Micro Bio 2460 Exam 3 Practice Questions and Correct Answers
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Course
BIO 2460
Institution
BIO 2460
Binary Fission 1. Growth of cell size and increase in cell components 2. Replication of DNA 3. Division of the cytoplasm (cytokinesis) 4. Septum formation and division of daughter cells
Binary fission step 1 (1. Growth of cell size and increase in cell components) "The most common mechanism of cel...
Micro Bio 2460 Exam 3 Practice
Questions and Correct Answers
Binary Fission ✅1. Growth of cell size and increase in cell components
2. Replication of DNA
3. Division of the cytoplasm (cytokinesis)
4. Septum formation and division of daughter cells
Binary fission step 1 (1. Growth of cell size and increase in cell components) ✅"The
most common mechanism of cell replication in bacteria is a process called binary
fission, ; Before dividing, the cell grows and increases its number of cellular
components."
Calculating Number of Cells ✅"The number of cells increases exponentially and can
be expressed as 2n, where n is the number of generations."
Binary fission (2. Replication of DNA) ✅"DNA Replication starts @ circular
chromosome(C.C) (origin of replication) C.C attaches to inner cell membrane, and cont.
To replicate in in opposite directions along the chromosome until the terminus is
reached."
Binary fission ( step 3. Division of the cytoplasm (cytokinesis) ✅"The center of the
enlarged cell constricts until two daughter cells are formed, each offspring receiving a
complete copy of the parental genome and a division of the cytoplasm (cytokinesis).
This process of cytokinesis and cell division is directed by a protein called ftsz."
Z ring Assembly ✅• Cytokinesis is directed by ftsz protein
• ftsz assembles Z ring to form divisome
• Divisome activates production of peptidoglycan and septum that divides into two
daughter cells
Generation Time ✅"In prokaryotes (Bacteria and Archaea), the generation time is also
called the doubling time and is defined as the time it takes for the population to double
through one round of binary fission.
In eukaryotic organisms, the generation time is the time between the same points of the
life cycle in two successive generations."
Growth Curve ✅Closed cultures have finite resources (i.e. Nutrients)
• Culture density - # of cells/unit vol.
• Predictable pattern occurs
,Culture Density ✅"defined as the number of cells per unit volume.
And also a measure of the number of cells in the population."
If cells divide every 30 minutes, after 24 hours, 48 divisions would have taken place.
✅"apply the formula 2^n,
N=48
2^48 = 281,474,976,710,656 cells at 48 generations (24 hours).
Or in scientific notation
2.8 × 10^14 cells."
1. Lag phase-inoculum cells added and adjust to culture medium
; no change in population ✅Initial cell numbers do not change
Cells grow larger; metabolically active
Damaged or shocked cells undergo repair
Duration of the lag phase determined by many factors including:
• Genetic make-up
• Media composition
• Initial inoculum size
2. Log(exponential)phase-binary fission occurs;
Cell replication > cell death ✅• Generation time is genetically determined (intrinsic
growth rate)
Time vs. # of cells is
Constant growth & uniform metabolism
; good for industrial applications
Most susceptible to disinfectants and antibiotics that affect protein, DNA, and cell-wall
synthesis
3. Stationary phase-resources become depleted
Cell replication = cell death ✅Waste accumulates; nutrients gradually used up
Culture density is constant
Cells enter survival mode; synthesis slows;
Less susceptible to antibiotics
Undergo sporulation for endospore-formers
Expression of virulence factors and secondary metabolite
4. Death phase-nb endospores can form
Cell replication < cell death ✅• Toxic waste accumulates; nutrients exhausted
, • Cells lyse and release nutrients for surviving cells and endospore-formers
• Persisters- surviving cells with slow metabolism
Growth Curve
Sustaining Growth: ✅Open system cultures have infinite resources
Nutrients & air are replenished
Dead cells & waste are
Removed
Beneficial for industrial microbiology
Chemostat
Measuring Growth ✅•Quantifying populations size is important for determining
infection, contamination of water or food supply, etc.
• Methods:
• Microscopic cell count
• Fluorescent staining for alive & dead cells
• Coulter count
• Viable cell count
• Optical Density
Measuring Growth
Direct microscopic cell count ✅- cells are counted under a microscope
• Known volume is transferred to a calibrated slide (Petroff-Hausser chamber) and cells
are manually counted
• Cannot distinguish live vs. Dead
•Fluorescence Staining ✅cells are counted under a microscope or flow cytometer
• Red stain binds to damaged cells to indicate dead cells
Coulter counter - ✅detects electrical resistance change due to cell density
• Does not differentiate live/dead
Viable plate counts ✅count of viable cells;
Samples are diluted and grown on solid media
Results expressed in colony forming units per volume (CFU/ml) ✅Limited only to easily
cultured species
Serial dilution is plated and counted via pour plate or spread plate technique
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