There are several kinds of RNA
Messenger RNA (mRNA):
Conveys genetic information from DNA to the ribosomes
Transfer RNA (tRNA):
Transfers amino acids to the ribosomes during translation.
Ribosomal RNA (rRNA):
Provides structure and enzyme activity for ribosomes
mRNA undergoes further processing & leaves the nucleus
A Codon is the 3 letter nucleotide sequence of
mRNA that encodes for 1 amino acid.
AUG is the first codon in protein synthesis, so it’s
it’s called the start codon
The codon sequence of mRNA
determines the amino acid
sequence of a protein.
The start codon marks the site at which translation
into protein sequence begins, and the stop
codon marks the site at which translation ends.
Clover-leaf shape RNA with 2 important regions
Small particle of protein & ribosomal RNA (rRNA)
Ribosomes have 2 subunits
Large subunit holds tRNA & amino acids
Small subunit binds to mRNA
Small subunit has 2 binding sites for adjacent mRNA codons
Ribosomes link amino acids by peptide bonds
Peptide bond forming
Binding sites with codons
1. mRNA binds to the small subunit of a Ribosome.
2. The ribosome ‘reads’ the mRNA sequence
3. tRNA brings amino acids to the ribosomes,
aligning their anticodons with mRNA codons
4. The Ribosome links the amino acids together
5. Polypeptide chain lengthens
Figure 4.23 overview of protein synthesis
Once translation is complete chaperone proteins
fold the protein into its configuration
enzymes may further modify proteins after translation
phosphorylation – adding a phosphate to the protein
glycosylation – adding a sugar to the protein
End of Chapter 4
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