Nucleotides, Nucleic Acids, and DNA Replication

Vocabulary practice flashcards covering nucleic acid monomers, RNA vs DNA, polynucleotide formation, DNA extraction practicals, and semi-conservative replication.

Nucleic acids

Polymers (polynucleotides) made of repeating monomers called nucleotides, containing $\text{C}$, $\text{H}$, $\text{O}$, $\text{N}$, and $\text{P}$.

Nucleotide

A molecule consisting of three components—a nitrogen-containing base, a pentose sugar, and a negatively charged phosphate group—joined through two condensation reactions, releasing two molecules of water.

Ribose

A five-carbon pentose sugar found in RNA that contains an $-\text{OH}$ group on carbon $2'$.

Deoxyribose

A five-carbon pentose sugar found in DNA that contains a hydrogen atom ($-\text{H}$) instead of an $-\text{OH}$ group on carbon $2'$.

Purines

Nitrogen-containing bases with a double-ring structure, consisting of adenine ($\text{A}$) and guanine ($\text{G}$).

Pyrimidines

Nitrogen-containing bases with a single-ring structure, consisting of cytosine ($\text{C}$), thymine ($\text{T}$), and uracil ($\text{U}$).

mRNA (Messenger RNA)

A type of RNA that carries a copy of the genetic code from DNA to a ribosome for protein synthesis.

rRNA (Ribosomal RNA)

A type of RNA that combines with proteins to form ribosomes, the site of protein synthesis.

tRNA (Transfer RNA)

A type of RNA that transfers amino acids to ribosomes during protein synthesis.

Phosphodiester bond

A strong covalent bond formed between the phosphate group attached to the $5'$ carbon of one nucleotide and the $-\text{OH}$ group on the $3'$ carbon of another nucleotide's pentose sugar.

Nucleases

Enzymes that catalyse the hydrolysis of phosphodiester bonds using water, breaking polynucleotides into shorter fragments or individual nucleotides.

Antiparallel strands

The structural arrangement in DNA where two polynucleotide strands run in opposite directions ($5' \rightarrow 3'$ and $3' \rightarrow 5'$), twisting to form a right-handed double helix with approximately $10$ base pairs per turn.

Complementary base pairing

The pairing rule where a purine always pairs with a pyrimidine (adenine pairs with thymine via $2$ hydrogen bonds, and cytosine pairs with guanine via $3$ hydrogen bonds) to maintain a constant width across the DNA molecule.

Washing up liquid (DNA extraction)

A detergent added during DNA extraction to break down the cell and nuclear membranes in order to release DNA.

Water bath at $60^\circ\text{C}$ for $15\text{ minutes}$ (DNA extraction)

A step used in DNA extraction to speed up the breakdown of membranes and destroy enzymes that might break down DNA.

Iced water bath for $5\text{ minutes}$ (DNA extraction)

A cooling step used in DNA extraction to prevent the breakdown of DNA after heating.

Coffee filter paper (DNA extraction)

A porous barrier used to remove solid cell debris, such as cell walls and organelles, while collecting the liquid filtrate containing DNA.

Protease enzymes (DNA extraction)

Enzymes added to $5\,\text{cm}^3$ of filtrate to break down proteins so that DNA, rather than proteins, precipitates out into ethanol.

Ice-cold ethanol (DNA extraction)

A chilled alcohol layer poured $1\,\text{cm}$ deep onto the filtrate to precipitate DNA, which is soluble in water but insoluble in ethanol.

DNA gyrase

An enzyme that untwists the DNA double helix during DNA replication.

DNA helicase

An enzyme that unzips the DNA double helix by breaking the hydrogen bonds between complementary base pairs.

Single-stranded binding proteins

Proteins that attach to separated single strands of DNA to prevent reannealing during replication.

DNA polymerase

An enzyme that synthesises a new DNA strand exclusively in the $5' \rightarrow 3'$ direction by catalysing the formation of covalent phosphodiester bonds.

Lagging strand

The template strand replicated discontinuously away from the replication fork into short segments.

DNA ligase

An enzyme that closes the gaps in the sugar-phosphate backbone by joining together short sections of the lagging strand.

Semi-conservative replication

The mechanism of DNA replication in which each newly formed double helix consists of one original (parental) strand and one newly synthesised strand.