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Proteins by Sakvinder S Khalsa

Proteins by Sakvinder S Khalsa. WE SHALL LOOK AT PROTEIN SYNTHESIS. CONSIDER PROTEIN STRUCTURE AT THE MOLECULAR LEVEL. DISCUSS DIFERENT USES OF PROTEINS. BREIFLY LOOK AT ENZYMES. Protein synthesis.

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Proteins by Sakvinder S Khalsa

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  1. Proteinsby Sakvinder S Khalsa

  2. WE SHALL LOOK AT PROTEIN SYNTHESIS. • CONSIDER PROTEIN STRUCTURE AT THE MOLECULAR LEVEL. • DISCUSS DIFERENT USES OF PROTEINS. • BREIFLY LOOK AT ENZYMES.

  3. Protein synthesis • Protein synthesis is the making of proteins, using the information that is found in DNA (Chromosomes). CELL chromosomes nucleus ribosomes ribosomes

  4. Proteins Nucleus The cell • Proteins are very important molecules for a cell. • Proteins are used to build cell structures and are used as enzymes. Chromosomes

  5. Proteins • Proteins are long chains of small molecules called amino acids. • Different proteins are made using different sequences of amino acids. • The pieces of information in DNA are called genes. • Genes describe how to make proteins by putting the correct amino acids into a long chain in the correct order.

  6. The cell Nucleus Piece of DNA Selected For study chromosomes

  7. Nucleus Let’s zoom in on This short segment of DNA to see how its information Is used. Piece of DNA Selected for study

  8. DNA inside the nucleus • Protein synthesis begins with the stored genetic information of a DNA molecule. • The DNA of this gene will ‘unzip’ like DNA does during replication. D N A

  9. Gene (information) Unused strand Only one side of the DNA is used now. [Both sides are used for DNA Replication, to copy the Chromosome.]

  10. RNA subunit A single-strand of RNA Forms, one subunit at a time, and Transcribes [copies] the genetic Information from the DNA.

  11. The new strand is an RNA molecule. Note that there is one difference in the subunits: RNA contains yellow Uricil instead of purple Thymine. D N A D N A RNA

  12. The RNA now has copied the subunit sequence of the gene. The DNA is no longer needed in the process of protein synthesis. D N A D N A RNA

  13. The DNA ‘zips’ closed and remains in the nucleus D N A D N A RNA DNA double strand

  14. Nucleus This RNA molecule Is called messenger RNA (now carrying the genetic ‘ message’). It will leave the nucleus and travel To a ribosome to build a protein molecule. RNA

  15. At the ribosome Code for one Amino acid Once the messenger RNA [mRNA] Is at the ribosome, the genetic information will be translated by ribosome to make a protein mRNA At the ribosome

  16. At the ribosome • The genetic information is interpreted and used to assemble a protein. • We should remember, the mRNA is a sequence of subunits (like a chain) that tells how to build a protein • A protein is a sequence of subunits – a chain of amino acids.

  17. The mRNA contains information in sets of three subunits. • Each set of three is the code for a particular amino acid. m R N A Code for a Particular amino acid

  18. The information of the messenger RNA (mRNA) describes which amino acids should be in the protein chain. A molecule of transfer RNA (tRNA) will carry in the proper amino acid, one at a time.

  19. Amino acid tRNA m R N A The tRNA matches up to the mRNA, Just like the two strands of DNA Molecule match up. The sequence of three subunits of the mRNA Can only match up with one particular tRNA.

  20. Amino acid m R N A

  21. A different set of three mRNA subunits means a different tRNA molecule. That means a different amino acid will be Carried in. Two different Amino acids m R N A Two different tRNA molecules

  22. Peptide bond Between amino acids The two amino acids are linked By a peptide bond. Then a tRNA molecule leaves The ribosome.

  23. The next tRNA will Carry in the proper amino acid and the process will continue.

  24. The chain of amino acids is called a ‘polypeptide’ And when it is very long it is called a protein. polypeptide

  25. A polypeptide chain • Even this is a very, very short polypeptide chain. Most have hundreds or thousands of amino acids. A very short polypeptide chain, or part of a protein

  26. The end of protein synthesis at the ribosome.

  27. PROTEIN STRUCTURE • We will look at the main elements found in proteins. • Recall how proteins are constructed. • Look at the structure of proteins. • Overview the major functions of proteins.

  28. The building blocks of proteins • Like carbohydrate and lipid molecules proteins contain the elements : Oxygen(O), Carbon(C),and Hydrogen(H) • In addition they always contain the element Nitrogen(N).

  29. Before we can understand how proteins are constructed, the structure of amino acids needs to be considered.

  30. R represents groups such as CH3 or C2H5 R O H Carboxylic acid group Amine group N C C H OH H AN AMINO ACID

  31. How are proteins constructed • First the Amino acids bond together. • They are joined together by what is known as a peptide bond.

  32. Formation of a peptide bond via condensation. H R O H R O N C C + N C C H H H OH H OH Amino acid Amino acid

  33. A peptide bond between two amino acids. H R O H H O N C C N C C H H R OH H20 [WATER] A condensation reaction

  34. Protein construction • When two amino acids join together they form a dipeptide. • When many amino acids are joined together a long-chain polypeptide is formed. • Organisms join amino acids in different linear sequences to form a variety of polypeptides in to complex molecules, the proteins.

  35. Amino acid Peptide bond Primary protein structure primary structure This is the linear sequence of amino acids

  36. Secondary protein structure Polypeptides become twisted or coiled. These shapes are known as the secondary Structure. There are two common secondary structures The alpha-helix and the beta-pleated sheet.

  37. Secondary protein structure Alpha-helix Amino acid Hydrogen bonds hold shape together

  38. Secondary Protein structure [The beta pleated sheet] Amino acid Hydrogen bonds Hold shape together

  39. Hydrogen bonds The polypeptides are held in position by hydrogen bonds. In both alpha-helices and beta pleated sheets the C=O of one amino acid bonds to the H-N of an adjacent amino acid. As below: C=O----H-N

  40. Secondary structures • Both secondary structures give additional strength to proteins. The alpha-helix helps make fibres like in your nails, e.g. Keratin. • The beta pleated-sheet helps make the strength giving protein in silk, fibroin. • Many proteins are made from both alpha-helix and beta-pleated sheet.

  41. Fibrous proteins • A fibrous protein only achieves a secondary structure . • The simple alpha-helix polypeptides do not undergo further folding.

  42. Structure of a fibrous protein Coiled alpha-helix structure

  43. Tertiary protein structure • This is when a polypeptide is folded into a precise shape. • The polypeptide is held in ‘bends’ and ‘tucks’ in a permanent shape by a range of bonds including: • Disulphide bridges [sulphur-sulphur bonds] • Hydrogen bonds • Ionic bonds.

  44. Tertiary protein structure

  45. Quaternary protein structure • Some proteins consist of different polypeptides bonded together to form extremely intricate shapes. • A haemoglobin molecule is formed for separate polypeptide chains. • It also has a haem group, which contains iron. • The inorganic group is known as the prosthetic group. • In haemoglobin it aids oxygen transport.

  46. Quaternary protein structure

  47. How useful are proteins? • Cell membrane proteins: Transport substances across the membrane for processes such as facilitated diffusion and active transport. • Enzymes: Catalyse biochemical reactions, e.g. pepsin breaks down protein in to polypeptides.

  48. Hormones: are passed through the blood and trigger reactions in other parts of the body e.g. insulin regulates blood sugar. • Immuno-proteins: e.g. antibodies are made by lymphocytes and act against antigenic sites on microbes. • Structural proteins: give strength to organs, e.g. collagen makes tendons tough.

  49. Transport proteins: e.g. haemoglobin transports oxygen in the blood. • Contractile proteins: e.g. actin and myosin help muscles shorten during contraction • Storage proteins: e.g. aleurone in seeds helps germination, and casein in milk helps supply valuable protein to babies. • Buffer proteins: e.g. blood proteins, due to their high charge, help maintain the pH of plasma.

  50. Enzymes • Living cells carry out many biochemical reactions. • These reactions take place rapidly due to enzymes. • All enzymes consist of globular proteins.

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