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Unit 4
Cellular Biology
Textbook Chapter 7
Review Book Topic 1
What is a Cell?
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All living things are made of cells
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Basic structural and functional unit of living things
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Can be composed of a single cell
(unicellular) or multiple cells (multicellular)
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Cells carry on all life processes of an
organism
Organization of Living Things
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In multicellular organisms
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Groups of specialized cells form tissues
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Different kinds of tissues are combined to
form organs which carry out life processes
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Each organ is part of an organ system
which transports materials throughout the
body
History of Cellular Biology

Robert Hooke (mid-1600s)
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Examined thin pieces of cork
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Observed boxlike structures of the dead walls of
a plant cell
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Called these boxes: “cells”
Never studied living cells
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Anton van Leewenhoek (mid-1600s)
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Observed pond water
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Saw microorganisms within the water samples
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Observed and described human blood cells
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Described bacteria
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Robert Brown (early 1800s)
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Observed small, dense, round bodies which
appeared in all plant cells
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Called the structure the
“nucleus”
Cell Theory
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All organisms are made up of one or more
cells
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All cells carry on life activities
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The combined activity of individual cells make up
the life activities of a multicellular organisms
New cells arise from pre-existing cells
Cell Types
Prokaryotic vs. Eukaryotic
Prokaryotic Organisms
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Lack internal membrane-bound organelles
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Prokaryotic = “Without nucleus”

1-10 µm (micrometers) – very small
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Ex. Archaebacteria and Eubacteria
Cell Characteristics

Lack a membrane bound nucleus, but instead
have a single, circular chromosome found in a
region called a nucleiod
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Contains:

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Cell wall
Plasma membrane
Capsule – secretion of a slime-like material to give added
protection to the cell
Characteristics Continued

Most life processes occur on the surface of the
plasma membrane

Ribosomes located throughout cytoplasm (protein
synthesis)

May use cilia or flagella for movement

Pili are sexual appendages used in conjugation
(reproduction)
Eukaryotic Cell

Internal membrane bound organelles

Eukaryotic = “True nucleus”

10-100 µm (micrometers) – larger than bacteria


Largest single cell can be seen in bird eggs (ex. ostrich)
Ex. Animals, plants, protists, fungi
Similarities
Similarities

Membrane which separates internal components
from the external environment

Contain genetic material

Contain ribosomes to make proteins
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Suspend materials in cytoplasm

Carry out the same life processes
Animal Cell
Plant Cell
Organelles
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Plasma membrane
Cell wall (PLANTS ONLY)
Nucleus
Cytoplasm
Endoplasmic Reticulum
Ribosomes
Golgi Complex
Organelles Continued
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Lysosomes
Mitochondria
Chloroplasts (PLANTS ONLY)
Microtubules/microfilaments
Centrioles
Cilia/flagella
Vacuoles
Cell Wall

Included in all plants and most bacteria

Lies outside of plasma membrane

Gives cell its shape and provides protection

Plants have cell walls made of cellulose (source
of fiber in our diets!)

Has small openings to allow materials to pass to
and from the cell membrane

ANIMAL CELLS DO NOT HAVE CELL WALLS

This is what Hooke observed in the mid-1600s
with his microscope when observing cork cells
Plasma Membrane
Function

Separates the cell from its surrounding
environment

Controls movement of materials into and
out of the cell (selectively permeable)
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Keeps internal conditions of the cell
constant by maintaining homeostasis
Function Continued

Signaling mechanism
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Used for making energy for the cell
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Used for cell to cell recognition
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Used to compartmentalize organelles
Structure

Two Layers (bi-layer)
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Composed of:
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Lipids
Proteins
Carbohydrates
Cholesterol
“Fluid-like” – called the fluid mosaic model
Phospholipids
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Composed of:
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Two fatty acid chains
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Phosphate group
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Glycerol backbone
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Hydrophobic (non-polar) region
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“Hates” water
Most important factor in the formation of
membranes
Fatty acid chain components
Hydrophilic (polar) region
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“Loves” water
Phosphate and glycerol components
Proteins
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Can be found:
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On the outer surface of membrane (glycoprotein)
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On the inner surface of membrane (peripheral)
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Extending through the membrane (transmembrane or integral)
Proteins Continued
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Function:
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Controls movement of substances through the
membrane (transport)
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Acts as a receptor to signaling the cell to start or
stop a metabolic activity (communication)
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Helps connect neighboring cells to each other or
structural elements inside the cell (structure)
Carbohydrates
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Linked to membrane proteins or lipids
(glycoproteins or glycolipids)
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Branching from external surface of the
membrane ONLY

Used in cell recognition and signaling
Cholesterol
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Has hydrophobic and hydrophilic regions
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Helps prevent membranes from being too “fluidlike”
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Without cholesterol, cell membranes wouldn’t be
firm enough and would be too permeable to some
molecules
Nucleus
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Round, membrane-bound structure in
Eukaryotic cells
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Serves as the control center for cell
metabolism and reproduction
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Largest organelle
Nucleus Continued
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Enclosed by the nuclear envelope
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Membrane surrounding the nucleus
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Double membrane
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Contains selectively permeable pores
Nucleus Continued
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Contains chromatin
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DNA bound to various
proteins
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Long, thin strands
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Make up chromosomes (hereditary material) by
coiling tightly during cell division
Nucleus Continued
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Within the nucleus is
a nucleolus
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Dense, solid
structure
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Site of ribosome
production
Cytoplasm
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Watery material within cell
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Contains dissolved materials for cell
metabolism
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Chemical reactions in the cell occur here
(metabolism)
Cytoplasm Continued
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All organelles are suspended in this
material
Endoplasmic Reticulum
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System of fluid-filled canals
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Paths for the transport of materials
throughout the cell
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Highly folded to increase the surface area
for chemical reactions to occur
Endoplasmic Reticulum
Continued
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Can be connected to the nuclear envelope
or free floating in the cytoplasm
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Rough ER
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Ribosomes are attached to the outer surface
Smooth ER
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No ribosomes
Ribosomes
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Site of protein synthesis
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Found attached to the endoplasmic
reticulum (rough ER) or in cytoplasm (free
ribosomes)
Golgi Complex
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Stacks of flattened membrane sacs
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Processes, packages and stores products being
released from the cell
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Animal cells usually have only one, located near the
nucleus
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Plant cells have several hundred (remember...they
are the main producers in our food chain ! )
Golgi Complex Continued
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Example:
 Proteins are produced by ribosomes on the rough ER
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These proteins are transported by the ER to the golgi
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Golgi process and package the proteins into vesicles
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Protein is transported to where it is needed in the
cell, stored or sent to the plasma membrane to be
sent out of the cell
Lysosomes
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Small, bubble-like structures surrounded by a single
membrane (vesicle)
 Contain no water…so this allows it to have a
single membrane
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Contains strong digestive acids
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In single-celled organisms:
 Involved in the digestion of food within the cell
Lysosomes Continued
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In multicellular organisms:
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Breaks down worn-out cell organelles
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Part of the body’s defense against disease
 Ex. White blood cells
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Involved in developmental processes
 Ex. Tadpole  frog, digestion of its tail
Vacuoles
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Fluid filled organelles enclosed by a membrane
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Plant cells contain a single, large vacuole which
occupies most of the space within a cell
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Used as a storage site (remember plants are
producers and need to store all that energy in the
form of sugar ! )
Vacuoles Continued
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Animal cells:
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Very small and few in number
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Excess water is collected in contractile vacuoles
(shaped like a star or sun)
Mitochondria
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Round or oval shaped
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Releases energy in food molecules for cell use
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By the process of cellular respiration
“Powerhouse” of the cell
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Usually 300-800 per cell depending on cellular
activity
Mitochondria Continued
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Cells requiring lots of energy contain large numbers of
mitochondria
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Ex. Muscle cells, heart cells
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Capable of moving independently throughout the cell
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Contain their own DNA and are capable of duplicating
themselves
Mitochondria Continued
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Surrounded by a double membrane
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Inner membrane is highly folded, forming
cristae that extend into the middle of
organelle
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Cristae provide a large surface area where
biochemical reactions can occur
Plastids
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Membrane-enclosed organelles that are found only
in photosynthetic, eukaryotic organisms
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ONLY IN PLANT CELLS (and some algae)
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Two types:
 Leucoplasts – colorless pigments
 Chromoplasts – colored pigments
 Most important is the chloroplast (green)
Chloroplasts
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Plastid containing a green pigment called
chlorophyll

Site of photosynthesis
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Food making process which uses light energy (autotrophic
nutrition carried out by producers)
Contains stacks of photosynthetic membranes
called grana which contain chlorophyll
Chloroplasts Continued
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Watery material that fills the remainder of
the chloroplast is known as the stroma
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Contain their own DNA and have the ability
to duplicate themselves
Microtubules
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Long, hallow, cylindrical structures found in the
cytoplasm (made of protein)
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“Skeleton” for the cell, giving it its shape
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Used during cell division
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Found in:
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Centrioles
Cilia
Flagella
Cilia & Flagella
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Hair-like organelles with the capacity for movement
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Single-celled organisms – cell movement
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Multicellular organisms – used to move
substances over the cell’s surface
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Extends from the surface of cells
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Structures are identical but flagella are longer and
fewer in number than cilia
Centrioles
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Found near the nucleus in animal cells
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Pair of cylindrical microtubules which lie at
a right angle (90º) to each other
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Involved in cell division in animals cells
Microfilaments
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Long, solid, threadlike strands made of protein
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Associated with cell movement
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Ability to contract (ex. muscle cells)
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Involved in cytoplasm movement (ex. cytoplasmic
streaming in ameoba)
Serve as supporting structures for the cell
Origins of the Eukaryotic Cell

The structural differences between
eukaryotic and prokaryotic cells are so
great, biologists have wondered how these
two kinds of cells are related
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Most ideas are based on evidence that has
been collected, called the endosymbiotic
theory
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Eukaryotic cells are the result of:
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Endosymbiosis – condition in which one
organism lives inside the cell of another
organism to the benefit of both (mutualism)

Mitochondria and chloroplasts are thought to be
the result of bacteria which were engulfed by,
then lived within, other larger cells
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Evidence – both contain their own DNA and can
reproduce themselves like bacteria, similar in size
to bacteria, have same metabolic machinery as
bacteria