1. TRANSCRIPTION /TRANSCRIPTION /
TRANSLATIONTRANSLATION
Take Notes on 17R
Transcription- process that makes mRNA from
DNA

2. The Central DogmaThe Central Dogma

3. AP Biology 2007-2008
Transcription
from
DNA nucleic acid language
to
RNA nucleic acid language
Only a specific part of DNA is Tx at one time,
NOT the entire strand of DNA

4. Beadle & Tatum 1941 | 1958
George Beadle Edward Tatum
Nobel Prize for their discovery that
genes act by regulating definite
chemical events
one gene : one enzyme hypothesis
one gene : one polypeptide
Enzymes are polypeptides- updated findings are:

5. Transcription
Making a single strand of mRNA
transcribed DNA strand = template strand
untranscribed DNA strand = coding strand
• same sequence as RNA
synthesis of complementary RNA strand at transcription
bubble
Enzyme used: RNA polymerase
template strand
rewinding
mRNA RNA polymerase
unwinding
coding strand
DNA
C C
C
C
C
C
C
C
C C
C
G
G
G
G
G G
G G
G
G
GA
A
A
A A
A
A
A
A
A A
A
AT
T T
T
T
T
T
T
T T
T
T
U U
5′
3′
5′
3′
3′
5′
build RNA 5′→3′
Transcription
animation

6. 3 Processes of
Transcription
In Nucleus
1. Initiation
DNA unzipped into 2 separate strands by DNA Helicase.
Promoter region identified, Initiation Complex Made
2. Elongation
Free floating RNA NITROGEN BASES in the nucleus pair up
w/unzipped DNA NITROGEN BASES by RNA Polymerase
Ex: DNA template: 3’ –C G T- 5’
3. Termination
Complement pairing is done at the end of gene
-a single strand of RNA is released

7. Which gene will be Tx?
1. Initiation
• Promoter region
– binding site before beginning of gene
– TATA box catches attention

8. At Promoter Region, Transcription
Factors make Initiation Complex
• Initiation complex
– transcription factors bind to promoter region
suite of proteins which bind to DNA
turn on or off transcription
– trigger the binding of RNA polymerase to DNA

9. 2. Elongation
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
5' 3'

10. 3. Termination
RNA Polymerase reaches the end of the gene
and the RNA P, DNA, and new mRNA
dissociate.

11. mRNA Strand Needs Processing:
After Transcription
• In our DNA there are sequences that are
not needed to make proteins.
• Due to complementing, these region end
up in mRNA after Tx.
• These regions (aka=some junk)must be
removed before Tl.

12. Eukaryotic genes have junk=
mRNA have junk!
• Eukaryotic genes are not continuous
– exons = the real gene
expressed / coding DNA
– introns = the junk
In between sequence
eukaryotic DNA
exon = coding (expressed) sequence
intron = noncoding (inbetween) sequence
introns
come out of RNA!

13. After Transcription
mRNA ProcessingmRNA Processing

14. AfterTranscription Review
Which mRNA sequences are removed?
Why are they removed?
mRNA Processing

15. Result:
Genetic code from DNA is transferred to mRNA
The code obtained from DNA lets the mRNA
know which amino acids to pick up:
• code is a set of 3 nitrogen bases = Codon
Overall Process of Transcription

16. mRNA
DNA
RNA
Polymerase
TranscriptionTranscription
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)

17. AP Biology 2007-2008
Translation
from
nucleic acid language
to
amino acid language

18. TranslationTranslation
• Process that converts mRNA into
protein
• Proteins are made of monomers
of AA
• Tl occurs on ribosomes
• Where are ribosomes?

19. Ribosomes
Facilitates coupling of
tRNA anticodon to
mRNA codon
• organelle & enzyme!!
Structure
ribosomal RNA (rRNA) & proteins
2 subunits
 large
 small E P A
Protein synthesis/quiz

20. Ribosomes
Met
5'
3'
U
U
A C
A G
APE
A site (acceptor site)
• holds the newest tRNA carrying the next
amino acid to be added to chain
P site (peptidyl-tRNA site)
• holds tRNA carrying growing polypeptide
chain
E site (exit site)
• empty tRNA leaves ribosome
from exit site
Protein synthesis 2

21. tRNA: remindertRNA: reminder
• tRNA = transfer RNA
• picks up the correct amino acids
and carries them to the mRNA
strand forming the protein
• Location of anticodon, the
complement to the mRNA
codon

22. 3 Steps of Translation
making proteins
1. Initiation
2. Elongation
3. Termination

23. Building a polypeptide
Initiation
brings together mRNA, ribosome subunits, initiator
tRNA
Elongation
adding amino acids based on codon sequence
Termination
end codon
123
Leu
Leu Leu Leu
tRNA
Met Met
Met Met
PE A
mRNA
5' 5' 5' 5'
3' 3' 3'
3'
U UA AA
AC
C
C
AU UG G
GU
U
A
AA
AC
C
C
AU UG G
GU
U
A
AA
AC
C
C
AU UG G
GU U
A
AAC
CAU UG G
G
A
C
Val
Ser
Ala
Trp
release
factor
A
A A
CC
U UGG
3'
How translation works

24. Step 1: Initiation
a)Ribosome attaches to the mRNA
b) Start codon is always AUG

25. Step 2: Elongation
a) tRNA anticodon matches with codon on mRNA
b) Peptide bonds are formed between the AA

26. Elongation (continued)
c) AA released from tRNA
d) Ribosome moves down the mRNA
and continues adding AA

27. Step 3: Termination
a)The ribosome reaches one of three stop
codons (UAA, UAG, UGA)
b) The mRNA and protein (polypeptide chain) is
released

28. The Decoder
This allows humans
to translate the
mRNA code into
proteins

29. There are 20 Amino Acids

30. mRNA Start codon
Ribosome
Methionine
Phenylalanine
tRNA
Lysine
Nucleus
TranslationTranslation
mRNA

31. mRNA
Codon on
mRNA Translation direction
Amino Acid
tRNA
tRNA
Ribosome
Growing polypeptide
chain
mRNA
Translation (continued)Translation (continued)
Anticodon
on tRNA

32. The Decoder
This allows humans
to translate the
mRNA code into
proteins

34. Prokaryote vs. Eukaryote genes
Prokaryotes
DNA in cytoplasm
circular chromosome
naked DNA
no introns
Tx & Tl can occur simultaneously
Eukaryotes
DNA in nucleus
linear chromosomes
DNA wound on histone proteins
introns vs. exons
time & physical separation b/w Tx & Tl:
~1 hr from DNA to protein