Biology Quiz on Decomposers and Cell Signaling

Cytogenetics (T209) Lecture 3 2024/2025

• The lecture was presented by Fotouh M. El-Domyati, Professor of Molecular Biology and Biotechnology.

The Endomembrane System

• Rough endoplasmic reticulum (RER) synthesizes proteins and packages them in vesicles, commonly transported to the Golgi apparatus.
• Transport vesicles shuttle proteins and lipids to various locations, including the Golgi apparatus.
• Golgi apparatus modifies proteins and lipids from the ER, sorts them, and packages them into vesicles for various destinations.
• Secretory vesicles fuse with the plasma membrane, releasing their contents via secretion.
• Smooth endoplasmic reticulum (SER) synthesizes lipids and performs other functions like detoxification.
• Transport vesicles shuttle proteins and lipids to different parts of the cell, like the Golgi apparatus.
• Lysosomes contain digestive enzymes that break down old cell parts or substances entering the cell.
• Incoming vesicles bring substances into the cell for digestion by lysosomes.

Endoplasmic Reticulum

• Keith R. Porter named the endoplasmic reticulum in 1953.
• The endoplasmic reticulum (ER) is a membranous network of flattened sacs, continuous with the nuclear envelope.
• The ER includes rough ER and smooth ER, interacting in processes like protein transport.
• Rough ER has ribosomes, producing proteins.
• Enzymes in rough ER add carbohydrates (sugars) to proteins (e.g., glycoproteins).
• Smooth ER helps produce lipids and detoxify drugs or substances.

Ribosomes

• Free ribosomes float in the cytosol, synthesizing proteins for use within the cell.
• Bound ribosomes are attached to the endoplasmic reticulum, synthesizing proteins primarily for secretion or lysosomes.
• Prokaryotic ribosomes consist of 30S and 50S subunits, while eukaryotic ribosomes have 40S and 60S subunits.

Golgi Apparatus

• Camillo Golgi discovered the Golgi apparatus in 1898.
• The Golgi apparatus is a stack of curved, flattened membranes, processing and packaging proteins.
• The Golgi apparatus has cis and trans Golgi networks (faces).
• It modifies carbohydrate chains attached to proteins from the rough ER, determining their destination.
• It sorts and packages molecules into vesicles for secretion or exocytosis.

Lysosomes

• Christian René de Duve discovered lysosomes in the 1950s.
• Lysosomes are membrane-bounded organelles found in animal cells, containing hydrolytic enzymes.
• Enzymes break down many biomolecules, nonfunctional organelles, and engulfed substances.
• Some white blood cells use lysosomes to digest bacteria.

Energy-Related Organelles

• Chloroplasts use solar energy to make sugars through photosynthesis.
• Mitochondria break down sugars to produce ATP (cellular respiration).
• Photosynthesis converts light energy to chemical energy in sugar molecules.
• Cellular respiration is a set of metabolic reactions in organisms that converts biochemical energy into ATP.
• The reactions of photosynthesis depend on light availability, and those of carbon fixation require ATP made by light reactions.

Photosynthesis vs Respiration

• Photosynthesis and cellular respiration are complementary reactions.
• Photosynthesis inputs are carbon dioxide and water while outputs are oxygen and glucose.
• Cellular respiration inputs are oxygen and glucose, and outputs are carbon dioxide and water.
• Autotrophs (like plants) perform photosynthesis and respiration.
• Heterotrophs (like animals) only perform respiration.

Stages of Photosynthesis

• Light reactions convert light energy into chemical energy, using enzymes to split water into hydrogen and oxygen.
• Carbon fixation (Calvin cycle) uses ATP and hydrogen (from light reactions) to produce sugars with carbon dioxide.

Stages of Cellular Respiration

• Glycolysis occurs in the cytosol, breaking down glucose into pyruvate.
• Krebs cycle (citric acid cycle) occurs in the mitochondria, producing energy-carrying molecules.
• Electron transport occurs in the mitochondria, generating ATP using energy from electrons.

Flow of Energy

• Photosynthesis and respiration are opposing reactions, converting energy between different forms.
• The ultimate energy source for photosynthesis is the sun.
• Cellular respiration converts carbohydrates' energy into ATP.
• Energy flows from chloroplasts to carbohydrates and then to mitochondria to ATP molecules.

Hypothesis of Endosymbiosis

• Mitochondria and chloroplasts have their own DNA and ribosomes similar to prokaryotes.
• The endosymbiotic hypothesis suggests that mitochondria and chloroplasts were once prokaryotic organisms that lived inside larger cells, forming an evolutionary interaction.

The Nucleus and Ribosomes

• The nucleus is essential for cell life, containing the genetic instructions.
• The nucleus holds chromatin, which coils into chromosomes, carrying genetic information.
• The nuclear envelope separates the nucleus from the cytoplasm, allowing selective material passage.

Ribosomes

• Ribosomes are particles for protein synthesis, composed of proteins and rRNA (ribonucleic acid).
• Eukaryotic ribosomes exist in free or bound forms (to the rough ER).
• Free ribosomes produce proteins needed within the cell.
• Bound ribosomes produce proteins destined for secretion, lysosomes or incorporation into membranes.

Peroxisomes

• Peroxisomes are membrane-bounded vesicles containing enzymes, breaking down molecules like hydrogen peroxide into water and oxygen.
• Peroxisomes are important in germinating seeds and detoxifying organs like the liver and kidneys.

Vacuoles

• Vacuoles are specialized sacs in cells for storing water, nutrients, and substances needing breakdown.
• Plant cells have a central vacuole taking up much of the cell volume.
• Plant vacuoles contain cell sap, sugars, salts, pigments, and toxic molecules.

Cell Junctions

• Adjacent animal cells are connected by specialized junctions for communication, interaction, and support.
• Tight junctions prevent leakage of extracellular fluid across epithelial layers.
• Anchoring junctions connect cells for structure and support.
• Gap junctions are channels allowing material transfer between cells.

Cell Walls

• Plant cells have rigid cell walls primarily composed of cellulose, providing structure, support, and protection for the cell.
• Plasmodesmata are channels in plant cell walls permitting communication between plant cells.

Cell Signaling

• Cell signaling is a process where cells interact with other cells and the environment.
• Pathways for communication include autocrine, intracrine, juxtacrine, paracrine, and endocrine.
• Paracrine signaling occurs over short distances.
• Endocrine signaling uses hormones traveling via the bloodstream to regulate distant organs.

Ligands and Receptors

• Ligands deliver chemical signals, while receptors are protein targets on the cell for these signals.
• Ligands bind to receptors initiating cellular responses.
• The complex between ligand and receptor determines the cell response.

Functional Categories of Cell Structures

• Organelles are grouped by their primary function, and structures are usually correlated with their function.
• Cell structures are categorized for easy understanding, focusing on specific roles.

Test your knowledge on the roles of decomposers in ecosystems and the mechanisms of cell signaling in multicellular organisms. This quiz covers essential concepts such as the types of decomposers, their importance, and various forms of cellular communication. Challenge yourself to understand the intricate relationships within biological systems.