Biology
Ch.10 Notes
DNA, RNA, AND PROTEIN SYNTHESIS
Ch.10:1 DISCOVERY OF DNA
“The Secret of Photo 51”
Ch.10:2 DNA STRUCTURE
DNA DOUBLE HELIX: Watson and Crick 1953
DNA NUCLEOTIDES
Nucleotides:
Building blocks of nucleic acids (DNA OR RNA)
Composed of phosphate-sugar-base
(Circle – pentagon – rectangle)
Bonds Hold DNA Together
Ladder Model:
Uprights = phosphate – sugar – phosphate – sugar – etc.
Held together with strong covalent bonds
Anti-parallel: due to asymmetry of pentose sugar 
Nitrogen bases
Rungs = nitrogen bases
Purines: double-ring bases
Pyrimidines: single-ring bases
Each rung = purine + pyrimidine (complementary)
Complementary bases are H-bonded
Base Pairing Rules: C-G; A-T(U)
COMPLEMENTARY BASES
Chargaff’s Rules: Cytosine = Guanine; Adenine = Thymine
Base Sequence: A T T C
TAAG
Figure out the complementary base sequence for this one:
TATGGCTCCCTGA
REVIEW
1. What piece of information did Franklin and Wilkins have that helped
Watson and Crick determine the double helix structure of DNA?
2. Name the three parts of a nucleotide.
3. Summarize the locations of covalent bonds and hydrogen bonds in a
DNA molecule.
4. Describe why the two strands of the double helix are considered to be
complementary.
5. State the base-pairing rules in DNA.
6. How do the base-pairing rules relate to the structure of DNA?
7. Which repeating part of the DNA double helix molecule is evidence for
the way it replicates (makes copies)?
Mrs. Loyd 
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Biology
Ch.10 Notes
DNA, RNA, AND PROTEIN SYNTHESIS
Ch.10:3 DNA REPLICATION DNA  DNA
How DNA Replication Occurs
Copied by semi-conservative replication during the S phase of
Interphase in the cell’s nucleus.
Steps of DNA Replication (fig.10-10, p.201)

DNA unwound by helicase breaking the H-bonds between
bases allows two strands to “unzip.”

DNA polymerase adds complementary nucleotides to
each strand
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Results in identical sister chromatids
Action at the Replication Fork:

Synthesis occurs in opposite directions
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“Leading” and “lagging” strands
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Ligase (think “ligament”) links gaps together
Prokaryotic and Eukaryotic Replication

Prokaryotic: Single circular chromosome unzips at two forks

Eukaryotic: Many “origins” of replication to speed up copying
DNA ERRORS IN REPLCATION
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One error in every billion added nucleotides
DNA polymerase functions to “proofread” DNA to avoid errors
Mutations result when mistakes are not caught and repaired
Chemicals (“toxins,” “carcinogens”), UV and other high-energy
radiation can cause errors.
DNA Replication and Cancer
Mutations that affect genes that control how a cell divides (p53 and Ras)
can lead to an abnormal mass of cells called a tumor.
Ch.10:4 PROTEIN SYNTHESIS
FLOW OF GENETIC INFORMATION
(DNA  mRNA  Amino Acid sequence (protein)
A gene is a segment of DNA is located on a chromosome and
codes for a hereditary character. Ex. Hair color determined by
the protein: melanin, a pigment.
Fig. 10-12
DNA  mRNA  Amino Acid sequence (protein)
Transcription: DNA  mRNA (nucleolus)
Translation: mRNA  Amino Acid sequence (cytoplasm)
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RNA STRUCTURE AND FUNCTION
Differences between RNA and DNA (fig.10-13)
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Single stranded vs. double stranded
Shorter vs. longer
Ribose sugar instead of Deoxyribose sugar
Uracil instead of Thymine
Types of RNA (fig.10-14)

mRNA: carries copy of DNA code to ribosome

rRNA: organizes translation (protein synthesis)

tRNA: transfers amino acids to ribosome (specific)
Mrs. Loyd 
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TRANSCRIPTION: DNA  mRNA (nucleolus)

DNA unzips temporarily

RNA polymerase “reads” template strand adds RNA nucleotide

mRNA transcript molecule peels away

DNA zips up

mRNA leaves nucleus through nuclear pore
THE GENETIC CODE

The term for the rules that relate how a sequence of nitrogenous bases in
nucleotides corresponds to a particular amino acid.

Codon: three adjacent nucleotides (“letters”) in mRNA specify an amino acid
(“word”)

Start codon: AUG: methionine

Stop codons: UAA, UAG, UGA

Table 10-1 lists 64 mRNA codons and AA they encode.

Universal to all life on Earth and supports the idea that all organisms
share an ancient common ancestor.
http://learn.genetics.utah.edu/content/begin/dna/transcribe/
Mrs. Loyd 
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TRANSLATION: mRNA  AA seq. (protein)
z
Protein Structure
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“The Players”
Protein is made of one or more polypeptides
>20 amino acids make up polypeptides
“One gene, one polypeptide”
Amino acids determine how it will twist and fold into
the 3-D structure of protein.
Shape = Function
Players in Translation (fig. 10-16)
mRNA:

copy of DNA sequence or “gene.”

Leaves nucleolus/nucleus through nuclear pore.

Single-stranded.
rRNA:

ribosomal RNA + proteins

in cytoplasm

attaches to mRNA
tRNA:

transfer RNA (also, think: taxi or translator) specific for
amino acids (AA), transfers AA to ribosome.

“Rosetta Stone” tRNA contains an anticodon which is
the complement to the codon on mRNA as well as an
AA, the monomer of protein. It can translate the
“language” of nitrogen bases into the “language” of
amino acids.
Translating Many Ribosomes at Once
Many ribosomes translate a single mRNA at the same time
to increase the rate of production of needed proteins.
Mrs. Loyd 
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This next diagram is just for fun. This shows a prokaryote’s transcription
and translation occurring simultaneously due to the lack of a nuclear
membrane. Compare it to the eukaryote in the previous diagram.
Prokaryotes can respond to the changing environment faster than
eukaryotes.
THE HUMAN GENOME
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Genome: the entire gene sequence of an organism
Human Genome Project: deciphered the order of the
3.2 billion
base pairs in the 23 human chromosomes.
Bioinformatics uses computer to compare different DNA sequences
and interpret where genes lie along the DNA.
30,000 genes in the human genome encodes for protein.
Current challenge:

Learn what information the DNA sequences actually encode.

Learn where and when human cells use each of the proteins.

Knowing which gene sequences control particular biological
functions may help diagnose, treat, and prevent genetic
disorders, cancer, and infectious diseases in the future.
Mrs. Loyd 
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