9.1 9.4 cell division

Cell Division

• All cells come from cells!• Why do cells divide?

– Repair and growth - Mitosis– Reproduction – Meiosis

• Two kinds of reproduction:– Asexual – Sexual

Which cell division is for growth and repair?

A) Mitosis

B) Meiosis

Asexual Reproduction

• Asexual reproduction – An organism duplicates its genetic material then splits into two cells

• All offspring are genetically identical to each other and the parent

• Ex: paramecium, hydra and sea stars

Sexual Reproduction

• Sexual reproduction – Genetic material from 2 parents combine

• Offspring are genetically unique (different from parents)

• ½ of the genetic material comes from each parent

Offsprings that are genetically identical to their parents are

products of A) Asexual reproduction

B) Sexual reproduction

DNA• When a cell divides the genetic material in the

original cell is passed to the new cells• DNA is the genetic material of all living organisms• DNA appears as either chromatin or

chromosomes.• DNA appears as chromatin during normal cell

activity.• During cell division (mitosis and meiosis) DNA

forms structures called chromosomes.

Chromosomes• Chromosomes are small condensed packages

that are easily moved around by the dividing cell.

Chromosome Structure• The two strands of a single chromosome are

called sister chromatids.• They are connected by a structure called a

centromere.• Sister chromatids are identical sequences of

DNA

Sister chromatids

Centromere

Chromatin

The structure of chromatin is similar to a bowl of spaghetti.

Chromatin and Chromosomes

True or False

DNA can take the form of chromatin or chromosome.

The black arrows are pointing at…

A) Centromere

B) Chromosome

C) Sister chromatids

D) Chromatin

The red box is…

A) Centromere

B) Chromosome

C) Sister chromatids

D) Chromatin

Stages of the Cell Cycle• The cell cycle is composed of interphase and the

mitosis

G’s stand for gaps. M stands for mitosis. S stands for synthesis. The G phases seemed to be gaps in cell activity during the cell cycle.

Interphase

• Interphase is in general a time of normal cell activity. Cells carry out their normal metabolic processes and perform their usual functions.

• DNA appears as chromatin in interphase.• Interphase is composed of 3 stages:

– G1, S and G2.

Interphase

• G1: Cell grows• S: DNA replicates

(synthesized)• G2: Cell prepares

to divide

Interphase

• During late G2 two centrosomes appear outside the nucleus.

• Spindle microtubules extend from the centrosomes and connect to chromosomes.

• Microtubules move chromosomes around during mitosis

S- phase

• DNA replicates itself• This is done to provide each daughter cell a

complete set of DNA

During interphase…

A) The cell stops its normal functions

B) DNA replicates

C) The cell divides

D) The cell prepares to divide

E) Both B and D

M phase

• M phase is composed of mitosis and cytokinesis

• A parent cell divides into 2 daughter cells• Mitosis is composed of four stages• Prophase, metaphase, anaphase and

telophase (PMAT)• Cytokinesis is when the cytoplasm actually

divides into 2 new cells.

M Phase is:

A) part of interphase

B) when the cell does normal cell activity

C) mitosis and cytokinesis

D) only mitosis

Prophase

• Nucleus disappears• Chromatin condenses into chromosomes• Centrosomes migrate to opposite poles(ends) of the

cell.• Spindle microtubules form

– They will eventually attach to the centromere of each chromosome

Metaphase

• Chromosomes move to the middle of the cell (metaphase plate)

• Microtubules pull chromosomes apart.

Anaphase

Telophase

• Nucleus reforms• Chromosomes unwind into chromatin• Microtubules disappear• Centrosomes migrate near nucleus• Telophase is the opposite of prophase!

Chromosomes line up in the middle of the cell at which phase?

A) Prophase

B) Metaphase

C) Anaphase

D) Telophase

Sister chromatids are pulled apart at which phase?

A) Prophase

B) Metaphase

C) Anaphase

D) Telophase

True or False

Microtubules disappear at Telophase.

Cytokinesis

• The actual division of the cytoplasm.• Usually occurs with telophase, but may start

during anaphase.• The first sign in animal cells is the indentation

around the middle of the cell.• In plants, a cell plate forms inside the cell.• The cell plate contains new cell wall material.

Plant Cytokinesis

True or False

Plant cytokinesis also occurs with the indentation around the middle of the cell.

Cancer

• Cancer is caused by severe disruption of the mechanisms that normally control the cell cycle.

• This disruption leads to uncontrolled cell division.

Cancer

• Benign tumor – an abnormal mass of essentially normal cells.

• Cells remain at their original site.• Can cause health problems depending on their

location, but can usually be completely removed by surgery.

Cancer

• Malignant tumors – mass of cells resulting from the reproduction of cancer cells.

• Malignant tumors displace normal tissue as they grow.

• They are characterized by their ability to rapidly spread.

• Metastasis – spread of cancer beyond its original site.

Cancer

• Treatment involves surgery, radiation therapy and/or chemotherapy.

Cancer involves

A) Treatment through surgery, radiation therapy, and/or chemotherapy

B) Malignant tumors displacing normal tissue

C) Severe disruption of the cell cycle

D) All of the above

E) None of the above