Ribosomes

Question 1

in eukaryotes what “S” are the ribosomes?

Answer 1

80S

Question 2

what “S” are the subunits of ribosomes in eukaryotes?

Answer 2

60S and 40S

Question 3

what does the S stand for in 80S?

Answer 3

Svedberg unit, which is a sedimentation coefficient. O larger things will sediment more quickly O higher S values

Question 4

what is the structure of ribosomes? ie what is it made of?

Answer 4

• RNA (2/3) core with PROTEINS (1/3) attached (mainly to surface)

Question 5

what is the nucleolus?

does it have a membrane?

Answer 5

• a DISCRETE area w/in nucleus

- NO MEMB

Question 6

what occurs in the nucleolus?

Answer 6

• site of ribosomal sub unit production and start of assembly

Question 7

what does the nucleolus form around?

Answer 7

• around parts of chromosomes called NUCLEOLAR ORGANISERS

Question 8

what is the advantage of having multiple copies of rRNA genes that produce rRNA?

Answer 8

• lots of copies can be transcribed at the same time to make lots of rRNA

Question 9

in the nucleolus, what are the dark coloured regions? what occurs here?

Answer 9

DENSE FIBRILLAR COMPONENT- RNA being transcribed

Question 10

in the nucleolus, what are the lighter coloured regions inside the darker regions? what occurs here?

Answer 10

FIBRILLAR CENTRE- DNA not being transcribed

Question 11

what makes up the majority of the nucleolus? what is found here?

Answer 11

GRANULAR COMPONENT- maturing ribosomes (and start to be assembled)

Question 12

what is the nucleolar organiser region? what is its function?

Answer 12

• the chromosome region which is active in NUCLEOLUS FORMATION
• functions in the synthesis of ribosomal RNA
• contains rRNA producing DNA

Question 13

what are the features of the DNA that produces RNA in the nucleolus?
what transcribes it?
what does it produce?

Answer 13

• genes in tandem
• contains non-transcribed SPACER DNA which varies in length
• high RATES OF TRANSCRIPTION
• transcribed by RNA POLYMERASE I
• produces PRECURSOR RNA (45S) which is then processed

Question 14

what processing does the precursor rRNA undergo? what does this produce?

Answer 14

• undergoes CHEMICAL MODIFICATION
• then CLEAVED so that some parts are DEGRADED
• produces 18S rRNA (inc into small ribo subunit) , 5.8 rRNA and 28 S rRNA (inc into large subunit)

Question 15

why is the rRNA for the small and large subunits transcribed together and just cleaved to separate after?

Answer 15

• more efficient to make all together and then just cleave, than transcribing individually

Question 16

where is the 5S rRNA made for the large ribsomal subunit?

Answer 16

• made in nucleus but not the nucleolus like all the other parts

Question 17

what transcribes the 5S RNA needed for the large subunit?

Answer 17

• RNA polymerase III

Question 18

what are ribosomal proteins made of?

what transcribes them? where translated?

Answer 18

• 5S structural proteins
• transcribed by RNA polymerase II
• translated in CYTOPLASM
• then transported into nucleus for subunit assembly