1. Transcription & Translation
Protein Synthesis
Biology 12

2. Genes and Proteins
Proteins become structures such as filaments in muscle tissue, and enzymes that control chemical reactions
Sequences of nucleotides in DNA contain information that is used in the production of proteins

3. Genes direct the production of proteins that determine the phenotypical characteristics of organisms.
Genes also direct the production of other physiologically essential proteins such as antibodies and hormones.
Proteins drive cellular processes such as metabolism; determining physical characteristics and producing genetic disorders by their absence or presence in an altered form.

4. The Central Dogma
An organism’s genome is housed within the nucleus. Proteins are synthesized outside the nucleus, in the cytoplasm, on ribosomes.
Since information for protein synthesis is specified by DNA (called the one gene-one polypeptide hypothesis), and DNA is not able to exist outside the nucleus, a problem exists as to how the blueprint of life is brought to the ribosomes.

5. SO…How does a cell make proteins anyway?

6. There are two important nucleic acids involved in this process...
DNA
RNA

7. Let’s Review DNA & RNA RNA: ribonucleic acid--contains sugar ribose.
RNA is single stranded.
RNA contains bases adenine, guanine, cytosine and uracil.
RNA can leave the nucleus.
DNA: deoxyribonucleic acid--contains sugar deoxyribose.
DNA is double stranded.
DNA contains bases adenine, guanine, cytosine, and thymine.
DNA never leaves the nucleus.
This is a review of DNA and RNA.
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Ameoba Sisters- DNA vs RNA

8. There are three types of RNA
mRNA
mRNA: messenger RNA
tRNA
towing
Amino acid
tRNA: transfer RNA
Remind students that there are three different RNA molecules that are involved with protein synthesis and briefly go over their function.
mRNA: messenger RNA. It carries the DNA message from the nucleus to the ribosomes. tRNA: transfer RNA. It carries amino acids from the cytoplasm to the ribosomes.
rRNA: ribosomal RNA. It is found at the ribosomes.
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rRNA: ribosomal RNA

9. Types of RNA
Genetic information copied from DNA is transferred to 3 types of RNA:
Messenger RNA: mRNA
Copy of information in DNA that is brought to the ribosome and translated into protein by tRNA & rRNA
Varies in length , the longer the gene the longer the mRNA>
Transfer RNA: tRNA
Brings the amino acid to the ribosome that mRNA coded for.
Ribosomal RNA: rRNA
Most of the RNA in cells is associated with structures known as ribosomes, the protein factories of the cells.
Provides the construction site for the assembly of polypeptides.
It is the site of translation where genetic information brought by mRNA is translated into actual proteins.
Messenger
Ribosomal
Transfer
Transcription & Translation

10. Overall process of protein synthesis
transcription
translation
DNA
RNA
Protein
During gene expression, the information in DNA is first transcribed in the nucleus as a molecule of mRNA and then translated in the cytoplasm and used to build a protein.
transcription
translation
Occurs in the
nucleus
Occurs in the cytoplasm
Ameoba Sisters – Protein Synthesis

11. The Connection Between Genes and Proteins Hank again!
Nucleic acids carry information in their nucleotide sequence.
Proteins carry information in their amino acid sequence.
To get from DNA (in nucleic acid language) to protein
(in amino acid language) requires two steps.
Transcription- a DNA strand provides a template for
the synthesis of a complementary RNA strand.
This molecule is called mRNA (messenger RNA).
DNA is too valuable to be allowed to exit the nucleus. This
could lead to the death of the cell and possible the
Death of the organism.

12. Genetic information contained in DNA.
- use of mRNA provides protection for the
Genetic information contained in DNA.
more protein can be made simultaneously
because many mRNA copies of a gene can be
made than if one strand of DNA left the nucleus.
- each mRNA can be translated many times.

13. mRNA delivers the encoded genetic
material to the ribosomes.
The ribosomes translate the message
into polypeptide chains, which are
processed into proteins.
This entire sequence is described as
the Central Dogma of Molecular
Genetics, first stated by Francis Crick
in 1958.

14. Central Dogma In nucleus Produced in nucleus Travels to cytoplasm
Produced in cytoplasm

15. Transcription vs Translation
Transcription involves the copying of the
information in DNA into mRNA.
(copy from one medium to another- think
of a medical or legal stenographer)
Translation involves ribosomes using the
Messenger RNA as a blueprint to synthesize
a protein composed of amino acids.
(converting into a different language, think English
to French)

16. Transcription

19. Definition: Transcription
Nucleus
Location
DNA
Template
(What is read)
To change DNA into a form that can make a protein
Purpose
Messenger RNA
(mRNA)
Outcome
(End result)

20. Definition: Translation
Location
Cytoplasm (by ribosome)
Template
(What is read)
mRNA
Purpose
Amino acids assembled in particular order to make a protein
Outcome
(End result)
Protein (polypeptide)

21. Transcription occurs in 3 steps:
Initiation, Elongation and Termination
Initiation:
RNA polymerase binds to the DNA at
a specific site known as a promotor.
DNA: A T G C A A
RNA: U A C G U U
The RNA transcript is known as
elongation.
After the RNA polymerase passes the end
of the gene, it stops transcribing which is termination.

22. Transcription : ‘to copy’
Initiation:
RNA polymerase binds to DNA at ‘promoter’
untwists the double helix 10 to 20 bases at a time
Elongation:
RNA polymerase builds mRNA
From DNA 3’ end
Uses complimentary base pairing
Remember: thymine (T) is replaced by uracil (U)

23. Termination: End Result: RNA polymerase reaches end of gene.
Stops transcribing
Double helix reforms as mRNA molecule peels away.
End Result:
mRNA breaks away from DNA
mRNA exits nucleus
If there is a high demand for a
protein, the cell can have several RNA
polymerases transcribing the gene at the same
time to produce several mRNA’s.

24. First, DNA unzips itself...
ATGACGATT
TACTGCTAA
DNA unzips itself, exposing free nitrogen bases.
The slide is animated; the DNA unzips automatically

25. First, DNA unzips itself...
ATGACGATT
TACTGCTAA
DNA unzips itself, exposing free nitrogen bases.
The slide is animated; the DNA unzips automatically

26. First, DNA unzips itself...
ATGACGATT
TACTGCTAA
DNA unzips itself, exposing free nitrogen bases.
The slide is animated; the DNA unzips automatically

27. First, DNA unzips itself...
ATGACGATT
TACTGCTAA
DNA unzips itself, exposing free nitrogen bases.
The slide is animated; the DNA unzips automatically

28. First, DNA unzips itself...
ATGACGATT
TACTGCTAA
When DNA unzips itself (exposing free nitrogen bases)…
The slide is animated; the DNA unzips automatically

29. Next, mRNA is made... ATGACGATT
mRNA matches with free DNA nitrogen bases in a complementary fashion
(mRNA is made from the DNA template)
ATGACGATT
Have students notice that the mRNA is made from ONE side of the DNA molecule
The slide is animated; the DNA unzips automatically

30. Next, mRNA is made... U ATGACGATT
mRNA matches with free DNA nitrogen bases in a complementary fashion
(mRNA is made from the DNA template)
The slide is animated; the RNA bases automatically pair up with DNA

31. Next, mRNA is made... U ATGACGATT
mRNA matches with free DNA nitrogen bases in a complementary fashion
(mRNA is made from the DNA template)
The slide is animated; the RNA bases automatically pair up with DNA

32. Next, mRNA is made... UA ATGACGATT
mRNA matches with free DNA nitrogen bases in a complementary fashion
(mRNA is made from the DNA template) UA
The slide is animated; the RNA bases automatically pair up with DNA

33. Next, mRNA is made... UA ATGACGATT
mRNA matches with free DNA nitrogen bases in a complementary fashion
(mRNA is made from the DNA template) UA
The slide is animated; the RNA bases automatically pair up with DNA

34. Next, mRNA is made... UAC ATGACGATT
mRNA matches with free DNA nitrogen bases in a complementary fashion
(mRNA is made from the DNA template)
UAC
The slide is animated; the RNA bases automatically pair up with DNA

35. Next, mRNA is made... UAC ATGACGATT
mRNA matches with free DNA nitrogen bases in a complementary fashion
(mRNA is made from the DNA template)
UAC
The slide is animated; the RNA bases automatically pair up with DNA

36. Next, mRNA is made... UACU ATGACGATT
mRNA matches with free DNA nitrogen bases in a complementary fashion
(mRNA is made from the DNA template)
UACU
The slide is animated; the RNA bases automatically pair up with DNA

37. Next, mRNA is made... UACU ATGACGATT
mRNA matches with free DNA nitrogen bases in a complementary fashion
(mRNA is made from the DNA template)
UACU
The slide is animated; the RNA bases automatically pair up with DNA

38. Next, mRNA is made... UACUG ATGACGATT
mRNA matches with free DNA nitrogen bases in a complementary fashion
(mRNA is made from the DNA template)
UACUG
The slide is animated; the RNA bases automatically pair up with DNA

39. Next, mRNA is made... UACUG ATGACGATT
mRNA matches with free DNA nitrogen bases in a complementary fashion
(mRNA is made from the DNA template)
UACUG
The slide is animated; the RNA bases automatically pair up with DNA

40. Next, mRNA is made... UACUGC ATGACGATT
mRNA matches with free DNA nitrogen bases in a complementary fashion
(mRNA is made from the DNA template)
UACUGC
The slide is animated; the RNA bases automatically pair up with DNA

41. Next, mRNA is made... UACUGC ATGACGATT
mRNA matches with free DNA nitrogen bases in a complementary fashion
(mRNA is made from the DNA template)
UACUGC
The slide is animated; the RNA bases automatically pair up with DNA

42. Next, mRNA is made... UACUGCU ATGACGATT
mRNA matches with free DNA nitrogen bases in a complementary fashion
(mRNA is made from the DNA template)
UACUGCU
The slide is animated; the RNA bases automatically pair up with DNA

43. Next, mRNA is made... UACUGCU ATGACGATT
mRNA matches with free DNA nitrogen bases in a complementary fashion
(mRNA is made from the DNA template)
UACUGCU
The slide is animated; the RNA bases automatically pair up with DNA

44. Next, mRNA is made... UACUGCUA ATGACGATT
mRNA matches with free DNA nitrogen bases in a complementary fashion
(mRNA is made from the DNA template)
UACUGCUA
The slide is animated; the RNA bases automatically pair up with DNA

45. Next, mRNA is made... UACUGCUA ATGACGATT
mRNA matches with free DNA nitrogen bases in a complementary fashion
(mRNA is made from the DNA template)
UACUGCUA
The slide is animated; the RNA bases automatically pair up with DNA

46. Next, mRNA is made... ATGACGATT UACUGCUAA
mRNA matches with free DNA nitrogen bases in a complementary fashion
(mRNA is made from the DNA template)
Remind students that the RNA strand has Uracil instead of Thymine and that the Uracil pairs up with Adenine.

47. Translation: ‘new language’
Initiation:
Ribosome binds at a specific sequence on the mRNA.
The ribosome moves along the mRNA three nucleotides at a time. This is called a codon.
Each set of three (a codon) codes for an amino acid. Why?
There are only 4 bases but 20 amino acids.
41 = 4 (1 base=1 acid) = = 64
One code two codes three codes

48. The codon AUG not only codes for the amino acid
Methionine, but it also indicates the start of a
translation.
Some amino acids are coded for by two or more
codons but a given codon ALWAYS only codes
for one amino acid.
GAA and GAG both code for glutamic acid,
but never mean any other amino acid.

49. here

50. mRNA tries to talk to the ribosomes…
AUGUGCUAA
I have a message
for you! It’s
from DNA!
mRNA leaves the nucleus and travels to the cytoplasm, where the ribosomes are located.
What does
he want now?
mRNA leaves the nucleus and travels to the cytoplasm, where the ribosomes are located.
Once there, mRNA meets up with the ribosomes.
It’s always
something!
Once there, mRNA
meets up with the
ribosomes

51. mRNA tries to talk to the ribosomes…but is unsuccessful.
AUGUGCUAA
Why don’t they
get it???
@%$!!
Why can’t we tell
what he’s saying?
However, the ribosomes cannot understand the message mRNA is carrying.
We need a
translator!

52. Now the cell can make a protein!
tRNA Saves the Day!
Methionine
UAC
We won’t work until
we know what to do!
Looks like trouble
for this cell…
I’d better help!
The boss will NOT
be happy about
this...
AUGUGCUAA
Now the cell can make a protein!
Where is that
translator?

53. tRNA: Transfer RNA UAC Chemically, tRNA is clover-leaf shaped.
At one end, it carries an amino acid.
At the other end, it has a three letter code known as an anticodon.
Methionine
UAC

54. Anticodon? What’s that? UAC AUGUGCUAA
This anticodon is the complement to the codons contained within mRNA.
Can you find the mRNA complement to the anticodon on tRNA?
Methionine
AUGUGCUAA
UAC

55. Elongation: Ribosome moves along mRNA From mRNA 5’ end
3 nucleotides of mRNA = codon = amino acid
The “interpreter” tRNA delivers the proper complimentary base to the ribosome. Anticodons are blocks of 3 tDNA bases that actually attach to the correct protein.
The anticodon( tRNA) binds by complimentary base pairing to the nucleotides of the codon.
Example: if the codon on a mRNA is UUU,
a tRNA with an AAA anticodon will bind to it.
The ribosome links adjacent amino acids with a peptide bond, causing the amino acid to let go of it tRNA.
The finished protein has a sequence of amino acids that have been determined by the mRNA base sequence which has been translated by the tRNA.

57. The Whole Picture Next amino acid to be added to polypeptide Growing
tRNA
mRNA

58. Ribosome reaches stop codon Stops translating End Result:
The ribosome then adds each amino acid
and the polypeptide chain is elongated.
Elongation occurs until a stop signal occurs.
Termination:
Ribosome reaches stop codon
Stops translating
End Result:
Ribosome falls off mRNA
Protein (polypeptide chain) is released

59. Start and Stop Codons Start Codon: Begins translation Stop Codon:
AUG (universal start codon)
ALSO Codes for methionine (Met)
Sometimes GUG or UUG
Stop Codon:
Ends translation
UGA, UAA, UAG

61. Codon Chart
Third letter

62. Example DNA template: 3’ TAC ACA CGG AAT GGG TAA AAA ACT 5’
Complimentary DNA
Read from DNA template (start reading at 3’)
mRNA codon
tRNA anticodon
Read from mRNA
Amino Acids (protein)

64. Review- From DNA to Protein

67. RNA types mRNA tRNA rRNA Messenger RNA End product of transcription
Takes message from DNA into cytoplasm
Used by ribosome to make protein
tRNA
Transfer RNA
Delivers amino acid to ribosome
rRNA
Ribosomal RNA
Helps form and maintain ribosomes

68. Transcription/Translation
Purpose:
To make mRNA from DNA
Location:
Nucleus
Translation
Purpose:
To make a specific protein from mRNA
Location:
Cytoplasm (ribosome)

69. Stop vs. Start Codon Start Codon mRNA code
Tells ribosome to begin translation
Example:
AUG
Also codes for methionine
And: UUG, GUG
Stop Codon
mRNA code
Stops translation of that specific amino acid chain
Examples:
UAA, UAG, UGA

70. Transcribe to mRNA DNA: GGA TCA GGT CCA GGC AAT TTA GCA TGC CCC AA
CCU AGU CCA GGU CCG UUA
AAU CGU ACG GGG UU

71. Translate to Amino Acids
mRNA sequence divided into codons:
GGC AUG GGA CAU UAU UUU GCC CGU UGU GGU GGG GCG UGA
*Protein translation*:
Gly Met(start) Gly His Tyr Phe Ala
Arg Cys Gly Gly Ala (stop)

72. Transcribe to mRNA DNA: TAC TAC GGT AGG TAT A *mRNA*:
AUG AUG CCA UCC AUA U

73. Change in 3rd Base May Not Result in Error
Why not?
Amino acids have more than one codon
Example: proline
Codons CCU, CCC, CCA, and CCG
CC - always codes for proline
Third base/nucleotide does not matter