🦠Microbiology Unit 3 – The Cell

What's This Unit All About?

• Explores the fundamental unit of life, the cell, and its role as the building block of all living organisms
• Examines the structure, function, and diversity of cells across various domains of life (Bacteria, Archaea, and Eukarya)
• Investigates the intricate processes and mechanisms that occur within cells to maintain homeostasis and support life
• Delves into the differences between prokaryotic and eukaryotic cells and their evolutionary significance
• Discusses the techniques and tools used by scientists to study cells and unravel their mysteries
• Highlights the importance of understanding cells in the context of microbiology and their implications in health, disease, and biotechnology

Key Concepts and Definitions

• Cell theory states that all living organisms are composed of one or more cells, the cell is the basic unit of life, and all cells arise from pre-existing cells
• Organelles specialized structures within cells that perform specific functions (mitochondria, ribosomes, endoplasmic reticulum)
• Plasma membrane selectively permeable barrier that separates the cell's interior from the external environment and regulates the movement of molecules in and out of the cell
• Cytoplasm gel-like substance within the cell where organelles and other cellular components are suspended
  • Cytosol the aqueous portion of the cytoplasm, excluding organelles
• Nucleus (in eukaryotic cells) houses the cell's genetic material (DNA) and serves as the control center for cellular activities
• Prokaryotes single-celled organisms that lack a membrane-bound nucleus and other organelles (bacteria and archaea)
• Eukaryotes organisms with cells that contain a membrane-bound nucleus and other organelles (animals, plants, fungi, and protists)

Cell Structure and Components

• Plasma membrane consists of a phospholipid bilayer with embedded proteins, carbohydrates, and other molecules
  • Phospholipids have hydrophilic heads and hydrophobic tails, forming a barrier between the cell's interior and exterior
  • Membrane proteins perform various functions, such as transport, signaling, and enzymatic reactions
• Cell wall (in some cells) provides structural support and protection, located outside the plasma membrane
  • Peptidoglycan a complex polymer that makes up the cell wall in bacteria, providing rigidity and shape
• Cytoskeleton network of protein filaments (microfilaments, intermediate filaments, and microtubules) that provides structure, support, and enables cell movement
• Ribosomes small organelles responsible for protein synthesis, found in both prokaryotic and eukaryotic cells
• Endoplasmic reticulum (ER) extensive network of membrane-bound channels and sacs involved in protein and lipid synthesis, modification, and transport
  • Rough ER studded with ribosomes, site of protein synthesis and modification
  • Smooth ER lacks ribosomes, involved in lipid synthesis and detoxification
• Golgi apparatus organelle that modifies, packages, and sorts proteins and lipids for transport to their final destinations within or outside the cell

Types of Cells: Prokaryotes vs. Eukaryotes

• Prokaryotic cells are typically smaller and simpler than eukaryotic cells, with a size range of 0.1-5 μm
  • Lack membrane-bound organelles and a true nucleus
  • DNA is circular and located in the nucleoid region, not enclosed by a nuclear membrane
  • Ribosomes (70S) are smaller than those found in eukaryotic cells
  • May possess additional structures such as plasmids, pili, and fimbriae
• Eukaryotic cells are larger and more complex, with a size range of 10-100 μm
  • Contain membrane-bound organelles, including a true nucleus that houses the genetic material
  • DNA is linear and organized into chromosomes within the nucleus
  • Ribosomes (80S) are larger and found in the cytoplasm, rough ER, and mitochondria
  • Possess a more extensive endomembrane system, including ER and Golgi apparatus
  • May have additional specialized structures depending on the cell type (chloroplasts in plant cells, flagella or cilia for movement)

Cell Functions and Processes

• Metabolism encompasses all the chemical reactions that occur within a cell to maintain life, including energy production, biosynthesis, and waste removal
• Energy production in cells involves the breakdown of nutrients to generate ATP (adenosine triphosphate), the primary energy currency of the cell
  • Glycolysis breaks down glucose in the cytoplasm, producing pyruvate and a small amount of ATP
  • Cellular respiration (in aerobic organisms) occurs in the mitochondria, oxidizing pyruvate to generate a large amount of ATP through the citric acid cycle and electron transport chain
• DNA replication the process by which a cell duplicates its genetic material before cell division, ensuring that each daughter cell receives an identical copy of the genome
• Transcription the synthesis of RNA from a DNA template, carried out by RNA polymerase enzymes
  • Messenger RNA (mRNA) carries the genetic information from DNA to ribosomes for protein synthesis
  • Ribosomal RNA (rRNA) and transfer RNA (tRNA) play essential roles in the translation process
• Translation the process of synthesizing proteins from the genetic code carried by mRNA, occurring at ribosomes
• Cell division the process by which a cell reproduces itself, giving rise to two genetically identical daughter cells
  • Binary fission in prokaryotes, where the cell divides into two equal halves
  • Mitosis in eukaryotes, involving the separation of duplicated chromosomes and the formation of two nuclei
  • Cytokinesis the division of the cytoplasm, completing the cell division process

Cellular Communication and Signaling

• Cells communicate with each other and respond to their environment through various signaling mechanisms
• Receptors proteins on the cell surface or within the cell that bind to specific signaling molecules (ligands), initiating a cellular response
• Signal transduction the process by which a signal is transmitted from the receptor to the cell's interior, often involving a cascade of molecular events
  • G protein-coupled receptors (GPCRs) a large family of cell surface receptors that associate with G proteins to initiate intracellular signaling cascades
  • Receptor tyrosine kinases (RTKs) cell surface receptors that possess intrinsic enzymatic activity, phosphorylating downstream signaling molecules upon ligand binding
• Second messengers small molecules (cyclic AMP, calcium ions) that relay signals from receptors to target molecules within the cell, amplifying the signal
• Gene regulation the control of gene expression in response to cellular signals, allowing cells to adapt to changes in their environment
  • Transcription factors proteins that bind to specific DNA sequences, promoting or inhibiting the transcription of target genes
• Cell-cell junctions specialized structures that allow cells to adhere to each other and communicate, such as tight junctions, gap junctions, and desmosomes

Techniques for Studying Cells

• Microscopy the use of microscopes to visualize cells and their components
  • Light microscopy uses visible light and lenses to magnify cells, allowing for the observation of live specimens
  • Electron microscopy (scanning and transmission) uses a beam of electrons to create high-resolution images of cell structures, providing greater detail than light microscopy
  • Fluorescence microscopy utilizes fluorescent dyes or proteins to label specific cellular components, enabling the visualization of dynamic processes within living cells
• Cell culture the growth and maintenance of cells in a controlled laboratory environment, allowing for the study of cell behavior, function, and interactions
  • Primary cell culture involves isolating cells directly from tissues and growing them in vitro
  • Immortalized cell lines are genetically modified to continuously divide, providing a consistent source of cells for research
• Flow cytometry a technique that analyzes the physical and chemical characteristics of individual cells in a fluid stream, using laser-based technology
  • Can rapidly measure cell size, granularity, and the presence of specific markers using fluorescent antibodies
• Cell fractionation the process of separating cellular components based on their physical properties (size, density, charge) using centrifugation or other methods
• Biochemical assays techniques used to study specific cellular processes or molecules, such as enzyme activity, protein-protein interactions, or gene expression
  • Western blotting detects specific proteins using antibodies after separating them by size via gel electrophoresis
  • Polymerase chain reaction (PCR) amplifies specific DNA sequences for analysis or manipulation
  • RNA sequencing (RNA-seq) determines the sequence and quantity of RNA molecules in a cell, providing insights into gene expression patterns

Real-World Applications and Cool Stuff

• Stem cell research and regenerative medicine harnessing the potential of stem cells to develop therapies for diseases and injuries
  • Induced pluripotent stem cells (iPSCs) adult cells reprogrammed to a pluripotent state, capable of differentiating into various cell types
• Cancer biology understanding the cellular basis of cancer and developing targeted therapies
  • Oncogenes genes that, when mutated or overexpressed, contribute to the development of cancer by promoting uncontrolled cell growth and division
  • Tumor suppressor genes genes that normally regulate cell growth and division, preventing cancer development; mutations in these genes can lead to cancer
• Synthetic biology designing and engineering cells with novel functions for various applications, such as biofuel production, biosensors, or drug delivery
• Microbiome research investigating the diverse microbial communities that inhabit the human body and their role in health and disease
  • Gut microbiome the collection of microorganisms in the human digestive tract, influencing metabolism, immunity, and overall health
• Biopharmaceuticals using living cells to produce therapeutic proteins, antibodies, and vaccines
  • Recombinant DNA technology inserting genes from one organism into another to produce desired proteins or modify cellular functions
• Cellular agriculture producing animal products (meat, leather, etc.) from cultured cells, reducing the environmental impact of traditional animal agriculture