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?

5. **REMEMBER THIS PHRASE**
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???

11. **REMEMBER THIS PHRASE**
“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
Transcribe the DNA molecule below:
ATTATCGCGTAATGCTAATAGC
TAATAGCGCATTACGATTATCG
Template
mRNA
transcript
AUUAUCGCGUAAUGCUAAUAGC

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

33. Mutation Practice ASPARAGINE AUGA CGCGUAUUGCUACUAG - mRNA U
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