1. Protein Synthesis

2. transcription and translation
The “Central Dogma”
Flow of genetic information in a cell
How do we move information from DNA to proteins?
transcription
translation
DNA
RNA
protein
trait
To get from the chemical language of DNA to the chemical language of proteins requires 2 major stages:
transcription and translation
replication

3. Comparing DNA and RNA

4. Allowed to travel from nucleus to cytoplasm
Comparing DNA and RNA
DNA
RNA
Shape
Double helix
2 strands
Single strand
Sugar
Deoxyribose
Ribose
Bases
A, T, C, and G
A, U, C and G
Location
Only in the nucleus
Allowed to travel from nucleus to cytoplasm

5. Types of RNA Messenger RNA (mRNA) RNA (rRNA) Transfer RNA (tRNA)
Sequence of nucleotides that determines the primary sequence of the polypeptide
RNA (rRNA)
Major component of ribosomes
Transfer RNA (tRNA)
Carries the amino acids to the mRNA

6. Protein Synthesis: From gene to proteinaa a
Protein Synthesis: From gene to protein
nucleus
cytoplasm
transcription
translation
DNA
mRNA
protein
ribosome
trait

7. Protein Synthesis: 1. Transcription – the synthesis of RNA using a DNA
template
Occurs in the nucleus of eukaryotic cells
2. Translation – the synthesis of a polypeptide using the
genetic information encoded in an mRNA
molecule
Occurs on the ribosome

8. Which gene is read on the DNA?
Specific sequences of nucleotides along the DNA mark where transcription of a gene begins and ends.
A promoter is a specific nucleotide sequence in DNA that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place

9. Initiation of Transcription
Certain sections of a promoter are especially important for binding RNA polymerase.
In prokaryotes, the RNA polymerase itself specifically recognizes and binds to the promoter
In eukaryotes, a collection of proteins called transcription factors mediate the binding of RNA polymerase and the initiation of transcription.

11. Transcription: DNA to mRNA
Takes place in the nucleus
A section of DNA is unzipped
RNA polymerase lays down nucleotides 5’ to 3’ direction.
The mRNA then leaves the nucleus through the nuclear pores and enters the cytoplasm

12. RNA Processing in Eukaryotes
mRNA must be modified before it leaves the nucleus
1) Introns are cut out of the mRNA and exons are
spliced back together
2) A 5’ GTP cap and a
3) A poly-A tail are added to the mRNA

13. Final mRNA 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 A
3' poly-A tail
mRNA 5'
5' cap 3' G P
A’s
eukaryotic RNA is about 10% of eukaryotic gene.

14. The Code You don’t need to memorize the codons (except for AUG)
Start codon
AUG
methionine
Stop codons
UGA, UAA, UAG
Strong evidence for a single origin in evolutionary theory.

15. mRNA codes for proteins in triplets
TACGCACATTTACGTACGCGG
DNA
codon
AUGCGUGUAAAUGCAUGCGCC
mRNA ?
Met Arg Val Asn Ala Cys Ala
protein

16. Ribosomes: Site of Protein Synthesis
Facilitate coupling of tRNA anticodon to mRNA codon
Structure
ribosomal RNA (rRNA) & proteins
2 subunits
large
small E P A

17. Translation A ribosome has three binding sites for tRNA:
The P site holds the tRNA that carries the growing polypeptide chain
The A site holds the tRNA that carries the next amino acid to be added to the chain
The E site is the exit site, where discharged tRNAs leave the ribosome

19. Transfer RNA Found in cytoplasm Carries amino acids to ribosome
Contains an “anticodon” of nitrogen bases
Anticodons use complementary bond with codons

20. Translation: mRNA to Protein
In the cytoplasm ribosomes attach to the mRNA
Ribosome covers 3 codons at a time
Initiation - The tRNA carrying an amino acid comes
into P-site and bonds by base pairing its
anticodon with the mRNA start codon
(what is the start codon?)
Elongation – The second tRNA then comes into A-site
and bonds to codon of mRNA
(what type of bond forms between adjacent amino acids?)
Termination – ribosome continues reading mRNA until
a STOP codon is reached
(doesn’t code for anything)

22. Protein Synthesis in Prokaryotes & Eukaryotes

23. Prokaryote vs. Eukaryote Differences
Prokaryotes
DNA in cytoplasm
circular chromosome
naked DNA
no introns
No splicing
Promoter & terminator sequence
Smaller ribosomes
Eukaryotes
DNA in nucleus
linear chromosomes
DNA wound on histone proteins
introns and exons
TATA box promoter
Transcription factors present
Walter Gilbert hypothesis:
Maybe exons are functional units and introns make it easier for them to recombine, so as to produce new proteins with new properties through new combinations of domains.
Introns give a large area for cutting genes and joining together the pieces without damaging the coding region of the gene…. patching genes together does not have to be so precise.