Protein Function and Structure Flashcards

Major Functions of Proteins

• Provide structural support for cells and tissues
• Facilitate movement within organisms
• Involved in signal transduction processes
• Bind to various molecules and ions
• Transport substances across cellular membranes
• Act as catalysts in biochemical reactions

Primary Structure of Proteins

• Defined by the linear sequence of amino acids (AA)
• Determines higher order structures including secondary structure
• Mutations in the primary structure can lead to functional deficiencies

Peptide Bonds

• Form connections between amino acids
• Result from a condensation reaction between the amino group of one AA and the carboxyl group of another

Sickle Cell Disease Mutation

• Caused by a mutation where glutamate is replaced with valine
• Alters the charge of the hemoglobin molecule, impacting its functionality

Secondary Structure of Proteins

• Comprises arrangements of the polypeptide chain stabilized primarily by hydrogen bonds
• Two main types: alpha helix and beta sheet

Alpha Helix

• Features a coiled, helical structure
• Side chains of amino acids extend outward from the helix

Beta Sheet

• Formed by the packing of beta strands
• Characterizes the orientation of adjacent strands, which can be parallel or antiparallel

Role of Proline

• Disrupts the formation of alpha helices
• Lacks a free hydrogen atom for hydrogen bonding due to its unique structure

Motifs in Protein Structure

• Comprise specific arrangements of secondary structures that adopt characteristic 3D shapes
• Also referred to as super secondary structures

Function of Super Secondary Structures

• Engage in binding small ligands, ions, and interact with DNA

Zinc Finger Structure

• A type of super secondary structure containing zinc ions coordinated with cysteine and histidine residues
• Important in DNA-binding proteins

Locations of Zinc Fingers

• Present in receptors for lipid-soluble hormones that exhibit DNA-binding activity

Leucine Zipper Structure

• Another super secondary structure where leucine residues from two alpha helices intertwine
• Facilitates protein dimerization

Locations of Leucine Zippers

• Found in DNA-binding proteins such as transcription factors

Prions

• Infectious proteins that induce structural changes in normal neural proteins
• Promote the conversion from alpha helices to beta sheets
• Form aggregates that resist degradation through digestion or heat

Diseases Linked to Prions

• Associated with conditions like kuru, mad cow disease, and Creutzfeldt-Jakob disease

Tertiary Structure of Proteins

• Refers to the complete 3D folded shape of a polypeptide
• Comprised of distinct structural and functional domains
• Stabilized by interactions between side chains and associations of supersecondary motifs

Stabilization of Secreted Proteins

• Achieved through the formation of covalent disulfide bonds

Quaternary Structure of Proteins

• Involves the assembly of two or more tertiary structures
• Common forms include dimers and tetramers
• Stabilized by noncovalent interactions and interchain disulfide bonds

Denaturation of Proteins

• Refers to the loss of native conformation leading to a loss of biological activity
• Denatured proteins can aggregate due to exposed hydrophobic side chains becoming insoluble

Levels of Structure Affected by Denaturation

• Denaturation disrupts secondary, tertiary, and quaternary structures but leaves primary structure intact

Denaturing Agents

• Extreme pH or ionic strength changes, detergents, elevated temperatures, and heavy metals contribute to protein denaturation

G6PD Deficiency and Denaturation

• Increased peroxide levels in red blood cells can denature hemoglobin, leading to the formation of Heinz bodies due to oxidative stress