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 membranesno
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 membrane2. nucleus-related
structures3. endomembrane
system organelles4. energy-producing
organelles
The Cell MembraneWe’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 self3. To act as a receptor for messages from
other cells in the body4. 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 nucleuschromatin
• 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
• 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
Nuclear pore
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)
Endoplasmic ribosomes
(RER)
Cytoplasmic ribosomes
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. SERRough 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 lipid-
filled 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 single-
celled organisms (intracellular digestion)
• Killing of bacteria by WBCs involves lysosomes
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 semifluidbut 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 plantswater)
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