8.5 Translation
KEY CONCEPT
Translation converts an mRNA message into a
polypeptide, or protein.
8.5 Translation
Amino acids (protein building blocks) are coded for by
mRNA base sequences.
• A codon is a sequence of three nucleotides that codes for
an amino acid.
codon for
methionine (Met)
codon for
leucine (Leu)
8.5 Translation
• The genetic code matches each codon to its amino acid or
function.
The genetic code matches each RNA codon with its amino acid or function.
– three stop codons
signal the end of a
chain of amino
acids.
– one start codon,
codes for
methionine and to
start translation
8.5 Translation
• Reading frame: multiple codons that code for a chain of
amino acids
• A change in the order in which codons are read changes
the resulting protein – this is why having a clear “start”
and “stop” is important
• Common (universal) language: Regardless of the
organism, codons code for the same amino acid.
8.5 Translation
Amino acids are linked to become a protein.
• An anticodon is a set of three nucleotides that is
complementary to an mRNA codon.
• An anticodon is carried by a tRNA. tRNA carries amino
acids from cytoplasm to the ribosome to become part of
the growing protein.
EXAMPLE:
mRNA codon=GUU
tRNA anticodon=CAA
Amino acid=Valine
8.5 Translation
• Ribosomes are the site of protein synthesis. They are
located in the cytoplasm & on the rough ER.
• Ribosomes are made of rRNA & proteins. They have a
large & small subunit.
• Helps form peptide bonds between amino acids.
8.5 Translation
1. For translation to begin, tRNA binds to a start codon (Met in
picture) and signals the ribosome to assemble.
– A complementary tRNA molecule binds to the exposed
codon (Leu in picture), bringing its amino acid close to
the first amino acid.
8.5 Translation
2. The ribosome helps form a polypeptide bond between
the amino acids.
The ribosome pulls the mRNA strand the length of one
codon.
8.5 Translation
3. The now empty tRNA molecule exits the ribosome.
– A complementary tRNA molecule binds to the next
exposed codon.
– Once the stop codon is reached, the ribosome
releases the protein and disassembles.
8.5 Translation
8.5 Translation
8.5 Translation
Describe how the processes of transcription and
translation are similar in all organisms.
Both prokaryotes and eukaryotes have DNA and follow the
same base pairing rules, so they both can change DNA into
RNA. The big difference here is that Eukaryotes carry out
transcription in the nucleus, prokaryotes carry it out in the
cytoplasm because they have NO nucleus.
Translation occurs at the site of a ribosome. Since both cell
types have ribosomes, ALL living things go through
translation aka protein synthesis.
• https://www.youtube.com/watch?v=K2_uB7ybfYM