Translation and Protein Synthesis - Video Notes (Vocabulary Flashcards)

Vocabulary flashcards covering key terms related to mRNA, ribosomes, translation initiation/elongation/termination, and protein synthesis.

Open Reading Frame (ORF)

Region of mRNA that is translated; allows for codon optimization, sequence modifications, and protein expression

Untranslated Region (UTR)

Regulatory elements around the ORF to modulate translation efficiency; includes 5’ cap, poly-A tail, and 5’ and 3’ UTRs

ribosome structure

Includes a large and small subunit, made up mostly of rRNA, with a small number of proteins. Includes a P-site tRNA, A-site tRNA, and mRNA

anticodon

Three-nucleotide sequence in tRNA that base-pairs with a codon on mRNA antiparallel via hydrogen bonding.

wobble

When several codons specify one AA, the difference is typically at position 3, allowing for certain tRNAs to recognize more than one codon. Some tRNA anticodons include inosinate (I), which can form weak hydrogen bonds with A, U, and C

degeneracy of the genetic code

Most amino acids are encoded by more than one codon; redundancy in the code.

Shine-Dalgarno sequence

Prokaryotic initiation signal in mRNA that base-pairs with 16S rRNA to position the ribosome.

fMet

N-formyl-methionine; inserted at the amino-terminal end by fMet-tRNA in response to the 5’AUG start codon; Met-tRNA inserts methionine in interior positions in response to interior AUG codons.

Kozak sequence

Eukaryotic initiation consensus around the start codon that enhances initiation.

eukaryotic translational initiation complex

Includes eIF4F (EIF4A, EIF4G, eIF4E); 43S (eIF3, small (40S) subunit, eIF2, GTP). mRNA is recruited to EIF4F complex via interaction of 3’ end and poly-A-binding protein (PABP) and the 5’ cap and eIF4E

ribosomal large subunit

60S in eukaryotes, 50S in prokaryotes

ribosomal small subunit

30 S in prokaryotes; 40S in eukaryotes

aminoacyl-tRNA

tRNA charged with its amino acid by an aminoacyl-tRNA synthetase; participates in elongation.

aminoacyl-tRNA synthetase

Enzyme that charges tRNA with its amino acid to form aminoacyl-tRNA using ATP.

Svedberg unit (S)

sedimentation coefficient; rate of sedimentation in a centrifuge

Genetic code

61 codons total; 3 termination codons (UAA, UGA, UAG); 1 start codon (AUG) - also codes for Met

Reading frames

Set when translation of mRNA begins; triplets are codons

Frame shifts

Occurs with the insertion/ deletion of one bp that alters the AA sequence

tRNA

brings amino acids to the ribosome; includes the AA arm, which carries a specific AA esterified by its carboxyl group to the 3’ end of the tRNA, and an anticodon arm containing the anticodon

translation initiation

small subunit with EPA binds to mRNA; tRNA binds at P site at the start codon.

Protein synthesis stages

1. Activation of AAs: tRNA is aminoacylated

2. Initiation: mRNA and aminoacylated tRNA bind to the small ribosomal subunit, then the large subunit binds

3. Elongation: successive cycles of aminoacyl-tRNA binding and polypeptide formation occur until ribosome reaches a stop codon

4. Termination: translation stops when a stop codon is encountered; mRNA and protein dissociate, and ribosomal subunits are recycles

5. Protein folding and posttranslational processing

Missense mutations

A single new base pair replaces another; in the third position, single base subs change the AA only 25% of the time

Silent mutations

the nucleotide is different, but the encoded AA stays the same

transcription factors

Influence transcription of proteins; can increase transcription (activators) or block transcription by blocking RNA Pol (repressors)

operons

A group of genes regulated together, allowing for coordinated gene expression in prokaryotes. “control switches” to turn genes on/ off

lac operons

Operons that control the metabolism of lactose. Includes an activator (CAP) and a repressor (lac repressor). This operon is only on when glucose is absent

lac repressor

physically blocks RNA Pol from binding to promoter when lactose is absent

Allolactose

Binds to lac repressor and changes its conformation, releasing the repressor and allowing RNA Pol to bind when lactose is present

CAP

Binds to the CAP site when glucose is absent in the presence of cAMP; without CAP, there is a low level of transcription if the lac repressor is not bound.

lac operon activation/ repression states

high glucose, no lactose: lac repressor bound; translation off

low glucose, no lactose: CAP and cAMP bound, lac repressor bound; translation off

low glucose, lactose present: CAP and cAMP bound, RNA Pol bound; translation on

high glucose, lactose present: nothing bound; translation on at low level

TRP operon

Group of 5 genes involved in tryptophan synthesis

trpL

Regulatory region in the TRP operon that senses tryptophan levels and influences transcription termination. Multiple binding arrangements are possible between the other 4 genes

Trp 3-4 loop

Terminates translation of tryptophan. This loop is prevented by the ribosome transcribing tryptophan, so translation continues, forming the loop again if the concentration of trp is high. With low trp, ribosome can’t incorporate the AA, stalling the ribosome and binding 2-3, preventing the termination loop: attenuation