Cell Structure and Microscopy SL

Cell

The basic structural and functional unit of life; the smallest unit capable of carrying out life processes.

Cell theory

A framework stating that all living things are composed of cells, the cell is the basic unit of life, and cells arise from preexisting cells.

Rudolf Virchow’s postulate

All cells arise from preexisting cells.

Hooke

First to observe and name cells while examining cork under a microscope.

Leeuwenhoek

Improved microscope lenses; first to observe living cells, calling them ‘animalcules.’

Schleiden

Botanist who proposed that all plants are composed of cells.

Schwann

Zoologist who extended Schleiden’s ideas to animals; helped formulate cell theory.

Prokaryote

A small, simple cell lacking a nucleus and most organelles; DNA in the nucleoid region.

Eukaryote

A cell with a nucleus and membrane-bound organelles; usually larger and more complex.

Nucleoid

Region in prokaryotes where DNA is located; not enclosed by a membrane.

Plasmid

Small, circular DNA molecule in some prokaryotes, separate from the chromosomal DNA.

Capsule

Outer protective layer surrounding some bacterial cells.

Pili

Protein filaments on prokaryotes that aid adhesion and genetic exchange.

Flagellum

Long, whip-like structure used for cell movement.

Cell wall

Rigid layer outside the plasma membrane; composition varies (peptidoglycan in bacteria, cellulose in plants, chitin in fungi).

Plasma membrane

Phospholipid bilayer that encloses the cell and controls movement of substances.

Cytoplasm (cytosol)

Internal fluid where metabolic processes occur; site of many reactions.

Ribosome (70S)

Prokaryotic ribosome; site of protein synthesis; smaller 70S ribosome.

Ribosome (80S)

Eukaryotic ribosome; site of protein synthesis; larger 80S ribosome.

DNA

Genetic material; in prokaryotes usually circular DNA in the nucleoid; in eukaryotes linear DNA in the nucleus.

RNA

Nucleic acid involved in coding, decoding, regulation, and expression of genes.

Nucleus

Membrane-bound organelle in eukaryotes that houses DNA and the nucleolus.

Nucleolus

Region within the nucleus where ribosome assembly begins.

Endoplasmic reticulum (ER)

Membrane network; rough ER has ribosomes and synthesizes proteins; smooth ER synthesizes lipids.

Rough ER

ER studded with ribosomes; synthesizes proteins for secretion or membranes.

Smooth ER

ER without ribosomes; synthesizes lipids and detoxifies chemicals.

Golgi apparatus

Stacked membranes that modify, sort, store, and ship proteins and lipids.

Mitochondrion

Double-membrane organelle; site of aerobic respiration and ATP production.

Cristae

Inner mitochondrial membrane folds that increase surface area for respiration.

Chloroplast

Organelle in plants/algae where photosynthesis occurs; contains chlorophyll.

Vesicles

Small membrane-bound sacs for transport and storage of substances.

Lysosome

Enzyme-filled organelle that digests waste, damaged organelles, and pathogens (animal cells).

Vacuole

Membrane-bound storage sac; large central vacuole in plants maintains turgor.

Cytoskeleton

Network of protein filaments (microtubules and microfilaments) that provides support and aids movement.

Microtubules

Tubular structures that organize cell shape, transport, and chromosome separation during mitosis.

Microfilaments

Actin filaments that support cell shape and enable movement.

Centrioles

Animal-cell structures that organize spindle fibers during cell division.

Compartmentalization

Organization of the cell into membrane-bound organelles to specialize functions.

Autotrophic

Organisms that produce their own food (e.g., via photosynthesis in plants).

Heterotrophic

Organisms that obtain energy by consuming other organisms.

Plant cell differences

Cell wall made of cellulose; chloroplasts for photosynthesis; autotrophic; generally lacks centrioles.

Animal cell differences

No cell wall; no chloroplasts; may have centrioles; often have cilia/flagella.

Fungal cell differences

Cell wall made of chitin; heterotrophic; often growth as aseptate hyphae.

Aseptate hyphae

Hyphae lacking septa (cell walls) between cells, resulting in a continuous cytoplasm.

Phloem sieve tube elements

Plant cells for transporting sugars; lack nuclei and many organelles to maximize transport.

Light microscope

Opens up to about 1500x magnification; uses visible light; can view living specimens; resolution ~200 nm.

Electron microscope

Uses electrons; TEM and SEM; much higher magnification/resolution; specimens must be dead and in vacuum.

TEM vs SEM

TEM transmits electrons through a sample to view internal structures; SEM scans surfaces to view topology.

Magnification

Number of times an image appears larger than its actual size.

Resolution

Ability to distinguish two close points as separate entities; measured in nm or Å.

Field of view (FOV)

Diameter of the area visible through the microscope.

Total magnification

Product of the ocular and objective magnifications.

Micrometer (µm)

Unit of length used in biology; 1 µm = 10^-6 meters; 1 mm = 1000 µm.

Nanometer (nm)

Unit of length equal to 10^-9 meters; used for very small structures.

Fluorescence

Emission of light by a substance after absorbing light; used to tag biomolecules.

Immunofluorescence

Fluorescent tagging of antibodies to detect antigen–antibody interactions.

Cryogenic electron microscopy (Cryo-EM)

Electron microscopy technique that images samples frozen at very low temperatures.

Freeze-fracture microscopy

Technique to fracture membranes to reveal interior structures for imaging.

MR SHENG

Mnemonic for the seven life processes: Metabolism, Reproduction, Sensitivity, Homeostasis, Excretion, Nutrition, Growth.

Metabolism

All chemical reactions in a living organism that maintain life.

Reproduction

Ability to produce offspring; sexual or asexual.

Sensitivity

Ability to respond to internal and external stimuli.

Homeostasis

Maintenance of a stable internal environment.

Nutrition

Process of obtaining and processing food/materials from the environment.

Excretion

Removal of metabolic wastes from the organism.

Growth

Increase in size or number of cells during development.