exam 2 w5-8
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Eukaryotic cells are divided into functionally distinct, membrane-enclosed compartments. What are the two major compartments within the plasma membrane?
• Nucleus • Cytoplasm The cytoplasm includes the cytosol and the organelles suspended within it.
What are the organelles found within eukaryotic cells?
• Endoplasmic reticulum (ER) • Golgi apparatus • Mitochondria • Lysosomes • Endosomes • Peroxisomes Organelles perform specific functions and vary in abundance based on cell specialization.
True or false: The cytosol occupies about half of the total cell volume.
TRUE Membrane-enclosed compartments occupy the other half of the cell volume.
The relationship between cell compartments reveals how eukaryotic cells likely originated from simple cells. What did these simple cells lack?
Internal membranes They relied on a single plasma membrane for all membrane-dependent functions.
What are the three major intracellular compartments of a eukaryotic cell?
• Mitochondria and chloroplasts (endosymbionts) • Nuclear envelope • Single membrane-enclosed organelles (ER, Golgi, etc.) The endosymbionts theory explains the origin of mitochondria and chloroplasts.
What are biomolecular condensates?
Membraneless organelles formed by nucleic acid or protein scaffold molecules They selectively segregate and partition macromolecules for specialized functions.
What is the best-known biomolecular condensate where ribosomes are assembled?
Nucleolus It is composed of ribosomal RNA and protein.
Fill in the blank: Condensate scaffolds are ______, meaning they can have many interactions.
multivalent Client-scaffold interactions are dynamic and can rearrange freely.
What are the four different mechanisms by which proteins are sent from the cytosol to another compartment?
• Translocation • Gated transport • Vesicular transport • Engulfment Each mechanism has distinct processes for transporting proteins.
What is a sorting signal in protein sorting?
A cellular address recognized by sorting receptors at the destination Sorting signals consist of specific amino acids and can be linear or three-dimensional.
The endoplasmic reticulum (ER) consists of two distinct regions. What are they?
• Rough endoplasmic reticulum (RER) • Smooth endoplasmic reticulum (SER) The RER has bound ribosomes, while the SER lacks ribosomes.
What does the RER produce?
• Soluble proteins • Membrane proteins These proteins are destined for most cellular organelles and the plasma membrane.
What is a polyribosome?
A complex of multiple ribosomes translating a single mRNA molecule Free polyribosomes translate cytosolic proteins, while membrane-bound polyribosomes translate ER-targeted proteins.
True or false: Transmembrane proteins use the same mechanism as soluble proteins to enter the ER.
TRUE They also use SRP and the Sec61 translocator for insertion into the membrane.
What is the role of chaperone proteins in post-translational translocation?
They keep proteins unfolded and prevent aggregation This is crucial for proteins that are fully translated in the cytosol.
What is a GPI anchor?
A covalent linkage that attaches proteins to the ER membrane GPI-anchored proteins can end up on the extracellular surface.
What is N-linked glycosylation?
The transfer of a precursor oligosaccharide to asparagine residues It is the most common form of glycosylation, comprising 90% of all glycoproteins.
What happens to misfolded proteins in the ER?
They are retrotranslocated back to the cytosol for destruction This process is triggered by sensors in the ER membrane.
What is the function of phospholipid translocator scramblase?
Transfers phospholipids non-selectively between monolayers This process does not require energy and helps equilibrate phospholipids.
What do peroxisomes contain?
Oxidative enzymes that produce hydrogen peroxide They play a role in the metabolism of specific organic substrates.
What do enzymes in peroxisomes use to remove hydrogen atoms from organic substrates?
Oxygen This process produces hydrogen peroxide.
How are proteins directed to peroxisomes?
• Through two mechanisms • By being inserted into the membrane in the ER • By being packaged in peroxisomal precursor vesicles These vesicles can fuse with existing peroxisomes or form new ones.
What are the double membrane enclosed organelles that originated from endosymbiants?
• Mitochondria • Chloroplasts This theory is supported by their double membranes and own DNA.
What are the subcompartments created by the double membranes of mitochondria?
• Outer membrane • Inner membrane • Intermembrane space • Cristae • Matrix space These structures are crucial for ATP synthesis.