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Chapter 12

Chapter 12. DNA and RNA. What is DNA again?. Deoxyribonucleic acid Long double-stranded molecule of nucleotides Stores genetic code that is transferred to future generations and cells Codes for synthesis of proteins. What is a nucleotide. A nucleotide has 3 parts:

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Chapter 12

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  1. Chapter 12 DNA and RNA

  2. What is DNA again? • Deoxyribonucleic acid • Long double-stranded molecule of nucleotides • Stores genetic code that is transferred to future generations and cells • Codes for synthesis of proteins

  3. What is a nucleotide • A nucleotide has 3 parts: • A sugar (deoxyribose for DNA) • A phosphate group • A nitrogen base

  4. Nitrogen base pairing • The order of nitrogen bases are what determines your genetic code • The order of the bases determines the proteins that are made • 4 different bases exist: • Purines: Guanine, Adenine Grade A Pure • Pyrimidines: Cytosine, Thymine • Pairing is also called Chargaff’s Rule

  5. Chargaff’s Rule Result: A=T, G=C

  6. But what is the structure? • In the early 1950s Rosalind Franklin used X-ray diffraction took a “picture” of DNA • Difficult to tell what the structure is from the image • Strands twisted around one another

  7. But what is the structure? • James Watson and Francis Crick used Franklin’s images and their models to determine the correct structure: double helix • Two strands wound around one another • “Twisted ladder” • Later discovered that hydrogen bonds hold the two sides of the ladder together • Can only from between adenine and thymine, or guanine and cytosine (A=T, G=C) • The base pairing explained Chargaff’s Rule

  8. DNA Structure

  9. DNA Structure • DNA is very long; E. coli’s contains 4,639,221 base pairs (length =1.6 mm) • Must fit in an organism 1/1000 its length • Must be packed very tightly to fit • Human cell contains almost 100 times the base pairs • Chromatin consists of DNA packed around proteins called histones • These compact together during mitosis to create our visible chromosomes

  10. DNA Structure

  11. DNA replication • Remember that before a cell divides it has to copy its DNA • If we separate each strand, we can use it to make a copy of the other • If we have an A, we match it with a T; if a G, we match it with a C (called complementary) • In prokaryotes, replication begins at one point and proceeds typically in both directions • In contrast, eukaryotes begin replication in hundreds of locations (due to its longer length)

  12. DNA Replication

  13. DNA replication • Two replication forks formed, each strand has a new complementary strand added • TACGTT  ATGCAA • Results in two identical DNA molecules • One strand is new, the other old • DNA was unzipped (breaking of hydrogen bonds) • DNA polymerase (enzyme) joins individual nucleotides to produce a DNA molecule

  14. What is RNA? • Ribonucleic acid • Intermediate molecule between DNA and proteins • Differs from DNA in 3 ways: • Single stranded (vs. double) • Ribose instead of deoxyribose • Utilizes uracil instead of thymine (A-U, G-C)

  15. Type of RNA • There are 3 types of RNA: • messenger RNA (mRNA)- carries copies of the protein instructions • ribosomal RNA (rRNA)- makes up the ribosome, along with several proteins • transfer RNA (tRNA)- take the appropriate (base pairing anti-codon to codon) amino acid to the ribosome

  16. Types of RNA

  17. Protein synthesis: how we make proteins? • Two processes or steps: • Transcription- mRNA is made from the DNA and travels to the cytoplasm to find a ribosome • Translation- tRNA brings to the ribosome the amino acids to build the primary structure of a protein and the result is a free polypeptide that will then fold up into the shape of the protein • Remember: amino acids are held together by peptide bonds

  18. Transcription

  19. Transcription • RNA polymerase binds to DNA and separates the strands • RNA polymerase uses one strand to serve as a template to create a strand of RNA • RNA polymerase only binds to regions of DNA called promoters (landing pad) • The RNA is next edited, removing the introns, while leaving the exons (exons=expressed)

  20. RNA Splicing

  21. Translation • Proteins are made by joining amino acids (1 of 20) into long chains (polypeptides) • How do 4 letters lead to so many different amino acids? • Read 3 letters at a time, called a codon • UCGCACGGU • UCG-CAC-GCU • Serine-Histidine-Glycine • Some codons code for the same amino acid • AUG is the start codon

  22. Translation • Codon – 3 nucleotides that code for an amino acid. Found on the mRNA. • Anticodon- Fit the codon. Found on the tRNA • DNA: master plan; never brought to work site • mRNA: blue prints made from master plan • Ribosomes: building site • tRNA: trucks unloading materials

  23. Codons

  24. Codons

  25. Translation

  26. Transcription and Translation

  27. Mutations • Mutations – changes made in the genetic material; can occur during copying • Point mutation – effect only one nucleotide.  • Frameshift mutation – an insertion or deletion that effects the remaining string of nucleotides. • Chromosomal mutations – changes in the number or structure of chromosomes. • Polyploidy – when an organism has extra sets of chromosomes.

  28. Mutations • THE FAT CAT ATE THE RAT • Delete H (Frameshift / deletion) • TEF ATC ATA TET HER AT • Change H to L (Point mutation) • TLE FAT CAT ATE THE RAT

  29. Mutations • DNA: TAC GCA TGG AAT • RNA: AUG CGU ACC UUA • AA: Met ArgThrLeu • Substitution • DNA: TAC GTA TGG AAT • RNA: AUG CAU ACC UUA • AA: Met His ThrLeu • Insertion • DNA: TAT CGC ATG GAA T • RNA: AUA GCG UAC CUU A • AA: Ile Ala Tyr Leu

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