BIOL 200 Lecture Notes - Polytene Chromosome, Karyopherin, Helicase

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ceruleanprairie-dog589

6 Apr 2012

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So far, all the mechanisms we have seen on dna and rna have taken place in the nucleus. Protein synthesis, however, takes place in the cytoplasm. So, these final mrnas must somehow be transferred from the nucleus to the cytoplasm and then associate with a bunch of new proteins associated with translation. Nuclear pores are complexes which resemble baskets and are located all over the nuclear membrane, which has a bilayer membrane. They make the nucleus look like a golf ball structure because of the perforations. The nuclear pore complex is a highly organized structure made of many protein subunits: they contain nucleoporins with fg repeat proteins, which are zones of increased hydrophobicity. Much of the transport through the nuclear membrane is mediated by these. The npc itself is huge, over 125 megadaltons in size (30 times bigger than a ribosome: it is composed of many proteins; 50 in yeast and 100 in humans.

Related Questions

1. The histones that form the core of the nucleosome get into the nucleus by which of the following?

a) Passive diffusion through nuclear pores

b) Selective and facilitated active transport through nuclear pores

c) Ribosomes located in the nucleus synthetize histones in the nucleus

d) Histones are made at the ER membrane and then diffuse to the nucleus

2. Membrane proteins that belong to the golgi, lysosome, or plasma membrane first pass through which organelle before reaching their final subcellular destination?

a) The golgi apparatus

b) The smooth ER

c) The nucleus

d) The ER membrane

e) The ER lumen

3. Where in the cell would a ribosomal protein be located if it has had its nuclear export signal inactivated (non-functional or non-existent).

a) The protein would be found in the ER lumen

b) The protein would remain in the nucleus

c) The protein would be secreted

d) The protein would remain in the cytoplasm

e) The protein would be in the ER membrane

4. Where would be the final destination of a protein if it contained a NLS anywhere in the protein sequence (and which is exposed to the cytoplasm after protein folding) but also contained an ER signal sequence at the carboxy terminus?

a) The ER lumen

b) The nucleus

c) The cytoplasm

d) The inner nuclear membrane

e) The ER membrane

5. The sequence K-D-E-L serves as a retention/retrieval signal for ER proteins.

a) True

b) False

6. The following are true for both cell membrane proteins and secretory proteins EXCEPT?

a) Precursors of the mature proteins contain signal sequence.

b) Both types of proteins contain stop-transfer sequences

c) Both types of proteins enter the ER while being synthetized

d) Both types of proteins pas through the golgi apparatus

e) Both are carried by clatherin-coated vesicles

7. If you isolate a regulated secreted protein from a secretory/storage vesicle and inject it into the cytosol, is will?

a) Be secreted through channels in the plasma membrane

b) Be taken up into secretory vesicle and secreted

c) Remain in the cytosol until it is degraded

d) Be taken up into the rough ER and follow the secretory pathway

goldmanatee250

1-Fill in the blank

Protein transport between the cytoplasm and the nucleoplasm requires a nuclear localization signal (NLS) at the C-terminus. The NLS binds to a/n ______ that binds it to a cytoplasmic filament of a nuclear pore.

2-Briefly summarize the four different levels of eukaryotic gene regulation

marooncicada200

1. DNA, or the instructions for making proteins, is found within the _____ of the cell; while protein synthesis machinery is found in the _____ of the cell.

nucleus; cytoplasm

nucleolus; nucleus

cytoplasm;nucleus

nucleus; plasma membrane

2.During transcription, double stranded DNA is transcribed into a complementary molecule of

single-stranded DNA.

double-stranded DNA.

single-stranded mRNA.

single-stranded tRNA.

15. Place the following steps in the order in which they occur during gene expression.

mRNA is carried to ribosomes in the cytoplasm, DNA is transcribed into mRNA in the nucleus, mRNA is translated into polypeptides by tRNA

mRNA is carried to ribosomes in the cytoplasm, mRNA is translated into polypeptides by tRNA, DNA is transcribed into mRNA in the nucleus

DNA is transcribed into mRNA in the nucleus, mRNA is translated into polypeptides by tRNA, mRNA is carried to ribosomes in the cytoplasm

DNA is transcribed into mRNA in the nucleus, mRNA is carried to ribosomes in the cytoplasm, mRNA is translated into polypeptides by tRNA

BIOL 200 Lecture Notes - Polytene Chromosome, Karyopherin, Helicase

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