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History of DNA
Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA
Proteins were composed of 20 different amino acids in long polypeptide chains
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2. DNA Replication

3. Replication Facts DNA has to be copied before a cell divides
DNA is copied during the S or synthesis phase of interphase
New cells will need identical DNA strands

4. Synthesis Phase (S phase)
S phase during interphase of the cell cycle
Nucleus of eukaryotes
Mitosis
-prophase
-metaphase
-anaphase
-telophase G1 G2 S
phase
interphase
DNA replication takes
place in the S phase.

5. DNA Replication Begins at Origins of Replication
Two strands open forming Replication Forks (Y-shaped region)
New strands grow at the forks
Replication
Fork
Parental DNA Molecule 3’ 5’

6. DNA REPLICATION http://www.youtube.com/watch?v=d1UPf7lXeO8

7. DNA Replication 1st the DNA must unwind
The enzyme (helicase) unzips h-bonds between base pairs
2nd enzyme (DNA polymerase) (ase=enzyme) catalyzes the replication of each strand by attaching nucleotides that pair with each base to form the new strand

8. -Ligase- follows polymerase by ‘double checking’ and sealing base pairs together -The two resulting identical strands are called COMPLIMENTARY STRANDS

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Proofreading New DNA
DNA polymerase initially makes about 1 in 10,000 base pairing errors
Enzymes proofread and correct these mistakes
The new error rate for DNA that has been proofread is 1 in 1 billion base pairing errors
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DNA Damage & Repair
Chemicals & ultraviolet radiation damage the DNA in our body cells
Cells must continuously repair DAMAGED DNA
DNA polymerase and DNA ligase replace and bond the new nucleotides together
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11. PROTEIN SYNTHESIS

12. Protein Synthesis
The production (synthesis) of polypeptide chains (proteins)
Two phases: Transcription & Translation
mRNA must be processed before it leaves the nucleus of eukaryotic cells

13. Anti-Parallel Strands of DNA
On the left is the DNA double helix. When the helix is unwound, a ladder configuration shows that the uprights are composed of sugar and phosphate molecules and the rungs are complementary bases. Notice that the bases in DNA pair in such a way that the phosphate-sugar groups are oriented in different directions. This means that the strands of DNA end up running antiparallel to one another, with the 3’ end of one strand opposite the 5’ end of the other strand.

14. RNA

15. RNA Differs from DNA RNA DNA has a sugar ribose
contains the base uracil (U)
molecule is single-stranded
has a sugar deoxyribose
has thymine (T)
is double-stranded

16. .
Two Types of RNA
Messenger RNA (mRNA) carries genetic information to the ribosomes
Transfer RNA (tRNA) transfers amino acids to the ribosomes where proteins are synthesized

17. Making a Protein

18. Genes & Proteins
Proteins are made of amino acids linked together by peptide bonds
20 different amino acids exist
Segment of DNA that codes for the amino acid sequence in a protein are called genes

19. Two Parts of Protein Synthesis
1st part:
Transcription makes an mRNA molecule from a portion of DNA

20. Overview of Transcription
in the nucleus,
a segment of DNA unwinds and unzips,
DNA serves as a template for mRNA formation
RNA polymerase joins the RNA nucleotides to the complementary DNA

21. During transcription, complementary RNA is made from a DNA template
During transcription, complementary RNA is made from a DNA template. A portion of DNA unwinds and unzips at the point of attachment of RNA polymerase. A strand of mRNA is produced when complementary bases join in the order dictated by the sequence of bases in DNA. Transcription occurs in the nucleus, and the mRNA passes out of the nucleus to enter the cytoplasm.

22. Genetic Code DNA contains a triplet code
Every three bases on DNA stands for ONE amino acid
Each three-letter unit on mRNA is called a codon
There are 20 amino acids with a possible 64 different triplets
The code is nearly universal among living organisms
The fact that the genetic code is about universal in living things suggests that the code dates back to the first organisms on earth and that all living things are related.

23. Messenger RNA (mRNA) Carries the information for a specific protein
Made up of 500 to 1000 nucleotides long
Sequence of 3 bases called codons

24. Translation Synthesis of proteins in the cytoplasm
Involves the following:
1. mRNA (codons)
2. tRNA (anticodons)
3. ribosomes
4. amino acids

25. Transfer RNA (tRNA) Made up of 75 to 80 nucleotides long
Picks up the appropriate amino acid floating in the cytoplasm
Transports amino acids to the mRNA
Have anticodons that are complementary to mRNA codons
Recognizes the appropriate codons on the mRNA and bonds to them with H-bonds

26. Protein Synthesis A U G C U A C C C G A G G U A G C C G C G U A U U
mRNA
start
codon
codon 2
codon 3
codon 4
codon 5
codon 6
codon 7
codon 1 U A C C C G A G G U A G C C G C G U A U U
tRNA
Anti
codon 2
codon 3
codon 4
codon 5
codon 6
codon 7
codon 1
aa1
aa2
aa4
aa5
aa6
aa7
peptide bonds
aa3

27. Translation A E P 5’ 3’ Large subunit mRNA Small subunit fMet UAC
GAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA 5’
mRNA 3’
Small subunit

28. Translation A E P 5’ 3’ Polypeptide Aminoacyl tRNA Ribosome mRNA Arg
Phe
Leu
Met
Ser
Gly
Polypeptide
CCA
UCU
Arg
Aminoacyl tRNA A E
Ribosome P
GAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA 5’
mRNA 3’

29. Translation A E P 5’ 3’ Polypeptide Aminoacyl tRNA Ribosome mRNA Phe
Leu
Met
Ser
Gly
Polypeptide
Arg
CCA
UCU
Aminoacyl tRNA A E
Ribosome P
GAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA 5’
mRNA 3’

30. Translation A P 5’ 3’ Polypeptide Ribosome mRNA Arg UCU Phe Leu Met
Ser
Gly
Polypeptide
CCA A
Ribosome P
GAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA 5’
mRNA 3’

31. Translation A E P 5’ 3’ Polypeptide Aminoacyl tRNA Ribosome mRNA Met
Arg
UCU
Phe
Leu
Met
Ser
Gly
Polypeptide
Aminoacyl tRNA
CGA
Ala
CCA A E
Ribosome P
GAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA 5’
mRNA 3’

32. Translation A P 5’ 3’ Polypeptide Ribosome mRNA Arg UCU Phe Leu Met
Ser
Gly
Polypeptide
CCA
CGA
Ala A
Ribosome P
GAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA 5’
mRNA 3’

33. Translation P 5’ 3’ Ribosome mRNA Met Phe Leu Ser Phe Gly Arg Ala CAU
CGA
Phe
Leu
Met
Ser
Gly
Phe
CAU
Ala
Ribosome P
GAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA 5’
mRNA 3’

34. Notice that in this chart, each of the codons (white rectangles) is composed of three letters representing the first base, second base, and third base. For example, find the rectangle where C for the first base and A for the second base intersect. You will see that U, C, A, or G can be the third base. CAU and CAC are codons for histidine; CAA and CAG are codons for glutamine.

35. Pathway to Making a Protein
DNA
mRNA
tRNA (ribosomes)
Protein

36. DNA  RNA  Protein Prokaryotic Cell DNA mRNA Ribosome Protein
Transcription
Translation
DNA
mRNA
Ribosome
Protein
Prokaryotic Cell

37. How Does it Work?
mRNA is like the waitress that takes your order (information) so that it can be made into a meal
The assistants to the chef is like the tRNA bringing the head chef the ingredients to make your meal
The head chef is the ribosome, his
job is to prepare the meal
mRNA

39. DNA (Deoxyribonucleic Acid)
Mutation
- Mistakes in the DNA
Example: albinism

40. DNA (Deoxyribonucleic Acid)
Mutation
Damaged chromosomes
Mismatched base pairs