The Cell Cycle and Mitosis

Objectives

what is the purpose of mitosis?

list, describe, and label all parts of the cell cycle.

understand how chromosomes are formed and label a diagram.

what is a checkpoint?

Recall

the nucleus has multiple parts and houses the genetic material of a cell

nuclear envelope (pores)

nucleoplasm (chromatin)

nucleolus (ribosome production)

Recall

chromosomes are hereditary material within the nucleus made of coiled DNA and proteins

formed only before the cell divides

prior to cell division they are chromatin strands within the nucleoplasm

Genetic Material

A cells DNA, it’s genetic material is called it’s “genome”

Eukaryotic genomes usually consist of a number of DNA molecules, packaged into “chromosomes”

Cell Division

functions in reproduction of the cell

functions in growth and repair

Cell Division

Cell division distributes identical sets of chromosomes to daughter cells

increases the number of somatic (body) cells

Vocabulary

Cell division: process by which cells reproduce

Chromosomes: cell parts that determine replication; a chromosome is made up of two identical chromatids

Daughter cells: new cells produced by cell division

Cytokinesis: a division of the cytoplasm of one parent cell into 2 daughter cells.

Nucleosomes: Beadlike structures formed by DNA and histone molecules.

https://www.youtube.com/watch?v=IePMXxQ-KWY

The Nucleus

Chromatin (DNA along with proteins) is actually a collection of separate structures called chromosomes, which are visible as separate units only in a dividing cell

During division, chromatin condenses becoming thick enough to be discerned as separate structures called chromosomes.

nucleosomes - formed from DNA around histone molecules

histones - proteins that are wrapped with DNA

Chromosome DistributionEach eukaryotic species has a certain number of chromosomes

Example: Human

Somatic (body cells): 46 chromosomes in nucleus (diploid; 2n)

Sex cells (sperm/egg): 23 chromosomes (haploid; n)

Chromosomesmade of DNA and protein - highly condensed and tightly wound so its easier to move from one cell to the next

counted by the number of centromere not the number of chromatids

before and after replication

VocabularyCentrioles: small, cylinder shaped structures found near the nucleus, involved in mitosis

only in animal cells

Aster - star like structure made of microtubules that extend from centrioles

Spindle fibers - web like structures made up of microtubule fibers - arranges and moves the chromosomes around

The Cell Cyclehttp://highered.mcgraw-hill.com/sites/0072943696/

student_view0/chapter3/animation__how_the_cell_cycle_works.html

The mitotic phase alternates with interphase in the cell cycle

G1 phase, S phase, G2 phase

Mitosis Phases: prophase, metaphase, anaphase, telophase

Cytokinesis: The mitotic spindle distributes chromosomes to daughter cells

The steps of mitosis ensure that each new cell has the exact number of chromosomes as the original

The Cell Cycle

Interphase

growth phase

technically not part of mitosis, but it is included in the cell cycle

Cell is in a resting phase, performing cell functions

G1 (growth 1), S (DNA Synthesis), G2 (growth 2)

Interphase G1normal cell function and cell growth

DNA is in the chromatin state (kind of like spaghetti)

cells duplicate contents excluding the chromosomes (organelles)

Interphase Schromatin begins to form chromosomes

DNA replicates copies of chromosomes

there are still 46 chromosomes

counted by centromeres

Interphase G2chromosomes are still forming, not yet visible

continues to prepare for division

double checks copies of chromosomes to ensure no errors - makes repairs

centrioles formed

ProphaseChromatin finishes condensing into chromosomes

Become visible

2 chromatids joined by a centromere

Centrioles move to the opposite sides of the nucleus

Nuclear membrane disintegrates

Nucleolus disappears

Spindle forms

Early & Late Prophase

MetaphaseChromosomes line up on the equator of cell

chromosomes meet in the middle; “they meta at the middle”

Chromosomes become attached to spindle fibers by centromeres

AnaphaseSpindle fibres contract dividing centromere

Chromosomes get pulled apart

there are 92 chromosomes in this phase

Chromatids separate and move to the opposite poles of the cell

TelophaseNow there are two nuclei with 46 identical chromosomes in each

Chromosomes unwind back into chromatin

Nuclear membrane reforms

Nucleolus reappears

Spindle disappears

Centrioles duplicate

Cytokinesis

Division of the cytoplasm to form 2 new daughter cells via the cellular membrane.

Process follows telophase

Daughter cells are genetically identical

Animals: cell pinches inward (cleavage furrow)

Plants: a new cell wall between the two new cells (cell plate)

following this stage, the cells individually begin interphase G1

Cytokinesis

Following DNA replication during interphase, each chromosome in the parental nucleus is duplicated and consists of two sister chromatids.

During mitosis, the centromeres divide and the sister chromatids separate, becoming daughter chromosomes that move into the daughter nuclei.

Therefore, daughter cells have the same number and kinds of chromosomes as the parental cells.

Daughter Cells

Regulating Cell CycleCyclins - regulate the timing of the cell cycle in eukaryotic cells

Internal regulators: proteins that respond to events inside the cell

External regulators: proteins that respond to events outside the cell

A molecular control system drives the cell cycle

http://highered.mcgraw-hill.com/sites/0072943696/student_view0/chapter3/

animation__control_of_the_cell_cycle.html

Additional Resources

Mitosis: https://www.youtube.com/watch?v=f-ldPgEfAHI

Chromosomes: https://www.youtube.com/watch?v=gcz1FOWw0Cg