DNA
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Nucleolus is made up of
Proteins and RNA
Function of nucleolus
Bring ribosomal RNA and combine it with proteins, forming ribosomes
Karyotype
Arrangement of full chromosome set
Direction of how DNA is read
5’ to 3’ direction
Enzyme that catalyses DNA synthesis
DNA polymerase
Fundamental reaction by which DNA is synthesised
Addition of a deoxyribonucleotide to the 3’ end of a polynucleotide chain
replication fork
produced when the DNA double helix is partially unwinded
Leading strand of DNA
DNA daughter strand that is being synthesised continuously
Lagging strand of DNA
daughter strand that is synthesised discontinuously into Okazaki fragments, later restitched together by DNA ligase synthesised in the opposite direction to the leading strand and slower than the leading strand
exonuclease activity
DNA polymerase monitors the base pairing between each incoming nucleotide and the template strand If the wrong base has been added, exonuclease clips off the wrong nucleotide, and DNA polymerase tries again
DNA is transcribed by enzyme ___
RNA polymerase
How does RNA polymerase transcribe DNA
It attaches to the RNA primer (3’ end), then moves stepwise along the DNA unwinding the DNA helix just ahead of the active site for polymerisation to expose a new region of the template strand for complementary base pairing
number of types of RNA polymerase in bacteria and eukaryotes
Bacteria: one Eukaryotes: three
Direction RNA Polymerase reads in
5’ to 3’
direction the template strand goes
from 3’ to 5’
RNA synthesis posttranscriptional modifications in eukaryotes (2)
Polyadenylation RNA Splicing
polyadenylation
adding caps (a poly-A tail) at the 3’ end of synthesised RNA to prevent degradation
purpose of polyadenylation (3)
differentiating mRNA from other types of RNA final maturation process of transcription, allowing it to proceed to translation used as a starting point for reverse transcription where reverse transcriptase binds to
presence of exons and introns in RNA synthesis
Introns are cut out and remaining exons are pasted together to form the transcript
RNA splicing
Where introns (non coding regions) are removed from a pre-messenger RNA strand, and exons (coding regions) are joined together to form a mature mRNA molecule that can be used to make a protein
How mRNA to leave the nucleus from transcription to translation
Through the nuclear pore complex
Codon bias
Certain organisms may use a particular codon more frequently than others
tRNA acts as ___ during ___ by
an adaptor during protein synthesis translating the genetic code from messenger RNA (mRNA) into a specific sequence of amino acids to form a protein
3 ribosome binding sites for tRNA
A (entry), P (holds tRNA), E site aminoacyl, peptidyl RNA and exit