MODULE 3: Cell Division

binary fission

A form of asexual reproduction in unicellular organisms by which one cell divides into two cells of the same size; unilateral growth; equal division

septum

inward growth of the cell wall in the cytoplasmic membrane; intercalorie growth

budding

Asexual reproduction in which a part of the parent organism pinches off and forms a new organism; unequal cell growth

fast growing microorganisms

E. coli - 15 to 20 mins

S. aureus - 27 to 30 mins

Bacillus - 26 mins

generation time

the time it takes for the cell population to double

slow growing microorganisms

Leptospira (causative agent of Leptospirosis) - 6 to 8 hours

Mycobacterium - 18 to 24 hours

Bacterial growth curve

a graph indicating the growth of a bacterial population over time; can be determined by growing a batch culture or a CLOSED CULTURE SYSTEM

red line in bacterial growth curve

indicates viable counts (counting live replicating organisms and counting the colonies on an aggro surface indicated by the y-axis)

green line in bacterial growth curve

indicates turbidites (turbidity measurements use a spectrophotometer - machine that detects how turbid a sample is or how cloudy a suspension is)

lag phase

"flat" period of adjustment, enlargement; little growth

logarithmic/exponential phase

growth and cell division occurs very rapidly; generation time may be determined; maintained via chemostat

chemostat

ensures logarithmic growth by constantly adding and removing equal amounts of culture media

stationary phase

period of equilibrium; microbial deaths balance production of new cells; limited nutrients; slowly becomes a toxic environment

death phase

cells die at an exponential rate; medium is extremely toxic; endospores may form; cells may undergo involution (cell shrinkage)

mitosis

"equational division" in which the nucleus divides into nuclei containing the same number of chromosomes

interphase

Cell grows, performs its normal functions, and prepares for division; consists of G1, S, and G2 phases

G1

cell growth and preparation; increased metabolic activity

S phase

DNA replication wherein chromatins become chromatid

G2

final preparation phase where the cell checks for DNA errors; chromatids start to condense

prophase

Chromosomes become visible, nuclear envelope dissolves, spindle forms

metaphase

chromosomes line up in the middle of the cell; kinetochore proteins digest the spindle fibers

anaphase

chromosomes separate and move to opposite ends of the cell; cell elongates

telophase

chromosomes are in opposite cell sides and the spindle apparatus disbands; genetic material loosens and nuclear envelopes form around each chromosome set

Cytokinesis

division of the cytoplasm

Meiosis

"reductional division" wherein diploid cells reproduce 4 haploid cells; chromosomes are halved; primary basis for genetic variation

gametes

sex cells (sperm and egg)

Interphase I

chromosomes duplicate (23 -> 46)

Prophase I

he chromosomes condense and the nuclear envelope breaks down; crossing-over occurs

Bivalents

AKA tetrads are pairs of homologous chromosomes

Anaphase I

homologous chromosomes separate

Telophase I

cytoplasm divides and 2 daughter cells are formed

Prophase II

The duplicated chromosomes and spindle fibers reappear in each new cell

Metaphase II

Chromosomes line up at the metaphase plate

Anaphase II

centromeres divides and chromatids move to the opposite poles of the cells

Telophase II and Cytokinesis

A nuclear envelope forms around each set of chromosomes and the cytoplasm divides; results in 4 daughter cells

genetic variation in meiosis

occurs in crossing over (Prophase I), recombination of chromosomes (Metaphase and Anaphase I & II), gamete fusion

genetic disorder

occurs when there is a NONDISJUNCTION of the chromosomes

monomy

A disorder in which an individual has only 1 single chromatid of a specific chromosome (2n-1)

trisomy

3 copies of a chromosome (2n+1)

Down Syndrome

Trisomy 21; causes flat face, broad nose, large tongue, upward-slanting eyes

Patau Syndrome

Trisomy 13; cleft palate and malformed face and/or ears

Klinefelter Syndrome

47, XXY; tall stature; small firm testes; considered male

Jacob's Syndrome

47, XYY; nondisjunction during spermatogenesis. Males are usually taller than average, persistent acne, and tend to have speech and reading problems. Once thought to be criminally aggressive, but this hypothesis was proven wrong.

Turner Syndrome

XO; lack of Y chromosome causes short stature; develops as females