Protein Structure and Bonds

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Questions and Answers

What is a peptide bond?

A peptide bond forms between the carboxylic acid of one amino acid and the amino group of the next amino acid with the loss of H2O.

How does the primary structure of proteins differ from the secondary structure?

Primary structure involves the peptide bonds that join one amino acid to the next, while secondary structure includes alpha helix and beta pleated sheet formations.

Define protein.

Composed of molecular building blocks called amino acids, if more than 50 amino acids are in the peptide chain with biological activity, it is a protein.

Identify major roles of proteins in the body.

Proteins make up skin, muscle, cartilage, hair, fingernails, enzymes, and hormones. Signup and view all the answers

What is protein shape and bonding at the primary level?

Linking two or more amino acids by peptide bonds. Signup and view all the answers

What is protein shape and bonding at the secondary level?

Alpha helix and beta pleated sheet formed by hydrogen bonding. Signup and view all the answers

What is protein shape and bonding at the tertiary level?

Interactions between side groups like ionic bonds, disulfide bonds, and hydrophilic interactions creating a compact shape. Signup and view all the answers

What is protein shape and bonding at the quaternary level?

Two or more tertiary units or polypeptide chains. Signup and view all the answers

Describe denaturation effects caused by temperature.

Disrupted hydrogen bonds and hydrophobic interactions. Signup and view all the answers

Describe denaturation effects caused by pH.

Disrupted hydrogen bonds between polar R groups and salt bridges. Signup and view all the answers

Describe denaturation effects caused by heavy metals.

Disulfide bonds are disrupted by ionic bonds formed with heavy metals. Signup and view all the answers

Describe denaturation effects caused by organic molecules.

Hydrophobic interactions are disrupted. Signup and view all the answers

What are the color changes associated with positive and negative tests of the Biuret test?

Positive test shows a violet color; negative test remains blue. Signup and view all the answers

What are the color changes associated with positive and negative tests of the Ninhydrin test?

Most amino acids give a blue-violet color; proline and hydroxyproline give a yellow color. Signup and view all the answers

What are the color changes associated with positive and negative tests of the Xanthoproteic test?

Positive results show yellow color; it reacts with aromatic amino acids. Signup and view all the answers

Why are heat and alcohol used to disinfect medical equipment?

They kill bacteria by denaturation, disrupting protein structure. Signup and view all the answers

Why is milk given to someone who accidentally ingests a heavy metal ion?

The heavy metal ions will act on the proteins in the milk rather than the body. Signup and view all the answers

How does a change in pH affect the structural levels of a protein?

It disrupts the bonds that hold the tertiary structure together. Signup and view all the answers

What might be the reason for a yellow spot on a student's hand after working with HNO3?

The nitric acid from the xanthoproteic test reacted with her skin. Signup and view all the answers

Which samples gave a negative Biuret test and why?

Glycine and Tyrosine because they do not have multiple peptide bonds. Signup and view all the answers

What functional group gives a positive test in the xanthoproteic test?

Aromatic ring. Signup and view all the answers

What tests could you use to determine whether an unlabeled test tube contained an amino acid or a protein?

Biuret test. Signup and view all the answers

Study Notes

Peptide Bonds

A peptide bond forms between the carboxylic acid of one amino acid and the amino group of another, releasing water (H2O).

Structure of Proteins

Primary structure: Sequence of amino acids linked by peptide bonds.
Secondary structure: Includes alpha helices (coiled peptide chains) and beta-pleated sheets (formed between protein strands).
Tertiary structure: 3D shape due to interactions between side groups (ionic bonds, disulfide bonds, hydrophilic interactions).
Quaternary structure: Combination of two or more tertiary structures or polypeptide chains.

Definition of Proteins

Composed of amino acids; a molecule is categorized as a protein if it contains more than 50 amino acids with biological activity.

Functions of Proteins

Essential for the structure of skin, muscle, cartilage, hair, fingernails, enzymes, and hormones.

Protein Bonding

Primary: Linking through peptide bonds, forming dipeptides, tripeptides, etc.
Secondary: Stabilized by hydrogen bonding; alpha helix resembles a spiral staircase, while beta pleated sheets resemble folding or pleating.

Denaturation of Proteins

Temperature: Breaks hydrogen bonds and disrupts hydrophobic interactions.
pH: Affects hydrogen bonds and salt bridges.
Heavy metals: Disrupt disulfide bonds through ionic bond formation.
Organic molecules: Disrupt hydrophobic interactions.

Biuret Test

Positive test indicates presence of peptide bonds; the solution changes from blue (Cu²⁺) to violet for proteins with two or more peptide bonds.
Negative reaction remains blue, showing only individual amino acids or dipeptides.

Ninhydrin Test

Used to detect amino acids in proteins; most amino acids yield a blue-violet color, while proline and hydroxyproline result in a yellow color.

Xanthoproteic Test

Detects amino acids with aromatic rings; concentrated nitric acid produces yellow-colored nitro-substituted products from tyrosine and tryptophan.

Disinfection Methods

Heat and alcohol disinfect by denaturing proteins, destabilizing secondary, tertiary, and quaternary structures.

Milk and Heavy Metal Ingestion

Milk acts as a buffer by reacting with heavy metal ions like silver or mercury, protecting the body from toxicity.

pH Changes and Protein Structure

Alterations in pH disrupt bonds maintaining tertiary structures.

Xanthoproteic Test Reaction

The yellow spot on skin after nitric acid exposure indicates oxidization leading to the formation of a yellow product.

Negative Biuret Test

Glycine and tyrosine yield negative results due to lacking multiple peptide bonds; biuret test requires the presence of those bonds for a positive outcome.

Functional Group in Xanthoproteic Test

The presence of an aromatic ring confirms a positive reaction in the xanthoproteic test.

Differentiating Amino Acids and Proteins

The biuret test can distinguish between amino acids and proteins in an unlabeled test tube.

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Description

This quiz covers the fundamental concepts of protein structure, including peptide bonds and the four levels of protein organization: primary, secondary, tertiary, and quaternary. Additionally, it highlights the biological significance of proteins and their various functions in the body.