How do we get from Genotype to Phenotype?
EX. The red eye color in a fruit fly requires:
*4 steps
1) The normal gene is transcribed into a functional mRNA molecule
2) The mRNA is translated into pigment precursor transport protein
3) Colorless pigment precursor molecules are transported into the cell through the transport protein
4) Intracellular enzymes convert colorless pigment precursor molecules into red pigment
What reason could there be to have a white eyed fly?
It can be cause by any problem which interrupts the flow of information from gene to protein
1) Mutation may prevent transcription of functional mRNA
2) Mutation may prevent translation of functional pigment precursor transport protein
The Central Dogma of Molecular Biology
An explanation of the flow of genetic information within a biological system
Transcription
DNA is transcribed into an RNA copy
The process by which the information contained in a section of DNA is transferred to a newly assembled piece of messenger RNA (mRNA)
- Creates a complement of the template strand (=to the nontemplate strand)
Translation
mRNA is translated into a polypeptide at the ribosome
The process in which cellular ribosomes create proteins
- Changing mRNA into polypetides
What are the parts of a gene?
Adenine & Thymine which are together
Cytosine & Guanine which are together
What is a polypeptide?
A polymer of amino acids joined together by peptide bonds
- Cysteine (
- Alanine
- Proline
- Lysine
What is the order of the Central Dogma?
Part of a chromosome –> Part of a gene –(Transcription)–>mRNA –(Translation)–> Polypeptide
Template strand
The sequence of the DNA from 3’ to 5’
- In transcription, RNA polymerase reads the 3’ to 5’ nucleotide sequence of the DNA template strans and makes a complementary RNA molecule
Non Template strand
The sequence of the DNA from 5’ to 3’
What happens to the DNA during transcription?
In transcription, RNA polymerase reads the 3’ to 5’ nucleotide sequence of the DNA template strand and makes a complementary RNA molecule.(which is the nontemplate strand 5’ to 3’)
How does the mRNA strand differ from the nontemplate strand?
It uses Uracile instead of Thymine, but all the others are kept the same
3’ G A T C T T G A 5’
1) What is the template strand?
2) What is the non template strand?
3) What is the mRNA strand?
1) 3’ G A T C T T G A 5’
2) 5’ C T A G A A C T 3’
3) 5’ C U A G A A C U 3’
Codon
A sequence of three adjacent nucleotides constituting the genetic code that determines the insertion of a specific amino acid
- in a polypeptide chain during protein synthesis or the signal to stop protein synthesis.
What happens to the DNA during translation?
In translation, each codon designates an amino acid in the resulting polypeptide
What are bacterial genes made up of? 4 parts
1) Promoter
2) Regulatory sequence
3) Transcribed Region
4) Terminator
Bacterial Gene:
1) Promoter
Binds the RNA polymerase and signals the start of the gene
Bacterial Gene:
2) Regulatory sequence
Reacts to signals from the cell to increase/decrease rates of transcription
Bacterial Gene:
3) Transcribed Region
Contains the information required to direct translation of the amino acid sequence
- Or the transcription start point
Bacterial Gene:
4) Terminator
Marks the end of the gene and signals the end of transcription
- Or transcription stop point
Within the promoter, there is a TATA box, which has which sequences in the DNA?
5’ TATAAAA 3’
3’ ATATTTT 5’
Genes on a chromosome are _______ to give mRNA
transcribed
Where do transcription and translation occur in the bacteria?
Cytoplasm
What is the 1st stage of Bacterial Transcription?
Also called the initiation stage
- Binding of the RNA polymerase & a stigma factor or the transcription factors
- They recognize the promoter region of the gene and direct the interaction of the RNA polymerase with the DNA strand
What is the 2nd stage of Bacterial Transcription?
Polymerization of the RNA transcript
- The stigma factor(transcription factor) releases the RNA polymerase, which opens the double helix and begins to move along the DNA strand, making a ‘mobile copy’ of the gene, called an mRNA
What is the 3rd stage of Bacterial Transcription?
As the RNA polymerase moves along the DNA strand, it rewinds the double helix behind it.
- When the RNA Pol reaches the termination signal, it and the new mRNA (5’ to 3’) molecule will dissociate from the DNA strand, ending transcription
mRNA
Messenger RNAs - transcribed genes that code for proteins
tRNA
Transfer RNAs - translation interpreters
rRNA
Ribososmal RNAs - structural part of the ribosome
What are all 3 types of RNA made by?
What are all 3 types of RNA are encoded by genes and made by RNA polymerases
Eukaryotic Gene:
Eukaryotic genes contain __________and __________, but also usually include additional structures called ______________ or __________
Eukaryotic genes contain promoters and terminators, but also usually include additional structures called intervening sequences or introns
What is a promoter?
A promoter is involved in RNA transcription from a DNA sequence.
- It regulates the binding of RNA polymerase and the rate at which RNA is transcribed.
- Promoters are specific sequences of DNA where polymerase initiates transcription.
What is a terminator?
The terminator is a sequence that signals the end of transcription
What are Exons?
Exons are stuck together to give the translatable sequence
Exons are any nucleotide sequence encoded by a gene that remains present within the final mature RNA product of that gene after introns have been removed by RNA splicing.
What are Introns?
Introns are sequences of DNA that are transcribed but are removed before translation (turned into a protein)
- Introns are any nucleotide sequence within a gene that is removed by RNA splicing while the final mature RNA product of a gene is being generated
How is the mRNA processed for the eukaryotic transcription?
1) A cap is added to the 5’ end of the mRNA
2) Poly(A) polymerase adds a string of 50-250 adenine nucleotides, one nucleotide at a time, to the 3’ end to produce a poly-A tail
3) Introns are removed by mRNA splicing
Is the a transcription terminator for eukaryote cell?
No, the transcription continues past the end of the gene and eventually stops
What is the 5’ cap at the end of the mRNA used for?
The 5’ cap is required for export of the mRNA from the nucleus and for binding of the mRNA to the ribosome so translation can occur
What is the importance of the poly-A tail?
The poly-A tail helps make eukaryotic mRNAs more stable
- generally as the mRNA ages, the tail will get shorter
- RNA is much less stable than DNA so the tail is very important
Ribosomes read the nucleotide code of the ______and make __________ by linking together the appropriate __________
Ribosomes read the nucleotide code of the mRNA and make a polypeptide by linking together the appropriate amino acids
The ribosomes reads the _____ in ____________called ______ and translates the code into a protein using specific ______
The ribosomes reads the mRNA in 3 base chunks called codons and translates the code into a protein using specific tRNAs
- 3 base codons are read by the _______ and translated into a _________
- There are __ possible codons, and ___ amino acids plus a ______
- Therefore the gentic code is said to be _______
- 3 base codons are read by the ribosome and translated into a single amino acid
- There are 64 possible codons, and 20 amino acids plus a stop signal
- Therefore the gentic code is said to be degenerate
In Eukaryotes, transciption occurs in the _____, and the ______ is exported to the cytosol for _________
In Eukaryotes, transciption occurs in the nucleus, and the mRNA is exported to the cytosol for translation
____ is a _____ _____ molecule, encoded by specific genes, binds an _________ at one end, and a _____ on the other end
tRNA is a short RNA molecule, encoded by specific genes, binds an amino acid at one end, and a anticodon on the other end
Anticodon
A sequence of three adjacent nucleotides located on one end of transfer RNA, with the corresponding amino acids at the other end
What translates the genetic code?
tRNA
Ribosomes are made up of ______ and ______
Ribosomes are made up of proteins and RNA
The ______ and _________ assemble into 2 subunits
The ribosomal RNA (rRNA) and ribosomal proteins assemble into 2 subunits
The bacterial ribosome requires _____ and _______
3 rRNAs and 55 proteins
What forms the 70S bacterial ribosome?
30S small subunits and 50S larger subunits
*also found in mitochondria & chloroplasts**
What theory does the fact that mitochondria and chloroplast have all their own genomes(DNA) and ribosomes support?
The Endosymbiotic theory (According to this theory, mitochondria and plastids (e.g. chloroplasts), and possibly other organelles, represent formerly free-living bacteria that were taken inside another cell as an endosymbiont)
The eukaryotic ribosome requires _____ and _______
4 rRNAs and at least 82 proteins
Therefore it is bigger then bacterial ribosome
What forms the 80S eukaryotic ribosome?
40S small subunits and 60S large subunits
Translation:
The ribosome acts as an _________ to make ______
The ribosome acts as an amino acid polymerase to make protein
* Same for bacterial translation & eukaryotic translation*
Translation:
The mRNA is read by the _______
The _______ brings the next amino acid
The ribosome connects ______ to ___________
The mRNA is read by the ribosome
The tRNA brings the next amino acid
The ribosome connects the new amino acid to the growing protein
What are the 3 steps to transcription?
1) Initiation= starting of transcription
2) Elongation = where we make the RNA
3) Termination = end the transcription
What are the 3 steps to translation?
1) Initiation= ribosomes starting of translation
2) Elongation = ribosome elongate the amino acid chain (polypeptide)
3) Termination = end the translation
* Set of signals that say when to do what*
What is needed for translation to begin? (Initiation)
The small subunit binds to the mRNA
Translation - Initiation (4 steps)
1) The initiator Met-tRNA has an anticodon 3’ UAC 5’ for the AUG start codon.
2) The initiator Met- tRNA with GTP bound to it, binds to the sm ribosomal subunit and forms a complex
3) Met-tRNA+GTP+sm ribosomal subunit complex binds to the 5’ cap of the mRNA, and moves along it (scanning)- until it reaches the AUG start codon in the P site
4) The large ribosomal subunit binds and GTP is hydrolyzed, completing initiation.
Where does base pairing occur?
Between the codon and the anticodon of the initiator Met-tRNA
What happens during the translation (elongation) phase?
During elongation, a new tRNA enters the A-site.
The tRNA will match the codon of the mRNA
What happens during the translation (termination) phase?
A release factor binds to the A site, where a stop codon is found
Translation (termination):
- Encoded by the genetic code, a _______ will tell the ribosome when to finish translation of a given ____________
- Rather than a _________, a release factor will bind in the _________ of the _________
- Encoded by the genetic code, a stop codon will tell the ribosome when to finish translation of a given polypeptide
- Rather than a stop tRNA, a release factor will bind in the A-site of the ribosome
In bacteria when do transcription and translation occur?
They occur almost at the same time
Polysomes (in bacteria & eukaryotes)
Many ribosomes that can translate the same mRNA at the same time
Where are the free polyribosomes & ribosomes of eukaryotes located?
Attached to the Rough ER
What is the major difference between bacteria and eukaryotes?
- Bacterial mRNA only exists for a few minutes
- Eukaryote mRNA lasts for a few hours