Study your flashcards anywhere!

Download the official Cram app for free >

  • Shuffle
    Toggle On
    Toggle Off
  • Alphabetize
    Toggle On
    Toggle Off
  • Front First
    Toggle On
    Toggle Off
  • Both Sides
    Toggle On
    Toggle Off
  • Read
    Toggle On
    Toggle Off

How to study your flashcards.

Right/Left arrow keys: Navigate between flashcards.right arrow keyleft arrow key

Up/Down arrow keys: Flip the card between the front and back.down keyup key

H key: Show hint (3rd side).h key

A key: Read text to speech.a key


Play button


Play button




Click to flip

62 Cards in this Set

  • Front
  • Back
How big is the nucleus?
generally about 10 um
relaxed and lightly staining
compact and darkly staining
How much of euchromatin is transcriptionally active?
How much of heterochromatin is active?
What is euchromatin enriched in?
Acetylated histones
-Histone H2A.Z
What turns off heterochromatin?
Heterochromatin protein-1 HP1
What is Gbanding?
Digesting chromatin with trypsin and then Staining with Giemsa to classify it in 3 types.
3 Classes of chromatin based on G-banding:
C-bands = constitutive
What is C-bands?
Highly condensed and darkly staining (like heterochromatin); it is the satellite DNA in centromere and telomere
What is G-dark chromatin?
Lighter than C-bands and contains tissue-specific genes
What is G-light chromatin?
Cell-survival genes for housekeeping - stains lightest of all bands.
When in S-phase is each type of chromatin replicated?
C-bands = last
G-dark = middle of Sphase
G-light = first in S-phase
Why does G-light stain lightly?
Because it is relaxed and unfolded
What is the consequence of the open nature of G-light?
It is susceptible to radiation and could be a good way to target cancer for chemotherapy.
What are drugs that target the genes in G-light chromatin?
OdNs and siRNAs.
What is OdNS therapy?
Using antisense oligonucleotides to hybridize with genes or mRNA and prevent their transcription.
What is more promising; siRNA or OdNS?
Why is siRNA therapy more promising?
Because it acts via naturally-occuring mechanisms.
What are the steps in siRNA therapy?
1. Transfect target cells with dsRNA complementary to target
2. Cleave with DICER to make many small siRNAs
3. Complex siRNAs to RISC - RNA induced silencing complex
4. RISC/siRNA recognizes target
5. RISC cleaves pathogenic RNA
What is the nuclear matrix?
The residual framework that remains after extracting >90% of it with detergents, nucleases, and salt.
Functions of the nuclear matrix:
-Organizes the genomic DNA into domains
-Framework of the nucleus
3 Parts to the Nuclear Matrix:
1. Nucleolus
2. Nuclear pore complex/lamina
3. Internal nuclear matrix
What is the nucleolus?
Site of rRNA production and assembly of ribosomal subunits.
How many chromosomes in humans have genes for ribosomes?
How many genes does each chromosome have for ribosomes?
About 40
So how many genes in the human genome encode ribosomal RNA?
What transcribes ribosomal genes? When?
RNA Pol I - transcribes ribosomes constantly.
AT what parts of the cell cycle are nucleoli prominent? Not seen?
Prominent = interphase

Not seen = mitosis
Does the nucleolus have a membrane?
What are the 3 parts of a nucleolus that can be seen at high magnification EM?
1. Light fibrillar center (the rDNA genes themselves)
2. Dense fibrillar area (surrounds light, site of trxn)
3. Granular - ribosome subunits
Important things to know about Ribosomal synthesis:
-Made in ribosomes
-Large and small subunits
-RNA Pol I makes a VERY LARGE TRANSCRIPT that is processed
How many layers are in the Nuclear envelope?
What is the double membrane nuclear envelope composed of?
-Outer membrane
-Inner membrane
-perinuclear space inbetween
What is the perinuclear space continuous with?
Endoplasmic reticulum
What is on the outer nuclear membrane?
What is on the inner membrane?
-Integral proteins that bind to the nuclear lamina
-Marginal heterochromatin
What is the integral protein that binds the inner nuclear membrane to the nuclear lamina?
Lamin-B receptor
What is the nuclear lamina?
What laminates the inner membrane - a layer of protein.
What is found then on the nuclear lamina?
The marginal heterochromatin.
What is the site where the inner and outer nuclear membrane layers merge called?
Nuclear Pore Complex
What is the diameter of a nuclear pore complex?
10 nm
What passes through the nuclear pore complex?
-Proteins in
-Proteins and RNA out
How small do proteins have to be to diffuse through pores?
40 kD or smaller
How are other larger proteins able to get into the nucleus?
By NLS - nuclear localizing sequences.
What are Nucleoporins?
proteins situated in the nuclear membrane pore complex strata.
(cytoplsmic/nuclear/middle strata)
How are nucleoporins situated within the nuclear pore?
As octamers in symmetry
What is the function of nucleoporins?
Docking sites for proteins that contain NLS's.
What is the NLS rich in?
Basic amino acids
How does the number of NLS correlate to transport?
The more sequences in a transcript, the more transport.
What allows proteins to bind to the nuclear pore complex?
Importin a/B heterodimer - a receptor that escorts nuclear proteins into the nucleus.
What does each function:
-Importin a
-Importin B
a binds the NLS of the protein

B docks the complex to a nucleoporin in the pore.
What happens after Importin a/B escort a protein to the pore?
Translocation - energy dependent and then release of the protein and Importin recycles to the cell.
How is protein import regulated?
By phosphorylation:
-of S/T/Y residues in the NLS sequence - inhibits Importin from binding
-If proteins mask NLSs, hormones can overcome it by phosphorylating the proteins and releasing them to allow Importin to bind.
What structures are important for getting Protein/Importin complexes into and through pores?
Intermediate filaments - acting as railroad tracks.
What is required for Export from the nucleus?
-Can be either protein or RNA
-NESs (export sequences)
What provides the energy for translocation into and out of the nucleus?
Where is Ran-GTP? Ran-GDP? What does each do at that site?
Ran-GTP = nucleus; binds importin B for release of cargo

Ran-GDP = cytoplasm; binds cargo and transports to nucleus
So export requires which type of Ran?
Import requires what type of Ran?
WHat amino acid are NLS sequences rich in?
ARginine and Lysine
What amino acid are NES sequences rich in?