Download Chapter 3: Cell Structure and Function

Chapter 7: Cell Structure and Function
I. A Look at Cells
What is a cell?
Remember: A cell is the smallest unit of life that carries out all the
functions of a living thing
Cells -> Tissues -> Organs -> (Organ) Systems -> Individuals (Organism)
A. Living things may be either unicellular (like bacteria) or
multicellular (humans)
B. Cells can vary greatly in size
1. Smallest: bacterium (about 8000 of smallest bacteria could
fit into a RBC)
2. Longest: Nerve cells of large animals
3. Greatest volume: Unfertilized ostrich egg
C. Cells vary in shape (shape is related to function)
D. The avg. human is composed of approximately 100 Trillion cells
E. There are at least 200 different kinds of cells in the human body
draw some examples:
History: Discovery of Cells
A. Invention of microscope was an essential breakthrough in biology
B. Microscope invented by trio of Dutch eyeglass makers in the 1500's
C. In 1665 Robert Hooke published illustrations of observations using
a microscope
1. Hooke coined the term “cell” after observing dead cork cells
D. Early 1670's Anton van Leeuwenhock used new type of lenses to
observe pond water and blood (first to observe living cells)
People of the Cell Theory
A. 1838 Matthias Schlieiden concluded all plants are made of cells
B. 1839 Theodor Schwann concluded all living things are made of cells
C. 1855 Rudolf Virchow infers that all new cells come from existing cells
--> Theories of Schleiden, Schwann, and Virchow make up modern
Cell Theory:
1. Cells are the basic units of all life
2. All organisms are made of one or more cells
3. All cells arise from existing cells
Frontiers in Biology
A. Light Microscope
1. Use real or artificial light (bright-field, dark-field, & phase
contrast)
2. Can be used to view live specimens (small enough)
3. Large specimens must be sliced thin (to allow light to pass
through)
4. Limited magnification (about 1000X)
B. Electron Microscopes
1. Uses electrons instead of light
a. Transmission Electron Microscope (TEM) pass
electrons through
b. Scanning Electron Microscope (SEM) bounce
electrons off specimen
c. Scanning Interferometric Apertureless Microscope
can view single atoms
2. Can magnify specimen up to 1,000,000X
3. Must be performed fixed, in a vacuum (dead specimens only)
II. Basic Cell Structures
A. Cell Membrane (aka. Plasma Membrane)
1. A thin layer of lipid & protein that separates the cell’s contents from
its environment
2. 5 - 10 nm thick; 10,000 membranes ~ thickness of a sheet of paper
3. Membranes are made of phospholipids
a. a phospholipid consists of a phosphate head with two fatty
acid chains
b. phosphate head is hydrophilic or “water-loving”
c. lipid tails are hydrophobic or “water-fearing”
d. in water, phospholipids form two layers called a lipid bilayer
i. hydrophobic tails face each other (to avoid water)
ii. proteins are embedded in and through the lipid bilayer
iii. cholesterol helps bilayer maintain fluidity
iiii. Fluid Mosaic Model of cell is the combination of all
these traits
B. The Cytoplasm
1. Cytoplasm: A semifluid substance made primarily of water and
organic compounds between the cell membrane and
nucleus and supports internal organelles in the cell
a. Organelles are structures within the cell that perform
individual and specific functions
b. Cytoskeleton: A network of protein fibers and tubes
extending throughout the cytoplasm
i. Supports cell and helps maintain cell shape
ii. Cell membrane and some organelles are anchored to
cytoskeleton
iii. Materials transported throughout cell on cytoskeleton
iiii. Cytoskeleton enables certain types of cell to move
C. The Nucleus
1. Nucleus: Control center of the cell, the nucleus contains most of
the cells genetic material
a. Nuclei are surrounded by a double membrane called the
nuclear envelope
i. Nuclear envelope made out of a lipid bilayer
ii. Separates nucleus from the cytoplasm
iii. Many pores allow proteins & other things to pass through
b. Chromosomes: Distinct structures found in the nucleus
made out of nucleic acids that carries the
genetic information for the organism
i. Definite number of chromosomes per organism
-->Example: Humans have 23 pair or 46 total
c. Nucleolus: Small, single-membraned organelle located
inside of the nucleus that produces ribosomes
(ribosomes manufacture proteins for the cell)
D. Two Kinds of Cells
1. Prokaryotes: Organisms whose cells have no definite nucleus
(Example: bacteria are prokaryotic cells)
2. Eukaryotes: Organisms whose have a nucleus surrounded by a
nuclear membrane (Example: plant and animal cells
are eukaryotic cells)
III. Cell Organelles
A. Cells are small but perform complex functions (run like a factory)
B. Organelles are like parts of a factory that perform specific functions
C. # of each type of organelle varies according to cell function
(form=function)
1. Ribosomes: Make proteins (out of amino acids) for the cell
a. Found free floating or bound to membranes
b. Found in eukaryotic and prokaryotic cells (only
organelle found in later)
c. Ribosomes do not have a membrane like other organelles
2. Endoplasmic Reticulum (ER): An extensive network of
membranes that produces materials for the cell
a. Two Types of ER
i. Rough ER
--> Rough due to presence of ribosomes on
the outside of the ER
--> Helps synthesize proteins & manufacture
new cell membrane
ii. Smooth ER
--> Smooth due to absence of ribosomes
--> Functions in making lipids, processes
carbohydrates, and modifies chemicals
toxic to the cell
3. Golgi Apparatus: Transports molecules produced by the ER
a. Series of flat, membrane-bound sacs
b. Molecules are sorted, modified, packaged, & distributed
4. Mitochondria: Provides most of the energy needed for a cell
a. Converts adenosine diphophate (ADP) to adenosine
triphosphate (ATP), which is the energy
currency for the cell
b. Double-membrane bound organelle that has a folded
inner membrane
5. Lysosome: Contain digestive enzymes that help break down
large molecules of carbohydrates, proteins, and
lipids for the cell
a. Single-membrane bound organelle
b. Also used to digest old organelles
c. If lysosomes break apart it means certain death for cells
(certain types of arthritis)
D. Structures for Movement
1. Two types of structures are extensions of cytoskeleton that aid
in movement
a. Cilia: Short, hair-like projections usually present in large
numbers (Example: Ciliates or small unicellular
eukaryotes; human tracheal cells)
b. Flagella: Long, tail-like structures that function like a
whip or propeller
i. Usually only one or two flagella present per cell
ii. Certain prokaryotic cells have flagella that spin like
propellers
iii. Specific eukaryotic cells have flagella that move in
a whip motion
IV. Cell Diversity
A. Plant and Animal Cells
1. Plant and Animal cells are both eukaryotic but have distinct
differences
a. Cell Wall: Tough, rigid outer covering that protects a
plant cell and maintains its shape
i. Fungi, algae, and bacteria have cell walls also
ii. Animal cells do not have cell walls but other
support systems
b. Chloroplasts: Structures that enable the plant to make
sugars through photosynthesis and allows
plants to produce their own food
i. Animal cells do not have chloroplasts and can not
make their own food
ii. Prokaryotic cells do not have chloroplasts
c. Central Vacuole: A large membrane-bound
compartment w/ many functions
i. Vacuoles may absorb water, store proteins, ions,
and waste products
ii. Animal cells do not have a central vacuole but do
have smaller vacuoles
iii. Prokaryotic cells do not contain any vacuoles
V. Cells and Their Environment
A. Semipermeable: Selective or only allows certain substances to
pass through
B. Passive Transport: No energy required for movement through the
membrane
1. Diffusion: Movement from area of high to low concentration
(rate depends upon temperature and size of
molecule involved)
a. Facilitated: Requires help (carrier protein)
b. Equilibrium: Evenly distributed throughout
2. Osmosis: Movement of water across a semipermeable
membrane
a. Hypertonic: High Solute Concentration
b. Hypotonic: Low Solute Concentration
c. Isotonic: Equal concentrations of solute
C. Active Transport: Requires the use of energy (ATP) to move from
area of low concentration to high concentration
1. Exocytosis: Movement from inside to outside of cell
(packaged in Golgi)
2. Endocytosis: Movement from outside to inside of cell
a. Pinocytosis: Cell drinking, intake of water
b. Phagocytosis: Cell eating or engulfing (Ex. WBC)