UNIT 2 - CELLS
Chapter 3 – Cell Structure and Function
Look at the picture on page 69 “Why do these look fried eggs?”
What is the SEM? Tell me about it.
What can we learn by looking at cells?
Activate prior knowledge-page 69
3.1 Cell Theory
Key Concepts: Cells are the basic unit of life.
Main Ideas:
Early studies led to the development of the cell theory.
Prokaryotic cells lack a nucleus and most internal structures of eukaryotic cells.
Objectives:
Describe developments that led to the cell theory.
Differentiate between prokaryotic and eukaryotic cells.
Vocabulary – past vocabulary: structure
New: cell theory
function
cytoplasm
organelle
prokaryotic cell
eukaryotic cell
CCC Video – The Living Cell (15 min 20 sec)
You tube – Cell Theory Rap Song/ Cell Theory Scientist Contributions
***Access Biozine at to learn about the variety of careers open to biologists at www.classzone.com
**Bell Ringer 3.1 – Page 72 Questions 1-5 – SC.912.
Early studies led to the development of the cell theory
1.
2.
3.
Before the microscope was invented, cells were too small to see and study.
Zacharias Janssen is usually credited with inventing the microscope.
A compound microscope combines the power of 2 or more lenses.
Discovery of Cells (Page 71 – Fig. 3.3 – Contributors to the Cell Theory)
1. In 1665, Robert Hooke used a triple lens compound microscope to examine thin slices of cork.
-He observed that the cork was made up of tiny compartments – he coined the term – cell.
2. In 1674, Anton van Leeuwenhoek used a single lens that was more powerful.
- examined in greater detail observing single celled organisms in pond water.
3. In 1838, Matthias Schleiden observed that plants were made up of cells.
4. In 1839, Theodor Schwann observed that animal cells were made up of cells.
- He concluded all living things were made of cells.
- Incorrectly stated that cells spontaneously grew by free cell formation.
5. In 1855, Rudolf Virchow proposed correctly that cells only come from pre-existing cells.
The Cell Theory
1. All organisms come from cells.
2. All existing cells are produced by other living cells.
3. The cell is the most basic unit of life.
Prokaryotic cells lack a nucleus and most internal structures of a eukaryotic cell
1. Cells are surrounded by a membrane and enclose a jelly like substances that contains dissolved molecular
building blocks (amino acids, proteins, lipids, etc.) called the cytoplasm.
2. In some types of cells, the cytoplasm contains small specialized structures that perform specialized functions
called organelles.( most are covered by a membrane)
1. Page 72 – Figure 3.4 Comparison between a prokaryotic and eukaryotic cell.
2. Prokaryotes:
- lack a nucleus
- Their DNA is disbursed throughout the cytoplasm
- All prokaryotes are single-celled organisms.
4. Eukaryotes:
- have a nucleus
- have internal membrane bound organelles.
- Their DNA is enclosed within the membrane bound nucleus.
- Eukaryotes can be single or multi-celled organisms.
**Lab Inquiry – Exemplary Lesson Plan – Lab on Plant and Animal Cells
**Classzone.com for further information on prokaryotes and eukaryotes.
3.2 Cell Organelles
Key Concept: Eukaryotic cells have many similarities.
Main Ideas:
1. Cells have internal structure.
2. Several organelles are involved in making and processing proteins.
3. Other organelles have various functions.
4. Plants have cell walls and chloroplasts.
Objectives:
1. Describe the internal structures of a eukaryotic cell.
2. Summarize the functions of organelles in plant and animal cells.
Vocabulary
Cytoskeleton
nucleus endoplasmic reticulum
Golgi apparatus
Lysosome
excretion
vesicle
centriole
Ribosome
mitochondrion
cell wall
Vacuole
chloroplast
secretion
http://www.youtube.com/watch?v=LP7xAr2FDFU&feature=related (Cell Structure)
Cells have internal structure
1. Cells are highly organized, membrane bound internal structures that:
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Perform specific functions.
Divide certain molecules into compartments.
Help regulate the timing of key events.
2. Organelles are not free floating; they are anchored in place at specific sites in the cell.
3. The cytoskeleton gives a framework made of proteins that change according to the needs of the cell.
4. The cytoskeleton is comprised of 3 different types of threads or fibers:
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a. Microtubules are long hollow tubes
Microtubules provide shape and act as tracks for the cell to move.
During cell division (mitosis) the mictotubules aid in forming a spindle to help separate DNA into 2 new
cells.
b. intermediate filaments are somewhat smaller than microtubules but provide strength for the cell.
c. Microfilaments are the smallest of the three.
Help the cell move and during cell division.
Important in muscle cells where they assist the muscles cells contract and relax.
** See page 74 – Figure 3.6 – Cell Structure of Plant and Animal Cells
4. The cytoplasm fills the area between the plasma membrane and the nucleus.
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It is made cytosol which is made of water and other materials that help dissolve chemicals and enzymes
for chemical reactions.
It is an important gel-like substance.
Several Organelles are involved in making and processing proteins
1.
2.
3.
4.
5.
Much of the cell is devoted to making proteins.
There are 20 different amino acids with different characteristics (size, polarity, acidity etc.)
Form very short or very long chains that fold into different shapes.
Multiple protein shapes can interact with each other.
Proteins carry out critical functions so they need to be made correctly.
Nucleus
1.
2.
3.
The nucleus is the storehouse for genetic information of the cell.(DNA)
DNA contains the genes that are instructions for making proteins.
2 Major demands of the nucleus:
a) Protect the DNA
b) DNA must be available at all times.
4. Molecules that would damage the DNA need to be kept out of the cell.
5. Many proteins are involved in turning genes on and off so they need access at certain times.
6. The nucleus is structured (built) to provide this function (job)Pg. 74 Fig. 3.7
7. The nucleus has a double membrane – the nuclear envelope – that has openings called pores.
8. The pores allow certain molecules and proteins to pass into and out of the nucleus.
9. The nucleolus is in the nucleus.
10. The nucleolus is responsible for making organelles that produce proteins for the cell, ribosomes.
Endoplasmic Reticulum and Ribosomes
1. The ER or endoplasmic reticulum is a interconnected network of folded membranes.
2. Numerous process including protein and lipid production occur in the inside (lumen) and outer surface of the ER.
3. Folded membranes allow the ER to have a much increased surface area. (Take a piece of paper and folder 10
times. The surface area is the same but the space it occupies is much smaller)
4. In some areas the ER is studded with ribosomes. This is the rough ER.
5. The areas without ribosomes are called the smooth ER.
7. The ribosomes are tiny organelles that link monomers, amino acids, together into long and short chains or
polymers, proteins. (protein synthesis)
Golgi Apparatus
1.
2.
3.
4.
5.
6.
7.
From the ER, proteins generally move to the Golgi apparatus.
The Golgi apparatus is a folded multi-layered membrane enclosed organelle.
The function of the Golgi apparatus is to process, sort and deliver proteins.
The GA may make additional changes to the proteins using enzymes stored in the membranes.
Proteins may also be packaged here and stored for later use.
Some proteins are transported to other organelles via the vesicles.
Other proteins are carried to the plasma (cell) membrane and secreted outside the cell. (enzymes and
other cell chemicals are secreted to assist in reactions and functions of the cell.
1. “Secretion” and “excretion” are the same in nature since both are involved in the passage or movement of
materials.
2. “Excretion” is the removal of material from a living thing while “secretion” is the movement of material from
one
point
to
another.
3. Excretion is mostly body wastes while secretion is important materials that can be metabolized and used by
our bodies.
Vesicles
1.
2.
3.
4.
Cells need to separate certain chemicals for use later in chemical reactions.
Vesicles are small membrane bound sacs that are temporary and recycled.
The divide materials from the rest of the cytoplasm and transport them to other parts of the cell.
After a protein has been made in the part of the ER pinches off to form is the new protein.
5.
6.
Once it is protected, it can be transported to the GA for modification.
The modified protein is packaged in a new vesicle for either transport, storage of secretion.
Other organelles have various functions
Mitochondria
1. Energy for use in the cell is produced in the mitochondria by cellular respiration. (Combining food broken
down into sugar with oxygen to use as energy)
2. The mitochondria is bean-shaped and has internal folds called cristae that increase the surface area for cell
respiration to occur.
Vacuoles
1. Vacuoles are fluid filled sacs that store water, food, enzymes, etc.
2. There are many smaller vacuoles in an animal cell.
3. There is one large central vacuole in plant cells.
4. See page 77 – Fig. 3.12
Lysosomes
1. Membrane bound organelle that contains enzymes.
2. Digest cell parts that are old or worn.
3. Protects the cell from viruses and bacteria.
4. Move to a target molecule and engulf the molecule.
5. Must be membrane bound to protect the cell as well as the enzymes since enzymes work better in the lysosome
than the cytoplasm.
6. Many lysosomes in animal cells. There are no or only a few in plant cells.
Centrosome and Centrioles
1. The centrosome is a small region of the cytoplasm that produces microtubules.
2. The centrosome is made up of 2 centrioles positioned perpendicular to each other.
3. Involved in cell division by forming a spindle to separate chromosomes into 2 new cells.
4. Also involved in some organisms and cells in the production of cilia and flagella.
Cell walls
1. Only in plants cells.
2. The cell wall is located outside the cell membrane.
3. Provides structure (shape) and protection for the plant cell.
Chloroplasts
1. Organelles that carry out photosynthesis.
2. Only in plant cells.
3. Contain chlorophyll, a green pigment that absorbs sunlight.
** Bell ringer 3.2 - Page 79 Questions 1-6.
3.3 Cell Membrane
Key Concept: The cell membrane is a barrier that separates the cell from the external environment.
Main Ideas:
1. Cell membranes are composed of 2 phospholipid layers.
2. Chemical signals are transmitted across the cell membrane.
Cell membranes are composed of 2 phospholipid layers (See page 82 Fig. 3.17)
1. The cell membrane is the boundary that protects the cell from the external environment.
2. The cell membrane controls the passage of materials into and out of the cell. It allows entry to beneficial
materials and denies access to harmful ones.
It also is the exit point of waste products from the cell.
4. The cell membrane is double layered because of their composition of phospholipids.
5. A phospholipid has a glycerol “head” end which is polar. (Remember from chapter 2) and a tail made of fatty
acids which is non-polar.
6. As you remember, water is also a polar molecule. As a result, water and the polar head of the phospholipid form
hydrogen bonds. They stick together.
7. The polar heads form the inside and outer surfaces of the membrane. The “filling” between the polar heads are
the “tails” which are non-polar.
8. This arrangement of phospholipids provides the membrane with characteristics it otherwise would not have.
 Cholesterol molecules strengthen the membrane.
 Some proteins extend through one or both layers of the cell membrane and help materials cross the
membrane.
 Different cell types have different membrane proteins.
 Carbohydrates attached to the membrane proteins serve as tags for identification tags that allow the cells
to distinguish one from the other.
Fluid Mosaic Model
1. This is a scientific model developed by scientists to represent the structure of the cell membrane.
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Cell membrane is flexible not rigid
Flexibility is achieved by having the double layer and enabling the phospholipids to slide past each other.
Behaves like a fluid (oil)
The “mosaic” refers to the variety of molecules embedded within the membrane. Similar to the many
colors and textures of tiles in a mosaic art piece.
Selectively Permeable
1. Selectively permeable means to allow some materials, but not all to cross the membrane. The membrane
regulates entrance into and out of the cell.
Quick lab – Page 83 – Modeling the Cell Membrane
3.4 Diffusion and Osmosis
Key concept: materials move across a membrane because of concentration differences.
Main Ideas:
1. Diffusion and Osmosis are types of passive transport
2. Some molecules diffuse through transport proteins
Objectives:
1. Describe passive transport.
2. Distinguish between osmosis, diffusion and facilitated transport.
Vocabulary:
Passive transport
Isotonic hypertonic
diffusion
osmosis
hypotonic
concentration gradient
facilitated diffusion
Diffusion and osmosis are types of passive transport
1. Passive transport is the movement of molecules across a cell membrane without input of energy from the cell.
2. Diffusion is the movement of molecules in a fluid or gas from an area of high concentration to an area of lower
concentration.
http://brainchemist.files.wordpress.com/2011/01/diffusion.gif
3. A concentration gradient is the difference in concentration of a substance from one location to another.
Osmosis
1. The movement of water molecules form an area of high concentration to an area of low concentration across a
selectively permeable membrane is called osmosis.
2. A solution is isotonic to a cell if it has the same concentration of dissolved particles as the cell.
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Water molecules move into and out of the cell at an equal rate so the cell’s size remains constant.
3. A solution is hypertonic if it has a higher concentration of dissolved particles than the cell.
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The water concentration inside the cell is higher than outside the cell.
The water will flow from inside to outside the cell so the cell will shrink or even die.
4. A solution is hypotonic if it has a lower concentration of dissolved particles than inside the cell.
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The water is more concentrated outside the cell than inside the cell.
This means the water molecules will diffuse into the cell.
If too much water enters the cell it could cause the cell to burst.
Some molecules diffuse through transport proteins
1. Facilitated diffusion is the diffusion of molecules across a membrane through by a transport protein.
2. Transport proteins make it easier to enter or exit the cell.
3. Still a form of passive transport.
4. Move DOWN a concentration gradient, from a region of high concentration to a region of low concentration.
5. Most allow only certain types of molecules to pass through.
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Some change shape when the molecule enters the channel
Some are tunnels that allow ions to pass through
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http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.html
3.5 Active Transport, Endocytosis and Exocytosis
Key Concept
Cells use energy to transport materials that cannot diffuse across a membrane.
Main Ideas
1. Proteins can transport materials against a concentration gradient.
2. Endocytosis and Exocytosis transport materials across the membrane in vesicles.
Objectives
1. Describe active transport.
2. Distinguish between phagocytosis, endocytosis and exocytosis.
Proteins can transport materials against a concentration gradient
1. Active transport drives materials across a membrane from areas of low concentration to an area of high
concentration.
http://www.youtube.com/watch?v=owEgqrq51zY&feature=fvwp&NR=1
Endocytosis and Exocytosis transport materials across the membrane in vesicles
1. Endocytosis is the process of taking in liquids or fairly large molecules and engulfing them in a membrane.
2. Phagocytosis is involved when the cell membrane engulfs large substances.
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It is involved when your immune system attacks foreign objects like germs and “eats” them.
3. Exocytosis is the reverse of endocytosis. It is the release of materials out of the cell by fusion with the
membrane.
http://www.youtube.com/watch?v=FJmnxbYBlr4 (Endo/Exo)
**Bell Ringer 3.5 page 91 Questions 1-5
http://www.youtube.com/watch?v=GigxU1UXZXo