Chapter 3 Notes - Cell Structure and Function PDF

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Cell Structure and Function...

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Chapter 3: Cell Structure and Function Bacterial traits: 1. Thick, complete outer envelope 2. Compact Genome 3. Tightly coordinated cell functions Achaea Traits: 1. Not Bacteria 2. Are prokaryotes 3. Have unique membrane and envelope structures Prokaryotes do not have organelles. Eukaryotic cells have a nucleus.

3.1: The Bacterial Cell Cytoplasm = gel-network. See DNA, enzymes, and proteins. Cell Membrane = encloses the cytoplasm. Cell Wall = covers the cell membrane Nucleoid = non-membrane bound area of the cytoplasm that contains the chromosome in the form of looped coils Flagellum = external helical filament whose rotary motor propels the cell. Some bacteria do not have flagella.

All cells share common chemical components: 1. Water 2. Essential Ions 3. Small organic molecules 4. Macromolecules Cell Fractionation – cells must be broken up to allow subcellular parts to remain intact. - Milk Detergent Analysis - Sonication - Enzymes - Mechanical Disruption Ultracentrifuge – high rotation rate produces centrifugal forces strong enough to separate particles by size. The parts are then subjected for structural and biochemical analysis. Based on this force, you can separate different parts of the bacterial cells. Genetic Analysis 1. Mutant strains that are selected for loss of a given function 2. Strains are intentionally mutated as to lose or alter a gene

3. Strains that are constructed with “reporter genes” fused to a gene encoding a protein of interest.

3.2: The Cell Membrane and Transport Cell Membrane – the structure that defines the existence of a cell No cell membrane = NOT alive If you do not have a cell membrane around the cytosol, all of the outside things like water and such, can get inside of the cell. The cell wall tries to get the cell to tolerate harsh conditions. Phospholipid = glycerol with ester links to two fatty acids and a phosphoryl head group. The two layers of phospholipids in the bilayer, are known as leaflets. - Membranes have equal parts of phospholipids and proteins The purpose of these membrane proteins includes: 1. Structural Support 2. Detection of environmental Signals 3. Secretion of virulence factors and communication signals 4. Ion transport and energy storage Diffusion = small uncharged molecules, like oxygen and carbon dioxide, easily permeate the membrane. Osmosis = water tends to diffuse across the membrane. Passive Transport = molecules move along their concentration gradient Active Transport = molecules move against their concentration gradient, and require energy.

Phospholipids use cardiolipin or diphosphatidylglyercol. - A double phospholipid linked by a glycerol - Concentration increases in bacteria grown to starvation - Localized to the cell poles Membranes also include planar molecules that gill gaps between hydrocarbon chains - In eukaryotic membranes, the reinforcing agents are sterols, like cholesterol - In bacteria, the same function is filled by hopanoids, or hopanes. Archaea have the most extreme variations in phospholipid side-chain structures. - Ester links between glycerol and fatty acids - Hydrocarbon chains are branches terpenoids

3.3: The Cell Wall and Outer Layers For most species, the cell envelope includes at least one structural supporting layer, and the most common structural support is the cell wall. The Cell wall is what we use to classify the bacteria The cell wall allows the cell to have shape and rigidity, and helps it withstand turgor pressure. The bacterial cell wall, or the sacculus, consists of a single interlinked molecule. The bacterial cell wall is made up of peptidoglycan. This molecule consists of long polymers of 2 dissacharidesbound to a peptide of four to siz amino acids. The peptides can form cross bridges connecting the parallel glycan strands. - N- acetylglucosamine - N- acetylmuramic acid Peptidoglycan is unique to bacteria, which helps to find pathogens. It helps to target antibiotics, like penicillin.

Gram Positive Bacteria – thick cell wall - It has multiple layers of peptidoglycan and is threaded by teichoic acids - The capsule is made of polysaccharide and glycoprotein. It protects cells from phagocytosis and is found also in gram-negative cells. - S – layer is an additional protective layer commonly found in free-living bacteria and Archaea. It is a crystalline layer of thick subunits consisting of protein or glycoprotein. It may contribute to cell shape and help protect the cell from osmotic stress. Gram Negative Bacteria – thin cell wall The thing peptidoglycan layer consists of one or two sheets. It is covered by an outer membrane, which helps with defensive abilities and toxigenic properties. It is an inward facing leaflet including lipoprotein. The outward facing leaflet contains lipopolysaccharides and porins. Eukaryotic Microbes possess their own structures to avoid osmotic shock. Bacterial Cytoskeleton = - FtsZ = Z-ring in spherical cells (diameter) - MreB = coil inside of rod-shaped cells (length) - CreS – forms a polymer along the inner side of crescent shaped bacteria (shape)

3.4: The Nucleoid, RNA, and Protein Synthesis

Eukaryotic cells have a nucleus in a nuclear membrane, while prokaryotic cells have a nucleoid region that extends throughout the cytoplasm. - RNA transcribes DNA into a single strand of RNA - mRNA binds to a ribosome for translation into a polypeptide - This is aided by tRNA, which brings amino acids to the ribosome. 1. Replication 2. Transcription 3. Translation

In prokaryotes, membrane proteins and secreted proteins are synthesized in association with the cell membrane. This is aided by the signal recognition particle (SRP).

3.5: Cell Division Cell division, or cell fission, requires highly coordinated growth and expansion of all the cell’s parts. Prokaryotes: - A circular chromosome begins to replicate (ori site) - 2 replication forks are generated, which proceed outward in both directions. At each fork, DNA is synthesized by DNA polymerase with the help of accessory proteins (replisome) - As the termination site is replicated, the 2 forks separate from the DNA. Parallel Planes – streptococci Random planes – staphylococci Perpendicular Planes – tetrads & sacinae

3.6: Cell Polarity & Aging Bacterial cell poles differ in their origin and “age” through polar aging.

Thlyakoids – extensively folded intracellular membranes Carbyoxysomes – polyhedral bodies packed with the enzyme Rubisco for CO2 fixation Gas Vesicles – increase buoyancy

3.7: Specialized Structures Storage Granules Magnetosomes Pili – straight filaments of pilin protein Sex pili – are used in conjugation

Stalks – are membrane-embedded extensions of the cytoplasm and the tips secrete adhesion factors called holdfasts. Nanotubes – are intercellular connections hat pass material fro one cell to the next. Flagella – help prokaryotes to motile or swim - They can swim towards the food or swim away from antibiotics - It is a spiral filament of protein monomers and the filament is rotated by a motor driven by the proton motive force. Lophotrichous cells have flagella at only ne end Monotrichous cells have a single flagella

Chemotaxis – the movement of a bacterium in response to chemical gradients. - Attractants cause the flagella to rotate Counter Clock Wise. The flagella bundle together, push the cell forward, and “run” - Repellents cause the flagella to rotate Clock Wise. The flagellar bundle falls apart, and the cell “tumbles” and the bacterium briefly stops, and then changes direction. - The alternating of runs and tumbles causes a “random walk”...