1. RNA and Protein Synthesis
Section 12–3
This section describes RNA and its role in transcription and translation.

2. The Structure of RNA
List the three main differences between RNA and DNA.
RNA has ribose sugar instead of deoxyribose.
RNA is generally single-stranded, instead of double-stranded.
RNA contains uracil in place of thymine.

3. Types of RNA
All types control protein synthesis in a cell
3 main types
- mRNA = messenger RNA
copies of instructions from DNA
- rRNA = ribosomal RNA
part of ribosomes
- tRNA = transfer RNA
transfers amino acids to ribosome

4. Bring amino acids to ribosome
RNA
can be
Messenger RNA
Ribosomal RNA
Transfer RNA
also called
which functions to
also called
which functions to
also called
which functions to
mRNA
Carry instructions
rRNA
Combine
with proteins
tRNA
Bring amino acids to ribosome
from to
to make up
DNA
Ribosome
Ribosomes

5. What is the importance of the cell’s ability to copy a single DNA sequence into RNA?
It makes it possible for a single gene to produce large numbers of RNA molecules.

6. POP QUIZ- Purpose of RNA
Is the following sentence true or false?
RNA is like a disposable copy of a DNA segment.
True

7. POP QUIZ- Types of RNA
What is the one job in which most RNA molecules are involved?
Most are involved in protein synthesis.

8. The Central Dogma

9. Figure 12–14 Transcription
Transcription = process of copying part of DNA into a complementary strand of RNA
run by enzyme called RNA polymerase
RNA
DNA
RNA polymerase
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)

10. POP QUIZ- Transcription
Circle the letter of each sentence that is true about transcription.
b. RNA polymerase uses one strand of DNA as a template to assemble a strand of RNA.
c. RNA polymerase binds only to DNA promoters, which have specific base sequences.

11. Translation
Translation = the decoding of an mRNA message into a polypeptide chain (protein)
Occurs on ribosomes

12. Process:
- mRNA binds to ribosome
- tRNA brings appropriate amino acid to ribosome
tRNA has anticodon that is complementary to codon on mRNA; begins with specific start codon - AUG
- peptide bonds are made between amino acids
- assembly line continues until a stop codon

13. Proteins are chains of amino acids - 20 different amino acids
The Genetic Code
Proteins are chains of amino acids
- 20 different amino acids
- the order of amino acids determines properties of the protein
- codon = 3 consecutive nucleotides that specify a single amino acid
- one amino acid can have multiple codons A U G C
mRNA
start
codon
codon 2
codon 3
codon 4
codon 5
codon 6
codon 7
codon 1

14. RNA Editing
Many RNA molecules from eukaryotic genes have sections, called _____, edited out of them before they become functional. The remaining pieces, called, _________are spliced together.
Introns
Exons

15. RNA Editing
What are two explanations for why some RNA molecules are cut and spliced?
It makes it possible for a single gene to produce several different forms of RNA.
It may play a role in evolution, making it possible for small changes in DNA to have dramatic effects in gene expression.

16. POP QUIZ- RNA Editing Is the following sentence true or false?
RNA editing occurs in the cytoplasm of the cell.
False

17. REVIEW - Translation Four Major Steps
A. Messenger RNA is transcribed in the nucleus then enters the cytoplasm and attaches to a ribosome.
B. Transfer RNA translation begins at AUG, the start codon. Each anti-codon of tRNA complements a codon of mRNA and binds a specific amino acid.

18. Translation Four Major Steps cont.
C. The polypeptides form an “assembly line.” As the codons bind amino acids the ribosome joins them together forming long chains of amino acids.
D. Completing the Polypeptide- the process continues until one of three stop codons is reached.

19. Why bother?
Transcription and translation keep master plans (DNA) safe in the nucleus, while blueprints (RNA) are sent to the worksite (ribosomes)
Proteins are needed to act as enzymes that produces the color of your skin, the type of blood cell, the rate of growth

20. POP QUIZ- The Genetic Code
Proteins are made by joining ________into long chains called polypeptides.
Amino acids

21. The Genetic Code
How can only four bases in RNA carry instructions for 20 different amino acids?
The genetic code is read three letters at a time, so that each “word” of the coded message is three bases long.

22. The Genetic Code What is a codon?
It consists of three consecutive nucleotides that specify a single amino acid that is to be added to a polypeptide.

23. RNA Decoding Chart

24. The Genetic Code
Circle the letter of the number of possible three-base codons. 4 12
c. 64
d. 128

25. The Genetic Code Is the following sentence true or false?
All amino acids are specified by only one codon.
False

26. The Genetic Code
Circle the letter of the codon that serves as the “start” codon for protein synthesis.
a.UGA
b.UAA
c. UAG
d. AUG

27. Translation What occurs during the process of translation?
The cell uses information from messenger RNA to produce proteins.

28. Where does translation take place?
Translation takes place on the ribosomes.

29. Circle the letter of each sentence that is true about translation.
Before translation occurs, messenger RNA is transcribed from DNA in the nucleus.
It is the job of transfer RNA to bring the proper amino acid into the ribosome to be attached to the growing peptide chain.
When the ribosome reaches a stop codon, it releases the newly formed polypeptide and the mRNA molecule.

30. What is an anticodon?
The three bases on a tRNA molecule that are complementary to one of the mRNA codons.

31. The Roles of RNA and DNA Match the roles with the molecules. Roles
Master plan - DNA
Goes to the ribosomes in the cytoplasm - RNA
Blueprint – RNA
Remains in the nucleus - DNA

32. Genes and Proteins
Many proteins are_____, which catalyze and regulate chemical reactions.
Enzymes

33. Is the following sentence true or false?
Genes are the keys to almost everything that living cells do.
false