WARMUP

Give three differences and three
similarities between DNA and RNA
AP Biology
WARMUP



Use the following words to write a
summary of transcription:
5’ cap, poly-A tail, introns, exons, premRNA, mature mRNA, template strand,
spliceosome, snRNPs, terminator,
promoter, RNA Polymerase.
Bonus, properly use transcription
factors, TATA Box, ribozymes
AP Biology
From Gene
to Protein
How Genes
Work
AP Biology
4/14/2020
What do genes code for?

How does DNA code for cells & bodies?

how are cells and bodies made from the
instructions in DNA
DNA
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proteins
cells
bodies
The “Central Dogma”

Flow of genetic information in a cell

How do we move information from DNA to proteins?
DNA
replication
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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
1941 | 1958
Beadle & Tatum
one gene : one enzyme hypothesis
George Beadle
Edward Tatum
AP Biology
"for their discovery that genes act by
regulating definite chemical events"
Beadle & Tatum
X rays or ultraviolet light
Wild-type
Neurospora
create mutations
asexual
spores
Minimal
medium
spores
Growth on
complete
medium
positive control
Select one of
the spores
Test on minimal
medium to confirm
presence of mutation
negative control
Grow on
complete medium
Minimal media supplemented only with…
experimentals
Choline
Pyridoxine
Riboflavin
Minimal
Nucleic
Arginine
control
amino acid p-Amino
Niacin
Inositol acid Folic
supplements
acid
Thiamine
benzoic acid
AP Biology
Another view:
AP Biology
Still need more help to get this?

Click on the
picture
AP Biology
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
4/14/2020
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
Eukaryotic genes have junk!

Eukaryotic genes are not continuous

exons = the real gene


expressed / coding DNA
introns
come out!
introns = the junk

inbetween sequence
intron = noncoding (inbetween) sequence
eukaryotic DNA
exon = coding (expressed) sequence
AP Biology
mRNA splicing

Post-transcriptional processing




eukaryotic mRNA needs work after transcription
primary transcript = pre-mRNA
mRNA splicing
 edit out introns
make mature mRNA transcript
intron = noncoding (inbetween) sequence
~10,000 base
eukaryotic DNA
exon = coding (expressed) sequence
pre-mRNA
primary mRNA
transcript
AP Biology
mature mRNA
transcript
~1,000 base
spliced mRNA
Splicing must be accurate

No room for mistakes!

a single base added or lost throws off the
reading frame
AUGCGGCTATGGGUCCGAUAAGGGCCAU
AUGCGGUCCGAUAAGGGCCAU
AUG|CGG|UCC|GAU|AAG|GGC|CAU
Met|Arg|Ser|Asp|Lys|Gly|His
AP Biology
AUGCGGCTATGGGUCCGAUAAGGGCCAU
AUGCGGGUCCGAUAAGGGCCAU
AUG|CGG|GUC|CGA|UAA|GGG|CCA|U
Met|Arg|Val|Arg|STOP|
RNA splicing enzymes

snRNPs



small nuclear RNA
exon
proteins
Spliceosome


exon
3'
spliceosome
5'
3'
cut & paste gene
No,
not smurfs!
“snurps”
AP Biology
intron
5'
several snRNPs
recognize splice
site sequence

snRNPs
snRNA
mature mRNA
lariat
5'
exon
5'
3'
exon
3'
excised
intron
Alternative splicing

Alternative mRNAs produced from same gene


when is an intron not an intron…
different segments treated as exons
Starting to get
hard to
define a gene!
AP Biology
More post-transcriptional processing

Need to protect mRNA on its trip from
nucleus to cytoplasm

enzymes in cytoplasm attack mRNA



protect the ends of the molecule
add 5 GTP cap
add poly-A tail
 longer tail, mRNA lasts longer: produces more protein
3'
mRNA
5'
AP Biology
P
G P
P
A
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
(Click to view)
AP Biology
Any Questions??
What color would a smurf turn
if he held his breath?
AP Biology
4/14/2020