12.3 DNA, RNA and protein

1. Learning Objectives
1. Explain how the code of DNA
transcribed into messenger RNA.
2. Explain how messenger RNA is
translated into a protein.
3. Describe how to make a protein
beginning with a gene.

2.  Bodies are made up of cells
 All cells run on a set of instructions
spelled out in DNA
Bodies → Cells → DNA

3.  How does DNA code for cells & bodies?
 how are cells and bodies made from the
instructions in DNA?
DNA → Cells → Bodies

4.  DNA has the information to build proteins
 genes
DNA → Proteins → Cells → Bodies
proteins
cells
bodies
DNA gets all the glory,
Proteins do all the work

5. How do proteins do all the work?
–Proteins run living organisms
–Enzymes control all chemical reactions in
living organisms
–Structure
• all living organisms are built out of proteins

6. cytoplasm
nucleus
Cell organization
– DNA is in the nucleus
• genes = instructions for making proteins
– want to keep it there = protected
• “locked in the vault”

7. Cell organization
• Proteins
– chains of amino acids
– made by a “protein factory” in
cytoplasm = ribosome
nucleus
cytoplasm
ribosome
build
proteins

8. Passing on DNA information
• Need to get DNA gene information
from nucleus to cytoplasm
– need a copy of DNA
– messenger RNA (mRNA) does this
nucleus
cytoplasm
ribosomemRNA
build
proteins

9. DNA vs. RNA
DNA
• deoxyribose sugar
• nitrogen bases
– G, C, A, T
– T : A
– C : G
• double stranded
RNA
• ribose sugar
• nitrogen bases
– G, C, A, U
– U : A
– C : G
• single stranded

10. mRNA
From nucleus to cytoplasm
DNA
transcription
nucleus
cytoplasm
translation
trait
protein

11. Transcription
• Making mRNA from DNA
• DNA strand is the
template (pattern)
– match bases
• U : A
• G : C
• Enzyme
– RNA polymerase

12. Matching bases of DNA & RNA
• Double stranded DNA unzips
A G GGGGGT T A C A C T T T T TC C C CA A

13. Matching bases of DNA & RNA
• Double stranded DNA unzips
A G GGGGGT T A C A C T T T T TC C C CA A

14. Matching bases of DNA & RNA
• Match RNA bases to DNA bases
on one of the DNA strands
U
A G GGGGGT T A C A C T T T T TC C C CA A
U
U
U
U
U
G
G
A
A
A C C
RNA
polymerase
C
C
C
C
C
G
G
G
G
A
A
A
A
A

15. Matching bases of DNA & RNA
• U instead of T is matched to A
TACGCACATTTACGTACGCGGDNA
AUGCGUGUAAAUGCAUGCGCCmRNA

16. How does mRNA code for proteins?
• mRNA leaves nucleus
• mRNA goes to ribosomes in cytoplasm
• Proteins built from instructions on mRNA
aa aa aa aa aa aa aa aa
How?
mRNA
U C CCCCCA A U G U G A A A A AG G G GU U

17. How does mRNA code for proteins?
How can you code for 20 amino acids with
only 4 DNA bases (A,U,G,C)?
TACGCACATTTACGTACGCGGDNA
AUGCGUGUAAAUGCAUGCGCCmRNA
Met Arg Val Asn Ala Cys Alaprotein
?
ribosome
aa aa aa aa aa aa aa aa

18. AUGCGUGUAAAUGCAUGCGCCmRNA
mRNA codes for proteins in triplets
TACGCACATTTACGTACGCGGDNA
AUGCGUGUAAAUGCAUGCGCCmRNA
Met Arg Val Asn Ala Cys Alaprotein
?
 Codon = block of 3 mRNA bases
codon
ribosome

19. The mRNA code
• For ALL life!
– strongest support for a
common origin for all life
• Code has duplicates
– several codons for each
amino acid
– mutation insurance!
 Start codon
 AUG
 methionine
 Stop codons
 UGA, UAA, UAG

20. How are the codons matched
to amino acids?
TACGCACATTTACGTACGCGGDNA
AUGCGUGUAAAUGCAUGCGCCmRNA
anti-codon
codon
tRNA
UAC
Met
GCA
Arg
CAU
Val
 Anti-codon = block of 3 tRNA bases
amino
acid

21. mRNA to protein = Translation
• The working instructions → mRNA
• The reader → ribosome
• The transporter → transfer RNA (tRNA)
mRNA
U C CCCCCA A U G U G A A A A AG G G GU U
aa
aa
aa
tRNA
GGU
aa
tRNA
U A C
aa
tRNA
GA C
tRNA
aa
A GU
ribosome

22. aa
aa
aa
aa
aa
aa
aa
mRNA
From gene to protein
DNA
transcription
nucleus
cytoplasm
protein
translation
trait
U C CCCCCA A U G U G A A A A AG G G GU U
ribosome
tRNA
aa

23. transcription
cytoplasm
nucleus
translation
trait
protein

24. From gene to protein
transcriptiontranscription
translationtranslation
proteinprotein

25. Whoops!
See what happens when
your genes don’t work right!
Any Questions??