5.1 The Cell Cycle TEKS 5A The student is expected to: 5A describe the stages of the cell cycle,...

5.1 The Cell Cycle TEKS 5A

The student is expected to:

5A describe the stages ofthe cell cycle, includingdeoxyribonucleic acid (DNA)replication and mitosis, and theimportance of the cell cycle to thegrowth of organisms


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


The cell cycle has four main stages.

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


• The main stages of the cell cycle are gap 1, synthesis, gap 2, and mitosis.

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

• Mitosis occurs only if the cell is large enough and the DNA undamaged.

– DNA synthesis (S): copies DNA

– Gap 2 (G2): additional growth

– Mitosis (M): includes division of the cell nucleus (mitosis) and division of the cell cytoplasm (cytokinesis)


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).

Limits to cell growthLimits to cell growth1.1. DNA “DNA “overload”overload”:: The larger a The larger a

cell becomes, the more cell becomes, the more demands the cell places on its demands the cell places on its DNA.DNA.

a)a) DNA stores the information that DNA stores the information that controls body functionscontrols body functions

b)b) WWhen a cell is small, DNA can hen a cell is small, DNA can easily control the cell’s easily control the cell’s functions and meet its needs.functions and meet its needs.

c)c) When a cell is large, it still only When a cell is large, it still only has one copy of DNA, so it is has one copy of DNA, so it is more difficult for the cell to more difficult for the cell to perform its functionsperform its functions. .

2.2. ExExchanging materialschanging materials: :

• Large cells have more trouble moving Large cells have more trouble moving substances across the cell membrane.substances across the cell membrane.

• If a cell is too large, it is difficult to get If a cell is too large, it is difficult to get enough oxygen and nutrients in and waste enough oxygen and nutrients in and waste products outproducts out

Limits to cell growth

Division of the CellDivision of the Cell

When a cell gets When a cell gets too large, it : too large, it :

1. makes a copy of its DNA (replication),1. makes a copy of its DNA (replication),

and then…and then…

2. divides to form two “daughter” cells.2. divides to form two “daughter” cells.


Cell size is limited.

• Volume increases faster than surface area.

Surface area to volume ratios

• 1 X 1 X 1 cube SA:______ volume: _____

• 2 X 2 X 2 cube SA:______ volume: _____

• 10X10X10 cube SA:______ volume: _____

• So when volume doubles, the surface area cannot “keep up” with it

6 1

24 8

600 1,000


• Surface area must allow for adequate exchange of materials.

– Cell growth is coordinated with division.

– Cells that must be large have unique shapes.

5.2 Mitosis and Cytokinesis TEKS 5A


5A describe the stages of

the cell cycle, including

deoxyribonucleic acid (DNA)

replication and mitosis, and the

importance of the cell cycle to the

growth of organisms


KEY CONCEPT Cells divide during mitosis and cytokinesis.

Before a cell gets too big, it will divide to form two “daughter cells”

Before a cell divides, it makes a copy of its DNA for each daughter cell.

Cell Division1. Cell division in eukaryotes is more complex than in

prokaryotes.2. There are two stages of eukaryotic cell division

a. Mitosis: Division of the cell nucleusb. Cytokinesis: Division of the cell cytoplasm

3. Unicellular organisms reproduce asexually by mitosis or something similar to mitosis (prokaryotes cant do mitosis!)

a. The daughter cells are identical to the parents cells

Asexual Reproduction

• Is one cell reproducing by itself

• Two types:

1. Binary Fission: organism replicates its DNA and divides in half, producing two identical daughter cells

• Example: bacteria

2. Budding: asexual process by which yeasts increase in number

Budding Binary Fission

Chromosomes1. Chromosomes are made of condensed

chromatin.2. Chromatin consists of DNA and the

proteins it is wrapped around.3. The cells of every organism have a specific

number of chromosomes 1. Ex. humans have 46 chromosomes


Chromosomes condense at the start of mitosis.

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

DNA doublehelix

DNA andhistones

Chromatin

SupercoiledDNA


• DNA plus proteins is called chromatin.

• One half of a duplicated chromosome is a chromatid.

• Sister chromatids are held together at the centromere.

• Telomeres protect DNA and do not include genes.

Condensed, duplicated chromosome

chromatid

telomere

centromere

telomere

At the ends of each chromatid is an area called the telomere.

- The telomere is filled with non-coding DNA- Like a protective cap- Gets shorter during each cell division- Shortening is believed to be linked to aging

Telomeres

Chromatin v. chromosomes

4. Chromosomes are only visible during cell division, when they are condensed. The rest of the time the chromatin is spread throughout the nucleus.

5. Before cell division, each chromosome is replicated (meaning copied)a) When a chromosome is replicated, it consists of

two identical “sister” chromatids.b) When a cell divides the chromatids separate,

and one goes to each of the two new cells.

c) Sister chromatids are attached to each other at the spot called the centromere.


Parent cell

centrioles

spindle fibers

centrosome

nucleus withDNA

Mitosis and cytokinesis produce two genetically identical daughter cells.

• Interphase prepares the cell to divide.

• During interphase, the DNA is duplicated.

The Cell Cycle• When a cell is NOT dividing, it is said to be

in interphase.

• The series of events that a cell goes through as it grows and divides is called the cell cycle.

Events of the cell cycleInterphase, when the cell is NOT dividing, has three

phases: G1, S, and G2.

1. G1 phase: period of activity in which cells do most of their growing.

a. Cells increase in size

b. Cells synthesize (make) new proteins and organelles

2. S phase: DNA (chromosomes) is replicated

3. G2: organelles and molecules required for cell division are produced

M phase is the phase of cell division. This includes:

1. Mitosis, the division of the cell nucleus, which is made up of four segments

including prophase, metaphase, anaphase, and telophase.

2. Cytokinesis, or the division of cytoplasm.

M phase

G2 phase

S phase

G1 phase


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

– During prophase, chromosomes condense and spindle fibers form.

MitosisThere are four phases in mitosis:

1. Prophase

a. Longest phase in mitosis (take 50- 60% of total time mitosis requires)

b. Chromosomes become visible because they are

condensed

c. Centrioles become visible on opposite sides of the nucleus

i. The centrioles help organize the spindle, a structure made of microtubules that helps

separate the chromosomesii. Chromosomes attach to the spindle

fibers near the centromereiii. Plant cells to not have centrioles but do

have mitotic spindles

d. Nucleolus disappearse. Nuclear envelope breaks down



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

2. Metaphasea. Chromosomes line up in the center of

the cellb. Microtubules connect to the

centromeres



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

3. Anaphasea. Centomeres split and the sister

chromatids separate and become individual chromosomes

b. Chromosomes move and separate into two groups

near the spindle

c. Anaphase ends when the chromosomes stop moving



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

4. Telophase

a. Chromosomes change form being condensed to dispersed

b. A nuclear envelope forms around each cluster of chromosomesc. Spindle breaks apartd. Nucleolus is visible in each daughter nucleus

Telophase in the midbodies of two daughter cells


• Cytokinesis differs in animal and plant cells.

– In animal cells, the membrane pinches closed.

– In plant cells, a cell plate forms.

Cytokinesis• Mitosis occurs within the cytoplasm of one cell.• Cell division is complete when the cytoplasm

divides.• In plants, a structure called the cell plate forms

between the two daughter nuclei. The cell plate develops into a cell membrane and cell wall.

• In animal cells, the cell membrane is drawn inward until the cytoplasm is pinched into two equal parts. Each part has a nucleus and cytoplasmic organelles.

Cytokinesis

The cleavage of daughter cells is almost complete; this is visualized by microtubule staining

Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomesMetaphase

Centriole

Spindle

CentrioleChromosomes (paired

chromatids)

Prophase

Centromere

Spindle forming

5.3 Regulation of the Cell Cycle TEKS 5A, 5B, 5C, 5D, 9C


5A describe the stages of

the cell cycle, including

deoxyribonucleic acid (DNA)

replication and mitosis, and the

importance of the cell cycle to the

growth of organisms;

5B examine specialized cells, including roots, stems, and leaves of plants; and animal cells such as blood, muscle, and epithelium;


(Continued)

5C describe the roles of DNA,

ribonucleic acid (RNA), and

environmental factors in cell

differentiation;

5D recognize that disruptions of

the cell cycle lead to diseases

such as cancer;

9C identify and investigate the role of enzymes


KEY CONCEPTCell cycle regulation is necessary for healthy growth.

Regulating the Cell Cycle

Different cell types divide at different rates.

Examples:– Muscle cells and nerve cells do not divide once

they have developed. – Skin cells and cells in the bone marrow that

make blood cells divide rapidly.

Regulating Cell Divisions

• Internal regulators – Signals from within the cell to regulate the cell cycle. – They make sure everything is complete

before moving on.

Regulating Cell Divisions

• External regulators – Stimulate or suppress cell growth by recognizing the surrounding situation. – Injury repair– Embryonic stem cell differentiation


Internal and external factors regulate cell division.

• External factors include physical and chemical signals.• Growth factors are proteins that stimulate cell division.

– Most mammal cells form a single layer in a culture dish and stop dividing once they touch other cells.


• Two of the most important internal factors are kinases and cyclins.

• External factors trigger internal factors, which affect the cell cycle.

Proteins called Cyclins are present when the cell is dividing and are absent when the cell is not dividing.

They regulate the timing of the cell cycle

Controls on cell division• Cell growth and cell division can be turned

on and off.

• When you are injured your cells divide rapidly to repair the injury. When the injury has healed, the cells stop dividing.


– a normal feature of healthy organisms– caused by a cell’s production of self-destructive

enzymes– occurs in

developmentof infants

webbed fingers

• Apoptosis is programmed cell death.

Uncontrolled cell growthWhen cells in your body CANNOT control cell growth and division, cancer may form.

1. Cancer cells cannot respond to the signals that regulate the division of cells.

2. When cancer cells have been dividing uncontrollably, tumors form.

3. Tumors can damage surrounding tissue.4. Cells from tumors can break free and travel to

other parts of the body, forming new tumors.


Cell division is uncontrolled in cancer.

• Cancer cells form disorganized clumps called tumors.

cancer cellbloodstream

normal cell

– Benign tumors remain clustered and can be removed.– Malignant tumors metastasize, or break away, and can

form more tumors.

Cancer• Cancer cells tend to have a damaged

oncogene. – This gene possess the information needed to

respond to internal and external regulators.

During the Reading

Define the following

1. Metastasis :

2. Benign:

3. Malignant:

The process or condition of abnormal cell migration and tissue invasion.

Cells that stay where they are usually considered as a Tumor. (Not Cancer)

Cells can break off and infect other areas of the body (Cancer)

There are several reasons that cells may lose the ability to control growth.

Examples:1. smoking2. radiation exposure3. viral infection

Scientists who study cancer are researching how cells divide.


• Cancer cells do not carry out necessary functions.

• Cancer cells come from normal cells with damage to genes involved in cell-cycle regulation.


• Carcinogens are substances known to promote cancer.

• Standard cancer treatments typically kill both cancerous and healthy cells.

Reviewing Mitosis

When does the following occur?

(Name the phase of the cell cycle. If it is in mitosis, name the phase of mitosis)

1. Sister chromatids separate.

2. Chromosomes line up across the center of the cell.

3. The cell’s DNA molecules are copied.

4. The cytoplasm pinches in half.

5. A spindle forms.

Mitosis - Anaphase

Mitosis - Metaphase

S Phase

Cytokinesis

Mitosis - Prophase

What are the structures shown?

How many copies of the cell’s DNA are

shown here?

A. Sister chromatids

B. Centromere

2

Cell Cycle

Interphase ? Phase

Mitosis Cytokinesis

? ? ??

M Phase

Prophase

Metaphase

Anaphase Telophase

A

B

C

What is the name of the structure labeled:

A? __________________

B? __________________

C? __________________

Chromosome

Centriole

Spindle fiber

If your were to examine a sample of 1000 cells undergoing mitosis, in which of the phases listed below would you expect to find most of the cells?

A. Prophase

B. Metaphase

C. Anaphase

D. Telophase

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5.1 The Cell Cycle TEKS 5A The student is expected to: 5A describe the stages of the cell cycle,...

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