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DNA

DNA. Chapter 8. Every cell in your body has its own DNA that is identical to every other cell in your body Your DNA is different from everyone else’s DNA, unless you have an identical twin. DNA is found inside the nucleus of every cell that has a nucleus

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DNA

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  1. DNA Chapter 8

  2. Every cell in your body has its own DNA that is identical to every other cell in your body • Your DNA is different from everyone else’s DNA, unless you have an identical twin

  3. DNA is found inside the nucleus of every cell that has a nucleus • If a cell does not have a nucleus, DNA is found floating around in the cytoplasm

  4. What we have been calling genes are really DNA • Chromosomes are made up of DNA • DNA is short for deoxyribonucleic acid

  5. DNA is a molecule that makes up genes and determines the traits of all living things • ALL living things contain DNA

  6. DNA is made up of units called nucleotides • A nucleotide consists of a nitrogenous base, a phosphate group and a 5 carbon sugar called deoxyribose (hence the name deoxyribonucleic acid)

  7. DNA looks very much like a twisted ladder • A ladder has two sides and many rungs • The sides of DNA are made up of two different chemicals – a sugar (deoxyribose) and an acid (phosphate group)

  8. The sugar and acid alternate on each side of the DNA • The rungs of the DNA ladder are made up of chemicals called nitrogen bases • There are four different nitrogen bases in DNA

  9. The 4 bases are adenine, thymine, guanine & cytosine • Adenine only fits with Thymine • Cytosine only fits with Guanine • There are only two bases on each DNA rung

  10. Adenine (A) & Guanine (G) are Purines • Cytosine (C) & Thymine (T) are Pyrimidines • A Purine is always paired with a Pyrimidine • Purines are bigger than Pyrimidines

  11. Between each base pair are hydrogen bonds which hold the two bases together • The ladder of DNA is twisted into a spiral, or helix • DNA is called a double helix

  12. It is called a double helix because it is made up of two strands that are twisted • Scientists did not know much about DNA until the 1900’s • Many different experiments provided info about DNA (8.1, pg 226-228)

  13. The order of nitrogen bases in DNA is the code for all your traits • If the order is changed in any way, there will be a different trait

  14. This works much the same way as the Alphabet • The word pen means one thing, but if we change the E to an I, it means something totally different • If we change the P to an H, it means something else

  15. However, if we change the E in pen to a D, the word would make no sense at all • It is the same with DNA – sometimes changes make the DNA say something else, & sometimes it makes no sense

  16. When DNA is changed to make no sense at all, it could mean death or a severe illness • The difference is there are only 4 letters in the DNA alphabet – but the words are much longer

  17. Question 1 • If one strand of DNA is: A T G G C A T G C What is the other strand going to look like?

  18. Question 2 • If one strand is: G G C T A G A G A T What is the other strand?

  19. DNA & Chromosomes • Prokaryotic cells lack a nucleus, so the DNA is located in the cytoplasm • Prokaryotes have one circular “chromosome” that contains most or all of the cells DNA

  20. Eukaryotic cells have at least 1000 times as much DNA as prokaryotic cells • Eukaryotic DNA is not free in the cytoplasm, but is in the nucleus • The number of chromosomes varies in eukaryotes

  21. Size & Length of DNA • DNA molecules are VERY long • E. coli DNA is 4,639,221 base pairs long = approx. 1.6mm • An E. coli cell is only 1.6mm! • The DNA must fit in a space one one-thousandth of its length!

  22. Chromosome Structure • The DNA must be folded numerous times to fit into the cell’s nucleus • A human cell contains almost 1000 times as many base pairs as E. coli – human DNA must be folded even more!

  23. Eukaryotic chromosomes contain protein & DNA (form a substance called chromatin) • The DNA is tightly coiled around proteins called histones • The DNA & histones form a nucleosome

  24. Nucleosomes coil together to form a thick fiber and supercoils • The supercoils form a chromosome • We saw chromosomes in Chapter 5 (figure 5.5)

  25. DNA Replication • DNA must be replicated before mitosis (and meiosis) • How does that occur? • Each strand of DNA has the info to make the other strand (B/C of base pairing)

  26. During DNA replication, the DNA molecule separates into two strands, then produces two new complimentary strands following the rules of base pairing

  27. In eukaryotes, DNA replication occurs in numerous places on the DNA • The place where the DNA is opening and replication is occurring is called the replication fork

  28. An important enzyme that helps in DNA replication is called DNA Polymerase • There are other enzymes that “unzip” the DNA and then zip the new strands back up again

  29. RNA & Protein Synthesis Chapter 8.4 & 8.5

  30. How does DNA code for traits? • DNA must remain in the nucleus – it is too fragile, & too important to be in the cytoplasm • DNA codes for proteins, but proteins are made in the cytoplasm

  31. How can this be? • DNA has a helper molecule to leave the nucleus and go into the cytoplasm to make proteins • This molecule is ribonucleic acid – or RNA

  32. RNA Structure • RNA is similar to DNA in that it is made of nucleotides • There is no Thymine in RNA – instead there is a base called Uracil (U), which is similar to thymine

  33. RNA Structure • RNA is single stranded, not double stranded (not a double helix) • The sugar in RNA is ribose, not deoxyribose

  34. RNA Structure • You can think of RNA as a disposable copy of DNA or a working copy of a single gene • One gene on DNA can make hundreds or thousands of RNA copies of that gene, which can in turn make that many proteins

  35. Types of RNA • There are 3 types of RNA, each with a specific structure and function • Messenger RNA (mRNA) is the copy of the DNA • Ribosomal RNA (rRNA) makes up the ribosomes

  36. Types of RNA • Transfer RNA (tRNA) is used in the making of proteins and brings the amino acids to the ribosome

  37. Making Proteins • There are two main stages of making proteins – Transcription & Translation • Transcription is going from DNA to RNA • Translation is going from RNA to protein

  38. Transcription • Transcription occurs in the nucleus • RNA polymerase is an enzyme that is needed, similar to DNA polymerase • Only one strand of DNA is used to make RNA

  39. Transcription • Transcription is similar to DNA replication, but the result is single stranded with Uracils in the place of Thymines • The resulting RNA will be complimentary to the DNA strand used

  40. Transcription • RNA polymerase knows where genes start because of pieces of DNA called promoters • Promoters have specific base sequences – they act as signals to the RNA polymerase

  41. Transcription • Similar pieces of DNA act as signals for the RNA polymerase to stop transcription • The RNA made from transcription needs to be edited before use

  42. Transcription • Large pieces of RNA will be cut out, called introns • The remaining pieces of RNA are called exons and are spliced back together with enzymes

  43. The Genetic Code • Proteins are made by joining amino acids together • How can an mRNA molecule make a protein if RNA is made of nucleotides?

  44. The Genetic Code • The genetic code has only four letters (A,U,G,C) • But, each word in the code is three letters long • Each three letter word makes a specific amino acid

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