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

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 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