MICROM 301

Cell envelope

The layers surrounding the contents of the cell; they include the cytoplasmic membrane, cell wall, and capsule

Cytoplasm

Contents of a cell, excluding the nucleus

Nucleoid

Region of a prokaryotic cell containing the DNA

Cytoplasmic membrane

A phospholipid bilayer embedded with proteins that surrounds the cytoplasm and defines the boundary of the cell

Fluid mosaic model

Model that describes the dynamic nature of the cytoplasmic membrane

Selectively permeable

Describes material that allows only certain substances to pass through freely

Aquaporins

Pore-forming membrane proteins that specifically allow water to pass through

Simple diffusion

Movement of solutes from a region of high concentration to one of low concentration; does not involve transport proteins

Osmosis

Movement of water across a membrane from a dilute solution to a more concentrated solution

Electron-transfer chain

Group of membrane-embedded electron carriers that pass from one to another and in the process, create a protein motive force

Protein motive force

Form of energy generated as an electron transport chain moves protons across a membrane to create a chemiosmotic gradient

Transport systems

Mechanisms used to transport nutrients and other small molecules across the cytoplasmic membrane

Efflux pump

A transporter that moves molecules out of the cell

Facilitated diffusion

Transport process that moves compounds across a membrane down a concentration gradient; does not require energy

Active transport

Energy-consuming process by which cells move molecules across a membrane and against a concentration gradient

Group translocation

Type of transport process that chemically alters a molecule during its passage through the cytoplasmic membrane

Secretion

Releasing a substance from a cell or tissue

Signal sequence

Amino acid sequence that directs cellular machinery to secrete a polypeptide

Gram-positive bacteria

Bacteria that have a cell wall characterized by a thick layer of peptidoglycan; when gram stained, these cells are purple

Gram-negative bacteria

Bacteria that have a cell wall characterized by a thin layer of peptidoglycan by an outer membrane; when gram stained, these cells are pink

Teichoic acids

Gram-positive cell wall component composed of chains of a common subunit, either ribitolphosphate or glycerolphosphate, to which various sugars and d-alanine are usually attached

Periplasm

The gel-like material that fills the region between the cytoplasmic membrane and the outer membrane of gram-negative bacteria and the cytoplasmic membrane and peptidoglycan layer of at least some gram-positive bacteria

Outer membrane

In prokaryotic cells; the unique lipid bilayer of gram-negative cells that surrounds the peptidoglycan layer

Lipopolysaccharide (LPS)

Molecule that makes up the outer layer of the outer membrane of Gram-negative bacteria

Endotoxin

The LPS component of the outer membrane of gram-negative bacteria

Lipid A

Portion of LPS that anchors the molecule in the lipid bilayer of the outer membrane of Gram-negative bacteria; it plays an important role in the body’s ability to recognize the presence of invading bacteria, but is also responsible for the toxic effects of LPS

O antigen

Antigenic polysaccharide portion of lipopolysaccharide

Porins

Proteins in the outer membrane of Gram-negative bacteria that form channels through which small molecules can pass

Penicillins

Group of antibiotics that includes penicillin and that interferes with the synthesis of the peptidoglycan portion of bacterial cell walls

Lysozyme

Enzyme that degrades peptidoglycan of the bacterial cell wall

Capsule

Gel-like structure outside the cell wall

Slime layer

A diffuse and irregular material that surrounds some microorganisms

Glycocalyx

Polysaccharide layer that surrounds some cells and generally functions as either a method of protection or attachment

Biofilm

Polymer-encased community of microorganisms

Flagellum

A type of structure used for cell movement

Peritrichous flagella

Distribution of flagella all around a cell

Polar flagellum

Single flagellum at one end of a cell

Chemotaxis

Movement of a cell toward or away from a certain chemical in the environment

Pili

Cell surface structures that allow cells to adhere to certain surfaces; shorter than flagella

Fimbria/common pili

Type of pilus that enables cells to attach to a specific surface and to host cells

Sex pilus

Pilus used for DNA transfer between bacteria

Chromosome

Structure that carries an organism’s essential genetic information

Plasmid

“Extra” genetic information

Ribosomes

Structure that serves as a decoding site for mRNA, functioning as a protein-synthesizing machine where tRNAs interact with codons; composed of ribosomal RNA and protein

Cytoskeleton

Cell framework (actin filaments, microtubules, intermediate filaments)

Storage granule

An accumulation of high-molecular-weight polymer synthesized from a nutrient that a cell has in relative excess

Gas vesicles

Small, rigid compartments produced by some aquatic bacteria that provide buoyancy to the cell

Bacterial microcompartment (BMC)

Protein-based structure in some bacteria that contains enzymes required for certain reactions

Encapsulin nanocompartment

Protein-based compartment in bacteria and archaea that holds certain proteins

Endospore

“Dormant” cell

Vegetative cell

Typical, actively multiplying cell

Sporulation

The process of producing an endospore

Germinate

Describes the behavior of an endospore or other resting cells as it exits the dormant stage and develops into a vegetative cell

Viruses

Consist of either DNA or RNA, surrounded by a protein coat. Obligate intracellular agents that use the machinery and nutrients of host cells to replicate

Viroids

Consist only of RNA; no protein coat. Obligate intracellular agents that use the machinery and nutrients of host cells to replicate

Prions

Consist only of protein; no DNA or RNA. Misfolded versions of normal cellular proteins that cause the normal versions

Organelle

A cell structure that performs a specific function

Tissue

Cooperative associations of cells in a multicellular organism

Organ

A structure composed of different tissues coordinated to perform a specific function

Receptors

Type of cell surface protein that binds to specific molecules in the environment, providing the cell a mechanism to sense and adjust to its surroundinigs

Ligand

A molecule that specifically binds to a given receptor

Channel

Pore-forming membrane protein that allows specific substances to diffuse into and out of a cell

Carrier

Type of protein found in cell membranes that transports certain substances across the membrane; may also be called a permease or transporter protein

Endocytosis

Process through which cells take up particles by enclosing them in a vesicle pinched off from the cell membrane

Pinocytosis

Eukaryotic cells take in liquid

Endosomes

Membrane-bound compartment involved in the process of endocytosis

Receptor-mediated endocytosis

Cells take in material that has been bound to receptors

Phagocytosis

The process by which a phagocyte engulfs microbial invaders and debris

Pseudopods

Transient arm-like extensions formed by phagocytes and protozoa; they surround and enclose extracellular material, including bacteria, during the process of phagocytosis

Phagosome

Membrane-bound vacuole that contains the material engulfed by a phagocyte

Exocytosis

Process by which eukaryotic cells expel material; membrane-bound vesicles inside the cell fuse with the plasma membrane, releasing their content to the external medium

Ribosome

Structure that serves as a decoding site for mRNA, functioning as a protein-synthesizing machine where tRNAs interact with codons; composed of ribosomal RNA (rRNA) and protein

Actin filaments

Cytoskeletal structures of a eukaryotic cell that form miotic spindles, cilia, and flagella; long, hollow cylinders composed of tubulin

Intermediate filaments

Cytoskeletal structures of a eukaryotic cell that strengthen the cell mechanically

Endomembrane system

A group of membrane-bound organelles in a eukaryotic cell that work together, to transport cellular materials within the cell or to the cytoplasmic membrane for secretion

Lumen

The interior of an organ or organelle

Nucleus

Membrane-bound organelle in a eukaryotic cell that contains chromosomes and the nucleolus

Endoplasmic reticulum

Complex series of membrane-bound compartments in a eukaryotic cell; its rough and smooth regions have different functions

Rough endoplasmic reticulum

Membrane-bound organelle in a eukaryotic cell where proteins destined for locations other than the cytoplasm are synthesized

Smooth endoplasmic reticulum

Membrane-bound organelle in a eukaryotic cell where lipids are synthesized and degraded and calcium ions are stored

Golgi apparatus

Series of membrane-bound flattened sacs within eukaryotic cells that serve as the site where macromolecules synthesized in the endoplasmic reticulum are modified before they are transported to other destinations

Lysosomes

Membrane-bound organelle in a eukaryotic cell where macromolecules are digested

Peroxisome

Membrane-bound organelle in a eukaryotic cell where reactive oxygen species are used to break down lipids and detoxify certain chemicals

Mitochondria

Membrane-bound organelle in a eukaryotic cell where energy released during the degradation of organic compounds is used to generate ATP

Endosymbiotic theory

Theory that the ancestors of mitochondria and chloroplasts were bacteria that had been residing within other cells in a mutually beneficial partnership

Chloroplasts

Membrane-bound organelles in a photosynthetic eukaryotic cell where the energy of sunlight is harvested to generate ATP, which is then used to convert CO2 to carbohydrates

Cilia

Extracellular eukaryotic feature that moves in synch and is shorter than pilus

Binary fission

Asexual reproduction process in which one cell divides to form two daughter cells

Generation time

The time it takes for the number of cells in a population to double in number

Extracellular polymeric substances (EPS)

Mixtures of hydrophilic polymers, including polysaccharides, DNA, and proteins, that are secreted by microbial cells as part of biofilm formation

Pure culture

A population descended from a single cell

Aseptic technique

Set of procedures used to prevent the accidental introduction of unwanted microbes

Colony

A distinct mass of cells arising from a single cell

Agar

Polysaccharide extracted from marine algae that is used to solidify microbial media

Petri dish

Two-part dish of glass or plastic that is used to contain a solid laboratory medium on which bacteria are grown

Agar plate

A petri dish that contains a solidified culture medium

Streak-plate method

Simplest and most commonly used technique for isolating bacteria; a series of successive streak patterns is used to sequentially dilute an inoculum on the surface of an agar plate

Closed system

A system such as a tube, flask, or agar plate in which nutrients are not replenished and wastes are not removed as microorganisms grow

Growth curve

Growth pattern observed when cells are grown in a closed system; consists of five stages - lag phase, log phase, stationary phase, death phase, and the phase of prolonged decline

Lag phase

In a bacterial growth curve, stage characterized by extensive macromolecule and ATP synthesis but no increase in cell number