protein synthesis Flashcards
what is mRNA
messenger RNA
a single polynucleotide strand - contains groups of three adjacent bases that are called codons
what does mRNA do?
made during transcription
carries the genetic code from the DNA to the ribosomes, where it’s used to main a protein during translation
what is tRNA
transfer RNA
single polynucleotide strand - folded into a clover shape
hydrogen bonds between specific base pairs hold this shape
molecule that has a specific sequence of three bases - anticodon
they have an amino acid binding site at the other end
what does tRNA do?
carries amino acids hat are used to make proteins in translation to the ribosomes
what is the first stage of protein synethesis
transcription
what is the first stage of transcription
RNA polymerase (enzyme) attaches to the DNA double-helix at the beginning of the gene
what is the second stage of transcription
in eukaryotes, the hydrogen bonds between the two DNA strands in the gene are broken by a DNA helicase attached to the RNA polymerase. This separates the strands and the DNA molecule uncoils at that point, exposing some of the bases
what is the third stage of transcription
one of the strands is then used as a template to make an mRNA copy
what is the fourth stage of transcription
the RNA polymerase lines up free RNA nucleotides alongside the exposed bases on the template strand
the free bases are attracted to the exposed bases
specific, complementary base pairing means that the mRNA strand ends up being a complementary copy of the DNA template strand
what is the fifth stage of transcription
once the RNA nucleotides have paired up with their specific bases on the DNA strand, they’re joined together by the RNA polymerase, forming an mRNA molecule
what is the sixth stage of transcription
the RNA polymerase moves along the DNA, separating the strands and assembling the mRNA strand
what is the seventh stage of transcription
the hydrogen bonds between the uncoiled strands of DNA re-form once the RNA polymerase has passed by and the strands coil back into a double-helix
what is eighth stage of transmission
when RNA polymerase reaches a particular sequence of DNA called a stop signal, it stops making mRNA and detaches from the DNA
what is the ninth stage of transcription
un eukaryotes, mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm, where the next stage of protein synthesis takes place
what are the different products from transcription in eukaryotes and prokaryotes
eukaryotes
- introns and exons are copied into the mRnA during transcription
- mRNA strands containing introns and exons are called pre-mRNA
- splicing occurs where introns are removed and exons are joined together forming mRNA strands
prokaryotes
- mRNA is produced directly from the DNA without splicing