A1.2 Nucleic Acids - Pre-IB Biology Work
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What are nucleic acids made of?
Nucleic acids are polymers made of repeating units called nucleotides.
What are the three components of a nucleotide?
A pentose sugar, a phosphate group, and a nitrogenous base.
To which carbon is the nitrogenous base attached in a nucleotide?
The 1′ carbon of the pentose sugar.
To which carbon is the phosphate group attached in a nucleotide?
The 5′ carbon of the pentose sugar.
How are nucleotides joined together?
By condensation reactions that release water.
What bond forms between nucleotides in a strand?
A covalent phosphodiester bond.
Which groups are involved in forming the phosphodiester bond?
The phosphate group of one nucleotide and the 3′ hydroxyl of another.
What are the two categories of nitrogenous bases?
Purines (double ring): A, G; Pyrimidines (single ring): C, T (DNA), U (RNA).
What forms the sugar-phosphate backbone of a nucleic acid?
Repeating sugars and phosphates.
Which bases pair together in DNA and RNA?
DNA: A–T, G–C RNA: A–U, G–C
Why must purines pair with pyrimidines?
To maintain a uniform width in the nucleic acid helix.
Replication:
One strand acts as a template for creating a new complementary strand
Expression:
A complementary RNA transcript is produced from the DNA template strand
How many hydrogen bonds form between A–T and G–C pairs?
A–T = 2 bonds, G–C = 3 bonds.
What is the sugar in DNA? What about RNA?
DNA = deoxyribose (no OH on 2′ carbon); RNA = ribose (OH on 2′ carbon).
What are the key structural differences between DNA and RNA?
DNA: Double-stranded, deoxyribose, uses thymine. RNA: Single-stranded, ribose, uses uracil.
Which molecule is more stable, DNA or RNA? Why?
DNA, due to its lack of a hydroxyl on the 2′ carbon and double-stranded structure.
What is the role of mRNA?
Carries DNA instructions for protein synthesis.
What is the role of tRNA?
Transfers amino acids to the ribosome during translation.
What is the role of rRNA?
Forms the catalytic core of ribosomes; helps form peptide bonds.
How does RNA structure differ among types?
• mRNA: Linear • tRNA & rRNA: Folded due to internal base pairing
What shape does DNA form?
A double helix with ~10–15 base pairs per twist.
Why are DNA strands antiparallel?
One runs 5′→3′ and the other 3′→5′, allowing proper base pairing.
What are DNA’s two main functions?
• Pass hereditary info • Serve as template for RNA transcription