The Nucleus and the Nuclear Envelope Flashcards
Eukaryotic cells have ? which increases control of ?
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
What does the nuclear pore enable ?
The nuclear pore enables movement of molecules in and out
A prokaryotic cell has ?
A single plasma membrane – often surrounded by protective cell wall – that encloses a single compartment containing cytoplasm and DNA
In eukaryotic cells, the DNA is ?
Enclosed by two concentric membranes – a double membrane – that that form the nuclear envelope
The outer nuclear membrane is continuous with the endoplasmic reticulum (ER), so the space between /
The inner and outer nuclear membranes is directly connected with the lumen of the ER
The outer nuclear membrane is functionally similar to ?
To the ER membranes, but differs slightly in protein composition
The inner nuclear membrane carries ?
Nuclear specific proteins such as the membrane proteins that organise the nuclear lamina, a fibrous network that provides structural support to the nucleus
The nuclear envelope and endoplasmic reticulum may have evolved through invagination of ?
The plasma membrane
Where does transcription (mRNA) occur ? and what happens ?
In the nucleus, DNA turns into RNA
Where does translation (protein) occur? and what happens ?
In the cytoplasm, RNA turns into protein
mRNA has to be exported from ?
The nucleus to be translated into protein
Transcription and replication require ?
Enzymes and these proteins have to be imported into the nucleus
The nuclear membrane is studded with ?
Nuclear pore complexes that are the sole channels through which polar molecules and macromolecules pass through the nuclear envelope
Nuclear pores are ?
Large multi-protein complexes composed of about 30 different proteins
What are nuclear localisation signals (NLS) ?
This is a protein tag that identifies proteins destined for the nucleus
The tag typically consists of?
One or two short sequences containing positively charged Lysine residues
Nuclear transport receptors?
Escort large molecules through the nuclear pore
What are Importins ?
Importins carry proteins into the nucleus
What are exportins ?
Exportins carry proteins out of the nucleus
Nuclear transport receptors are made up of ?
Repeated α-helices that stack into large arches or snail-shaped coils
Cargo and Ran-GTP bind ?
Different arches
RanGTP covers ?
Loop (red) which is important for NLS binding
The most prominent structure in the nucleus is ?
The electron dense nucleolus
Function of nucleolus ?
Site of ribosome biogenesis
Ribosomes translate ?
mRNA into proteins in the cytoplasm (rough ER and in cytosol)
The ribosome is ?
A very large and complex structure, composed of two-thirds RNA and one-third protein
Explain the small subunit ?
Platform where tRNAs are matched to the codons of the mRNA
Explain the large subunit ?
Catalyses the formation of the
peptide bonds linking amino acids into a polypeptide chain
What do the small and large subunit contain ?
Small subunit - 33 ribosomal proteins + 1 rRNA molecules
Large subunit - 49 ribosomal proteins + 3 rRNA molecules
In higher eukaryotes, the ribosome contains four types of ? and what are they ?
Ribosomal RNAs (rRNAs), 5S, 5.8S, 18S, and 28S
The genes encoding the 5.8S, 18S, and 28S rRNAs are?
Clustered in the genome in large tandem arrays
The 5.8S, 18S and 28S rRNAs are transcribed as ?
A single pre-rRNA that is then sequentially cleaved to give rise to the three mature rRNAs
The 5S rRNA is encoded by?
A separate gene
rRNA processing occurs in?
The nucleolus
Ribosomes are assembled in?and exported to ?
Ribosomes are assembled in the nucleus and exported to the cytoplasm
The proteins are imported into the nucleus and assemble on ?
The pre-rRNA in the nucleolus
As the rRNAs mature, additional ribosomal proteins are added to form ?
Pre- ribosomal particles
These particles are exported from the ?
Nucleus via the nuclear pores to yield active ribosomal subunits
GTP hydrolysis by ? drives what ?
GTP hydrolysis by the Ran-GTPase drives transport in and out of the nucleus
The nucleolus is ?
An aggregation of rRNA gene clusters and the site of ribosome assembly
Ribosomal proteins assemble?
Ribosomal proteins assemble on pre-rRNAs in the nucleolus
Pre-ribosome particles are ?
Then exported through the nuclear pores
