Determining Amino Acid Sequence Quiz

Determining Amino Acid Sequence

• Frederick Sanger received the Nobel Prize for sequencing the insulin protein, utilizing protein cleavage into smaller fragments.
• His method involved analyzing overlapping fragments to determine amino acid order, influencing future protein sequencing techniques.

Importance of Primary Structure

• Primary structure is crucial both genetically and structurally, dictated by nucleotide order in messenger RNA.
• The sequence of amino acids directs the formation of secondary and tertiary protein structures.

Secondary Structure

• Secondary structure is formed by hydrogen bonding between NH and CO groups in the polypeptide backbone.
• Two primary patterns emerge: α helices and β sheets.

The α Helix

• The α helix features a spiral shape with R groups extending outward; it has 3.6 amino acids per turn.
• Hydrogen bonds form between NH groups of one amino acid and CO groups of another one turn away.

The β Sheet

• The β sheet has a sheetlike conformation with alternated peaks and troughs due to the arrangement of polypeptide atoms.
• Characterized by extensive hydrogen bonding, it can form with different polypeptides or regions of the same polypeptide and can be parallel or antiparallel in orientation.

Structure of Hair

• Hair structure exemplifies the arrangements of proteins in cellular components.

Globular Proteins

• Globular proteins are compact structures with unique tertiary forms, comprising most enzymes.
• They can be primarily α helical, β sheet, or a combination, often containing multiple functional domains.

Protein Domains

• A domain is a folded region of a protein, typically 50–350 amino acids long, with specific functions.
• Proteins often share common domains, and proteins with multiple functions usually contain separate domains for each role.

Prediction of Tertiary Structure

• Primary structure dictates a protein's final folded shape, but predicting folding patterns, especially for larger proteins, remains challenging.

Quaternary Structure

• Quaternary structure involves the interaction and assembly of multiple protein subunits, characteristic of multimeric proteins.
• Proteins can consist of identical or different polypeptide subunits, exemplified by hemoglobin.

Nucleic Acids

• Nucleic acids are polymers of nucleotides linked via phosphodiester bonds, exhibiting 5′ to 3′ directionality.
• Nucleotide sequences are conventionally expressed in this direction, with base pairing essential for synthesis.

Complementary Base Pairing

• A pairs with T through two hydrogen bonds, while G pairs with C through three hydrogen bonds, a fundamental property of nucleic acids.

DNA Structure

• The double helix structure of DNA, proposed by Watson and Crick in 1953, consists of two antiparallel strands that twist around each other.
• This structure accounts for DNA's replication mechanism and complies with its chemical properties.

RNA Structure

• RNA typically exists as a single strand but can base pair within the same molecule, forming less extensive structures compared to DNA.

Polysaccharides

• Polysaccharides are long-chain polymers of sugars, serving structural and storage roles, consisting of repeating units called monosaccharides.
• Short sugar polymers or oligosaccharides can attach to cell surface proteins.

Classification of Sugars

• Sugars vary from three to seven carbons, classified as trioses, tetroses, pentoses, hexoses, and heptoses.

Glucose

• D-glucose (C6H12O6) is the most common monosaccharide, existing in dynamic equilibrium between linear and cyclic forms.
• It forms the structural basis of carbohydrates, with a formula of CnH2nOn.

Starch

• Starch, composed of amylose and amylopectin, is stored in plastids like chloroplasts and amyloplasts, crucial for energy storage in plants.
• Amylopectin contains branches, while amylose is generally unbranched.

Structural Polysaccharides

• Cellulose is the primary structural polysaccharide in plants, composed of β-D-glucose repeating units, indigestible by most mammals.
• Fungal and bacterial cell wall compositions differ, involving unique sugar linkages.

Chitin

• Chitin consists entirely of GlcNAc units linked by β(1→4) bonds, found in fungal cell walls and exoskeletons of insects and crustaceans.

Glycosidic Bonds

• The type of glycosidic bonds (α vs β) significantly affects polysaccharide structure.
• α-linked polysaccharides like starch form loose helices, while β-linked cellulose forms rigid rods, contributing to structural integrity in plant and fungal cells.

This quiz explores the groundbreaking work of Fred Sanger in determining the amino acid sequence of proteins, including the insulin protein. Learn about the methods he developed and their impact on protein sequencing. Test your knowledge on protein structure and sequencing techniques used in biochemistry.