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DNA Replication

DNA Replication. How does every cell get a copy of DNA?. Before a cell divides, it has to copy its DNA so the new cell can have a copy. Why?. Remember that DNA Replication happens during the S phase of INTERPHASE, when the cell is growing.

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DNA Replication

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  1. DNA Replication

  2. How does every cell get a copy of DNA?

  3. Before a cell divides, it has to copy its DNA so the new cell can have a copy. Why?

  4. Remember that DNA Replication happens during the S phase of INTERPHASE, when the cell is growing.

  5. Also remember that DNA runs opposite directions on either side (one side is upside down). This is called an antiparallel pattern.

  6. To start, the DNA unwinds with the help of the enzyme helicase.

  7. Then, the DNA ladder splits in two. The hydrogen bonds that hold the bases together are broken. The A’s separate from the T’s and the G’s separate from the C’s. It is like the DNA “unzips”.

  8. This unzipped area is called a replication fork. Typically DNA unzips into a bubble with a fork at either end.

  9. Once the DNA is unzipped, pre-made nitrogenous bases (ATG & C) that are loose in the nucleus come and “fill in” each split half of the DNA like a puzzle.

  10. This process is aided by the enzyme DNA polymerase.

  11. Where there is a nucleotide with a Guanine base on the DNA, a nucleotide with a Cytosine base is filled in by DNA polymerase.

  12. Where there is a nucleotide with a Thymine base on the DNA, a nucleotide with an Adenine base is filled in by DNA polymerase.

  13. When there is: DNA Polymerase will fill in: T A C G T G C A

  14. Once all of the bases are filled in, you have two complete, perfect copies of DNA. It is perfect because each unzipped half of DNA provides a pattern, or template, to fill in the other half.

  15. In the two resulting copies of DNA, each is half original DNA, and half new DNA. So, we say that DNA replication is semi-conservative. X

  16. What Does it Actually Do? DNA

  17. DNA controls living things because it holds the genetic code. The instructions in the genetic code are used to build proteins.

  18. Remember that proteins are the tools that cells need to do their jobs.

  19. Proteins make up many structures in a cell!!(your fingernails and hair are also made of protein).

  20. Enzymes that make important chemical reactions in a cell go faster are also proteins.

  21. Proteins are made up of chains of AMINO ACIDS

  22. Transcription

  23. Transcription is the first step to making proteins. It involves making a copy of the genetic code.

  24. The genetic code is made up of the order of the nitrogen bases (ATGC) in the steps of the DNA ladder.

  25. Every three bases make up a code that stands for a certain AMINO ACID. • This group of 3 bases is called a CODON. • So, the code on the DNA decides what order the amino acids are put together in and what kind of protein is made.

  26. 3 Nitrogen Bases 3 Nitrogen Bases

  27. Codon for one amino acid Codon for one amino acid

  28. Codon for second amino acid

  29. Codon for third amino acid

  30. Codon for fourth amino acid

  31. Codon for fifth amino acid

  32. For example, the Codon CTG codes for the amino acid Aspartic acid. The Codon T T C codes for the amino acid Lysine.

  33. The process that turns the DNA code into an actual protein is called…. PROTEIN SYNTHESIS.

  34. Varying the code in the DNA changes the order of Amino Acids in the protein, which makes a different protein with different properties.

  35. For example, Changing this one Amino Acid changes blood cells:

  36. The RBC on the right has sickle cell anemia due to a 1 AA change RBC with Sickle Cell Anemia Nor mal Red Blood Cell

  37. Protein Synthesis uses a molecule like DNA called RNA. • RNA is single stranded • it is only made of one half of the ladder • RNA has a different nitrogen base • URACIL (U) instead of Thymine (T) • So, RNA’s bases are AUGC.

  38. Double-Stranded Single-Stranded

  39. There are 3 important kinds of RNA • mRNA (messenger RNA) • tRNA (transfer RNA) • rRNA (ribosomal RNA)

  40. To start protein synthesis, the DNA unzips, like if it were going to copy itself. Instead of copying DNA, though, a copy of MESSENGER RNA (mRNA) is made using the DNA template.

  41. The enzyme RNA polymerase helps build mRNA just as DNA polymerase helped build DNA.

  42. This RNA Where DNA has: Base will be filled in: A UT A G C C G

  43. Certain sections of DNA code called promoterstell the RNA polymerase where to attach to DNA and start making mRNA.These act as a start signal for transcription.

  44. Thus, the genetic code is re-written (transcribed) in mRNA.

  45. The mRNA has extra “junk” code in it called introns. These introns are cut out and the good code (called exons) are put together and their ends are capped. The mRNA is now complete.

  46. Introns Removed!

  47. When the mRNA is made, it leaves the nucleus and heads for a ribosome (WHERE PROTEINS ARE MADE).

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