What do you want to be when you grow up???

Cell Differentiation

• Zygotes (sperm + egg) first divide into embryonic stem cells.

• Stem cells develop in two stages. – Determination-cells commit to become one

cell type– Differentiation-cells acquire specialized

structures and functions of highly specialized cells

• Specific genes are turned on and off

Quick Question…

• How does the process of cell determination differ from the process of cell differentiation?

Cell Cycle &

MitosisChapter 5

Hmm…

• Why do you have to keep cutting your fingernails….grass……hair??

Cell cycle has 3 main phases

Cell Cycle

G1 phase S phase G2 phase

The cell grows The DNA replicates The cell prepares to divide

INTERPHASE

Parts of the Cell Cycle

• A. Interphase – Growth period of the cell. Consists of 3 phases:

• 1. G1 = Rapid growth and metabolic activity

(production of organelles)

• 2. S = DNA synthesis (replication)

• 3. G2 = Growth and protein synthesis (centrioles replicate)

G1 or gap 1

• phase in which daughter cells are growing and carrying out their normal functions (example: skeletal muscle cells-contract and joints move)

• the cells are 2n and 2c (they are diploid and have 2 copies of each of the chromosomes)

S phase or synthesis

• DNA replication occurs, making duplicate copies of each of the chromosomes in preparation for cell division (each chromosome consists of 2 sister chromatids which are tightly bound to each other)

• the cells are 2n and 4c (they are diploid, but have 4 copies of each chromosome)

A Chromosome

Chromosome

• Chromosome-one long continuous thread of DNA that consists of numerous genes along with regulatory information

G2 or gap 2

• the cells may grow more at this point

• at the end of G2, chromosomes begin to condense in preparation for cell division

Interphase

Interphase

• the "holding" stage or the stage between two successive cell divisions.

• Some 90% of a cell's time in the normal cellular cycle may be spent in this phase

C= chromatinI = nucleolus

Mitosis

Prophase Metaphase Anaphase Telophase

M Phase

2 processes involved in Division– Mitosis-division of cell nucleus and its

contents– Cytokinesis-process that divides the cell

cytoplasm

– Result of mitosis is two daughter cells that are genetically identical to the original

Cells divide at different rates

• Prokaryotes typically divide faster because they do not have membrane bound organelles and cytoskeleton

Prophase

The nuclear membrane breaks down and the chromosomes become short and thick.

By late prophase, individual chromosomes are visible, appearing as two parallel threads attached at a constriction point called the centromere.

Prophase

• the chromatin condenses into discrete chromosomes.

• The nuclear envelope breaks down and spindles begin to move to the opposite "poles" of the cell.

Prophase

Metaphase

The spindle fibers attach to each chromosome on either side of its centromere. The spindle fibers force the chromosomes into a tight plane which is a circle around the middle of the cell

Metaphase

• the nuclear membrane disappears completely.

• The spindle fully develops and the chromosomes align at the metaphase plate (a plane that is equally distant from the two spindle poles).

Ch= chromosomeS= spindle

Metaphase

Anaphase

• Anaphase is the shortest stage of mitosis and is the separation of the chromosomes. The chromatids that were attached to the same centromere now separate and move to opposite poles of the spindle. The chromosome arms from a “V” as they are dragged through the cytoplasm. By the end of anaphase, chromosomes have been separated into two genetically identical nuclei.

Anaphase

• the paired chromosomes (sister chromatids) separate. Spindle fibers attached to the sister chromatids shorten and begin moving them to opposite ends (poles)

Anaphase

Early Telophase

• nuclei begin to form at opposite poles. Cytokinesis, the division of the original cell's cytoplasm, also begins.

• In plants, the cell begins to form a cell wall.

Late Telophase

• the chromosomes are cordoned off in distinct new nuclei in the emerging daughter cells.

• The division of the original cell's cytoplasm is called cytokinesis

Telophase

Telophase is prophase in reverse. The spindle fibers disappear, a nuclear membrane forms around each of the two sets of chromosomes, and a nucleoli appears in each new nucleus. The chromosomes become longer.

Telophase

Cytokinesis

Cytokinesis splits the cytoplasm of dividing cell into daughter cells.

Cytokinesis

Can you identify?

Can you identify?

What phase?

What phase?

Name that phase!

Name that phase!

Onion Root Tip

Onion Root tip