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

2. 12–3 RNA and Protein Synthesis
Genes are coded DNA instructions that control the production of proteins. 1 gene = 1 protein
However, the DNA cannot leave the nucleus and proteins are made on ribosomes outside of the nucleus. The solution to this problem is RNA!
RNA can copy DNA’s coded information for making proteins and leave the nucleus with the information.
Copyright Pearson Prentice Hall

3. Copyright Pearson Prentice Hall
The Structure of RNA
The Structure of RNA
There are four main differences between RNA and DNA:
The sugar in RNA is ribose instead of deoxyribose.
RNA is single-stranded. DNA is double-stranded.
RNA contains uracil in place of thymine.
DNA stays in the nucleus, but RNA can leave the nucleus and go into the cytoplasm.
Copyright Pearson Prentice Hall

4. Copyright Pearson Prentice Hall
Types of RNA
Types of RNA
There are three main types of RNA:
Messenger RNA (mRNA)
Ribosomal RNA (rRNA)
Transfer RNA (tRNA)
Copyright Pearson Prentice Hall

5. Copyright Pearson Prentice Hall
Types of RNA
The three main types of RNA are messenger RNA, ribosomal RNA, and transfer RNA.
Messenger RNA (mRNA) carries copies of instructions for assembling amino acids into proteins.
Copyright Pearson Prentice Hall

6. Copyright Pearson Prentice Hall
Types of RNA
Ribosome
Ribosomal RNA
The three main types of RNA are messenger RNA, ribosomal RNA, and transfer RNA. Ribosomal RNA is combined with proteins to form ribosomes.
Ribosomes are made up of proteins and ribosomal RNA (rRNA).
Copyright Pearson Prentice Hall

7. Copyright Pearson Prentice Hall
Types of RNA
Amino acid
The three main types of RNA are messenger RNA, ribosomal RNA, and transfer RNA.
Transfer RNA
During protein construction, transfer RNA (tRNA) transfers each amino acid to the ribosome.
Copyright Pearson Prentice Hall

8. Copyright Pearson Prentice Hall
Transcription
Transcription
Protein synthesis begins in
the nucleus with a process
called transcription.
DNA is copied in the form of a single strand of RNA
The process begins at a section of DNA called a promoter.
Copyright Pearson Prentice Hall

9. Copyright Pearson Prentice Hall

10. Copyright Pearson Prentice Hall
Transcription
RNA
RNA polymerase
DNA
During transcription, RNA polymerase uses one strand of DNA as a template to assemble nucleotides into a strand of RNA.
Copyright Pearson Prentice Hall

11. Copyright Pearson Prentice Hall
An enzyme, RNA Polymerase, acts on the DNA molecule and causes it to unzip.
It chemically tells RNA nucleotides to come and base pair with the open DNA molecule according to the base-pairing rules:
Adenine-Uracil (A-U) and Cytosine-Guanine (C-G)
Copyright Pearson Prentice Hall

12. Copyright Pearson Prentice Hall
RNA Editing
RNA Editing
Some DNA within a gene is not needed to produce a protein.
Remember, DNA stays in the nucleus, but the edited mRNA leaves the nucleus and goes into the cytoplasm to the ribosome
Copyright Pearson Prentice Hall

13. Copyright Pearson Prentice Hall
The Genetic Code
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).
Adenine, Uracil, Cytosine, Guanine
Copyright Pearson Prentice Hall

14. Protein Synthesis DNA molecule DNA strand (template) 3′ 5′
TRANSCRIPTION
mRNA 5′ 3′
Codon
TRANSLATION
Protein
Amino acid

15. Copyright Pearson Prentice Hall
Translation
Translation
Translation is the decoding of a mRNA message into an amino acid (protein).
Translation takes place on ribosomes.
During translation, the cell uses information from messenger RNA to produce proteins.
Nucleus
mRNA
Copyright Pearson Prentice Hall

16. Copyright Pearson Prentice Hall
Translation
The ribosome binds new tRNA molecules and amino acids as it moves along the mRNA by matching tRNA anticodons to mRNA codons according to base pairing rules:
A-U
C-G
Lysine
Phenylalanine
tRNA
Methionine
Ribosome
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
Start codon
Copyright Pearson Prentice Hall

17. Copyright Pearson Prentice Hall
Translation
As the amino acids are brought close together, they are joined
by bonds to make a protein.
Protein Synthesis
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

18. Copyright Pearson Prentice Hall
Translation
The process continues until the ribosome reaches a stop codon.
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.
mRNA
Copyright Pearson Prentice Hall

19. 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

20. Copyright Pearson Prentice Hall
The Genetic Code
Codons are read from the center out
For example: The codon “AAC” codes for the amino acid “Asparagine”.
The genetic code shows the amino acid to which each of the 64 possible codons corresponds. To decode a codon, start at the middle of the circle and move outward.
GCU codes for Alanine. What other codons will produce Alanine?
Copyright Pearson Prentice Hall

21. Copyright Pearson Prentice Hall

22. Amino acids within a polypeptide
Genes and Proteins
Codon
Codon
Codon
DNA
mRNA
Protein
Single strand of DNA
Codon
Codon
Codon
mRNA
This diagram illustrates how information for specifying the traits of an organism is carried in DNA. The sequence of bases in DNA is used as a template for mRNA. The codons of mRNA specify the sequence of amino acids in a protein, and proteins play a key role in producing an organism’s traits.
Alanine
Arginine
Leucine
Amino acids within a polypeptide
Copyright Pearson Prentice Hall

23. Protein Synthesis DNA molecule DNA strand (template) 3′ 5′
TRANSCRIPTION
mRNA 5′ 3′
Codon
TRANSLATION
Protein
Amino acid

24. Copyright Pearson Prentice Hall
12–3
Write the letters that correspond to your answers on the quiz below in you summary section. You do not need to write out the question or answer ifself.
Copyright Pearson Prentice Hall

25. Copyright Pearson Prentice Hall
12–3
The role of a master plan in a building is similar to the role of which molecule?
messenger RNA
DNA
transfer RNA
ribosomal RNA
Copyright Pearson Prentice Hall

26. 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

27. 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

28. 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