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Controls the production of proteins (proteins control cell processes)
Store and use info to direct cell activities
Copy itself exactly for new cells (every cell needs exact copies of DNA)

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Forms a double helix (2 strands twisted around like a winding staircase. Twisted ladder)
Made of repeating nucleotides
A. Nucleotides have 3 parts
1. deoxyribose: 5-carbon sugar
2. phosphate
3. 1 base: A,T,C,G
B.
Deoxyribose and phosphates are the same for each nucleotide.

c. 4 different nitrogen bases
1.
Guanine
2.
Adenine
3.
Thymine
4.
Cytosine d. Sides of the ladder are alternating deoxyribose and phosphate e. Middle of the ladder “ steps of ladder” are the bases. f. bases or the middle of the ladder are held together by hydrogen bonds.
g. phosphates and deoxyribose sugar are held together by peptide bonds.

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Two types a. Pyrimidines: single ring bases b. Purines: Double ringed

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4 bases: bases attach to the sugar molecule
-- pyrimidines (1 ring of carbon): Thymine,
Cytosine
-- purines (2 rings of carbon): Adenine,
Guanine
Bond through hydrogen bonds!
Adenine bonds with thymine cytosine bonds with Guanine
The two strands are complementary to each other. The sequences of bases of one strand determines the sequence of the bases of the other strand.
Example: ATTCGATTCGCTA
TAAGCTAAGCGAT

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Process of making DNA
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Occurs during the s phase of interphase
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Watson and Crick: proposed that one strand serves as a template or pattern on which the other strand is built
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Must be copied exactly the same for each cell

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1 . DNA helicases (enzyme) attaches to the DNA molecule and breaks the hydrogen bonds between the bases. This separates the two strands.
-- Replication forks are the areas at the end of the DNA where the strands have been separated. (they have a y shape)
2. DNA polymerase (enzyme) attaches at the replication fork and reads each DNA strand. It attaches the correct bases making new nucleotides for each strand. Two new strands are made. This makes 2 new DNA molecules
3. Each new DNA molecule contains and old and new strand of
DNA. The DNA is identical to each other and the original DNA molecule.

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* Only 1 error per billion nucleotides made called a mutation
* Errors do happen
* How are they fixed?
* DNA polymerase has a proofreading mechanism.
It can check to see if the correct base is bonded correctly. It can only move on to the next base and continue to make a new strand if the previous nucleotide is correctly bonded to the correct base. If not, it can back track and fix it.

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* With one replication fork it would take about 33 days to replicate one chromosome.
* However, each chromosome is replicated in about 100 sections. Each section has its own starting point at a replication fork.
With multiple replication forks, a human chromosome can be replicated in about 8 hours.

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* Where an error occurs in the sequence of the DNA from the original sequence.
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Mutations occur 1 in 1,000,000,000 nucleotides
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Types of Mutations:
1. GERMLINE mutations can be passed from a parent to child. If a child inherits a germline mutation from their parents, every cell in their body will have this error in their DNA. Germline mutations are what cause diseases to run in families.
2. POINT MUTATION is a change in one base of the gene sequence.
Point mutations are divided into three types a. NONSENSE = failure of expression b. MIS-SENSE = base code for a different protein. (sickle cell anemia) c. SILENT = no significant change

3. FR AME SHIFT A mutation in a DNA chain that occurs when the number of nucleotides inserted or deleted is not a multiple of three, so that every codon beyond the point of insertion or deletion is read incorrectly during translation.
4. DELETIONS are mutations that result in missing DNA.
5. INSERTIONS are mutations that result in the addition of extraa DNA.
Insertions can also cause frame shift mutations, and generally result in a nonfunctional protein.
6. INVERSION mutations occur when entire sections of DNA is reversed.
A small inversion may involve only a few bases within a gene, while longer inversions involve large regions of a chromosome containing several genes.