Nuclear Structure (Lec 7+)

Question 1

What is a Localization Signal?

Answer 1

A group of AAs acting as an “address” or “tag” directing protein to a particular destination. (can be sequence or patch)

Question 2

In what stage of the cell cycle are nuclear lamins phosphorylated?

Answer 2

G2 –> M transition

Completely phosphorylated by prophase due to rise in protein kinase activity; depolymerize

Question 3

In what stage(s) of the cell cycle are nuclear lamins dephosphorylated?

Answer 3

At anaphase, at start of M –> G1 transition.

Due to rise in protein phosphatase activity; re-polymerize.

Question 4

Nuclear pores

Answer 4

production of cytoplasmic ribosomes requires extensive traffic in and out of nucleus. Both RNA and protein (and completed subunits) must pass through pores.

Question 5

Where is rRNA for cytoplasmic ribosomes made? Using what enzyme?

Answer 5

RNA pol I makes large molecules rRNA in the nucleolus. RNA pol III makes small molecules of rRNA.

Question 6

What does RNA pol II make?

Answer 6

mRNA

Question 7

What does RNA pol III make?

Answer 7

tRNA and small molecules of rRNA (5S)

Question 8

Where are the genes for rRNA located?

Answer 8

Multiple copies of the genes for rRNA are located in tandem in clusters called NORs. Multiple copies are needed bc rRNA is made directly off of DNA. (no mRNA for amplification)

Question 9

NOR

Answer 9

Nuclear Organizing Region for DNA.
Region of the DNA coding for rRNA = rDNA = genes for rRNA.
Has multiple copies of the rRNA genes.
NORs are permanent– are part of DNA

Question 10

Nucleolus

Answer 10

Structure seen at interphase; not in meiosis/mitosis.
Forms during interphase at location of one or more NORs.
Nucleoli are only visible when NOR is being transcribed and ribosomes are being assembled

Question 11

Organelle ribosomes

Answer 11

Location: found in mito and chloroplasts
Made and assembled differently from cytoplasmic ribosomes:
rRNA for mito ribs is encoded into mito DNA & made inside the mtio.
proteins for mito ribosomes are encoded in the nucleus and made in the cytoplasm.

Question 12

TFs (Eukaryotic Transcription Factors)

Answer 12

-RNA pol won’t bind to DNA directly: requires TFs
Two kinds: Basal (all the same in all cells) and regulatory (decrease or increase basal transcription depending on cell type)