1. Copyright Pearson Prentice Hall
12–3 RNA and Protein Synthesis
Copyright Pearson Prentice Hall

2. Copyright Pearson Prentice Hall
What is RNA?
Ribonucleic acid.. It too like DNA is a nucleic acid!
RNA contains codes for making proteins (body tissues such as muscle, hair, enzymes, etc..)
Copyright Pearson Prentice Hall

3. Let’s compare RNA to DNA
Deoxyribose
Sugar
Ribose
A, T, G, C
Nitrogenous Bases
A, U, G, C
Double
Strands
Single
Nucleus
Location
Anywhere in cell

4. Copyright Pearson Prentice Hall
3 Types of RNA
Messenger mRNA
Ribosomal rRNA
Transfer tRNA
Copyright Pearson Prentice Hall

5. The three main types of RNA are messenger RNA, ribosomal RNA, and transfer RNA.
Messenger RNA (mRNA) Makes a copy of DNA. Every 3 letters on an mRNA is a codon (we will get there, don’t worry )

6. ribosomal RNA (rRNA) are what ribosomes are made of.
The three main types of RNA are messenger RNA, ribosomal RNA, and transfer RNA. Ribosomal RNA is combined with proteins to form ribosomes.
ribosomal RNA (rRNA) are what ribosomes are made of.

7. Copyright Pearson Prentice Hall
Types of RNA
The three main types of RNA are messenger RNA, ribosomal RNA, and transfer RNA.
transfer RNA (tRNA) Carry or “transfer” amino acids to the ribosome.
Copyright Pearson Prentice Hall

8. Copyright Pearson Prentice Hall
The Genetic Code
The genetic code is the “language” of mRNA instructions.
The code is written using four “letters” (the bases: A, U, C, and G).
Copyright Pearson Prentice Hall

9. Copyright Pearson Prentice Hall
The Genetic Code
A codon consists of three consecutive nucleotides on mRNA that specify a particular amino acid.
A codon is a group of three nucleotides on messenger RNA that specify a particular amino acid.
Copyright Pearson Prentice Hall

10. For Example… Consider the following RNA sequence: UCGCACGGU
This sequence would be read 3 bases at a time as:
UCG-CAC-GGU
The codons represent the different amino acids:
Serine-Histidine-Glycine
Copyright Pearson Prentice Hall

11. Because there are 4 different bases….
There are 64 possible 3-base codons (4 x 4 x 4 = 64).
Look at Figure in your book on pg. 303.
This shows all 64 possible codons of the genetic code.
See mRNA Codon/Amino Acid Chart Handout!!!
Copyright Pearson Prentice Hall

12. Looking at Figure 12-17….
As you can see, some amino acids can be specified by more than one codon.
For example, 6 different codons specify the amino acid Leucine and 6 others specify Arginine.
There is also one codon, AUG, that can either specify methionine or serve as the initiation, or “start” codon for protein synthesis.
Copyright Pearson Prentice Hall

13. See if you can figure this out…
What amino acid is specified by CAU?
What is the codon for tryptophan?
What are two possible codons for glutamine?
What amino acid is usually the first amino acid of a protein? How do you know?
Copyright Pearson Prentice Hall

14. Video Time

15. So… What the heck is protein synthesis?
Copyright Pearson Prentice Hall

16. Step 1 of Protein Synthesis
Transcription: mRNA is transcribed from DNA in the nucleus and released into the cytoplasm
Copyright Pearson Prentice Hall

17. Step 2 of Protein Synthesis
Translation: mRNA attaches to a ribosome and an amino acid is brought by a tRNA to the mRNA.
Copyright Pearson Prentice Hall

18. It works like an assembly line
Lysine
tRNA
During translation, or protein synthesis, the cell uses information from messenger RNA to produce proteins. The cell uses all three main forms of RNA during this process.
mRNA
Translation direction
Ribosome
Copyright Pearson Prentice Hall

19. Copyright Pearson Prentice Hall
-The process continues until the ribosome reaches a stop codon. -It then releases the newly formed polypeptide (which creates a protein) and the mRNA molecule completes the process of translation.
Polypeptide
Ribosome
tRNA
During translation, or protein synthesis, the cell uses information from messenger RNA to produce proteins. The cell uses all three main forms of RNA during this process.
Copyright Pearson Prentice Hall
mRNA

20. Why do we care about what protein synthesis does?
Proteins determine eye color, hair color, etc...
Copyright Pearson Prentice Hall

21. Copyright Pearson Prentice Hall
RNA Editing
Some DNA within a gene is not needed to produce a protein. These areas are called introns.
The DNA sequences that code for proteins are called exons.
Copyright Pearson Prentice Hall

22. Copyright Pearson Prentice Hall
12–3
Copyright Pearson Prentice Hall

23. Copyright Pearson Prentice Hall
12–3
A base that is present in RNA but NOT in DNA is
thymine.
uracil.
cytosine.
adenine.
Copyright Pearson Prentice Hall

24. Copyright Pearson Prentice Hall
12–3
The nucleic acid responsible for bringing individual amino acids to the ribosome is
transfer RNA.
DNA.
messenger RNA.
ribosomal RNA.
Copyright Pearson Prentice Hall

25. Copyright Pearson Prentice Hall
12–3
A region of a DNA molecule that indicates to an enzyme where to bind to make RNA is the
intron.
exon.
promoter.
codon.
Copyright Pearson Prentice Hall

26. Copyright Pearson Prentice Hall
12–3
A codon typically carries sufficient information to specify a(an)
single base pair in RNA.
single amino acid.
entire protein.
single base pair in DNA.
Copyright Pearson Prentice Hall