Microbiology Exam 1 - Cell Structure and Shape

What is the cell structure defined by?

cell membrane

The cell membrane acts as a...

permeability barrier

What are membranes fragile due to?

thermal damage, osmotic damage, and chemical damage

What is thermal damage?

when a cell is in an environment that is too hot or too cold

How do membranes protect themselves from thermal damage?

adjust fatty acid content - heat speeds up molecular motion so cell uses tightly packed fatty acids, cold slows down movement so cell uses poorly packed fatty acids

What is osmotic damage?

cells can burst from increased water pressure due to hydrophobicity and slightly permeable membranes

How do membranes protect themselves from osmotic damage?

by using peptidoglycan in the exoskeleton to prevent bursting

What is peptidoglycan?

hybrid of protein and polysaccharide

What is peptidoglycan composed of?

polysaccharides NAG and NAM joined by beta linkages which are then crosslinked by amino acids

Even when purified, peptidoglycans...

retain shell

What do peptidoglycans surround?

plasma membrane

What is peptidoglycan a part of?

cell envelope - everything beyond cytoplasm

What are strengths of peptidoglycan?

beta-linkages connecting sugars are biologically difficult to break, D-amino acids increase peptidoglycan resistance to proteases, allows for crosslinking

What is chemical damage?

when hydrophobic molecules insert selves into membrane and destabilize bilayer

What chemicals can damage the membrane?

detergents (SDS). soap molecule, forms micelles

What architectures protect membranes from chemical damage?

Gram positive and Gram negative

Describe Gram positive architecture.

thick external layer of peptidoglycan, elastic external wall protects membrane from osmotic pressure, uses teichoic acids

What are teichoic acids?

negatively charged glycerol phosphate polymers attached to peptidoglycan

What do teichoic acids do?

repel hydrophobics, provide chemical protection, discourages diffusion through hydrophobic zones, repels hydrophobic detergents from inserting in membrane

Describe Gram negative architecture.

outer membrane shields plasma membrane and thin layer of peptidoglycan

What are special features of Gram negative architecture?

outer membrane, lipopolysaccharide, Braun's lipoprotein, porins, periplasm

What is LPS?

lipopolysaccharide, negatively charged to repel hydrophobic molecules, has three domains, amphipathic

What does lipopolysaccharide (LPS) do?

charge barrier for chemical defense, reduce effectiveness of antibiotics

How does the size of LPS compare to phospholipids?

LPS is much larger

What are the three domains of lipopolysaccharide (LPS) structure?

O-antigen, core, lipid A

What is the O-antigen of lipopolysaccharide structure?

repeating pattern of highly variable sugars, has unknown function but each Gram negative bacterial species has a unique one

What is in the core of LPS?

highly negatively charged, repels detergents

What is lipid A of LPS?

anchors LPS to outer membrane, hydrophobic

What is Braun's lipoprotein?

attaches outer membrane to peptidoglycan, fatty acid fused to protein, most abundance protein Gram negative bacteria make

What are porins?

permeability gates, outer membrane is diffusion barrier

What is periplasm?

chemical defense w detox enzymes + chemical binding proteins, is a SPACE between plasma and outer membrane

What are common cell shapes?

coccus, rod, vibrio, prosthecate, spirillum, spirochete, filamentous

What imparts cell shape?

peptidoglycan

What makes rods rod-shaped?

MreB

What is MreB?

rod shaped, forms moving filaments,

How does MreB-GFP move inside cells?

laterally

What makes vibrios vibrio-shaped?

CreS

What is CreS?

Forms vibrio-shaped

What makes a coccus coccus-shaped?

a lack of MreB and CreS

Describe the cytoplasm of bacteria.

70% water (very dry), no empty space, little free water, hydration shells around molecules, wide variety of proteins and metabolites

What is the nucleoid?

region of bacterial cell containing the chromosome

Describe the structure of the nucleoid.

well defined but not membrane bound, constrained by proteins - specifically SMC that corrals DNA into loops

Why don't bacteria need organelles?

surface area to volume ratio - bacteria has small radius and therefore small volume which is much easier to support

What do organelles do?

restrict diffusion, concentrate reactants, isolate incompatible reactions, effectively reduce volume to size of bacterium

What are bacterial membrane invaginations?

part of plasma membrane that increase surface area and decrease volume (MamK from magnet organism)

What do invaginations allow for?

more interactions with the environment

What are the three storage granules?

energy storage, element storage, and damaged proteins

Types of storage granules

energy storage, element storage, damaged proteins (clumped are protein inclusion bodies)

What are element storage granules?

sulfur and iron

What are damaged protein granules?

protein inclusion bodies

What is the advantage of nucleoids?

rapid signaling because it couples transcription and translation

What do ribosomes do?

translate mRNA into new proteins

Describe endospores.

not an organelle, metabolically dormant + germination triggered by nutritionally favorable conditions, resistant to desiccation, mechanical stress, heat, radiation

What are flagella?

protein machines that rotate like propellers

What are the parts of the cell exterior?

EPS, S-layer, and pili

What is EPS?

extracellular polysaccharides, extra, non-essential layers beyond envelope

What is considered EPS?

capsule and slime layer

How can extracellular polymeric substances EPS be indicated?

colony morphology - no EPS=smooth, capsule=rough, slime layer=wet

What are advantages of extracellular polymeric substances (EPS)?

adhesive, cohesive, desiccation resistance, protection from immune system, clogs circulatory systems of hosts

What is S-layer?

shell made of protein, function unknown

What is pili?

rigid fibers made of protein typically involved in adhesion

Which Gram architecture makes the capsule?

Gram positive

Which Gram architectures makes the slime layer?

Gram negative

What is an indicator of a lipid/mycolic acid?

long carbon tail