Chapter 4: Eurkaryotic Microbioal Structure And Function

Front 1

Eukaryotic Microorganisms

Back 1

prominent members of ecosystems
useful as model systems and industry
some are major human pathogens
two groups:
-protists
-fungi

Front 2

Common Features of Eukaryotic Cells

Back 2

membrane-delimited nuclei
membrane-bound organelles that perform specific functions – analogous to the function of organs
intracytoplasmic membrane complex serves as transport system
more structurally complex and generally larger than bacterial or archaeal cells

Front 3

Cellular partitioning

Back 3

different biochemical and physiological functions in separate compartments under independent control

Front 4

Purpose of Intracellular Membranes

Back 4

Large surface area for greater respiratory and photosynthetic activity

Front 5

Eukaryotic Cell Envelopes

Back 5

consists of the plasma membrane and all coverings external to it

Front 6

plasma membrane is a lipid bilayer

Back 6

major membrane lipids include phosphoglycerides, sphingolipids, and cholesterol, all of which contribute to strength of membrane – due to tight packing
Microdomains participate in variety of cellular processes
Membranes participate in cell movement, cell division and signal transduction

Front 7

cytoplasm

Back 7

consists of liquid, the cytosol, and many organelles

Front 8

cytoskeleton

Back 8

vast network of interconnected filaments within the cytoplasmic matrix
filaments that form the cytoskeleton – 3 Types:
microfilaments (actin)
microtubules (tubulin)
intermediate filaments (mixture of proteins, e.g., keratin & vimentin)
Also motor proteins (myosin, kinesin & dynein) – track along the cytoskeletal filaments to move cell structures from one location to another

Front 9

Microfilaments - Actin

Back 9

minute protein filaments, 4 to 7 nm in diameter
scattered within cytoplasmic matrix or organized into networks and parallel arrays
composed of actin protein- similar to the actin contractile protein of muscle tissue
involved in cell motion and shape changes – endocytosis, cytokinesis
Used by bacterial pathogens to rapidly invade host cells

Front 10

Intermediate Filaments

Back 10

heterogeneous elements of the cytoskeleton, ~10 nm in diameter
keratin and vimentin classes of proteins
role in cell is unclear (studied only in animal cells)
play structural role
some shown to form nuclear lamina
Some help position organelles in cells
others help link cells together to form tissues

Front 11

Microtubules - tubulin

Back 11

shaped like thin cylinders ~25 nm in diameter of σ- and β-tubulin - helical
help maintain cell shape
involved with microfilaments in cell movements
participate in intracellular transport processes
Form spindle apparatus during mitosis and meiosis
Found in cilia and flagella

Front 12

Organelles of the Secretory and Endocytic Pathway

Back 12

intricate complex of membranous organelles and vesicles that move materials into the cell from outside, from inside to outside, and within the cell

Front 13

Endocytic Pathway

Back 13

move materials into the cell from the outside

Front 14

Secretory Pathway

Back 14

move materials from the inside of the cell to the outside and within the cell

Front 15

Endoplasmic Reticulum (ER)

Back 15

irregular network of branching and fusing membranous tubules and flattened sacs (cisternae – s., cisterna)

Front 16

rough ER

Back 16

ribosomes attached to outside
synthesis of secreted proteins by ER-associated ribosomes

Front 17

smooth ER

Back 17

devoid of ribosomes
synthesis of lipids by ER-associated enzymes

Front 18

Functions of ER

Back 18

transports proteins, lipids, and other materials within cell
Involved in lipid and protein synthesis
major site of cell membrane synthesis

Front 19

The Golgi Apparatus

Back 19

membranous organelle made of cisternae stacked on each other – no ribosomes
cis face – forming face - associated with the ER
trans face – maturing face
dictyosomes
stacks of cisternae
involved in modification, packaging, and secretion of materials

Front 20

lysosomes

Back 20

membrane-bound vesicles found in most eukaryotes – roughly spherical and enclosed in a single membrane
involved in intracellular digestion
contain hydrolases, enzymes which hydrolyze molecules and function best under slightly acidic conditions - (pH 3.5 – 5.0)
maintain an acidic environment by pumping protons into their interior

Front 21

The Secretory Pathway

Back 21

used to move materials to various sites within the cell, as well as to either the plasma membrane or cell exterior
proteins destined for the cell membrane, endosomes, and lysosomes or secretion are synthesized by ribosomes on rough endoplasmic reticulum (RER)
targeted to RER lumen and are released in small budding vesicles from RER by glycosylation

Front 22

two types of vesicles deliver proteins to cell membrane

Back 22

constitutive delivery to membrane (unregulated)
Secretory vesicles in multicellular eukaryotes store proteins until signal to release (regulatory controlled, e.g., immune system)

Front 23

quality assurance mechanism of secretion

Back 23

unfolded or misfolded proteins are secreted into cytosol, targeted for destruction by ubiquitin polypeptides
proteasomes destroy targeted proteins

Front 24

endocytosis

Back 24

Feeding pathway found in all eukaryotic cells
used to bring materials into the cell
solutes (pinocytosis) or particles (phagocytosis) taken up and enclosed in vesicles pinched from plasma membrane
in most cases materials are then delivered to lysosome and destroyed
Some viruses and pathogens use these pathways to enter host cells

Front 25

types of endocytosis

Back 25

clathrin-dependent endocytosis

Front 26

phagocytosis

Back 26

use of cell surface protrusions to surround and engulf particles
fuse with lysosomes and resulting vesicles called phagosomes

Front 27

clathrin-dependent endocytosis

Back 27

involves membrane regions coated on cytoplasmic side with the protein clathrin (coated pits)
coated pits have external receptors that specifically bind macromolecules-concentrates molecules
pinching off of coated pits forms coated vesicles
called receptor-mediated endocytosis

Front 28

caveolae-dependent endocytosis (little caves)

Back 28

enriched in cholesterol and the membrane protein caveolin
when caveolae pinch off membrane are called caveolar-coated vesicles
do not deliver their contents directly to lysosomes
may play role in signal transduction (mechanism for sensing the environment and turning on and off genes in response), transport of small as well as large molecules, cholera toxin, used by pathogens to invade hosts

Front 29

autophagy

Back 29

delivery of materials to be digested by route that does not involve endocytosis
macroautophagy involves digestion and recycling of cytoplasmic components
double membrane surrounds cell component forming an autophagosome
autophagosome fuses with a lysosome

Front 30

Once Lysosome Is Formed…

Back 30

digestion occurs without release of lysosome enzymes into cytoplasmic matrix
as contents are digested, products leave lysosome and can be used as nutrients
resulting lysosome, called a residual body, can release contents to cell exterior by process called lysosome secretion

Front 31

nucleus

Back 31

membrane-bound spherical structure that houses genetic material of eukaryotic cell
contains dense fibrous material called chromatin
complex of DNA, histones, and other proteins
five types of histones form nucleosomes
H1, H2A, H2B, H3, and H4
chromatin condenses into chromosomes during division

Front 32

nuclear envelope

Back 32

double membrane structure that delimits nucleus
continuous with ER
penetrated by nuclear pores
associated proteins make up the nuclear pore complex
pores allow materials to be transported into or out of nucleus

Front 33

nucleolus

Back 33

organelle but not membrane enclosed
important in ribosome synthesis
directs synthesis and processing of rRNA
directs assembly of rRNA and ribosomal proteins to form partially completed ribosomal subunits which leave the nucleus through the nuclear pores
ribosomes mature in cytoplasm

Front 34

Eukaryotic Ribosomes

Back 34

larger than the 70S bacterial and archaeal ribosomes
80S in size
60S + 40S subunits
may be attached to ER or free in cytoplasmic matrix
60S is bound subunit to ER
proteins made on ribosomes of RER are often secreted or inserted into ER membrane as integral membrane proteins
free ribosomes synthesize nonsecretory and nonmembrane proteins
some proteins are inserted into organelles

Front 35

Endosymbiotic Hypothesis

Back 35

mitochondria, hydrogenosomes, and chloroplasts are all thought to have evolved from bacterial cells that invaded or were ingested by early ancestors of eukaryotic cells
mitochondria and chloroplasts are very similar to extant bacteria and cyanobacteria, respectively

Front 36

Mitochondria

Back 36

“the power houses of the cell” are found in most eukaryotic cells
site of tricarboxylic acid cycle activity (TCA cycle)
site where ATP is generated by electron transport and oxidative phosphorylation
about the same size as bacterial cells
reproduce by binary fission as do bacterial cells

Front 37

Mitochondrial Structure

Back 37

contains porins similar to the outer membrane of gram-negative bacteria

Front 38

Mitochondrial Structure

Back 38

highly folded to form cristae (s., crista)
location of enzymes (e.g., ATP synthase) and electron carriers for electron transport and oxidative phosphorylation

Front 39

Mitochondrial Structure

Back 39

matrix enclosed by inner membrane:
contains ribosomes (same size as bacterial), mitochondrial DNA (may be closed circular like bacterial DNA), and large calcium phosphate granules
contains enzymes of the tricarboxylic acid cycle and enzymes involved in catabolism of fatty acids

Front 40

Hydrogenosomes

Back 40

small energy conservation organelles in some anaerobic protists
descended from common mitochondrial ancestor
double membrane, no cristae, usually lack DNA
ATP is generated by fermentation process rather than respiration
CO2, H2, and acetate are products

Front 41

Chloroplasts

Back 41

type of plastid:
pigment-containing organelles observed in plants and algae
site of photosynthetic reactions
surrounded by double membrane

Front 42

Chloroplast Structure

Back 42

the stroma (a matrix) is within inner membrane
contains DNA, ribosomes, lipid droplets, starch granules, and thylakoids

Front 43

thylakoids

Back 43

flattened, membrane-delimited sacs
grana (s., granum) – stacks of thylakoids
site of light reactions (trapping of light energy to generate ATP, NADPH, and oxygen)

Front 44

stroma

Back 44

is site of dark reactions of photosynthesis (formation of carbohydrates from water and carbon dioxide)

Front 45

cilia (s., cilium)

Back 45

5-20 μm long
beat with two phases, working like oars

Front 46

flagella (s., flagellum)

Back 46

100-200 μm long
move in undulating fashion
tinsel – tip pulls cell along
whiplash – naked flagellum

Front 47

Ultrastructure of Flagella and Cilia

Back 47

-membrane-bound cylinders ~2 μm in diameter
-axoneme:
set of microtubules in a 9 + 2 arrangement
Dynein arms interact with the tubules to cause sliding
basal body:
at base of flagellum or cilium
directs synthesis of flagella and cilia
Growth is at tips

Front 48

Comparison of Bacterial, Archaeal, and Eukaryotic Cells

Back 48

differences in eukaryotic cells:
-eukaryotic nucleus
-larger, more complex
-meiosis, mitosis
-complex processes
molecular unity basic to all three cells:
-biochemical processes, metabolic pathways
genetic code