30 Questions
What percentage of the cytoplasmic volume of a eukaryotic cell do mitochondria occupy?
Up to 20%
What is the typical length of mitochondria?
1–2μm
Which fluorescent dye can be used to view mitochondria in living cells?
Mito-Tracker Red
In which type of cells can mitochondria move long distances?
Highly polarized cells such as neurons
Where do mitochondria remain fixed at points of high energy demand?
Skeletal or cardiac muscle cells
What is the main function of mitochondria?
Providing the cell with ATP generated by oxidative phosphorylation
Which of the following is NOT a metabolic function of mitochondria?
Synthesis of glucose
What does mitochondria regulate in the cell?
The cellular redox state
Which organelle is often associated with the microtubular cytoskeleton?
Mitochondria
Which complex is responsible for recognizing the N-terminal signal sequence of the mitochondrial precursor protein?
TOM complex
What determines the orientation and distribution of mitochondria in different cell types?
Microtubular cytoskeleton
What is the function of the PAM import motor in mitochondrial protein import?
Completing the translocation of the precursor protein into the matrix
Which protein is responsible for cleaving off the signal sequence in the matrix space?
Matrix processing peptidase
Which complex is responsible for translocating proteins into the inner mitochondrial membrane without requiring the PAM import motor?
TIM22 complex
Which defect can cause the X-linked recessive neurodegenerative Mohr-Tranebjaerg syndrome?
Defect in a small Tim protein
Which complex is responsible for inserting proteins into the inner mitochondrial membrane after removal of the presequence?
Oxa1
Which family of heat shock proteins maintains the precursor protein in an unfolded state?
Hsp70
Which proteins are targeted to the inner mitochondrial membrane and do not contain presequences?
Carrier proteins
Which complex is responsible for translocating proteins across the outer membrane into the intermembrane space?
Tom40
Which complex is responsible for inserting proteins into the inner mitochondrial membrane by recognizing a different receptor in the mitochondrial outer membrane?
TIM22 complex
What is the main function of the outer membrane of mitochondria?
Form channels for the passage of molecules less than 5000Da
What is the structure of the human mitochondrial genome?
Circular, double-stranded DNA with 37 genes encoding ribosomal RNAs, transfer RNAs, and proteins
How is mitochondrial DNA inherited?
Maternally inherited
What is the role of the TOM complex in mitochondria?
Catalyze protein translocation across mitochondrial membranes
What is the function of the inner membrane of mitochondria?
Surround the internal mitochondrial matrix compartment and greatly increase the membrane area available for oxidative phosphorylation
What is the origin of mitochondria?
Engulfment of a bacterium by the progenitor of eukaryotic cells
What is the protein density of cristae membranes in mitochondria?
High protein density
What is the mutation rate of mitochondrial DNA compared to the nuclear genome?
Much higher mutation rate
Where are most mitochondrial proteins encoded?
Encoded by nuclear genes
What is the function of the TIM23 complex in mitochondria?
Catalyze protein translocation across mitochondrial membranes
Study Notes
Mitochondria: Structure and Function
- Mitochondria are central regulators of programmed cell death (Apoptosis).
- They are thought to have originated from the engulfment of a bacterium by the progenitor of eukaryotic cells, establishing a symbiotic relationship.
- Mammalian cells typically contain hundreds or thousands of mitochondria, depending on the cell's metabolic requirements.
- Mitochondria have two membranes with distinct functions: outer membrane and inner membrane, creating separate compartments.
- The outer membrane contains a major integral protein called porin, which forms channels for the passage of molecules less than 5000Da.
- The inner membrane surrounds the internal mitochondrial matrix compartment and is highly folded to form invaginations known as cristae.
- Cristae membranes have a high protein density and greatly increase the membrane area available for oxidative phosphorylation.
- The human mitochondrial genome is a circular, double-stranded DNA with 37 genes encoding ribosomal RNAs, transfer RNAs, and proteins involved in electron transport and oxidative phosphorylation.
- Mitochondrial DNA is maternally inherited, polyploid, and has a much higher mutation rate than the nuclear genome.
- Most mitochondrial proteins are encoded by nuclear genes and imported from the cytosol, with specific targeting signals directing them to the organelle.
- The TOM, TIM, SAM, and OXA complexes are multimeric membrane protein assemblies that catalyze protein translocation across mitochondrial membranes.
- On the matrix side, the TIM23 complex is bound to a multimeric protein complex containing mitochondrial hsp70, which acts as an import ATPase.
Test your knowledge of mitochondria with this quiz on their structure and function. Explore topics such as mitochondrial DNA, membrane structure, protein import, and their role in apoptosis.
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