Lab 6: Cell Division

what is a cell’s DNA packaged as a double-stranded DNA molecule called?

a genome

chromosomes

structures within the nucleus that are made up of DNA in the nuclei of its cells

how many chromosomes do human body or somatic cells have?

43

how many chromosomes do human sex or gametes cells have?

23

diploid

a typical body cell contains two matched or homologous sets of chromosomes (one set from each biological parent)

haploid

human cells that contain one set of chromosomes and are designated 1n

homologous chromosomes

upon fertilization, each gamete contributes one set of chromosomes, creating a diploid cell containing matched pairs of chromosomes

how many sister chromatids do eukaryotic chromosomes have?

2

where are sister chromatids attached at?

the sister chromatids are identical to one another and attached at a compressed region called the centromere

chromatin

DNA double helix wrap around a core of eight histone proteins at regular intervals along the entire length of the chromosome

nucleosome

the beadlike, histone DNA complex. a DNA molecule in this form is about seven times shorter than the double helix without the histones

the ____________ level of compaction occurs as the nucleosomes coil into a chromatin ______. this coiling further __________ the chromosome so that it is now about 50 times shorter than the extended form.

second, fiber, condense

in the _______ level of compaction, a variety of ___________ __________ is used to “pack the chromatin”

third, fibrous proteins

DNA replicates in the ___ phase of interphase. after replication, the chromosomes are composed of two linked sister ________. the connection between the sister chromatids is closest in a region called the ___________.

S, chromatids, centromere

cell division cycle

G1: cell growth

S: DNA synthesis

G2: cell growth

Mitotic phase: Mitosis and Cytokinesis → formation of 2 daughter cells

G1 Phase (first gap)

getting ready by prepping for replicating each chromosome in the nucleus. includes proteins and energy reserves

S Phase (Synthesis of DNA)

results in the formation of identical pairs of DNA molecules — sister chromatids — that are firmly attached to the centromeric region. centrosomes also duplicate

G2 Phase (Second Gap)

increases energy stores and synthesizes proteins necessary for chromosomes manipulation and movement. additional growth

prophase

• chromosomes condense and become visible

• spindle fibers emerge from the centrosomes

• nuclear envelope breaks down

• nucleolus disappears

prometaphase

• chromosomes continue to condense

• kinetochores appear at the centromeres

• mitotic spindle microtubules attach to kinetochores

• centrosomes move toward opposite poles

metaphase

• mitotic spindle is fully developed, centrosomes are at opposite poles of the cell

• chromosomes are lined up at the metaphase plate

• each sister chromatid is attached to a spindle fiber originating from opposite poles

anaphase

• cohesin proteins binding the sister chromatids together break down

• sister chromatids (now called chromosomes) are pulled toward opposite poles

• non-kinetochores spindle fibers lengthen, elongating the cell

telophase

• chromosomes arrive at opposite poles and begin to decondense

• nuclear envelope material surrounds each set of chromosomes

• the mitotic spindle breaks down8

cytokinesis

• animal cells: a cleavage furrow separates the daughter cells

• plant cells: a cell plate separates the daughter cells

what’s the difference in cytokinesis in animals cells vs. plant cells?

an animal cell uses a cleavage furrow and contractile ring to separate while a plant cell uses a cell plate and golgi vesicles

onion root tip

formation of tissues begins with the root apical meristem (RAM). just below the tip of the root, there is a region of small, densely packed cells that are actively dividing

microscope parts

• ocular lens (eye piece)

• objective lens

• illuminator (light source)

• mechanical stage

• coarse adjustment

• fine adjustment

• brightness adjustment

what are the two major phases of the cell cycle?

interphase and mitotic phase

multinucleate cells

interphase and mitosis (karyokinesis) may take places without cytokinesis, in which cells with multiple nuclei are produced

where is cell division in plants limited to?

the meristems: specialized regions of the undifferentiated cells

apical meristem in the root tip

in this region, cells are rapidly progressing through the cell cycle to increase cell number. as cells accumulate, they are pushed out of this region and exit the cell cycle. these cells then go through the process of cell elongation followed by differentiation

how is the meristem protected?

its protected from the environment by several layers of differentiated cells that form a root cap at the very tip of the root and an epidermal layer of cells along the root length. the cells in the root cap and the epidermal layer are constantly being lost and replaced by new cells arising in the meristem. other cells that leave the meristem and exit the cell cycle will differentiate into other types of cells including those specialized for starch storage and nutrient uptake