Brooker Biology: Chapter 4 - Evolutionary Origin of Cells and Their General Features

prebiotic soup

The medium formed by the slow accumulation of organic molecules in the early oceans over a long period of time prior to the existence of life.

protobiont

The term used to describe the first nonliving structure that could have evolved into a living cell.

liposome

A vesicle surrounded by a phospholipid bilayer.

ribozyme

A biological catalyst that is an RNA molecule.

chemical selection

The process that occurs when a chemical within a mixture has special properties or advantages that cause it to increase in amount relative to other chemicals in the mixture. May have played a key role in the formation of an RNA world.

chemical evolution

The process by which a population of molecules changes over time to become a new population with a different chemical composition.

RNA world

A hypothetical period on primitive Earth when both the information needed for life and the catalytic activity of living cells were contained solely in RNA molecules.

microscope

A magnification tool that enables researchers to visualize the structures and inner workings of cells.

micrograph

An image taken with the aid of a microscope.

resolution

In microscopy, the ability to observe two adjacent objects as distinct from one another; a measure of the clarity of an image.

contrast

In microscopy, relative differences in lightness, darkness, or color between adjacent regions in a sample.

magnification

The ratio between the size of an image produced by a microscope and the object's actual size.

light microscope

A microscope that utilizes light for illumination.

electron microscope

A microscope that uses an electron beam for illumination.

transmission electron microscopy (TEM)

A type of microscopy in which a beam of electrons is transmitted through a biological sample to form an image on a photographic plate or screen.

scanning electron microscopy (SEM)

A type of microscopy that utilizes an electron beam to produce an image of the three-dimensional surface of a biological sample.

protein-protein interactions

The specific interactions between proteins that occur during many critical cellular processes.

genome

The complete genetic material of an organism or species.

gene

A unit of heredity. At the molecular level, a gene is an organized unit of base sequences in a DNA strand that can transcribed into RNA and ultimately results in the formation of a functional product.

prokaryotic cell

A cell lacking a membrane-enclosed nucleus and cell compartmentalization; the cells of all members of the domains Bacteria and Archaea are prokaryotic cells.

Bacteria

One of the three domains of life; the other two are Archaea and Eukarya.

Archaea

One of the three domains of life; the other two are Bacteria and Eukarya.

plasma membrane

The biological membrane that separates the internal contents of a cell from its external environment.

cytoplasm

The region of the cell that is contained within the plasma membrane.

nucleoid

The site in a bacterial cell where the genetic material (DNA) is located.

ribosome

A structure composed of proteins and rRNA that is the site where translation of mRNAs and synthesis of polypeptides occurs.

cell wall

A relatively rigid, porous structure located outside the plasma membrane of prokaryotic cells and cells in plants, fungi, and certain protists; provides support and protection.

glycocalyx

1. An outer viscous covering surrounding a bacterium that traps water and helps protect the bacterium from drying out. 2. A carbohydrate-rich zone on the surface of animal cells; also called a cell coat.

capsule

A very thick, gelatinous glycocalyx produced by certain strains of bacteria that may help them avoid being destroyed by an animal's immune (defense) system.

pili (singular, pilus)

Threadlike surface appendages that allow bacteria to attach to each other during conjugation or to move across surfaces.

flagella (singular, flagellum)

Relatively long cell appendages that facilitate cellular movement or the movement of extracellular fluids.

eukaryote

A member of the domain Eukarya. The distinguishing feature of eukaryotes is cell compartmentalization, including a cell nucleus; eukaryotes include protists, fungi, plants, and animals.

organelle

A subcellular structure or membrane-bound compartment with its own unique structure and function.

compartmentalization

A characteristic of eukaryotic cells, in which many membrane-bound organelles separate the cell into different regions. Cellular compartmentalization allows a cell to carry out specialized chemical reactions in different places.

liquid-liquid phase separation

The phenomenon in which aggregated solutes, such as proteins and RNA molecules, separate from the bulk solvent, and form a droplet.

droplet organelle

An organelle that is not surrounded by a membrane but exists as a droplet formed by liquid-liquid phase separation.

proteome

The complete complement of proteins that a cell or an organism makes.

cytosol

The region of a eukaryotic cell that is inside the plasma membrane and outside the organelles.

metabolism

The sum of all bodily activities and chemical reactions that occur within an organism to maintain life. Also, a specific set of chemical reactions that occur at the cellular level.

enzyme

A protein that acts as a catalyst to speed up a chemical reaction in a cell.

catabolism

A metabolic pathway that results in the breakdown of larger molecules into smaller molecules. Such reactions are often exergonic.

anabolism

A metabolic pathway that results in the synthesis of cellular molecules and macromolecules; requires an input of energy.

cytoskeleton

In eukaryotes, a network within the cytosol consisting of three different types of protein filaments called microtubules, intermediate filaments, and actin filaments.

microtubule

A type of hollow protein filament composed of tubulin proteins that is part of the cytoskeleton and is important for cell shape, organization, and movement.

intermediate filament

A type of protein filament of the cytoskeleton of animal cells that helps maintain cell shape and rigidity.

actin filament

A thin type of protein filament that is composed of actin proteins, forms part of the cytoskeleton, and supports the plasma membrane; plays a key role in cell strength, shape, and movement.

dynamic instability

The oscillation of a single microtubule between growing and shortening phases; important in many cellular activities, including the sorting of chromosomes during cell division.

microtubule-organizing center (MTOC)

A site in a eukaryotic cell from which microtubules grow.

centrosome

A single structure often near the nucleus of a eukaryotic cell that forms a nucleating site for the growth of microtubules; also called a microtubule-organizing center.

centrioles

A pair of structures within the centrosome of animal cells. Most plant cells and many protists lack centrioles.

microfilament

See actin filament.

motor protein

A type of cellular protein that uses ATP as a source of energy to promote movement; consists of three domains called the head, hinge, and tail.

cilia (singular, cilium)

Cell appendages that have the same internal structure as flagella and function like flagella to facilitate cell movement; cilia are shorter and more numerous than are flagella.

axoneme

An internal structure of eukaryotic flagella and cilia that contains microtubules, the motor protein dynein, and linking proteins.

basal body

A site at the base of flagella or cilia from which microtubules grow. Basal bodies are anchored on the cytosolic side of the plasma membrane.

nucleus (plural, nuclei)

1. In cell biology, an organelle found in eukaryotic cells that contains most of the cell's genetic material. 2. In chemistry, the region of an atom that contains protons and neutrons. 3. In neurobiology, a group of neuronal cell bodies in the CNS that are involved in a particular function.

endomembrane system

A network of membranes that includes the nuclear envelope, the endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, peroxisomes, and plasma membrane.

nuclear envelope

A double-membrane structure that encloses the cell's nucleus.

nuclear pore

A passageway for the movement of molecules and macromolecules into and out of the nucleus; formed where the inner and outer nuclear membranes make contact with each other.

chromosome

A discrete unit of genetic material composed of DNA and associated proteins. Eukaryotes have chromosomes in their cell nuclei and in plastids and mitochondria.

chromatin

The complex of DNA and proteins that makes up eukaryotic chromosomes.

nuclear matrix

A filamentous network of proteins that is found inside the nucleus and lines the inner nuclear membrane. The nuclear matrix serves to organize the chromosomes.

nuclear lamina

A collection of protein fibers that line the inner nuclear membrane; part of the nuclear matrix.

chromosome territory

A distinct area where each chromosome is located within the cell nucleus of eukaryotic cells; chromosome territories do not overlap.

nucleolus

A droplet organelle in the nucleus of nondividing cells where ribosome assembly occurs.

endoplasmic reticulum (ER)

A convoluted network of membranes in a cell's cytoplasm that forms flattened, fluid-filled tubules, or cisternae.

cisternae

Flattened, fluid-filled tubules of the endoplasmic reticulum.

lumen

The internal space or hollow cavity of an organelle or an organ, such as the endoplasmic reticulum, the stomach, or a blood vessel.

ER lumen

A single compartment enclosed by the ER membrane.

rough endoplasmic reticulum (rough ER)

The part of the ER whose outer surface is studded with ribosomes; this region plays a key role in the initial synthesis and sorting of proteins that are destined for the ER, Golgi apparatus, lysosomes, vacuoles, plasma membrane, or extracellular environment.

membrane vesicle

A small sphere enclosed by a membrane.

glycosylation

The covalent attachment of a carbohydrate to a protein or lipid, producing a glycoprotein or glycolipid, respectively.

smooth endoplasmic reticulum (smooth ER)

The part of the ER whose outer surface is not studded with ribosomes. This region is continuous with the rough ER and functions in diverse metabolic processes such as detoxification, carbohydrate metabolism, accumulation of calcium ions (Ca2+), and synthesis and modification of lipids.

Golgi apparatus

A stack of flattened, membrane-bound compartments that performs three overlapping functions: secretion, processing, and protein sorting.

proteolysis

A processing event within a cell in which enzymes called proteases cut proteins into smaller polypeptides.

protease

An enzyme that cuts proteins into smaller polypeptides.

secretory vesicle

A membrane vesicle carrying different types of materials that fuses with the cell's plasma membrane to release the contents extracellularly.

secretory pathway

A pathway for the movement of larger substances, such as carbohydrates and proteins, from the ER to the outside of a cell.

lysosome

A small organelle found in animal cells that contains acid hydrolases that degrade molecules and macromolecules.

acid hydrolase

A hydrolytic enzyme found in lysosomes that functions at acidic pH and uses a molecule of water to break a covalent bond.

vacuole

Specialized organelles found in eukaryotic cells that function in storage, the regulation of cell volume, and degradation.

central vacuole

An organelle that often occupies 80% or more of the volume of a plant cell and stores a large amount of water, enzymes, and inorganic ions.

contractile vacuole

A small, membrane-enclosed, water-filled compartment that eliminates excess liquid from the cells of certain protists.

peroxisome

A relatively small organelle that is found in all eukaryotic cells and that catalyzes detoxifying reactions.

catalase

An enzyme within peroxisomes that breaks down hydrogen peroxide to water and oxygen gas.

glyoxysome

A specialized organelle within plant seeds that contains enzymes needed to convert fats to sugars.

membrane transport

The movement of ions or molecules across a biological membrane.

cell signaling

A vital function of the plasma membrane in which cells sense changes in their environment and communicate with each other.

cell adhesion

A vital function of the cell membrane that allows cells to bind to each other. Cell adhesion is critical in the formation of multicellular organisms and provides a way to convey positional information between neighboring cells.

mitochondrion

A semiautonomous organelle found in eukaryotic cells that supplies most of a cell's ATP.

cristae

Projections of the highly invaginated inner membrane of a mitochondrion.

mitochondrial matrix

A compartment enclosed by the inner membrane of a mitochondrion.

chloroplast

A semiautonomous organelle found in plant and algal cells that carries out photosynthesis.

photosynthesis

The process whereby light energy is captured by plant, algal, or photosynthetic bacterial cells and is used to synthesize organic molecules from CO2 and H2O (or H2S).

thylakoid membrane

A membrane within the chloroplast that forms many flattened, fluid-filled tubules that enclose a single, convoluted compartment. The membrane contains chlorophyll and is the site where the light-dependent reactions of photosynthesis occurs.

granum

A structure composed of stacked membrane-bound thylakoids within a chloroplast.

stroma

The fluid-filled region of the chloroplast between the thylakoid membrane and the inner membrane.

plastid

A general name given to organelles found in plant and algal cells that are bound by two or more membranes and contain DNA and large amounts of either chlorophyll (in chloroplasts), carotenoids (in chromoplasts), or starch (in amyloplasts).

proplastid

A type of unspecialized structure from which a plastid is derived.

mitochondrial genome

The chromosome found in mitochondria.