Chapter 5

Cell Growth and Division

Think about baking cookies… If you want to make two batches of cookies,

what do you need to do to the recipe? Double all of the ingredients in the recipe

For cells to be functional after division, what needs to be present? A complete set of DNA, organelles, cell membrane,

and a cell wall if it is a plant cell.

5.1 The Cell Cycle Why do you always have to cut your hair and

nails? Growth is caused by new cells being made

The cell cycle has four main stages The cell cycle is a regular pattern of growth,

DNA duplication, and cell division that occurs in eukaryotic cells.

Four stages: Gap 1, Synthesis, Gap 2, Mitosis Gap 1, Synthesis, and Gap 2 make up a phase

called interphase

1. Gap 1 (G1) First stage of the cell cycle. 2. Cells carry out normal

functions during this stage. Example: If it is a muscle cell

it contracts to move joints. During this phase the cell is

increasing in size and making organelles.

Cells need specific signals from other cells telling them if they are ready to move onto the synthesis stage.

3. Synthesis (S) Second stage 4. Cell makes a copy of its DNA By the end of the S stage, the cell nucleus

contains two complete sets of DNA

Two identical copies of DNA

Original DNA

5. Gap 2 (G2) Third stage Cells continue to (6) carry out their normal

functions during this stage, and additional growth occurs.

There is also a critical checkpoint at this stage.

7. Mitosis (M) 8. Cell Division Fourth stage Includes two processes:

9. Mitosis: Division of the cell nucleus and its contents During mitosis the nuclear membrane dissolves, the

duplicated DNA condenses around proteins and separates, and two nuclei form.

10.Cytokinesis: Process that divides the cell cytoplasm Results in two daughter cells that are genetically

identical to the original cell.

Predict: What might happen if the G2 checkpoint

stopped working in cells? Cells may be the wrong size, have damaged DNA

and fail to divide.

Cells divide at different rates Prokaryotic cells typically divide much faster

than eukaryotic cells. Why? They do not have membrane-bound organelles or

a cytoskeleton In human cells, S, G2, and M phases typically

take 12 hours G1 phase varies widely Cells that rarely divide are thought to go

through a phase called G0

Infer Do you think a skin cell would have a long G1

or a short G1? Why?

Cell size is limited Cells have upper and lower size limits Lower limit depends on the ability to hold

organelles Some cells must be large, but have unique

shapes Upper limit depends on the ratio of cell

surface area to volume Volume increases faster than surface area

Connect Which has the larger ratio of surface area to

volume, a tennis ball or a soccer ball? Explain your reasoning. A tennis ball, because volume increases more

rapidly than does surface area as a ball gets larger.

Check for understanding During which stage of the cell cycle is the DNA

copied? Synthesis (S)

Which stages of the cell cycle generally require about the same amount of time in all human cells? Synthesis, Gap 2, and Mitosis

What limits the maximum size of a cell? Ratio of surface area to volume

Cancer Case Study Read pages 233-235 with your partner, alternating

back and forth for each paragraph. As you read, think of 4-5 words that you feel are the

most important for describing what the article is about Write each word on the blank side of a notecard (one

per notecard) Start reading Identify terms that support your main term on the

notecard and make a web. Find another group and choose the 4 most important

words out of both groups. Write a summary using at least 4 of your cards on the

board.

Section 5.2

Mitosis and Cytokinesis

Cell Division The process by which a

cell divides into two new cells

Why do cells need to divide? Living things grow by

producing more cells, NOT because each cell increases in size.

Repair of damaged tissue If cell gets too big, it cannot

get enough nutrients into the cell and wastes out of the cell.

Chromosomes condense at the start of mitosis A chromosome is one long continuous thread

of DNA Your body cells have 46 chromosomes each DNA wraps around proteins that help

condense it

DNA doublehelix

DNA andhistones

Chromatin

SupercoiledDNA

Loose DNA is called chromatin DNA warps around histones which help

organize the chromosomes

Chromosomes condense at the start of mitosis

DNA doublehelix

DNA andhistones

Chromatin

SupercoiledDNA

DNA plus proteins are called chromatin

One half of a duplicated chromosome is a chromatid

Sister chromatids are held together at the centromere

Telomeres protect the DNA and do not include genes

Chromosomes condense at the start of mitosis

Condensed, duplicated chromosome

chromatid

telomere

centromere

telomere

Mitosis and cytokinesis produce two genetically identical daughter cells 1. Interphase

prepares the cell to divide

DNA is duplicated during interphase

Parent cell

centrioles

spindle fibers

centrosome

nucleus withDNA

Prophase 2. During prophase, chromosomes condense

and spindle fibers form

Metaphase 3. During metaphase, chromosomes line up in

the middle of the cell

Anaphase 4. During anaphase, sister chromatids

separate to opposite sides of the cell

Telophase 5. During telophase, the new nuclei form and

chromosomes begin to uncoil

Cytokinesis 6. Differs in

animal and plant cells

7.– In animal cells,

the membrane pinches closed.

– In plant cells, a cell plate forms.

DNA photographed for the first time!

http://www.foxnews.com/science/2012/12/03/dna-directly-photographed-for-first-time/

Section 5.3

Regulation of the Cell Cycle

Internal and external factors regulate the cell cycle Internal factors:

Often triggered by external factors. Two of the most important internal factors are

kinases and cyclins. Kinases: Increases the energy of the target molecule or

changes its shape. Cyclins: Proteins that activate kinases for the cell cycle

Internal and external factors regulate the cell cycle External factors:

External factors come from outside the cell. They include cell-cell contact and other physical

signals. Include chemical signals such as growth factors. Growth factors may stimulate growth in a wide

variety of cells or may stimulate only specific cells to divide.

Carcinogens Carcinogens are substances known to

promote cancer. Examples:

Tobacco smoke Air pollutants Radiation Mutated genes

Standard cancer treatments typically kill both cancerous and healthy cells. Chemotherapy Radiation Therapy

Cell division is uncontrolled in cancer Characterized by uncontrolled cell division.

Continue to divide despite cell-cell contact or lack of growth factors. Tumors:

Disorganized clumps of cancer cells that do not carry out specialized functions needed by the body.

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

cancer cellbloodstream

normal cell

Apoptosis Programmed cell death

A normal feature of healthy organisms Caused by a cell’s production of self-destructive

enzymes Occurs in

developmentof infants

webbed fingers

Section 5.4

Asexual Reproduction

Binary fission is similar in function to mitosis Asexual reproduction of a single-celled

organism by division into two roughly equal parts. Binary fission produces two daughter cells

genetically identical to the parent cell. Binary fission occurs in

prokaryotes.

parent cell

DNA duplicates

cell begins to divide

daughter cells

Some eukaryotes reproduce through mitosis Budding forms a new organism from a small

projection growing on the surface of the parent.

Some eukaryotes reproduce through mitosis Fragmentation is the splitting of the parent

into pieces that each grow into a new organism.

Vegetative reproduction forms a new plant from the modification of a stem or underground structure on the parent plant.

Asexual Reproduction Asexual reproduction is the creation of

offspring from a single parent. Genetically identical offspring from one parent

organism. Does not involve fusion of gametes.

Environment determines what form of reproduction is most advantageous. Asexual

reproduction is an advantage in consistently favorable conditions.

All organisms can potentially reproduce.

Organisms to not need to spend resources finding a mate.

Sexual reproduction is an advantage in changing conditions.

Section 5.5

Multicellular Life

Multicellular organisms depend on interactions among different cell types.

Cells: Smallest, most basic structural unit of life; typically become specialized

Tissues: Groups of cells that work together to perform a similar function

Organs: groups of tissues that work together to perform similar or related functions

Organ Systems: organs that carry out similar functions

CELL TISSUE ORGAN vascular tissue

leaf

stem

lateralroots primary

root

SYSTEMS

root

syste

msh

oot

syste

m

Specialized cells perform specific functions.

Cells develop into their mature forms through the process of cell differentiation.

Cells differ because different combinations of genes are expressed.

A cell’s location in an embryo helps determine how it will differentiate.

Outer: skin cells Middle: bone cells Inner: intestines

Stem cells are unique body cells.

Defining Characteristics: Stem cells have the ability to divide and renew themselves remain undifferentiated in form develop into a variety of specialized cell types

Stem cells are classified into three types.

– totipotent, or growing into any other cell type– pluripotent, or growing into any cell type but a totipotent cell– multipotent, or growing into cells of a closely related cell family

Possible uses: The use of stem cells offers many currently realized and potential benefits.

– Stem cells are used to treat leukemia and lymphoma.– Stem cells may cure disease or replace damaged organs.– Stem cells may revolutionize the drug development process.

First, an egg is fertilized by a sperm cell in a petri dish. The egg divides, forming an inner cell mass. These cells are then removed and grown with nutrients. Scientists try to control how the cells specialize by adding or removing certain molecules.

Stem cells come from adults and embryos.

– Adult stem cells can be hard to isolate and grow.– The use of adult stem cells may prevent transplant rejection.

– The use of embryonicstem cells raisesethical issues

– Embryonic stem cellsare pluripotent andcan be grown indefinitelyin culture.