10.2 the cell cycle - mrs. hazel's class website -...

Lesson Overview The Process of Cell Division

10.2The Cell Cycle


Review: Limits to Cell Size

• As a cell becomes larger, volume increases faster than surface area

• Causes problems with material transport

• Larger cells need more “stuff”, but only so much can cross the membrane at a time

• Cell division solves a cell’s size problem

• A cell needs a large surface area relative to its volume (high surface to volume ratio).


THINK ABOUT IT

What role does cell division play in your life?

Does cell division stop when you are finished growing?


Role of Cell Division

• Growth! Must increase the number of cells.


Role of Cell Division

• Replace dead or damaged cells.


Chromosomes• Essential genetic

information

Contained in the nucleus

• Hold the code or “instructions” for organisms

• Must make a copy beforedividing! Human Male Karyotype (23 pairs of chromosomes)


Chromosomes carry genetic information that is passed on

from one generation of cells to the next.

• Cells must copy their genetic information before cell

division.

• Each daughter cell (new cell) gets a copy of genetic

information.

Cells of every organism have a specific number of

chromosomes.

Chromosomes


Chromosomes

What is the role of chromosomes in cell division?

Chromosomes make it possible to separate DNA

precisely during cell division.

**It is critical that each daughter cell gets the same

amount of DNA!!


Prokaryotic Chromosomes

Prokaryotic cells lack nuclei.

• DNA molecules are found in the cytoplasm.

• Most contain a single, circular DNA molecule

(chromosome)


Eukaryotic Cells

• DNA contained in a nucleus

• More DNA = multiple chromosomes

• Ex: Humans have 46 chromosomes, Fruit flies have 8 chromosomes and carrots have 18 chromosomes

• DNA packaged very tightly

Chromosomes make it possible to separate DNA precisely during cell division.


Eukaryotic Chromosomes

In eukaryotic cells,

chromosomes are

located in the

nucleus, and are

made up of

chromatin (DNA &

protein).Chromatin


Chromatin is made of DNA and histone proteins.

Chromatin


DNA coils around histone proteins to form nucleosomes.

Chromatin


The nucleosomes interact with one another to form

coils and supercoils that make up chromosomes.

Chromatin


1. Overall, DNA has a negative charge. Look at the histone proteins in the figure. What type of overall charge do you think they have?

2. What is the relationship between a molecule of DNA and a chromosome?


The Cell Cycle

What are the main events of the cell cycle?

During the cell cycle, a cell grows, prepares for

division, and divides to form two daughter cells.


The Prokaryotic Cell Cycle

The prokaryotic cell cycle is a regular pattern of growth, DNA

replication, and cell division.

Most prokaryotic cells begin to replicate, or copy, their DNA once they

have grown to a certain size.

When DNA replication is complete, the cells divide through a process

known as binary fission.


• Pattern of growth, DNA replication, and cell

division.

• Begin to replicate, or copy, their DNA once they

have grown to a certain size.

• Cells divide through a process known as binary

fission.

• Binary fission is when two genetically

identical cells are produced (asexual)

• Ex: bacteria

The Prokaryotic Cell Cycle


The Eukaryotic Cell Cycle

Four phases: G1, S, G2, and M.

Interphase includes G1, S, & G2 and

is a period of growth between cell

divisions.

M phase is the period of cell division.


Information from this point is addressed in the Cell Cycle & Mitosis small group activities completed in class.


G1 Phase: Cell Growth

Cells:

• Increase in size

• Synthesize new proteins

and organelles


S Phase: DNA Synthesis (Replication)

• New DNA is synthesized by

replicating the chromosomes


G2 Phase: Preparing for Cell Division

• Organelles and molecules

required for cell division are

produced.


M Phase: Cell Division

Two stages:

1. Mitosis is the division of

the cell nucleus.

2. Cytokinesis is the division

of the cytoplasm.


Mitosis: Prophase, Metaphase,

Anaphase, Telophase…. PMAT

What events occur during each of the four

phases of mitosis?


Important Cell Structures Involved in

Mitosis

Chromatid – each strand of a duplicated chromosome

Centromere – the area where each pair of chromatids is joined

Centrioles – tiny structures located in the cytoplasm of animal cells that

help organize the spindle

Spindle – a fanlike microtubule structure that helps separate the

chromatids


1. Prophase

a. Duplicated chromosome

condenses and becomes visible.

b. Centrioles move to opposite sides

of nucleus to help organize the

spindle.

c. Mitotic spindle forms and DNA

strands attach at centromere.

d. Nucleolus disappears & nuclear

envelope breaks down.


2. Metaphase

a. Chromosomes line up across

the middle of the cell.

b. Spindle fibers move the

centromere of each

chromosome to the two poles

of the spindle.


3. Anaphase

a. Centromeres are pulled

apart

b. Chromatids separate to

become individual

chromosomes near the

poles of the spindle.


4. Telophase

a. Chromosomes spread out

into a tangle of chromatin

b. Nuclear envelope re-forms

around each cluster of

chromosomes.

c. Spindle breaks apart, &

nucleolus becomes visible in

each daughter nucleus.


Cytokinesis

How do daughter cells split apart after mitosis?


Cytokinesis

How do daughter cells split apart after mitosis?

Cytokinesis completes the process of cell division – it splits one cell into

two.


Cytokinesis is the division of the cytoplasm.

The process of cytokinesis is different in animal and plant cells.

Cytokinesis


Cytokinesis in Animal Cells

The cell membrane is drawn in until the cytoplasm is pinched into

two equal parts.

Each part contains its own nucleus and organelles.


Cytokinesis in Plant Cells

In plants, the cell membrane is not flexible enough to draw inward

because of the rigid cell wall.

Instead, a cell plate forms between the divided nuclei that develops into

cell membranes.

A cell wall then forms in between the two new membranes.


The Stages of the Cell Cycle

10.2 the cell cycle - mrs. hazel's class website -...

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