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Let’s start with DNA…

This article provides a detailed explanation of the basic structure of DNA, including monomers, nucleotides, and the double helix shape. It also covers DNA replication, transcription, and translation processes for protein synthesis.

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Let’s start with DNA…

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  1. Let’s start with DNA…

  2. Basic DNA structure Made of monomers called nucleotides, each containing 3 basic parts: 1. 5 carbon sugar called deoxyribose 2. Phosphate group 3. Nitrogenous (nitrogen-containing) base - adenine - guanine - cytosine - thymine Purines Pyrimidines Adenine Guanine Cytosine Thymine Phosphate group Deoxyribose

  3. Basic DNA structure The shape is referred to as a “Double Helix”… like a twisted ladder. Nucleotide Hydrogen bonds Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G)

  4. Basic DNA structure Figure 12-10 Chromosome Structure of Eukaryotes

  5. Nucleus Cytoplasm at the ribosome attached to the ER Replication, Transcription, Translation • Replication- DNA makes a copy of itself inside the nucleus for cell division purposes • Transcription- DNA to mRNA - mRNA makes a copy of a segment of DNA and transports it out of the nucleus - • Translation- mRNA code is used to make proteins • Remember proteins are made up of amino acids

  6. First, let's start with DNA Replication • Using DNA to make DNA (copying itself) • Again, this is for CELL DIVISION purposes only! • DNA does not make a copy of itself to make proteins! mRNA makes the copy. • This is a separate function from making proteins!!!

  7. Figure 16.7 A model for DNA replication: the basic concept (Layer 1) DNA Replication

  8. Figure 16.7 A model for DNA replication: the basic concept (Layer 2) DNA Replication

  9. Figure 16.7 A model for DNA replication: the basic concept (Layer 3) DNA Replication

  10. Figure 16.7 A model for DNA replication: the basic concept (Layer 4) DNA Replication * Semi-conservative in that one half of each new strand is old, and the other half is new.

  11. Figure 5.30 The DNA double helix and its replication

  12. DNA Replication • Occurs in a Replication bubble; each end is called a Replication fork • Catalyzedby enzymes (helicase and DNA polymerase for starters) • Helicase unwinds the original double strand by using ATP to break hydrogen bonds • DNA polymerase moves along the single strands of DNA recruiting free phosphates, sugars, and bases to “fill” the gaps • New nucleotides float in and pair in a complementary fashion – A to T, C to G and vice versa…

  13. Figure 16.10 Origins of replication in eukaryotes

  14. Is Replication of DNA error-free?NO!!!, but it is relatively rare… • Errors in completed DNA moleculeamount to only one in a billion nucleotides • Initial pairing errors – error rate of 1 per 10,000 base pairs * Exposure damage – due to things such as reactive chemicals, radiation, X-rays, ultraviolet light -- unpredictable, but common Ex. Skin cells and uv damage * Mismatch repair – DNA will occasionally put incorrect bases together…cells use special enzymes to fix incorrectly paired nucleotides

  15. The Structure of RNA RNA, like DNA, consists of a long chain of nucleotides There are 3 main differences between RNA & DNA: • The sugar in RNA is ribose instead of deoxyribose • RNA is generally single stranded instead of double stranded • RNA contains uracil in place of thymine

  16. Now, to make a protein… • DNA is used IN PART. • Transcription and Translation make it possible • Need mRNA, tRNA, and rRNA to make a protein (the three types of RNA)

  17. Figure 5.28 A diagrammatic overview of information flow in a cell

  18. RNA and Protein Synthesis • Messenger RNA (mRNA) – carries information from DNA in the nucleus to the ribosomes where the proteins are assembled. It is a partial copy of ONLY the information needed for that specific job. It is read 3 bases at a time – codon. 2. Transfer RNA (tRNA) – transfers the needed amino acids from the cytoplasm to the ribosome so the proteins dictated by the mRNA can be assembled. (The three exposed bases are complementary to the mRNA and are called the anticodon) 3. Ribosomal RNA (rRNA) – found in ribosomes and helps in the attachment of mRNA and in the assembly of proteins.

  19. The structure of messenger RNA (mRNA) Job: Make a copy of a segment of DNA (in the nucleus) and transport the message to the ribosomes for protein synthesis.

  20. The structure of transfer RNA (tRNA) Job: Transport amino acids that are coded for in the DNA that match up with the mRNA codons.

  21. How is the code of mRNA transferred? • Codon- mRNA is made up of nucleotide codes in sets of that each (set of 3) code for an amino acid • Anticodon- tRNA has which brings in specific amino acids have 3 letter code which match the codon, these are called anticodons. • tRNA is a transfer molecule that will bring in an amino acid that matches the mRNA codon. The amino acids will fall off the tRNA inside the ribosome during protein assembly 3

  22. Nucleus Transcription Uses mRNA mRNA What is actually happening in the nucleus In the Cytoplasm at the ribosome attached to the ER Translation Amino Acids Uses mRNA, tRNA, and rRNA tRNA mRNA

  23. Figure 17.3 The triplet code Genes code for traits. Each gene has a specific DNA sequence. Only the part of the DNA that has the needed code unzips so that mRNA can copy JUST that information. mRNA forms in the nucleus to make a reversed+ image of the DNA sequence . mRNA, tRNA, and rRNA work together to assemble the proteins coded for in the gene sequence.

  24. Transcription Section 12-3 Adenine (DNA and RNA) Cystosine (DNA and RNA) Guanine(DNA and RNA) Thymine (DNA only) Uracil (RNA only) RNApolymerase DNA RNA Go to Section:

  25. Translation begins… Section 12-3 Nucleus Messenger RNA Messenger RNA is transcribed in the nucleus. mRNA Lysine Phenylalanine tRNA Transfer RNA The mRNA then enters the cytoplasm and attaches to a ribosome. Translation begins at AUG, the start codon. Each transfer RNA has an anticodon whose bases are complementary to a codon on the mRNA strand. The ribosome positions the start codon to attract its anticodon, which is part of the tRNA that binds methionine. The ribosome also binds the next codon and its anticodon. Methionine Ribosome Start codon mRNA Go to Section:

  26. Translation (continued) Section 12-3 Growing polypeptide chain Ribosome tRNA Lysine tRNA mRNA mRNA Translation direction Ribosome Go to Section:

  27. Figure 17.4 The dictionary of the genetic code

  28. Another dictionary… Section 12-3 Go to Section:

  29. Mutations • Mutations are changes in the DNA sequence that affect genetic information • Gene mutations result from changes in a single gene • Chromosomal mutations involve changes in whole chromosomes • Mutations that affect one nucleotide are called point mutations • Frameshift mutations are those that shift the “reading” frame of the genetic message by inserting or deleting a nucleotide

  30. Gene Mutations: Substitution, Insertion, and Deletion Section 12-4 Deletion Insertion Substitution Go to Section:

  31. Working with the Code – use the box from your textbook (page298) • Given TACGGGCCCCAAACT—(what replace T in mRNA?) a. what is the mRNA made? b. what is the tRNA needed for translation? c. what is the protein made? (amino acid chain) 2. Given TACGCACATAATACT do a, b, and c as above…

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