The Nucleus

Question 1

What is the main feature that distinguised eukaryotic cells form prokaryotic ones

Answer 1

The nucleus

Question 2

What is the nucleus?

Answer 2

• Houses the genome (genetic information)

- Cells control center

Question 3

What role does the separation of the genome from the site of mRNA translation play?

Answer 3

Eukaryotic gene expression

The nuclear envelope separates the nuclear contents form the cytoplasm, controlling traffic of proteins and RNA through nuclear pore complexes.
This regulates gene expression as the envelope decides what gets in and what doesn’t.

Question 4

Describe the anatomy of the nuclear envelope

Answer 4

• Two nuclear membranes
• An underlying nuclear lamina (thin layer or plate)
• Nuclear pore complexes

Question 5

What organelle is connected with the outer membrane of the nucleus?

Answer 5

The endoplasmic reticulum
(Important for transferring proteins out of the cell)
The space between in the inner and outer membranes is directly connected with the lumen of the ER

Question 6

Does the inner membrane have any proteins attached to it?

Answer 6

Yes, it has integral proteins.

Ex. One that binds the nuclear lamina

Question 7

What are nuclear membranes made of?

Answer 7

Phospholipid bilayers

Question 8

Are nuclear membranes permeable?

Answer 8

Yes, but only to small, non polar molecules.

Question 9

What are nuclear pore complexes?

Answer 9

Channels in the nuclear membranes that allow passage of:

• small polar molecules
• ions
• macromolecules

Question 10

What is the nuclear lamina?

Answer 10

A fibrous mesh that provides structural support to the nucleus

Question 11

What is the nuclear lamina made of?

Answer 11

Fibrous proteins called lamins, and other various proteins

Question 12

What types of proteins are lamins?

Answer 12

Intermediate (refers to middle ranged size) filament protein that associate to form higher order structures

Question 13

What is a dimer?

Answer 13

A polymer of 2 identicle proteins (in this case lamins) bonded together.

Question 14

How are lamins bonded to form dimers?

Answer 14

alpha-helical regions wind around each other to form a coiled coil

Question 15

What happens when multiple lamin dimers associate with each other?

Answer 15

It forms the nuclear lamina.

Question 16

What are the 3 main inner membrane proteins that lamins bind to?

Answer 16

Emerin
Lamin B REceptor (LBR)
LINC protein complexes

Question 17

What are LINC protein complexes connected to?

Answer 17

The cytoskeleton

Question 18

Do lamins connect to chromatin?

Answer 18

Yes

Question 19

What is the purpose of lamins binding to the nuclear envelope?

Answer 19

To anchor and support the inner and outter membranes and to create the foundation of the lamina.

Question 20

How can mutations in lamin genes effect an organism

Answer 20

It results in several inherited tissue-specific diseases

Question 21

What happens when the lamina gene is deleted by accident?

Answer 21

Results in -> Hutchinson-Gilford Progeria

Deletion of the lamin gene that occurs when RNA is being spliced and reordered into the desired sequence when a specific 150 nucleotides are removed.

Question 22

How many nuclear pore complexes have we identified so far?

Answer 22

30!

Question 23

What is the structure of nuclear pore complexes like?

Answer 23

Large

Question 24

What is another name for nuclear pore complex proteins?

Answer 24

Nucleoporins

Question 25

What happens to RNAs after it is synthesized in the nucleus?

Answer 25

It exported to the cytoplasm for protein synthesis

Question 26

How does the nucleus obtain proteins that it needs to function?

Answer 26

By importing them through the nuclear envelope using nucleoporins.
They come from their respective synthesis sites in the cytoplasm

Question 27

How do molecules pass through the pore complexes in the nuclear membrane?

Answer 27

Passive Diffusion

Protein and RNA transport

Question 28

Describe passive diffusion through the nuclear membrane

Answer 28

An energy free method

Small, nonpolar molecules can pass directly through the membranes freely in any direction

Question 29

Describe selective transport through the nuclear membrane

Answer 29

Requires energy

—

Question 30

What type of microscopy allows us to see pore complexes in the nuclear membrane?

Answer 30

Electron microscopy

Question 31

Describe the general structure of pore complexes

Answer 31

8 subunits/spokes are connected to rings at both the nuclear and cytoplasmic surfaces.
They are organized in a circle around a central channel.
Protein filaments extend from the rings, forming a basketlike structure on the nuclear side (inside the envelope)

Question 32

What are Nuclear Localization Signals and what do they do?

Answer 32

They are amino acid sequences that are recognized by the nuclear transport receptors and allow the proteins to enter the nucleus through a channel

Question 33

What are nuclear transport receptors?

Answer 33

NLS

Recognized importins.

Question 34

How and when were nuclear localization signals discovered?

Answer 34

1984
A signal sequence responsible for nuclear localization was determined using T antigen mutants.
This was proved by attaching that same amino acid sequence to other proteins. These proteins were then let into the nucleus.

Question 35

What is the T antigen nuclear localization signal?

Answer 35

A single stretch of amino acids that allow entry into the nucleus.

Question 36

What makes the T antigen localization signal different from other signals?

Answer 36

The T antigen is a single stretch of amino acids, where other signals are bipartite.

Question 37

Define bipartite

Answer 37

Two amino acids sequence, separated by another unrelated amino acid sequence.

Question 38

What are importins?

Answer 38

Receptors that identify NLS and carry proteins through the nuclear pore complex.

Question 39

What is Ran?

Answer 39

GTP-binding protein that controls the direction of movement of the proteins being pulled in by the importin.