Pre-Medicine Program - Cell Types

From CellBiology

Life - Eukaryotes and Prokaryotes

  • blue ring - bacteria
  • white ring - white blood cell
  • red ring - red blood cell

Scale bar = 10 microns

(MP4 version)

Gram-positive Micrococcus luteus bacteria.jpg Escherichia coli.jpg
Bacteria - Micrococcus luteus Bacteria - Escherichia coli


This lecture introduces the cell as the unit of life. Firstly, by the methods we use to see cells and biological structures and what we consider to be "alive". Then by looking at major differences between cell types and their organisation as unicellular or multicellular organisms. Finally, the presence or absence of a nucleus which is the definition of the major 2 classes of cells. For more introductory background information read American Society Cell Biology - Booklet Exploring the Cell.

  • We are multicellular organisms.
  • Specialised groups of cells form tissues and organs.
  • Each cell absorbs nutrition and follows specific metabolic pathways; chemical reactions required for cell for proliferation, growth and energy production.
  • Pancreatic insulin and glucagon are 2 main hormones involved in regulating cell metabolism.


  • Introduction to biological molecules
  • Understand the dimensions cells
  • Understand differences between prokaryotes and eukaryotes
  • Understand differences between unicellular and multicellular organisms
  • Brief understanding of viruses and prions

About Human Body

Human Cells

  • 210+ cell types in body
  • total number of estimated cells in the body - 1013 (American ten trillion/British ten billion)


  • bacteria, fungi and archaea
  • found on all surfaces exposed to the environment
    • skin and eyes, in the mouth, nose, small intestine
  • most bacteria live in the large intestine
  • 500 to 1000 species of bacteria live in the human gut
  • total number of estimated flora ten times as many bacteria 1014 (American One hundred trillion/British One hundred billion)

Cell Sizes

Biological relative sizes
  • frog or fish egg are the largest individual cells easily visible, approx 1mm diameter
  • human or sea urchin egg, approx 100 micron (µm) diameter
  • typical somatic cell, approx 20 micron diameter (red blood cell 6 - 8 microns)
  • plant cells are larger, approx 30 x 20 micron
  • bacteria are smaller, approx 2 x 1 micron
Salamander-oocyte.jpg Red White Blood cells.jpg Mycobacterium tuberculosis bacteria.jpg
Salamander egg (oocyte) 1 mm scale bar

(light microscope)

Red Blood Cell, Platelet and White Blood Cell

(electron microscope image)

Mycobacterium tuberculosis bacteria

(electron microscope image)

Images above are not to scale.

Divisions of Life

Greek, Karyose = kernel, as in a kernel of grain - refers to the nucleus of the cell.



File:Leukocyte phagocytosis of yeast
  • plants
  • animals
  • fungi
  • protists

MBoC -Divisions of Life

Unicellular and Multicellular


  • All prokaryotes and some eukaryotes
  • Yeast (budding, non-budding)
  • Protozoa (classified by means of locomotion: flagellates, amoeboids, sporozoans, ciliates + often "feed" on bacteria)


  • Eukaryotes - Plants and Animals
  • Allowed development of specialized cells - functions and tissues


Escherichia coli
Micrococcus luteus bacteria
Prokaryote cell cartoon
Bacterial morphologies

Prokaryotes Cell Wall

  • Bacterial Shape - Bacterial shapes and cell-surface structures
  • Bacterial Membranes - A small section of the double membrane of an E. coli bacterium
    • Bacterial outer membranes - outer membrane contains porins
  • Bacterial cell walls - Bacterial cell walls
    • Gram-negative bacteria surrounded by a thin cell wall beneath the outer membrane
    • Gram-positive bacteria lack outer membranes and have thick cell walls

(MH - note that some unicellular eukaryotes can also have a cell wall)

  • Antibiotics - inhibit either bacterial protein synthesis or bacterial cell wall synthesis Antibiotic targets Gram-positive and Gram-negative bacteria
  • Bacterial Replication - DNA replication and cell division in a prokaryote MCB - DNA replication and cell division in a prokaryote

File:Bacterial cell

Bacterial Growth Movie

Prokaryote Mycoplasmas

  • smallest self-replicating organisms
  • smallest genomes (approx 500 to 1000 genes)
  • spherical to filamentous cells
  • no cell walls
  • surface parasites of the human respiratory and urogenital tracts
    • Mycoplasma pneumoniae infect the upper and lower respiratory tract
    • Mycoplasma genitalium a prevalent sexually transmitted infection
    • Mycoplasma hyorhinis found in patients with AIDS

Prokaryotic and Eukaryotic Cells

The following links describe the major differences between prokaryotic and eukaryotic cells, the way they divide and the way in which antibiotics have their action on prokaryotic cells.

Plant Cell

Plant Cell cartoon
Plant Plastid types
  • plant cells are larger than mammalian cells approx 30 x 20 micron
  • Additional Organelles
  • Central Vacuole - storage (water, ions, and nutrients such as sucrose and amino acids, and waste products)
  • Plastids - organelles found in plants and algae (chloroplasts for photosynthesis; Amyloplasts for starch storage; Chromoplasts for pigment synthesis and storage; Leucoplasts - can differentiate into more specialized plastids (Amyloplasts - starch storage, Elaioplasts - storing fat, Proteinoplasts - storing and modifying protein)
    • (MH - plastids and mitochondria and have own DNA)
  • Cell Wall - Rigid structure outside cell membrane, No ability to move, Resist osmotic stresses
    • Structure - cellulose, hemicellulose, pectin
Plant organelles

Animal and Plant Cell

Plant Cell Structure.jpg


Dengue virus Herpes virus - CDC electron micrograph

NPR Virus Infection video

  • not a cell Latin, virus = toxin or poison
  • not alive - infects living cells (animal, plant and bacterial), unable to grow or reproduce outside a host cell
  • Classified by genetic structure - RNA or DNA viruses, double or single stranded

Virion - contains the genetic material, DNA or RNA within a protective protein coat (capsid)

Bacteriophage - name for a virus that infects bacteria

Links: 6.3. Viruses: Structure, Function, and Uses | Figure 6-22. Retroviral life cycle


VCJD brain
  • not alive - an infectious prion protein, misfolded normal protein (three-dimensional structure), can form aggregates

Several Types

  • Creutzfeldt-Jacob disease (CJD) and Kuru a human neural prion disease
  • Bovine spongiform encephalopathyvery (BSE) in cattle, "mad cow disease"
  • Scrapie in sheep

Links: Figure 6-89. Protein aggregates that cause human disease | Prions Are Infectious Proteins | Gene Reviews - Prions | Neuroscience - Prion Disease

Biological Levels

A way of classifying cell structure by breaking into smaller parts

  • Whole cell
  • Organelles - nucleus, mitochondria, Golgi apparatus, vesicles
  • Components
  • Biological polymers - chains of molecules, consisting of monomer subunits (DNA, RNA, Protein, sugars, cellulose)
  • Organic molecules - monomer subunits (nucleotides, amino acids, carbohydrate)

Eukaryotic Cell Organelles

  • Organelle - specialized part of a cell that has its own particular function
  • Membrane bound (enclosed) - forms "compartments" within the cell

Related Online: Undergraduate Science Lecture