DNA, RNA, and PROTEIN SYNTHESIS
1. DNA Double Helix
a. Early 1950’s James Watson and Francis Crick teamed up to determine the structure of
DNA.
b. At the same time Maurice Wilkins and Rosalind Franklin were working on x-rays of the
structure of DNA.
c. Watson and Crick got their hands on Wilkins and Franklin’s work and were the first to
publish the DNA double helix in 1953.
d. 1962 Watson, Crick, and Wilkins receive the Nobel Prize in medicine for their discovery.
Franklin dies of cancer before they received the award. She was eventually recognized
with her peers.
2. DNA Nucleotides
a. Nucleotides consist of 3 parts
i. A five carbon sugar called deoxyribose (blue)(5 sided)
ii. A phosphate group (red)(6 sided)
iii. 1 of 4 nitrogenous bases (yellow)(circle)
1. Adenine abbreviated (A)
2. Guanine abbreviated (G)
3. Cytosine abbreviated (C)
4. Thymine abbreviated (T)
*Adenine and guanine are called purines because they consist of a double ring
of carbon and nitrogen. Cytosine and thymine are called pyrimidines because
they consist of a single ring of carbon and nitrogen.
iv. Covalent bonds hold deoxyribose sugar to the phosphate group and to its
nitrogenous base.
v. Hydrogen bonds form between the nitrogenous bases of two nucleotides.
b. Base Pairing rules
i. Adenine pairs with thymine
ii. Cytosine pairs with guanine
iii. The number of adenine and thymine will be equal and the number of cytosine
and guanine will be equal.
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3. DNA Replication- process by which DNA is copied in a cell before mitosis, meiosis, or binary
fission. It occurs in the s-phase of interphase.
4. Steps of Replication in eukaryotic cells

a. Helicase, an enzyme, separates the DNA at the hydrogen bonds between the
nucleotides.
b. This forms a Y shaped region called the replication fork.
c. DNA polymerase , an enzyme, adds complementary nucleotides floating around
the nucleus to each original strand.
d. A second DNA polymerase , an enzyme, checks to make sure the right
nucleotides have been added.
e. DNA replication results in 2 new identical DNA molecules.
f. DNA polymerase can add 50 nucleotides in one second. It would take 53 days
for the largest human chromosome to copy itself so replication occurs
simultaneously at thousands of sites on the same chromosome.
In prokaryotic cells replication occurs simultaneously at opposite ends of the DNA it ends
when they meet at the middle
5. Mutations- a change in the nucleotide sequence. They can be
a. Non-harmful (silent)
b. Harmful
c. Lethal
Mutations play a major role in the development of cancers.
6. Errors in DNA synthesis
a. DNA polymerase II is the first line of defense by proofreading the nucleotide sequencing
and correcting any errors.
i. Only one in every billion base pairs produces an error during replication.
ii. A change in the original nucleotide sequence is called a mutation.
b. UV rays can damage DNA causing mutations.
i. These mutations can lead to skin cancer.
ii. Cancer is the unregulated growth of cells forming tumors.
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