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Unit 7: DNA and Protein Synthesis

Unit 7: DNA and Protein Synthesis. 1 DNA. chromatin and chromosomes. 2 DNA – genetic code. - directs cell activities. 3 Nucleotides. DNA is a nucleic acid made up of nucleotides joined into long strands or chains by covalent bonds.

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Unit 7: DNA and Protein Synthesis

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  1. Unit 7: DNA and Protein Synthesis

  2. 1 DNA chromatin and chromosomes

  3. 2 DNA – genetic code - directs cell activities

  4. 3 Nucleotides DNA is a nucleic acid made up of nucleotides joined into long strands or chains by covalent bonds. Each nucleotide is made up of three parts: a 5-carbon sugar called deoxyribose, a phosphate group, and a nitrogenous base.

  5. 4 Nitrogenous Bases Contain Nitrogen There are four bases: adenine, thymine, guanine and cytosine. Often referred to as A, T, G and C. The four bases, like the 26 letters of the alphabet, can be strung in many different sequences and lengths to create thousands of different genes. Adenine and guanine have two rings, and cytosine and thymine are made of one ring.

  6. 5 DNA shape - double helix Two strands wound into a helix. The two strands are held together with base pairing. • base pairing • A – T • G - C

  7. 6 Chargaff’s Rule The percentage of A is almost equal to the percentage of T, and the percentages of G and C are nearly equal (all four always add up to 100%). This lead scientists to believe that A complimentary base pairs with T and that G complimentary base pairs with C. Complimentary base pairing between the two strands is what holds them together. The bond between the bases is a hydrogen bond, which is weak bond that can be easily broken.

  8. C G G C T A

  9. 9 DNA Replication Refers to copying, or replicating the DNA. Why would a cell need to copy its DNA? When does this occur in the cell cycle? During replication, the two strands separate, or unzip. Each strand will serve as a template , or model, for a new strand to be created through complimentary base pairing. So, if one strand reads TACGTT, what will the new strand being created from it read?

  10. 10 The role of Enzymes First, an enzyme (helicase) must unzip the two strands of DNA by breaking the hydrogen bonds. Next, the enzyme called DNA polymerase joins new nucleotides to the separated strands to produce new complimentary strands. DNA polymerase also proofreads the new strands to make sure they are correct. Telomerase helps to replicate the ends of the DNA strands, called telomeres, which are more difficult to replicate.

  11. 11 Prokaryotic vs. Eukaryotic Replication Because prokaryotes only have on strand of DNA in a circular shape, replication begins from a single point and proceeds in two directions until the entire chromosome is copied. In eukaryotic cells, there are many chromosomes and they are often longer. So replication may begin at dozens or even hundreds or places on the DNA molecule, proceeding in both directions until each chromosome is completely copied.

  12. semi-conservative replication

  13. RNA – ribonucleic acid • mRNA - straight chain - reads DNA and takes a copy of the code to the ribosome • tRNA - hairpin shape - corresponds to mRNA to bring in proper amino acids for protein • rRNA - globular shape, - forms ribosomes which are the sites of protein synthesis - 2 parts - large and small unit

  14. transcription - when mRNA copies DNA code - occurs in nucleus transcript = a copy translation - when mRNA, tRNA, and rRNA work together to change the mRNA code into protein - protein synthesis - occurs at ribosomes in cytoplasm

  15. translation – protein synthesis proteins - Why important? amino acids - 20 amino acids (Page 303) peptide bonds - monomer polymer amino acid + amino acid + amino acid protein

  16. CODE STRUCTURE DNA codon - set of 3 bases on DNA that code for an amino acid *64 different codons code for 20 amino acids - some repeat (see chart - page 303) start codon - methionine – AUG - initiates protein synthesis stop codons - end protein synthesis mRNA codon - 3 bases on mRNA tRNA anticodon - 3 bases on tRNA

  17. UAC ACC GGC ACU AAA UCG GCA UAG

  18. assignment: Translate the following DNA code into the proper amino acids. TAC AAG CCG AAA GAC GGT ACT

  19. AUG UUC GGC UUU CUG CCA UGA methionine phenylalanine glycine phenylalanine leucine proline stop

  20. mutation - mistake in DNA - may lead to no mistake at all - may result in an improper amino acid, how important depends on what amino acid in what protein mutation in somatic cells (body) - disease mutation in gametes (sex cells) - birth defect or hereditary disease

  21. types of mutations 1. point mutation - involves one base 2. frameshift - involves entire code from point of mistake correct code: ABCDE FGHIJ examples: substitution ABBDE FGHIJ addition ABCCDE FGHIJ deletion ABDE FGHIJ inversion ACBDE FGHIJ translocation ABCDFGE HIJ

  22. MUTAGEN - anything that causes mutations 1. radiation 2. asbestos 3. tar 4. coal 5. hardwood dusts 6. mercury 7. lead 8. formaldehyde 9. nitrous oxide

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