Cell Growth Cell Cycle Mitosis & Cytokinesis

Chapter 10

Limits to Cell Growth

– The larger a cell becomes, the more demands the cell places on its DNA.

– In addition, the cell has more trouble moving enough nutrients and wastes across the cell membrane.

Ratio of Surface Area to Volume

•  As the size of a cell increases, its volume increases faster than the surface area.The decrease in the cell’s ratio of

surface area to volume makes it more difficult for the cell to move needed materials in and waste products out quickly enough for the cell to survive.

Ratio of Surface Area to Volume

Cell Cycle Micrograph

Cell Cycle

Events of the Cell Cycle

Cell Cycle

The cell cycle is the series of events that cells go through as they grow and divide.

Interphase is the period of growth that occurs between cell divisions.

90% of the cell’s time is spent here.

The Phases of the Cell Cycle

The cell cycle consists of four phases:

– G1 (First Gap Phase)

– S Phase (Synthesis Phase)

– G2 (Second Gap Phase)

– M Phase (cell division)Mitosis (Prophase, Metaphase,

Anaphase, Telophase) Cytokinesis (division on cytoplasm)

G1, S, G2= INTERPHASE

Events of the Cell Cycle

During G1 (First Gap phase) the cellincreases in sizesynthesizes new proteins and organelles

During the S (Synthesis phase),chromosomes are replicated or copiedDNA synthesis takes place

– Once a cell enters the S phase, it usually completes the rest of the cell cycle.

During G2 Phase (Second Gap Phase) Copying of certain organelles and molecules required for cell division occursOnce G2 is complete, the cell is ready to start the M phase—Mitosis

Interphase

“Intermission” Normal metabolic

activities Major state cell

spends 90% of time here

DNA= chromatin NOT a stage of

mitosis

Late Interphase (S and G2)

Prepares for mitosis

DNA doubles=Sister chromatidsCentrioles

double in animals

Cell Division

In eukaryotes, cell division occurs in two major stages. The first stage, division of the cell nucleus, is called

mitosis. The second stage, division of the cell cytoplasm, is

called cytokinesis. FYI Some books will put cytokinesis as the last step of

mitosis

Why do cells divide by Mitosis?

Growth &Repair

Reproduction of single celled organisms under conditions Amobea

Reproducing

Cells dividing by Mitosis…….

Identical to original cell

Same chromosome #

Identical chromosome makeup

Skin

Duplicated Chromosome(After S phase of Interphase):

SisterChromatids

Centromere

A Duplicated Chromosome

one chromatid

its sisterchromatid

One chromosome in the duplicated state

centromere

Diploid vs. Haploid

Diploid= 2 sets of chromosomes– One set from mom and one set from dad– Chromosomes come in pairs– Humans have 23 pairs of chromosomes– Somatic Cells all cells except sperm and

egg

Diploid vs. Haploid

Haploid = 1 set of chromosomes– Sperm or egg (sex cells) have

23 single chromosomes

Stages of Mitotic Cell Division

ProphaseMetaphaseAnaphaseTelophase

“1st” or “before”“middle”

“apart”“far” or separate

Stages of the cell cycle

Prophase

Nuclear membrane disappears

Doubled DNA = condensed

“chromosomes” form

Spindle fibers start to form

Metaphase

Mitotic spindle now formed

– By centrioles in animals– Spindle apparatus in

plants

Chromosomes line up mid- cell or center of cell

Anaphase

Chromosomes move to opposite pole pulled by spindle fibers

Separate chromosomes

Spindle & spindle fibers: Pull apart the sister chromatids

Spindle fibers

Telophase Cell divides Cell plate (plants) or

membranes (animals) form

Nucleus reappears (now 2 of them)

Chromosomes gather at opposite ends of the cell and lose their distinct shape.

Nuclear envelope reappears (now 2 of them)

Cytokinesis:cell’s cytoplasm divides & splits apart

Plant versus Animal Mitosis

Plant:Cell wall form from cell plate

Spindle apparatus

Animal:No cell wallmembrane

cytokinesis = cleavage furrow

Centrioles

Cytokinesis in Plants

In plants, a structure known as the cell plate forms midway between the divided nuclei. This will become the spot where the cell walls will form

Cell wall

Cell plate

Cytokinesis in Animals

Cleavage furrow forms

Cancerous cells……...

1.Divide too many times

2.Divide into more than two cells!

Masses of cells =– “tumors”

benign malignant

Onion Root Tip Micrographs of the Interphase and mitosis

Interphase

Prophase

Metaphase

Anaphase

Telophase

Identify the following

Identify the following

Identify the following

Identify the following

Identify the following

Identify the numbered cells

1.

2.

3

4

5.

Identify the numbered cells6

7 8