The Nucleus and the Nuclear Envelope

Question 1

Eukaryotic cells have ? which increases control of ?

Answer 1

Eukaryotic cells have a nucleus that compartmentalises the DNA away from the cytoplasm. This increases control of processes but creates a problem as large molecules (mRNA and proteins) have to move in and out of the nucleus

Question 2

What does the nuclear pore enable ?

Answer 2

The nuclear pore enables movement of molecules in and out

Question 3

A prokaryotic cell has ?

Answer 3

A single plasma membrane – often surrounded by protective cell wall – that encloses a single compartment containing cytoplasm and DNA

Question 4

In eukaryotic cells, the DNA is ?

Answer 4

Enclosed by two concentric membranes – a double membrane – that that form the nuclear envelope

Question 5

The outer nuclear membrane is continuous with the endoplasmic reticulum (ER), so the space between /

Answer 5

The inner and outer nuclear membranes is directly connected with the lumen of the ER

Question 6

The outer nuclear membrane is functionally similar to ?

Answer 6

To the ER membranes, but differs slightly in protein composition

Question 7

The inner nuclear membrane carries ?

Answer 7

Nuclear specific proteins such as the membrane proteins that organise the nuclear lamina, a fibrous network that provides structural support to the nucleus

Question 8

The nuclear envelope and endoplasmic reticulum may have evolved through invagination of ?

Answer 8

The plasma membrane

Question 9

Where does transcription (mRNA) occur ? and what happens ?

Answer 9

In the nucleus, DNA turns into RNA

Question 10

Where does translation (protein) occur? and what happens ?

Answer 10

In the cytoplasm, RNA turns into protein

Question 11

mRNA has to be exported from ?

Answer 11

The nucleus to be translated into protein

Question 12

Transcription and replication require ?

Answer 12

Enzymes and these proteins have to be imported into the nucleus

Question 13

The nuclear membrane is studded with ?

Answer 13

Nuclear pore complexes that are the sole channels through which polar molecules and macromolecules pass through the nuclear envelope

Question 14

Nuclear pores are ?

Answer 14

Large multi-protein complexes composed of about 30 different proteins

Question 15

What are nuclear localisation signals (NLS) ?

Answer 15

This is a protein tag that identifies proteins destined for the nucleus

Question 16

The tag typically consists of?

Answer 16

One or two short sequences containing positively charged Lysine residues

Question 17

Nuclear transport receptors?

Answer 17

Escort large molecules through the nuclear pore

Question 18

What are Importins ?

Answer 18

Importins carry proteins into the nucleus

Question 19

What are exportins ?

Answer 19

Exportins carry proteins out of the nucleus

Question 20

Nuclear transport receptors are made up of ?

Answer 20

Repeated α-helices that stack into large arches or snail-shaped coils

Question 21

Cargo and Ran-GTP bind ?

Answer 21

Different arches

Question 22

RanGTP covers ?

Answer 22

Loop (red) which is important for NLS binding

Question 23

The most prominent structure in the nucleus is ?

Answer 23

The electron dense nucleolus

Question 24

Function of nucleolus ?

Answer 24

Site of ribosome biogenesis

Question 25

Ribosomes translate ?

Answer 25

mRNA into proteins in the cytoplasm (rough ER and in cytosol)

Question 26

The ribosome is ?

Answer 26

A very large and complex structure, composed of two-thirds RNA and one-third protein

Question 27

Explain the small subunit ?

Answer 27

Platform where tRNAs are matched to the codons of the mRNA

Question 28

Explain the large subunit ?

Answer 28

Catalyses the formation of the | peptide bonds linking amino acids into a polypeptide chain

Question 29

What do the small and large subunit contain ?

Answer 29

Small subunit - 33 ribosomal proteins + 1 rRNA molecules | Large subunit - 49 ribosomal proteins + 3 rRNA molecules

Question 30

In higher eukaryotes, the ribosome contains four types of ? and what are they ?

Answer 30

Ribosomal RNAs (rRNAs), 5S, 5.8S, 18S, and 28S

Question 31

The genes encoding the 5.8S, 18S, and 28S rRNAs are?

Answer 31

Clustered in the genome in large tandem arrays

Question 32

The 5.8S, 18S and 28S rRNAs are transcribed as ?

Answer 32

A single pre-rRNA that is then sequentially cleaved to give rise to the three mature rRNAs

Question 33

The 5S rRNA is encoded by?

Answer 33

A separate gene

Question 34

rRNA processing occurs in?

Answer 34

The nucleolus

Question 35

Ribosomes are assembled in?and exported to ?

Answer 35

Ribosomes are assembled in the nucleus and exported to the cytoplasm

Question 36

The proteins are imported into the nucleus and assemble on ?

Answer 36

The pre-rRNA in the nucleolus

Question 37

As the rRNAs mature, additional ribosomal proteins are added to form ?

Answer 37

Pre- ribosomal particles

Question 38

These particles are exported from the ?

Answer 38

Nucleus via the nuclear pores to yield active ribosomal subunits

Question 39

GTP hydrolysis by ? drives what ?

Answer 39

GTP hydrolysis by the Ran-GTPase drives transport in and out of the nucleus

Question 40

The nucleolus is ?

Answer 40

An aggregation of rRNA gene clusters and the site of ribosome assembly

Question 41

Ribosomal proteins assemble?

Answer 41

Ribosomal proteins assemble on pre-rRNAs in the nucleolus

Question 42

Pre-ribosome particles are ?

Answer 42

Then exported through the nuclear pores