1. 12.1 DNA

2. DNA Function Controls production of proteins Heredity
Proteins form structures of cells and controls all chemical process in cells
Heredity
Every new cell made in the body needs an exact copy of DNA (Mitosis)
Parents pass DNA to their offspring

3. Dna Structure Nucleotides have 3 parts:
Composed of repeating units called nucleotides
Nucleotides have 3 parts:
5 – carbon sugar called deoxyribose
A phosphate group
A nitrogen base

4. There are 4 kinds of bases:
Adenine Purines Guanine = 2 rings Thymine Pyrimidines Cytosine = 1 ring

5. Purines

6. Pyrimidines

7. Dna Structure Nucleotides bond together to form a long strand
2 strands bond together
The two strands twist around a central axis to form a spiral structure that is called a double helix

8. DNA structure 2 strands bond together Held together by hydrogen bonds
Bonds form between the purines & pyrimidines
Adenine – Thymine (2 H-bonds)
Guanine --- Cytosine (3 H-bonds)
This forms two complementary strands

9. Nitrogenous base pairing

10. Dna’s double helix

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Antiparallel Strands
One strand of DNA goes from 5’ to 3’ (sugars)
The other strand is opposite in direction going 3’ to 5’ (sugars)
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12. DNA History
Griffith
Experimented on mice and observed some harmless strains of bacteria could change into disease-causing strains. He called this transformation.
Avery
Discovered that DNA is the nucleic acid that stores and transmits the genetic information from one generation to the next.

13. More DNA History Hershey-Chase
Concluded that the genetic material in bacteria was DNA not proteins

14. Discovery of dna
They all, except for Chargaff & Franklin, won the Nobel Prize in 1962.

15. Discovery of dna Structure of DNA was discovered by: Chargaff:
A=T & G=C : His rule is that the # of adenines must equal the # of thymines; cytosines=guanines
Maurice Wilkins & Rosalind Franklin:
She took the famous X-ray diffraction picture of DNA
James Watson & Francis Crick:
Discovered the helix shape

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Question:
If there is 30% Adenine, how much Cytosine is present?
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Answer:
There would be 20% Cytosine
Adenine (30%) = Thymine (30%)
Guanine (20%) = Cytosine (20%)
Therefore, 60% A-T and 40% C-G
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18. Question:
If there is 15% Thymine, how much Cytosine is present?

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Answer:
Adenine (15%) = Thymine (15%)
Therefore, 30% A-T and 70% C-G
Guanine (35%) = Cytosine (35%)
There would be 35% Cytosine
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20. 12.2 DNA Replication

21. How Is DNA copied? Replication Fork`
DNA replication is the process of making a copy of DNA
Enzyme called DNA helicase opens up DNA helix by breaking the hydrogen bonds (unzips it)
The ends where the DNA separates are called replication forks
An enzyme, DNA polymerase, attaches at the replication forks and will begin the replication process
Replication
Fork`

22. 3. DNA polymerase and the replication process
DNA polymerase moves along each of the DNA strands
As it moves, unpaired bases in each strand connect with complementary bases of nucleotides that are floating freely in the nucleus
The nitrogen bases attach via hydrogen bonds

23. Practice
If you are given the following sequence, what would be the complementary sequence?
Old strand : Atcgagt
New strand : tagctca

24. How is dna copied?
DNA polymerase continues until all of the DNA has been copied
a. The end results is two identical DNA molecules
b. Each of these DNA molecules is half “old” and half “new”
= semiconservative replication
c. The 2 DNA strands should be identical to each other and to the original

26. Synthesis of the New DNA Strands
The Leading Strand is synthesized as a single strand from the point of origin toward the opening replication fork
RNA
Primer
DNA Polymerase
Nucleotides 3’ 5’

27. Synthesis of the New DNA Strands
The Lagging Strand is synthesized discontinuously against overall direction of replication
This strand is made in MANY short segments It is replicated from the replication fork toward the origin
RNA Primer
Leading Strand
DNA Polymerase 5’ 3’
Lagging Strand 5’ 3’

28. Lagging Strand Segments
Okazaki Fragments - series of short segments on the lagging strand
Must be joined together by an enzyme
Lagging Strand
RNA
Primer
DNA
Polymerase 3’ 5’
Okazaki Fragment

29. Joining of Okazaki Fragments
The enzyme Ligase joins the Okazaki fragments together to make one strand
Lagging Strand
Okazaki Fragment 2
DNA ligase
Okazaki Fragment 1 5’ 3’

30. Replication of Strands
Replication Fork
Point of Origin

31. How are Errors Fixed?
Incorrect nucleotides will be put into DNA sometimes
DNA polymerase also has a proofreading role
It can add nucleotides only if the previous nucleotide is paired up correctly
This prevents most errors
Only 1 error per billion occurs

32. How is speed of replication increased?
In circular bacterial DNA, two forks begin at a single point and work away from each other
In eukaryotes, about 100 replication works open in each DNA molecule at the same time
a. Replication occurs at the same time along each fork until all of the forks meet