CHAP6 Nucleic Acids and Protein Synthesis Flashcards

Vocabulary flashcards covering structure of nucleic acids, DNA replication, protein synthesis, and gene mutations.

Nucleotide

The monomer of nucleic acids, consisting of a pentose sugar, a nitrogenous base, and a phosphate group.

Phosphodiester Bond

The strong covalent bond formed between adjacent nucleotides after a condensation reaction, forming the sugar-phosphate backbone.

Purine Bases

Nitrogenous bases containing two fused rings, which include Adenine and Guanine.

Pyrimidine Bases

Nitrogenous bases containing a single ring, which include Cytosine, Thymine (found in DNA only), and Uracil (found in RNA only).

Adenosine Triphosphate (ATP)

An RNA nucleotide consisting of one adenine nitrogenous base, one ribose sugar, and three phosphate groups.

Antiparallel Strands

The structural arrangement of double-stranded DNA where one strand runs in the 5' to 3' direction while the opposing strand runs in the 3' to 5' direction.

Helicase

An enzyme that unwinds the DNA double helix and breaks hydrogen bonds between complementary base pairs during replication and transcription.

DNA Polymerase

An enzyme that synthesises a new DNA strand in the 5' to 3' direction by linking activated nucleotides, catalysing phosphodiester bond formation, and proofreading DNA.

DNA Ligase

An enzyme that joins Okazaki fragments together on the lagging strand by catalysing the formation of phosphodiester bonds.

Leading Strand

The parent DNA strand that is replicated continuously in the 5' to 3' direction toward the unwinding replication fork.

Lagging Strand

The parent DNA strand that is replicated discontinuously in short segments known as Okazaki fragments in the 5' to 3' direction.

Okazaki Fragments

Short sections of newly synthesised DNA produced on the lagging strand during semi-conservative DNA replication.

Semi-Conservative Replication

The mechanism of DNA replication in which each generated daughter DNA molecule contains one original parental strand and one newly synthesised strand.

Meselson and Stahl's Experiment

The 1958 experiment using E. coli grown in heavy nitrogen-15 ($^{15}\text{N}$) and light nitrogen-14 ($^{14}\text{N}$) media that proved DNA replicates semi-conservatively.

Genome

The total set of genes and genetic material present in a cell or organism.

Gene

A specific region of DNA that codes for a polypeptide, determining its exact amino acid sequence and primary structure.

Triplet Code

A sequence of three nucleotide bases in DNA that codes for one specific amino acid.

Degenerate Code

A property of the genetic code where more than one triplet code or codon can code for the same amino acid.

Transcription

The first stage of protein synthesis occurring in the nucleus, where a DNA gene sequence is copied by RNA polymerase to produce pre-mRNA.

Translation

The process occurring at ribosomes where the nucleotide sequence of mRNA is converted into an amino acid chain to form a polypeptide.

Codon

A sequence of three consecutive bases on mRNA that specifies a particular amino acid or signals translation start/stop.

Anticodon

A sequence of three exposed bases on a tRNA loop that binds complementary to a specific mRNA codon via hydrogen bonding.

Introns

Non-coding nucleotide sequences in eukaryotic pre-mRNA that are removed during RNA splicing before translation.

Exons

Coding nucleotide sequences in pre-mRNA that remain after splicing and are joined together to form mature mRNA.

Peptidyl Transferase

An enzyme in the large subunit of the ribosome that catalyses peptide bond formation between adjacent amino acids.

Polyribosomes

A group of multiple ribosomes attached to and translating a single mRNA strand simultaneously to increase the rate of polypeptide synthesis.

Gene Mutation

A random change in the base sequence of a gene, which can alter mRNA codons and result in new alleles.

Point Mutation

The simplest form of gene mutation involving a change in only a single nucleotide base.

Silent Mutation

A base substitution mutation where the altered codon still codes for the exact same amino acid, causing no change to the polypeptide sequence.

Nonsense Mutation

A gene mutation that replaces an amino acid codon with a STOP codon (UAA, UAG, or UGA), leading to premature chain termination and a non-functional polypeptide.

Missense Mutation

A base substitution mutation where an altered codon codes for a different amino acid, changing the polypeptide chain structure.

Frameshift Mutation

A mutation caused by base insertions or deletions not in multiples of three, which shifts the reading frame and alters all subsequent downstream codons.

Sickle Cell Anaemia

An inherited blood disorder caused by a base substitution in the gene coding for $\beta$-globin, which replaces polar glutamic acid with non-polar valine as the 6th amino acid.