IBDP Bio (2025) - D1.2 AHL Protein Synthesis

Exon

sequence of DNA that codes information for protein synthesis that is transcribed to messenger RNA.

Intron

segment of a gene situated between exons that is removed before the translation of messenger RNA and does not function in coding for protein synthesis.

Promoter

site in a DNA molecule at which RNA polymerase and transcription factors bind to initiate transcription of mRNA.

5' to 3' direction

the only direction that DNA polymerase can synthesize DNA; it does so by adding nucleotides to the 3' end of a DNA strand.

Gene expression

conversion of the information from the gene into mRNA via transcription and then to protein via translation resulting in the phenotypic manifestation of the gene.

Genome

total genetic contents of an organism.

Non-coding DNA components

of an organism's DNA that do not encode protein sequences. Some non-coding DNA is transcribed into functional non-coding RNA molecules while others are not transcribed.

Splicing of mRNA

removal of introns from a primary transcript and the subsequent joining of exons in the production of a mature RNA molecule.

Transcription

process by which messenger RNA is synthesized from a DNA template resulting in the transfer of genetic information from the DNA molecule to the messenger RNA.

RNA Polymerase

Separating the two strands of DNA in to two at the start of DNA transcription.

Sense strand

The strand that you want a copy of during transcription.

Antisense Strand

The strand that is used for a template for transcription.

Post transcriptional modification

The removal of the introns leaving the coding regions for a gene.

transcription factors

Collection of proteins that mediate the binding of RNA polymerase and the initiation of transcription.

transcription regulators

bind to DNA to switch genes on or off

Telomeres

Repeated DNA sequences at the ends of eukaryotic chromosomes.

Directionality of DNA

Transcription occurs in the 5' to 3' direction

rRNA

ribosomal RNA; type of RNA that makes up part of the ribosome

tRNA

transfer RNA; type of RNA that carries amino acids to the ribosome

pre-mRNA

a form of messenger RNA that contains both introns and exons

mature mRNA

The final product that results when the pre-mRNA in eukaryotes undergoes processing events before it exits the nucleus

5' cap

The 5' end of a pre-mRNA molecule modified by the addition of a cap of guanine nucleotide.

poly-A tail

Modified end of the 3' end of an mRNA molecule consisting of the addition of some 50 to 250 adenine nucleotides.

spliceosome

A large complex made up of proteins and RNA molecules that splices RNA by interacting with the ends of an RNA intron, releasing the intron and joining the two adjacent exons.

alternative splicing

Splicing of introns in a pre-mRNA that occurs in different ways, leading to different mRNAs that code for different proteins or protein isoforms. Increases the diversity of proteins.

initiation of translation

mRNA is attached to a subunit of the ribosome, the first codon is always AUG

elongation (translation)

codon recognition, peptide bond formation, translocation

termination of translation

occurs when a stop codon in the mRNA reaches the A site of the ribosome

start codon

AUG (methionine)

initiator tRNA

Special tRNA that initiates the translation of an mRNA in a ribosome. It always carries the amino acid methionine.

A site of ribosome

acceptor site holds the tRNA that carries the next amino acid to be added to the chain

P site of ribosome

the processing site, holds the tRNA carrying the growing polypeptide chain

E site of ribosome

the exit site, where discharged tRNAs leave the ribosome

Golgi apparatus

A system of membranes that modifies and packages proteins for export by the cell

post tranlational modification

covalent processing events that change the properties of a protein by proteolytic cleavage and adding a modifying group, such as acetyl, phosphoryl, glycosyl and methyl, to one or more amino acids

pre-proinsulin

an inactive precursor molecule of insulin that includes a signal peptide

Proinsulin

precursor of insulin

Proteasomes

A giant protein complex that recognizes and destroys proteins tagged for elimination by the small protein ubiquitin.

Proteome

the entire set of proteins expressed by a given cell or group of cells