Cytology Study Guide
Cells
The cell theory states three things:
1. All living things have cells (viruses are considered NONLIVING because they don’t have cells)
2. Cells are the basic unit of structure and function
3. All cells come from a pre-existing cell
The cell theory wouldn’t have been a success if it wasn’t for the invention of the microscope. The
microscope allows us to see cells and study them.
All cells contain the genetic material in the form of DNA.
DNA is used to create protein in the following order: DNA RNA  Protein
All cells arise from stem cells; however, certain genes are activated for each type of cell to give them
their specific function.
You may wonder how cells recognize themselves if they do not have eyes. Cells use sugars
(carbohydrates) on the surface of their membranes for recognition. These sugars are referred to as
glycocalyx; they are combinations of glycoprotein and glycolipids.
The domain Eukarya contains a nucleus and membrane-bound organelles. The domain Bacteria and
Archaea DO NOT contain a nucleus and membrane-bound organelles.
Cell Organelles
Rough Endoplasmic reticulum is studded with ribosomes. The rough ER creates proteins to be exported
from the cell. It is found in Eukaryotic cells.
Lysosomes are cell vesicles found in eukaryotic cells that contain enzymes that digest harmful
substances and destroy old or damaged cell organelles.
The mitochondria are the power-house of eukaryotic cells. They create energy in the form of ATP. The
mitochondria also have their own DNA. Mitochondria look like sausages.
Chloroplast are organelles found in plants used for making food. They use the pigment chlorophyll to
convert sunlight into chemical energy. The process by which plants make food is called photosynthesis.
Keep in mind that photosynthesis is used to make food, not oxygen. Oxygen is plant waste.
The nucleus is a large organelle in the center of eukaryotic cells. It controls and regulates cell function
and contains the cell’s genetic instructions in the form of deoxyribonucleic acid (DNA).
Animal cells vs. Plant cells
Animal cells and plant cells are both eukaryotic cells. This means that they both contain a nucleus and
membrane-bound organelles.
Plant cells are different from animal cells because plants have chloroplast, a large central vacuole, and a
cell wall.
Animal cells are different from plant cells because animal cells have centrioles and some animal cells
have a flagellum.
Animal and plant cells both have mitochondria.
Cell Membrane
Cells contain a phospholipid bilayer called the cell membrane, or plasma membrane.
The heads of the phospholipids are polar (hydrophilic); they love water.
The tails of the phospholipids are non-polar (hydrophobic); they hate water.
The main function of the cell membrane is to separate the inside of the cell from the outside. Thus, it
defends the cell against foreign particles trying to invade the cell.
Cell Transport
Cells use energy in the form of ATP to move substances against their concentration gradient (up the
gradient). In other words, cells use ATP in active transport to move substances from a lower
concentration to a higher concentration.
The Sodium/Potassium Pump (Na+/K+) is an example of active transport. It is made up of carrier
proteins on the cell membrane that pump 3 Sodium (Na+) ions out of the cell and 2 Potassium (K+) ions
into the cell.
Osmosis is the movement of water from an area of higher water concentration to an area of lower
water concentration through a semi-permeable (or selectively permeable) membrane.
Osmosis is a form of passive transport. No energy is required because water is moving DOWN its
concentration gradient.
Diffusion is the movement of particles from an area of higher particle concentration to an area of lower
particle concentration. Diffusion does not need a membrane, unlike osmosis.
Diffusion is a form of passive transport. No energy is required because particles are moving DOWN their
concentration gradient.
Simple diffusion does not require “help” from a channel or carrier protein. An example of simple
diffusion is when oxygen and carbon dioxide diffuse across the alveoli in the lungs.
Facilitated diffusion requires “help” from a channel or carrier protein. This protein will “help” the
particle move from an area of higher concentration to an area of lower concentration.
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Remember that DIFFUSION is PASSIVE = No Energy needed
Osmosis is a special type of diffusion. It is the diffusion of water across a membrane.
Receptor proteins on the cell membrane transmit information into the cell by responding to signal
molecules.
Carrier proteins on the cell membrane carry substances in or out of the cell. Hydrophilic (polar)
substances are usually carried because they cannot go through the hydrophobic (non polar) membrane.
Channel proteins on the cell membrane act as channels to allow certain substances in or out of the cell.
Water goes in and out of the cell through special channels called aquaporins.
Cells regulate what goes in and out in order to maintain a constant internal balance called homeostasis.
Solutions
A cell placed in a hypertonic solution – the solution has more salt than the cell.
The cell will begin to shrivel as it LOSES water to the solution.
A cell placed in a hypotonic solution – the solution has less salt than the cell.
The cell will begin get very large is it GAINS water from the solution. The cell will eventually burst, or
lyse.
A cell placed in an isotonic solution – the solution has the same salt concentration than the cell.
The cell will gain and lose equal amounts of water from the solution, and it will stay the same size.
Isotonic solutions are great.
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Remember Osmosis: water likes to go to where there is LESS water concentration.
Macromolecules
DNA is made up of Nucleic Acids, which are made up of Nucleotides.
Nucleotides are made up of a sugar, a phosphate group, and a nitrogen base.
(FYI: the sugar can be deoxyribose or ribose)
Proteins are made up of amino acids.
Endosymbiosis
The endosymbiotic theory states that the mitochondria and chloroplast of cells used to be independent
cells themselves. Eventually the mitochondria and chloroplast were engulfed by a larger cell and lived
together symbiotically.
The endosymbiotic theory is based on the fact that mitochondria and chloroplast have their own DNA
that is separate from the DNA found in the nucleus of eukaryotic cells.
It is believed that the mitochondria and chloroplast evolved from Archaebacteria.