Cell Growth and DivisionChapter 10

In Your Notebook• 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.• 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 take to 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?

Think About It• When a living thing grows, what

happens to its cells?• Does an organism get larger because

each cell increases in size or because it produces more cells?

• What is there about growth that requires cells to divide and produce more of themselves?

Limits to Cell Size• All cells can increase in size• Eventually they have to divide• Two Reasons for division

• Larger cells place more demands on DNA

• Larger cells less efficient moving materials across cell membrane

Reason #1 – Information Overload• Even though the cell gets larger its

DNA does not• Example:

• small town – small library – limited number of books – people have to wait to borrow books

• If town grows – so does demand for books – have to build bigger library

• DNA is our “genetic library”

Reason #2 – Exchanging Materials• Need to get food in and waste out as

quickly as possible• Want large surface area to volume ratio

Traffic Problems• If town only had two-lane main street

leading to center of town – as town grows – traffic gets congested –

becomes difficult to move

goods in and out• Same for cell – can’t get

Oxygen and nutrients in

and waste products out• So – cells don’t keep

growing larger even if

organism does

Cell Division• Process by which a cell divides into

two new daughter cells• DNA replicates

•Cuts down on DNA overload• Reduces cell volume

•So materials can move in and out

quickly

In Your Notebook• Write two short summary statements

that explain why information overload and exchanging materials limit cell size.

Types of Reproduction - #1• Asexual

• Production of genetically identical offspring from a single parent•Simple, efficient, effective•Population can grow quickly•Used by single-celled organisms

•Bacteria•Used by multi-celled organisms

•budding

Asexual – The Good & The Bad• Advantages

• For bacteria, when conditions are right, faster reproduction means better chance of survival

• As long as conditions stay right being genetically identical is also good

• Disadvantage• When conditions change –

everyone dies

Types of Reproduction - #2• Sexual

• Fusion of two cells• Need mommy and daddy• Offspring inherit some of their

genetic information from each parent

• Used by most animals and plants•Also many single celled organisms

Sexual – The Good & The Bad• Advantages

• When seasons affect food supply it can be better to take time to find mate and grow and develop offspring

• Provides genetic diversity• If environment changes some

offspring may have right combination of characteristics to survive

• Disadvantage• Takes a long time• Can’t do it alone

In Your Notebook• Use a Venn Diagram to compare

asexual and sexual reproduction

• Look on page 277 if you need ideas

10.2 – Cell Division• The cell cycle represents the events that

take place as a cell grows, prepares for division, and then divides into two new cells. Once two new cells have formed, they each begin the cycle anew.

• Like other cycles, the cell cycle is broken into phases. Different types of cells and cells from different organisms may show slight variations in some of the phases of the cycle, but the general course of events is similar for all living things.

In Your Notebook1. Why do you think it is advantageous for cells to

go through the different events of the cell cycle (such as copying their genes or building

the materials needed for division) in an ordered way? What might happen if a cell underwent all of these activities at once?

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 of the events leading up to cell division took place as they should, but the cell did not divide?

Think About It• What role does cell division play in your

life?• What happens when you are finished

growing?• Does cell division stop?• What if you break a bone or get a cut?• What about general wear and tear

• Like on your skin, digestive system or even your blood?

Chromosomes• Bundled packages of DNA

• Read “What is the role of chromosomes in cell division” on page 279

Prokaryotic Chromosomes• Prokaryotes have no nucleus• DNA

• Found in cytoplasm• Single, circular chromosome

Eukaryotic Chromosomes• More DNA than prokaryotes• Multiple chromosomes in cell

• Fruit flies – 8• Humans – 46• Carrots - 18

• Found in nucleus• Contain DNA and proteins (histones)

Eukaryotic Chromosomes• Which side, left or right, shows the

smallest structures, and which shows the largest?

The Cell Cycle• A series of events during which the

cell grows, prepares for division then divides into two daughter cells.

Prokaryotic Cell Cycle

• Binary Fission• Result: Two genetically

identical daughter

cells

In Your Notebook• Why does the cell duplicate its DNA?

• What might happen if

the membrane did not

indent and pinch off?

The Eukaryotic Cell Cycle

• Four phases• G1, S, G2 and M

• Timing of cycle

depends on the

type of cell

Phases of Cell Cycle• G1

• Most growing happens here• Cell increases in size• Makes new proteins

and organelles

G = Gap

Phases of Cell Cycle• S phase

• S = Synthesis• DNA replicated

Phases of Cell Cycle• G2

• Preparing for division• Organelles and

molecules for division

produced

G1, S and G2 are

together known as

Interphase

Phases of Cell Cycle• M Phase• Cell division

• Includes mitosis and cytokinesis•Mitosis

•Division of nucleus•Cytokinesis

•Division of cytoplasm

What’s a Chromosome?• Chromatin – uncoiled DNA• Chromatid – coiled DNA• Centromere – where duplicate

strands attach

Mitosis – Four steps to divide nucleus prophase, metaphase, anaphase & telophase

• Prophase• Genetic material in nucleus condenses• Chromosomes become

visible• Spindle starts to form• Centrioles move toward

poles• Nucleolus disappears• Nuclear envelope starts

to break down

Mitosis – Four steps to divide nucleus

prophase, metaphase, anaphase & telophase

• Metaphase• Chromosomes line up in middle of

cell• Spindle fibers

connect to

centromeres

Mitosis – Four steps to divide nucleusprophase, metaphase, anaphase & telophase

• Anaphase• Sister chromatids separate and move

apart• Move along spindle

fibers to opposite

ends of cell

Mitosis – Four steps to divide nucleusprophase, metaphase, anaphase & telophase

• Telophase• Chromosomes spread out into tangle

of chromatin• Nuclear envelope

reforms• Spindle breaks

apart• Nucleolus reforms

In Your Notebook• Create a chart that lists two important

pieces of information about each phase of mitosis.

Cytokinesis• Now that the nucleus is split we have

to divide the cytoplasm• Animals

• Membrane drawn in

and pinches apart

• Plants• Cell plate forms

between new nuclei

Cells Alive

• http://cellsalive.com/mitosis.htm

In Your Notebook• You are going to write a memoir as if you

were a cell that just divided. Answer the following as you go:

• Why did you decide to divide?• Were there signals that told you it was time?• Describe how you divided.

• What happened?• In what order?

• Talk about why each process you went through was important to you and your daughter cells.

10.3 & 10.4• Regulating The Cell Cycle and• Cell Differentiation

• In Your Notebook• Name two things that might go

wrong if the cell cycle is not carefully regulated.

Controls on Cell Division• Cells grown in dish in lab will stop dividing when

they touch other cells• Scrape away neighboring

cells and the cells left start

dividing again• When you are injured the

cells at the edge start dividing

until healing process is done.

Cyclins and Regulatory Proteins• Cyclins

• Family of proteins that tell cell when it is time to divide, duplicate chromosomes of enter next phase of cell cycle

• Internal Regulators• Respond to events inside cell• Won’t let cell enter mitosis without duplicating

chromosomes first

• External Regulators• Looks at things outside the cell• Growth factors stimulate growth and division

Apoptosis• Programmed cell death• Helps shape structure of tissues and organs• We don’t have webbed feet because cells in

between toes are

programmed to die• If they don’t you

have disease known

as syndactily

Cancer• These cells don’t respond to

signals that control growth• Divide uncontrollably• Caused by:

• Gene defect• Smoking• Chewing tobacco• Radiation exposure• Viral infection

Cancer Treatments• Surgery

• Physical removal of tumor

• Radiation• Targeted beam that kills rapidly dividing cells

• Chemotherapy• Targets rapidly dividing cells throughout body• Hair, skin and digestive system cells normally divide

rapidly so the healthy cells as well as the cancer cells are damaged• This makes your hair fall out• Gives you mouth sores• Intense nausea

In Your Notebook• What makes cancer cells different from healthy

cells?

• When researchers develop drugs to fight cancer, what characteristics of cancer cells do you think they target?

• The human body contains 100,000,000,000,000 cells. Starting with one cell – how many divisions would you need to get to this number?

One Cell To Many• We are start out as a single cell, become

embryo, then adult• Differentiation

• Process by which cells become specialized

Pg 293

Stem Cell Development• Embryo

• Totipotent• Can become anything

• Blastocyst• Four days of development• Hollow ball with cluster

of cells inside• Pluripotent

• Can become

almost anything

Stem Cell Development• Embryonic Stem Cells

• The cluster of cells inside the blastocyst• Pluripotent

• Can become practically anything in the body• Adult Stem Cells

• Multipotent• More limited potential but can develop into many

different types of cells• Bone marrow stem cells can become several

different types of blood cells• Stem cells in brain can produce neurons or nerve

cells

Stem Cell Research• Benefits

• These cells could be used to repair or replace damaged cells and tissues• Heart attack• Paralysis

• Ethical Issues• Right now using embryonic stem cells kills embryo• Is the embryo entitled to the rights and protections of

any human being?• On the horizon

• Working to extract cells without harming embryo• Finding ways get adult stem cells to act like

embryonic ones

In Your Notebook• Why is differentiation important to

multicellular organisms?

• What are the three different types of stem cells and their respective potential to differentiate?

• How might technological advances help address the ethical concerns surrounding stem cell research?