protein synthesis Flashcards
what are the 3 steps of protein synthesis?
transcription
splicing (only in eukaryotic cells)
translation
where does each of the 3 steps of protein synthesis take place?
- Transcription- nucleus
- Splicing- nucleus
- Translation- ribosomes
what is the first step of transcription?
DNA uncoils and unzips along the length of one gene. This requires DNA helicase
what is the role of DNA helicase in transcription?
needed to uncoil and unzip DNA as breaks the hydrogen bonds between nucleotide bases break along the length of one gene
causes the two strands to separate
how many strands of the DNA is used as the template strand?
only one strand (called the sense strand)
what comes in to the template strand?
Free RNA nucleotides that complementary base pair with the strand of DNA.
U pairs with A and C with G. If T is present it pairs with A.
what is the role of RNA polymerase in transcription?
catalyses the formation of phosphodiester bonds required to join the nucleotides in the pre-mRNA together
(forms sugar phosphate backbone)
what happens to the molecule of pre-mRNA formed and the DNA?
detaches from the sense strand
DNA re-coils and re-zips
why does splicing only occur in eukaryotic cells?
prokaryotic DNA does not have introns
what is splicing?
process of introns being cut out of the pre-mRNA and exons joined together
what does splicing produce?
mRNA from pre-mRNA
what happens to the mRNA in translation?
moves out of the nucleus via a nuclear pore
attaches to a ribosome which covers two codons
what does the first specific tRNA molecule do in translation?
brings in the first specific amino acid
the anticodon of the tRNA molecule complementary base pairs with the codon of the mRNA
this process repeats with the second specific tRNA
how do the first two amino acids join?
a condensation reaction occurs to form a peptide bond between the amino acids. This requires energy from ATP
what happens after the first two amino acids join?
the ribosome moves on one codon
and the first tRNA molecule detaches and moves to the cytoplasm where it can pick up its specific amino acid to be used again
(energy from ATP required to attach the amino acid to the tRNAs amino acid binding site
the process of specific tRNA molecules coming in continues until…
the stop codon is reached
mRNA then detaches rom the ribosome and the polypeptide produced can fold into a protein with a 3D shape (tertiary structure)
