1. Chapter 17 Protein Translation (PART 4)
From Gene to Protein
AP Biology
Ms. Gaynor

2. mRNA  polypeptide (protein)
Translation
mRNA  polypeptide (protein)

3. tRNA
A cell translates mRNA message into protein with help from transfer RNA (tRNA)
Type of RNA
~80 nucleotides
“t” shape
Carries amino acids
Matches codons to
anticodons

4. tRNA Molecules of tRNA are not all identical
Each carries a specific amino acid
Each has an specific anticodon on the other end
Aminoactyl tRNA Synthase (enzyme) puts tRNA together with it amino acid

5. Aminoactyl tRNA Synthase
tRNA Assembly
Aminoactyl tRNA Synthase
ACTIVATED tRNA

6. Ribosomes
Help bind tRNA anticodons with mRNA codons during translation
Found on ROUGH Endoplasmic Reticulum RER (“bound”) or in cytoplasm (“free”)
Anticodon (tRNA) = codon (mRNA)

7. tRNA
(with anticodons)
mRNA
(with codons)

8. Ribosomes There are 2 ribosomal subunits
Constructed of proteins and ribosomal RNA or rRNA

9. Binding Sites in a Ribosome
The ribosome has three binding sites for tRNA
The P site
The A site
The E site
P site (Peptide Bond-tRNA
binding site)
E site
(Exit site)
mRNA
binding site
A site (Amino acid-
tRNA binding site)
Large
subunit
Small E P A

10. tRNA mRNA Growing polypeptide Amino acid Next amino acid
to be added to
polypeptide chain
tRNA
mRNA
Codons 3 5 \

11. Building a Polypeptide
Translation can be divided into 3 phases
Initiation
Elongation
Termination

12. Initiation of Translation
initiation stage brings together
mRNA
tRNA bearing 1st amino acid (“start”) called MET
2 subunits of a ribosome come together

13. Translation initiation complex
Large
ribosomal
subunit
Initiator tRNA
mRNA
mRNA binding site
Small
Translation initiation complex
P site
GDP
GTP
Start codon
Met U A C G E 3 5
Figure 17.17

14. Elongation
Amino acids are added one by one to the preceding amino acid
Peptide bonds are formed
Amino acid

16. Termination of Translation
When the ribosome reaches a stop codon on the mRNA
There are 3 stop codons
UAA, UAG, and UGA
Release factor (protein) binds to stop codon in A site (NOT tRNA)  polypeptide released

17. Termination of Translation
Release
factor
Free
polypeptide
Stop codon
(UAG, UAA, or UGA) 5 3

18. Phe tRNA Anticodon 5 3 Amino acids “EMPTY” tRNA tRNA with amino acid
TRANSCRIPTION
TRANSLATION
DNA
mRNA
Ribosome
Polypeptide
Amino
acids
tRNA with
amino acid
attached
tRNA
Anticodon
Trp
Phe
Gly A G C U
Codons 5 3
“EMPTY”
tRNA
Figure 17.13

19. Polyribosomes

20. Polypeptide  3D Protein
Primary Structure
Amino acids is a row (LINEAR)
Secondary Structure
Amino Acids BEND and FOLD towards each other
Tertiary Structure
Amino acids BIND to each other
3D shape made
Quartnary structure (only some)
2 or more polypeptides BIND to each other

21. 1 2 4 3

22. Completing and Targeting the Functional Protein
Polypeptide chains undergo modifications after the translation process
Proteins may be modified in ways that affect their three-dimensional shape

23. PROTEINS THAT LEAVE THE CELL…
Proteins destined for the endomembrane system or for secretion (ROUGH ER)
Must be transported into the ER
Have signal peptides to which a signal-recognition particle (SRP) binds, enabling the translation ribosome to bind to the ER

24. The signal mechanism for targeting proteins to the ER

25. Translation (Protein Synthesis) Animation

26. What happens to proteins?

27. RNA plays multiple roles in the cell: a review
Can H-bond to other nucleic acid molecules
Can assume a specific 3-D shape
Has functional groups that allow it to act as a catalyst

28. Types of RNA in a Eukaryotic Cell

29. What is a gene? REVIEW A gene
region of DNA  final product either a polypeptide OR an RNA molecule
Genes determines 1º structure
1º determines 2º and 3º structure

30. Key differences in gene expression in prokaryotes & eukaryotes
Prokaryotic cells
NO nucleus
Allowing translation to begin while transcription is still in progress
Eukaryotic cells
The nuclear envelope separates transcription from translation
Extensive RNA processing occurs in the nucleus
Polyadenylation signal = termination signal on DNA