Characteristics of Cells

1
Characteristics of Cells

• Cell (cytoplasmic) membrane
• Cytoplasm - liquid portion of the cell that
  contains organelles
• Macromolecules (proteins, nucleic acids,
  carbohydrates, and lipids)
• Ribosomes - nonmembrane-bound organelles, the
  site of protein synthesis
• Cell wall - provides structure to plant, fungal,
  and microbial cells.

2
Prokaryotic vs. Eukaryotic Cells

• Smaller, less complex
• Contain no membrane-bound organelles
• Contain ribosomes
• DNA is contained in the nucleoid
• DNA is organized into 1 circular chromosome
• Include Bacteria and Archaea
  
• Are ribosomes membrane-bound organelles?

• Larger, more complex
• Contain membrane-bound organelles, ex. nucleus,
  mitochondria, chloroplasts
• Contain ribosomes
• DNA is contained in the nucleus
• DNA is organized into 2 linear chromosomes
• Include algae, fungi, protozoa, plant, and animal
  cells

3
Prokaryotic vs. Eukaryotic Cells (Refer to Fig.
2.1 in the text)
4
Viruses

• Are not true cells because they
• are not open systems
• do not carry on metabolism
• do not have a cell membrane
• do not contain all 4 of the macromolecules common
  to cells

5
Viruses (continued)

• Do
• contain genetic material (DNA or RNA, but not
  both)
• contain a protein coat called a capsid
• may contain a lipoprotein envelope
• reproduce, but only with the machinery of a cell
• undergo evolution
• infect all types of cells, including bacteria
• How big are viruses in relation to bacteria?
  Refer to Fig. 2.3 in the text.

6
Characteristics of Prokaryotic DNA

• Organized into a single circular chromosome
  (usually)
• Haploid - bacteria only have one copy of each
  gene
• The chromosome aggregates to form a visible mass
  called the nucleoid.
• Most prok. also contain small amts. of
  extrachromosomal DNA, which is arranged in a
  circular fashion and called plasmids. Plasmids
  usually contain genes that confer special
  properties (ex. unique metabolic properties or
  antibiotic resistance) and are not necessary for
  basic survival.

7
What are Mitosis and Meiosis and Do Prokaryotes
Undergo These Processes?

• Mitosis occurs in eukaryotes only. Eukaryotes
  are usually diploid (at least) - contain 2 copies
  of each gene. Mitosis is the process by which
  the doubled chromosomes (replicated DNA) are
  sorted into the 2 new daughter cells.
• Meiosis also occurs in eukaryotes only. Meiosis
  is the process by which the sex cells of
  eukaryotes (ex. eggs and sperm) halve the diploid
  genetic material so that each sex cell gets only
  one copy of each gene (haploid egg haploid
  sperm diploid organism)
• Why dont prokaryotes undergo mitosis or meiosis?

8
How Many Genes to Prok. And Euk. Have?

• Escherichia (E.) coli genome has been sequenced,
  contains 4.6 million base pairs making up 4300
  genes (on one chromosome, remember).
• Other bacteria can range from having 3X this
  amount to having 1/8 this amount.
• Human cell contains 1,000X as much DNA and 7X as
  many genes as E. coli (much of the DNA in euk. is
  noncoding).
• Both prok. and euk. can control the expression of
  their genes (not all genes are expressed to the
  same extent or at the same time).

9
What is Phylogeny?

• Phylogeny The evolutionary relationships
  between organisms.
• rRNA molecules are excellent barometers of
  evolutionary relationship. Refer to Fig. 2.6 in
  the text for this process of comparison.
• Comparative rRNA sequence analysis indicates the
  existence of 3 domains Bacteria (prok.),
  Archaea (prok.), and Eukarya (euk.)., which
  evolved from a universal ancestor. Refer to
  the phylogenetic tree in Fig. 2.7 of the text.

10
Phylogenetic Tree of Life (Refer to Fig. 2.7 of
the text)
11
What is Interesting about the Phylogenetic Tree
of Life?

• Species of Archaea are more closely related to
  the Eukarya than to the Bacteria.
• What evidence do we have that eukaryotes evolved
  from the Bacteria?
• How does the concept of endosymbiosis relate to
  this evidence?

12
Microbial Diversity

• What is microbial diversity a function of?
• How long has this taken to happen?
• Does it have to take this long in every case?
• What characteristics of microbes represent
  evidence of microbial diversity?

13
Energy

• All cells require it!
• 3 ways energy can be obtained
  1. from organic chemicals
  2. from inorganic chemicals
  3. from light
• How is energy obtained? By oxidizing the
  compound, but what does this mean?
• In what form is energy conserved in the cell?
  Well talk more about this form of energy later.

14
What kind of air are they able to breathe?

• Aerobes (obligate) extract energy from a
  compound only in the presence of oxygen.
• Anaerobes (obligate) extract energy only in the
  absence of oxygen.
• Facultative organisms can break down organic
  compounds either in the presence or absence of
  oxygen.

15
What do they eat in order to get energy?

• Chemoorganotrophs metabolize organic compounds.
  This occurs in most microbes that have been
  cultured.
• Chemolithotrophs metabolize inorganic
  compounds. This only occurs in prokaryotes (both
  Bacteria and Archaea). Is there any advantage to
  this? What does chemolithotroph mean anyway?
• Phototrophs use light as an energy source. How
  are they able to do this how is this process
  advantageous?

16
Carbon Source(s)

• All cells require carbon as a major nutrient.
• Heterotrophs require one or more organic
  compounds as their carbon source.
• Autotrophs get their carbon from CO2 in the
  atmosphere. What does autotroph mean?
• Self-Quiz
  - Are chemoorganotrophs
  also heterotrophs? - Where do many
  chemolithotrophs and virtually all phototrophs
  get their carbon? - What is
  the ecological term for autotrophs?

17
Environmental Extremes

• What are considered to be ideal temp. and pH
  conditions for humans?
• What are some extreme environments in which
  prokaryotes live?
• Believe it or not, the prokaryotes that live in
  these environments dont only just tolerate the
  conditions, but require them in order to grow!
• What are the prokaryotes that live in these
  extreme environments called?
• Refer to Table 2.1 in the text for the record
  holders of these extreme games! (New FOX reality
  TV show maybe?)
• Further deep thought if we find life on Mars,
  what kind of life do you think well find? Why?

18
Phylogenetic Tree of the Bacteria (Fig. 2.9 in
the text)
19
Proteobacteria

• Largest division (phylum) of the Bacteria.
• Includes chemoorganotrophic, as well as several
  phototrophic and chemolithotrophic species.
• Examples
  - Escherichia (E.) coli (a
  chemoorganotroph) the model organism of
  microbial physiology, biochemistry, and molecular
  biology (organism in which many of these types of
  studies are done). - Pseudomonas sp.
  capable of degrading complex and toxic natural
  and synthetic organic compounds.
  -
  Azotobacter a nitrogen-fixing bacterium
  (nitrogen-fixing incorporating atmospheric N
  into a form that is usable by other organisms).

20
Gram-positive bacteria

• Gram-staining is a staining procedure developed
  by Christian Gram in which structures present in
  the cell walls of bacteria are stained. If the
  bacterial walls are of one composition they stain
  purple gram-positive, but if the bacterial
  walls are of another composition they stain pink
  gram-negative. Well talk more about this
  technique in Ch. 4 of the text.
• The Gram-positive lineage includes species united
  by a common phylogeny (evolution) and cell wall
  structure.

21
Gram-positive bacteria (continued)

• Examples
  - Bacillus and Clostridium
  form internal spores (resistant stage) called
  endospores.
  - Streptomyces produces antibiotics
  - Streptococcus and
  Lactobacillus lactic acid bacteria that inhabit
  decaying plant material and dairy products (ever
  heard of Lactobacillus acidophilus?)
  -
  Mycoplasmas (ex. genus Mycoplasma) are
  considered to be Gram-positive because they
  relate to the other organisms in this phylum, but
  lack a cell wall. They are often pathogenic.

22
Cyanobacteria

• Are oxygenic phototrophs they generate or make
  oxygen and they get their energy from light. Why
  is the fact that these organisms are oxygenic so
  important in the evolution of life as we know it
  today?

23
Planctomyces and Spirochetes

• Planctomyces cells have a distinct stalk that
  allows the organisms to attach to a solid
  substratum. Refer to Fig. 2.13 in the text.
• Spirochetes are helically shaped, and causes
  diseases such as syphilis and Lyme disease. What
  does helical mean?

24
Green Sulfur Bacteria vs. Green Nonsulfur Bacteria

• Both contain similar photosynthetic pigments and
  can grow as autotrophs (get C from CO2).
• Green Nonsulfur Bacteria are known as the
  Chloroflexus group. Chloroflexus inhabits hot
  springs and shallow marine bays, forms mats, and
  is an important link in the evolution of
  photosynthesis.

25
Chlamydia and Deinococcus

• Chlamydia most sp. are pathogens causing
  respiratory and veneral diseases in humans, are
  obligate intracellular parasites (what does this
  mean and why do these organisms do this?)
• Deinococcus contains sp. with unusual cell
  walls and an innate resistance to high levels of
  radiation, ex. Deinococcus radiodurans. What
  does innate mean?

26
Archaea

• Many are extremophiles - what does this mean?
• All are chemotrophic, but there is something
  special about Halobacterium (see next slide).
• May be chemoorganotrophs or chemolithotrophs.
  What is a favorite energy source for the
  chemolithotrophs?

27
Archaea (continued)

• Heat lovers Aquifex, Pyrolobus (the ultimate
  heat-lover)
• Gas producers Methanogens, ex.
  Methanobacterium, strict anaerobes (what does
  this mean?), energy is obtained by producing
  methane (natural gas) as a product, important in
  degrading organic matter and providing most all
  of the natural gas on Earth!
• Salt lovers a.k.a. halophiles, ex.
  Halobacterium, require large amounts of salt
  (NaCl) for metabolism and production, require
  oxygen (what is the science term for this?)
  Halobacterium does not contain chlorophyll like
  true phototrophs, but still contains
  light-sensitive pigments that can trigger ATP
  production.

28
Archaea (continued)

• Thermoacidophiles (what the ? Just break it
  down thermo heat, acid acid, o have to
  throw this in for pronunciation, philes
  lovers) ex. Thermoplasma, are cell wall-less
  (which other proks. are cell wall-less?), grow
  best at moderately high temps. and extremely low
  (acidic) pH. Picrophilus most acidophilic of
  all known proks.
• Not all Archaea are extremophiles! However, most
  are not culturable (what does this mean?). If
  they are not culturable, how do we know they
  exist?

29
Eukaryotic Microbes

• Diplomonads ex. Giardia, lack mitochondria and
  other key organelles, descendents of primitive
  euks. that did not engage in endosymbiosis,
  metabolically deficient, pathogenic parasites of
  humans and other animals. Giardia can be a
  contaminant in drinking water and cause
  intestinal illness.
• Algae phototrophic, contain chloroplasts, major
  primary producers, contain a cell wall.
• Fungi lack photosynthetic pigments, are
  unicellular (yeasts) or filamentous (molds),
  major biodegraders and recyclers of organic
  matter in the environment, contain a cell wall.

30
Eukaryotic Microbes (continued)

• Protozoa most are motile, ex. some may be
  flagellated or ciliated (Paramecium), lack cell
  walls, some are parasitic.
• Slime molds motile, lack cell walls, cells
  aggregate to form a fruiting body, which produces
  reproductive spores.
• Lichens mutualistic relationship between a
  fungus protector and supporter, and a
  phototrophic organism, ex. an alga (euk.) or
  cyanobacterium (prok.) primary producer.