From Gene
to Protein
How Genes
Work
AP Biology
2007-2008
What do genes code for?

How does DNA code for cells & bodies?

how are cells and bodies made from the
instructions in DNA
DNA
AP Biology
proteins
cells
bodies
The “Central Dogma”

Flow of genetic information in a cell

How do we move information from DNA to proteins?
DNA
replication
AP Biology
RNA
protein
DNA gets
all the glory,
but proteins do
all the work!
trait
Metabolism taught us about genes

Inheritance of metabolic diseases
suggested that genes coded for enzymes
 each disease (phenotype) is caused by
non-functional gene product





lack of an enzyme
Tay sachs
PKU (phenylketonuria)
albinism
metabolic pathway
A

AP Biology enzyme 1
Am I just the
sum of my proteins?
disease
disease
disease
disease
B
C
D
E

enzyme 2

enzyme 3

enzyme 4
a
a
From gene to protein
nucleus
cytoplasm
transcription
DNA
a
a
translation
mRNA
a
a
a
a
a
a
a
a
a
a
a
protein
a
a
a
a
a
a
a
ribosome
trait
AP Biology
Transcription
from
DNA nucleic acid language
to
RNA nucleic acid language
AP Biology
2007-2008
RNA


ribose sugar
N-bases
uracil instead of thymine
U : A
C : G



single stranded
lots of RNAs

DNA
AP Biology
mRNA, tRNA, rRNA, siRNA…
transcription
RNA
Transcription

Making mRNA


transcribed DNA strand = template strand
untranscribed DNA strand = coding strand


synthesis of complementary RNA strand


same sequence as RNA
transcription bubble
enzyme

RNA polymerase
5
C
DNA
G
3
A
G
T
A T C
T A
53
G
A G C
A
T
C G T
A
C
T
3
G C A U C G U
C
G T A G C A
T
T
A
C
A G
C T
G
A
T
A
T
3
5
unwinding
rewinding
mRNA
AP Biology
build
RNA
coding strand
5
RNA polymerase
template strand
Matching bases of DNA & RNA

Match RNA bases to DNA
bases on one of the DNA
strands
A
G
C
A
G
G
U
U
C
A
AG
U
C
G
A
U
A
C
5'
RNA
A C C polymerase G
A
U
3'
T G G T A C A G C T A G T C A T CG T A C CG T
AP Biology
U
C
Translation
from
nucleic acid language
to
amino acid language
AP Biology
2007-2008
How does mRNA code for proteins?
DNA
TACGCACATTTACGTACGCGG
4 ATCG
mRNA
4 AUCG
protein
AUGCGUGUAAAUGCAUGCGCC
?
Met Arg Val Asn Ala Cys Ala
20
AP Biology
How can you code for 20 amino acids
with only 4 nucleotide bases (A,U,G,C)?
mRNA codes for proteins in triplets
DNA
TACGCACATTTACGTACGCGG
codon
mRNA
AUGCGUGUAAAUGCAUGCGCC
?
protein
AP Biology
Met Arg Val Asn Ala Cys Ala
Cracking the code

1960 | 1968
Nirenberg & Khorana
Crick

determined 3-letter (triplet) codon system
WHYDIDTHEREDBATEATTHEFATRAT

Nirenberg (47) & Khorana (17)
determined mRNA–amino acid match
 added fabricated mRNA to test tube of
ribosomes, tRNA & amino acids



AP Biology
created artificial UUUUU… mRNA
found that UUU coded for phenylalanine
The code

Code for ALL life!


strongest support for
a common origin for
all life
Code is redundant


several codons for
each amino acid
3rd base “wobble”
Why is the
wobble good?

Start codon



AP Biology
AUG
methionine
Stop codons

UGA, UAA, UAG
How are the codons matched to
amino acids?
DNA
mRNA
3
5
5
3
TACGCACATTTACGTACGCGG
AUGCGUGUAAAUGCAUGCGCC
3
UAC
tRNA
amino
acid
AP Biology
Met
codon
5
GCA
Arg
CAU
Val
anti-codon
Transfer RNA structure

“Clover leaf” structure
anticodon on “clover leaf” end
 amino acid attached on 3 end

AP Biology
Loading tRNA

Aminoacyl tRNA synthetase


enzyme which bonds amino acid to tRNA
bond requires energy



ATP  AMP
bond is unstable
so it can release amino acid at ribosome easily
Trp C=O
OH
OH
Trp C=O
O
Trp
H2O
O
activating
enzyme
tRNATrp
anticodon
AP Biology
tryptophan attached
to tRNATrp
AC C
UGG
mRNA
tRNATrp binds to UGG
condon of mRNA
Ribosomes

Facilitate coupling of
tRNA anticodon to
mRNA codon


organelle or enzyme?
Structure
ribosomal RNA (rRNA) & proteins
 2 subunits



AP Biology
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small
E P A
Can you tell
the story?
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