Tour of the Cell and Origins of Life

Vocabulary flashcards covering the origins of life, cell theory, measurement conversions, microscopy, and the structures/functions of prokaryotic and eukaryotic organelles.

Special Creation

A hypothesis on the origin of life suggesting a benevolent supreme being suspends the laws of physics and chemistry to create life; it is not a testable hypothesis.

Panspermia

The extraterrestrial hypothesis that life was formed elsewhere in the universe and “seeded” Earth via astronomical phenomena.

Chemical Evolution

The hypothesis that life evolved from the assembly of larger chemical compounds.

Miller-Urey Experiment

A 1953 laboratory simulation of early Earth's reducing atmosphere using water vapor, $H_2$, methane ($CH_4$), and ammonia ($NH_3$) with electrical sparks to produce organic molecules like amino acids.

Protobionts

Aggregates of abiotically produced molecules surrounded by a membrane or membrane-like structure that can form spontaneously.

Liposomes

Small membrane-bounded droplets that can form when lipids or other organic molecules are added to water and can exhibit simple reproduction and metabolism.

Ribozymes

RNA molecules that can catalyze reactions, including self-splicing and making complementary copies of short RNA sequences.

Endosymbiotic Theory

The theory that mitochondria and plastids originated as formerly small prokaryotes living within larger host cells as undigested prey or internal parasites.

Cell Theory

The concept that all organisms are composed of one or more cells, cells are the basic units of organization, and cells arise only by division of pre-existing ones.

Centimeter (cm)

$10^{-2}\,m$ ($1/100\,m$), which is approximately $0.4\,\text{inch}$.

Millimeter (mm)

$10^{-3}\,m$ ($1/1,000\,m$) or $1/10\,cm$.

Micrometer ($\mu m$)

$10^{-6}\,m$ ($1/1,000,000\,m$) or $1/10,000\,cm$. Also known as a micron.

Nanometer (nm)

$10^{-9}\,m$ ($1/1,000,000,000\,m$) or $1/10,000,000\,cm$.

Surface-to-Volume Ratio

A measurement that imposes upper limits on cell size; smaller cells have a more favorable ratio for moving material in and out of the cell.

Magnification

The apparent increase in the size of an object.

Resolution (Resolving Power)

The ability of a microscope to distinguish two adjacent structures as separate, determining the clarity and detail of the image.

Light Microscope

A microscope using light and glass lenses with a resolution of $1\,\mu m$; it is beneficial for viewing live and moving samples.

Transmission Electron Microscope (TEM)

A microscope using electrons and magnets with a resolution of $1\,nm$; it is used to visualize internal cell structures.

Scanning Electron Microscope (SEM)

A microscope using electrons and magnets with a resolution of $1\,nm$; it visualizes surface structures and provides a 3D image.

Prokaryotic Cell

A small, simple cell (approx. $1.0\,\mu m$) that lacks a nucleus and membrane-bound internal compartments; examples include bacteria and archaea.

Peptidoglycan

The material that makes up the cell wall of most bacteria, distinguishing them from archaea and plants.

Nucleoid

The localized region in a prokaryotic cell where chromosomal DNA is found.

Eukaryotic Cell

A larger ($10-100\,\mu m$), complex cell with a membrane-surrounded nucleus and various membrane-bound organelles.

Nuclear Envelope

A double membrane that separates DNA from the cytoplasm and regulates the flow of molecules through nuclear pores.

Nucleolus

A region inside the nucleus where ribosomes are assembled from RNA and proteins.

Ribosomes

Organelles made of rRNA and proteins that assemble amino acids into proteins during protein synthesis.

Mitochondrion

The site for conversion of stored energy to ATP; it features an inner membrane folded into cristae and an internal mitochondrial matrix.

Peroxisomes

Small, single-membrane rounded organelles that break down fatty acids and amino acids and detoxify poisons.

Centrosome

Found in animal cells, this complex consists of two centrioles made of nine triplets of microtubules and serves as a microtubule organizing center.

Chloroplasts

Double-membrane plant organelles that contain stroma, thylakoids (stacked into grana), their own DNA, and ribosomes for photosynthesis.

Central Vacuole

A large plant cell organelle that regulates water concentration and contributes to cell expansion.

Endomembrane System

A group of internal membranes and organelles in eukaryotic cells, including the ER, Golgi apparatus, and lysosomes, that work to modify, package, and transport lipids and proteins.

Lysosomes

Animal cell organelles containing digestive enzymes that break down large biomolecules and worn-out organelles via processes like phagocytosis.

Rough Endoplasmic Reticulum (RER)

A region of the ER with attached ribosomes that modifies proteins and synthesizes phospholipids for cellular membranes.

Smooth Endoplasmic Reticulum (SER)

A region of the ER lacking ribosomes that synthesizes carbohydrates, lipids, and steroid hormones, detoxifies medications, and stores calcium ions.

Golgi Apparatus

A series of flattened membranes (cis face and trans face) that sort, package, and tag lipids and proteins for transport.

Microfilaments

Cytoskeleton components made of actin monomers involved in movement and stabilizing cell shape.

Microtubules

Cytoskeleton components made of tubulin dimers that form a rigid internal skeleton and provide a framework for motor proteins.

Plasmodesmata

Channels passing between plant cell walls that connect cytoplasm and allow material movement between cells.

Tight Junctions

Watertight seals between animal cells, primarily epithelial cells, that prevent material leakage.

Desmosomes

Cadherin protein 'spot welds' in the plasma membranes of animal tissues that stretch, such as the heart or lungs.

Gap Junctions

Animal cell connectors formed by six proteins (connexins) into a connexon, allowing the transfer of ions and small molecules between cells.