Chapter 5 - Structure & Function in Protists Flashcards
Most eukaryotes are ___________________.
Microbes
What is another name for eukaryotic microbes?
Protists
How long did eukaryotic microbes have before macroscopic lineages (i.e., animals) arose?
1 billion years
Eukaryotic cells are characterized by what two things. What are they?
- An endomembrane system
- A cytokeletal system
Why is it believed that the endomembrane and cytoskeletal system led to the evolutionary success of the eukaryotes?
Because these two systems are the basis for the ability to phagocytose particular food
What were the crucial first events in the evolution of the eukaryotic cell?
The development of a rudimentary cytoskeletal system and the ability to manage the flow of material from one membrane to the next
What 7 organelles make up the endomembrane system?
- The cell membrane
- The endoplasmic reticulum
- The Golgi body
- The endosome
- The nuclear membrane
- The lysosome
- The vacuole
What is not included as part of the endomembrane system?
The mitochondrial and cholorplast membrane
What does the cytoskeletal system consist of?
Microtubules and microfilaments
What targets proteins to particular places in the eukaryotic cell?
Special signal sequences
There are two types of targeting mechanisms in the eukaryotic cell. What are they?
Cotranslation and posttranslation
Why do eukaryotic cells require proteins to have signal sequences?
Because the endomembrane system partitions the cell into multiple compartments each of which has its own distinctive proteins
What type of protein undergoes cotranslational targeting?
Those targeted for the ER and/or secretion
Proteins destined for the mitochondria and/or chloroplast undergo the __________________________ mechanism for protein sorting.
Post-translation
What is required for post-translational signaling?
A chaperone protein
What are the steps to co-translational targeting?
- mRNA exists the nucleus
- Ribosome binds and begins translation in the cytosol
- The amino-terminal 20 or so amino acids constitute a signal sequence that targets the protein to the ER
- The signal recognition particle (SRP) binds to the ribosome and the signal peptide, halting translation
- The ribosome binds to the translocation complex on the ER membrane, displacing the SRP and recommencing translation
- When translation is completed, the signal sequence is cleaved and degraded
- The translocation complex dissociates
What binds to the ribosome and signal peptide, halting translation?
The signal recognition particle
To what does the ribosome bind on the ER membrane in co-translational targeting?
The translocation complex
What are the steps for post-translation protein targeting?
- As mitochondrial or chloroplast proteins are translated, chaperone proteins bind to them
- The chaperone conducts the protein to the organelle where it is translocated to the interior
- The signal sequence is cleaved off and the protein folds into its mature configuration
How many signal sequences do proteins that cross two membranes have?
Two signal sequences: one directs them to the mitochondrion or chloroplast and is cleaved off as the polypeptide enters the organelle; as the polypeptide enters, it is bound by organelle chaperone proteins to keep it unfolded; these chaperones conduct the protein to a second translocation complex where the second signal sequence directs their transfer across the second membrane
What type of destinations require two signal sequences?
Intermembrane spaces (mitochondria or chloroplast)
Thylakoids
How does the endomembrane system exchanges materials by ________________ and ___________________ of membrane vesicles
Budding
Fusion
How are vesicles transported in the cell?
Organized and moved by the cytoskeleton
Is budding and fusion energy-dependent or energy-independent?
Energy-dependent; it requires ATP