NUCLEIC ACIDS & PROTEINS
HL BIOLOGY
Van Roekel
11/6/14
BILL
• Draw and label a simplified structure of DNA.
Enzyme Lab
• Lab Report Due – Friday, November 14.
• If data is not completed, schedule time with
me to complete it.
• Be sure to graph processed data and figure
our averages and standard deviations.
• Print copy off, no google docs!
Nucleic Acids
• Nucleic Acids are organic compounds that
code for protein sequences.
• REMEMBER:
DNA 
RNA
Protein
DNA Structure
• Two antiparallel strands in the shape of a
double helix.
• Each strand is a chain of nucleotides bonded
together
• Nucleotides are composed of phosphate
group, deoxyribose sugar, and one of four
nitrogenous bases.
Nucleotide
Phosphate
Group
O
O=P-O
O
5
CH2
O
N
C1
C4
Nitrogenous base
(A, G, C, or T)
Sugar
(deoxyribose)
C3
C2
6
DNA Structure-Nucleotide
• For HL (IB BIO II) you need to be familiar with
the numbering of carbon atom in sugar
DNA Structure- Backbone
• DNA backbone is composed of alternating
deoxyribose sugar and phosphate groups
• Held together by covalent bonds called a
phosphodiester bond.
– Phosphate—oxygen—carbon
DNA Structure-Backbone
• Condensation reactions occur between the
phosphate group of the 5’ carbon and the
hydroxyl group on the 3’ carbon.
• Nucleotides are always added to the 3’ side of
chain.
• DNA strands always have a free 5’ carbon end
with a phosphate group and a free 3’ carbon
end with a hydroxyl group attached
Nucleotides are bonded together by
condensation reactions
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DNA Structure-Base Pairing
• Nitrogenous bases are held together by
hydrogen bonds
• Purines always pair with Pyrimidines
• Adenine pairs with Thymine via two hydrogen
bonds
• Guanine pairs with Cytosine via three
hydrogen bonds
DNA Structure-Base Pairing
Purines
• Double ring structures
Pyrimidines
• Single ring structures
2 minute convo
• Summarize how nucleic acids are formed.
15
DNA vs RNA
• DNA
1- Deoxyribose sugar
2- Bases: Adenine, Thymine, Cytosine,
Guanine
3- Double-stranded helix arrangement
• RNA
1- Ribose sugar
2- Bases: Adenine, Uracil, Cytosine, Guanine
3- Single stranded
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BILL - Compare DNA and RNA
DNA
• Deoxyribose Sugar
• Thymine as a base
• Double stranded
RNA
• Ribose Sugar
• Uracil as a base
• Single Stranded
DNA Packaging
• DNA is paired with a type of protein called a
histone to form a nucleosome
• Nucleosome: the basic unit of DNA packaging
– DNA wrapped around two protein molecules,
each of which has 4 different histones
– Negatively charged DNA is attracted to Positively
charged histones
DNA packaging-Nucleosome
http://www.youtube.com/watch?v=gbSIBhFw
Q4s
DNA Packaging-Nucleosome
• When DNA is wrapped around histones, it is
inaccessible to transcription enzymes
• Packaging thus controls transcription process,
only allowing certain areas to be involved in
protein synthesis
• Nucleosomes are essential to the
“supercoiling” of DNA molecules to form
chromosomes-tightly packs all genetic
material into condensed chromosomes.
DNA Sequencing
• Protein-Coding Sequences
– Single copy genes with coding functions.
– Provide base sequences essential to produce
proteins at cell ribosomes.
– 2% of human genome codes for proteins
• Determined by Human Genome Project:
began in 1970s, completed in 2001
DNA Sequencing
• Protein-Coding Sequences
– Genes are made of numerous fragments of
protein encoding information, and non-encoding
fragments.
– Protein encoding fragments are exons
– Non-protein encoding fragments are introns
DNA Sequencing
• Highly repetitive sequences
– 5-45% of human genome
– Composed of 5-300 base pairs per repetition
– Up to 100,000 replications
….GTTACGTTACGTTACGTTACGTTACGTTAC….
– Satellite DNA: clusters of repetitive DNA in
discrete areas
• Repetitive DNA does not code for proteins
DNA Sequencing-Structural
• Structural DNA is highly coiled DNA that does
not have a coding function.
• Generally located around centromere and on
ends of chromosomes.
• A.K.A “Pseudogenes” which have no function
Review Questions
• Draw the two strands of a DNA molecule
representing their antiparallel relationship and
complementary base pairing.
• Explain how nucleosomes would contribute to
transcription control.
• Would exons or would introns be more likely
to contain highly repetitive sequences? Why?