Cytology: the Study of the
Structure and Function of Cells
LO Covered: B1
A Bit of History
• Cell research began in the 17th century
• 3 researchers are credited with developing
the cell theory:
– Schleiden&Schwann: all living things are
composed of cells
– Virchow: all cells come from pre-existing cells
Some Cell Terms & Basic Info
• There are 2 basic types of cells
– Prokaryotic: (no internal membranesno
nucleus or membrane-bound organelles)
– Eukaryotic: (nucleus & membrane-bound
organelles)
• Organelle: a distinct sub-cellular structure
which carries out a specific function
• Ultrastructure: the inner makeup of a cell
Meet the Organelles..
4 groups:
1. cell membrane
2. nucleus-related
structures
3. endomembrane
system organelles
4. energy-producing
organelles
The Cell Membrane
We’ll focus on this later in the unit but why do
all cells have a membrane? In our bodies
cell membranes have 4 functions:
1. Act as a barrier to pathogens, toxins, etc.
2. To mark the cell as self
3. To act as a receptor for messages from
other cells in the body
4. To allow things to be transported in and
out of cell
(Big Marty Rips Tops)
All of These Functions Allow the
Cell to Maintain Homeostasis
Homeostasis is
maintenance of a
relatively constant
internal environment
…it’s one of the BIG
concepts this year!!
Associated With the Cell
Membrane are some Vesicles and
Vacuoles
• Secretory Vesicles carry things out of the
cell by fusing with the membrane so that
their contents are released outside the cell
(exocytosis)
• Vesicles and Vacuoles are created by the
cell membrane when it pinches in
(endocytosis)
The Nucleus-related Organelles&
Structures
• The Nucleus contains the cell’s
chromosomes and therefore controls the
cell’s ability to:
– make proteins
– undergo cell division
• Related structures: nuclear envelope,
nucleolus, nucleoplasm, chromosomes,
chromatin, and ribosomes (all but
ribosomes are part of the nucleus)
Proteins: VIMs (Very Important
Molecules!)
• Many of the cells important structures are
made from proteins
• Enzymes which are needed for the cell to
carry most cellular reactions necessary for
life are also proteins
• The type of proteins that your cells make
determine who you are
Chromosomes, Chromatin,
Chromatids...Confusion!
• When the cell is in its normal state
(not dividing) the cell’s genetic
information (encoded in DNA) is
dispersed within the
nucleuschromatin
• When a cell is replicating (mitosis
or meiosis) the chromatin
condenses to form chromosomes
• Each chromosome consists of 2
sister chromatids
The Nucleolus: The Instructions
for Making Ribosomes
• Makes ribosomal RNA
(rRNA) which is a
building block of
ribosomes
• There may be more
than one present
(nucleoli)
• Surrounded by
semifluid medium:
nucleoplasm
The Nuclear Envelope
Nuclear
pore
• Surrounds the nucleus
• Continuous with the
ER
• A double membrane
• Has openings: nuclear
pores to allow certain
things in and out
Function? Regulate
entry/exit of materials
The Connection Between the
Nucleus and Ribosomes
• Nucleus is where the instructions for
making proteins are located (genes)
• Ribosomes actually synthesize (make)
proteins
• How do the instructions get from the
nucleus to the ribosomes?
• mRNA
An Analogy
nucleus
ribosomes
There Are Two Types of
Ribosomes
Cytoplasmic
• Free-floating in the
cytoplasm, make
proteins (such as
enzymes) needed
within the cell
Endoplasmic
• Attached to
endoplasmic reticulum
• When attached to ER
the ER is called Rough
ER (RER)
• Proteins made here are
often secreted (e.g. a
peptide hormone)
Cytoplasmic
ribosomes
Endoplasmic
ribosomes
(RER)
Ribosomes: a connection
between prokaryotes and
eukaryotes
• Ribosomes are the smallest and most
numerous organelle in the average
eukaryotic cell. They differ from other
organelles because they lack membranes
• Bacteria also have ribosomes
• Eukaryotic cells also have ribosomes within
their mitochondria and chloroplasts
•
•
•
•
Endomembrane System
Organelles
There are 2 types of Endoplasmic Reticulum
Rough (has ribosomes attached to it)
Smooth (lacking ribosomes)
Associated with the ER are:
– Transition or transport vesicles
– the Golgi Apparatus (Bodies)
– Lysosomes
• All of these organelles compartmentalize the cell
so that chemical rxns take place only in certain
areas
RER Vs. SER
Rough ER
• Continuous with the
nuclear envelope
• Studded with ribosomes
• Proteins that are made by
these ribosomes are
processed, modified and
transported within the
lumen of the RER
• Protein may pass on to the
SER for packing into
vesicles
(See figure 3.5c p53)
Smooth ER
• Continuous with the RER
• Lacks attached ribosomes
• There are various
functions assoc .with the
SER:
– Synthesis of lipids(fats)
• membrane phospholipids
• steroid hormones (e.g..
Testosterone)
– Detoxification of drugs in
liver
– Forms vesicles to transport
ER products to GA or PM
Golgi Apparatus: processing,
packaging, secretion
• A stack of curved saccules
• Receives protein or lipidfilled vesicles from ER
• GA modifies the contents
of the vesicles (e.g. adds
sugar groups or makes a
protein’s toxin active)
• Vesicles leave GA for
plasma membrane
(secretion) others become
lysosomes
Lysosomes: Prepare to Die Mr.
Bond
• The cell’s poison pill:
– Contains digestive
(hydrolytic) enzymes
– Involved in autodigestion:
• Digest old organelles
• Allows cell to commit
suicide if infected with a
virus
• Programmed cell death
(e.g.. tadpole’s tale)
• Produced by the GA
• Digestion of food in singlecelled organisms
(intracellular digestion)
• Killing of bacteria by
WBCs involves lysosomes
http://www.cellsalive.com/mac.htm
The Energy-related Organelles
• Mitochondria and chloroplasts are both related to
obtaining energy
• Chloroplasts are only found in plant cells. They
are the site of photosynthesis
• Mitochondria are found in both plant and animal
cells and make ATP—the cell’s main energy
currency (how energy requiring processes are
“paid” for by the cell)
What’s Left?
• Cytoplasm and Vacuoles
• The cytoplasm is the site of many of the cell’s key
biochemical rxns
• It is semifluidbut cytoskeleton is located here
• Plant cells have one large vacuole whereas animal
cells have smaller and more numerous vacuoles
• Vacuoles are storage areas for important
substances (e.g.. In plantswater)
Your Assignment:
• Complete the Cell organelle chart and practice
questions (all)
• Read pages 56&57 and write a summary about the
structure and functions of chloroplasts and
mitochondria
• Your summary should be:
– Brief
– Point form
– Contain what you consider to be the essential
information about these organelles