October 2, 2009
We discuss the various stages of the bacterial growth cycle.
Exponential growth vs logarithmic growth
Exponential-Number of bacteria at a given time
*2^x, x=number of generations since originally had 1 bacterium
If true that bacteria growth is exponential X=1, then the number of bacteria in culture we have would be 2, there are bacteria that have generation times of 15 and 20 minutes long so how many 15 min periods do you have in 1 hour and in 24 hours?
15 periods in one 24 hour day=296 to the power
X=96 bacteria=296
X=288 bacteria=2^288 (since we inoculated the bottle of broth on Tuesday)
Bacterial growth is not exponential because the exponential end times do not go on forever
Bacterial growth is only part exponential for part of bacterial growth, and mostly logarithmic growth
Logarithmic Growth-only part of bacteria grows exponentially
a. Replication of the chromosome (Picture)
-DNA polymerase copies DNA: need 2 copies of chromosomes: 1 for each cell
b. Elongation of the cell
-two new bacteria but only part have new cell envelope
c. formation of Ftsz ring at septum
-pinching in middle of cell; chromosomes seperated to either side of cell
2. Replication of Chromosome:
a. DNA polymerase-enzyme that synthesizes new DNA molecules complementary to template strand
*DNA is double-stranded, interacting via complementary bases (A=T) and (C=G)
*A=T has two hydrogen bonds that hold them together and C=G has three hydrogen bonds that hold them together
(See Picture in other notes)
Because a chromosome is attached to the cell wall that is why when the bacteria elongates in the middle of the bacterium, if you have one newly replicated chromosome attached in two different spots its going to pull those chromosomes apart
Ftsz pinches off the middle of the cell and it knows the middle of the cell because there is a min protein that stops Ftsz from working; they bounce from one end of the cell to another
*Interpretive Dance*
Additional Point: II continued
How long does it take bacteria to do all four of these steps for the bacterium to divide (depends on the bacterium)
Bacterial Generation times
E. coli: has a generation time of about 15-20min (gram +) not much of a cell wall; has about 5 million bps in its chromosome
Staphyloccocci: Has a generation time of about 30 min (gram -) in ten hours 1,048,576
Mycobacterium tuberculosis: generation time of 23 hours (acid-fast)
Things that may influence the generation time:
Bacterial Chromosomes
*Size Range:
-1 million bps (base pairs)
-8 million bps
Copy letters on the board as fast as we can: akclllmk, gggptadcc, aptakatzk, atgcataaa, tcactacatc
How often do you think E.coli is wrong in making copies?
