Introduction to the Cell

Question 1

____ can be identified with a scanning EM, and mediate communication between cytoplasm and nucleus. What are?

Answer 1

nuclear pores

[EM = electron microscopy]

Question 2

which of these organelles is NOT membrane bound?
mitochondria 
Golgi apparatus
ribosome
peroxisome
lysosome
RER

Answer 2

ribosomes are NOT membrane bound

Question 3

cells that secrete proteins have extensive [smooth/rough] endoplasmic reticulum

Answer 3

cells that SECRETE proteins have extensive RER to which ribosomes are attached

Question 4

Plasma cells synthesize and secrete immunoglobulins. Considering this, are they likely to have more free floating ribosomes or RER ribosomes?

Answer 4

cells that secrete proteins have extensive RER with ribosomes attached

Question 5

what constitutes a free polysome?

Answer 5

mRNA + ribosomes

Question 6

the nuclear envelope is a continuous inner and outer membrane. the outer membrane is continuous with the RER and has ribosomes attached.

Within the nuclear envelope are chromatin and nucleoplasm. Describe the components of each of these

Answer 6

chromatin = DNA + histones

nucleoplasm: soluble nucleotides and enzymes

Question 7

what kind of chromatin are actively transcribed

Answer 7

euchromatin - actively transcribed, diffuse

heterochromatin - inactive DNA, condensed around periphery of nucleus (darker EM/electron microscopy stain)

Question 8

site of rRNA synthesis and ribosome subunit assembly occurs here

Answer 8

nucleolus (within the nucleus)

[ribosome subunit assembly includes rRNA and proteins synthesized in cytosol and transported into nucleus]

Question 9

what is the purpose of the nuclear lamina and what modification regulates it?

Answer 9

nuclear lamina (composed of lamin proteins) forms dense layer under the nuclear membrane to maintain structure

de/phosphorylation of nuclear lamins regulates stability of nuclear envelope
[phosphorylation of lamin B causes nuclear envelope degradation during prophase of mitosis]

Question 10

mutations in these proteins causes Progeria, a condition characterized by premature aging

Answer 10

nuclear lamins, regulate stability of nuclear envelope

Question 11

movement of molecules through nuclear pores is bidirectional. what types of molecules enter, and what kinds leave?

Answer 11

entering via nuclear pore: proteins used in gene regulation (histones, DNA/RNA polymerases, transcription factors) and ribosomal subunit proteins

exiting via nuclear pore: molecules involved in protein synthesis (mRNA, tRNA, ribonucleoproteins - assembled ribosome subunits)

Question 12

name the three proteins that form the framework of the cytoskeleton (and what filaments they form)

Answer 12

actin —> microfilaments
tubulin —> microtubules
intermediate filaments (similar to nuclear lamins)

Question 13

actin-containing filaments =

Answer 13

microfilaments

Question 14

ribosomes that become attached to RER will produce proteins that enter _____ pathway

Answer 14

secretory

Question 15

what kind of ribosomes synthesize proteins for use within the cell

Answer 15

free polysomes (mRNA + ribosomes)

Question 16

for proteins made by free-floating ribosomes (for use within cell) to be directed towards the nucleus, they need to contain this

Answer 16

Nuclear Localization Amino Acid Sequence

Question 17

where are ribosomal subunits assembled?

Answer 17

nucleus - mRNA for ribosomal proteins is transcribed from nuclear DNA and transported via pore to cytoplasm, where ribosomal proteins are translated on free ribosomes, then enter nucleus via pore

in nucleus, ribosomal proteins associate with rRNA (transcribed in nucleolus) to produces large (60S) and small (40S) subunits

subunits exit independently, assemble to maturity in presence of mRNA

Question 18

drug X specifically inhibits function of membrane-bound polyribosomes. What process is most likely disrupted by this drug?

a. production of nuclear lamins
b. production of nuclear pore proteins
c. production of proteins entering secretory pathway
d. production of proteins made for use within the cell

Answer 18

production of proteins entering secretory pathway

Question 19

if nuclear transport is blocked, which of these events will still be able to occur?

a. rRNA synthesis
b. appearance of new ribosomal subunits in the cytoplasm
c. production of protein from mRNA

Answer 19

rRNA synthesis - occurs in the nucleolus in the nucleus