4-5-3+4 Transcription and translation Flashcards
3 steps of transcription
1) initiation 2) elongation 3) termination
transcription initiation
Step 1 of transcription: RNA polymerase binds to the gene promoter and unwinds the double helix, exposing the DNA nucleotides on each strand.
transcription elongation
Step 2 of transcription: complementary RNA nucleotides are added, following the base-pairing rules U with A and C with G.
transcription termination
Step 3 of transcription: Transcription stops when RNA polymerase comes upon a “stop” signal in the gene. The mRNA strand then detaches from the DNA, and the RNA polymerase detaches, too.
Transcription follows the base-pairing rules for DNA replication, except that in RNA …
uracil (U) pairs with adenine (A).
Where does RNA Polymerase bind to DNA
the gene’s promoter, which is a specific DNA sequence that acts like a “start” signal
RNA polymerase
The enzyme that does transcription (from DNA to RNA)
Uracil
the base that pairs with adenine (A) in RNA. (instead of thymine).
When does transcription stop?
When RNA polymerase reaches the “stop” signal in the DNA.
As RNA is being formed and RNA polymerase moves down the chain of the DNA molecule, what happens to the unzipped DNA strands behind the RNA polymerase?
They close up and form hydrogen bonds between the complementary bases.
Does transcription make only mRNA?
No, it makes other kinds of RNA, too, inlcuding rRNA and tRNA.
Translation
The step in protein synthesis in which cells use the different types of RNA created in transcription to put together the amino acids that make a protein.
Before translation can begin, mRNA must leave _____ and enter _____.
leave the nucleus and enters the cytoplasm.
Where in the cell and on which organelle does translation occur?
in the cytoplasm and on the ribosomes
Ribosomes: what are they made of and what are they used for in the cell?
complex organelles used in translation that are made of rRNA (ribosomal RNA) and protein.
codon
It is the “word” on mRNA that tells which amino acid to add or what action to take (such as “stop”). It is a 3-base sequence on mRNA that binds with the 3 base anticodon on the tRNA.
anticodon
There is a three-base sequence on the tRNA that will bind with the three base codon on the mRNA.
stop codon
a codon within messenger RNA that signals a termination of translation.
4 steps of translation
steps that occur during translation: 1) activation 2) initiation 3) elongation 4) termination
translation activation
first step of translation. The correct amino acids are linked to the correct tRNA molecules.
translation initiation
Step 2 of translation. mRNA binds with the small subunit of the ribosome. Then, the initiator tRNA carrying methionine binds to the initiator codon (AUG) on the mRNA, forming the initiation complex consisting of the initiator tRNA, mRNA, and ribosome small subunit. The large ribosome subunit attaches to the initiation complex.
translation elongation
Step 3 of translation. The next tRNA with its amino acid enters at the A site. A peptide bond is made between successive amino acids. The process repeats, and the protein chain gets longer. The tRNA molecules are ejected from the ribosome after losing their amino acid. (they can be reused).
translation termination
Step 4 of translation: When the codon in the A site is a stop codon, a release factor binds to the site, translation stops, and the protein is separated from the ribosome.
