DNA & RNA Flashcards
Human genome contains approximately how many base pairs?
3 billion
How many amino acids are encoded by DNA?
20
Codon
A sequence of three DNA or RNA nucleotides that corresponds with a specific amino acid or stop signal during protein synthesis
A nucleotide consists of:
A nitrogenous base + ribose/deoxyribose sugar + phosphate group
Main differences between DNA and RNA
- RNA is single stranded
- Uracil replaces thymine in RNA
- Ribose replaces deoxyribose as the sugar in RNA
- Various forms of RNA exist: tRNA, mRNA, rRNA
Where in the cell does transcription occur?
Within the nucleus in eukaryotic cells and in the cytoplasm of prokaryotic cells.
Where in the cell does translation take place?
In the cytoplasm in both prokaryotic and eukaryotic cells.
How many essential amino acids in humans?
9
How many proteinogenic amino acids exist in eukaryotes?
21 - 20 in the standard genetic code plus selenocysteine.
Of the 64 possible codon combinations, how many code for aa?
61, the other 3 codons are stop-signals.
What is the start codon?
The codon AUG codes for Methionine and signals start of sequencing.
In transcription, nucleotides are added to which end of the growing pre-mRNA molecule?
Nucleotides are added to the 3’ end. The growing pre-mRNA strand is being built in a 5’→ 3’ direction.
In transcription, the template DNA strand is being copied in which direction?
3’→5’
In transcription, what modifications is made to the 5’ end of the pre-mRNA molecule?
Addition of a 5’ cap composed of phosphates
In transcription, what modifications is made to the 3’ end of the pre-mRNA molecule?
Addition of a poly-A tail composed of recurring sequences of adenine residues
