1. RNA & Protein Synthesis
12-3

2. Intro
Genes code DNA instructions that control the production of proteins within the cell.
The first step in decoding these genetic messages is to copy DNA into RNA
These RNA molecules contain coded information for making proteins.

3. The Structure of RNA RNA consists of a long chain of nucleotides.
Each nucleotide is made up of
5-carbon sugar
a phosphate group
a nitrogenous base.

4. 3 Differences of RNA & DNA
There are three main differences between RNA and DNA:
The sugar in RNA is ribose instead of deoxyribose
RNA is generally single-stranded
RNA contains uracil in place of thymine.

5. RNA
You can think of an RNA molecule as a disposable copy of a segment of DNA.
RNA molecule is a working copy of a single gene.

6. Types of RNA
RNA molecules have many functions, but in the majority of cells most RNA molecules are involved in just one job—protein synthesis.
The assembly of amino acids into proteins is controlled by RNA.  

7. There are three main types of RNA:
messenger RNA
ribosomal RNA
transfer RNA.

9. Messenger RNA
The RNA molecules that carry copies of protein making instructions are known as messenger RNA (mRNA)
They serve as “messengers” from DNA to the rest of the cell

10. Ribosomal RNA Proteins are assembled on ribosomes
Ribosomes are made up of several dozen proteins and RNA-ribosomal RNA (rRNA)

11. Transfer RNA
During the construction of a protein RNA transfers each amino acid to the ribosome based on the messages in mRNA.
These RNA molecules are known as transfer RNA (tRNA).

12. Checkpoint Ribosomes are made of ribosomal RNA and A.) Transfer RNA
B.) Protein
C.) Messenger RNA

13. Transcription
RNA molecules are produced by copying part of a sequence of DNA into a complimentary sequence in RNA
called transcription.
Transcription requires an enzyme known as RNA polymerase.  

14. Transcription Continued
RNA polymerase
binds to DNA
separates the DNA strands.
RNA polymerase uses one strand of DNA as a template and nucleotides are assembled into a strand of RNA.

16. Promotors
The enzyme will bind only to regions of DNA known as promoters
They have specific base sequences.
Promoters are signals that “tell” enzymes where to bind to make RNA.

17. RNA Editing
Many RNA molecules require editing before they are ready to go into action.
Remember that an RNA molecule is produced by copying DNA.

18. Introns are not involved in protein synthesis
Introns and Exons
Eukaryotic genes contains sequences of nucleotides called introns
Introns are not involved in protein synthesis

19. Introns and Exons Exons are“expressed” in protein synthesis
The DNA sequences that code for proteins are called exons
Exons are“expressed” in protein synthesis
When RNA molecules are formed, both the introns and the exons are copied from the DNA.

20. Introns and Exons The introns are cut out of RNA molecules
The remaining exons are then spliced back

21. Checkpoint
If the introns are not removed from the pre-mRNA, the resulting protein would be
A.) Made correctly
B.) Made incorrectly
C.) Not made at all

22. Why Throw Away RNA?
Some RNA molecules may be cut and spliced in different ways so a single gene can produce several different forms of RNA.
It is thought that introns and exons may play a role in evolution
Small changes in DNA sequences could have dramatic effects in gene expression.

23. Checkpoint Intervening sequences of DNA are known as A.) introns
B.) Exons
C.) Codons

24. The Genetic Code
Proteins are made by joining long chains called polypeptides
combination of any or all the 20 different amino acid
Properties of proteins depend on order of AA
The “language” of mRNA instructions is called the genetic code.

25. The Genetic Code As you know, RNA contains four different bases:
Adenine
Uracil
Cytosine
Guanine.
The genetic code is read three letters at a time
Each “word” of the coded message is three bases long.

26. Codon Each three-letter “word” in mRNA is known as a codon
A codon consists of three consecutive nucleotides that specify a single amino acid
The amino acid will be added to the polypeptide.

28. write the amino acids that correspond to the codons on page 303
partnerwork
mRNA code
UCGCACGGU
mRNA codon
UCG-CAC-GGU
write the amino acids that correspond to the codons on page 303

30. Answer
Serine
Histidine
Glycine

31. Codon Numbers
Because there are four different bases, there are 64 possible, three-base codons
(4 *4 *4 = 64)
Six different codons specify the amino acid leucine
Six other codons specify arginine.

32. AUG AUG can either specify:
methionine
“start”
There are three “stop” codons that do not code for any amino acid.
UAG, UAA, UGA

33. AUG Stop codons act like the period at the end of a sentence
They signify the end of a polypeptide, which consists of many amino acids

34. Translation
The decoding of an mRNA message into a polypeptide chain (protein) is known as translation.
Translation takes place on ribosomes.
During translation, the cell uses information from messenger RNA to produce proteins.

36. Overall Summary
Messenger RNA is transcribed from DNA in the nucleus and released into the cytoplasm
Translation begins when an mRNA molecule attaches to a ribosome.
In the ribosome, the amino acid is transferred to the growing polypeptide chain.

37. Anti-codon Each tRNA molecule carries only one kind of amino acid.
In addition to an amino acid, each tRNA molecule has three unpaired bases.
These bases, called the anticodon, are complementary to one mRNA codon.

38. Steps
1. mRNA attaches to a ribosome, where codons move thru ribosome, and are read 1 at a time
2. tRNA enters ribosome, carrying an amino acid and anticodon
Translation always starts with the start codon AUG (methionine)

39. 3. Ribosomes form peptide bonds between each amino acid
Also breaks the bond between amino acid and tRNA
tRNA is released back into cytoplasm
Continues until stop codon is reached
Protein is released and translation is complete

40. The Roles of RNA and DNA
The cell uses the vital DNA “master plan” to prepare RNA “blueprints.”
The DNA molecule remains within the safety of the nucleus, while RNA molecules go to the protein-building sites in the cytoplasm—the ribosomes.

41. Genes and proteins
Many proteins are enzymes which catalyze and regulate chemical reactions
A gene that codes for an enzyme can produce skin color or blood type
Genes for certain proteins can regulate growth, controlling size and shape
Proteins are the keys to almost everything that living cells do

42. 1. List the three main types of RNA.
2. What happens during transcription?
3. What happens during translation?
4.Describe the three main differences between RNA and DNA.