what makes up more than 80 percent of RNA in a cell?
ribosomal rna , this forms the core of a ribosome
why is so much rRNA needed?
its because most cells contain 10 million ribosomes in every cell, there for each ribosome needs a copy of each rRNA type
what is the nucleolus ?
is it surrounded by a membrane ?
its the site of ribosome synthesis within the nucleus, it is not surrounded by a membrane
what does the nucleolus contain in humans?
- newly made ribsomes subunits
- newly made rRNA transcripts
- dna clusters from five diff chromosomes where rRNA genes are present
how many times does the gene encoding rna transcripts repeat?
they repeat hundreds of times in these clusters
what is the nucleolus seperated based on?
it is seperated based on how it looks under the scope,
its divided into the fibrillar (where dna encoding rRNA genes is transcribed and resulting rRNA is processed)
and the granular (ribosomal assmebly occures, proccessed rRNA and ribosomal protiens join to form large and small ribosomal subunits
how many parts can the fibrillar portion be subdivided into? what are they?
include what is present in these subdivisons ?
2 parts” the fibrillar centre and the surrounding dense fibrillar component
in the fibrillar centre it contains dna that encodes for rRNA
transcription of these genes by RNA polymerase tends to occur in the FC and processing of pre-rRNA occurs in the DFC
what happens to the nucleolus during mitosis?
1)nuclear envelope breaks , nucleolus disappears
2)telophase =nucleolus comes back
3)interphase=cells have one nucleolus, size of nucleous dependent on number of ribsomoes being made at a certain time
what does each ribosome contain? what does this make the ribosome?
contains : protein components (Diff protein) & rRNA component
rRNA predominant component and has a catalytic component as well=makes ribosome the enzyme ribozyme
how is the rRNA base pairing and folding found in all domains of life?
it is highly conserved
how many subunits of ribosomes are there?
there are two main subunits(one large and one small)
prokaryotes=50S L and 30S s
eukaryotes=60S L and 40S s
what does the S stand for ?
S stands for Svedberg unit, which measures how fast a particle (settles) during centrifugation. Larger, denser particles have higher S values.
What does the bacterial large(50s) subunit that has 2 rRNA and 34 proteins contain?
it has 5s rRNA and 23S
what does the bacterial small subunit (30s) that has 1 rRNA and 21 proteins contain?
it has 165 rRNA , in total the entire bacterial ribosome is 70s
what are the S units in the large(60s,3 rrna and 49 protiens) and small (40s, 1 rrna and 33 proteins)?
in the large =5s, 5.8S, 28S
in the small= 185 rRNA
both subunits in total=80S
what are the two locations that encode rRNA ?
the gene that codes for 5S rRNA is located outside the nucleolus but still in nucleus
the gene that codes for 5.8S,18S , 28S rRNA is located in the nucleolus that codes for large pre -rRNA transcript
total precursor is 35S
what does the larger rRNA gene contain? what is the location of these ? what seperates it?
the larger rna has 200 + copies found in the clusters
found in one or more locations within nucelolus
seperated by intergenic spacer
what transcribes the repeating gene ?
the rna polymerase I
if one gene includes the coding segments for three different rRNAs what is found in between each copy of the gene ?
intragenic spacers
what are the steps in producing the 35S pre-rRNA molecule?
1) transcription factors recruit RNA polymerase I to bind to a single promoter and create an initiation complex
2) entire gene and intragenic spacers are transcribed in one go
what does processing do to the transcribed intragenic spacers?
it removes the transcribed intragenic spacers to release three seperate rRNA segments
what does the processing of the pre rRNA transcript?
it occurs by the small nucleolar ribonucleoprotiens (snoRNP)
these will have folded ,catalytic snoRNA within its structure
what does snoRnp help do ?
it helps cleave the transcribed spacers to release the three seperate rRNA molecules
the process is similar to the one we saw with snRNPs(have their own snRNA) and mRNA splicing
what can we indentify in a single nucleolus under the TEM?
1)rDNA
2)rRNA
3)Transcription start and end
4)intergenic spacers
5)RNA pol I
6)snoRNPS
