
All enzymes are globular proteins

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3
Q

Importance of protein

A

Protein may be broken down to provide energy or provide raw materials for the synthesis of other macromolecules

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4
Q

What are the levels of protein structure

A

Primary structure
Secondary structure
Tertiary structure
Quanternary structure

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5
Q

Primary structure

A

Is the sequence of amino acid in a protein in which a peptide bond connects the alpha carboxyl group of each amino acid to the alpha amino group of the next chain

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6
Q

Secondary structure

A

It refers to the repeating patterns formed by the backbone of at least part of a polypeptide chain which is stabilized by hydrogen bonding

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7
Q

Tertiary structure

A

These are structure with single three dimensional structure and stabilized by bonding between amino acids

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8
Q

Quaternanry structure

A

It is the complete three dimensional structure including the interaction between the component polypeptide chains

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9
Q

Bonds involved in the maintenance of protein structure

A

Hydrogen bond
Disulphide bridges
Van DER Waals bonds
Co ordinate bonds

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10
Q

How to determine a primary structure

A

By the isolation of polypeptide chain i.e to determine the number of different N terminal amino acid and the number of different C terminal amino acids in a polypeptide chain

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11
Q

What reagent is used to identify N terminal amino acids

A

Dansyl chloride
Sanger’s reagent (1-fluoro-2,4-dinitrobenzene)
Edman’s reagent

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12
Q

What added advantage does dansyl cloride has when it reacts with alpha amino groups

A

Dansyl amino acids are highly fluorescent and can be identified in very small quantities by HPLC

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13
Q

How is the c terminal amino acid identified

A

1.It is identified by treating the protein with a reagent that attacks the free carboxyl group e.g sodium borohydride

2.it can also be treated with anhydrous hydrazine at high temperature for several hours in the presence of a catalyst.

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14
Q

What happens when the protein is treated with anhydrous hydrazine

A

Each free carboxyl group react to form a hydrazide

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15
Q

What happens when protein is treated with sodium borohydride

A

The side chain carboxyl group will be reduced with the subsequent production of amino alcohols

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16
Q

Ways by which the linkages between various polypeptide chain may be broken

A

Disulphide bridges maybe broken by treatment with performic acid
Non covalent bond is broken by extremes of pH at high salt concentration or in presence of reagents

17
Q

Determination of the amino acid composition of each polypeptide chain

A
  1. By determining the molecular weight of the polypeptide by the use of size exclusion chromatography then the polypeptide is then completely hydrolysed to it’s component amino acid and the concentration of each determined
  2. By ion exchange chromatography in which the eluate is mixed with a reagent such as ninhydrin which reacts with the most amino acid to give blue purple colour.
18
Q

Enzymes used to split long polypeptide chain

A

Cyanogen bromide which breaks the bond of methionine
Trypsin which breaks the bond on lysine or arginine side chain
Chymotrypsin which breaks the bond on phenylalanine, tryptophan and tyrosine side chain

19
Q

What are the effects of the enzymes on polypeptide chain

A

It produces a number of peptide fragments which are separated from each other by chromatography or electrophoresis

20
Q

Peptides consisting up to 25 amino acid residues maybe separated directly by means of

A

Tandem mass spectrometry