Download Slide 1 Cells are the fundamental structural units of life

Slide 1
Cells are the fundamental structural units of life. The properties of life emerge at the
level of the cell; in other words, a cell can perform all of the activities required for life.
Cell Theory states that every living organism is composed of cells, that the cell is the
basic unit of life, and that cells arise only from pre-existing cells.
A cell is usually a microscopic structure containing nuclear and cytoplasmic material
enclosed by a semi-permeable membrane and, in some instances, a cell wall.
Slide 2
There are two main categories of cells – prokaryotic and eukaryotic.
What is the difference? A prokaryotic cell is simpler and usually much smaller than a
eukaryotic cell.
Prokaryotic cells do not contain a membrane-bound nucleus, nor any other membraneenclosed organelles. A bacterial cell is a good example of a prokaryotic cell.
Eukaryotic cells are larger cells that have membrane-enclosed nuclei and organelles.
All organisms except for bacteria and archaea are composed of eukaryotic cells.
Slide 3
Cells share certain characteristics. For example, every cell is enclosed by a plasma
membrane. This membrane is vital because it regulates the passage of materials
between the cell and its environment. Cells have chromosomes which carry genes
made of DNA. All cells contain ribosomes, which are small structures that make
proteins.
Slide 4
Let’s take a closer look at the structure of a prokaryotic cell.
In this cutaway diagram, we can see the simple structures common to these cells.
The pili are attachment structures on the surface of some prokaryotes.
The nucleoid is the area of the cell where the genetic material is found. This differs
from the nucleus in eukaryotic cells in that it is not enclosed in a membrane to separate
it from the cytoplasm.
Ribosomes are structures that synthesize proteins. These ribosomes differ from
eukaryotic ribosomes in that they are smaller and also have molecular differences that
allow for the action of some antibiotics, which target prokarytoc ribosomes. This action
interrupts protein synthesis for the bacterial cell but not for the eukaryotic organism
taking the drug.
The plasma membrane is a semi-permeable membrane enclosing the cytoplasm.
The cell wall, found on most prokaryotes, is a rigid structure outside the plasma
membrane. This wall protects the cell and helps it to maintain its shape.
Some bacteria are enclosed within a sticky outer coat called a capsule. This capsule
provides protection while also serving as a sticky glue-like material that allows
prokaryotic organisms to attach to surfaces.
Finally, flagella are long projections that allow for locomotion through a liquid
environment.
Slide 5
Next, let’s look at eukaryotic cells. These cells are quite different from prokaryotic cells.
All eukaryotic cells have a membrane-bound nucleus and other membrane-enclosed
organelles. All eukaryotic cells are fundamentally similar to one another. Eukaryotic
cells include both plant and animal cells, which are shown here.
Let’s take a closer look at some of the structures and organelles of these cells.
We can divide the structures and organelles into four basic functional groups –
(1) manufacturing, (2) breakdown, (3) energy processing, and (4) structural support,
movement, and communication
Slide 6
First, we have the nucleus, ribosomes, endoplasmic reticulum, and Golgi apparatus.
These are all involved in manufacturing.
The nucleus is the most obvious difference between prokaryotic and eukaryotic cells.
This is the genetic control center of the cell, as it contains the DNA.
Ribosomes function as the site of protein synthesis. Proteins that are made can be
used in the cell or for export.
The endoplasmic reticulum is an extensive membranous network and is responsible
for the production of the protein and lipid components of most of the cell's organelles.
There are two types of ER - rough, which is coated with ribosomes, and smooth, which
isn't.
The Golgi apparatus functions to modify, store, and ship products of the endoplasmic
reticulum. The Golgi is principally responsible for directing molecular traffic in the cell–
nearly all molecules pass through the Golgi complex at some point in their existence.
Slide 7
Organelles involved in the breakdown of molecules include lysosomes, vacuoles, and
peroxisomes.
A lysosome contains digestive enzymes enclosed in a membranous sac. Lysosomes
have digestive functions and help to break things down, such as food particles and
damaged organelles.
Vacuoles are membranous sacs that have a variety of functions. In plant cells, the
central vacuole might help a plant grow in size by absorbing water and enlarging. It can
also store waste products, chemicals, or pigments. It may even contain poisons to
protect the plant against predators. In an animal cell, there might be a contractile
vacuole, which allows the cell to pull in and expel water.
Peroxisomes are involved in various metabolic functions, such as the detoxification of
alcohol and other harmful substances and the breakdown of fatty acids to be used as
fuel.
Slide 8
Mitochondria in all cells and chloroplasts in plant cells are involved in energy
processing.
Mitochondria convert the chemical energy of foods to the chemical energy of ATP.
ATP is the main energy source for cellular work and most of the cell’s ATP is made in
this organelle.
Chloroplasts convert solar energy to chemical energy. These organelles absorb
sunlight and use it to drive the synthesis of sugars from carbon dioxide and water.
Slide 9
Structural support, movement, and communication among cells are the functions of
components of the cytoskeleton, plasma membrane, and cell wall.
The cytoskeleton is a network of protein fibers which extends throughout the
cytoplasm of a cell. Both structural support and cell motility are provided by the
cytoskeleton. Recent evidence also suggests that the cytoskeleton transmits signals
from the cell’s surface to its interior.
The plasma membrane sets a cell off from its surroundings and acts as a selective
barrier to the passage of ions and molecules in and out of the cell.
Plant cells have a cell wall which helps protect the cell and maintain its shape.
You can see that eukaryotic cells are pretty complicated when compared to prokaryotic
cells.