Introduction to the Cell Flashcards
____ can be identified with a scanning EM, and mediate communication between cytoplasm and nucleus. What are?
nuclear pores
[EM = electron microscopy]
which of these organelles is NOT membrane bound? mitochondria Golgi apparatus ribosome peroxisome lysosome RER
ribosomes are NOT membrane bound
cells that secrete proteins have extensive [smooth/rough] endoplasmic reticulum
cells that SECRETE proteins have extensive RER to which ribosomes are attached
Plasma cells synthesize and secrete immunoglobulins. Considering this, are they likely to have more free floating ribosomes or RER ribosomes?
cells that secrete proteins have extensive RER with ribosomes attached
what constitutes a free polysome?
mRNA + ribosomes
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
chromatin = DNA + histones
nucleoplasm: soluble nucleotides and enzymes
what kind of chromatin are actively transcribed
euchromatin - actively transcribed, diffuse
heterochromatin - inactive DNA, condensed around periphery of nucleus (darker EM/electron microscopy stain)
site of rRNA synthesis and ribosome subunit assembly occurs here
nucleolus (within the nucleus)
[ribosome subunit assembly includes rRNA and proteins synthesized in cytosol and transported into nucleus]
what is the purpose of the nuclear lamina and what modification regulates it?
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]
mutations in these proteins causes Progeria, a condition characterized by premature aging
nuclear lamins, regulate stability of nuclear envelope
movement of molecules through nuclear pores is bidirectional. what types of molecules enter, and what kinds leave?
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)
name the three proteins that form the framework of the cytoskeleton (and what filaments they form)
actin —> microfilaments
tubulin —> microtubules
intermediate filaments (similar to nuclear lamins)
actin-containing filaments =
microfilaments
ribosomes that become attached to RER will produce proteins that enter _____ pathway
secretory
what kind of ribosomes synthesize proteins for use within the cell
free polysomes (mRNA + ribosomes)
for proteins made by free-floating ribosomes (for use within cell) to be directed towards the nucleus, they need to contain this
Nuclear Localization Amino Acid Sequence
where are ribosomal subunits assembled?
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
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
production of proteins entering secretory pathway
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
rRNA synthesis - occurs in the nucleolus in the nucleus
