Cell Organelles: Mitochondria and Peroxisomes

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Questions and Answers

What is the primary component of the mitochondrial genome?

Linear DNA molecules

Circular DNA molecules (correct)

Chromosomal DNA

RNA molecules

How many proteins does the human mitochondrial genome encode that are involved in electron transport and oxidative phosphorylation?

13 (correct)

Which type of genes encode the proteins necessary for transcription and translation in mitochondria?

Plasmid genes

Nuclear genes (correct)

Mitochondrial genes

Cytoplasmic genes

What is the size of the human mitochondrial genome?

16 Kb Signup and view all the answers

Where are mitoribosomal proteins (MRPs) synthesized?

Cytosol Signup and view all the answers

What is the complete mitoribosome complex called?

55S monosome Signup and view all the answers

Which mitochondrial structure interacts with the translocase OXA1L?

Inner mitochondrial membrane Signup and view all the answers

What is primarily encoded by the mitochondrial genome apart from proteins?

tRNA and rRNA Signup and view all the answers

What is the main goal of mitochondrial replacement techniques?

To avoid transmission of mitochondrial diseases to offspring Signup and view all the answers

How many proteins are estimated to be encoded by the nuclear genome for mammalian mitochondria?

1,500 Signup and view all the answers

What is the primary function of the Tom complex?

To direct protein translocation across the outer membrane Signup and view all the answers

Which sequence is crucial for directing proteins to the mitochondrial matrix?

Amino-terminal presequence Signup and view all the answers

What process converts glucose into pyruvate in animal cells?

Glycolysis Signup and view all the answers

What role does the electrochemical potential play in mitochondrial protein import?

It aids in the translocation of matrix proteins across the inner membrane. Signup and view all the answers

What is the primary role of the enzymes within the citric acid cycle?

To oxidatively degrade carbohydrates and fatty acids Signup and view all the answers

Which process is NOT associated with mitochondrial replacement techniques?

Cloning of mitochondrial DNA Signup and view all the answers

Which protein complex is responsible for transferring proteins to the inner membrane of mitochondria?

Tim23 Signup and view all the answers

Which of the following statements about the inner mitochondrial membrane is true?

It contains 70% proteins involved in oxidative phosphorylation. Signup and view all the answers

How is the energy used for ATP synthesis generated during oxidative phosphorylation?

Through the proton gradient across the inner membrane Signup and view all the answers

Which of the following describes the structure of mammalian mitochondria?

A double membrane system Signup and view all the answers

What is the fate of pyruvate after glycolysis?

It is oxidized to acetyl CoA in the mitochondria. Signup and view all the answers

Which type of molecules can freely pass through the outer mitochondrial membrane?

Small molecules and ions Signup and view all the answers

What type of relationship is believed to have led to the evolution of mitochondria?

Symbiotic relationship Signup and view all the answers

Which statement correctly describes the fate of the high-energy electrons from NADH and FADH2?

They are transferred to oxygen through transporters. Signup and view all the answers

What is the primary function of mitochondria in cells?

Generate ATP from the breakdown of carbohydrates and fatty acids Signup and view all the answers

What unique feature do mitochondria possess that distinguishes them from peroxisomes?

Capable of protein synthesis from their own DNA Signup and view all the answers

How are most mitochondrial proteins synthesized?

On free ribosomes in the cytoplasm Signup and view all the answers

What structural feature increases the surface area of the inner mitochondrial membrane?

Cristae Signup and view all the answers

What is the role of enzymes contained within peroxisomes?

Facilitate metabolic pathways such as fatty acid breakdown Signup and view all the answers

Which compartments of mitochondria are primarily involved in oxidative metabolism?

Mitochondrial matrix and inner membrane Signup and view all the answers

What process describes the dynamic changes in mitochondria as they fuse and divide?

Fusion and fission Signup and view all the answers

What type of genetic material is found within the mitochondrial matrix?

Mitochondrial DNA coding for tRNA and rRNA Signup and view all the answers

What is the primary role of cardiolipin in the mitochondria?

It enhances the efficiency of oxidative phosphorylation. Signup and view all the answers

Which statement about peroxisomes is correct?

Human cells may contain between 100 and 1000 peroxisomes depending on activity. Signup and view all the answers

How are lipids transferred from the ER to the mitochondria?

At close contact points mediated by phospholipid transfer proteins. Signup and view all the answers

What distinguishes the enzymes found in peroxisomes from those in mitochondria?

Peroxisome enzymes resemble typical eukaryotic proteins. Signup and view all the answers

What is produced as a result of oxidative reactions in peroxisomes?

Hydrogen peroxide. Signup and view all the answers

Which of the following is NOT a characteristic of peroxisomes?

They generate energy through ATP synthesis. Signup and view all the answers

Cardiolipin is classified as which type of lipid?

Double phospholipid. Signup and view all the answers

Which structure in the cell is responsible for the synthesis of phospholipids that may end up in the mitochondrial membranes?

Endoplasmic reticulum (ER). Signup and view all the answers

What is the primary function of catalase in peroxisomes?

To break down hydrogen peroxide Signup and view all the answers

Which two signals are used for the targeting of internal peroxisomal proteins?

PTS1 and PTS2 Signup and view all the answers

Which of the following is NOT involved in the import of matrix proteins into peroxisomes?

Pex19 Signup and view all the answers

What is a key function of plasmalogens formed in peroxisomes?

Phospholipid synthesis for cell membranes Signup and view all the answers

How are most transmembrane proteins for peroxisomes synthesized?

Synthesized in the ER Signup and view all the answers

Which peroxin is specifically involved in recognizing the PTS1 signal?

Pex5 Signup and view all the answers

What is one of the mechanisms through which new peroxisomes can form?

Budding from the ER Signup and view all the answers

Which of the following components are recognized by Pex19 during the import of peroxisomal membrane proteins?

Peroxisomal targeting signal (mPTS) Signup and view all the answers

Study Notes

Mitochondria and Peroxisomes

Mitochondria are responsible for generating most of the cell's usable energy from the breakdown of lipids and carbohydrates.
Peroxisomes contain enzymes involved in various metabolic pathways, including fatty acid breakdown and photorespiration.
Proteins destined for mitochondria and peroxisomes are synthesized on free ribosomes in the cytosol, except for membrane proteins of the peroxisome.
Proteins import into target organelles, in the form of complete polypeptide chains.
Mitochondria contain their own genomes, which include genes transcribed and translated within the organelle itself.
Mitochondria are surrounded by a double membrane system, an inner and outer mitochondrial membrane separated by an intermembrane space
The inner membrane folds into numerous cristae, which extend into the mitochondrial matrix
The matrix and inner membrane are the primary functional compartments of mitochondria.
Mitochondria are dynamic and undergo fusion and fission.
The matrix contains mitochondrial genetic system and enzymes responsible for central reactions of oxidative metabolism.
The primary source of metabolic energy involves the breakdown of glucose and fatty acids.
The oxidation of acetyl CoA to CO2 is linked to the reduction of NAD+ and FAD to NADH and FADH2, respectively.
Most energy from oxidative metabolism is produced by oxidative phosphorylation in the inner mitochondrial membrane.
High-energy electrons from NADH and FADH2 are transferred to oxygen via membrane transporters.
The energy from electron transfer is converted into a proton gradient used to synthesize ATP.
The inner mitochondrial membrane has high protein content, is involved in oxidative phosphorylation, and maintains a critical proton gradient.
Outer membrane is completely permeable to small molecules via porins, which allow passage of molecules smaller than 1000 daltons.
The composition of the intermembrane space is similar to that of the cytosol.

Genetic System of Mitochondria

Mitochondria evolved from bacteria.
Mitochondrial genome forms a circular DNA molecule and several copies per organelle.
Size of the mitochondrial genome varies between different species.
Mitochondrial DNA encodes essential components for oxidative phosphorylation (tRNA, rRNA, some proteins).
Other mitochondrial proteins are encoded by nuclear genes and transferred from ancestral mitochondrial genomes.
Human mitochondrial genome is only 16 kb, while yeast and plants have larger genomes
Human mitochondrial genome codes for 13 proteins, 16S and 12S ribosomal RNA, and 22 transfer RNAs.
Nuclear genes provide the rest of the proteins required for mitochondrial functions.

Mitochondrial Diseases

Mitochondrial DNA mutations, primarily transmitted through the maternal line, are often harmful to the organelle.
Mitochondrial inheritance means defects in mtDNA are inherited from the mother.
Homoplasmy means the multiple copies of mitochondrial DNA in the cell are identical, while heteroplasmy means a combination of wild-type and mutated mitochondrial DNA.

Mitochondrial Protein Internalization and Formation

Mammalian mitochondria contain about 1,500 proteins encoded by nuclear genome.
Nuclear-encoded proteins are synthesized by free ribosomes in the cytoplasm and transported into mitochondria.
Protein import is complex due to the double membrane of mitochondria.
Proteins with amino terminal pre-sequences are the most studied.
These pre-sequences bind to the Tom complex on the outer membrane for initial translocation.
Mitochondrial matrix proteins cross the inner membrane via the Tim23-complex, utilizing the electrochemical gradient.
Other proteins utilizing a transmembrane sequence laterally insert into the inner membrane via other transport mechanisms.
Matrix proteases remove pre-sequences.
Protein import through complex pathways in the matrix and inner membrane, necessitating chaperones

Peroxisomes

Peroxisomes are small organelles (0.1-1 µm) with a membrane.
Human cells have a variable number (100-1000) depending on activity.
Peroxisomes lack a genome and utilize ribosomes in the cytoplasm for protein synthesis, while some proteins from the ER.
Peroxisome function includes various metabolic reactions and protein synthesis.
Peroxisomes are responsible for oxidation reactions that produce hydrogen peroxide.
Catalase, a key peroxisomal enzyme, breaks down hydrogen peroxide.
Peroxisomes oxidize branched and longer-chain fatty acids, along with other substrates.
Peroxisomes participate in plasmalogen synthesis (important membrane component of heart and brain).

Peroxisome Assembly

Internal peroxisomal proteins synthesize in the cytosol, while the bulk of transmembrane proteins are synthesized in the ER.
Transmembrane proteins (peroxins, Pex proteins) are important for metabolite transport.
PTS1 (Ser-Lys-Leu) signal, is widely used for proteins targeting peroxisomes.
PTS2 (amino-terminal sequences of 9 aa) is another targeting designation.
Peroxins (Pex5, Pex7, etc), as cytosolic receptors, bind to PTS1/PTS2 to initiate import to the peroxisome.
The Pex complex anchors proteins to peroxisome membrane and helps them enter.

Lipid Transfer and Lipids in Peroxisomes

Lipid transfer between ER and mitochondria happens at contact points and requires phospholipid transfer proteins to extract phospholipid molecules from ER and introduce them to the mitochondria.
Lipids can then transport via an aqueous environment.
Lipids move between the inner and outer mitochondrial membranes at contact points.
The majority of lipids in the mitochondrial membranes originate from the cytosol and undergo synthesis in the ER.
Phosphatidylethanolamine is produced from phosphatidylserine.
Cardiolipin, a four fatty acid chain phospholipid, is synthesized in the inner membrane and enhances oxidative phosphorylation.

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Description

This quiz covers the key functions and characteristics of mitochondria and peroxisomes within cells. You'll explore their roles in energy production, metabolism, and protein synthesis. Perfect for anyone studying cell biology or biochemistry!