Prokaryotic and Eukaryotic Cell Structures and Functions

Prokaryotic cell

Cell of the bacteria and archaea domains; "pro" = before, "karyo" = nucleus; lacks membrane-bound organelles

Prokaryotic cell anatomy

Has a cell membrane, usually a cell wall, no membrane-bound organelles, few associated proteins, and one major circular DNA molecule

Bacteria domain

Domain whose cell walls are made of peptidoglycan

Archaea domain

Domain whose cell walls are made of pseudopeptidoglycan

Prokaryotic DNA

Single major DNA molecule that is circular, like a bracelet

Ribosome

Organelle on which proteins are made; like the table where dehydration reactions happen

Eukaryotic cell

"Eu" = true, "karyo" = nucleus; contains a nucleus; belongs to domain Eukaryota (which includes humans)

Eukaryotic DNA

Linear (not circular), multiple molecules, associated with lots of histone proteins

Four kingdoms of Eukaryota

Protist, Animal, Fungus, and Plant

Protist examples

Algae, seaweed, amoeba

Eukaryotic cell size

Generally about 10x larger than prokaryotic cells

Eukaryotic cell wall materials

Plants: cellulose; Fungi: chitin; some protists: various materials

Nucleus

Membrane-bound organelle containing the DNA

Chromatin

DNA with its associated histone proteins; "chroma" = color

Chromosomes

Neat packages of wound-up DNA formed when a cell is ready to divide; "chromo" = color, "some" = body

Nucleolus

Group of genes coding for ribosomal RNA and the site where ribosomes are assembled; busy cells may have multiple

Ribosomes (eukaryotic)

Site of protein assembly; larger in eukaryotic cells than in prokaryotic cells

Cytoskeleton

"Cyto" = cell; provides support, protection, and movement, like a human skeleton

Microfilaments

Cytoskeleton component made of two strands of globular actin proteins

Microfilament functions

Muscle cell contraction, amoeboid movement, cytoplasmic streaming/motility, animal cell division

Microtubules

Cytoskeleton component made of tubulin; formed by the MTOC (centrosome)

Microtubule-organizing center (MTOC)

Also called the centrosome; the organelle that forms microtubules

Microtubule functions

Major component of cilia and flagella, pathways through the cell, separating chromosomes during cell division

Flagellum cross section

Shows a 9+2 pattern of microtubules

Intermediate filaments

Cytoskeleton component made of the fibrous protein keratin

Intermediate filament functions

Strictly structural; stabilize cell shape and fix organelle position (e.g., hold the nucleus in a cage)

Mitochondria

Powerhouse of the cell; major producer of ATP in all eukaryotes

Plastids

Organelles found only in photosynthetic organisms (algae, seaweed, plants, etc.)

Chloroplasts

"Chloro" = green; make food from CO2 and water (photosynthesis)

Chromoplasts

Plastids that store hydrophobic pigments like orange and yellow

Amyloplasts

"Amylo" = starch; plastids that store starches (e.g., potatoes)

Peroxisomes

Organelles that produce peroxide; involved in fatty acid metabolism, with peroxide as a reactive byproduct

Endomembrane system

Set of organelles including the nuclear membrane, endoplasmic reticulum, Golgi apparatus, vacuoles, and lysosomes

Endoplasmic reticulum (ER)

"Reti" = network; membranous canal system within the cytoplasm

Rough ER

ER covered in ribosomes; makes proteins for use outside the cytoplasm (cell membrane, inside organelles)

Smooth ER

ER without ribosomes; makes phospholipids, steroids, and triglycerides

Golgi apparatus

Named after Camillo Golgi; receives proteins from the rough ER via transport vesicles

Vacuoles

Membrane-bound spaces with storage functions

Central vacuole

Plant vacuole that maintains turgor pressure, stores hydrophilic pigments (blue and red), may hold noxious substances (e.g., nicotine in tobacco), and sequesters harmful materials (e.g., arsenic in rice)

Contractile vacuole

Found in freshwater protists like paramecia; acts as a pump to remove water from the cell

Food vacuole

Forms in phagocytosis when food is pinched off by the membrane

Lysosomes

"Lyso" = break, "some" = body; digest phagocytosed material and worn-out organelles

Autophagy

Digestion of worn-out organelles by lysosomes

Desmosomes

"Desmo" = join; junctions between cells in skin tissue

Tight junctions

Junctions between cells in the stomach and bladder; prevent harmful materials like stomach acid from slipping between cells

Gap junctions

Allow rapid passage of material between cells; found in cardiac muscle and uterine smooth muscle so cells contract in unison

Plasmodesmata

Plant junctions joining the cytoplasm of two cells; function like gap junctions

Functions of cellular reproduction

Organism growth, cellular repair, and cellular regeneration

Why cells divide for growth

Cells have a size limit; the larger a cell gets, the longer it takes molecules to cross it, so organisms must increase cell number

Cellular repair

Repairing cuts or gashes

Cellular regeneration

Regenerating entire limbs or removed body parts

Asexual reproduction

Reproduction in which offspring are clones of the parent

Binary fission

Prokaryotic cell division: DNA replicates, then the cytoplasm divides (cytokinesis); can take as little as 20 minutes

Chromosome number

Does not determine the organism; the genes on the chromosomes do

Homologous chromosomes

Pairs of chromosomes that are the same

Diploid (2n)

Organisms with two sets of chromosomes

Cell cycle

The time from one cell division to the next

G1 phase

First gap; the cell carries out its day-to-day job

G0 phase

Cells that do not reproduce and stay in G1 (e.g., spinal cord nerve cells)

S phase

Synthesis; DNA and the MTOC are replicated

G2 phase

Second gap; production of proteins for division (e.g., tubulin for microtubules)

Mitosis

Division of the nucleus; prokaryotes do not undergo it

Prophase

Chromatin condenses into chromosomes, nucleolus disappears, MTOCs move to poles and make microtubules forming the spindle

Spindle

Structure formed by microtubules made by MTOCs at the poles

Prometaphase

Nuclear membrane breaks down and spindle microtubules attach to centromeres

Centromere

Region that joins sister chromatids together

Metaphase

"Middle"; sister chromatids line up in the middle of the cell

Anaphase

Sister chromatids separate to become daughter chromosomes

Telophase

"Telo" = end; chromosomes decondense to chromatin, nucleolus reappears, spindle disassembles, nuclear membrane reforms, giving two nuclei

Cytokinesis

Division of the cytoplasm; often overlaps telophase

Cytokinesis in animals

Cleavage furrow forms; microfilaments make a bracelet around the cell center and tighten until the cell pinches off

Cytokinesis in plants and fungi

Cell plate formation; vesicles fuse to form the cell plate

Coenocytic

"Coeno" = shared; cells that undergo mitosis without cytokinesis, giving multiple nuclei in one cytoplasm

Result of the cell cycle

Two identical cells from one parent cell

Sexual reproduction

Involves two parents; offspring are not identical to either parent

Meiosis

"To lessen"; process that takes a 2n cell to a 1n cell

Meiosis products

Animals form 1n eggs and sperm; plants and fungi form 1n spores

Oogenesis

production of eggs

Spermatogenesis

Production of sperm

Sporogenesis

Production of spores