Biology Quiz on Mitochondria and Peroxisomes

Cell Science - Exam Topic List 2019

• Origin of Life (1st lecture of DGCI):
  • Urey-Miller experiment (1953) tested Oparin and Haldane's ideas about early Earth's atmosphere. A closed system containing water and gases (H₂O, NH₄, CH₄, N₂) simulated early Earth, and electrical sparks mimicked lightning.
  • The experiment produced amino acids, sugars, lipids, and other organic molecules. Complex molecules like DNA and proteins were missing, but the experiment demonstrated that basic building blocks could form spontaneously.
  • Chemical evolution steps included solidification of Earth's crust, atmosphere development, formation of small & large organic molecules, protocells, and then biological evolution (prokaryotes, eukaryotes, multicellular organisms).
  • Three domains of cellular life are Bacteria, Archaea, and Eukaryotes, with LUCA (last universal common ancestor). 16S rRNA is a molecule conserved in all cellular life forms.

Eukaryotic Cell Organisation and Medicinal Model Cells (ECB)

• Eukaryotic vs. Prokaryotic Cells:

  • Eukaryotic cells have a true nucleus containing DNA, while prokaryotic cells do not.
  • Eukaryotic cells have a more complex structure, containing membrane-bound organelles.
  • The presence of numerous organelles allows for greater specialization and complexity in function.
  • Eukaryotic cells have a plasma membrane while prokaryotic cells have a cell wall with an inner and an outer membrane.

• Components of Eukaryotic Cells:

  • Plasma membrane: A selectively permeable boundary surrounding the cell.
  • Cytosol: The gel-like fluid within the cell containing dissolved molecules.
  • Golgi complex: Processes and modifies proteins for transport to various destinations.
  • Endoplasmic reticulum (ER): Rough ER contains ribosomes for protein synthesis; smooth ER is involved in lipid synthesis.
  • Ribosomes: Synthesize proteins.
  • Mitochondria: Cellular powerhouses, responsible for ATP production (energy).
  • Centrosome: Organizes microtubules, critical for cell division.
  • Lysosomes: Intracellular digestion.
  • Microvilli: Increase surface area for absorption.
  • Cytoskeleton: Provides structural support and facilitates intracellular transport. Composed of microtubules, actin filaments, and intermediate filaments.
  • Nucleus: Contains the genetic material (DNA) of the cell & nucleolus.

Structure and functions of plasma membrane

• Types and Role of Membranes components:
  • Lipids: Phospholipids and cholesterol form the basic structure (lipid bilayer). Hydrophilic (water-loving) heads and hydrophobic (water-fearing) tails create a barrier.
  • Proteins: Integral proteins span the membrane; peripheral proteins are located on one side. They determine the membrane's functions—selective transport, channels, receptors, anchors.
  • Carbohydrates: Attached to proteins (glycoproteins) or lipids (glycolipids), forming the glycocalyx. They play a role in cell recognition and communication..

Structure and functions of cell-nucleus

• Nuclear Envelope: A double membrane surrounding the nucleus. The envelope has nuclear pores to regulate movement of substances in and out, and nuclear lamina is a supporting network of filaments found inside.
• Nucleolus: A dense structure within the nucleus involved in ribosome biogenesis (synthesis).
• Chromatin: Consists of DNA and proteins (histones) that condense to form chromosomes during cell division.
• Evolution of the Nucleus: In early life forms, DNA is directly attached to the plasma membrane, which gradually invaginated to form a double-membraned envelope—the beginning of a nucleus.

General Features of Chromatin Organization

• Chromatin Fibers: DNA strands wound around histone proteins to form nucleosomes creating the “beads-on-string” form.
• Heterochromatin: Tightly packed form often containing repetitive DNA sequences; genetically inactive.
• Euchromatin: Loosely packed form that allows for gene expression.
• Nucleosome structure: Proteins that bind to DNA, particularly histones, form the first level of chromatin packing. Nucleosomes are small proteins packs of proteins with DNA forming the “beads” that form the chromatin fibers.

Model Cells and Their Benefits

• General: There are several types of cells (e.g. HeLa, stem cells) that can be studied in a lab setting to find out the biological structure or function of an organ or tissue.
• Benefits: Enables experimentation under standard laboratory conditions which may easily be modified and can facilitate statistical evaluations and may save many experimental animal lives.
• Examples: Escherichia coli (E. coli) — widely used for ease of growth & genetic manipulation, which make it easy to use as a model.

Structure and Function of Endoplasmic Reticulum

• Rough ER: Synthesizes transmembrane and secreted proteins with embedded ribosomes, and involved in protein modification & transport.
• Smooth ER: Lipid synthesis, detoxification, and calcium storage.

Protein Sorting, Targeting, and Membrane Transport

• Sorting: Signals (specific amino acid sequences) on proteins direct proteins to their appropriate cellular destinations. Some are destined for secretion, the cell membrane, lysosomes, or the ER itself.
• Process: After reaching the ER, the protein either crosses or becomes embedded in the membrane. Then, proteins are moved to the Golgi for further modification.
• Methods: Transport vesicles carry proteins from one compartment of the endomembrane system to another; protein receptors are part of the destination to ensure delivery.

Membrane Transport (Simple, Passive, Facilitated, Active Transport)

• Simple diffusion: Movement of molecules from high to low concentration without protein assistance.
• Passive transport: Net movement of molecules down their concentration gradient (without ATP expenditure), facilitated by specific membrane proteins.
• Facilitated diffusion: Uses transport proteins (channels or carriers) to move molecules down their concentration gradient without needing ATP.
• Active transport: Movement against a concentration gradient, requiring energy (ATP). Uniporters move one molecule; symporters move two in the same direction; antiporters move in opposite directions.

Structure and Function of Golgi Complex

• Polarity: The Golgi has distinct cis and trans faces, a "receiving" (cis) and a "shipping" (trans) side. Materials/molecules enter at the cis and are sent out from the trans.
• Function: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles. Adds or modifies carbohydrates; important for membrane synthesis.

Vesicular Transport

• General: Transport of molecules in sacs (vesicles) between compartments. Membrane fusion is important to transport cargo to specific destination.
• Important proteins: Receptors, coat proteins, SNAREs (facilitate fusion), and Rab (direct docking) proteins.

Endocytosis

• General: The internalization of molecules from the extracellular environment via vesicles.
• Types: Phagocytosis (taking in large particles), pinocytosis (taking in fluid), and receptor-mediated endocytosis (taking in specific molecules).

Digestion of components

• Autophagy: A cellular cleaning process that involves the digestion of damaged or misfolded proteins and organelles.
• Lysosomes & Autophagosomes: Lysosomes contain enzymes that break down the engulfed material in autophagosomes.
• Autolysis: The spontaneous destruction of cells by their own enzymes.
• Necrosis: Cell death associated with damage or inflammation.

Cell Cycle and Regulation

• Stages of Cell Cycle: G1, S, G2, and M phases. Crucial regulatory mechanisms checkpoints maintain correct order to prevent cellular errors or damage.
• Checkpoints: G1, G2, and M checkpoints monitor cell cycle events. They help ensure the integrity of the genetic material and conditions before moving to the next phase.

Mitochondria

• Structure: Double-membraned organelle containing inner membrane folds (cristae which increase surface area), outer membrane (permeable), intermembrane space, and matrix.
• Function: ATP synthesis via oxidative phosphorylation (electron transport chain and ATP synthase) and other metabolic pathways. Important roles in calcium regulation, lipid homeostasis, and nucleotide metabolism.
• Special molecules: Porin (outer membrane), cardiolipin (inner membrane)—play crucial roles in functions.

Peroxisomes

• Structure: Single-membraned organelles.
• Function: Contain enzymes (e.g., catalase) that degrade hydrogen peroxide (H₂O₂), a by-product of metabolism. Also important for fatty acid oxidation and other metabolic processes.

Cytoskeleton

• Microtubules: Hollow tubes made of tubulin dimers. They play a critical role in cell shape, division, and intracellular transport (along tracks for vesicles).
• Microfilaments: Two interwound strands of actin. Essential for cell movement, muscle contraction, and maintaining cell shape.
• Intermediate filaments: Provide tensile strength to cells.

Cell Motility and Signaling

• Cell Motility: Cells move by various mechanisms—taxis (directional movement in response to a stimulus like chemicals), chemokinesis (movement directed by chemicals) and kinesis (undirected movement). Motor proteins and cytoskeletal interactions are key for movement; examples are cilia and flagella.
• Cell Signaling: Cell communication through different types of channels, ligands (molecules). Types of signaling like endocrine (hormones), paracrine (local mediators), synaptic signaling (neurotransmitters), and contact-dependent (proteins on the membrane).
• Signal Transduction: The process of conversion of one type of signal into another (e.g. external signal to intracellular). Secondary messengers amplify the signals during the process, include cAMP, IP3, DAG, and Ca²+.

Stem Cells

• General: Specialized cells that have the ability to self-renew and differentiate into specialized cells.
• Potency: Totipotent (forms entire organism), Pluripotent (forms most cells in the organism), Multipotent (forms a few related types of cells), and unipotent (forms only one cell type). Types include embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs).
• Importance: Stem cell research is vital in understanding development, diseases, and creating potential cell replacements.

Cell Aging and Death

• Mechanisms: Senescence (when cells stop dividing). DNA damage accumulation, telomere shortening, environmental/genetic factors, and accumulation of harmful substances.
• Types of Cell Death:
  • Apoptosis: Programmed cell death vital for development, tissue homeostasis (the cell removes itself in an organized way so it does not harm surrounding cells).
  • Necrosis: Uncontrolled cell death resulting damage to the surrounding cells; occurs in response to injury or disease.
• Importance: Apoptosis and necrosis are crucial processes in maintaining health and homeostasis.

Test your knowledge on mitochondrial DNA, its inheritance, and the functions of peroxisomes in cellular biology. This quiz covers key concepts including the formation of new mitochondria, roles of enzymes, and the relationship between macromolecules. Challenge yourself and see how well you understand these essential cellular structures!