Chapter 3Cell Structure

I. History of Cells• Cells were first observed only

after microscopes were invented in the 1600s

• Robert Hooks, “The Cell Guy” used a microscope to observe a thick slice of cork in 1665

- He saw a lot of little boxes that reminded him of the small cells in which monks lived, so he called them cells

• Anton van Leeuwenhoek used a microscope to view water from a pond

- discovered many living creatures; first single-celled organisms

Ameoba Bacteria Yeast

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II. The Cell Theory• 3 parts 1. All living things are made of one or more cells 2. Cells are the basic units of structure and

function in organisms 3. All cells arise from existing cells

A. Cell size• Small cells function more efficiently than large

cells because of the higher surface are-to volume ratio

- substances do not need to travel as far to reach the center of a small cell, therefore they can enter and leave the cell in numbers large enough to meet the cell’s needs

B. Common Features of Cells 1. Cell membrane: outer boundary

• Encloses the cell and separates the cell interior from its surrounding

• Regulates what enters and leaves a cell

2. Cytoplasm: cell interior 3. Cytoskeleton

• Microscopic fibers that support a cells structures in the cytoplasm

Outside of Cell

Inside of CellCytoplasm

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4. DNA• Provides instructions for making proteins• Regulates cellular activities• Enables cells to reproduce

5. Ribosomes: one type of cellular structure• Makes proteins

III. Prokaryotes• Single-celled organisms that lack a

nucleus and other internal compartments

A. Characteristics of Prokaryotes• A prokaryote’s enzymes and

ribosomes are free to move around in the cytoplasm because there are no internal structures that divide the cell into compartments

• Genetic material is a single, circular molecule of DNA, often located near the center of the cell

• Prokaryotic cells have a cell wall surrounding their cell membrane that provides structure and support

• Some prokaryotic cell walls are surrounded by a capsule

• Many have flagella, which are long, threadlike structures that enable movement

IV. Eukaryotic Cells• Eukaryotes are organisms whose cells have a

nucleus• The nucleus houses the cell’s DNA• Organelles are structures that carry out specific

activities allowing eukaryotic cells to function in ways different from prokaryotes

• Some eukaryotic cells have hair like structures called cilia that help some cells propel them through their environment and others move substances across their surfaces

V. The Cytoskeleton• Provides the internal

framework and the shape of an animal cell

• Composed of an intricate network of protein fibers anchored to the inside of the plasma membrane

• Some fibers attach the nucleus and other organelles to fixed locations in the cell

• Three types A. Microfilaments (Actin Fibers)

• Form a network just beneath the cell surface attached to membrane proteins embedded within the cell membrane

• By contracting or expanding, actin fibers control the shape of animal cells

Cell membrane

Microfilaments

B. Microtubules• Hollow tubes made of the protein tubulin• Act as “rails” for motor proteins to move along

that carry RNA molecules

C. Intermediate Fibers• Thick ropes that anchor particular enzymes and

ribosomes near one another

VI. The Cell Membrane• Cell membranes are fluid because of the lipids

that form them• The cell membrane only allows certain substances

in the cell’s environment to pass through; it is selectively permeable

A. The Cell Membrane as a Barrier• The cell membrane has a

double layer of phospholipids called a lipid bilayer

- a phospholipid is made of a phosphate group and two fatty acids

- the phosphate group acts as a polar “head,” it is attracted to water, or hydrophilic

- the fatty acids act as nonpolar “tails,” they are repelled by water, or hydrophobic

B. Membrane Proteins• Some proteins are located in the lipid bilayer to

indicate cell type, bind specific substance, and move substances into and out of the cell with the help of enzymes

• Proteins are made of amino acids that anchor the proteins in the bilayer

- polar amino acids are attracted to the polar “head” groups and water on either side of the cell membrane

- nonpolar amino acids are attracted to the nonpolar “tail” groups on the inside of the lipid bilayer

VII. Nucleus• The nucleus is surrounded by

two lipid bilayers called the nuclear membrane, or nuclear envelope

• Nuclear pores are scattered over the surface of the nuclear envelope

• Ribosomes are assembled in a region of the nucleus, called the nucleolus

• Ribosomes and RNA are moved out of the nucleus to the cytoplasm through the nuclear pores

• Hereditary information is coded in the cell’s DNA which is stored in the nucleus

VIII. Ribosomes and the Endoplasmic Reticulum• Ribosomes make proteins• Ribosomes themselves are made of proteins as

well as RNAA. Production of Proteins 1. Some ribosomes are suspended in the cytosol

and make proteins that remain inside the cell

2. Other ribosomes are attached to the endoplasmic reticulum and make proteins that are exported from the cell• The endoplasmic reticulum, or ER, helps move

proteins and other substances through the cell - it too is made of a lipid bilayer

a. ER with ribosomes attached to its surface is called rough ER• Helps transport proteins that are made by the

attached ribosomes by pinching them off into vesicles and moving them to the Golgi apparatus

b. ER without ribosomes is called smooth ER• Helps make lipids and break down toxic

substances

B. Packaging and Distribution of Proteins 1. Ribosomes make proteins on the rough ER; the

proteins are packaged into vesicles 2. The vesicles transport the newly make proteins

from the rough ER to the Golgi apparatus

3. In the Golgi apparatus, proteins are processed and then packaged into new vesicles

4. Many of these vesicles move to the cell membrane and release their contents outside the cell

5. Other vesicles, including lysosomes, remain within the cytoplasm; Lysosomes digest and recycle the cell’s used component by breaking down proteins, nucleic acids, lipids, and carbohydrates

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IX. Mitochondria• Mitochondria harvests energy to

make ATP, the main energy of cells• Mitochondria has two membranes 1. an outer, smooth membrane 2. an inner, folded membrane• Chemical reactions occur in

between the two membranes that produce ATP

A. Mitochondrial DNA• Mitochondria has its own DNA and ribosomes

that make their own proteins• Mitochondrial DNA comes from your mother

X. Structures of Plant Cells A. Unique Features of Plant Cells 1. Cell Wall

• Composed of proteins and carbohydrates, including the polysaccharide cellulose

• Helps support and maintain the shape of the cell

2. Chloroplasts• Use light energy to make carbohydrates from

carbon dioxide and water• Found in a variety of eukaryotic algae• Also contain two membranes, supply energy to

the cell, and contain their own DNA like mitochondria

3. Central Vacuole• Stores water and can contain other substances

including ions, nutrients, and wastes• When full, it makes the cell rigid allowing for the

plant to stand upright

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