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VICBiologyQuick questions
Unit 3: How do cells maintain life?
Quick questions on Nucleic acid structure (DNA and RNA): VCE Biology Unit 3
14short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is the nucleotide?Show answer
Every nucleotide has three components:
What is dNA structure?Show answer
DNA is a double-stranded helix. The two strands run antiparallel (one 5' to 3', the other 3' to 5') and twist into a right-handed double helix.
What is rNA structure?Show answer
RNA is usually single-stranded. Its nucleotides contain ribose (with a 2' hydroxyl), and uracil (U) replaces thymine. A pairs with U; G pairs with C. RNA can fold back on itself to form short double-stranded regions held by intramolecular base pairing.
What is bases?Show answer
The four DNA bases are the purines adenine (A) and guanine (G), and the pyrimidines thymine (T) and cytosine (C).
What is complementary base pairing?Show answer
A pairs with T through two hydrogen bonds; G pairs with C through three hydrogen bonds. Because pairing is specific, each strand carries the complementary sequence of the other, which allows accurate replication.
What is stability and access?Show answer
The sugar-phosphate backbone is on the outside; bases face inward. Hydrogen bonds between bases are individually weak but collectively stable, while still allowing the strands to separate when enzymes such as helicase unzip the helix.
What is messenger RNA?Show answer
A linear single strand that carries the genetic message from DNA to the ribosome. It is read in codons (triplets of bases). In eukaryotes, mature mRNA has a 5' cap, a 3' poly-A tail, and introns removed by splicing.
What is transfer RNA?Show answer
A short folded RNA (about 76 to 90 nucleotides) shaped like an inverted L (cloverleaf in two dimensions). It carries a specific amino acid on its 3' end and presents a three-base anticodon that pairs with a codon on mRNA. There is at least one tRNA for each of the 20 amino acids.
What is ribosomal RNA?Show answer
Combines with proteins to form the two subunits of the ribosome. rRNA does the catalytic work of forming peptide bonds, so the ribosome is described as a ribozyme.
What is complementary DNA strand?Show answer
5' ATGCCGTAT 3' (A pairs with T, G with C).
What is mRNA transcribed from this template?Show answer
5' AUGCCGUAU 3' (U replaces T; the message is read 5' to 3' by the ribosome).
What is reading frame?Show answer
The first codon AUG codes for methionine, the start codon. CCG codes for proline; UAU codes for tyrosine. The matching tRNA anticodons would be 3' UAC, GGC, AUA 5'.
What is forgetting antiparallel?Show answer
The two strands run in opposite 5' to 3' directions. Without this detail, replication and transcription cannot be explained.
What is mixing up base pairing numbers?Show answer
A and T have two hydrogen bonds; G and C have three. GC-rich regions are therefore more thermally stable.