Lecture 8 Flashcards
Bacteria replicates by
Binary fission
- Parent cell divides into two new cells
Bacteria population grows
exponentially - reaches enormous number in short time
Bacterial growth with E.coli
One cell becomes 8 cells after 1 hour
One cell becomes 0.26 million after 6 hours
One cell becomes 69B after 12 hours
More cell division for bacteria means
More DNA replication which leads to more chances for DNA to mutate
Reproducing to huge populations increases the chance that
some members of the population by chance have the mutation to react to new challenges in the environment
Antibiotic resistance in bacteria
Some members of population mutated into antibiotic resistance strains by chance (red cells)
Antibiotic resistant strains survive antibiotics (natural selection)
Survivors grow back into a population of antibiotic resistant bacteria
Requirements of life/growth
- Energy
- Carbon source
- Among many other elements like nitrogen
Photoautotrophs vs chemoheterotrophs
Photo: Make organic molecules such as glucose from sunlight, water and CO2
Chemo: Use these organic molecules to extract energy and as a carbon source
Glycolysis: extract energy from glucose
- Glucose is a 6 carbon sugar
2 ATP is used to begin the reaction where it splits the glucose into half while extracting energy
Glycolysis generates:
- 2 pyruvate (3 carbon sugar)
- 4 ATP
- 4 electrons + 4 protons (H+)
Net ATP gain per glucose: 2
Of the 4 ATP produced after splitting 1 glucose where is it used for
- 2 get used to split another glucose
- 2 get used for other jobs in the cell
Where do the 4 electrons made from glucose go?
NAD+ is an organic molecule which can bind to electrons. Accepts 2 electrons and turns into NADH
NAD+ + H+ +2e = NADH
Every time glucose gets split, NAD+ is used to accept electrons
Problem with NAD+
Limited number in cell
Can not do glycolysis once NAD+ gets depleted
- need to regenerate NAD+
Fermentation
Uses pyruvate to regenerate NAD+
- Pyruvate is the other product produced by glycolysis
Pass electrons from NADH to pyruvate to regenerate NAD+
Pyruvate + NADH = NAD+ _ fermented products
Pyruvate gets turned into fermentation products in the process (alcohols, acids)
- Happens anaerobically
Fermentation is not efficient because
Pyruvate is a 3 carbon molecule which has more energy stored
Fermentation does not use this extra energy since it uses pyruvate to regenerate NAD+
TCA cycke
extracts energy which is left inside pyruvate aka krebs cycle, citric acid cycle
One pyruvate eventually becomes 3CO2
Makes more NADH (and other electron carriers) + ATP
NADH gives electrons to
Electron transport chain
- regenerates NAD+
Energy is produced as electrons pass through ETC which is used to make ATP
- At the end of ETC, electrons are put onto O2, the terminal electron acceptor
Aerobic respiration extracts the
maximum amount of energy from glucose, producing up to 38 ATP per glucose
- Fermentation produces 2 ATP
O2’s role in the ETC
- very powerful electron acceptor
- Used as the terminal electron acceptor to allow electrons to pass through ETC at max efficiency extracting max energy
Aerobic organisms are dependent on O2 to produce energy
Anaerobic respiration
Respiration can be done using molecules other than O2 as terminal electron acceptors
- NO3 (nitrate)
- SO4^2- (sulphate)
Non O2 electron acceptors are not as effective as O2 to drive electrons through ETC
- Does not produce as much energy than aerobic but produces much more than fermentation
Examples of Microorganisms and respiration
Obligate aerobes: Oxygen required for survival
Facultative anaerobes
- Can use oxygen when available
- Can survive by anaerobic respiration and/or fermentation if necessary
Obligate anaerobes
- Can not survive when oxygen is present
- Oxygen is extremely reactive and is poisonous for organisms who do not have protective measures
Humans and fermentation
- are Obligate aerobes
- Glucose is consumed using O2 during aerobic exercise but during intense anaerobic exercise, oxygen gets depleted in our body
- We ferment pyruvate into lactic acid to produce more energy anaerobically
Accumulation of lactic acid is said to be correlated with muscle fatigue
Anaerobic exercise
High intensity
Interval training
- weight lifting
Yogurt fermentation
Must be done anaerobically
* Lactobacillus bulgaricus and Streptococcus-thermophilus are put into milk
* Both Gram positive lactose-fermenting bacteria
Lactose fermented to
lactic acid
* Acidifies the product, thickening the solution
* In addition, L. bulgaricus and S. thermophilus performs other other metabolic activities
* All of this contributes to the taste and texture of yogurt
Acidification of yogurt (+ high incubation temperature) suppresses growth
of other bacteria such as E. coli
Milk anaerobic and aerobic processes
Lactose -> glucose -> pyruvate
No oxygen: Lactic acid fermentation
Oxygen: Aerobic respiration
Yeast
(Saccharomyces cerevisiae), a unicellular eukaryote (Fungi)
* Used for many food processes, including production of alcohol from various sources of starch
* Type of starch contributes to the type of alcoholic beverage produced
Alcohol production begins to inhibit
yeast growth after a while
* Distillation is necessary to produce alcoholic beverage with a higher alcohol %
Alcohol fermentation
Starch -> glucose -> pyruvate
No oxygen: Ethanol formation: distillation for some alcohols
Oxygen: Aerobic respiration
Cyanobacteria
- Gram negative photoautotrophic bacteria
- Only clade of bacteria capable of photoautotrophy
- Use sunlight to produce organic molecules like glucose from CO2
- Carbon fixation
- Chemical energy generated by sunlight gets stored in glucose
CO2 + H 2O + sunlight = glucose + O2
Nitrogen fixation in cyanobacteria
- Some cyanobacteria are also capable of nitrogen fixation: convert atmospheric N2 to ammonia (NH3)
Is nitrogen essential
- Nitrogen is essential for making DNA, proteins, etc.
- Most organisms can not use N2 as their nitrogen source and depend on ammonia produced by nitrogen fixers
Problem with nitrogen fixation in cyanobacteria
- Nitrogen fixation cannot happen when there are O2 near-by
- Cyanobacteria produces O 2 via oxygenic photosynthesis during carbon fixation
Multi cellularity
- Filamentous bacteria show true multicellularity
- Cells in multicellular body specialize their function and depend on one another for survival
Multi cellularity in cyanobacteria
- Some cells in cyanobacteria filament terminally differentiate to heterocysts: cells specialized for nitrogen fixation
Heterocysts
can not survive on its own
* Can not photosynthesize and depends on neighboring vegetative cells to provide glucose etc
form barrier to block O2 entry, allowing nitrogen fixation inside their cell
* Heterocysts provide fixed nitrogen to neighboring cells
