2. Proteins by Sakvinder S Khalsa

3. WE SHALL LOOK AT PROTEIN SYNTHESIS. CONSIDER PROTEIN STRUCTURE AT THE MOLECULAR LEVEL. DISCUSS DIFERENT USES OF PROTEINS. BRIEFLY LOOK AT ENZYMES.

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

5. Proteins Proteins are very important molecules for a cell. Proteins are used to build cell structures and are used as enzymes. Chromos omes The cell Nucleus

6. 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.

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

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

9. 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. DNADNA

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

11. TRANSCRIPTION -- a simple copying of the desired information in DNA into RNA through the action of enzyme RNA polymerase TRANSLATION -- the complex formation of a chain of amino acids based on the sequence of nucleotides in the RNA through the action of ribosomes

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

13. DNA DNA DNADNA RNA The new strand is an RNA molecule. Note that there is one difference in the subunits: RNA contains yellow Uricil instead of purple Thymine.

14. DNA DNA DNADNA The RNA now has copied the subunit sequence of the gene. The DNA is no longer needed in the process of protein synthesis.

15. DNADNA DNADNA RNA The DNA ‘zips’ closed and remains in the nucleus DNA double strand

16. Nucleus RNA 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.

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

18. 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.

19. The mRNA contains information in sets of three subunits. Each set of three is the code for a particular amino acid. AKA Codon Code for a Particular amino acid mRNAmRNA

20. 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.

21. Amino acid tRNA 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. mRNAmRNA

22. mRNAmRNA Amino acid

23. Two different Amino acids Two different tRNA molecules A different set of three mRNA subunits means a different tRNA molecule. That means a different amino acid will be Carried in. mRNAmRNA

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

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

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

27. 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

28. The end of protein synthesis at the ribosome.

29. 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. PROTEIN STRUCTURE

30. 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).

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

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

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

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

35. 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

36. 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.

37. 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.

38. 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.

39. 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.

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

41. The lock and key theory Substrate Enzyme + Enzyme-substrate complex

42. A catabolic reaction [substrate broken down] enzyme-substrate complex enzyme 2 x products

43. An anabolic reaction [substrates used to build a new molecule] enzyme substrate

44. Anabolic reaction continued Enzyme substrate complex Single product formed Enzyme ready to Use again

45. Metabolic reactions Metabolic reactions = anabolic reaction + catabolic reaction. Metabolism is a summary of build up and break down reactions.

46. Induced fit theory The active site is a cavity of a particular shape. Initially the active site is not the correct shape in which to fit the substrate. As the substrate approaches the active site, the site changes and this results in it being a perfect fit. After the reaction has taken place, and the products have gone, the active site returns to its normal shape.

47. Induced fit theory Enzyme Substrate +

48. Induced fit continued Induced fit Enzyme-substrate complex

49. Lowering of activation energy Every reaction requires the input of energy. Enzymes reduce the level of activation energy needed as seen in the graph. substrate Reaction without enzyme Reaction with enzyme products Progress of reaction energyenergy

50. Interesting Fact about Cats- Can you tell which of these cats have to be a female?

51. Cats with more than two colors have to be females The gene for color of fur for cats is on the X chromosome. Male cats have one X chromosome and can only have one color of spots. Female cats on the other hand have two X chromosomes and can have two colors of spots

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