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Microbiology chapter 3

Terms in this set (59)

Uptake of Nutrients
Microbes can only take in dissolved particles across a selectively permeable membrane
Some nutrients enter by passive diffusion
Microorganisms use transport mechanisms
facilitated diffusion - all microorganisms
active transport - all microorganisms
group translocation - Bacteria and Archaea
endocytosis - Eukarya only
Passive Diffusion
►Molecules move from region of higher concentration to one of lower concentration between the cell's interior and the exterior
►H2O, O2, and CO2 often move across membranes this way
Facilitated Diffusion
Similar to passive diffusion
movement of molecules is not energy dependent
direction of movement is from high concentration to low concentration
size of concentration gradient impacts rate of uptake
Facillitated Diffusion Differs from passive diffusion
►uses membrane bound carrier molecules (permeases)
►smaller concentration gradient is required for significant uptake of molecules
►effectively transports glycerol, sugars, and amino acids
►more prominent in eukaryotic cells than in bacteria or archaea
Active Transport
►energy-dependent process
►ATP or proton motive force used
►move molecules against the gradient
►concentrates molecules inside cell
►involves carrier proteins (permeases)
►carrier saturation effect is observed at high solute concentrations
ABC Transporters
►Primary active transporters use ATP
►ATP-binding cassette (ABC) transporters
►Observed in Bacteria, Archaea, and eukaryotes
Secondary Active Transport
Major facilitator superfamily (MFS)
Use ion gradients to cotransport substances
protons
symport - two substances both move in the same direction
antiport - two substances move in opposite directions
Group translocation
►Energy dependent transport that chemically modifies molecule as it is brought into cell
►Best known translocation system is phosphoenolpyruvate: sugar phosphotransferase system (PTS)
Eukaryotic Microorganisms
►Prominent members of ecosystems
►Useful as model systems and industry
►Some are major human pathogens
►Two groups of eukaryotes commonly possess microbial members
protists
fungi
Common Features of Eukaryotic Cells
►Membrane-delimited nuclei
►Membrane-bound organelles that perform specific functions
►Intracytoplasmic membrane complex serves as transport system
►More structurally complex and generally larger than bacterial or archaeal cells
Eukaryotic Cell Envelopes
►Consists of the plasma membrane and all coverings external to it
►Plasma membrane is a lipid bilayer
►major membrane lipids include phosphoglycerides, sphingolipids, and cholesterol, all of which contribute to strength of membrane
►microdomains participate in variety of cellular processes
Eukaryotic Cell Envelopes more
►Unlike the peptidoglycan in the cell wall of Bacteria and Archaea, many eukaryotes lack or have a chemically distinct cell wall
►Cell walls of photosynthetic algae have cellulose, pectin, and silica
►Cell walls of fungi consist of cellulose, chitin, or glucan
The Cytoplasm of Eukaryotes
Consists of liquid, the cytosol, and many organelles
Cytoskeleton
Cytoskeleton
►vast network of interconnected filaments within the cytoplasmic matrix
►filaments that form the cytoskeleton: microfilaments (actin), microtubules, intermediate filaments, and motor proteins
►plays role in both cell shape and cell movement
Microfilaments
Small protein filaments, 4 to 7 nm in diameter
Scattered within cytoplasmic matrix or organized into networks and parallel arrays
Composed of actin protein
Involved in cell motion and shape changes
Intermediate Filaments
Heterogeneous elements of the cytoskeleton, ~10 nm in diameter
Keratin and vimentin classes
Role in cell is unclear
play structural role
some shown to form nuclear lamina
others help link cells together to form tissues
Microtubules
Shaped like thin cylinders ~25 nm in diameter of σ- and β-tubulin
Help maintain cell shape
Involved with microfilaments in cell movements
Participate in intracellular transport processes
Secretory Endocytic Pathway
Intricate complex of membranous organelles and vesicles that move materials into the cell from outside, from inside to outside, and within the cell
Endoplasmic reticulum (ER)
Golgi apparatus
Lysosomes
Endoplasmic Reticulum (ER)
Irregular network of branching and fusing membranous tubules and flattened sacs (cisternae - s., cisterna)
Rough ER
ribosomes attached
synthesis of secreted proteins by ER-associated ribosomes
Smooth ER
devoid of ribosomes
synthesis of lipids by ER-associated enzymes
Functions of ER
Transports proteins, lipids, and other materials within cell
Major site of cell membrane synthesis
The Golgi Apparatus
Membranous organelle made of cisternae stacked on each other
Cis and trans faces
Dictyosomes=stacks of cisternae
Involved in modification, packaging, and secretion of materials
Lysosomes
Membrane-bound vesicles found in most eukaryotes
Involved in intracellular digestion
Contain hydrolases, enzymes which hydrolyze molecules and function best under slightly acidic conditions
Maintain an acidic environment by pumping protons into their interior
The Secretory Pathway
►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
Secretory Pathway path
Released in small vesicles→ cis face of Golgi apparatus→ trans face of Golgi apparatus
modification of proteins occurs in Golgi; targets protein for final destination
Transport vesicles released from trans face of Golgi
The Secretory Pathway after
After release some vesicles deliver their contents to endosomes and lysosomes
Two types of vesicles deliver proteins to cell membrane
constitutive delivery to membrane
secretory vesicles in multicellular eukaryotes store proteins until signal to release
Quality assurance mechanism
: secretory pathway
►or misfolded proteins are secreted into cytosol, targeted for destruction by ubiquitin polypeptides
►proteasomes destroy targeted proteins
The Endocytic Pathway: endocytosis
used by all eukaryotic cells
used to bring materials into the cell
solutes or particles taken up and enclosed in vesicles pinched from plasma membrane
in most cases materials are then delivered to lysosome and destroyed
Phagocytosis types of endocytosis
use of cell surface protrusions to surround and engulf particles
clathrin-dependent types of endocytosis
blank protein-coated pits have external receptors that specifically bind macromolecules
Caveolae-dependent endocytosis:
type of endocytosis
may play role in signal transduction, transport of small as well as macromolecules
Autophagy
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
Once Lysosome Is Formed...
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 which can release contents to cell exterior by process called lysosome secretion
Organelles Involved in Genetic Control of the Cell
Nucleus
Ribosomes
The Nucleus
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
Nuclear envelope
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
The Nucleolus
1 nucleolus/nucleus
Organelle but not membrane enclosed
Important in ribosome synthesis
directs synthesis and processing of rRNA
directs assembly of rRNA to form partial ribosomal subunits
ribosomes mature in cytoplasm
Eukaryotic Ribosomes
Larger (more mass) 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
More on ribosomes
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
Organelles Involved in Energy Conservation
Mitochondria
Hydrogenosomes
Chloroplasts
Endosymbiotic Hypothesis
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
Mitochondria
"The power houses of the cell" are found in most eukaryotic cells
Site of tricarboxylic acid cycle activity
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
Mitochondrial Structure: Outer membrane
contains porins similar to the outer membrane of Gram-negative bacteria
Mitochondrial Structure: inner membrane
highly folded to form cristae (s., crista)
location of enzymes and electron carriers for electron transport and oxidative phosphorylation
Mitochondrial Structure: matrix
enclosed by inner membrane
contains ribosomes (same size as bacterial), mitochondrial DNA (may be closed circular like bacterial DNA)
contains enzymes of the tricarboxylic acid cycle and enzymes involved in catabolism of fatty acids
Hydrogenosomes
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
Chloroplasts
Type of plastid
pigment-containing organelles observed in plants and algae
Site of photosynthetic reactions
Surrounded by double membrane
Chloroplast Structure
The stroma (a matrix) is within inner membrane
contains DNA, ribosomes, lipid droplets, starch granules, and thylakoids
thylakoids
flattened, membrane-delimited sacs
grana (s., granum) - stacks of blank
site of light reactions (trapping of light energy to generate ATP, NADPH, and oxygen)
Stroma is site of
of dark reactions of photosynthesis (formation of carbohydrates from water and carbon dioxide)
Algal chloroplasts
many contain a pyrenoid
participates in polysaccharide synthesis
External Cell Covering
cillia
flagella
Flagella
100-200 μm long
move in undulating fashion
Cilia
5-20 μm long
beat with two phases, working like oars
Ultrastructure of Flagella and Cilia
Membrane-bound cylinders ~2 μm in diameter
Axoneme
Basal body
Axoneme:
set of microtubules in a 9+2 arangemnet
Basal body
at base of flagellum or cilium
directs synthesis of flagella and cilia
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