7.1 Human Diseases, Cell Structures and Disease-causing Agents
1. Categorize diseases by their causes
2. Identify basic cell structure and understand their relevance to diseases and pathogens.
3. Distinguish among bacteria, viruses and eukaryotic cells and different pathogens.
Readings: 18:467-476, 2: 41-46, 3: 66-69
Disease – abnormal condition(s) of an organism that impair its normal bodily functions.
Diseases can be caused by external or internal factors.
1. Poor nutrition e.g., rickets, scurvy, spinal bifida;
2. Genetic or internal dysfunction e.g., Huntington’s, Muscular dystrophy, autoimmune diseases, and
some forms of cancer.
Toxins (e.g., 2 nd hand smoke (cancer), heavy metals (lead poisoning)
1. Microbes (pathogens) = disease causing organisms
a) Bacteria (e.g., bird flu, cholera, plague, tuberculosis)
b) Protists (e.g., malaria, Lyme disease, dysentery)
2. Viruses (e.g., flu, SARs, West Nile, AIDS, smallpox, polio)
3. Prions (infectious proteins) e.g., mad cow disease
Although a number of pathogens
have likely been with us through our
evolutionary history, a great change
occurred in the makeup of human
disease 8 to 10 000 years ago as
humans made the switch from being
hunter-gatherers to farmers.
1. We domesticated animals as livestock and pets. This led to disease transmission from animals to humans. (e.g.,
2. We began domesticating and cultivating plants for food crops. Both actions changed our diet and had profoundly
affected the type and diversity of human diseases (e.g., ergot in grain Saint Antho,Food storage ailments e.g.,
3. Increases in human population size led to diseases whose success depends on direct person to person transmission.
4. The build up of human and animal wastes led to contaminated water/environment. This brought humans (and
sometimes our animals) in contact with a new array of pathogens including both bacteria and eukaryotic parasites (e.g.,
Cholera, typhoid fever, dysentery, tapeworms). 5. We made profound changes to the natural environment and this favoured some pathogens. For example, slash and
burn agriculture (deforestation) increased the number of breeding spots for malaria carrying mosquitoes.
QUESTION: From your study of biology so far what would say is the “prime motive” of all living organisms?
(What do all living organisms do? What are the purposes of their actions and behaviour?)
Find a suitable habitat to live and acquire energy and resources to grow, and to reproduce
Not all living organisms want to grow to an old age because you do not have to be that old to
reproduce, and once you have reproduced you have already successfully passed on your genes and
thus you will not need to live longer
As living organisms, most pathogens also follow this prime motive.
Habitats for pathogens the host they infect.
During reproduction or energy acquisition, many pathogens make their host ill. (The time when they cause
disease. As they reproduce they happen to produce toxins or they kill other cells which cause people to have
– Viruses infect cells and take them over to produce more viruses, kills cells to spread to a new host
- Some produce toxins cause the host to expel the newly made pathogens (e.g., vomiting or diarrhea).
In this unit, we will focus on the Biology of infectious diseases. Some major causes of infectious diseases
through the development…
2. What are some of the necessary conditions, in terms of the capability of the pathogens and their
environment, for successful spread of new disease-causing organisms such as HIV, SARS or swine flu?
Being able to invade hosts (suitable habitats);
Overcome or evade the defense systems of the hosts and grow within the hosts;
Being able to spread to new hosts (reproduction);
3. How do diseases become more virulent, more resistant, or more infectious?
4. How do pathogens evade immediate destruction by the host’s immune system?
enter human bodies along with food or water;
hide from immune system by residing inside host cells (viruses);
some may actually target the very cells which would normally kill the pathogen (e.g., HIV).
5.Where or how do new human diseases often originate?
By close contact with animals
By close contact with domesticated plants
Due to changing environment (climate change and degradation of natural environments)
Anton van Leeuwenhoek and Robert Hooke first observed microscopic organisms. They proposed the cell
theory: all livings things are composed of cells. "In the morning I used to rub my teeth with salt and rinse my mouth
with water and after eating to clean my molars with a toothpick.... I
then most always saw, with great wonder, that in the said matter
there were many very little living animalcules, very prettily a-moving.
The biggest sort had a very strong and swift motion, and shot through
the water like a pike does through the water; mostly these were of
-Anton van Leeuwenhoek Every cell consists of a plasma membrane surrounding internal fluids or cytoplasm and a form of DNA. All
cells also have a mechanism for making proteins involving tiny ribosomes.
Prokaryotic and eukaryotic cells share these characteristics in common but have many more differences.
Cell structure Prokaryotic cells Eukaryotic cells
Smaller cells: Domains Bacteria and Domain Eukarya
transportation across Archaea
cells is easier
Bigger cells: more
(can be accounted for
by having many small
cells with varying
functioning). If you
have only large cells,
you will be more
impacted if they got
destroyed. Big cells
material within the cell
complicated). It can
hold more specialized
for the large size of
size 1- 10 µm 10 – 100 µm
Location and in cytoplasm contained inside nucleus
arrangement of arranged in a circular DNA strands are coiled around histone proteins
genetic information chromosome and small circular and highly condensed into chromosomes during
ribosomes √ √
Microtubules some √ for cytoskeleton
Endoplasmic reticulum None √ for processing proteins and transportation
Golgi apparatus None √ for sorting, packaging proteins
Mitochondria None, but may have same Most have except for a few anaerobic protists
enzymes in cytoplasm Perform chemical reactions in cytoplasm involving
None, if photosynthetic, perform
Chloroplasts in cytoplasm Plantae and some protists
1. Flagella some some 2. Plasma membrane
All cells have a plasma membrane made of phospholipids.
In membranes, lipids are arranged in a double layer and
only allow some small uncharged molecules to pass
through (e.g., C2 ; Fig 3.11a of your textbook).
All living things have the ability to maintain homeostasis (constant internal environment); therefore, they must
have boundaries from the outside world to mediate what comes in and out (cell membrane).
Protein carriers/channels in membranes
Water enters cells through “aquaporins” (small pores in the plasma membrane made of proteins).
Other small molecules (e.g., glucose) can also be transported by protein carriers through membranes.
Charged molecules (e.g., Na , sodium ions) must
pass through ion channels which are also composed
of proteins sitting in the membrane and have
specificity to only allow specific ions through.
Facilitated diffusion (Fig 3.11b) - no energy is
required to move some molecul