Download Protein Synthesis

Section 12-3
Interest Grabber
•
Information, Please
•
DNA contains the information that a cell needs to carry out all of its functions.
In a way, DNA is like the cell’s encyclopedia. Suppose that you go to the library
to do research for a science project. You find the information in an
encyclopedia. You go to the desk to sign out the book, but the librarian informs
you that this book is for reference only and may not be taken out.
1. Why do you think the library holds some books for reference only?
2. If you can’t borrow a book, how can you take home the information in it?
3. All of the parts of a cell are controlled by the information in DNA, yet DNA
does not leave the nucleus. How do you think the information in DNA might
get from the nucleus to the rest of the cell?
Go to
Section:
Protein Synthesis
• Occurs in 2 steps:
• In nucleus- Transcription
• In cytoplasm/ ribosomesTranslation
Concept Map
Section 12-3
RNA
can be
Messenger RNA
also called
which functions to
mRNA
Go to
Section:
Ribosomal RNA
Carry instructions
also called
which functions to
rRNA
Combine
with proteins
from
to
to make up
DNA
Ribosome
Ribosomes
Transfer RNA
also called
which functions to
tRNA
Bring
amino acids to
ribosome
Figure 12–14 Transcription
Section 12-3
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA
polymerase
RNA
Go to
Section:
DNA
Figure 12–17 The Genetic Code
Section 12-3
Go to
Section:
Figure 12–18 Translation
Section 12-3
Nucleus
Messenger RNA
Messenger RNA is transcribed in the nucleus.
Phenylalanine
tRNA
The mRNA then enters the cytoplasm and attaches
to a ribosome. Translation begins at AUG, the start
codon. Each transfer RNA has an anticodon whose
bases are complementary to a codon on the mRNA
strand. The ribosome positions the start codon to
attract its anticodon, which is part of the tRNA that
binds methionine. The ribosome also binds the
next codon and its anticodon.
Ribosome
Go to
Section:
mRNA
Transfer RNA
Methionine
mRNA
Lysine
Start codon
Figure 12–18 Translation (continued)
Section 12-3
The Polypeptide “Assembly Line”
The ribosome joins the two amino acids—
methionine and phenylalanine—and breaks the
bond between methionine and its tRNA. The tRNA
floats away, allowing the ribosome to bind to
another tRNA. The ribosome moves along the
mRNA, binding new tRNA molecules and amino
acids.
Lysine
Growing polypeptide chain
Ribosome
tRNA
tRNA
mRNA
Completing the Polypeptide
mRNA
Ribosome
Go to
Section:
Translation direction
The process continues until the ribosome reaches one
of the three stop codons. The result is a growing
polypeptide chain.