Lecture 7 Cellular Organelles Flashcards
Prokaryote do not have a true ____
-nucleus
Nucleoid =
region of condensed DNA
Exocytosis/endocytosis occurs in _______ but not in prokaryotes
- eukaryotes
Mitosis and meiosis in ______
- Eukaryotes
Binary fission in ________
- prokaryotes
Surface Area/Volume ratio
- *Need adequate surface area for nutrient/waste exchange
- > As cells get larger, the surface area to volume ratio ________
- decreases
Therefore, nutrient/waste exchange becomes more problematic due to insufficient surface area for a large volume cell
Diffusion within the cell becomes problematic as the volume becomes _____
- Larger
Potential for inadequate concentrations of _____ and ______
- reactants and catalysts
How do some large cells overcome these limitations? An example would be muscle fibers…
- Each fiber has hundreds of nuclei (myonuclei) to support synthesis of RNA and proteins
Each fiber not really an individual cell – syncitium
Syncitium = large cell formed via the fusion of many smaller cells (myoblasts)
In order for a fiber to grow (hypertrophy), it must add additional ______
- Myonuclei
Where do myonuclei come from for hypertrophy of muscle cells?
- Additional myonuclei come from satellite cells that reside just outside of the muscle fiber
- The additional nuclei are required to support the increased level of RNA and protein synthesis
The nucleus is surrounded by the ______ ________
- nuclear envelope
Nucleoplasm =
=inside of the nucleus (except for the nucleolus)
What are dissolved in the nucleoplasm (3)
Nucleotides, transcription factors, and enzymes
Heterochromatin is _______ packaged
- Densely
Constitutive heterochromatin is ______ condensed
-always
Facultative heterochromatin is __ ___ condensed
- not always
Euchromatin, as opposed to heterochrmation is packaged how?
- this allows for what?
- loosely packed
- > Allows for proteins to interact with the DNA- gene transcription
Chromatin is a…..
- material that makes up a chromosome
Muscle Fiber – myonucleus (the nuclei of a muscle fiber or cell)
…. have a very _____ level of ______, and is ______ in gene transcription
- High/ euchromatin
- Very active
Muscle Satellite Cell – nucleus
- as opposed to a myonucleus, ___1__
levels of ____2___, and higher levels of __3___
- Low
- euchromatin
- heterochromatin
Nuclear pores are….
- Large pores that allow for transport into and out of the nucleus through the nuclear envelope
Nucleolus (nucleoli) is the site for
- rRNA and ribosomal protein synthesis
* Cells with high amounts of protein synthesis generally have large distinct nucleoli (neurons)
Movement of proteins and rRNA through the nuclear pores is necessary for:
- ribosome assembly (protein synthesis)
- physiological signals to regulate gene expression
4 main structural components of nuclear pore
- Cytoplasmic Ring
- Nuclear ring and basket - regulation
- Lumenal rings – anchor (include anular ring)
- Transporter (central granule) – involved in physical transport
The function of the nuclear pore is to (2)
- mediate the energy dependent (GTP) transport of nuclear proteins, mRNA, and rRNA into and out of the nucleus
- Allows passive diffusion of small molecules and ions, even some small proteins up to ~30,000 daltons
Protein destined for the nucleus must have….
- nuclear localizing signal (NLS)
NLS must be recognized by a ______ in order to get into the nucleus
- karyopherin
In this case an importin
Karyopherins are a…
….Class of proteins that assist in shuttling proteins across the nuclear envelope
Protiens that assist in nuclear import =
- importins
Proteins that assist in nuclear export =
- exportins
Importins have both an _____ and _____ complex
alpha/beta (will usually function together)
Importin ____ can sometimes function alone
- beta
Importin α binds to the target protein at its _____ and to importin β. Thus, Importin α acts as an _____ protein between the cargo protein and importin β
- NLS (nuclear localization signal)/ adapter
For nuclear export, there will be high ____ in the nucleus, and high _____ outside the nucleus
GEF, GAP
Slide #27!!!!
Look at notes too
mRNA rRNA are bound to protein to form _________ particles
- ribonucleoprotein (RNP) particles
The proteins to be exported (including a protein in the RNP) must have a ____ ____ _____
-nuclear export signal (NES)
The NES interacts with an exportin, which facilitates nuclear export
In the nucleus the exportin: (4)
- Bind with ran-GTP (ran-GTP is high in nucleus)
- This allows it to bind its cargo (which must have a protein with an NES, except for tRNA)
- Exportin then interacts with the NPC
- And moves cargo out of nucleus
Steps for cargo to exit the nucleus:
- Exportin binds to Ran-GTP
- Exportin-Ran-GTP binds to the cargo (at NES of Cargo)
- Entire complex is exported via exportin interation with the nucleoporins of the NPC
- In the cytosol, GTP is hydrolyzed and the Cargo and exportin are released
- Exportin is then recycled back into the nucleus
How does Ran get back into the nucleus?
- In the cytosol, Ran-GDP associates with NTF2 (nuclear translocation factor 2)
- Ran-GDP-NTF2 complex interacts with the NPC and translocates into the nucleus
- The NTF2 releases Ran in the nucleus where Ran interacts with the GEF which binds a new GTP to Ran
- Thus Ran-GTP levels are high in the nucleus providing the concentration gradient that helps to drive import and export
NFAT is:
Transcription factor protein involved in many cellular processes… Along with calcineurin, NFAT transduces cellular signals (changes in Ca2+ concentration) into molecular signals (changes in gene expression)
NFAT translocates into the nucleus upon dephosphorylation by calcineurin
-Binds to DNA and alters transcription of specific genes
The Nuclear lamina is:
Meshwork of fibrous proteins that line the inner surface of the nuclear envelope
Nuclear lamina acts to (3)
- Form a supporting network of proteins that maintains the 3-D shape of the nucleus
- Anchor and organize the chromatin
- Act to transmit mechanical signals to the genes
The Nucleolus is the site of ______ synthesis and ________ proteins
- rRNA/ ribosomal
Core of nucleolus = Nucleolus Organizing Region (NOR), NOR is:
- segments of DNA with repeated sequences that code for rRNA and ribosomal protein
Why does nucleolus appear dark
- Nucleolus appears dark due to a dense accumulation of rRNA and ribosomal protein
Nucleolar fibrils=
- DNA and rRNA
Nucleolar granules=
-ribosomal subunits
