protein synthesis

1. Section 5, Chapter 4
Transcription & Translation

4. 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
4

5. Messenger RNA (mRNA):
Delivers genetic information from the DNA inside the nucleus to
the cytoplasm
mRNA is formed beside a strand of DNA
RNA nucleotides are complementary to DNA nucleotides with
one exception – no thymine in RNA; replaced with uracil)
mRNA
DNA
S
P
A
U
T
A
G
C
C
G
G
C
P
Direction of “reading” code
S
S
P
P
S
S
P
P
S
S
P
P
S
S
P
S
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P

6. 5.
mRNA undergoes further processing & leaves the nucleus

7. 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

8. Protein Synthesis
The codon sequence of mRNA
determines the amino acid
sequence of a protein.
Figure 4.23

9. The start codon marks the site at which translation
into protein sequence begins, and the stop
codon marks the site at which translation ends.
amino acid

11. tRNA
Clover-leaf shape RNA with 2 important regions
Amino acid
binding site
Anticodon

12. Ribosomes
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

13. Ribosomes
Peptide bond forming
large subunit
anticodons
small subunit
Binding sites with codons

14. 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

15. Anchors polypeptide.

16. tRNA released

17. Figure 4.23 overview of protein synthesis
TRANSCRIPTION

18. Once translation is complete chaperone proteins
fold the protein into its configuration
post-translational modification
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