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MBIO 1010 > Cell Structure and Function Part 2 > Flashcards

Cell Structure and Function Part 2 Flashcards

1
Q

Nutrient Transport

A
  • Carrier-mediated transport systems
    • Show saturation effect
    • Highly specific
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2
Q

What are the three transport events?

A
  1. Uniport
  2. Symport
  3. Antiport
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3
Q

Uniport

A

uniporters transport in one direction across the membrane

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4
Q

Symport

A

Symporters function as co-transporters

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5
Q

Antiport

A

Antiporters transport a molecule across the membrane while simultaneously transporting another molecule in the opposite direction

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6
Q

Simple Transport

A
  • Lac permease of Escherichia coli
    • Lactose is transported into E. coli by the simple transporter lac permease, a symporter - two molecules move across membrane in same direction
  • Activity of lac permease is energy-driven
  • Transports lactose and a H+ into the cell simultaneously
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7
Q

ABC (ATP-binding cassette) transport systems

A
  • More than 200 ABC transporter
  • Involved in uptake of organic compounds (e.g. sugars, amino acids), inorganic nutrients (e.g. sulfate, phosphate), and trace metals
  • Typically display high subtrate specificity
  • Gram-negatives employ periplasmic-binding proteins and ATP-driven transport proteins
  • Gram-positive employ subtrate-binding lipoproteins (anchored to external surface of cell membrane) and ATP-driven transport proteins.
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8
Q

Nutrient Transport

A
  • ABC transporters (ATP-binding cassette)
  • Solute binding protein
    • Periplasm
    • Binds specific subtrate
  • Integral membrane proteins (transporter)
  • ATP-hydrolyzing protein
    • Supply energy for the transport event
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9
Q

Group Translocation

A
  • e.g. phosphotransferase system in E. coli
  • Sugar is phosphorylated during transport across the membrane
  • Moves glucose, fructose, and mannose
  • Phosphoenolpyruvate (PEP) donates a P to a phosphorelay system
  • P is transferred through a series of carrier proteins and deposited onto the sugar as it is brought into the cell
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10
Q

What are the three major classes of transport systems in prokaryotes?

A
  • Simple transport
  • Group translocation
  • ABC system
    • All require energy in some form, usually proton motive force or ATP
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11
Q

Simple Transport (Simple)

A
  • One protein
  • Driven by the energy in the proton motive force
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12
Q

Group Translocation (Simple)

A
  • Two protein
  • Chemical modification of the transported substance driven by phosphoenolppyruvate
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13
Q

ABC Transporter (Simple)

A
  • Three protein
  • Periplasmic binding proteins are involved and energy comes from ATP
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14
Q

Cell Wall of Bacteria and Archaea

A
  • Outside the cell membrane
    • Rigid
      • Helps determine cell shape
  • Not a major permeability barrier
  • Porous to most small molecules
  • Protects the cell from osmotic changes
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15
Q

Function of the cell wall

A
  • Cell wall prevents cell expansion - protects against osmotic lysis
  • Protects against toxic substances - large hydrophobic molecules
    • EX) detergents, antibiotics
  • Pathogenicity
    • Helps evade host immune system
    • Helps bacterium stick to surfaces
  • Partly responsible for cell shape
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16
Q

Peptidoglycan (PG)

A
  • Species of Bacteria separated into two groups based on Gram stain
  • Gram-positives and gram-negatives have different cell wall
    • Gram-negative cell wall
      • Two layers: LPS and peptidoglycan
    • Gram-positive cell wall
      • one layer: peptidoglycan
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17
Q

Peptidoglycan (Part 2)

A
  • Rigid layer that provides strength to cell wall
  • Polysaccharide composed of:
    • N-acetylglucosamine and N-acetylmuramic acid
    • Amino acids
    • Lysine or diaminopimelic acid (DAP)
    • Cross-linked differently in gram-negative bacteria and gram-positive bacteria
    • Form glycan tetrapeptide
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18
Q

Peptidoglycan (Part 3)

A
  • More than 100 different PG structures identified
  • Vary in peptide cross-links and/or interbridge
  • No interbridge is present in gram-negative Bacteria (e.g. E. coli)
  • The interbridge in Staphylococcus aureus (gram positive) is made up of 5 glycine residues
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19
Q

Peptidoglycan (Part 4)

A
  • Gram-positive cell walls
    • Contain up to 90% peptidoglycan
    • Common to have teichoic acids (acidic substances) embedded in their cell wall
      • Lipoteichoic acids: teichoic acids covalently bound to membrane lipids
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20
Q

Model of Peptidoglycan Surrounding the Cell

A
  • Backbone formed of NAM and NAG connected by glycosidic bonds
  • Crosslinks formed by peptides
  • Peptidoglycan strand is helical
    • Allows 3-dimensional crosslinking
  • E. coli has one layer
  • Some cell walls can be 50 - 100 layers thick, e.g. Bacillus species
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21
Q

Prokaryotes that lack cell walls?

A
  • Mycoplasmas
  • Thermoplasma
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22
Q

Mycoplasmas

A
  • Group of pathogenic bacteria
  • Have sterols cytoplasmic membrane - adds strength and rigidity to membrane
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23
Q

Thermoplasma

A
  • Species of Archaea
  • Contain lipoglycans in membrane that have strengthening effect
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24
Q

LPS: The Outer Membrane

A
  • Total cell wall contains around 10% peptidoglycan
  • Most of cell wall composed of outer membrane, aka lipopolysaccharide (LPS) layer
    • LPS consists of core polysaccharide and O-polysaccharide
    • LPS replaces most of phospholipids in outer half of outer membrane
    • Endotoxin (lipid A): the toxic component of LPS
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25
Q

LPS: The Outer Membrane (Part 2)

A
  • Periplasm: space located between cytoplasmic and outer membranes
    • around 15 nm wide
    • Contents have gel-like consistency
    • Houses many proteins
  • Porins: channels for movement of hydrophilic low-molecular-weight substances
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26
Q

Relationship of Cell Wall Structure to Gram Stain

A
  • In Gram stain reaction, insoluble crystal violet-iodine (CV-I) complex forms inside cell
  • Complex is extracted by alcohol from gram-negative, not gram-positive bacteria
  • Gram-positive bacteria have thick cell walls consisting mainly of
    peptidoglycan
    • Becomes dehydrated during alcohol step so pores in wall close
    • Prevents CV-I complex from escaping
  • Gram-negative bacteria – alcohol penetrates OM
    • CV-I extracted from cell
    • Cells appear nearly invisible until counterstained with second dye (safarin)
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27
Q

Archaeal Cell Walls

A
  • No peptidoglycan
  • Typically no outer membrane
  • Pseudomurein
    • Polysaccharide similar to peptidoglycan
    • Composed of N-acetylglucosamine and N-acetyltalosaminuronic acid
    • Found in cell walls of certain methanogenic Archaea
  • Cell walls of some Archaea lack pseudomurein
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28
Q

Archaeal Cell Walls (S-layers )

A
  • Most common cell wall type among archaea
  • Consist of protein or glycoprotein
  • Paracrystalline structure
  • Some Archaea have only S-layer (no other cell wall components)
  • Most have additional cell wall elements
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29
Q

Summary of Archaeal Cell Wall

A
  • Variety of structure possible
  • Some closely resemble peptidoglycan
  • Others lack polysaccharide completely
  • Most Archaea contain some type of cell wall structure - functions to prevent osmotic lysis and give shape
  • Because they lack peptidoglycan, Archaea are resistant to lysozyme and penicillin
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30
Q

Cytoplasm

A

Material bounded by plasma membrane (PM)

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31
Q

Protoplast

A
  • PM and everything within
    • Macromolecules: amino acids, nucleotides, etc
    • Soluble proteins
    • DNA and RNA (nucleoid)
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32
Q

Proteins

A
  • Serve many functions:
    • Enzymes: Catalyze chemical reactions
    • Transport proteins: Move other molecules across membranes
    • Polypeptide: A long polymer of amino acids joined by peptide bonds
  • Proteins are made of polypeptides
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33
Q

Structural Proteins

A
  • Help determine shape of the cell
    • Involved in cell division
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34
Q

The Nucleoid

A
  • Region that contains the genome
  • The typical bacterial genome:
    • Single circular double stranded (ds) DNA chromosome
    • May have one or more plasmids
      • Smaller circular dsDNA
      • Self-replicating
      • Carry non-essential genes
        • Selective advantage
        • EX) Genes for antibiotic resistance
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35
Q

DNA

A
  • Carries genetic info of all living cells
  • Polymer of deoxyribonucleotides
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36
Q

Ribosomes

A
  • Site of protein synthesis
  • 70S ribosome
  • 2 parts
    • 30S subunit (Small subunit)
      • Protein
      • 16S rRNA
    • 50S subunit (Large subunit)
      • Protein
      • 23S and 5S rRNA
  • Cytoplasmic ribosomes
    • Cytoplasmic proteins
  • PM associated ribosomes
    • Membrane proteins
    • Proteins to be exported from the cell
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37
Q

Cell Surface Structure (Capsule and Slime Layers)

A
  • Polysaccharide / protein layers
  • May be thick or thin, rigid or flexible
  • Assist in attachment to surfaces
  • Protect against phagocytosis
  • Resist desiccation
38
Q

Cell Surface Structure (Fimbriae)

A
  • Filamentous protein structures
  • Enable organisms to stick to surfaces or form pellicles
39
Q

Cell Surface Structure (Pili)

A
  • Filamentous protein structures
  • Typically longer than fimbriae
  • Assist in surface attachhment
  • Facilitate genetic exchange between cells (conjugation)
  • Type IV pili involved in twitching motility
40
Q

Cell Inclusion Bodies

A
  • Visible aggregates in cytoplasm
  • Carbon storage polymers
    • Poly-B(Beta)-hydroxybutyric acid (PHB): lipid
    • Glycogen: glucose polymer
  • Polyphosphates: accumulations of inorganic phosphate
  • Sulfur globules: composed of elemental sulfur
  • Magnetosomes: magnetic storage inclusions
41
Q

Inclusion Bodies

A
  • Carbon storage polymers
    • Poly-B(Beta)-hydroxybutyric acid (PHB)
      • Lipid storage
    • Glycogen granules
      • Polymer of glucose
  • Inorganic inclusions
    • Polyphosphate granules: volutin
      • Storage of phosphate and energy
    • Sulfur globules
      • Storage of sulfur used in energy generation
42
Q

Inclusion Bodies (Magnetosomes)

A
  • Magnetic inclusions
  • Intracellular granules of F3O4 or Fe3S4
  • Gives the cell magnetic properties
    • Allows it to orient itself in a magnetic field
    • Bacteria migrate along Earth’s magnetic magnetotaxis
43
Q

Gas Vesicles

A
  • Confer buoyancy in planktonic cells
  • Spindle-shaped, gas-filled structures made of protein
  • Function by decreasing cell density
  • Impermeable to water
44
Q

Endospores

A
  • Highly differentiated cells resistant to heat, harsh chemicals, and radiation
  • “Dormant” stage of bacterial life cycle
  • Ideal for dispersal via wind, water, or animal gut
45
Q

Endospores (Part 2)

A
  • Produced only by some gram positives
    • EX) Bacillus sp. - aerobic Gram + rods
    • Clostridium sp. - anaerobic Gram + rods
  • Vegetative cell - capable of normal growth
    • Metabolically active
  • Endospore - dormant cell, formed inside of a mother cell
    • Metabolically inactive
    • Triggered by lack of nutrients
    • Takes about 8 - 10 hours
46
Q

Endospores (Layers + Core)

A
  • Layers:
    • Spore coat and cortex - protect against chemicals, enzymes, physical damage, and heat
    • Two membranes - permeability barriers against chemicals
  • Core:
    • Dehydrated - protects against heat
    • Ca-dipicolinic acid and SASPs (small acid soluble proteins)
    • Protect against DNA damage
47
Q

Endospores can resist to?

A
  • Boiling for hours
  • UV, y radiation
  • Chemical disinfectants
  • Dessication
  • Age
48
Q

Lifecycle of a spore forming bacterium

A
  • Stage I: Asymmetric Cell Division
  • Stage II: Septation
  • Stage III: Mother Cell engulfs the Forespore
  • Stage IV: Formation of the Cortex
  • Stage V: Coat synthesis
  • Stage VI: Endospore matures
  • Stage VII: Mother cell is lysed
49
Q

Stage I: Asymmetric Cell Division

A
  • DNA replicates
  • Identical chromosomes pulled to opposite ends of the cell
50
Q

Stage II: Septation

A
  • Divides cell into 2 unequal compartments:
  • Forespore (prespore)
  • Mother cell
51
Q

Stage III: Mother Cell engulfs the Forespore

A
  • Forespore surrounded by two membranes
52
Q

Stage IV: Formation of the Cortex

A
  • Thick layers of peptidoglycan form between two membranes
    • Highly cross-linked layer - core wall
    • Loosely cross-linked layer - cortex (around 1/2 of spore volume)
53
Q

Stage V: Coat synthesis

A
  • Protein layers surround the core wall
    • Spore coat
    • Exosporium (found in some G+)
    • Protect the spore from chemicals and enzymes
54
Q

Stage VI: Endospore matures

A
  • Core is dehydrated
  • around 10 - 30 % of a vegetative cell’s water content
55
Q

Stage VII: Mother cell is lysed

A
  • Mother cell disintegrates
  • Mature spore is released
56
Q

Flagella and Swimming Motility

A
  • Hollow protein filaments
    • Impact motility
  • Must be stained to view
    • Flagella stain
  • Can be used for identification:
    • Monotrichous - single flagellum
      • Polar or subpolar
    • Amphitrichous: Flagella at opposite ends
    • Lophotrichous: Multiple flagella in a single tuft
    • Peritrichous: Flagella distributed around cell
57
Q

Flagellar Structure

A
  1. Filament
  2. Hook
  3. Basal Body (motor)
58
Q

Filament

A
  • Rigid helical protein (around 20µm long)
  • Composed of identical protein subunits - flagellin
59
Q

Hook

A

Flexible coupling between filament and basal body

60
Q

Basal Body (motor)

A
  • Consists of central rod that passes through series of rings:
    • L ring - LPS layer
    • P ring - Peptidoglycan
    • MS ring - Membrane
    • C - ring - Cytoplasm (associated with membrane)
61
Q

Flagella Movement

A
  • Energy to turn the flagella comes from the proton motive force (PMF)
    • Gradient of protons (H+) across the cytoplasmic membrane
      • High [H+] outside
      • Low [H+] inside
    • Mot proteins form a channel that allows H+ to move into the cytoplasm
    • Provides the energy to turn the flagellum
  • Flagellum turns like a propeller to drive the cell forward
62
Q

Flagellar Synthesis

A
  • Several genes are required for flagellar synthesis and motility
  • MS ring is made first
  • Other proteins and hook are made next
  • Filament grows from tip
63
Q

Differences in swimming motions

A
  • Peritrichously flagellated cells move slowly in a straight line
  • Polarly flagellated cells move more rapidly and typically spin around
64
Q

Gliding Motility

A
  • Flagella-independent motility
  • Slower and smoother than swimming
  • Requires surface contact
  • Mechanisms
    • Excretion of polysaccharide slime
    • Type IV pili
    • Gliding-specific proteins
65
Q

Chemotaxis and Other Taxis

A
  • Taxis: directed movement in response to chemical or physical gradients
    • Chemotaxis: response to chemical
    • Phototaxis: response to light
    • Aerotaxis: response to oxygen
    • Osmotaxis: response to ionic strength
    • Hydrotaxis: response to water
66
Q

Chemotaxis

A
  • Best studied in E. coli
  • Bacteria respond to temporal, not spatial, difference in chemical concentration
  • “Run and tumble” behavior
  • Attractants and repellants sensed by chemoreceptors
  • Directed movement toward an attractant or away from a repellent
    • Biased random walk
  • EX) E. coli shows biased random walk toward glucose when there is a concentration gradient
  • The cell still exhibits a series of runs and tumbles
    • If it senses that the [glucose] is increasing:
      • The tumble is delayed
      • The run lasts longer
67
Q

Measuring Chemotaxis

A
  • Measured by inserting a capillary tube containing an attractant or a repellent in a medium of motile bacteria
  • Can also be seen under a microscope
68
Q

Cell Size (Eukaryotes)

A
  • Lower surface area to volume ratio
    • Need more sophisticated transport mechanisms
  • Grow slower
69
Q

The Nucleus and Cell Division (Eukaryotes)

A
  • Genetic material is housed in a nucleus
  • Generally larger than prokaryotes
  • Complex internal structure
    • Membrane bound organelles
  • Intra-cytolplastic membranes used for transport
  • Cytoskeleton
  • Divide by mitosis and meiosis
70
Q

Key Differences Between Prokaryotic & Eukaryotic Cells

A
  • Prokaryotic
    • Size of Cell: Typically 0.2 - 2.0 um diam
    • Nucleus: No nuclear membrane or nucleolus (nucleoid)
    • Membrane-enclosed organelles: Absent
    • Ribosomes: Smaller size (70S)
    • Chromosomal DNA: Singular, circular
    • Cell Division: Binary fission
  • Eukaryotic
    • Size of Cell: Typically 10 - 100 um diam
    • Nucleus: True nucleus with nuclear membrane and nucleolus
    • Membrane-enclosed organelles: Present (e.g. Golgi, mitochondria, chloroplasts, etc.)
    • Ribosomes: Larger Size (80S)
    • Chromosomal DNA: Multiple linear chromosomes with histones
    • Cell Division: Mitosis
71
Q

The Nucleus

A
  • The nucleus holds the genetic information
    • Multiple linear dsDNA chromosomes
72
Q

Chloroplasts

A
  • Site of photosynthesis
  • Chlorophyll
  • Surrounded by 2 membranes
  • DNA and ribosomes (70S)
  • Most closely related to Cyanobacteria
  • Blue-green algae
73
Q

Mitochondria

A
  • Site of respiration and oxidative phosphorylation
  • Surrounded by 2 membranes
  • DNA and ribosomes (70S)
  • Most closely related to Rickettsia
  • Proteobacteria
  • Obligate intracellular pathogens
  • EX) Rocky-mountain spotted fever
74
Q

The Endosymbiotic Hypothesis

A
  • Mitochondria and Chloroplasts evolved from bacteria
    • Evidence
      • Semi-autonomous
      • Circular chromosomes
        • Lack histones
      • 70S ribosomes
      • Two membranes
      • Outer membrane has porins
75
Q

Viruses

A
  • Acellular infectious particles
  • Obligate intracellular pathogens
    • Reproduce only inside of living cells
    • Lack independent metabolism
  • Composed of at least 2 parts:
    • Nucleic acid genome (DNA or RNA) and protein coat (capsid)
      • Together = Nucleocapsid
  • Some viruses have an envelope – layer of lipid surrounding the
    nucleocapsid
76
Q

Viral Genomes

A
  • DNA or RNA - never both (at the same time)
  • Single stranded or double stranded
  • Circular or linear
  • Can be in several pieces - segmented
  • Genome size
    • Smallest: around 3.6 kb (3,600) for some ssRNA viruses (3 genes)
    • Largest > 150 kb (150,000) for some dsDNA viruses (> 100 genes)
77
Q

Virion Structure (Capsid)

A
  • Protein coat that surronds the genome
    • Allows transfer of viral genome between host cells
    • Made of identical polypeptides - Protomer
    • Helical capsids
      • Protomers form a spiral cylinder
      • Nucleic acid genome coiled inside
      • Ex. Tobacco mosaic virus capsid is made of around 2100 identical protomers
78
Q

Structure of the Virion (Icosahedral capsids)

A
  • Regular geometric shape with 20 triangular faces
  • Exhibit symmetry
  • Protomers aggregate to form capsomeres
  • Ex. Human papillomaviruses have form their capsids from pentamers (clusters of 5)
79
Q

Structure of the Virion (Binal capsids)

A
  • Geometric head with an attached helical tail
  • Ex. T4 bacteriophage of E. coli
  • Genome is carried in a polyhedral head, helical tail is used to inject DNA into a host cell
80
Q

Nucleocytoplasmic Large DNA Viruses

A
  • Viruses with complex multi-layered structure
  • Ex. Mimivirus (infects amoebae)
  • 0.75 µm in diameter, 1200 kbp DNA
    • Larger than some bacteria
81
Q

Structure of the Virion (Envelope)

A
  • A lipid bilayer surrounding the nucleocapsid that was acquired from the host membrane
    • Consists of host lipids and viral proteins - spikes
    • Ex. Influenza virus
    • Flexible helical capsid, surrounded by an envelope
    • Two major spikes: hemagglutinin (H) and neuraminidase (N)
82
Q

Host Range

A
  • Viruses infect all domains of life
  • Bacteriophage (phage) - viruses that infect bacteria
    • Ex) T4 Phage - infects E. coli
  • Animal viruses - infect and multiply only inside of animal cells
    • Ex) Human papillomavirus - infects human epithelial cells
    • Causes benign tumors (warts)
83
Q

Host Range (Part 2)

A
  • Most viruses are specific to a single host species
  • Virus must attach to specific receptors on the host cell surface
    • Ex) HIV binds to CD4
    • Chemoreceptor on surface of some human
      immune system cells
    • HIV infects only humans
  • Some viruses infect more than one species
    • Ex) Influenza attaches to a glycoprotein found on
      surface of several animal cells
    • Infects humans, pigs, chickens, seals etc.
84
Q

Viral Replication Cycle

A
  1. Adsorption - attachment to the host cell
  2. Penetration and uncoating - entry into the host cell
  3. Synthesis of viral nucleic acids and protein
  4. Assembly of new virions
  5. Release of new virions
85
Q
  1. Adsorption - attachment to the host cell
A
  • Involves specific receptors on the host cell surface
  • Ex) LPS, outer membrane proteins or glycoproteins
86
Q
  1. Penetration and uncoating - entry into the host cell
A
  • Bacteriophage - usually inject their nucleic acid into the cell
  • Leave the capsid outside the cell as a “ghost”
87
Q

Entry by Animal Viruses

A
  • Fusion with the plasma membrane (Only possible with an envelop viruses)
  • Endocytosis
    • BInding to specific receptors triggers normal endocytic activity (Naked viruses and Envelop Viruses)
  • In either case, once inside:
    • The capsid is removed
    • Viral genome is released into the cell
88
Q
  1. Synthesis of viral nucleic acids and protein
A
  • Viral genes are expressed and viral proteins are synthesized (by the host’s own ribosomes)
  • Viral genome is replicated (by the host’s replication machinery)
89
Q
  1. Assembly of new virions
A
  • Viral proteins are assembled into capsids, and then genomes are packaged into nucleocapsids
    • Viruses do not reproduce by division
90
Q
  1. Release of new virions
A
  • Two basic strategies:
    • Naked viruses usually accumulate, eventually lysing the host cell to release progeny - lytic infection
    • Enveloped viruses are usually released by budding
      • Virions push through the cytoplasmic membrane without killing the host cell - persistent infection
91
Q

Viral Replication Cycle (Budding)

A
  • Release of enveloped viruses
    • Viral proteins inserted into the host membrane - Spikes
      • Nucleocapsid associates with the spikes, and buds through the membrane to form the envelope
    • Ex) Influenza
      • Neuraminidase allows new virions to exit the host cell
      • Hemagglutanin allows viruses to absorb to the next host

MBIO 1010 (13 decks)

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