Mitosis and the

Cell CycleChapter 8

2010

Comprehension CheckThink about it: Which has larger cells,

an adult or child?• Based on your answer, explain how organisms

get larger and grow.

• Children and adults have the same-sized cells. All organisms grow larger because their cells multiply in number, NOT size.

Cell Division Cellular Reproduction occurs when one cell divides

and forms two new cells Multicellular organisms can only grow by

increasing the number of cells through cell division Body cells that divide under this process are called

somatic cells/autosomal cells Reproductive cells (sex cells) are known as

gametes

Cell Division Cells must……

Divide (there are limits on cell division: Hayflick Limit/Telomeres)

Pass on their genes to new cells Produce NEW cells that replace worn

out or damaged cells Produce NEW cells to heal cuts,

repair damaged tissues Replace cells that have a short life-

span. Cells know to divide from……

Contact/ Density Dependent Inhibition

Chemical Signals

Cell Division Cells know to divide from……

Contact/ Density Dependent Inhibition

Crowded cells stop dividing Chemical Signals

Growth factor- stimulates cells to divide

Comprehension Check• Describe the structure of a

chromosome.• How many different forms of DNA

have we talked about this year?

Many forms of DNA DNA is bound with proteins called

histones When DNA is not coiled (relaxed),

referred to as chromatin “Fried Egg” Cell

When DNA is in coiled form, called chromosomes During cell division, DNA will

replicate (copy) Only during this time does DNA coil

in chromosomes If this were a human cell, there

would be 46 chromosomes now visible in nucleus

“C” Vocab Chromosome – tightly coiled DNA Chromatid – ½ of a symmetrical chromosome Chromatin – uncoiled DNA “relaxin”

Make sure you understand the differences between these terms!!!

“C” Vocab Centromere – holds DNA together (holds two halves) Centrioles – aid in cell division Centrosomes – houses centrioles

Make sure you understand the differences between these terms!!!

“C” Vocab Chromosome versus Replicated Chromosome

Make sure you understand the differences between these terms!!!

Chromosome Numbers Every species has a specific number of

chromosomes (Check out the chart in your book!) In sexually reproducing organisms, chromosomes

occur in pairs (WHY?) These pairs are called homologous

chromosomes A cell that with both homologous pairs of

chromosomes is called Diploid (2n) A cell that has only one member of the pair is

called Haploid (n) (What type of cells would be haploid?)

Human Chromosomes Humans have a diploid number of 46 and

haploid number of 23 Sperm and eggs cells (gametes) have 23

chromosomes Somatic cells have 46 (or 23 pairs) Remember the human sex chromosomes?

*Diploid always means somatic cell in human cells, Haploid always means gamete in human cells

Comprehension Check• How many words can you list that mean

sex cells?• How many words can you list that mean

non-sex cells?• What differences can you list between

sex chromosomes and autosomes?• Can you name two haploid and two

diploid cells?

LIMITS TO CELL SIZE DNA “Overload”:

-All cells must follow DNA instructions to make proteins -As cell gets too large, DNA cannot supply instructions to make enough protein for the entire cell to function

Exchanging Materials/Ratio of Surface Area to Volume:-As a cell gets bigger, its volume grows at a faster rate than its

surface area. Eventually the cell cannot transport enough materials across its membrane to survive.

-HINT: Think of an intersection in a small town. What would happen if the population continued to increase in the town but the intersection did not grow with it?

Cell Cycle Five main parts to the

cell cycle: 3 phases of

interphase (G1,S,G2) Mitosis (M Phase) Cytokinesis

Cytokinesis

G0 Stage G0 Stage

Non-dividing stage Nerve cells Heart muscle

cells

Cytokinesis

Cyclin and p53 Cyclin: protein that moves the cell

cycle from G1 to Mitosis. (COMMITMENT POINTS)

P53 (often called the guardian of the genome) prevents cell from completing the cell cycle if:

DNA is damaged Cell has suffered other types of damage

If damage is minor, p53 halts cell cycle until the damage is repaired – OR – if the damage is major or cannot be repaired, p53 triggers apoptosis or cell death.

What causes the cell to move through different parts of the cycle?

Proteins and Chemical Signals

Comprehension Check• How are prokaryotes and

eukaryotes different?• How is their DNA different?• What are different reasons cells

divide?

Eukaryotes and Prokaryotes How do their differences affect cell

division?

Binary Fission

Mitosis

Types of Reproduction Asexual (Binary Fission) Reproduction Sexual Reproduction = Meiosis in

humans!

Interphase Period of growth,

development and rest for cell 3 distinct phase

G1: Cell grows S: chromosomes are

duplicated & cell continues to grow as it copies its chromosomes

G2: Grows more as it completes preparations for cell division

Mitosis Process of nuclear division in

preparation for cell division Phases of mitosis

Prophase Metaphase Anaphase Telophase

This is a picture of approximately 3% of the DNA found in a single human chromosome. It has been treated to remove the histones.

You can get an idea of how the cell will have to go to great lengths to prevent tangles and problems during mitosis!

Prophase Nucleolus and nucleus disappear Centrosomes form centrioles by dividing in

half and moving to opposite sides of the cell Spindle fibers (asters) begin to form Chromosomes form

Metaphase Chromosomes line up on equator of the

cell Spindle fibers (microtubules) attach to the

kinetochore at the centromere of each chromosome

Lots of terms . . . • Mitotic Spindle – football shaped structure of microtubules that

guides the separation of the two sets of daughter chromosomes• Centrosomes – clouds of cytoplasmic material that house

centrioles (microtubule organizing centers)

Lots of terms . . . Centrioles – cylinders of microtubule triplets to aid in cell division Kinetochore Fibers – come out of the middle of the centromereAsters – hold mitotic spindle in place

Anaphase Chromatid pairs separate from each

other This stage ends when chromatids

reach the poles of the cell

Telophase Chromatids relax to form chromatin Spindle fibers disappear Nucleus reforms around DNA Stage ends with Cytokinesis

Cytokinesis Cell membrane pinches inward and the two new

cells separate Animals: Cleavage Furrow Plants: Cell Plate

Root WordsPrefix/Suffix Meaning

Centro- Central

-mere Part, segment

-some Body

-logous Proportional or equivalent to

Homo- Same

Hap- Single, simple

Kineto- Moveable

Karyo- Cell nucleus

Mit- Thread

-osis Act, process or condition

Comprehension Check• What are the stages of the cell cycle?• What are the stages of mitosis?• What are the differences between plant

and animals cells in mitosis?– Animals: centrioles, asters, cleavage furrow– Plants: Cell Plate

Try these

Can you identify these stages?

Can you identify these stages?