1 / 56

Proteins

Proteins. Chapter 3 A. P. Biology Mr. Knowles Liberty Senior High School. Proteins are Most Common. Functions of Proteins. Enzymes - Metabolism Structural - Collagen and Keratin Cell Recognition - proteins on cellular surface.

varana
Download Presentation

Proteins

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Proteins Chapter 3 A. P. Biology Mr. Knowles Liberty Senior High School

  2. Proteins are Most Common

  3. Functions of Proteins • Enzymes- Metabolism • Structural- Collagen and Keratin • Cell Recognition- proteins on cellular surface. • Regulation of Gene Expression- Gene Repressors or Enhancers. • Defense- Antibodies.

  4. Table 5.1 • An overview of protein functions

  5. Two Types of Proteins • Fibrous Proteins- rope-like, structural proteins; form shape of cells and tissues. Ex. Collagen-the most abundant protein of vertebrates. • Globular Proteins- have specific shapes for their functions. Ex. Enzymes and antibodies.

  6. 1. Proteins can be Structural

  7. 2. Proteins can be Globular

  8. X-raydiffraction pattern Photographic film Diffracted X-rays X-ray beam X-raysource Crystal Nucleic acid Protein (b) 3D computer model (a) X-ray diffraction pattern X-ray crystallography: Is used to determine a protein’s three-dimensional structure. Figure 5.24

  9. Papain

  10. Proteins • Most diverse organic compound. • Composed of amino acids- each with an amino group (NH2) and a carboxylic acid group (COOH). • Different chemical group(s) attached to central C- R group .

  11. Peptidebond OH SH CH2 CH2 CH2 H H H C C H C C N C OH H C OH N N DESMOSOMES H O H O H O (a) H2O OH DESMOSOMES DESMOSOMES Side chains SH OH Peptidebond CH2 CH2 CH2 H H H N OH C C C C C H C N N Backbone H H O O H O Amino end(N-terminus) Carboxyl end(C-terminus) Figure 5.18 (b) Amino Acid Polymers OH • Amino acids • Are linked by peptide bonds

  12. CH3 CH3 CH3 CH CH2 CH3 CH3 H CH3 H3C CH3 CH2 CH O O O O O H3N+ H3N+ C H3N+ C H3N+ C C C C C C H3N+ C C O– O– O– O– O– H H H H H Valine (Val) Leucine (Leu) Isoleucine (Ile) Glycine (Gly) Alanine (Ala) Nonpolar CH3 CH2 S H2C CH2 O NH CH2 C C H2N CH2 CH2 O– CH2 O O O H H3N+ H3N+ C C C C H3N+ C C O– O– O– H H H Phenylalanine (Phe) Proline (Pro) Methionine (Met) Tryptophan (Trp) Figure 5.17 • 20 different amino acids make up proteins

  13. OH NH2 O C NH2 O C OH SH CH2 CH3 OH Polar CH2 CH CH2 CH2 CH2 CH2 O O O O O O H3N+ C H3N+ C H3N+ C C H3N+ C C H3N+ C C C C C H3N+ C O– O– O– O– O– O– H H H H H H Glutamine (Gln) Tyrosine (Tyr) Asparagine (Asn) Cysteine (Cys) Serine (Ser) Threonine (Thr) Basic Acidic NH3+ NH2 NH+ O– O –O O CH2 C NH2+ C C NH Electrically charged CH2 CH2 CH2 CH2 CH2 O O CH2 CH2 C CH2 C H3N+ H3N+ C C O O– O– CH2 C H3N+ CH2 C H O H O– C C H3N+ CH2 H O O– C C H3N+ H O– H Lysine (Lys) Histidine (His) Arginine (Arg) Glutamic acid (Glu) Aspartic acid (Asp)

  14. Amino Acids • Are the monomers of proteins. • Only 20 naturally occurring amino acids. • The R group gives each of the amino acids its unique property. • All 20 amino acids can be grouped into 5 basic groups.

  15. 5 Groups of Amino Acids (Fig. 3.15) • Nonpolar- have R groups that contain CH2 and CH3. • Polar Uncharged- R groups that have O or only H. • Ionizable- have R groups that are acids and bases. • Aromatic- R groups that have organic rings.

  16. 5 Groups of Amino Acids (Fig. 3.15) 5. Special-function- amino acids that are only used for very specific functions; methionine begins protein synthesis, proline causes kinks in the protein polymer, cysteine links chains together.

  17. The 20 Common Amino Acids (Fig. 3.15) Click below for another view!

  18. Proteins • Are polymers of amino acids. • Joined by peptide bonds. • Di- Tri- and Polypeptides.

  19. Globular Proteins • Are long amino acids chains folded into complex shapes. • All of the internal amino acids are nonpolar. • Water excludes nonpolar amino acids – hydrophobic interactions.

  20. Globular Proteins Have Four Levels of Structure • Primary- the specific sequence of amino acids in the polypeptide chain. • R groups have no role in the backbone, so any sequence of amino acids is possible. • Therefore, 100 amino acids may be rearranged in 20100 different possible sequences.

  21. Pro Thr Gly Gly Thr +H3NAmino end Gly Amino acid subunits Glu Seu Lys Cys Pro Leu Met Val Lys Val Leu Asp Arg Ala Val Gly Ser Pro Ala Glu Lle Asp Thr Lys Ser Tyr Trp Lys Ala Leu Gly lle Ser Pro Phe His Glu His Ala Glu Val Thr Phe Val Ala Asn lle Thr Asp Ala Tyr Arg Ser Ala Arg Pro Gly Leu Leu Ser Pro Tyr Ser Tyr Ser Thr Thr Ala o Val c Val Glu Lys – o Thr Pro Asn Carboxyl end Figure 5.20 Primary Structure: Is the unique sequence of amino acids in a polypeptide.

  22. Globular Protein Structure 2.Secondary- folding or coiling of the chain into a pattern due to weak H bonds between amino acids. • H bonds form between the main chain of amino acids. • Two Kinds of Secondary Structure

  23. Secondary Structures • Alpha Helix- H bonds between one amino acid and another further down the chain. Pulls the chain into a coil. • Beta Sheet- H bonds occur across two separate chains. If chains are parallel, they may form a sheet-like structure.

  24. H H H H O O O O O O O H H H H H H H H R R R R R R R C C C C C C C C C C C C C N N N N N N N N N N N N N C C C C C C C C C C C C C C R R R R R R H H H H H H H O O O O O O O H H H H H H H  pleated sheet H O H H C Amino acidsubunits C N N N C C C R O H H H H N N N H H H N N N  helix C C O C R H H H C C C R R R R H H C C C C C C O O O O H C R O C C O O C H N N H C C H H R R Figure 5.20 Secondary Structure: • Is the folding or coiling of the polypeptide into a repeating configuration. • Includes the  helix and the  pleated sheet.

  25. Alpha Helix- The First Type of Secondary Protein Structure

  26. Beta Sheet- Another Type of Protein Secondary Structure

  27. Show me the levels of protein structure.

  28. Secondary Structures • Some patterns of alpha helices and/or beta sheets are very common in protein structures. • When secondary structures are organized into specific structures within proteins-motifs. Ex. Β-Barrel or α-turn-α motifs

  29. Β-barrel Motif in a Cell Membrane Protein

  30. Globular Protein Structure 3. Tertiary Structure- folding and positioning of nonpolar R groups into the interior of the protein (hydrophobic interactions). • Held together by weak van der Waal’s forces. • Precise fitting of R groups within the interior. A change may destabilize a protein’s shape.

  31. Hydrophobic interactions and van der Waalsinteractions CH CH2 CH2 H3C CH3 OH H3C CH3 Polypeptidebackbone Hydrogenbond CH O HO C CH2 CH2 S S CH2 Disulfide bridge O C CH2 -O CH2 NH3+ Ionic bond Tertiary Structure: • Is the overall three-dimensional shape of a polypeptide. • Results from interactions between amino acids and R groups.

  32. Globular Protein Structure • Quaternary Structure- two or more polypepetide chains associate to form a protein. • Each chain is called a subunit. • Subunits are not necessarily the same. • Ex. Hemoglobin = 2 α-chain subunits + 2 β-chain subunits.

  33. Polypeptidechain Collagen  Chains Iron Heme  Chains Hemoglobin Quaternary Structure: • Is the overall protein structure that results from the aggregation of two or more polypeptide subunits.

  34. +H3N Amino end Amino acid subunits helix The four levels of protein structure

  35. Quaternary Structure of Hemoglobin

  36. Normal hemoglobin Sickle-cell hemoglobin Primary structure . . . . . . Primary structure Exposed hydrophobic region Val His Leu Thr Pro Glul Glu Val His Leu Pro Glu Thr Val 5 6 7 5 6 7 1 2 3 4 1 2 3 4 Secondaryand tertiarystructures Secondaryand tertiarystructures  subunit  subunit     Hemoglobin A Quaternary structure Quaternary structure Hemoglobin S     Function Molecules interact with one another tocrystallize into a fiber, capacity to carry oxygen is greatly reduced. Function Molecules donot associatewith oneanother, eachcarries oxygen. 10 m 10 m Red bloodcell shape Normal cells arefull of individualhemoglobinmolecules, eachcarrying oxygen Red bloodcell shape Figure 5.21 Hemoglobin structure and sickle-cell disease Fibers of abnormalhemoglobin deform cell into sickle shape.

  37. Is Protein Folding Important?

  38. Normal PrionScrapie Prion

  39. Reverse Transcriptase of HIV

  40. Cobra Toxin

  41. Shape of the Protein • Tertiary and Quaternary structures provide shape. • These structures are maintained by H bonds and other weak forces between R groups of amino acids.

  42. Protein Folding

  43. Conditions that Affect Protein Shape Can disrupt H bonds by: • High Temperature • pH Changes (Acidic or Basic) • Ion Concentration (Salt) Disrupting the 2°, 3°, 4° structure is called denaturation.

  44. Denaturation Normal protein Denatured protein Renaturation Figure 5.22 Denaturation: Is when a protein unravels and loses its native conformation.

More Related