Transcription and Translation Flashcards
What is transcription?
Transcription and Translation
An mRNA copy of a gene is made from DNA
In eukaryotes this happens in the nucleus
In prokaryotes it’s in the cytoplasm
s1. RNA polymerase attaches to DNA
Transcription and Translation
RNA polymerase attaches to DNA double-helix at beginning of gene
Hydrogen bonds between the 2 strands are broken down
Strands seperate and DNA molecule uncoils, exposing some bases
One strand is used as a template to make an mRNA copy
s2. Complementary mRNA is formed
Transcription and Translation
RNA polymerase lines up free RNA nucleotides alongside exposed bases on template strand
Free bases are attracted to exposed bases
Specific, complementary base pairing means that mRNA strand ends up being a complementary copy of the template strand
Once RNA nucleotides have paired up with specific bases on DNA strand, they are joined by RNA polymerase, forming an mRNA strand
s3. RNA polymerase moves down the DNA strand
Transcription and Translation
RNA polymerase moves along DNA, assembling mRNA strand
Hydrogen bonds between uncoiled strands of DNA reform once RNA polymerase passes and strans coil back into double helix
s4. RNA polymerase reaches stop signal
Transcription and Translation
When RNA polymerase reaches a stop signal, it stopes making mRNA and detaches from DNA
In eukaryotes, mRNA moves out of nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm
What is splicing?
Transcription and Translation
The process which removes introns from pre-mRNA, forming mRNA strands
Takes place in nucleus
Splicing doesn’t occur in prokaryotes as they have no introns
What is translation?
Transcription and Translation
Amino acids are joined together to make a polypeptide chain, following the sequence of codon carried by mRNA
Translation occurs at ribosomes
s1. mRNA attaches to a ribosome
Transcription and Translation
mRNA attaches itself to a ribosome and tRNA molcules carry amino acids to it
ATP provides energy needed for bond between amino acid and tRNA molecule to form
s2. Complementary anticodons
Transcription and Translation
A tRNA molecules (carry an amino acid) with an anticodon that’s complementary to the first codon on the mRNA attaches to mRNA by complementary base pairings
A second tRNA molecules attaches to next codon in same way
s3. Peptide bonds are formed
Transcription and Translation
The 2 amino acids attached to the tRNA molecules are joined by a peptide bond
The 1st tRNA molecule moves away, leaving its amino acid behind
s4. A polypeptide chain is formed
A 3rd tRNA molecule binds to next codon on mRNA
Its amino acid binds to the first two and the 2nd tRNA molecules moves away
This process continues, producing a chain of linked amino acids until there is a stop signal on the mRNA molecule
Polypeptide chain moves away from ribosome and translation is complete
