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Cell Structure and Function - Lecture Notes | BIOL 2051, Study notes of Biology

Louisiana State University (LSU) - System OfficeBiology
Prof. K. Sullivan

Material Type: Notes; Professor: Sullivan; Class: GEN MICROBIOLOGY; Subject: Biological Sciences; University: Louisiana State University; Term: Fall 2009;

Typology: Study notes

Pre 2010

Uploaded on 10/31/2009

ymoham1
ymoham1 🇺🇸

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Chapter 3 Cell Structure and Function
Basic cellular structures:
1. Cytoplasm-all of the internal contents of the cell, water organelles
2. Cytoplasmic membrane holds all contents in
3. Nucleus or nucleiod
4. ribosomes- protein synthesis, not organelles so even prokaryotes have them, protein
5. _cell wall_- found in plants & most prokaryotes; not in animals, optional organelle
Two types of cells:
1. Prokaryote
simpler internal structure , not organelles or inner membrane structure
lack membrane enclosed organeeles
Bacteria & Archaea –two domains
2. Eukaryote
larger & more complex
_membrane enclosed organelles_ (nucleus, chloroplast, mitochondria, etc)
algae, fungi, protozoa, plants, animals
Viruses –totally different category
Non-cellular
Reproduce only inside a host cell, if outside like on desk cannot reproduce they are dormant
Lack many characteristics of living things, not mobile cannot reproduce on their own
Ex. HIV virus, Rhinoviruses (colds)
Arrangement of DNA in Microbial Cells
•genome - a cell's complete set of genes mine is all of my chromosomes
•DNA is arranged to form chromosomes
•Prokaryotes - have a single circular chromosome and sometimes circular extrachromosaomal DNA(
plasmids)
•Eukaryotes - _several linear___ chromosomes
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Chapter 3 Cell Structure and Function Basic cellular structures:

  1. Cytoplasm-all of the internal contents of the cell, water organelles
  2. Cytoplasmic membrane holds all contents in
  3. Nucleus or nucleiod
  4. ribosomes- protein synthesis, not organelles so even prokaryotes have them, protein
  5. cell wall- found in plants & most prokaryotes; not in animals, optional organelle Two types of cells: 1. Prokaryote  simpler internal structure , not organelles or inner membrane structure  lack membrane enclosed organeeles  Bacteria & Archaea –two domains 2. Eukaryote  larger & more complex  membrane enclosed organelles (nucleus, chloroplast, mitochondria, etc)  algae, fungi, protozoa, plants, animals Viruses –totally different category  Non-cellular  Reproduce only inside a host cell, if outside like on desk cannot reproduce they are dormant  Lack many characteristics of living things, not mobile cannot reproduce on their own  Ex. HIV virus, Rhinoviruses (colds) Arrangement of DNA in Microbial Cells
  • genome - a cell's complete set of genes mine is all of my chromosomes
  • DNA is arranged to form chromosomes
  • Prokaryotes - have a single circular chromosome and sometimes circular extrachromosaomal DNA( plasmids )
  • Eukaryotes - several linear__ chromosomes
  • Nucleus - membrane-enclosed structure that contains the chromosomes – found in eukaryotes
  • Nucleoid - mass of DNA not bound by a membrane-found in prokaryotes The Bacterial Cell  Cytoplasm surrounded by envelope o Cytoplasm contains DNA in nucleoid  Envelope has lipid (Fatty) membrane boundary o Plus structural cell wall –gives structure and prevents cells from rupturing Bacterial cell structures  cytoplasmic membrane - “fluid” selective permeability barrier made of phospholipids and proteins that form a bilayer with hydrophilic exteriors and a hydrophobic interior o CM is a phosholipid by laver o Phospholipid-  hydrophilic_ group faces cytoplasm or periplasm  hydrophobic(don’t dissolve in water) fatty acids line up inside membrane o Attraction of nonpolar fatty acid portions of one phospholipid layer for other layer result in selective permeability of cell membrane. o Integral membrane proteins- span membrane o Peripheral membrane proteins- are bound to surface membrane (don’t span whole membrane) o Cytoplasmic Membrane: Functions
  1. Permeability barrier: a. Prevents _leakage of cytoplasm into environment. b. Transports of substances (nutrients & waste products) into & out of cell  Due to hydrophilic outside and hydrophobic center of membrane, only water can freely diffuse through membrane  Other compounds must be transported- usually by integral and peripheral membrane proteins

o Archaea  lack peptidoglycoan (different cell walls bc of this)  cell walls made of other polysaccharides or proteins  Some Archaea cell walls contain psuedopeptidoglycan  Other Archaea have a paracrystalline surface layer (S-layer) cell wall made of protein. o Gram-negative Bacteria  Only a few layers of peptidoglycan (only _10%of cell wall) o Gram-positive Bacteria  Many layers of peptidoglycan (as much as 90% of cell wall)  negatively charged _teichoic acids  Crosslinks within peptidoglycan are different- often have L-lysine instead of Meso- diaminopimelate.  Teichoic acids- negatively charged polymers in only Gram positive cell wall that help give cell wall more stability

  • Lysozyme  Enzyme that destroys peptidoglycan, leading to cell lysis (found in our tears)  This protects us from infection in our eyes o Get it in your eyes you cry and it kills the bacteria  found in _animal secretion & thought to be a major line of defense against infection by Bacteria  The Outer Membrane of Gram-Negative Bacteria o Found only in Gram-negative bacteria o Made of a lipid bilyaer  Outer lipoppollysaccaride (LPS) layer  Inner phosophlipid layer o Proteins (porins) within the membrane involved in _transport o Endotoxin- lipid A- toxic portion of LPS

 When your sick bc of a gram negative bacteria you have to becareful not to kill them all of quicly cause it would release a bunch of endotoxin and that can make you sick o Porins- transmembrane_ proteins allow for permeability__ through the outer__ membrane by creating  Non-specific porins- water-filled channels through which small substances can pass.  Specific proins- channels with binding sites for certain molecules that only allow those molecules to pass through. o Periplasm  space between the outer and cytoplasmic membranes  mainly in gram negative bacteria, positive have a small one  contains proteins such as hydrolytic enzymes & binding proteins  they will break down large substances into small sunstances  binding-get in our out of the cell or take something to get broken down  The Gram-Positive Envelope o Capsule (not all species)  Polysaccharide  Very outside  Slime layer that protects the cell o S-layer (not all species)  Made of protein  After capsule o Thick _cell wall____  amino acid crosslinks in peptidoglycan  Teichoic acids for strength  Under s-layer o Thin _periplasm_____ o Plasma membrane o Under cell wall

  • Consintaly replicating DNA  Cell undergoes septation (Separation) o Usually at equator o Each daughter has same shape  Fts Proteins (involved in forming the divide zone), the Cell Division Plane, and Cell Morphology o Divisome- division apparatus in the cell formed by Fts proteins o Fts proteins_– required for cell division & chromosome replication
  • FtsZ protein (most important Fts protein) o defines the division plane in prokaryotes o polymerizes to form a ring_ where cell division will occur
  • FtsA protein o ATP-hydrolyzing enzyme  Hydrolyzed the ATP to ADP which results in the release on energy o provides energy for assembly of other proteins to the ring
  • FtsI protein o involved in peptidoglycan synthesis for the new cell wall  as the cell wall divides more of this is need o activity is blocked by penicillin  if you take it it will block this protein
  • MreB o helps define cell shape o forms filamentous long spiral shaped bonds arounf the inside of the cytoplasmic membrane (CM) o defines cell shape by directionally exerting pressure against CM  how it exerts pressure determines the shape of the cell o Coccus shaped bacteria lack MreB gene  No proteins that exert pressure on cytoplasmic membrane o default bacterial shape- sphere, no pressure so a circle is formed

Peptidoglycan Synthesis and Cell Division

  • New cell wall is synthesized during bacterial growth by inserting new glycan units into preexisting wall material - Critical process if done incorrectly get a opening in cell wall=lysis
  • Autolysins create openings in existing cell wall to make space for new cell wall glycans to be inserted
  • Autolysis (spontaneous cell lysis) may occur if there is an error in inserting new cell wall material
  • bactoprenol :
    • hydrophocbic (gives ability to cross the cytoplasmic membrane since the cytoplasm is very hydrophobic) lipid alcohol
    • binds the N-acetylglucosamine / N-acetylmuramic acid / pentapeptide peptidoglycan precursors
    • helps transport these new glycan in its through the cell to become part of growing cell wall  Transpeptidation -
    • formation of peptide cross links btwn the NAM sugars
    • bonds peptidoglycan precursors into expanding peptidoglycan layer
    • reaction is inhibited by penicillin (cell lysis occurs than they die) Cell Inclusions  Prokaryotic cells often contain internal granules that function as storage materials or to orient the cell.  Inclusion Granules- o Magnetosomes- intracellular particles of magnetite (fe3o4); allow organism to respond to a magnetic field.  Usually found in the soil, anaerobic o Glycogen- carbon and energy source o Polyphosphate- stores inorganic phosphate o Poly-B-hydroxybutyrate (PHB)-carbon & energy source o Sulfur- energy source  Some gram negative prokaryotes can store elemental sulfur in globules in the periplasm.

o Arrangement of Flagella

  • Monotrichous- single flagellum at one end of the cell
  • Lophotrichous- several flagella at one or both ends
  • Peritrichous- several flagella all around cell
  • Amphitrichous- one flagella at each end (usually spiral shaped organisms have this) o Structure of the flagella 3 parts:
  1. Basal body –in cell envelpe
  2. Hook-cell envelope
  3. Filament-part that we see o Basal Body
  • Imbedded within cell envelope
  • Made of 2 or 4 protein rings connected by a central rod
  • ____C___ ring- in G+ & G-
  • __MS____ ring- in G+ & G-
  • P_ ring- in G- only
  • ___L____ ring- in G- only
  • C ring- In ___Cytoplasm_____. Attached to inner surface of cytoplasmic membrane
  • MS ring- In _cytoplasmic membrane____. End of central rod is attached to MS ring.
  • P ring- In __peptidoglycan_____ layer
  • L ring- In _LPS____ layer Gram-negative Bacterium Gram-positive Bacterium cytoplasmic membrane peptidoglycan outer L ring membrane P ring MS ring C ring MS ring C ring

o Hook

  • Curved structure made of proteins; connects filament to basal body o Filament-what we see
  • Long, rigid, helical structures made of protein called flagellin  Prokaryotes such as filamentous cyanobacteria, Myxococcus , Cytophaga & Flavobacterium move by gliding motility instead of flagella  Gliding can occur from slime secretion that moves cell along solid surfaces_  Motile bacteria can respond to to chemical and physical gradients(sense things like maybe one needs O2 it senses it and moves towards it) in environment by moving toward or away from the signal molecule.  Directed movements toward or away from a chemical or physical signal are known as TAXES o Chemataxis – directed movement of organisms in response to chemical signals(towards or away from) o Phototaxis – directed movement of organisms in response to light(towards or away from) o Aerotaxis – directed movement of organisms in response to oxygen(towards or away from) o Osmotaxis - directed movement of organisms in response to ionic strength (towards or away from).  Attractants cause counterclockwise rotation o Flagella bundle together o Push cell forward
  • “Run”- organism moves in one direction  Repellents cause clockwise rotation o Flagella fly apart
  • “tumble” = change of direction  Runs + tumbles cause “random walk” go toward attrachtent tumbles, runs tumbles…. o Receptors detect attractant concentrations
  • Sugars, amino acids o Attractant concentration increases and prolongs runs and shorter tumbles
  • Net movement of bacteria toward attractant