DNA transcription, replication and translation Flashcards
wk 11
What are two similarities in the structure of DNA and RNA?
Phosphates always attached to 5’ and 3’ carbon of each sugar
Nitrogenous bases always attached to 1’ carbon of each sugar
bases = purine or pyrimidine
Where is the Nitrogenous bases always attached to?
1’ carbon of each sugar
Describe the structure of purines vs pyrimidines.
Purine = double ring structure
Pyrimidine = single ring structure
In which direction can polynucleotides of DNA and RNA only be synthesised?
Polynucleotides
Where are additional nucleotides added in RNA and DNA?
3’ end
What enzyme adds the precursor (nucleotide triphosphate) to DNA and RNA?
polymerase
Transcription
When the code of DNA is temporarily transferred to RNA (Copying of DNA –> RNA)
What enzyme is responsible for unwinding and separating DNA in replication
Helicase
What enzyme is responsible for reading strand template and inserting complementary bases in replication
polymerase
How is the leading strand of DNA produced?
continuously due to the polarity of 5’-3’
How is the lagging strand of DNA produced?
discontinuously replicated. Therefore is synthesized as Okazaki fragments
What enzyme seals the gap between Okazaki fragments?
DNA Ligase
What is the role of RNA Polymerase?
Required to make RNA from free nucleoside triphospates
moves along DNA from 3’ end to 5’ end inserting complementary bases
What are the three steps of transcription? Explain
Initiation – RNA polymerase moves to precursor and starts to unwind DNA
Elongation – RNA polymerase reads DNA (3’-5’) and produces RNA transcript adding nucleotides in a (5’-3’) direction.
Termination – RNA polymerase reaches termination site, RNA transcpit set free and polymerase dissociates
What is an example of gene regulation?
TATA box: DNA sequence where genetic sequence can be rad and decoded = promoter sequence that specifies where transcription begins.
What occurs in the transcription initiation step and act as important control.
Transcription factors
promoter sequences
regulatory sequences
enhancer sequence
What are the non coding regions of eukaryotic DNA and how are they removed?
Introns
via mRNA splicing
What are the seven regions of Eukaryotic DNA?
Gap
2- 5’-non coding region
3- start codon (AUG)
4- Coding region/ open reading frame
5- Stop codon (UGA)
6- 3’ non coding region
7- ply A tail
What is the code for start codon?
AUG
What is the code for end codon?
UGA
What are the five steps in mRNA Processing?
1- 5’ capped with modified Guanine reside
2- 3’ polyadenylated (add strong of A)
3- Poly A tail of mRNA generated
4- spliced
5- transported to cytoplasm
Outline main differences in prokaryotic and eukaryotic DNA.
Prokarotic are coded in a continous blcok where as Eukaryotic have exons (coding) and introns (non coding)
E undergoes mRNA processing (cap, tail) and mRNA slicing but P does not
General overview of translation
After mRNA is exported from nucleus it becomes bound to a ribosome which reads mRNA and uses tRNA to assemble a polypeptide.
Amino acids selected, collected and carried to ribosome by tRNA
TRNA enters ribosome and mind to mRNA chain
What three steps are used in both transcription and translation?
Initiation
Elongation
Termination
What are the 4 steps of translation elongation?
Codon recognition (incoming tRNA anticodon pairs with mRNA codon)
Peptide bond formation- ribosome catalyses bond formation between amino acids
Translocation- tRNA leaves P site of ribosome, ribsome moves down mRNA 3 bases
Repeat as required
What occurs in translation elongation?
Reaches stop codon which does not bind to any anticodons of tRNA
Release factor binds to stop codon to promote hydrolysis of peptide bond between polypeptide and tRNA at P site.
What are the different types of point mutations?
Silent, nonsense and missense
Describe silent mutations
base change but codon does not alter AA sequence
Describe nonsense point mutations
Base change creates a stop codon
translation ends prematurely = mutant protein
Describe missense point mutation. Define Conservative and non-conservative ones.
base change resulting in new AA
C= properties of new AA similar = normal protein function
NC= new AA different properties = loss of protein function
What is a frameshift mutation?
Insertion / deletion of base that alters sequence of codon
