H1 Biology: DNA Replication and Gene Expression

Fill-in-the-blank practice flashcards covering DNA replication, the Meselson-Stahl experiment, transcription, post-transcriptional modifications, and translation.

In the Meselson-Stahl experiment, after one round of replication in a $^{14}\text{N}$ medium, the DNA appeared as a single band with density __________ between that expected for DNA with $^{15}\text{N}$ and $^{14}\text{N}$.

intermediate

During DNA replication, DNA helicase unwinds and unzips the DNA molecule by breaking the __________ bonds between complementary bases.

hydrogen

Primase synthesises a short RNA primer that provides a free __________ group for DNA polymerase III to add new deoxyribonucleotides.

$$3'\text{OH}$$

During lagging strand synthesis, DNA ligase seals the gaps between Okazaki fragments by forming __________ bonds.

phosphodiester

DNA polymerase III synthesizes the daughter strand continuously on the leading strand in the __________ direction towards the replication fork.

$$5' \rightarrow 3'$$

In eukaryotic promoters, transcription factors and RNA polymerase recognize the TATA box, whereas the corresponding sequence in prokaryotes recognized by RNA polymerase is known as the __________ box.

Pribnow

The genetic code is described as __________ because more than one mRNA codon can code for the same amino acid.

degenerate

During eukaryotic post-transcriptional modification, non-coding sequences called __________ are excised and exons are spliced together.

introns

Every tRNA molecule possesses an amino acid attachment site at its $3'$ end that terminates in the sequence __________.

CCA

During translation termination, the release factor binds to the stop codon and recruits a __________ molecule to hydrolyse the bond between the completed polypeptide and the last tRNA.

water

The Meselson-Stahl experiment provided evidence that DNA replicates via the __________ model, as evidenced by a single hybrid density band after one replication cycle.

semi-conservative

During DNA replication initiation, the enzyme __________ synthesises a short RNA primer to provide a free $3'\text{OH}$ group required for elongation.

primase

The enzyme __________ relieves tighter strain ahead of the advancing replication fork by breaking, swivelling, and rejoining parental DNA strands.

topoisomerase

Discontinuous DNA replication on the lagging strand produces Okazaki fragments that are joined together by the action of the enzyme __________.

DNA ligase

The genetic code is described as __________ because more than one triplet codon can code for the same amino acid.

degenerate

In eukaryotic transcription initiation, transcription factors first recognise and bind to a specific region within the promoter called the __________.

TATA box

During eukaryotic post-transcriptional modification, non-coding regions called __________ are removed from the pre-mRNA transcript while exons are joined together.

introns

On every transfer RNA (tRNA) molecule, the amino acid attachment site situated at the $3'$ end always consists of the nucleotide sequence __________.

CCA

The attachment of a specific amino acid to its corresponding tRNA during amino acid activation is catalysed by the enzyme __________.

aminoacyl-tRNA synthetase

During the elongation phase of translation, peptide bond formation between adjacent amino acids is catalysed by __________, a ribozyme within the large ribosomal subunit.

peptidyl transferase