The Cell Cycle

Interest GrabberGetting Through

Materials move through cells by diffusion. Oxygen and food move into cells, while waste products move out of cells. How does the size of a cell affect how efficiently materials get to all parts of a cell?

Work with a partner to complete this activity.

Section 10-1

1. On a sheet of paper, make a drawing of a cell that has the following dimensions: 5 cm x 5 cm x 5 cm. Your partner should draw another cell about one half the size of your cell on a separate sheet of paper.

2. Compare your drawings. How much longer do you think it would taketo get from the cell membrane to the center of the big cell than from the cell membrane to the center of the smaller cell?

3. What is the advantage of cells being small?

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The Cell Cycle

Section Outline

• 10–1 Cell GrowthA. Limits to Cell Growth

1. DNA “Overload”

2. Exchanging Materials

3. Ratio of Surface Area to Volume

4. Cell Cycle

Section 10-1

Go to Section:

The Cell Cycle

1. Why can’t cells just get bigger and bigger?

2. Why do cells need to divide?

3. What is the cell cycle?

4. What are the stages of Mitosis?

5. What regulates cell division?

6. What happens if cells just keep on dividing?

The Cell Cycle

What limits Cell Growth?Materials (nutrients, wastes, signals, etc.) have to travel farther to get to and from the cell membrane.

DNA demandsMore proteins must be made from its DNA directions. A large cell would need more information from the command center and the ability to make more proteins, store food, water etc.

The Cell Cycle

A. DNA Overload

• If a cell gets too big, then there isn’t enough DNA directions to make all of the needed proteins.

• Imagine we were doing a lab to make a particular protein in class and we all had to share a single set of directions.

The Cell Cycle

What are the surface area to volume ratio problems?

As a cell gets larger its surface area to volume gets smaller. That means that a larger cell has less surface to get nutrients to the center.

The Cell Cycle

Cell size is limited.

• Volume increases faster than surface area.

There aren’t enough places on the membrane to get enough stuff in and out of the cell for the increasing volume that needs materials.

The Cell CycleB. Can’t Move Materials Efficiently

• Imagine 4 students in the corners of the gym passing an egg diagonally across the gym. Would be easier or harder for these 4 students to pass an egg in our classroom?

1. If the cell gets too big, food, gases, etc. cannot travel across the cell fast enough.

2. Volume grows faster than surface area of the cell membrane.

– surface area – the total area of the cell membrane

– Volume – how much material is in the cell

The Cell Cycle

What are the problems that cell division solves?

Each daughter cell receives its own set of DNA instructions.Each daughter cell is smaller and has a greater surface area, more materials can pass through the cell membrane.

The Cell Cycle

KEY CONCEPT Cells have distinct phases of growth, reproduction, and normal functions.

The Cell Cycle

A. Why do we need more cells?

1. Reproduction - Make more organisms

2. Growth and Development – all organisms start out as a single cell

3. Repair and Replacement – millions of our cells die every second of every day

The Cell Cycle

Checkpoint

1. Does surface area or volume change faster as a cell grows?

2. What are two problems a cell may have if it grew too big?

3. Why do we need to make more cells?

12

ANY QUESTIONS?

The Cell Cycle

Interest Grabber 10-2Cell Cycle

The cell cycle represents recurring events that take place in the period of time from the beginning of one cell division to the beginning of the next. In addition to cell division, the cell cycle includes periods when the cell is growing and actively producing materials it needs for the next division.

Section 10-2

1. Why is the cell cycle called a cycle?2. Why do you think that it is important for a cell to grow in size during its

cell cycle?3. What might happen to a cell if all events leading up to cell division took

place as they should, but the cell did not divide?

Go to Section:

The Cell Cycle

What are the contents of the nucleus?

Nucleolus: Small dense area in the nucleus where production of ribosomes begins.

DNA:

Genetic storage chains

Chromatin:

Condenses into chromosomes

The Cell Cycle

What are the chromosomes?They carry the DNA strands and proteins.The number of chromosomes identifies the organism. (Humans have 46)Before cell division chromosomes are replicated.

What are chromatids?The chromosome becomes a chromatid at the beginning of cell division. Two daughter chromatids are formed with a centromere at the center.

The Cell CycleB. Cell Division Requires Preparation!

• Do we have two of everything in our cells?

NO!

Most important = Cells only have one set of DNA instructions!!

1. First step in cell division is make a copy of the DNA.

2. Then copies must be separated and sorted into the two sides of the cell.

3. Then cell can split into two.

The Cell Cycle

Cell or Binary FISSION – Prokaryotes Divide

1. Single strand of circular DNA copied

2. DNA separates to opposite sides of the cell

3. Cell membrane/wall divides into two cells

The Cell Cycle

D. Asexual Reproduction

Reproduction of genetically identical offspring from a single parent (NO SEX!)

• Prokaryotic fission produces clones!• Daughter cells are identical to parent cell and only

one cell needed to make more organisms.• One way some organisms reproduce.

The Cell Cycle

Asexual Reproduction: Fission

Bacillus undergoing Fission

The Cell Cycle

E. Eukaryotes divide to make identical cells too.• More stuff to worry

about • nucleus with

nucleolus and nuclear membrane

• Chromosomes – not just one

• all that ‘stuff’ in the cytoplasm has to be dealt with.

Nucleus must divide before the cell can.

The Cell Cycle

The cell cycle has four main stages.

• The cell cycle is a regular pattern of growth, DNA replication, and cell division.

• During the cell cycle

a cell grows; prepares for division; and divides to form two daughter cells, each of which begins the cycle again

The Cell Cycle

– Gap 1 (G1): cell growth and normal functions

– DNA synthesis (S): copies DNA

– Gap 2 (G2): extra organelles and other materials needed for division are made

• 2 Phases of the cell cycle with each divided into more phases: Interphase and Mitosis

Interphase

The Cell Cycle

Events of the Cell Cycle

2. M phase = when cell is actually dividing –quick phase–Broken into 2 more phases

1.Mitosis = division of the nucleus- Prophase, metaphase, anaphase &

telophase (PMAT)

2.Cytokinesis = division of the cytoplasm

The Cell CycleThe Cell Cycle

M PHASE

G1

S

G2

Draw this in your notes!

The Cell Cycle

Cells divide at different rates.

The rate of cell division varies with the need for those types of cells.

Some cells are unlikely to divide (G0).

The Cell Cycle

• Surface area must allow for adequate exchange of materials.

– Cell growth is coordinated with division.

– Cells that must be large have unique shapes.

The Cell Cycle

Checkpoint

1. Why do eukaryotes need more preparation for cell division?

2. What are the two main phases of the cell cycle?

3. What happens during the S phase?

4. What are the two parts of the M phase?

27

ANY QUESTIONS?

The Cell Cycle

Mitosis and Cytokinesis

The Cell Cycle

KEY CONCEPT Cells divide during mitosis and cytokinesis.

The Cell Cycle

Chromosomes condense at the start of mitosis.

• DNA wraps around proteins (histones) that condense it.

DNA doublehelix

DNA andhistones

Chromatin SupercoiledDNA

The Cell Cycle

WHY?Organizes DNA so easy to separate copies correctly during cell division

The Cell Cycle

Chromosomes made of two identical chromatids.

chromatids - duplicated chromosomes attached at the center by the centromere

Centromeres - like a “twist tie” that holds the sister chromatids together.

• # of centromeres = # of chromosomescentromere

Draw/label in your notes!

The Cell Cycle

DNA copied in S phase condenses into

chromosomes during Prophase.

The Cell Cycle

Parent cell

centrioles

spindle fibers

centrosome

nucleus withDNA

• Interphase prepares the cell to divide.

• During interphase, the DNA is duplicated.

Mitosis and cytokinesis produce two genetically identical daughter cells.

The Cell Cycle

• Mitosis divides the cell’s nucleus in four phases.

– During prophase, chromosomes condense and spindle fibers form.

The Cell Cycle

• Mitosis divides the cell’s nucleus in four phases.

– During metaphase, chromosomes line up in the middle of the cell.

The Cell Cycle

• Mitosis divides the cell’s nucleus in four phases.

– During anaphase, sister chromatids separate to opposite sides of the cell.

The Cell Cycle

• Mitosis divides the cell’s nucleus in four phases.

– During telophase, the new nuclei form and chromosomes begin to uncoil.

The Cell Cycle

• Cytokinesis differs in animal and plant cells.

– In animal cells, the membrane pinches closed.

– In plant cells, a cell plate forms.

The Cell Cycle

1. Mitosis

• Division of the nucleus has 4 steps• PMAT

1. Prophase – DNA condenses, nuclear membrane dissolves, spindles form

2. Metaphase – Chromosomes line up on the equator (mid-line)

3. Anaphase – Chromatids pulled apart4. Telophase – nuclear membrane

reforms and cytokinesis begins

The Cell CycleINTERPHASE

a)Chromosomes line up on cell “equator”

a)Spindles pull chromatids apart

a)Single chromosomes at ends

b)nuclear membrane reforms

c)Cytokinesis

a)G1, S, G2b)Normal activities

c)DNA & stuff copied

3.ANAPHASE

2. METAPHASE

1. PROPHASEa)DNA condensesb)Spindles form at

polesc)Nuclear

membrane dissolves4. TELOPHASE

STAGES OF MITOSIS

Label handout!

The Cell CycleStages of Mitosis

1. Prophase– “first”

2. Metaphase– “middle”

3. Anaphase– “apart”

4. Telophase– “far” or “separate”

The Cell Cycle2. Cytokinesis - division of cytoplasm

• takes place during telophase

• animal cells – cytoplasm is pinched inward by cell membrane

• plant cells – a cell plate forms midway

The Cell Cycle

Checkpoint

Place these in order and name each stage.