(22-25) Ribosomes and rRNA

Ribosomes consist of [] different RNAs and [] different proteins

4;70

Eukaryotic ribosome size is what? What is its diameter?

80s; 23 nm

What does the s refer to when referencing ribosome size?

sedimentation coefficient. Based on size relative to another molecule

A typical cell has about [_] ribosomes. This can make up to []% of the mass of the cell

10 million; 25%

A ribosome is about [__] times the size of a DNA double helix

10

What is the ratio of RNA to protein by mass in a ribosome?

about 50/50

Most of the RNA in a ribosome serves as a what?

scaffold

Give the size of each RNA that is in a ribosome as well as which ribosomal subunit each is in. also give the size of each ribosomal subunit.

large subunit (60s)-28s,5.8s,5s; small subunit (40s)-18s

How much energy is required to assemble a ribosome once its components are made?

practically none

What are the three large rRNAs?

5.8s, 18s, and 28s

Nucleolus

electron dense structure seen in the middle of the nucleus through histological preparations. Forms or dissolves based on the stage of the cell cycle. Fibrous on the inside and granular on the outside. Where most rRNA is produced.

Fibrillar region

innermost region of nucleolus. Area with extremely high rRNA production. Specifically responsible for large rRNA production.

Granular region

outermost region of the nucleolus. “Assembly line”. Where the 60s and 40s subunits are synthesized

There may be up to [__] nucleoli in a human cell

5

Spacer region

area between large rRNA genes that are not transcribed in the nucleolus. Contain promoter-like regions (PLRs) which hasten large rRNA transcription.

Secondary constriction

area on a chromatid which is constricted. This area of the chromosome forms the fibrillar region of a nucleolus . aka nucleolar organizer.

What is the nucleolar organizer derived from?

fibrillar region of the nucleolus

Draw a representation of the “christmas trees” in the production of large rRNA (draw at least two and label the region in between). What does the central line represent? What about the black dots? About the lines coming out of the dots?

the central line is the DNA that is transcribed and the dots is RNA polymerase 1. The lines coming off the dots represent large rRNA.

There may be around to [__] RNA polymerase [1,2, or 3?] transcribing large rRNA on one gene at a time.

100; 1

What is the termination sequence for RNA polymerase 1?

a row of Ts (remember this from the prokaryotic mRNA synthesis)

There are [word] repeats of large rRNA genes each which are repeated [#] of times each of which are transcribed [#] of times at the same time will provide the [#_] of ribosomes that are necessary for the cell, All of which occurs in the [word] region of the nucleolus

tandem.100s; 100s; millions; fibrillar

Draw a representation of immature large rRNA (just draw a line with boxes represent each section of mRNA

Each time a large rRNA gene is transcribed, how many of each large rRNA molecule is made?

1 18s, 1 5.8s, and 1 28s is made

The promoter for the large rRNA gene is [__] nucleotides [upstream or downstream?] from the gene

140 nucleotides upstream

Between nucleotide number [] and [] in the large rRNA gene’s promoter are the significant conserved sequences of the promoter

-114 and -72;

T.f the large rRNA gene could be transcribed with only itself and its promoter

true

It has been found that the [____] region is responsible for making the transcription of the large rRNA gene [faster or slower?] than when the gene is transcribed with only its promoter.

spacer; faster

Promoter like region (PLR)

a 60-80 nucleotide region in the spacer region upstream from the large rRNA gene and promoter which is 90% homologous to the central region of the promoter. helps attract RNA polymerase 1 and transcription factors, speeding up large rRNA transcription.

What areas in the spacer regions promote faster transcription of the larger rRNA gene? Why does it do that?

PLR (promoter like region). It helps attract RNA polymerase 1 and transcription factors

t/f there is only one PLR in each spacer region

false, there may be multiple

The proteins that make up ribosomes are made in the []. The large rRNA is made in the [] region of the []. The 5s rRNA is made in the [] and ribosomes are synthesized in the [] region of the [__]

cytoplasm; fibrillar; nucleolus; nucleoplasm; granular; nucleolus

t/f the 80s ribosome is made in the nucleoplasm

false, the 60s and 40s subunits are made in the nucleus. They only combine into an 80s ribosome in the cytoplasm

Two types of 5s genes

O-type and S-type

In any given cell (both gamete and somatic) there are [] 5s genes, [] of which are O type, [] of are S-type. In somatic cells []% of the 5s RNA is O-type while [] is S-type. In gametes []% of the RNA is O-type while [_] os S-type

20,000 genes ;19,000 O type genes ;1,000 S type genes; ~100% S type and ~0% O type RNA in somatic; ~95% O type and 5% S type RNA for gametes

Differential gene expressioN

cells of different types express genes in different ways. Allows for cell specialization.

Which RNA polymerase transcribes 5s rRNA?

RNA polymerase III

The promoter of a 5s rRNA is gene is located where

downstream of the #1 nucleotide in the middle of the gene itself. Located on the coding strand between nucleotides 50 and 83.

ICR

internal control region. Another name for the promoter of the 5s rRNA gene

What transcription factor binds to the ICR of the 5s rRNA gene

TFIIIA

Why does it not matter that TFIIIA “blocks” the strand when it binds to the ICR?

it binds to the coding strand of DNA. RNA polymerase synthesizes RNA using the template strand, so it is not “blocked”.

Termination sequence for RNA polymerase III

a row of Ts (like RNA polymerase I)

t/f 5s rRNA must be modified with a G-cap and poly-A tail after transcription

false

5s RNA is [_] nucleotides long

120

TFIIIA

transcription factors which bind to the ICR of 5s rRNA genes and attract RNA polymerase 1. Also binds to the central region of the 5s rRNA and protects it as it is transported to the granular region of the nucleolus (acts as a chaperone).

7sRNP

ribonucleoprotein which is the combination of a 5s rRNA and a TFIIIA protein. Mode of transportation for 5s rRNA to the granular region of the nucleolus.

What is the difference between the S-type and O-type rRNA gene that explains why it is differentially expressed in gametes and somatic cells?

there is a six nucleotide difference in the ICR of the gene creating a different affinity for TFIIIA. The S-type has a higher affinity for TFIIIA than the O-type. In somatic cells, there is not an excess of TFIIIA, so only S-type is transcribed. However in gametes, there is an excess of TFIIIA so more O-type is produced due to the higher amount of O-type 5s rRNA genes.

One of the essential ways to regulate genes is to produce [_] at specific levels

transcription factors

t/f there may be introns/exons that get spliced in immature rRNA

false, that is only eukaryotic mRNA business