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Questions and Answers
What discovery is associated with Altmann in relation to mitochondria?
What discovery is associated with Altmann in relation to mitochondria?
Which of the following best describes mitochondrial inheritance in mammals?
Which of the following best describes mitochondrial inheritance in mammals?
What is the predominant component of mitochondrial protein found in the matrix?
What is the predominant component of mitochondrial protein found in the matrix?
How do mitochondria reproduce?
How do mitochondria reproduce?
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What is one of the three major ways for ATP production indicated in the material?
What is one of the three major ways for ATP production indicated in the material?
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What is the total number of ATP molecules produced during the TCA cycle and ETC?
What is the total number of ATP molecules produced during the TCA cycle and ETC?
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Which part of the mitochondrion is responsible for large channel proteins that allow permeability for proteins of 10,000 daltons or less?
Which part of the mitochondrion is responsible for large channel proteins that allow permeability for proteins of 10,000 daltons or less?
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What are the enzymes in the cytoplasm primarily responsible for?
What are the enzymes in the cytoplasm primarily responsible for?
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Where does the synthesis of ATP primarily occur in mitochondria?
Where does the synthesis of ATP primarily occur in mitochondria?
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Which molecule is involved in the addition and removal of phosphate groups in ATP?
Which molecule is involved in the addition and removal of phosphate groups in ATP?
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What role does glycogen play in the context of cellular energy?
What role does glycogen play in the context of cellular energy?
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Which component of mitochondria contains enzymes required for the oxidation of pyruvate and fatty acids?
Which component of mitochondria contains enzymes required for the oxidation of pyruvate and fatty acids?
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What is the primary function of porins in the outer mitochondrial membrane?
What is the primary function of porins in the outer mitochondrial membrane?
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Which lipids are specifically mentioned as abundant in the outer mitochondrial membrane?
Which lipids are specifically mentioned as abundant in the outer mitochondrial membrane?
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What is the protein to lipid ratio in the inner mitochondrial membrane?
What is the protein to lipid ratio in the inner mitochondrial membrane?
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What type of enzyme is found in the mitochondrial matrix that facilitates the oxidation of pyruvate?
What type of enzyme is found in the mitochondrial matrix that facilitates the oxidation of pyruvate?
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Which of the following is NOT a function of mitochondria?
Which of the following is NOT a function of mitochondria?
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What is the role of cytochrome C in the mitochondria?
What is the role of cytochrome C in the mitochondria?
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How does the inner mitochondrial membrane differ from the outer membrane in terms of cholesterol content?
How does the inner mitochondrial membrane differ from the outer membrane in terms of cholesterol content?
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Which of the following enzymes is primarily involved in the TCA cycle and is located in the mitochondrial matrix?
Which of the following enzymes is primarily involved in the TCA cycle and is located in the mitochondrial matrix?
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What is the function of proteases in the mitochondrial matrix?
What is the function of proteases in the mitochondrial matrix?
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What is the primary function of lysosomes?
What is the primary function of lysosomes?
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Which process describes the engulfing and destruction of foreign antigens by lysosomes?
Which process describes the engulfing and destruction of foreign antigens by lysosomes?
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What maintains the internal acidic environment of lysosomes?
What maintains the internal acidic environment of lysosomes?
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What happens during autolysis in a cell?
What happens during autolysis in a cell?
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What describes the composition of primary lysosomes?
What describes the composition of primary lysosomes?
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Which statement about the lysosomal membrane is true?
Which statement about the lysosomal membrane is true?
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Which of the following processes involves lysosomes discharging their enzymes outside the cell?
Which of the following processes involves lysosomes discharging their enzymes outside the cell?
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What type of organelle does autophagy involve?
What type of organelle does autophagy involve?
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What is the typical half-life of liver mitochondria?
What is the typical half-life of liver mitochondria?
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Study Notes
Cell Biology 1 - Z 211
- Course taught by Prof/ Dr: Amel Ibrahim Othman
- This course covers Lectures 7, 8, and 9 on Mitochondria, Ribosomes, and the Endomembrane System.
The Mitochondria
- Discovered by Altmann in 1890, initially named "Bioblasts", stained with Altmann's acid fuchsin.
- Benda (1937) introduced the terms 'mito=thread' and 'chondrion=granules'.
- Hans Krebs described the Krebs cycle (TCA cycle).
- Number and distribution are directly related to energy demands.
- Variable shape: rods, filaments, ~0.5-1 µm in diameter, variable length.
- Originate by binary fission from pre-existing mitochondria.
- Contain the necessary requirements for their own replication.
- In mammals, mitochondrial genes are maternally inherited.
Mitochondria - Ultrastructure and Biochemical Composition
- First extensive electron microscope (EM) study by Palade in 1953.
- Smooth outer membrane covering the entire organelle.
- Folded inner membrane forms cristae to increase membrane surface area.
- Intermembrane space is a fluid-filled space between the outer and inner membranes.
- Matrix is the space inside the cristae.
- Mitochondrial protein composition: matrix (67%), inner membrane (21%), outer membrane (6%), intermembrane space (6%).
ATP Production
- Three major pathways for ATP production:
- Glycolysis (cytoplasm): anaerobic, one sugar molecule → 2 ATPs; Glucose → 2 Pyruvate molecules.
- Chloroplasts (plant cells): using sunlight.
- Mitochondria (TCA cycle & ETC): produces 36 ATPs.
Adenosine Triphosphate (ATP)
- Organic molecule containing high-energy phosphate bonds.
Chemical Structure of ATP
- ATP molecule consists of:
- Adenine base
- Ribose sugar
- Three phosphate groups
The ADP-ATP Cycle
- ATP synthesis and breakdown are facilitated by respective enzymes.
- ATP-ase (removes phosphate), energy release, and synthesis of ATP by ATP synthetase are key parts of the cycle.
Overview of ATP Role
- ATP production fuels energy needed for rest, activity, and temperature control.
- Synthesis used during growth, reproduction, and repair; used to store energy as glycogen (animal starch) and fat.
Diagram of the Process of ATP Production
- Explains how glucose is broken down to produce energy in the form of ATP via glycolysis, Krebs cycle, and electron transport chain in mitochondria.
- Glycolysis occurs in cytoplasm, Krebs cycle in matrix, and Electron Transport Chain occurs across cristae.
Citric Acid Cycle (Krebs Cycle)
- Comprehensive diagram illustrating the citric acid cycle with detailed chemical structures of reactants and products.
- Shows the series of chemical reactions in the cycle.
- Includes key intermediates and enzymes.
Electron transport chain (ETC)
- Shows the structure of the inner mitochondrial membrane, with detailed steps showing how electrons are transported from complex I-IV, producing ATP.
- Shows a diagram demonstrating how the products of the citric acid cycle are used to produce ATP
Mitochondrial Matrix, Inner Membrane Space, and Outer Membrane
- Matrix contains enzymes for fatty acid and pyruvate oxidation, mitochondrial DNA, ribosomes, and tRNA, and gene expression enzymes.
- Inner membrane contains proteins for redox reactions of the respiratory chain, ATP-ase.
- Specific transport proteins control metabolites movement into and out of the matrix.
- Outer membrane permeability for proteins (≤10,000 daltons), high cholesterol content, and enzymes for lipid substrate processing.
Outer Mitochondrial Membrane
- Thinner than the inner membrane with a lower protein-to-lipid ratio.
- Contains porins for easy permeability below 10,000 daltons
- Contains enzymes for lipid metabolism, including fatty acid oxidation.
- Contains specialized receptors for passage of certain enzymes and cytochrome C
The Intermembrane Space
- Contains enzymes that use ATP for nucleotide phosphorylation.
- Cytochrome C shuttles electrons from complex III to complex IV.
Inner Mitochondrial Membrane
- Thicker than the outer, with a higher protein-lipid ratio ( ~4:1).
- Contains complexes (I-IV) and coenzymes responsible for carrying out oxidation.
- Contains enzymes such as a-glycerophosphate dehydrogenase, succinate dehydrogenase, and ATP synthase (active site).
- Special transport proteins control the movements of metabolites in and out of the matrix.
- Contains Phospholipids like Cardiolipin which controls permeability of the inner membrane ions.
- No cholesterol.
The Matrix
- Contains enzymes for oxidation of pyruvate and fatty acids, producing Acetyl CoA, NADH, and FADH₂ as key products in the citric acid cycle.
- Essential for mitochondrial DNA-RNA synthesis, and protein synthesis.
- Contains essential proteases to remove leader sequences on proteins.
- Contains essential enzymes like catalase and dismutase for free radical scavenging.
- Stores Ca²⁺ in the form of Ca₃(PO₄)₂ granules.
Mitochondrial Function Summary
- Energy production (ADP → ATP).
- Oxidation of fatty acids.
- Cytochrome formation.
- Heme production in animals.
- Calcium regulation.
The Glyoxylate Cycle
- A modified TCA cycle, associated with acetate conversion to oxaloacetate.
Fatty Acid Chain Elongation
- Synthesis of saturated fatty acids (e.g., palmitic acid) occurs by successive addition of acetyl CoA to the COOH end of the growing fatty acid (in the endoplasmic reticulum).
- Elongation occurs through addition of malonyl CoA
Protective Enzymes
- SOD and catalase protect against damaging free radical production.
Amphibolic and Anaplerotic Reactions
- TCA cycle intermediates participate in catabolic and anabolic pathways.
- Reactions replenish depleted oxaloacetate for optimum TCA cycle function.
Ribosomes
- Ribosmal RNA makes the ribosomes.
- Ribosomes consist of two subunits, 80S (40S + 60S).
- Cells with high protein synthesis rates contain larger numbers of ribosomes.
- Formed in the nucleolus
- Pass through the nuclear pores to reach the cytoplasm.
Ribosome Chemical Structure
- Primarily made of ribosomal RNA, rRNA (60%), proteins (40%)
- Carbohydrates and lipids are absent.
- Magnesium plays a structural role in ribosomes.
- Large subunit contains ~40 types of proteins and some RNA; small subunit contains ~30 types of proteins and some RNA
Ribosome Assembly
- 45S RNA molecule (precursor) forms, with proteins, a giant ribonuclear protein complex (RNP).
- During processing, some proteins are released.
- Nuclear proteins are reutilized.
- Ribosomal proteins are assembled in the cytoplasm and then return to the nucleus
- RNPs with enzymes divide into 3 fragments
- 18S RNA + protein fragment produces small subunit 40S
- Large fragments 60S form after combining with 5S RNA
Types of Ribosomes
- Free ribosomes synthesize structural proteins for the cytosol.
- Bound ribosomes attach to the endoplasmic reticulum and synthesize membrane-bound or secretory proteins.
Mitochondrial Ribosomes
- Mitochondria have their own ribosomes.
- Either free in the matrix or attached to the cristae membrane.
- Smaller than cytoplasmic ribosomes (50S or 60S).
- Contain specific rRNA and lesser proteins.
Endomembrane System
- A system of interrelated membranous organelles.
- Key components include the nuclear envelope, endoplasmic reticulum (ER), Golgi apparatus, and vesicles
Microbodies
- Heterogeneous group of small vesicle-like organelles in eukaryotic cells.
- Primarily involved in oxidation.
- Typically spherical or oval and enclosed by a single membrane.
Peroxisomes
- Important organelles for numerous metabolic processes, including
- Generate hydrogen peroxide (H₂O₂)
- Oxidation
- About 0.5–1.5 µm in size, and abundant in kidney and liver cells.
- Increase in number by splitting
- Many metabolic pathways occur in their crystalline core
- Important for detoxification and oxidation
- Found in mitochondria & cells
- Specialized for the synthesis of certain products
Peroxisome Structure and Origin
- Single smooth membrane structure.
- Contains several specific enzymes (e.g., D-amino acid oxidase, urate oxidase, catalase).
- Oxidized products and enzymes are synthesized in the RER. Specific recognition processes within the peroxisome membrane.
Peroxisome Function
- Participate in fatty acid oxidation, producing acetyl CoA for entry into the citric acid cycle within the mitochondria.
- Important detoxification role
- Breakdown of purines (e.g., AMP, GMP) to uric acid.
- Participate in cholesterol, bile acid, and myelin lipid synthesis.
Peroxisome and Mitochondria Resemblance
- Both utilize oxygen in metabolic activities.
- Both are involved in fatty acid oxidation
- Both contain catalase to control H₂O₂ levels.
- Both participate in glyoxylate synthesis.
- Both participate in the synthesis of products needed in many pathways.
Lysosomes
- Membranous sacs with a single smooth membrane.
- Contain ~60 hydrolytic enzymes that function optimally in an acidic medium (pH 5–6).
- Intracellular digestion of foreign material and cellular debris.
- Originate from the Golgi apparatus.
- Aid in cell renewal, breakdown of old parts, digestion of invaders.
- Excessive leakage can cause autodigestion, cell death,
- Intracellular (heterophagy and autophagy).
Lysosomes - Intracellular Digestion
- Heterophagy: Engulfing and digesting foreign antigens (e.g., bacteria).
- Autophagy: Digestion of old or damaged organelles.
Lysosomal Membrane
- Protects against enzymes' self-degradation.
- Impermeable to enzymes and substrates.
- Permeable to final digestion products for cell recycling.
- Internal ATP-dependent proton pump regulates the internal pH of lysosomes at ~5.
Types of Lysosomes
- Primary lysosomes: Contain hydrolytic enzymes, but no substrate.
- Secondary lysosomes: Formed when primary lysosomes fuse with endocytosis vacuoles (phagosomes/endosomes).
Lysosomes and Diseases
- Lung diseases (silicosis, asbestosis, black lung disease).
- Lysosomal storage disorders: Lacking specific enzymes for digesting macromolecules, leading to their accumulation and cellular damage (e.g., Pompe's, Tay-Sachs, Hurler’s).
Protein Degradation
- Enzymatic breakdown of specific proteins
- Degradation occurs by enzymatic breakdown of proteins into amino acids; lysosomes may be the primary structure responsible.
Lysosomes and Cell Senility
- Accumulation of undigested material in lysosomes can signify the senility of the cell.
Lysosomal Enzymes
- Proteases: digest proteins
- Nucleases: digest nucleic acids
- Glycosidases: digest polysaccharides
- Lipases: digest lipids
- Phosphatases: digest organic-linked phosphates
Distribution of Lysosomes
- Vary according to the cell type and circumstances affecting that cell
- Abundant in white blood cells, kidney ,intestine, lung, uterus, and reticulo-endothelial system
The Nucleus
- Cell control center – contains DNA instructions for all functionalities.
- Discovered by Watson, Crick, and Franklin (1953).
- DNA encased by the nuclear envelope with pores for material exchange.
The Nucleolus
- Ribosome-producing structure; ribosome assembly, containing ribosomal RNA genes.
- No membrane.
- Consists of 3 regions (pale-staining, granular component, dense fibrillar).
- Size is related to cellular activity (diminished during mitosis).
The Nucleoplasm
- Fluid substance containing nucleus solutes and some RNAs.
- Contains numerous enzymes and other molecules.
The Nuclear Matrix
- Fibrillar network of proteins.
- Important for transcription and DNA replication processes.
- Contains binding sites for hormones involved in these processes.
Chemical Structure of Chromatin
- DNA and proteins (mostly histones and some nonhistones).
- Histones: H1, H2A, H2B, H3, and H4. H2A-H4 are nucleosomal histones, H1 responsible for nucleosome packaging, essential for the long DNA molecule wrapping.
- DNA is wrapped around nucleosomes.
- Nucleosomes give chromatin the "beads-on-a-string" appearance.
Chemical Structure of Chromatin - Continued
- Nucleosomes can be removed by nucleases.
- Each nucleosome (structural units of chromosomes) contains a set of eight histones (two copies of H2A, H2B, H3, and H4) and about 146 base pairs of DNA.
- A linker DNA segment of ~60 base pairs separates nucleosomes.
Chromatin Fibres
- Nucleosomes pack tightly forming 30 nm chromatin fibers.
- H1 molecules assist in packing to form 30nm fibres,.
- Structure plays an important role in the structure and arrangement of genetic material.
Chromatosome
- Consists of a histone octamer bound by linker DNA (and DNA H1).
- Basic building block within a chromatin structure
The Solenoid
- 30nm chromatin fibers coil to form coiled structures called solenoids.
- Facilitates further packing and organization of genetic material.
Supercoiling
- Arrangement of DNA strands in a regular supercoiled structure.
- Stepwise packaging of DNA
- DNA → double helix → nucleosomes → solenoid → supercoils → chromosomes.
DNA and Chromosomes – Eukaryotic structure
- A diagrammatic depiction of how DNA is wrapped around histone proteins in a series of structural levels to form the eukaryotic chromosome.
The Nuclear Envelope
- Two membranes separated by a perinuclear space (~20-40 nm).
- The outer membrane is continuous with the rough endoplasmic reticulum (RER).
- Pores connect the two membranes, allowing material exchange.
The Nuclear Lamina
- Electron-dense layer on the inner nuclear membrane face.
- Functions in supporting and organizing chromosomes and nuclear pores.
- Composed of specialized proteins that organize pores in the nuclear membrane
- Contains three main structural proteins
Nuclear Lamina Function
- Holds nuclear pores in place and shapes the nuclear envelope.
- Plays a role in organizing interphase chromosomes within the nucleus.
Nuclear Transport and Nuclear Pores
- Nuclear pores transport material using a complex mechanism.
- Large supramolecular structures that surround nuclear pores, arranged in an octagonal pattern.
- The pores act as channels for water-soluble molecules and control large molecule movement.
- Active transport systems may be used to facilitate large molecule transfer or transport by receptor.
- Specialized mechanisms/ specialized proteins needed for molecule transport, in and out of the nucleus.
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Description
Test your knowledge on mitochondria, their functions, and energy production processes in mammalian cells. This quiz covers topics such as mitochondrial inheritance, ATP production, and the roles of various mitochondrial components. Perfect for biology enthusiasts and students studying cellular biology!
