All Cells Come From Cells - PowerPoint Presentation

Slide1

All Cells Come From CellsSlide2

Why Would A Cell Divide?

Growth

RepairSlide3

The Cell Cycle, Mitosis, and

Meiosis

New cells can only be made when existing cells divide. All cells have the ability to divide – but some cells lose this ability.

Intestinal epithelial lining - replaced every five days by cell division

Liver

cells - divide only to repair damage, and then stop dividingMeristem cells (tips of roots and shoots) – divide to produce new

growthSlide4

In eukaryotic cells, there are two types of cell division –

mitosis

and meiosis.

Mitosis is used to produce new cells for growth and repair. Meiosis is used in the formation of gametes (sex cells) only. In prokaryotes (bacteria), cell division does not involve mitosis or meiosis – bacteria reproduce asexually, by a type of cell division termed by binary fission.

The cell cycle is the process that all body cells from multicellular organisms use to grow and divide. The cell cycle starts when a cell has been produced by cell division and ends with the cell dividing to produce two identical cells.Slide5
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Slide7

Reproduction

Asexual reproduction - Mitosis

Produces offspring that inherit all their genetic material from just one parent

Ex – Paramecium and Sponges

Sexual reproduction - MeiosisGenetic material from each of two parents combinesEx: Most animals (Including you)Slide8

Reproduction in bacteria

Binary

Fision

(Bacteria)Slide9

MITOSIS

(M)

Process by which a

nucleus

divides into two – each with an identical set of chromosomes – the nuclei are genetically identical

Four phases – prophase, metaphase, anaphase, and telophase

Followed by cytokinesis – division of the cell into two genetically identical daughter cells

INTERPHASE

Period of cell growth; cell prepares cell for cell division (mitosis); genetic material (DNA) is copied and checked for errors – prevents mutations being passed on

No apparent activity

New organelles and proteins are made

Divided into three phases (G1, S, and G2 phase)

CELL

CYCLE

G1

S phase

G2

Mitosis (M)

Two daughter cells – genetically identicalSlide10

The Cell Cycle

Mitosis : Cell division in which two cells, with the same number of chromosomes identical to the parent, are produced from one cellSlide11

Most

cells in the

Human body have

46 chromosomes

with

23 pairsSlide12
Slide13

G1 + S + G2 = INTERPHASE

No apparent observable activity

Cytokinesis – cell divides into two

DNA content = 20

G1

-

First growth phase – longest phase

Protein synthesis – cell “grows”

Most organelles producedVolume of cytoplasm increasesCell differentiation (switching on or off of genes)Length depends on internal and external factors

If cell is not going to divide again it remains in this phase

DNA content =

23

(

arbitary

)

S -

Replication phase

DNA replication – this must occur if mitosis is to take place

The cell enters this phase only if cell division is to follow

DNA content =

46

G2 -

Second growth phase - short

Short gap before mitosis (cell division)

Cytoskeleton of cell breaks down and the protein microtubule components begin to reassemble into spindle fibres – required for cell division

DNA content =

46

The Cell CycleSlide14

I P M A T

I Pro MatSlide15

Interphase

Up to 90% of a cells time is here

Normal cell functions:

Producing energyProducing enzymesG

1 phase – cell growsS phase – genetic material replicatesG2

phase – prepares for mitosisSlide16

Centrioles

show up

Cell is in the

first stage of mitosis.Slide17

Prophase (1

st

phase)

Centrioles divide and go to opposite sides of the cellSpindle fibers – appear from the centrioles and stretch to both poles

Nuclear envelope breaks down Nucleolus disappears (this results in what organelle no longer being produced?)Slide18
Slide19

Metaphase (2

nd

Phase)

Chromosomes attach to spindle fibersChromosomes migrate to the center of the spindle fibersSlide20

Anaphase (3

rd

phase)

Centromeres separateEach

sister chromatid = 2 daughter chromosomes (move to the poles)Slide21

Telophase (4

th

Phase)

Spindle fibers disappearNuclear envelopes reformDaughter chromosomes begin to uncoil

Nucleolus reforms – protein production returnsCytokinesis occurs (cytoplasm divides)Two complete identical cells are formedSlide22
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INTERPHASE

Before

a cell divides, its

chromosomes

are copied exactly in INTERPHASE to form two chromatids (“sister” chromosomes). This process is called replication; ATP is synthesised – provides energy for cell division; organelles are replicated and proteins are made, chromosomes condense – becoming shorter and fatter

PROPHASE

Nuclear

envelope breaks down; chromosomes lie freely in cytoplasm; centrioles move to opposite ends of the cell, forming protein (tubulin) fibres across it called a spindle – fibres extend to the equator of the cell

METAPHASE

Chromosomes line up at the equator; the spindle fibres from each pole become attached to the centromere of the chromosomes

ANAPHASE

The spindle fibres contract; the centromeres are split and the pairs of sister chromatids are separated and dragged to opposite poles assuming a “V” shape – the centromeres lead; a complete set of chromosomes is therefore found at each pole; energy (ATP) is required

TELOPHASE

Chromatids reach their respective poles and uncoil – become thin and long again – now called chromosomes again – no longer visible under LM; spindle fibres break down; nuclear envelope forms around each group of chromosomes – forming two nuclei; cytokinesis follows – cytoplasm divides and a plasma membrane forms two form two individual cells; cell enters interphase once again Slide24

Animation

http://www.cellsalive.com/mitosis.htm