The Cell CycleReview

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Animal Cell Plant Cell

Cell Size Limitations

Text - Ch 7 Wide variety of sizes and shapes

RBC (1 um) to nerve cells (1 m) Egg yolk (ostrich) Most are 2-200 um cell scale

Diffusion limits cell size

Selectively permeable membraneI.e. Nutrients in and wastes out

Becomes slow and inefficient as distance between organelles and membrane increases

DNA limits cell size

DNA supports protein needs of cell More than one nucleus

Surface area-to-volume ratio

As cell grows the volume increases faster than the surface area

If cell doubles Nutrients requirements increase 8-fold Waste also increases 8-fold Surface area only increases 4-fold

The cell, therefore, will either starve to death or be poisoned.

Cell Reproduction

Cells divide before they become too large.

Recall: all cells come from pre-existing cells

The Redi Experiment

Pasteur’s swan neck flask experiment

Chromosomes Discovered

Become visible just before cell division Vanish soon after cell division Contain DNA Chromosome (X’me) number varies

Humans 46

Chromosomal Structure

Exist as chromatin most of cell’s life Long strands of DNA Wrapped around proteins called

histones Appear as beads on a string Reorganize before cell division

The Cell Cycle

Def’n: Sequence of growth and division about 3 000 000 cells die in your body

every minute. Cells die due to damage or when they

don’t get enough food or oxygen. Regeneration - Healing of damaged tissue

or the replacement of body parts is called regeneration.

Mitosis

Mitosis is responsible for the cell division that all plants and animals require for:

Growth Repair (and replacement) of body cells

Characteristics of Mitosis

Always only one parent Offspring identical to parents (fast,

convenient, safe)

I.e. asexual reproduction

Phases of the Cell Cycle

IPMAT

Interphase

Most of cell’s life Longest and busiest phase

DNA in thin strands called Chromatin replicate.

Chromatin coils up to form double stranded X’mes.

Interphase

A Centromere connects the original chromatin with its identical replicate.

The cell has a complete extra copy of DNA.

http://www.pitt.edu/~super1/lecture/lec19281/004.htm

Chromosome

Prophase

Prophase Duplicate DNA is easily seen under

microscope. Nucleolus and Nuclear Membrane

disappear. Centrioles move to opposite sides of the

cell. Spindle fibres (like a scaffold) grow out of

each centriole and attach to centromere.

Metaphase

http://www.madsci.org/posts/archives/2000-11/974783537.Cb.1.jpg

Metaphase Spindle fibres pull on centromeres double X’mes pulled into a line across

the middle Shortest phase

Anaphase

Anaphase Spindle fibers contract fully Centromeres are pulled apart 1 copy of DNA goes to each side of the

cell

Telophase

Telophase A complete set of X’mes arrives at each

centriole. Two daughter cells have formed Spindle fibers disappear Nuclei/nucleoli and nuclear membrane

form. X’mes uncoil into thin chromatin.

Telophase (cont’d) Animal cells

Cleavage furrow – cytokinesis (cell membrane pinches off)

Plant cell A cell plate grows across the cell

Parent Cell Daughter Cells

Animations

NOVA Online | Life's Greatest Miracle | How Cells Divide: Mitosis vs. Meiosis (Flash)

mitosis = cell division hybridmedical-mitosis hybridmedical-mitosis youtube DNA repl'n & spindle