1.1: CELL THEORY, CELL SPECIALIZATION, AND CELL REPLACEMENT

Guidance- Students are expected to be able name and briefly explain these functions of life: nutrition, metabolism, growth, response, excretion, homeostasis, and reproduction.- Chlorella or Scenedesmus are suitable photosynthetic unicells, but Euglena should be avoided as it can feed heterotrophically. - Scale bars are useful as a way of indicating actual sizes in drawings and micrographs.

Understandings• According to the cell theory, living

organisms are composed of cells.• Organisms consisting only of one cell

carry out all functions of life in that cell.• Surface area to volume ratio is important

in the limitation of cell size.• Multicellular organisms have properties

that emerge from the interaction of their cellular components.

• Specialized tissue can develop by cell differentiation in multicellular organisms.

• Differentiation involves the expression of some genes and not others in a cell’s genome.

• The capacity of stem cells to divide and differentiate along different pathways is necessary in embryonic development and also makes stem cells suitable for therapeutic uses.

Applications and Skills

• A: Questioning the cell theory using atypical examples, including striated muscles, giant algae, and aseptate fungal hyphae.

• A: Investigation of functions of life in Paramecium and one named photosynthetic unicellular organism.

• A: Use of stem cells to treat Stargardt’s disease and one other named condition.

• A: Ethics of the therapeutic use of stem cells from specially created embryos, from the umbilical cord of a newborn baby, and from an adult’s own tissues.

• S: Use a light microscope to investigate the structure of cells and tissues, with drawing of cells. Calculation of the magnification of drawings and the actual size of structures and ultrastructures shown in drawings or micrographs.

The Cell Theory• All organisms are composed of one or more cells.• Cells are the smallest unit of life.• All cells come from pre-existing cells.

Hooke’s Micrographia in full! http://lhldigital.lindahall.org/cdm/ref/collection/nat_hist/id/0

1665 Hooke names “cells” in his book “Micrographia” after observing cork under a lens.

All living things are made of cells.

1676van Leeuwenhoek, a master microscope maker identifies “animalcules” and becomes the father of microbiology.

All

livin

g th

ings

are

m

ade

of c

ells

.

http://en.wikipedia.org/wiki/Antonie_van_Leeuwenhoek

Robert Remak: http://en.wikipedia.org/wiki/Robert_Remak

1855 Robert Remak discovers cell division and confirms the existence of the plasma membrane. Cells come only from pre-existing cells.

Image from Amoeba Mike’s Blog (go read the original post): http://amoebamike.wordpress.com/2009/10/06/spontaneous-generation-a-brief-history-of-disproving-it

1864Pasteur disproves the prevailing theory of “spontaneous generation” with his swan-neck flask experiments. Populations need to be seeded by existing populations: cells come only from pre-existing cells.

Properties of living things• Made of cells• Metabolism• Reproduce• Homeostatic• Excretion• Grow• Respond to stimuli • Nutrition

http://scienceblogs.com/notrocketscience/2008/08/the_virophage_a_virus_that_infects_other_viruses.php

VIRUSESAre they living or non-living?

Hmm…..

Image: Swine Flu H1N1 virus influenza 9.0 by hitthatswitch on Flickr (CC) http://flic.kr/p/74e4SP

Some units to use & knowUnit abbr. Metric equivalent

kilometer km 1,000m 1 x 103m

meter m 1m 1mcentimeter cm 0.01m 1 x 10-2m

millimeter mm 0.001m 1 x 10-3m

micrometer μm 0.000 001m 1 x 10-6m

nanometer nm 0.000 000 001m 1 x 10-9m

X1,000

X1,000

X1,000

÷1,000

μm = micrometersWe usually use this in discussion of cells.

There are 1,000μm in one mm.

write this correctly

LIMITING CELL SIZE

IN: Oxygen Nutrients Water

OUT: Carbon dioxide Waste Products (e.g. proteins)

The plasma membrane of a cell is the surface of exchange for materials between the inside and the outside of the cell.

http://commons.wikimedia.org/wiki/Sphere

As the cell gets larger, it requires more resources to be imported

and produces more products (and waste) to be exported.

Therefore, a larger volume requires more exchange across

the membrane.

http://commons.wikimedia.org/wiki/Sphere

http://commons.wikimedia.org/wiki/Sphere

As the cell gets larger the surface area tovolume ratio actually gets smaller, so the exchange processes become lessefficient with increasing size.

http://commons.wikimedia.org/wiki/Sphere

Diffusion Pathways

are shorter (and more efficient) in smaller cells with a larger surface are to volume ratio.

DIVIDE

Surface are to volume ratio is a factor that

limits the size of cells.

By dividing to make more, smaller cells, the efficiency of the exchange processes

across the membranes (into and out of the cells)

can be kept high.

Shorter diffusion paths.

More surfaces for reactions.

Removal of heat and waste

4-cell stage of a sea biscuit by Bruno Vellutini on Flickr (CC) http://flic.kr/p/daWnnS

CELLS

Mammalian liver mitochondria: http://commons.wikimedia.org/wiki/File:Mitochondria,_mammalian_lung_-_TEM_(2).jpg

Natural selection favours adaptations that give an advantage. Folded structures are everywhere in nature, maximising the surface area to volume ratio for exchange of materials.

Structure/Function

Emergent Properties

Photo by Stephen Taylor: http://www.flickr.com/photos/gurustip/9668701965/in/photostream

the whole is

more than the sum

of its parts

Stem Cells

A cluster of nascent retinae generated from 3D embryonic stem cell cultures, by UCL News on Flickr (CC): http://flic.kr/p/ffPBPT

Stem Cells retain the capacity to divide and can differentiate along divergent pathways. TotipotentCan differentiate into any type of cell.

PluripotentCan differentiate into manytypes of cell.

MultipotentCan differentiate into a few closely-related types of cell.

UnipotentCan regenerate but can only differentiate into their associated cell type (e.g. liver stem cells can only make liver cells).

Image from: http://en.wikipedia.org/wiki/Stem_cell

Differentiation (specialization) of cells: All diploid (body) cells have the same chromosomes.

So they carry all the same genes and alleles.BUT

Not all genes are expressed (activated) in all cells.The cell receives a signal.

This signal activates or deactivates genes.Genes are expressed accordingly and the cell is

committed. Eventually the cell has become specialized to a function.

Key Concept: Structure vs FunctionHow do the structures of specialized cells reflect their functions? How does differentiation lead to

this?

Therapeutic Uses of Stem Cells

Animated tutorials from: http://outreach.mcb.harvard.edu/animations/thera7c.swf

Treatment for Leukemia

ProblemCancer of the blood or bone marrow, resulting in abnormally high levels of poorly-functioning white blood cells.

Treatment

Chemotherapy and radiotherapy can be used to destroy the white blood cells, but these need to be replaced with healthy cells. Bone marrow transplants are often used for this.

Role of Stem Cells

Hematopoetic Stem Cells (HSCs) can be harvested from bone marrow, peripheral blood or umbilical cord blood. As these can differentiate to form any type of white blood cell, they can be used to repopulate the bone marrow and produce new, healthy blood cells. The use of a patient’s own HSCs means there is far less risk of immune rejection than with a traditional bone marrow transplant.

From: http://en.wikipedia.org/wiki/Pluripotential_hemopoietic_stem_cell

Animation of this process:

HomeworkVocab

• Cell theory• Metabolism• Growth• Reproduction• Response• Homeostasis • Nutrition• Excretion• Surface area to volume ratio• Differentiation• Emergent properties• Inert• Stem cells• Therapeutic cloning• Stargardt’s disease

• Compare/contrast light microscopes and electron microscopes

• Outline how stem cells can be used to treat Stargardt’s disease

• Pg 11- Exercises 1,3,4