The Cell Cycle and Mitosis

Chapter 5.1

5.1 The Cell Cycle and Mitosis

Due to the loss and death of cells must replace them.

How many cells in your body?

• 50-100 million trillion

• Every minute your body produces about 300 million new cells

Three stages in the cell cycle:

1. Interphase: cell carries out normal functions.

2. Mitosis: nucleus contents duplicated and divided into two equal parts.

3. Cytokinesis: separation of two nuclei and cell contents into two daughter cells.

See pages 150 - 153

Parts of the Cell Cycle

Interphase

Interphase - the longest cell cycle stage (lasts 15 hrs.

– months). • cell performs normal functions and grows.

In late interphase, DNA copies itself in the process of replication.

Replication involves several steps: 1. The DNA molecule unwinds with the help of an enzyme.

2. New bases pair with the bases on the original DNA.

3. Two new identical DNA molecules are produced. Now, double the amount of DNA in nucleus it divides (Mitosis)

DNA Unraveling (video)

Late Interphase cont’d.

Chromatin is in its loosely coiled form so that DNA can be copied into RNA for proteins to be made in preparation for cell division.

At the end of interphase, the cell continues to grow and make proteins in preparation for mitosis and cytokinesis.

Chromosomes

As the nucleus prepares to divide, replicated DNA in interphase joins to form sister chromatids, joined by a centromere.

Mitosis Overview: (BC Science 9 animation)

Mitosis is the shortest stage of the cell cycle where the nuclear contents divide, and two daughter nuclei are formed.

It occurs in 4 stages: 1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

Helpful saying to remember the order: • “I picked many apples today.”

Mitosis - Prophase

Chromosomes start to coil and become visible.

Pairs of centrioles start to separate.

The nuclear membrane disappears.

Spindle fibers start to form between the centriole pairs.

Chromosomes move more evenly throughout the nucleus.

Mitosis - Metaphase

Centriole pairs move to opposite ends of the cell.

Spindle fibers are still attached to the centriole pairs.

Chromosomes line up along the midline of the cell and are attached to the spindle fibers.

Mitosis - Anaphase

The pair of chromatids split at the centromere and move to opposite ends of the spindle.

Now there are twice the number of chromosomes within the cell membrane.

Movement of the chromosomes towards the opposite ends of the cell membrane is aided by the spindle fibers.

Mitosis - Telophase

Nuclear membranes form around the two new sets of chromosomes.

The spindle fiber disappears.

Chromosomes start to uncoil (chromatin) and become less visible.

Cell starts to make a groove (furrow) in the middle to eventually split into two identical cells.

Cytokinesis

The division of material outside of the nucleus.

• Occurs after telophase.

Divides the organelles and other substances in the cytoplasm into roughly two equal halves.

Animal cells furrow while plant cells form a cell plate

# chromosomes in daughter cell = the # chromosomes in parent cell.

Daughter cells are genetically identical to parent.

Cytokinesis

Video

Cell Cycle Problems

Checkpoints in the cell cycle will prevent

cell division if: • If the cell is short of nutrients

• If the DNA within the nucleus has not been

replicated

• If the DNA is damaged

Cell Cycle Problems

Mutations in genes involving checkpoints can

result in an out-of-control cell cycle. The result

can be uncontrolled cell division: cancer (12 slides of

Flash animation)

• Cancer cells have large, abnormal nuclei

• Cancer cells are not specialized, so they serve no function

• Cancer cells attract blood vessels and grow into tumours.

• Cells from tumours can break away to other areas of the

body

See pages 159 - 161

Cancer

Asexual Reproduction

Chapter 5.2

5.2 Asexual Reproduction

Reminder, most (~95%) of the time the cell is

in interphase (doing its job, growing,

surviving, etc.)

Reminder, when the cell gets too big (If its

volume outgrows its surface area), it must

divide/reproduce

5.2 Asexual Reproduction

is how the cells of multi-cellular organisms (like your body cells) reproduce and multiply

is a common method of reproduction among single-celled organisms, such as the paramecium

clone – offspring is an identical genetic copy of its parent

•E.g. used in agriculture and research to copy desired organisms, tissues and genes

Binary fission

Budding

Fragmentation

Vegetative reproduction

Spore formation

Types of Asexual Reproduction

Binary fission

– a single cell

(unicellular) splits into

identical copies

(Ex. Bacteria)

Budding

can occur in unicellular

or multi-cellular

organisms. Buds

develop into a new

organism (Ex. Hydra)

Fragmentation

Part of an organism breaks off due to injury

The part grows into a clone of the parent

Example: Starfish, milfoil

Vegetative reproduction

-special cells in plants that develop into structures that

form new plants identical to the parent (Ex. Spider plants,

grafting fruit trees, runners and rhizomes, tubers and bulbs)

Spore formation

- some bacteria, micro-organisms and fungi can form spores - single cells that can grow into a whole new organism

(ex. Penicillium)

Asexual Reproduction

See page 175

Human Assisted Cloning

Two types: reproductive and therapeutic cloning

Reproductive cloning - purpose is to produce a genetic duplicate of an existing or dead organism.

Steps involved (adult DNA cloning) :

1. Remove nucleus from an egg cell

2. A mammary gland cell is removed from an adult female

3. Electricity fuses mammary and egg cell

4. Fused cell begins dividing

5. Dividing embryo is inserted into surrogate mother

See pages 176 - 177

Reproductive Cloning

Therapeutic cloning

purpose is to correct health problems

• Stem cells

• cells that can become different types of cells

• can be used to replace cells damaged from injuries or disease

• Diabetes, spinal injuries, Parkinson’s disease are only a few that can benefit from stem cell therapy

• Controversial because the best stem cells are from embryos which are destroyed when harvesting cells

See pages 177 - 178

Cloning - debate

Therapeutic Cloning