prokaryotic growth and reproduction Flashcards
reproduction in bacteria
bacteria reproduce by an asexual process called binary fission.
what is the generation time?
the generation time is the interval of time between one division and the next.
the generation time may last for a few minutes to several hours.
what is bacterial conjugation?
the process of transferring genetic information from one prokaryotic cell to another prokaryotic cell through direct contact.
what is binary fission?
binary fission is an asexual reproductive process.
during binary fission there is a duplication of chromosomes, and daughter chromosomes are pulled apart to seperate halves of the cell whilst the cell elongates to its biggest size.
there is a division of the cell by the growth of a new cell membrane and cell wall to give two identical cells.
growth of microbial cultures
when a unicellular microorganism multiplies by binary fission the new cell grows to double its size and then divides into two equal parts that repeat the process.
what is growth?
growth is the orderly increase in all the components of a cell, that is going on all of the time.
what is exponential growth?
when microbes divide, they double in number at every genetation, this leads to exponential growth, which is an extremely rapid increase.
exponential growth must be plotted on a log scale.
what is the growth curve of a batch culture?
the growth curve is plotted on a log scale with the Y-axis being labelled ‘cell number (log)’, and the X- axis being labelled ‘time (hours)’.
the growth curve consists of a lag phase, a log (exponential) phase, a stationary phase, and a death (decline) phase.
what is the lag phase of a growth curve?
initially there is a lag phase, in which the bacterial cells are producing DNA, ribosomes and the enzymes necessary to use the new food source.
the lag phase is a period with no multiplication/ no growth occurring, this represents a time when the inoculum cells are adapting themselves to active growth in the new environment.
NO GROWTH OCCURS. CELLS ARE ADAPTING TO THEIR NEW ENVIRONMENT. IN THIS PHASE OF GROWTH ENZYMES CAN BE SYNTHESISED, METABOLISM IS ADJUSTED AND DAMAGE REPAIRED.
what is the log (exponential) phase of a growth curve?
during the log phase the cells are growing exponentially.
in the log phase, cell number doubles at regular intervals, which means that the generation time is constant.
during the log phase microorganisms produce primary metabolites because they are actively
RAPID CELL GROWTH OCCURS AND CELL NUMBER DOUBLES AT REGULAR INTERVALS
PRIMARY METABOLITES ARE PRODUCED
what is the stationary phase of a growth curve?
stationary phase occurs when the food source begins to be depleted or the level of toxic waste products becomes too high, as the death rate of cells catches up to the growth rate.
during stationary phase there is no net change in population size, as the rate of cell division equals the rate of cell death.
in the stationary phase secondary metabolites are produced, and production of antibiotics and enzymes by certain bacteria occur.
in endospore forming bacteria, sporulation occurs as the bacteria enter stationary phase.
THERE IS NO NET CHANGE IN POPULATION SIZE AS THE RATE OF CELL DIVISION EQUALS THE RATE OF CELL DEATH.
SECONDARY METABOLITES ARE PRODUCED.
what is the death (decline) phase of a growth curve?
when the death rate exceeds the growth rate, the cells enter the death phase.
in the death phase, there is a rapid decrease in the population.
cells die due to factors such as lack of nutrients, build-up of toxic waste products, and a lack of oxygen.
THE RATE OF CELL DEATH OVERTAKES THE RATE OF CELL DIVISION, CELLS DIE DUE TO THE BUILD UP OF TOXIC WASTE, LACK OF NUTRIENTS AND IN AEROBIC MICROBES A LACK OF OXYGEN.
what happens to the growth curve in unfavourable conditons?
the log phase is not as steep as the growth rate would slow as there is less energy available for growth and reproduction because cell respiration is reduced.
the stationary phase would begin at a lower level of cells as the maximum size of the population would be less.
the death phase would begin earlier as the numbers of dying bacterial would overtake new cells being produced at an earlier stage.
if bacteria could form endospores it would do so as levels of oxygen are depleted.
how is bacterial growth measured?
bacterial growth can be measured using total population measurements, or by counting cells.
what is total population measurements?
dry mass of cultures (mg)
protein concentration (mg/ml)
optical density (OD) at 600nm - this measures the degree light is scattered by cells; more cells = more scattering of light. optical density uses a spectrophotometer.
