1. Transcription & Translation
Protein Synthesis
Biology 12

2. 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.
Metabolism is a term that is used to describe all chemical reactions involved in maintaining the living state of the cells and the organism.
Metabolism can be conveniently divided into two categories:
Catabolism - the breakdown of molecules to obtain energy
Anabolism – the synthesis of all compounds needed by cells )

3. 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.

4. The Connection Between Genes and Proteins
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.

5. 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.

6. 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.

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

8. 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)

10. 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)

11. 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)

12. Central Dogma

13. RNA RNA: How is it difference from DNA? - contains a ribose sugar
- contains the base Uracil (not thymine)
- single stranded
- found in both nuclues and cytoplasm
Purine Bases (double ring)
Adenine & Guanine
Pyrimidine Bases (single ring)
Cytosine & Uracil
Base Pairs:
(purine always pairs with pyrimidine)
Adenine + Uracil
Guanine + Cytosine
Guanine + Cytosine
Adenine + Uracil
Image:

14. 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

15. 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.

16. 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)

17. 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.

18. 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

19. 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.

20. 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.

22. 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

23. 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

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

26. 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)

30. Task A: #2 – Central Dogma
DNA makes RNA (mRNA)
through transcription
RNA makes proteins
through translation

31. #4 – 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

32. #5 – DNA vs. RNA DNA Sugar – deoxyribose Double stranded
Base pair – thymine
Stays in nucleus
Can replicate itself
Longer strands
RNA
Sugar – ribose
Single Stranded
Base pair – uracil
Can leave nucleus
Cannot replicate itself
Shorter strands

33. #6 – Transcription/Translation
Purpose:
To make mRNA from DNA
Location:
Nucleus
Translation
Purpose:
To make a specific protein from mRNA
Location:
Cytoplasm (ribosome)

34. #9 – 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

35. #10 – Transcribe to mRNA DNA: GGA TCA GGT CCA GGC AAT
TTA GCA TGC CCC AA
*mRNA*:
CCU AGU CCA GGU CCG UUA
AAU CGU ACG GGG UU

36. #11 – 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)

37. Task B: #2 – Transcribe to mRNA
DNA:
TAC TAC GGT AGG TAT A
*mRNA*:
AUG AUG CCA UCC AUA U

38. Task C: #3 – Anticodons

39. #4 – 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

40. #6 – Translate to Amino Acids
mRNA:
GGC CCA UAG AUG CCA CCG GGA AAA GAC UGA GCC CCG
*Protein translation*:
Met (start) Pro Pro Gly Lys Asp (stop)