y5 bio: cluster 3 (protein synthesis)

what is the central dogma of molecular biology?

DNA is transcribed into RNA, which is then translated into a polypeptide chain, that can be made into structural protein or enzyme

4 big processes of protein synthesis

transcription, post-transcription process, translation, post-translation process

what happens during transcription?

RNA polymerase synthesises an RNA molecule using a DNA template strand

what is mRNA?

an RNA transcript that carries genetic code from the nucleus to ribosomes for translation

what is tRNA?

a cloverleaf-shaped RNA that carries specific amino acids to the ribosome based on anticodon pairing

what is rRNA?

the primary RNA component that provides catalytic and structural framework for ribosomes

what is the difference between the sense and anti-sense strands?

sense strand matches the mRNA sequence (with T instead of U) + is from 5’ to 3’. anti-sense strand acts as the complementary template (also using T, no U) + is from 3’ to 5’.

transcription is the most important (_____) for gene expression

control point (if transcription increases, translation increasesm GE also increases)

what happens during translation?

ribosomes synthesises a polypeptide chain with its amino acid sequence determined by base sequence of mRNA

where does translation occur?

at the ribosomes in the cytoplasm and/or RER

what is a codon?

a triplet of 3 consecutive bases on mRNA that codes for a particular amino acid, or signals start/stop of translation

what is an anticodon?

a sequence of 3 complementary bases at one end of tRNA molecule. it pairs with the mRNA codon via hydrogen bonds during translation

why is the genetic code called degenerate and whats the advantage of it?

cuz multiple different codons can code for the same amino acid. its good cuz it can protect against harmful same-sense mutations, as same amino acid is produced

why is the genetic code considered unambiguous?

cuz any single given codon specifies only one specific amino acid

start and stop codons?

start: AUG stop: UAA, UAG, UGA

what are the main structural components of a eukaryotic ribosome?

small subunit, large subunit, mRNA binding site, and three tRNA sites (aminoacyl site, peptidyl site, exit site).

what happens at the Aminoacyl (A) site of a ribosome?

incoming tRNA carrying an amino acid binds to the complementary mRNA codon

what occurs at the Peptidyl (P) site of a ribosome?

holds the tRNA attached to the growing polypeptide chain while peptide bonds form

what is the purpose of the Exit (E) site on a ribosome?

uncharged tRNA moves here after donating its amino acid and exits the ribosome

what steps repeat during the elongation phase of translation?

tRNA binding at a site, peptide bond formation, and translocation of ribosome, where ribosome shifts one codon (3 bases) in the 5’ to 3’ direction

how does translation terminate?

a release factor binds to a stop codon in the a site, causing the polypeptide chain and ribosome complex to disassemble.

how does sickle cell mutation happen?

1. normal HbA changed to sickle cell HbS 2. GAG codon changed to GTG codon 3. mRNA GAG codon changed to mRNA GUG codon 4. Glu hydrophilic amino acid change to Val hydrophobic amino acid, causing haemoglobin to aggregate under low oxygen and distort red blood cells

how is the initiation of translation in prokaryotes and eukaryotes different?

eukaryote needs transcription factors to recruit RNA polymerase but prokaryotes dont need (they just start with RNA polymerase binding to promoter)

what is post-translational modification?

polypeptides are chemically and structurally modified before becoming functional proteins

first and second phade of post-translational modification?

first phase uses these 4 steps of: side chain changes, folding, (both steps in RER) cleavage and quaternary structure (both steps in golgi). second phase recycles free amino acid for new protein synthesis

how are polypeptides modified to become functional?

proteolysis (cleaving the polypeptide), glycosylation (adding sugars), phosphorylation (adding phosphate groups to alter shape)

what’s proteasome’s role in amino acid recycling (2nd phase of post translational modification)?

they degrade selected, ubiquitin tagged proteins to maintain the cell’s functional protein pool