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At the Boundary of the Cell

________________________________ - The smallest unit that can carry out all the activities necessary for life.

________________________________ - The outer surface of the cell that shields the delicate internal machinery. It refulates what goes into & out of the cell.

Cells must be small so that necessary materials (food, water, etc) can reach the "machinery" efficiently.

The size to which a cell can grow is limited by its _____________________________________, which must be large enough to meet the needs of its volume. An appropriate ______________________to ______________________ ratio allows the cell to take in enough food & water, and remove enough wastes.

When the ______________________ of a cell increases, its ______________________________ increases at a slower rate.


Water and the Cell

Water is necessary for all functions of the cell.

The ______________________________ is shaped by water found __________________ & _________________ the cell.

Water is a ________________________ molecule. This means that is has a partial negative charge on one side, and a partial positive charge on the other.

The _________________charge on the hydrogen atom of one water molecule is attracted to the ________________ charge on the oxygen atom of another water molecule. This attraction is called a ____________________________.

When water molecules form hydrogen bonds with one another, they are at a ________________________________ state, which makes them more ________________________. (They like this state!)


Water and the Cell Membrane

Cell membranes are composed of _________________________, which are _________________________. This type of molecule has no positive or negative poles. Water, on the other hand, is polar.

Polar & Non-polar substances will ________________________ after being mixed (water & oil example). Because water molecules __________________________ one another, the oil is pushed away. The force of water molecules pushing a sheet of lipids is the force that shapes the cell membrane. (figure 3-6d)





Membrane Architecture

Structure of the Lipid Bilayer

Cell Membranes are made up of a _________________________________________ & _________________________________________.

____________________________ - A lipid molecule which has nonpolar & polar regions:

Phospholipids have two layers:






Characteristics of the Lipid Bilayer

Protein "passageways" allow necessary polar molecules through the membrane.

This allows proteins to "float" within the membrane





Types of Cell Membrane Proteins























Protein Structure & the Cell Membrane

There are 20 _____________________________ that construct proteins. Some are polar, and some are non-polar. How they are arranged in the protein determines the _________________________ of the protein. The amino acids bend, fold, or twist into a specific ___________________ with a unique ______________________.





Non-Polar Regions Anchor Proteins in the Membrane

The amino acids in this region of the
protein are mostly polar. Therefore,
this region is compatible with the
water outside of the cell.

The amino acids in this region of the protein
are non-polar, and are compatible with the
non-polar center of the membrane. This region
anchors the protein in the membrane.

This region is also polar, and is compatible
with water inside the cell


Inside the Cell

There are two types of cells: (Complete the following table)




No Nucleus

Many Membrane-bound organelles


Most 1-10 um

Evolved 1.5 billion years ago


Only bacteria


Both Prokaryotic & Eukaryotic Cells contain:


Eukaryotic Cells have Organelles: Specialized compartments that carry out one or more specific functions



Plant Cells Differ from Animal Cells…

Plant cells have a few structures that Animal Cells don't have:


The Origin of Eukaryotes

The main difference between prokaryotic & eukaryotic cells is that eukaryotic cells have organelles. How did these structures arise???

The Theory of Endosymbiosis proposes that 1.5 billion years ago, tiny prokaryotic cells were "swallowed" by larger cells, but were not digested. The prokaryotic "trespassers" remained inside the larger cells, gradually losing their ability to live independently. Thus, they became mitochondrion & chloroplasts of eukaryotic cells! What proof is there that this may be true? Turn to page 54 of your book and find out!


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