“That which does not kill us, makes us stronger.” Friedrich Nietzsche , Kelly Clarkson and Kanye.
Well, maybe. Martin Seligman has tested this theory since the 1960’s and has found that it is only true if the animal feels it has some control over its situation. If the animal feels that there is nothing it can do to improve its situation, it may enter into a state called “learned helplessness“. In this state, the animal will not even try to improve its situation, even to the point of not even trying to avoid pain, because it has learned in the past that there is no point.
I bring this up in class, because I do see this in some of my students…. and frankly, its the most frustrating thing in the world to see a student who is intelligent and capable, and watch them just give up. If you feel like no matter how hard you study, you’ll still fail… you will. You’ll fail to take action, you’ll fail to see the opportunities that exist to improve yourself, and you’ll end up failing in class.
Seligman has put forth another theory… Called PERMA. This is an acronym that describes, what he thinks, are the five components of well being. The five components are below, with my interpretations of how they can be asserted in class:
- Positive emotion: Staying positive, looking at the bright side, finding the silver lining.
- Engagement: Continuing to participate. Paying attention. Avoiding distraction
- Relationships: Studying in groups, having an accountability partner, enjoying other’s successes, having others celebrate your success
- Meaning: Not every class is going to be your favorite, but you can find SOMETHING in each class that is relevant to you or what you want to do. Focus on what is relevant to you.
- Achievement: Enjoy every success, even the little tiny ones. Create small goals for yourself, and make a plan to achieve them. You may not get an A on the exam, but you can be proud of yourself that you completed a personal goal like studying 2 hours per day, turning the paper in on time, etc.
Back to biology….
This week we studied bacterial nutrition, growth and control.
When we refer to “bacterial growth” this usually does not mean the bacteria getting bigger (we call that cell enlargement), but rather that the size of the bacterial population is increasing. This is because the individual bacteria are undergoing binary fission ( a type of asexual reproduction).
Binary fission includes: DNA replication (the copying of the chromosome and all the plasmids), cell enlargement, and septation/cytokenesis.
The Cell enlarges.: increasing the size of the cell by adding new components to the cell wall, PTG and plasma membrane. In order to make things, we need the raw materials (carbon compounds) and we need ATP and electrons to create energy (see how metabolism ties in nicely here?)
DNA replication starts on the OriC of the chromosome, proceeds in BOTH directions (going in opposite directions) around the circle, and ending at the terminus. Plasmids are replicated independently and differently (not discussed in class).
The new chromosomes are tangled together, and must be resolved apart by topoisomerase, and then they are pulled to opposite sides of the cell by being attached to the plasma membranes.
The cell “pinches” together by forming a septum, then the cytoplasm is completely separate and they are two new daughter cells (equal to each other, and equal to the mother).
Here’s a really nice animation of bacterial chromosomal replication
The timing of replication is also crucial… we see DnaA here in this video…. how does SeqA also contribute to the “timing” of DNA replication?
The bacterium also enlarges in size. In order to do this, it must bring molecules into its cell (WHAT it brings in is totally dependent on its nutritional class)
Diffusion brings molecules in WITH their concentration gradient (from high to low), active transport brings molecules AGAINST their concentration gradient (from low to high) and requires some sort of energy – either ATP hydrolysis or coupling the motion with the movement of another molecule that is being moved from high to low concentration (kind of piggybacking on a molecule that is moving without the need of energy). Things have to be moved out too, and this involves secretion systems. Why do Gram negative cells have so many more types of secretion systems than Gram positive?
Next we talked about growing bacteria on solid and liquid media. Plates can be streaked or spread with bacteria (and the agar can even be mixed with bacteria while still warm!)
You’ll never look at jello salad the same way.
A variety of different growth media was discussed as well, and how we can add ingredients to assist us in identifying bacterial species.
The bacterial growth curve was discussed, and what happens at each area (and why bacteria move from one area to the next)
Followed by a discussion of how to count them. Viable cell counting was differentiated from direct cell counting, and techniques like spectrophotometry were introduced. Would spectophotometry be a viable or direct technique??
We also did an exercise about how to count bacteria in a population using some formulas. Generation time (the amount of time to complete binary fission, or for the population to double) and mean growth rate constants (the number of doublings per hour) were determined.
Lastly we talked about how to kill bacteria (my favorite past time!)
Bacteria replication can be stopped (bacteriostatic), they can be killed (bacteriocide) or they can be completely blown up (bacteriolytic). The most common ways to kill bacteria were discussed, including heat and antibiotics.
Death can be monitored by the D value (how many minutes does it take to reduce the bacterial population by one log at a specific temperature) and the Z value (how many degrees do you have to increase the heat to reduce the D value by one log). D and Z values are only applicable when killing by heating.
Antibiotics were last on the list. We’ve talked about how antibiotics can prevent or destroy the PTG, but there are other targets as well. Any structure or process that is necessary for the bacteria replication or survival AND unique to the bacteria, is a potential target. However, no matter how judiciously we use antibiotics, bacteria WILL become resistant.
We can slow that down, however, by using antibiotics rarely and correctly. Did you know that most of the antibiotics used in the USA are not used by people? They are used in agriculture on farm animals!
Things to focus on from this week:
- Draw the complete process of binary fission
- Describe how DnaA and SeqA contribute to the timing of chromosome replication
- Be able to describe the fundamentals of DNA replication initiation, elongation and termination
- Explain why secretion is different in Gram positives versus Gram negatives.
- Give an example of a secretion system that acts more like an “injector”
- DNA replication in bacteria is semi-conservative and bi-directional… what does that mean?
- Understand the difference between:
- Minimal (general) and enriched media
- Selective and differential media
- Defined and complex media (seriously guys, DIGESTS).
- Be able to draw a bacterial growth curve and describe whats happening at each part of it
- Be able to calculate generation times, and growth rate constants (with units!) from an example.
- Give an example of how to count cells using a viable and a direct technique
- Be able to calculate D and Z values from a graph or example
- Describe the three ways that bacteria can become antibiotic resistant
Questions or comments? Leave them below!