BIOL Lecture 3-5.pdf

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16 Mar 2012
05/10/10 2:23 AM
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
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
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)
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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
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
Cell wall - prokaryotes yes (peptidoglycan in bacteria only), eukaryotes yes in some
Photosynthesis prokaryotes yes (in some), eukaryotes yes (in some)
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
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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
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
Variety due to diverse habitats and long evolutionary history
Generalized bacterium structure
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?
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