comparative anatomy of prokaryotic and eukaryotic cells

nucleus

• contains chromatin: DNA complexed with histones (nucleosomes)

• site of mRNA, tRNA and rRNA synthesis

• euchromatin/ heterochromatin (denser)

• inside of nucleus, all sorts of nucleic acids

rough endoplasmic reticulum

• membrane network covered with ribosomes

• site of protein synthesis (outerface allows them to be modified)

• specific sorting signals allow import into RER

smooth ER

• no protein synthesis

• lipid synthesis

• toxin breakdown

golgi complex

• carbohydrate synthesis

• modification of proteins for specific targeting

• involved in protein trafficking through the membrane

lysosomes

• originate from golgi, can fuse with other vesicles

• contains digestive enzymes to hydrolyse macromolecules

• originate from ER → incorporate lipids and proteins from cytoplasm

• oxidises alcohols and fatty acids

mitochondria

• organelle with its own genome (15kbp and 37 genes)

• mitochondria multiply by division

• rich in membranes

• produces ATP and reducing power

chloroplasts

• made of thylakoids and found in the stroma

• converts light into organic compounds via calvin cycle

• own circular DNA/ translation machinery and multiply by division

flagella/ cilia

• consists of a bundle of 9 pairs of microtubbules surrounding central pair (axoneme)

• microtubules are connected to adjacent ones via nexin molecules

• motion is driven by ATP hydrolysis, carries out by dynein molecules

• microtubules slide against one another, giving a whiplike movement

• made up of cytoskeleton

nucleoid

• usually a singular, circular chromosome

• DNA complexes with histone-like proteins (compact)

• genetic material also includes plasmids

cytoplasm

• some prokaryotes do contain organelles

• contains several inclusion bodies

• carboxysomes

• storage granules (S, PO₄^3-, N)

• gas vesicles

envelope

• made up of multiple layers: cytoplasmic membrane, peptidoglycan, polymers covalently bound to peptidoglycan and outer membrane

appendages

• pilus: appendage dedicated to conjugation

• fimbriae/pili: involved in adherence to host cells/surfaces; antigenic structures made of 1 major protein

• flagella: supramolecular assembly involved in bacterial motility

• ATP hydrolysis causes a conformational change causes rotation

endosymbiotic origin of eukaryotes

• stable incorporation of endosymbiotic bacteria resulted in the formation of mitochondria and chloroplasts

• nucleus appears before the acquisition of mitochondria and chloroplasts by endosymbiosis

origin of organelles

• mitochondria: originated from engulfment of H₂- producing bacterium by a H₂-consuming archarea

• nucleus: genes for lipid synthesis were transferred to host

• chloroplasts: acquired later by endosymbiosis

protozoa ecological importance

• ciliates play a role in a food web (zooplankton)

• apicomplexans have a major impact on human health

• dinoflagellates are key players in the carbon cycle

alveolates

• contains alveoli- cytoplasm sacs of fluid surrounded by a lipid membrane

• motile organisms

• mostly aquatic but not exclusively

ciliates

• alveoli under cytoplasmic membrane

• cilia and trichocyst (protusible filaments)

• contains many digestive vacuoles

• 2 (can vary) micronuclei and a macronuclei

• the micronuclei is usually diploid and the macronuclei is haploid, allows for transcription of RNA

• undergoes binary fission or conjugation

• use cilia for motility and to capture prey

ampicomplexa

• spore-forming protozoans

• contains an apical complex involved in entry into the host cell

• apicoplast: generates chloroplast (no chlorophyll) carrying out fatty acid metabolism

• undergoes many morphological changes during its life cycle

predatory algae: dinoflagellates

• mixotrophs: uses sources of energy that are not light or carbon (other than CO2)

• responsible for algal blooms

• 2 flagella including 1 wrapped around the cell

• cell walls can be made of cellulose plates called thecae

• contains extrusome

• mostly vegetative reproductions and can exist as dormant

other parasitic protozoa: metamonads and trypanosomes

• mobile, mostly harmful parasites

• can be transmitted via a vector or direct contact

• transmitted through a fly

• 2 successive phases of the disease: fever, headache, lymph node inflammation or if not treated; the parasite invades the central nervous system, disrupting sleep cycles

• can also infect cattle

slime molds and amoebas

• very common predatory organisms found in damp environments

• display a complex life cycle with distinct morphology

• both share developmental stages with a similar morphology

• differentiate to multicellular reproductive stage when food supply is low

• amoebas are responsible for human diseases

amoebas

• shape is extremely variable

• conferred by pseudopods created by actin polymerisation/ disassembly

• the mechanism is shared with human phqgocytes

Cellular slime mold: Dictyostelium discoideum

• grows as an amoeboid unicellular organism that divides by binary fission

• under starvation, cells produce a metabolite (cAMP) that drives aggregation to form a slug which undergoes differentiation onto a fruiting body

• spores (cysts) are released to initiates a new cycle

Plasmodial slime mold: physarum polycephalum

• physarum grows and divides by binary fission as an ameboid single cell

• individual cells can aggregate to form a plasmodium

• the plasmodium then undergoes differentiation into a fruiting body

• spores (cysts) are released to initiate a new cycle