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Understanding Proteins: Structure, Functions, and Importance in Biological Systems

Proteins are among the most diverse and essential molecules in living organisms, coded by genes in DNA. They serve various roles such as structural building blocks, catalysts, and facilitators of immunity and molecular transport. Comprised of amino acids linked by peptide bonds, proteins can be further classified into four structural levels: primary, secondary, tertiary, and quaternary. These structures determine the protein’s shape and function, which is often affected by environmental factors like pH and temperature. Proper understanding of proteins is crucial for studying life sciences.

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Understanding Proteins: Structure, Functions, and Importance in Biological Systems

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  1. Proteins SBI4U0 Ms. Manning

  2. Most diverse molecules in living organisms. • Coded for by genes in the DNA • Used as: • Structural building blocks • Catalysis • Immunity • Transport of other molecules across the cell membrane • Monomer: • Amino acid amino group H O carboxyl group H-N-C-C-OH 20 possible R groups H R

  3. 8 amino acids are essential (body cannot make them, therefore they must be in the diet) • Polymer • Polypeptide • Amino acids are held together by peptide bonds which form when the –OH from the carboxyl of one amino acid and the –H from the amino of another amino acid form water via dehydration synthesis • Polypeptides can be >100 aa long • Polypeptides fold into 3-D shapes, which may be polar (hydrophilic) or non-polar (hydrophobic) or charged (acidic or basic)

  4. Protein consists of one or more polypeptides twisted and coiled into a specific shape • Shape is determined by the ORDER of amino acids • Many proteins are globular (rounded shape), especially enzymes.

  5. Proteins have 4 levels of structure • PRIMARY – linear sequence of amino acids (unique), that is determined by the DNA sequence, this order determines the final protein shape • Shape is critical for function! • SECONDARY – folding and coiling of a single polypeptide chain held together by J-bonds of amino acids (O of the carboxyl and H of the amino group) • -helix or -pleated sheets

  6. Secondary Diagrams

  7. TERTIARY – 3D folding (more complex) of polypeptide held in place by: • Hydrophobic bonding of non-polar side chains • Ionic bonds between charged side chains • Covalent disulfide bridges of cysteines

  8. QUARTERNARY – Two or more polypeptides wound together

  9. Protein shape also influenced by... • Chemical and physical environmental factors • i.e. pH and temperature • changes in environmental conditions may cause changes in protein shape – called denaturation, protein becomes non-functional • Protein can resume shape under normal conditions if primary structure is maintained.

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