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Dna and protein synthesis

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Dna and protein synthesis

  1. 1. DNA AND PROTEIN SYNTHESIS
  2. 2. DNA REPLICATION DNA carries the genetic information from one generation to the next When cells divide, each cell must have a copy of the organisms DNA When organisms reproduce their genetic information is passed on to the offspring via the DNA. DNA must be able to replicate itself. When DNA replications occurs, each new strand of DNA has one of the old strands plus one new strand. This process of DNA replication is called: semi-conservative replication
  3. 3. SEMI – CONSERVATIVE REPLICATION & TRANSCRIPTION mRNA is synthesized from a gene on the DNA by “semi-conservative replication” DNA is a double stranded molecule, one of the strands act as a template to produce a molecule of RNA for transcription. In this process the original DNA double helix unzips exposing the DNA bases (Helicase Enzyme). DNA nucleotides that are floating free within the nucleus link in a complementary manner with the help of the enzyme DNA Polymerase.
  4. 4. Two new strands are formed, with each strand having one of the original strands and one new strand. When transcription is completed the new strand is released as a mRNA molecule moving out of the nucleus through the nuclear pores into the cytoplasm ready for translation. The “master” copy of DNA never leaves the nucleus
  5. 5. GENETIC CODE The functional unit of information on the chromosome is the gene A gene consists of a unique sequence of bases that code for a polypeptide or an RNA molecule. For the DNA molecule to influence the activities of a cell, it has to first be translated into proteins. One gene codes for a polypeptide or an RNA molecule. So how can 4 bases be translated into a sequence of amino acids when there are 20 possible amino acids to code for?
  6. 6. TRIPLETS CODONS If each base coded for one amino acid only 4 amino acids could be sequenced. If we had pairs of bases coding for amino acids, how many combinations would then be possible? 16 still not enough The answer is to use 3 bases to code for each amino acid. With three bases 64 combinations are possible. More than enough for the 20 amino acids and start and stop signals. This is called the Triplet Code.
  7. 7. Experiments have verified that the genetic code is made up of base triplets. These base triplets are called codons. Each triplet codes for an amino acid. Most amino acids have more than one triplet codon. Start (AUG) and Stop (UGA) codons initiate and terminate polypeptide sequences
  8. 8. MRNA CODONS FOR ALL AMINO ACIDS
  9. 9. PROTEIN SYNTHESIS As we have already learnt: For the DNA molecule to influence the activities of a cell, it has to first be translated into proteins. The flow of information for most organisms is unidirectional. It only flows in one direction. DNA  RNA  Protein There are two main processes involved in Protein Synthesis: Transcription Translation
  10. 10. DNA--> RNA --> PROTEINS DNA deoxy ribo nucleic acid nitrogen bases are: A-T and C- G RNA ribo nucleic acid nitrogen bases are: A - U and C – G U= uracil the base which substitutes for
  11. 11. THE FLOW OF INFORMATION FROM DNA TO PROTEIN IS UNIDIRECTIONAL DNA RNA Protein (transcription) (translation)
  12. 12. COMMON ABBREVIATIONS FOR AMINO ACIDS
  13. 13. DNA REPLICATION SUMMARY
  14. 14. DNA EXTRACTION PRACTICAL
  15. 15. TRANSCRIPTION DNA  RNA Basically it is a process in which the message written in DNA code is transcribed into a working copy of mRNA (messenger RNA). The process is: RNA polymerase enzymes separate the two strands of DNA. One strand of the DNA is used as a template for mRNA synthesis The mRNA molecule forms using Uracil instead of Thymine When the mRNA molecule is complete, it breaks away from the DNA and travels through the nuclear pores to ribosomes in the cytoplasm
  16. 16. TRANSCRIPTIO N
  17. 17. TRANSLATION A polypeptide chain is built using the codon sequence on the mRNA molecule. tRNA transfer free amino acids in the cytoplasm to the many ribosomes which synthesize mRNA on the basis of codons on the m RNA base pairing with the anti-codons on the tRNA. Translation is commenced by the start codon “AUG” Stop codons are the sequences UAG, UAA and UGA.
  18. 18. RNA  PROTEIN Basically it is a process in which a polypeptide chain is built from a codon sequence on the mRNA molecule. The process is: The mRNA molecule attaches to a Ribosome. tRNA molecules bring specific amino acids to the ribosome according to the codon on the mRNA. There is a different tRNA molecule for each of the 20 amino acids. Each tRNA molecule is about 80 nucleotides long and is folded into a clover shape. At one end there is an exposed triplet of bases called an anticodon and at the other a specific amino acid. The anticodon on the tRNA matches the codon
  19. 19. The ribosomes provide the platform where the tRNA and mRNA are brought together As the amino acids are bought alongside one another they are joined together by enzymes to form a polypeptide. Translation begins with a signal code, the start codon AUG AUG codes for the amino acid Methionine The ribosome moves along the mRNA strand one codon at a time.
  20. 20. As the tRNA molecule deposits its amino acid, it is released back to the cytoplasm to link with another amino acid. When a stop codon is reached, translation ceases and the polypeptide chain is completed and released from the ribosome. The polypeptide folds into its final protein shape If the protein is more than one polypeptide, the chains link and form their tertiary structure.
  21. 21. T RNA WITH ATTACHED AMINO ACID
  22. 22. TRANSLATION
  23. 23. PROCESS OF TRANSLATION
  24. 24. RELATIONSHIP BETWEEN TRIPLETS, CODONS, ANTI- CODONS AND AMINO ACIDS
  25. 25. SUMMARY OF PROTEIN SYNTHESIS
  26. 26. Note key points Do focus questions on p15 Protein synthesis simulation
  27. 27. MODELLING TRANSCIPTION 1. Organise your own DNA code using the acetate sugar phosphate backbones and complementary base. Record the DNA base sequence in your book 2. Unzip the DNA to expose one strand and use felt tip pen to record the complementary base on the tabs of the exposed strand. Record this exposed strand in black/blue pen 3. Use the exposed DNA strand as a template to
  28. 28. MODELLING TRANSLATION 3. Use the paper tRNA “molecules’ to construct the anticodons. 4. Refer to the table of mRNA codons ( pg 8 Key Ideas) choose one coloured ball to represent each amino acid and constuct the polypeptide coded for by your mRNA. 5. Link three different polypeptide sequences together to form a longer polypeptide chain.
  29. 29. STRUCTURE OF A CELL MEMBRANE
  30. 30. MOLECULAR RECOGNITION An important aspect of life is the capacity of cells to exchange materials in and out through their membranes. The cell membrane has its own unique collection of proteins that are embedded in a phospholipid bi-layer The human red blood cell membrane has more than 50 Cell membranes need to select molecules to pass through and recognise signals from the environment.
  31. 31. PROTEINS IN THE CELL MEMBRANE Found on inner and outer surface of cell membrane. Many move freely (fluid mosaic model) while others are fixed. Act as receptors for chemical messengers from other cells. Will display a particular shape to bind to a specific messenger such as a hormone. Other proteins act as one-way transport channels allowing specific molecules through cell membrane.
  32. 32. EXAMPLES OF MOLECULAR RECOGNITION INCLUDE: Cell membrane receptor molecules Transport proteins in the cell membrane Hormone receptors in cell membranes Antibodies enzymes
  33. 33. CELL MEMBRANE RECEPTORS These are protein and glycoprotein molecules embedded in the cell membrane. They have distinctive shapes so as to allow cells to recognise each other. This is critical when cells are differentiating to form tissues.
  34. 34. COMPLEMENTARY BINDING TO MEMBRANE CELL RECEPTOR MOLECULES
  35. 35. TRANSPORT PROTEINS These are transport proteins embedded in the cell membrane. They have specific binding sites for the substance being transported. They help with: facilitated diffusion (moving with the concentration gradient) Active transport (moving against the concentration gradient using energy)
  36. 36. HORMONES Hormone receptors can be embedded in cell membranes or in the cytoplasm of the cell. Hormones are chemical messengers produced by specialised cells in one part of the body to act on target cells in another part. The receptors are protein molecules: Cell membrane: Insulin Induces cell to take in more glucose and convert it to glycogen Cytoplasm : Steroids Lipid soluble and pass through the cell membrane to bind with receptors in the cytoplasm
  37. 37. UPTAKE OF GLUCOSE BY INSULIN
  38. 38. HORMONES Adrenalin Binds to protein receptors on the surface of liver cells and activates the conversion of glycogen to glucose which is released into the bloodstream for energy provision by aerobic respiration – “fight or light response”
  39. 39. ANTIGEN – ANTIBODY BINDING Antibodies are part of the immune system. They are protein molecules (immunoglobulins) with antigen binding sites that detect and bind to antigens. Antigens are foreign substances like bacteria or viruses. The binding of the two must be complementary to inactivate the antigen
  40. 40. ANTIBODY STRUCTURE
  41. 41. SELF AND NON-SELF The immune system is able to distinguish between foreign molecules and their own body molecules or cells. They do this using antigen recognition. Cancer occurs when the body recognises cancerous cells as normal cells of the organism. The immune system will not attach to them and destroy them because they think they are normal body cells.
  42. 42. ENZYMES Enzymes are globular protein molecules with an active site that binds to substrate molecules to catalyse reactions. The active site is complementary to the substrate. Specific shape of active site Enzymes are specific to a particular substrate. Small changes to the shape of the enzyme may affect the recognition of
  43. 43. ACKNOWLEDGEMENTS Orange tone tables and images taken from Adelaide Tuitions Essential textbook for the course.

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