16 Mar 2012
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05/10/10 2:23 AM
LECTURE 3: DIVERSITY OF LIFE AND PROKARYOTES
Pre-Lecture Vocabulary
• Cell wall – A relatively rigid structure that encloses cells of plants, fungi, many protists, and most
prokaryotes. Gives these cells their shape and limits their expansion in hypotonic media
• Membrane-enclosed organelle – Organized structures found in or on eukaryotic cells. Examples
include ribosomes, nuclei, mitochondria, Golgi apparatus
• Nucleus – The centrally located compartment of eukaryotic cells that is bounded by a double
membrane and contains the chromosomes
• Cytoskeleton – the network of microtubules and microfilaments that gives a eukaryotic cell its shape
and its capacity to arrange its organelles and to move
• Photosynthesis
• ATP (adenosine triphosphate) – an energy storage compound containing adenine, ribose and three
phosphate groups. When it is formed from ADP, useful energy is stored; when it is broken down (to
ADP or AMP), energy is released to drive endergonic reactions.
• Cellular respiration – the catabolic pathways by which electrons are removed from various molecules
and passed through intermediate electron carriers to O2, generating H2O and releasing energy
• Taxon – a biological group (specifically a species or a clade) that is given a name
• Glycolysis – The enzymatic breakdown of glucose to pyruvic acid. One of the evolutionary oldest of
the cellular energy-yielding mechanisms.
Lecture Notes
Lecture Outline
• Diversity of life
o What is diversity
o How is diversity measured
o Which groups show the greatest diversity
• Prokaryotes
o Prokaryotes vs eukaryotes
o Cell structure and morphology
o 3 challenges of life
What is diversity?
• Diversity in life (degree of difference in: )
o Genetic variation (within a species?)
o Species composition (within a community)
o Interactions within and between ecosystems
• Biodiversity (more diverse = healthier)
• Species diversity
o This is commonly reserved for indices that measure both the number of species in a habitat as
well as their relative abundance
We have no idea how many species of life exist today – can’t estimate the diversity of prokaryotes
• Prokaryotes first appeared in the Precambrian era
• 3-100 million extant eukaryotic species
• Bacteria and Archaea’s numbers are completely unknown
• ~99% of all species are extinct
• Most species live in the tropics (Neotropics – brazil, etc)
• Arthropods most diversity > plants > Molluscs > fungi > vertebrates(fish > reptiles & amphibians >
birds > mammals)
o Most taxonomists are vertebrate, invertebrate or fossil
• Man factors that control diversity
o Area (In general doubling the area increases number of species by 10-25%)
o Climate (Warm, wet areas have more species, not sure why)
• Other measures of diversity
o So far we have focused on numeric diversity ie number of species
o Genetic diversity = measure of genetic distance (=evolutionary separation)
! Prokaryotes show greatest
o Functional diversity = differences in shape, size, and generally ways of making a living
(types of food, places lived, etc)
! Prokaryotes show greatest
Summary on diversity of life
• There are likely ~ 7-10 million extant species
• ~99% of Earth’s species are extinct
• Diversity is greatest near equator on large landmasses with good(warm wet) climates
• Taxonomists have quantified animals/insects/beetles as most diverse
Prokaryotes
• Are the earth’s oldest organisms
• Two major groups
o Bacteria
o Archaea (which are closer to eukaryotes)
Prokaryotes vs Eukaryotes
• Nucleus - Eukaryotes have, prokaryotes do not
• DNA - Prokaryotes have 1 chromosome (circular) and plasmids – eukaryotes have linear chromosomes
• Membrane bound organelles - Prokaryotes do not have, eukaryotes hace
• Ribosomes - Prokaryotes have smaller (70s) (photosynthesis?), eukaryotes have larger (80s)
• Cytoskeleton - Prokaryotes no, eukaryotes have
o Prokaryotic cells lack a cytoskeleton, and in the absence of organized cytoskeletal proteins,
the lack mitosis. Prokaryotes divide by their own method, binary fission, after replicating their
DNA
• Cell wall - prokaryotes yes (peptidoglycan in bacteria only), eukaryotes yes in some
• Photosynthesis – prokaryotes yes (in some), eukaryotes yes (in some)
Archaea
Defining characteristics
• Know very little
• Absence of peptidoglycan in cell wall
• Distinctive lipids present in their cell membranes (not found in eukaryotes or bacteria)
• Many archaea also have lipid monolayer (cell membrane may be made of long chain hydrocarbons that
span the membrane)
• Many archaea and bacteria have a single chromosome & plasmids
o Chromosome not highly coiled
o In nucleoid region
o Plasmid – extra-chromosonal DNA; small rings; easily exchanged during sex
Bacteria
• Bacteria do not have membrane-bound organelles
• Cell membrane is highly folded
o This is where they perform cellular respiration (ATP synthesis) and photosynthesis
• Bacterial ribosomes are different than eukaryotes
o Lack of nucleus, allows simultaneous
transcription and translation = fast growth and
reproduction
• Have variety of morphology
o Unicellular, colonial
o In spheres = cocci
o Rods = bacilli
o Helical = spirili
• Cell wall structure varies, which determines the results of
Gram staining
o Gram positive (purple) = thick cell wall with
outer peptidoglycan layer
o Gram negative (pink) = think cell wall between two membranes
• Typically antibiotics are ineffective against gram neg bacteria
Bacteria and the three big challenges
1. Make nearly faithful copies of themselves (reproduce)
• Rapid, short generation times
• Asexual reproduction – binary fission
• Sexual reproduction
• Genes on plasmids are easily transferred
• 3 main methods to obtain new genetic material
a. conjugation – bacteria form protein tube (sex pilus) and plasmids or even
chromosomes are shared
b. dead bacteria cells get absorbed
c. viruses transfer genetic material
2. Respond to the outside environment by resisting internal changes in physical and chemical
characteristics (maintain homeostasis)
• Respond to harsh environmental conditions
• Move towards or away from chemical signals = chemotaxis
• Use flagella (different from eukaryotes, rotates)
a. Made from different protein
b. Thinner and more numerous
! Also glide, roll, use gas floats inside cell
• Can from spore called endospore, which protect bacteria from adverse conditions (eg anthrax)
• Can form surface-coating communities called biofilms
• Form polysaccharide gell, trapping debris and other cells
! Can be hundreds of cells thick, and release signal molecules, attracting more
• Composed of single or many species
• Eg plaque,
3. Transform energy to synthesis new molecules (energy transformation)
• Despite their simplicity in cell structure, prokaryotes are extremely diverse in their metabolic
abilities
• Variety due to diverse habitats and long evolutionary history
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Generalized bacterium structure
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Bacteria do not have membrane-bound organelles.
• cell membrane is highly folded
• site of ATP synthesis & photosynthesis
Where do they perform
cellular respiration and photosynthesis?