Polypeptide Synthesis - Transcription + Slicing Flashcards
What determines which proteins a cell manufacturers?
The instructions provided by the DNA in the cell’s nucleus at any given time
What is the name of the process where a complementary section of DNA is made into pre - mRNA?
Transcription
How does DNA provide instructions for protein synthesis?
In the form of a long sequence of bases
What is the role of mRNA in protein synthesis?
It acts as a template for complementary tRNA molecules to attach
What is transcription?
Transcription is the process of making pre - mRNA using part of the DNA as a template
Which DNA strand is used during transcription, and what happens to it?
The template strand is used, and its bases pair with complementary RNA nucleotides from the nucleus
What enzyme joins RNA nucleotides together during transcription?
RNA polymerase
What base pairing occurs between DNA and RNA nucleotides during transcription?
Guanine (DNA) pairs with Cytosine (RNA)
Cytosine (DNA) pairs with Guanine (RNA)
Thymine (DNA) pairs with Adenine (RNA)
Adenine (DNA) pairs with Uracil (RNA), not Thymine
What happens to the DNA strand as RNA polymerase moves along?
The DNA strands rejoin behind the RNA polymerase, so only ~ 12 base pairs are exposed at a time
What causes RNA polymerase to detach from the DNA?
A specific sequence of bases known as a “stop” triplet code
What is the product at the end of transcription?
A strand of pre - mRNA
What is the full steps of transcription? (4 steps)
1/ An enzyme acts on a specific region of the DNA, causing the two strands to separate and expose nucleotide bases in the region
2/ The template strand pairs with their complementary nucleotides from the “pool” present within nucleus. The enzyme RNA polymerase then moves along the strand, joining nucleotides together to form a pre - mRNA
3/ As RNA polymerase adds nucleotides one at a time to build a strand of pre - mRNA, DNA strands rejoin behind it
4/ When RNA polymerase reaches a sequence of bases on DNA that it recognises as a “stop” triplet code it detaches. The production of pre - mRNA is then completed
What is the difference in transcription products between prokaryotic and eukaryotic cells?
Prokaryotic cells produce mRNA directly from DNA, while eukaryotic cells produce pre - mRNA which must be spliced to form mRNA
What are exons?
What are introns?
Exons = Sections of DNA that code for proteins
Introns = Non - coding sections of DNA that do not code for proteins
Why must introns be removed from pre - mRNA?
Introns must be removed because they would prevent the synthesis of a polypeptide
What is splicing?
Do prokaryotic cells require splicing of mRNA? Why or why not?
The process of removing introns from pre - mRNA and joining the exons together to form functional mRNA
Prokaryotic cells do not require splicing because most do not have introns
Why can’t mRNA simply diffuse out of the nucleus?
They are too large to diffuse out on their own
How does spliced mRNA exit the nucleus?
Through a nuclear pore
What happens to mRNA after it exits the nucleus?
It becomes attracted to a ribosome in the cytoplasm, which it then attaches to, marking the beginning of translation
