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DNA Replication…Notes

DNA Replication…Notes. Steps: A section of the DNA molecule unwinds and becomes a straight ladder. The 2 nucleotide chains are separated by helicase enzymes, which break the hydrogen bonds between the bases.

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DNA Replication…Notes

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  1. DNA Replication…Notes Steps: • A section of the DNA molecule unwinds and becomes a straight ladder. • The 2 nucleotide chains are separated by helicase enzymes, which break the hydrogen bonds between the bases. • DNA polymerases bind to the 2 sides of DNA moving along in opposite directions, attaching free nucleotides to the existing DNA chain. • Covalent bonds join sugars and phosphates, hydrogen bonds join base pairs.

  2. The process of replication happens at many different locations along the DNA simultaneously, not just from one end to the other. • Result: 2 new strands of DNA that are exact copies of the original, and the cell is ready to undergo cell division (Mitosis!).

  3. Picture: (see in your book 12-2, page 333-334) Let’s watch an animation of how this happens!

  4. Overview

  5. Mutations… • When the bases mis-match themselves in base-pairing, this is one type of mutation. • There is about one error in every 10,000 paired nucleotides but DNA can proof-read itself and repair the mutation, helping keep the error rate to about one error per 1 billion nucleotides. • This has serious effects in new cells. • Mutations can be bad or good…

  6. Good and Bad… • Mutations drive evolution to happen! • Good mutations – help the organism survive longer so that their genes can be passed down • Examples: camouflage, drug resistant bacteria (good for them, bad for us!) • Bad mutations – cause the organism to die and not allow those genes to be passed down • Examples: genetic disorders that cause early death, cancer

  7. 50 years! Trivia! If you typed 60 words a minute, 8 hours a day, how many years would it take you to type out all the bases (letters) in one set of our DNA?

  8. Transcription and TranslationProtein Synthesis • What is it? • Transcription happens when DNA is transcribed (making a template) into RNA • Translation is when the information is translated into a protein

  9. Transcription: the process by which genetic information is copied from DNA to RNA. Steps: • RNA transcription starts on the DNA strand (the template) at the “promoter” (initiator or start) gene. • RNA polymerase binds to the promoter gene and travels down one side of the template (original DNA) attaching complementary RNA bases and nucleotides.

  10. 3. The base pairing rules are the same except U replaces T on the RNA strand. 4. This continues until it reaches a DNA region called the “termination signal” (or stop). 5. The RNA polymerase releases both the DNA molecule and the newly formed RNA molecule (travels to cytoplasm). 6. DNA closes back up! This newly formed strand is called mRNA or messenger RNA.

  11. Complementary mRNA • What would the mRNA strand be for this section of DNA? A A T G C T A C C T T G A A C T G G U U A C G A U G GA A C U U G A C C Note: The mRNA strand is what is used to determine what amino acids are made (using the codon chart)!

  12. After mRNA is formed • We are able to make a protein in the cytoplasm. (Translation) • Remember… • The amount and kind of proteins that are produced in a cell determine the structure and function of the cell. • In other words, proteins carry out the genetic instructions (genes) encoded in our DNA.

  13. mRNA is now grouped into letters of 3 (a group of 3 letters is called a codon). • Each codon will code for one amino acid (AA). • AAs are the building blocks of proteins. • A few codons do not code for an AA, instead they signal for translation of an mRNA to start (initiator/start codon/promoter) or stop (stop codon/ termination signal). • mRNA is ready to be “decoded” by 2 other types of RNA…

  14. How to read the Amino Acid Table

  15. What does all this mean!!!????How are we making a protein? Let’s watch an animation

  16. rRNA or Ribosomal RNA • When the mRNA gets to the cytoplasm, rRNA (which is in globular form) will attach itself over the strand. • It helps attach the tRNA to the mRNA • This is where ribosomes are made!

  17. tRNA or Transfer RNA • tRNA will locate the start codon on the mRNA strand and will form the appropriate AA for that codon • tRNA travels down the mRNA to the next codon and forms the appropriate AA for that codon • The second AA attaches to the 1st & the tRNA molecule detaches from the 1st mRNA codon • This continues until a string/chain of AA are formed = a protein is made!

  18. Homework • Words to know: • Synthesizes: puts together • Initiates: starts • Binding: stick to • Transcripts: what is created by transcription (the RNA strand) • Cytosol: cytoplasm

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