Exam 1 Lecture 7
UIC BioS 101 Nyberg
1
BACTERIA & ARCHAEA
These small cells have the potential for rapid population growth.
Bacterial diseases have been effectively controlled thru public health.
Speaker Notes:
1
Archaea? What are they?
Exam 1 Lecture 7
UIC BioS 101 Nyberg
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Reading Assignment
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For lectures 7 and 8 read Chapter 28 up to section 28.4.
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Be sure to read the Box 28.2 on lateral gene transfer (p588).
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Read p. 589 &590 on Archaea
Speaker Notes:
2
Exam 1 Lecture 7
UIC BioS 101 Nyberg
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Recent Exciting Developments
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1) The Domain ARCHAEA was discovered in the last 30 years (at the University of Illinois (UIUC) by Prof. Carl Woese).
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2) Direct Sequencing has revealed new species.
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3) Movement of genes from one species to distant species (horizontal gene transfer).
Speaker Notes:
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Direct sequencing finds pieces of DNA in the environment including some from organisms that have never been described.
Exam 1 Lecture 7
UIC BioS 101 Nyberg
4
Characteristics of DOMAINS
Character Bacteria Archaea Eukarya
Circular DNA Yes Yes NO
DNA histones NO Yes Yes
Organelles NO NO Yes
Eusex NO None known Common
Cell wall muramic acid no muramic most no wall
Transcription simple complex complex
Translation f-MET Methionine Methionine
Table 28.1 in Freeman
Speaker Notes:
4
Because the 3 domain tree puts the bacteria as the ‘outgroup’, ie Archaea and Eukarya are closest of the 3, the term prokaryote previously used to collectively describe bacteria and archaea is falling out of use.
Exam 1 Lecture 7
UIC BioS 101 Nyberg
5
Relationships of the three Domains
Bacteria Eukarya Archaea
Small Subunit RNA sequence
Speaker Notes:
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Originally Archaea were known only from extreme environments but more recently Archaea have been found in ordinary evironments.
Exam 1 Lecture 7
UIC BioS 101 Nyberg
6
Horizontal Gene Movement
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Genes are transmitted from parent to offspring. The continuity over generations is called vertical transmission.
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The appearance of a bacterial gene in a mammal suggests that pieces of DNA can move horizontally into the genome of other species.
Speaker Notes:
6
Horizontal gene movement means movement from one species to another presumably via a virus.
Exam 1 Lecture 7
UIC BioS 101 Nyberg
7
Gene Transfer between species
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Many of the innovations of genetic engineering are based on moving genes from one species into another. It should not surprise us that evolution has also done this.
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When the phylogeny of gene A does not match the phylogeny of most other genes in the species, one may suspect that gene A entered from another species.
Speaker Notes:
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The further the donor and recipient are apart phylogenetically the easier it is to detect the horizontal transfer.
Exam 1 Lecture 7
UIC BioS 101 Nyberg
8
DIRECT SEQUENCING
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DNA sequences can be amplified from a sample without first culturing the organisms.
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Many ‘species’ have been discovered that have never been cultured.
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Archaea, originally thought to be limited to extreme environments, have proved to be common in soil, but remain difficult to culture.
Speaker Notes:
8
A ‘species’ in this case is a sequence that is sufficiently different from all known sequences.
Exam 1 Lecture 7
UIC BioS 101 Nyberg
9
Culture of microorganisms
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One of the common ways to grow bacteria is on a nutrient gel in a petri dish.
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The gel is mostly (98%) water with some nutrients but it behaves like a solid.
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The ‘daughters’ of the original cell do not move much and the population (colony) becomes visible as a dot (spot) on the gel.
Speaker Notes:
9
Figure 27.6B shows a petri dish but it that case the bacterial ‘dots’ are so close together the bacteria appear as a streak.
Exam 1 Lecture 7
UIC BioS 101 Nyberg
10
Binary cell division
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A cell dividing into two cells after a period of growth (increase in mass) is the most common form of reproduction, getting more individuals in the population.
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When a cell divides into two approximately equal sized daughters it is called binary cell division.
Speaker Notes:
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A clone is a population of cells derived from a single cell. Unequal cell divisions are known.
Exam 1 Lecture 7
UIC BioS 101 Nyberg
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Cell Division Increases Cell Number
Time
1
2
4
Speaker Notes:
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If the time between divisions were exactly constant the number of cells would increase dramatically all at once.
Exam 1 Lecture 7
UIC BioS 101 Nyberg
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Doubling time
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The interval between cell divisions is called the doubling time as well as the length of the cell cycle.
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Smaller cells generally have shorter doubling times.
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Escherichia coli, a common bacteria, has a doubling time as short as 20 minutes.
Speaker Notes:
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If the doubling time is 20 minutes then the number of cells would increase by a factor of 8 each hour.
Exam 1 Lecture 7
UIC BioS 101 Nyberg
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Population Growth
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A constant doubling time leads to a pattern of exponential growth.
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Exponential growth and geometric growth are two expressions of the same pattern.
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Exponential growth assumes time is continuous.
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Geometric models assumes an integer number of time intervals, e.g. years.
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Speaker Notes:
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The constant half life leads to exponential decay.
Exam 1 Lecture 7
UIC BioS 101 Nyberg
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Models of Population Growth
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Discrete or Geometric
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Nt+1 = • Nt
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Continuous or Exponential
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Nt = N0•er•t
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Speaker Notes:
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Memorize these equations and learn how to use them.
Exam 1 Lecture 7
UIC BioS 101 Nyberg
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More on population growth
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Nt = No•2# of doubling times is another formula for population growth.
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A single E. coli cell would have 224hr•3doublings per hour =272 = 4.72•1021 descents in 24 hours and 9•1042 in 48 hrs.
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This is not possible because the cells will run out of resources.
Speaker Notes:
15
Exponential growth assumes that there are no resource limitations.
Exam 1 Lecture 7
UIC BioS 101 Nyberg
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Microbial Growth in Batch Cultures
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The “batch” is an unexploited resource.
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Cell(s) arrive in an environment with resources. After a lag during which they ‘crank up’ the enzymes needed for growth, they grow at their maximum rate until they exhaust the resources necessary for growth (energy & materials).
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Cells go into shutdown mode and eventually die (except those that are able to get to a new “batch”).
Speaker Notes:
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The conceptual alternative to the ‘batch’ mode of growth is the chemostat.
Exam 1 Lecture 7
UIC BioS 101 Nyberg
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The Cultural Growth Cycle
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Lag
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Exponential
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Stationary
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Decline
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Death
N
Time
Speaker Notes:
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Learn the order of these stages.
Exam 1 Lecture 7
UIC BioS 101 Nyberg
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Ways to Graph Growth
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If a population is growing exponentially (or geometrically) a graph of the log (or ln) of the population size versus time will be a straight line.
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‘Straightness’ is an attribute effectively evaluated by ‘eye’ and also by mathematical procedures. Most graphs of growth present the log of N rather than N.
Speaker Notes:
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Always check a graph for the scale on the y axis and the x axis.
Exam 1 Lecture 7
UIC BioS 101 Nyberg
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METABOLIC DIVERSITY
of Bacteria and Archaea
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SOURCES OF ENERGY
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Light
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Reduced organic molecules
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Reduced inorganic molecules
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SOURCES OF CARBON
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Inorganic =CO2 & CO3- & CH4 (Autotrophs)
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Reduced organic compounds (Heterotrophs)
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Speaker Notes:
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Exam 1 Lecture 7
UIC BioS 101 Nyberg
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SOURCES of CARBON
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Autotrophs (inorganic carbon)
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CO2
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CH4
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Heterotrophs (reduced organic compounds produced by autotrophs)
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Sugar
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Fat
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Protein
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Speaker Notes:
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Exam 1 Lecture 7
UIC BioS 101 Nyberg
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SYMBIOSIS
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Many protists, plants and animals have bacteria (and Archaea?) that live inside of them that do much of the metabolic work.
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Rhizobium, a bacterial symbionts of legumes that is able to fix nitrogen (plant trades carbon for nitrogen).
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Speaker Notes:
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Many pairs of species live together and essentially function as one. Lichens are a pairing of an algae and a fungus. The connection is so unique and stable that the associations are given ‘species’ names.
Exam 1 Lecture 7
UIC BioS 101 Nyberg
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Problem
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Using the log scale for population size on the Y axis and years on the X axis, graph the following values of population size on consecutive years;
1, 3, 8, 25, 81, 250, 700, 800, 900, 1000
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What would you say about your graph?
Speaker Notes:
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Do this using excel. Interpret the graph.
Exam 1 Lecture 7
UIC BioS 101 Nyberg
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Vocabulary
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Archaea
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Batch culture
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Cultural growth cycle
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Direct sequencing
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Doubling time
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Geometric growth
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Horizontal transfer
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Log growth
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Metabolic diversity
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Nitrogen fixation
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Rhizobium
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Symbiosis
Speaker Notes:
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