Gene Expression Flashcards
How does DNA become RNA?
Transcription
How does RNA become a protein?
Translation
Where does transcription happen?
In the nucleus
Where does translation occur?
In the cytoplasm
MRNA leaves through the nuclear pore
What starts/stops transcription + translation?
A signal such as Transcription/translation initiation/termination
What is the standard template of requirements for making a polynucleotide or polypeptide?
Needs an enzyme
Needs activated substrates
Needs a template
3 stage process=initiation, elongation, termination
Fill in the regular template for making DNA.
Enzyme=DNA polymerase
Substrates=dNTPs
Template=DNA
Process=initiation, elongation, termination
Fill in the regular template for making RNA (transcription)
Enzyme=RNA polymerase
Substrates=NTPs
Template=DNA
Process= initiation, elongation and termination
Fill in the template for making a polypeptide (Translation)
Enzyme=ribosome
Substrate=amino acids
Template=mRNA
Process=initiation, elongation and termination
Describe the initiation in DNA replication
Initiation=recognition of origin of replication, initiate proteins and DNA polymerase
Describe the elongation in DNA replication
5’ to 3’ chain growth
Describe the termination step in DNA replication.
Termination=when the replication forks meet
Describe the initiation step in transcription
Initiation=promotor region recognised, transcription infatuation factors, RNA polymerase
Describe the elongation step in Transcription.
Elongation=5’ to 3’ chain growth
Describe the termination step in transcription.
Sequence dependant (the way it terminates depends on the sequences coding)
How can a gene also be referred to in transcription?
The transcription unit (the bit that forms the DNA)
Give a difference between RNA and DNA polymerase.
RNA polymerase doesn’t need the same kickstart as DNA polymerase
What does upstream refer to?
The DNA behind the RNA polymerase enzyme. Eg there may be other proteins binding upstream
What does downstream refer to?
The DNA after the RNA polymerase protein, transcription occurs in this direction.
What is a promotor sequence?
It interacts with RNA polymerase to begin transcription. Uses an activator to help it interact as it may be many bases away from the transcription site
How is the DNA coding strand related to mRNA production?
It is not involved in the transcription process itself but contains the same sequence to mRNA (except for the T/U difference). This is because the coding strand is complementary to the strand used as the template (the DNA template strand) for mRNA
How does pre-mRNA get to mature RNA?
Capping - at 5’ end to protect against degradation
Tailing/polyadenlyation - at the 3’ end, protect against degradation
Splicing-to remove introns, is sequence independent
What is capping?
Happens at the 5’ end.
A 5’-5’ linkage is created with the end nucleotide and a mentholated Guanine.
It plays a role in protection against nucleotide degradation.
What is Polyadenylation?
On the 3’ end a specific endonuclease is used to cleave the new mRNA from the RNA polymerase.
This cleaved mRNA then uses the enzyme to add a large number of Adenine nucleotides to the mRNA.
What happens in splicing?
The non-coding Introns are removed from the pre-mRNA leaving only the coding Exons to make up the mRNA.
What are Prokaryotic ribosomes used for?
Can be used to program antibiotic targeting as they are different to eukaryotic ribosomes. It gives the antibiotic something to target.
What are 3 key types of RNA?
Ribosomal RNA= rRNA
Messenger RNA= mRNA
Transfer RNA= tRNA
What type of RNA is most prominent in the cell?
Ribosomal RNA makes up 80% of a cells RNA at one time
Why is Translation regarded as more complicated than Transcription?
From 4-letter nucleotides to 20 amino acids
Adaptor molecule is needed
What features of the DNA sequence are important in sequencing?
Triplet Code
Degenerate (multiple triplets produce same amino acids
Non-overlapping
Comma-less (no gaps between codons)
5’-3’ strand produces N to C polypeptide chain
What adapter molecule is needed in translation?
-tRNA
What is the initiation codon?
AUG
Fill in the standard template for translation?
Enzyme=ribosome
Substrate=amino acids
Template=mRNA
Process=initiation, elongation, termination
What shape is tRNA?
A clover
Has anticodon at bottom
Is a single stranded molecule that forms double stranded sections
What are stem loops in tRNA and why are they important?
They occur when hydrogen bonds are formed between anti-parallel , complimentary sequences.
They are important as they allow the clover shape to form
What does Amino-acyl tRNA refer to?
A tRNA molecule that has a specific aminoacyl group attached to it. It is specific to the anti codon on the molecule.
What is a “wobble” region on tRNA?
The 5’ base of the codon and hence the 3’ base of the codon is the “wobble” position. Contains an I base on the anticodon . This can be complementary to any base T,A,C,G on ,RNA, and so a single tRNA can recognise more than one mRNA codon. This means different codons on mRNA can code for the same amino acid (as they have the same anticodon)
How are amino acids activated?
ATP binds to a specific enzyme (aminoacyl-tRNA synthetase) and this binds to the specific amino acid. The ATP looses phosphate giving the amino acid the energy to bind to the tRNA. The enzyme helps the AA bind to the tRNA molecule with the matching anticodon (this is when the now AMP is released). The bond is created and the anticodon (now holding an AA) is released from the enzyme.
What is the initiation step in Translation?
Initiation=AUG codon is recognised, special Methionyl tRNA activated , ribosome active
What is the elongation process in Translation?
Elongation=N to C chain growth using aminoacyl tRNA’s
What is the termination step in Translation?
Termination=STO codon reached
What are the two exposed sites on the ribosome called and what are there roles?
P site and A site
The P site has the first AA and then the second picks one up. This then moves from the A site and binds to the AA on the P site, starting a chain.
