Nucleic Acids & Protein Synthesis

Comprehensive vocabulary flashcards covering nucleic acid structures, semi-conservative DNA replication, transcription, translation, and gene mutations based on the lecture notes.

Nucleotides

The monomers of nucleic acids (DNA and RNA), each consisting of a pentose sugar containing $5$ carbon atoms, a nitrogen-containing base, and a phosphate group.

Purines

Nitrogenous base molecules that have a double ring structure, which include adenine and guanine.

Pyrimidines

Nitrogenous base molecules that have a single ring structure, which include cytosine, thymine, and uracil.

Adenosine triphosphate (ATP)

An energy-carrying phosphorylated nucleotide and nucleic acid containing a pentose sugar, the nitrogenous base adenine, and three phosphate groups.

Phosphodiester bonds

Covalent bonds linking the $5\text{-carbon}$ of one sugar molecule to a phosphate group, which is linked to the $3\text{-carbon}$ of the adjacent sugar molecule to form the sugar-phosphate backbone.

Complementary base pairing

The specific pairing of nitrogenous bases where the purine adenine pairs with the pyrimidine thymine via $2$ hydrogen bonds, and the purine guanine pairs with the pyrimidine cytosine via $3$ hydrogen bonds.

Antiparallel

The arrangement of the two polynucleotide strands in a DNA molecule running side by side in opposite directions, one running $5'$ to $3'$ and the other $3'$ to $5'$.

Semi-conservative replication

The method of DNA replication before mitosis where each daughter DNA molecule contains one strand from the parental DNA and one newly synthesised strand.

DNA helicase

An enzyme that breaks the hydrogen bonds between complementary base pairs within a double helix, causing the parental DNA double helix to unwind.

DNA polymerase

An enzyme that catalyses the condensation reaction forming phosphodiester bonds between adjacent nucleotides to build a new DNA strand in the $5'$ to $3'$ direction.

Okazaki fragments

Short segments of DNA synthesised discontinuously on the lagging strand as DNA polymerase moves away from the replication fork.

DNA ligase

An enzyme that joins Okazaki fragments together on the lagging strand to form a continuous complementary DNA strand.

Messenger RNA (mRNA)

A single-stranded transcript copy of a gene that encodes a specific polypeptide and carries the code to the cytoplasm.

Gene

A sequence of nucleotides that forms part of a DNA molecule and codes for the sequence of amino acids in a polypeptide.

Degenerate code

The feature of the genetic code where multiple triplet codons code for the same amino acid, as there are $64$ possible triplets ($4^3$) for only $20$ biological amino acids.

Transcription

The stage of protein synthesis occurring in the nucleus where part of a DNA molecule unwinds and a complementary single-stranded mRNA molecule is synthesised by RNA polymerase.

RNA polymerase

The enzyme that joins the sugar-phosphate groups of RNA nucleotides via phosphodiester bonds to form the backbone of an mRNA molecule during transcription.

Splicing

The post-transcriptional process where non-coding introns are removed from the primary transcript and coding exons fuse together to form mature mRNA.

Translation

The stage of protein synthesis occurring in the cytoplasm where an mRNA attaches to a ribosome to direct the synthesis of a polypeptide chain.

Transfer RNA (tRNA)

A type of RNA molecule in the cytoplasm that features a triplet anticodon of three unpaired bases at one end and a specific amino acid attachment site at the other.

Stop codon

A specific codon on the mRNA molecule that signals the termination of translation, causing the completed polypeptide chain to be released.

Gene mutation

A change in the sequence of base pairs in a DNA molecule that occurs continuously and may result in an altered polypeptide.

Frameshift mutation

A knock-on effect caused by the insertion or deletion of nucleotides that shifts the grouping of base triplets further on in the DNA sequence.

Substitution mutation

A mutation occurring when a base in the DNA sequence is randomly swapped for a different base, affecting only the specific triplet in which it occurs.

Silent mutation

A substitution mutation that does not alter the amino acid sequence of the polypeptide due to the degenerate nature of the genetic code.

Missense mutation

A substitution mutation that alters a single amino acid in the polypeptide chain, as seen in sickle cell anaemia.

Nonsense mutation

A substitution mutation that creates a premature stop codon, causing the resulting polypeptide chain to be incomplete, as seen in cystic fibrosis.