Proteins Multipurpose molecules Proteins Most structurally functionally diverse
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Proteins Multipurpose molecules
Proteins • Most structurally & functionally diverse group • Some Functions of Proteins: – – enzymes (pepsin, DNA polymerase) Biological structures (keratin, collagen) carriers & transport (hemoglobin, aquaporin) cell communication • signals (insulin & other hormones) • receptors – defense (antibodies) – movement (actin & myosin) – storage (bean seed proteins)
Protein Structure – Monomer( 1 unit) = amino acids • 20 different amino acids – polymer = polypeptide • protein can be one or more polypeptide chains folded & bonded together • large & complex molecules • complex 3 -D shape hemoglobin Rubisco growth hormones
Amino acids H O H | || – central carbon —C— C—OH – amino group (typically ionized) —N— – carboxyl group (an acid which is | H also ionized) R – R group (side chain) • Structure • variable group • different variable group makes a different amino acid • confers unique chemical properties to each amino acid Recall: Structure determines function
Amino Acids cont’d • Amino acids have both acidic (carboxyl) and basic (amino) properties. • When dissolved in water, the carboxyl group donates a H+ ion to the amino group to possess an extra hydrogen and therefore a net +ve charge.
R groups • Amino acids may be polar, non-polar, or charged (acidic or basic). • This depends on the nature of the side chains. • Generally, acidic aa’s possess a carboxyl group on the side chain and basic aa’s contain an amino group on the side chain.
Effect of different R groups: Nonpolar amino acids nonpolar & hydrophobic Why are these nonpolar & hydrophobic?
Effect of different R groups: Polar amino acids polar or charged & hydrophilic Why are these polar & hydrophillic?
Building proteins • Peptide bonds – Formed by a condensation reaction between NH 2 (amine) of one amino acid & COOH (carboxyl) of another (amide bond) – C–N bond dehydration synthesis H 2 O peptide bond
Protein structure & function • Function depends on structure – 3 -D structure • twisted, folded, coiled into unique shape pepsin hemoglobin collagen
Now…. LETS DISCUSS LEVELS OF PROTEIN ORGANIZATION Please review pg. 27 in your textbook tonight!
Primary (1°) Structure • Order of amino acids in chain – amino acid sequence determined by gene (DNA) – slight change in amino acid sequence can affect protein’s structure & its function • even just one amino acid change can make all the difference!
Sickle Cell Anemia
Secondary (2°) structure • “Local folding” – folding along short sections of polypeptide – interactions between adjacent amino acids • H bonds – weak bonds between R groups – forms sections of 3 -D structure • -helix • -pleated sheet
Secondary (2°) structure
Tertiary (3°) structure • “Whole molecule folding” – interactions between distant amino acids • hydrophobic interactions – cytoplasm is water-based – nonpolar amino acids cluster away from water • H bonds & ionic bonds • disulfide bridges – covalent bonds between sulfurs in sulfhydryls (S–H) – anchors 3 -D shape
Quaternary (4°) structure • More than one polypeptide chain bonded together – only then does polypeptide become functional protein • hydrophobic interactions collagen = skin & tendons hemoglobin
Protein structure (review) R groups hydrophobic interactions disulfide bridges (H & ionic bonds) 3° multiple polypeptides hydrophobic interactions 1° amino acid sequence peptide bonds determined by DNA 4° 2° R groups H bonds
Protein denaturation • Unfolding a protein – conditions that disrupt intermolecuar bonds • temperature • p. H • Exposure to chemicals – destroys functionality • some proteins can return to their functional shape after denaturation, many cannot
Nucleic Acids Information storage
Nucleic Acids • Function: – genetic material • stores information – genes – blueprint for building proteins » DNA RNA proteins DNA • transfers information – blueprint for new cells (mitosis) – blueprint for next generation (meiosis) proteins
Nucleic Acids • Examples: – RNA (ribonucleic acid) • single helix – DNA (deoxyribonucleic acid) • double helix • Structure: – monomers = nucleotides DNA RNA
Nucleotides • 3 parts – nitrogen base (C-N ring) – pentose sugar (5 C) • ribose in RNA • deoxyribose in DNA – phosphate (PO 4) group – enzymes facilitate the formation of covalent bonds between the phosphate group of one nucleotide and the hydroxyl group on C 3 of the adjacent nucleotide (see right). This is called a phosphodiester bond.
Types of nucleotides • 2 types of nucleotides – different nitrogen bases – purines • double ring N base • adenine (A) • guanine (G) – pyrimidines • • single ring N base cytosine (C) thymine (T) uracil (U)
Nucleic polymer • Backbone – sugar to PO 4 bond – phosphodiester bond • new base added to sugar of previous base • Polymer (aka a strand) grows in one direction – N bases hang off the sugar-phosphate backbone
Pairing of nucleotides • Nucleotides bond between DNA strands – H bonds – purine : : pyrimidine – A : : T • 2 H bonds – G : : C • 3 H bonds
DNA molecule • Double helix – H bonds between bases join the 2 strands • A : : T • C : : G
Macromolecule Review
Carbohydrates • Structure / monomer – monosaccharide • Function – energy – raw materials – energy storage – structural compounds glycosidic bond • Examples – glucose, starch, cellulose, glycogen
Lipids • Structure / building block – glycerol, fatty acid, cholesterol, H-C chains • Function – energy storage – membranes – hormones • Examples ester bond (in a fat) – fat, phospholipids, steroids
Proteins • Structure / monomer – amino acids – levels of structure • Function – enzymes – transport – signals defense u structure u receptors u peptide bond • Examples – digestive enzymes, membrane channels, insulin hormone, actin
Nucleic acids • Structure / monomer – nucleotide • Function – information storage & transfer • Examples – DNA, RNA phosphodiester bond
RNA & DNA • RNA – single nucleotide chain • DNA – double nucleotide chain • N bases bond in pairs across chains – spiraled in a double helix
Homework: • Learning Check • Pg. 28 #19 -23 Fill in back of Macromolecule Handout ( Proteins & Nucleic Acids) Complete Functional Group Review handout
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