Cell Growth

• A cell is limited by its cell size

• The larger the cell the harder it is to move through tissue and get nutrients

• In order to stay alive and not grow continuously, the cell will divide

Reasons why to divide

• DNA– Genetic information stored– Found in the nucleus of the cell– DNA would not be able to keep up with demand of

the cell

• Transport– Rate decreases as the cell size increases– Takes too long for nutrients and wastes to move in

and out of cell

Surface Area to Volume• Surface Area

– Area on outside of cell where reactions can occur

– As a cell increases, the surface area decreases

Chromosomes

• Made up of our DNA

• Holds genetic information

• Tight coils or rod like structures

• Organisms have a specific amount of chromosomes.– Humans have 46 chromosomes of DNA in

every somatic cell

Chromosome Structure• Histones are proteins that DNA wraps around

to make the chromosome shape

• Chromosomes are made of two sister chromatids– Identical to each other

Chromosomes• Centromeres are in the center of a chromosome

• Chromosomes are tightly coiled strings of DNA called chromatin

• Chromatin is the string-like form of DNA

Chromosome Numbers

• There is a specific number of chromosomes in each organism

• Humans autosomes and sex chromosomes

• We have 2 sex chromosomes– Either X or Y

• We also have 22 autosomes – Which do not code for gender

Karyotype•A karyotype is a lab picture of one set of chromosomes

Diploid/Haploid

• A diploid cell contains 2 sets of each chromosome– Prefix di = 2

• A haploid cell contains only 1 set of each chromosome– Half of the total number– Usually sex cells

Cell Division in Prokaryotes• Prokaryotes

– No nucleus– No organelles– Ex: Bacteria

• Reproduction is VERY fast– Copy DNA– Split into two cells

• Cell division is called binary fission

Eukaryotic Cell Reproduction

• Eukaryotes– Have a nucleus– Have organelles– Ex: Humans, plants

• Complex reproduction – Everything needs to be controlled!

• Much longer process – about 18 hours!

Cell Reproduction• A cell splits to make 2

identical copies

• If asexual reproduction– Only 1 cell involved

• This occurs in 3 main stages1. Interphase – Growth

2.Mitosis – Splitting of the cell

3.Cytokinesis – Splitting of the cytoplasm

Interphase• Cell growth

• 90% of cell’s life is spent in interphase.

• 3 Part of Interphase: –G1, S, G2

G1 Phase

• The cell is growing

• The organelles are doubling

S Phase• Takes place when

cells are too big

• S = Synthesis of DNA

• DNA is replicated so there is a set for each new cell

DNA replicates in Interphase so the daughter cells exact copies of

the DNA

G2 Phase

• Cell growth again

• Replication of organelles

• Last stage of interphase

• Cell prepares for cell division

•cell is not dividing

• cell is growing, performing respiration, producing, photosynthesizing, doing whatever functions it is supposed to do

•At some point, the cell can’t diffuse fast enough and that signals the end of interphase

•At the very end of interphase, the chromatin makes an exact copy of itself in a process called DNA replication.

How is DNA copied?

• Each cell has an protein called helicase– Enzyme the unwinds the DNA making 2

identical strands– http://www.youtube.com/watch?v=zdDkiRw1P

dU

Mitosis• The part of a cell’s life cycle when the cell divides it nuclear contents into 2 nuclei which are identical

•Mitosis consists of 4 steps:

•Prophase

•Metaphase

•Anaphase

•Telophase

• all sub-cellular organelles disappear

• centrioles separate and move to opposite poles

• chromatin become chromosomes

• centrioles shoot off spindle fibers (short and long)

chromosomes line up at the equator

• centromere splits

•sister chromatids attach to the short spindle fibers

•short spindle fibers shorten and bring the sister chromatids to opposite poles.

• chromatids become chromatin (one at each pole)• spindle disappears• subcellular organelles reappear

Cytokinesis• Once mitosis has finished!

• Last stage of cellular reproduction

• This process is when the cytoplasm splits apart

• There are now 2 identical cells

Cytokinesis in Plant Cells• Cell plate forms at equator and grows out to the cell

wall

• Cell plate

Cytokinesis in Animal Cells• Cell membrane pinches in at equator

• Cleavage furrow

Control of Cell Division

• G1 Checkpoint– Enzymes will kick in if cell is large enough and

conditions are favorable to reproduce

• G2 Checkpoint– DNA repair enzymes will fix any mutations, if

checkpoint is passed mitosis will occur

• Mitosis checkpoint – if all is correct, the 2 daughter cells will enter G1 phase and start over again

Uncontrolled Mitosis

is cancer.

When Control is Lost

• Enzyme proteins are not functioning properly causing cell to reproduce out of control

• Could cause cancer• Cancer cells do not respond to body’s

signals that control mechanisms

Compare/Contrast

How else can our body control cancer?