Mitochondria and Chloroplasts Overview

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Questions and Answers

What are the shared properties of mitochondria and chloroplasts?

Both have their own ribosomes but lack DNA.

Both have a single membrane structure.

Both are involved in energy conversion and ATP synthesis. (correct)

Both are exclusively found in prokaryotic cells.

Which of the following statements about mitochondrial structure is true?

The inner membrane has a protein composition of 45%.

Mitochondria only have a single membrane.

Mitochondria are large organelles, typically 10-15 μm long.

Mitochondrial outer membrane contains 6% protein. (correct)

What is the primary function of chlorophyll in chloroplasts?

To harvest energy from sunlight. (correct)

To assist in protein synthesis.

To facilitate the transport of proteins into the chloroplast.

To regulate the synthesis of ATP.

Which of the following processes is part of mitochondrial oxidative metabolism?

Electron transport chain. Signup and view all the answers

Which characterizes the structure of peroxisomes?

They are involved in lipid metabolism and detoxification. Signup and view all the answers

What differentiates the genomes of mitochondria from chloroplasts?

Mitochondrial genomes are larger than chloroplast genomes. Signup and view all the answers

What role does the proton gradient play in mitochondria?

It is essential for ATP synthesis through ATP synthase. Signup and view all the answers

Which of the following processes occurs during the Calvin cycle?

Carbon fixation. Signup and view all the answers

What is the role of Hsp70 in the chloroplast import process?

It acts as a cytosolic receptor for precursor proteins. Signup and view all the answers

Which process is NOT involved in the import of proteins into the thylakoid?

GTP hydrolysis Signup and view all the answers

What is the primary function of the light reactions in photosynthesis?

Absorb light energy and produce ATP. Signup and view all the answers

Which enzyme is primarily responsible for CO2 reduction in light-independent reactions?

Rubisco Signup and view all the answers

Where does the ATP synthesis occur during the light reactions of photosynthesis?

Thylakoid membrane. Signup and view all the answers

What is cleaved by stromal processing peptidase (SPP)?

Signal sequence of precursor proteins. Signup and view all the answers

What are the products of the light-dependent reactions in photosynthesis?

ATP and NADPH + O2. Signup and view all the answers

Which of the following is a characteristic of the Tic complex?

Uses ATP hydrolysis for protein import. Signup and view all the answers

What is the primary function of catalase within peroxisomes?

Breakdown of hydrogen peroxide Signup and view all the answers

Which process leads to the formation of new peroxisomes from ER precursor membranes?

De novo biogenesis Signup and view all the answers

What is the primary role of peroxisomes in oxidative metabolism?

Production of hydrogen peroxide Signup and view all the answers

Which of the following statements correctly describes the protein import process in peroxisomes?

ATP hydrolysis provides the energy for the translocation process. Signup and view all the answers

What process occurs first in the light reactions of photosynthesis?

Light absorption by pigments Signup and view all the answers

What is the primary product of fatty acid β-oxidation within the peroxisomes, and where does it go next?

Acetyl CoA, directed to the citric acid cycle (TCA) Signup and view all the answers

Which component is part of the antenna complex in a photosystem?

Chlorophyll Signup and view all the answers

What role do chaperons play in the intermembrane space of mitochondria?

They assist in folding proteins Signup and view all the answers

Which molecule acts as the final electron acceptor in the linear electron transport chain?

NADP+ Signup and view all the answers

What type of structure do porins form in the outer mitochondrial membrane?

β-barrel Signup and view all the answers

What is the main role of Rubisco in the light-independent reactions?

Carbon fixation Signup and view all the answers

Which pathway is NOT involved in protein import to the inner mitochondrial membrane?

Carrier-mediated pathway Signup and view all the answers

What product is formed during the Calvin cycle as a result of CO2 reduction?

Glyceraldehyde 3-phosphate Signup and view all the answers

In cyclical photosynthesis, what is produced?

ATP only Signup and view all the answers

What is the final electron acceptor in the mitochondrial electron transport chain?

O2 Signup and view all the answers

Which process directly results from the pumping of protons to the intermembrane space during the electron transport chain?

ATP synthesis Signup and view all the answers

How is the electron donor replenished in photosystem II?

Photolysis of water Signup and view all the answers

Which step is NOT part of the Calvin cycle?

Energy transfer Signup and view all the answers

What is formed from acetyl-CoA during the Krebs cycle?

NADH and CO2 Signup and view all the answers

Which complex in the electron transport chain is associated with NADH?

Complex I Signup and view all the answers

Which of the following is NOT a function of mitochondria?

Protein synthesis Signup and view all the answers

Study Notes

Mitochondria & Chloroplasts

Both are double membrane organelles
Both were formed by endosymbiosis
They are semi-autonomous
Both contain their own DNA and ribosomes
Both replicate independently from the nucleus
Both are involved in energy conversion
Both use ATP synthase to synthesize ATP

Mitochondria

Present in all eukaryotic cells
Small organelles, typically 0.5 - 3μm long
Number varies depending on the cellular requirements
Dynamic in shape
Contains two membranes: outer and inner
Outer membrane contains 6% proteins
Intermembrane space contains 6% proteins
Inner membrane contains 21% proteins, it is folded into cristae
Matrix contains 67% proteins
Outer membrane contains porins, these are β-barrel proteins that allow the insertion of proteins into the outer membrane
Proteins are sorted to different locations
Folded proteins are sorted to the intermembrane space
Unfolded proteins are sorted to the outer membrane
Proteins are translocated through Tom complex (Translocase of the outer mitochondrial membrane)
Inner membrane proteins are synthesized in the cytosol
Inner membrane proteins are translocated through different pathways
Some mitochondrial DNA-synthesized proteins are inserted into the inner membrane

Function of Mitochondria

Involved in mitochondrial oxidative metabolism
Pyruvate and fatty acids are converted to acetyl-CoA
Acetyl-CoA is converted to NADH and CO2 in the Krebs cycle (also known as the Citric acid cycle)
Electron transport chain is involved in oxidative phosphorylation
ETC uses the energy derived from oxidation to create an electrochemical gradient
NADH and FADH2 donate their electrons to the ETC
Electrons are transported across complexes I, II, III, and IV located in the inner mitochondrial membrane
Protons are pumped into the intermembrane space as electrons move across the ETC
Oxygen is the final electron acceptor, which forms water
The proton gradient is used in ATP synthesis

Chloroplasts

Double membrane organelles, outer and inner membrane
Own DNA and ribosomes
Proteins are imported from both the cytosol and the nucleus
Proteins are translocated as precursors (unfolded)
Contains a third membrane, the thylakoid membrane

Protein Import into Chloroplasts

Proteins are synthesised in the cytosol
Proteins are transported to the chloroplast as unfolded polypeptides
N-terminal transit peptide acts as a signal sequence
Proteins are bound by cytosolic receptor Hsp70
Translocation through the Toc complex (Translocase of the outer chloroplast membrane) happens with the help of Hsp70 and GTP hydrolysis
Following outer membrane translocation, proteins cross the inner membrane using the Tic complex (Translocase of the inner chloroplast membrane) with the help of Hsp93 and ATP hydrolysis
The transit peptide is cleaved off by stromal processing peptidase (SPP)

Sorting of Proteins from Stroma

Chloroplast and nuclear encoded proteins can further be sorted
Thylakoid membrane proteins are targeted to the thylakoid membrane via a N-terminal thylakoid target sequence
Folded proteins are translocated through the pH-dependent pathway (Tat)
Unfolded proteins are translocated through the Sec pathway and SRP pathway
The thylakoid target sequence is cleaved by thylakoid protein peptidase (TPP)

Function of Chloroplasts

Involved in photosynthesis, which converts light energy into chemical energy
Two stages of photosynthesis: light-dependent and light-independent
Light-dependent reactions (light capture) occur on the thylakoid membrane
Light-dependent reactions convert light energy into chemical energy
Light is absorbed by chlorophyll a
Water and light are used to produce ATP, NADPH, and oxygen as byproducts
Light-independent reactions (CO2 fixation) occur in the stroma and cytosol
Light-independent reactions reduce CO2 to sugars
Rubisco enzyme is involved in this process
ATP and NADPH produced during light-dependent reactions are used to fix CO2
The Calvin cycle has three stages: carbon fixation, sugar formation, and regeneration of ribulose 1,5-bisphosphate
The end product of the Calvin cycle is 3-phosphoglycerate, which is further converted to other organic molecules

Light-dependent Reactions

Contain two photosystems: light harvesting and reaction centre
Antenna complex absorbs light and transfers energy via resonance
Two chlorophyll a molecules form the reaction centre
High energy electrons are donated by reaction centre molecules to acceptor molecules in the ETC
These high energy electrons are replenished by electrons from water photolysis (PSII) or plastocyanin (PSI)

Light-dependent ETC

Photosystems, plastoquinone, plastocyanin, and ferredoxin contribute to the ETC
Electrons move linearly from PSII to PSI, producing a proton gradient and NADPH during linear photosynthesis
Cyclic photosynthesis uses electrons from PSI to further generate a proton gradient
Ferredoxin transfers energy to plastoquinone
The proton gradient is used to produce ATP by ATP synthase located on the thylakoid membrane

Peroxisomes

Small, single membrane-bound organelles
Contain enzymes that catalyze oxidation reactions, including catalase
0.1 - 1 μm in size
They lack DNA and ribosomes
Formed by fission of pre-existing peroxisomes or de novo formation from the ER
Biogenesis requires peroxin proteins
Proteins are imported into peroxisomes from the cytosol in a folded conformation
C-terminal PST1 or N-terminal PST2 acts as a signal sequence for proteins destined for the matrix
Signal sequences are not cleaved
Peroxins act as cytoplasmic receptor proteins
ATP hydrolysis provides energy for translocation
Membrane protein import involves different signal sequences and the ER pathway

Function of Peroxisomes

Involved in oxidative metabolism of fatty acids, amino acids, methanol, and toxins
Produces hydrogen peroxide as a byproduct of oxidation
Contains catalase which breaks down hydrogen peroxide
Involved in β-oxidation of very long-chain fatty acids, producing H2O2 and acetyl CoA
H2O2 and Acetyl CoA enter the citric acid cycle
No ATP is produced during fatty acid β-oxidation
Biosynthesis of lipids including plasmalogens, important lipids found in the heart and brain

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Description

Explore the fascinating world of mitochondria and chloroplasts, two vital organelles present in eukaryotic cells. This quiz covers their structure, function, similarities, and unique characteristics, including their role in energy conversion. Test your knowledge on these double membrane organelles and their implications in cellular processes.