chapter 3: cell structure section 2 3: cell features/organelles 1 chapter 3: cell structure section...

Chapter 3: Cell Structure Section 2 & 3: Cell Features/Organelles

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Chapter 3: Cell Structure

Section 2: Cell Features


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Objectives1. List the three parts of the cell theory.2. Determine why cells must be relatively

small.3. Compare the structure of prokaryotic

cells with that of eukaryotic cells.4. Describe the structure of cell

membranes.


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The Cell Theory


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The Cell Theory

Cell theory is an excellent example of how scientific concepts are developed by the accumulation of observations over time.


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The Cell Theory

It also shows how scientific discovery is often dependent upon advances in technology; in this case, the microscope.


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The Cell TheoryHistory of Cell Theory• 1665—Robert Hooke discovers and

names cells while observing thin slices of cork.

• 1675—Anton Van Leeuwenhoek discovers living microorganisms

• 1830s– Mattias Schleiden, after many observations, concludes that plants are made of cells and Theodor Schwann concludes that animals are made of cells.


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The Cell Theory• 1858—Rudolf Virchow determines that

cells come only from other cells.These observations form Cell Theory:1. All organisms are made of one or

more cells.2. Cells are the basic units of structure

and function in organisms.3. All cells arise from pre-existing cells.


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Cell Size


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Cell SizeCells are small.

Cells must be small in order to maintain a high surface area to volume ratio.


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High surface area to volume ratio allows for efficient exchange of materials into and out of cells.


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Also, in multicellular organisms, many small cells are easier to support on a skeletal framework than a few large cells.


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The Cell Theory

Here we see that as the size of a cell increases its surface area to volume ratio decreases.


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Cell Features

Common Features of Cells


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Common Features of CellsCell membrane

Cytoplasm (containing ribosomes)

DNA (within nucleus in most eukaryotic

cells)[movie]

Cell Features


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Cell FeaturesCommon Feature of Cells• Cell (plasma) membrane

–Outer boundary, separates cell contents from surroundings

–Regulates the passage of materials into/out of the cell


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Cell FeaturesCommon Feature of Cells• Cytoplasm

–Cell’s interior–Includes:

• cytosol—fluid portion • ribosomes—sites where proteins

are made• organelles (in some types)


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Cell FeaturesCommon Feature of Cells• DNA (present in all cells at some point)

–Provides genetic instructions for making proteins

–Regulates cell functions and reproduction


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Cell FeaturesCells are divided into two distinct types:

PROKARYOTICand

EUKARYOTIC


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Prokaryotes


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Prokaryotes

Are the smallest, simplest cells


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Prokaryotes

Single-celled organisms that lack a nucleus and other membrane bound compartments (organelles).


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Prokaryotes

The most familiar representatives are bacteria.


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Prokaryotes


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Prokaryotes• Are metabolically diverse

–Some do not need oxygen–Some cannot survive when

oxygen is present


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Prokaryotes• Are metabolically diverse

–Some are autotrophic (able to make their own food by either photosynthesis or chemosynthesis)


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Prokaryotes• Are structurally similar

–Genetic material is a single circular molecule of DNA.• Located in nucleoid region


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Prokaryotes• Are structurally similar

–Have outer cell wall• Provides protection and support

• May be surrounded by a capsule composed of polysaccharides


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Eukaryotes


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Eukaryotic Cells

Are much larger than prokaryotic cells.

Have a nucleus, and other membrane-bound organelles.


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Eukaryotic Cells

Organelle = a structure that carries out specific activities in the cell.


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Eukaryotic Cells

The nucleus is an organelle that contains the cell’s DNA.

Cells contain many organelles.


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Eukaryotic Cells

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Chromatin Nucleus


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Eukaryotic Cells


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The Cell Membrane


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The Cell MembraneCell membranes are: • Fluid

–Fluidity caused by phospholipids• Phospholipids form the foundation of the membrane.


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The Cell MembraneCell membranes are: • Selectively permeable

–Determines which substances enter and leave the cell

–Due to the way phospholipids interact with water


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The Cell MembranePhospholipids:• Recall that

–The phosphate head is polar and attracts water

–The fatty acid tails are nonpolar and repelled by water


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The Cell MembranePhospholipids:• Phospholipid bilayer

–Lipids are arranged in a double layer with the nonpolar fatty acid tails on the interior


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The Cell Membrane


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The Cell MembraneMembrane Proteins:• Various proteins are located in the

lipid bilayer and have different functions:

MarkersReceptorsEnzymes

Transporters


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The Cell MembraneMembrane Proteins:

–Marker proteins—attached to surface carbohydrates, they serve to identify the cell


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The Cell MembraneMembrane Proteins:

–Receptor proteins—bind specific signal molecules outside the cell


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The Cell MembraneMembrane Proteins (cont.):

–Enzymes—involved in important biochemical reactions in the cell


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The Cell MembraneMembrane Proteins (cont.):

–Transport proteins—aid the movement of substances into/out of the cell.


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The Cell Membrane


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Guided Practice1. What determines the maximum size of

a cell?– The ratio of the cell’s surface area to its

volume

2. In what way(s) do eukaryotic cells differ from prokaryotic cells?

– Eukaryotic cells have a nucleus and other membrane bound organelles


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Guided Practice3. Explain how the cell membrane

contributes to a cell’s ability to maintain homeostasis.

– The cell membrane regulates what substances enter and leave the cell.

4. In the cell membrane, the fatty acids of phospholipid molecules are located _____________________________.on the interior of the lipid bilayer

chapter 3: cell structure section 2 3: cell features/organelles 1 chapter 3: cell structure section...

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