Cell Growth & Reproduction

MITOSIS

Cell GrowthWhen a living thing grows it does so by producing more cells INSTEAD of making the cells it has larger

Whether it be elephant, human, jellyfish or earthworm – all the cells are about the same size

There are two reasons why this happens:

DNA OverloadExchange of Materials

Why are cells so small?

DNA Overload Exchange of Materials

All the information to run a cell is located in the nucleus as a code of DNA

If the cell were to get bigger and bigger there would not be enough “information” to run the whole cell

The cell must transport everything it needs through the membrane

If there isn’t enough membrane space, cells can’t get or get rid of what they need.

So there must be a balance between surface area (room to move stuff in & out) and volume (stuff)

Why must cells divide?What does the Cell Theory say?

3 Major Reasons Cells Divide:

◦Growth – you start as one cell◦Development – you get bigger, learn

& change◦Repair – your cells get worn out

What does a cell need to survive?

A FULL set of genetic material (DNA or RNA)

Biggest hurdle to cell division is making sure each cell transfers ALL the DNA when it makes new cells

This gets more difficult as there becomes more DNA to transfer

To Prevent Mistakes: CHROMOSOMES!

A Cell’s LifeA cell’s life can be divided into 2 stages:

Interphase (3 Parts) – Non-dividing stages

Gap 1 (G1)Growth phase #1 – cells get biggerMost cells are found in this phase – “Normal Cells”

Synthesis (S)New DNA is synthesized, or made

Gap 2 (G2)Growth phase #2Preparations for division are made

Mitosis (4 parts) – Dividing stagesProphaseMetaphaseAnaphaseTelophase

Cell Cycle: Interphase

Three phases of Interphase:• G1 – growing, increasing in

size, synthesis of new proteins and organelles

• S phase – Chromosomes are duplicated

• G2 – shortest phase, synthesis of organelles and molecules needed for cell division

Mitosis – Prophase

ProphaseChromatin condenses to Chromosomes• chromatids are joined by

centromere • Centrioles move to

opposite ends of cell• Nucleolus disappears• Nuclear membrane

dissolves

Mitosis – Metaphase

• Chromosomes line up at the equator

• Chromosomes attach to spindle fibers (from the centrioles) at centromeres

Mitosis – Anaphase

• Chromosomes get pulled apart

• Spindle fibers shorten and pull sister chromatids to the opposite ends of the cell

Mitosis – Telophase

• Chromosomes de-condense

• Spindle fibers disintegrate

• Nuclear membrane forms

• Nucleolus becomes visible

• Animal Cells – a contractile ring forms around the middle of the cell

• Plant cells – a band of cytoskeletal proteins called the cell plate forms

Cytokinesis – division of the cytoplasm

• Animal Cells – the contractile ring pinchesin the middle to fuse the membrane and separate the new nuclei

• Plant Cells – a new section of cell wall forms from the cell plate, between the nuclei to form two distinct cells

A B

C

D E

This is a complicated process… what happens when things go wrong?

There are several factors that try to control the cell cycle:

1. Before a cell divides the DNA is checked to make sure it was replicated correctly

2. Chemical signals tell a cell when to start and stop dividing

http://www.cancerquest.org/index.cfm?page=193

3. Cells also communicate to neighboring cells to tell them to stop growing

1. http://www.cancerquest.org/index.cfm?page=2463

Cancer