View
212
Download
0
Category
Preview:
Citation preview
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.
Section 12-3
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/ ribosomes-
Translation
from to to make up
Concept MapSection 12-3
also called which functions to also called also called which functions towhich functions to
can be
RNA
Messenger RNA Ribosomal RNA Transfer RNA
mRNA Carry instructions rRNACombine
with proteins tRNABring
amino acids toribosome
DNA Ribosome Ribosomes
Go to Section:
RNADNA
RNApolymerase
Figure 12–14 TranscriptionSection 12-3
Adenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)
Go to Section:
Figure 12–17 The Genetic CodeSection 12-3
Go to Section:
Messenger RNA Messenger RNA is transcribed in the nucleus.
Transfer RNAThe 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.
mRNA Start codon
Ribosome
Methionine
Phenylalanine tRNALysine
Nucleus
Figure 12–18 TranslationSection 12-3
mRNA
Go to Section:
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.
mRNARibosome
Translation direction
Lysine tRNA
tRNA
Ribosome
Growing polypeptide chain
mRNA
Completing the PolypeptideThe process continues until the ribosome reaches one of the three stop codons. The result is a growing polypeptide chain.
Figure 12–18 Translation (continued)Section 12-3
Go to Section:
Recommended