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What does DNA look like? What are the elements that makeup DNA?

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Presentation on theme: "What does DNA look like? What are the elements that makeup DNA?"— Presentation transcript:

1 What does DNA look like? What are the elements that makeup DNA?
DNA and RNA What does DNA look like? What are the elements that makeup DNA?

2 DNA Structure= String of nucleotides (sugar, phosphate, base). Adenine
DNA Structure= String of nucleotides (sugar, phosphate, base) *Adenine *Thymine *Guanine *Cytosine purines - adenine, guanine pyrimidines - cytosine, thymine

3 Figure 12–5 DNA Nucleotides
Purines Pyrimidines Adenine Guanine Cytosine Thymine Phosphate group Deoxyribose

4 Hydrogen Bonds are the “glue” that keeps the two strands together
Francis Crick and James Watson (1953) Twisted Double Helix Hydrogen Bonds are the “glue” that keeps the two strands together Each strand of the helix is a chain of nucleotides What holds the strands together?

Always Together….Great Couple Y T O S I N E U A N I E D E N I H Y M I N E A & T G & C

6 Figure 12–7 Structure of DNA
Nucleotide Hydrogen bonds Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G)

7 Remember Chromatin?? How is DNA organized in a chromosome?
Did You Know? ONE nucleus of ONE human cell = more than 1 meter of DNA!!! Remember Chromatin?? What exactly is chromatin? DNA tightly coiled around proteins forming Chromatin which pack together to form thick fibers.

8 Prokaryotic Chromosome Structure
Section 12-2 Chromosome E. coli bacterium Bases on the chromosome

9 Chromosome Structure of Eukaryotes
Nucleosome Chromosome DNA double helix Coils Supercoils Histones

10 How can DNA use its double-stranded structure to its advantage for replication???

“Something Old…Something New”

12 DNA Replication When does this occur in the cell cycle?
Template 1) Enzymes un-twist and unzip the molecule (break H bonds between base pairs). 2) Each strand serves as a template (something “OLD”) 3) Free nitrogen bases form bonds and make complementary strands (Something “NEW”) 4) DNA Polymerase bonds the nucleotides and proofreads the molecule

13 Figure 12–11 DNA Replication
Original strand DNA polymerase New strand Growth DNA polymerase Growth Replication fork Replication fork Nitrogenous bases New strand Original strand

14 DNA vs. RNA RNA – also a long chain of nucleotides (5-carbon sugar, phosphate group, nitrogenous base) Differences: RNA sugar = ribose, instead of deoxyribose RNA – usually single-stranded RNA has uracil to replace thymine (so U binds with A) “Always United & Great Couple”

15 RNA is in charge of assembling Amino Acids into Proteins

16 From DNA(Gene) to Protein
The players: DNA - sequences of nitrogen bases forms the genetic code mRNA - messenger RNA - makes a copy of the DNA in the nucleus and brings it to the rRNA tRNA - transfer RNA - reads the mRNA and brings specific amino acids to the rRNA rRNA - ribosomal RNA - location of protein synthesis uses tRNA to make proteins

17 Step 1: Transcription = recording the message
Occurs in nucleus New mRNA strand forms from one of DNA strands (creating the message) Let’s Practice…

18 Transcription Practice

19 Figure 12–14 Transcription
Adenine (DNA and RNA) Cystosine (DNA and RNA) Guanine(DNA and RNA) Thymine (DNA only) Uracil (RNA only) RNA polymerase DNA RNA

20 Step 2: Editing of mRNA Introns are removed – non coding regions of the DNA molecule Exons remain – sequences that will be expressed

21 Step 3: Translation = Protein Synthesis
Occurs at ribosome tRNA reads mRNA which has message from genetic code (DNA) Genetic code is read 3 letters at a time, so each word is 3 bases long

22 Every 3 letters is a CODON
Each codon codes for a specific amino acid. What does an Amino Acid do again? Helps make proteins! We need codons for Protein Synthesis (Translation) They are like directions to make proteins Every set of directions tells you where to START and where to STOP We too have these, we call them the “start and stop codons”

23 Codons to remember… START is always: AUG STOP is always: UAA UAG UGA

24 Translation Explained
tRNA UAC mRNA AUGCGCAUAACGCAU methionine Start Codon

25 There are 20 different amino acids to be coded for.
Alternate sequence: There are 20 different amino acids to be coded for. There are 64 possible codons. Stop codon Start codon

26 Figure 12–17 The Genetic Code

27 Translation Practice AUGAUCGCGUAUUGCUACUAG - mRNA
Make a polypeptide (chain of amino acids) chain from the mRNA molecule AUGAUCGCGUAUUGCUACUAG - mRNA methionine-isoleucine-alanine-tyrosine-cysteine-tyrosine STOP

28 Figure 12–18 Translation Section 12-3

29 Figure 12–18 Translation (continued)
Section 12-3

30 Mutations - changes in the DNA sequence
Gene mutation- changes in a single gene Point Mutations - substitution of one nucleotide for another Frame Shift Mutations - shifting of the genetic code due to insertion or deletion of nucleotide Chromosomal mutation changes in the entire chromosome (containing many genes)

31 Figure 12–20 Chromosomal Mutations
Deletion Duplication Inversion Translocation

32 Mutation Analogy THE FAT CAT ATE THE RAT
substitution THE FAT CAT ATE THE CAT *The letter “C” was substituted for the “R” insertion THE FAT CAT ATE THE RAT THC EFA TCA TAT ETH ERA T *Because the “C” was added, all other letters shifted down, thereby changing the amino acids that are made. C Deletion THE F A T CAT ATE THE RAT THE FTC ATA TET HER AT *Again, the amino acids will change b/c the “F” was removed

What will the new amino acid be if the 5th nucleotide is substituted with an adenine? ASPARAGINE What will the new amino acid sequence be if a guanine is inserted between the 9th and 10th nucleotide ? G GUA = VALINE

34 When a mutation occurs…
If the amino acid sequence is stopped early (a STOP codon is reached) = Nonsense If the amino acid sequence continues but the wrong amino acids are coded for = Missense

35 Putting it all together
What is the amino acid sequence that forms from the following DNA molecule? (DNA synthesis) TACTACACCGTATAACAGGGCCTAGCAACT Template ATGATGTGGCATATTGTCCCGGATCGTTGA

36 (Transcription) DNA TACTACACCGTATAACAGGGCCTAGCAACT mRNA AUGAUGUGGCAUAUUGUCCCGGAUCGUUGA (Translation) amino acid sequence methionine-methionine-tryptophan-histidine-isoleucine-valine-proline-aspartic acid-arginine-stop

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