MOLECULES OF LIFE
90% of the human body is composed of just four elements. They are carbon,
hydrogen, oxygen, and nitrogen. These elements combine to larger units called
molecules. There are two types of molecules in our bodies; organic and inorganic.
INORGANIC MOLECULES are not made of carbon atoms.
1. SALTS are found in body fluids. They are needed for muscle contraction
and nerve conduction.
2. WATER
The body is about 70% water. All of our body’s chemical reactions require it.
It keeps the body from overheating
It also prevents drastic changes in temperature.
Last spring, a baby finch collapsed with exhaustion on my patio. Since it was exhausted,
it probably wasn’t good at finding food and water yet. That means it was dehydrated and
hungry. I knew to get an eyedropper and give it water with sugar in it because those are
the two main things it needs right away. We discussed water, now lets get to sugars.
ORGANIC MOLECULES are made of carbon, which is what our body is mostly
made of. The three main types of organic molecules in our body are carbohydrates,
lipids, and proteins.
1. CARBOHYDRATES are molecules that store energy a short time.
a) SIMPLE CARBOHYDRATES known as sugars, such as those
found in candy. They are used for a quick source of energy, and they are burned off
fast. The main sugar form is glucose.
b) STARCH is a storage form of glucose in plants, especially flour and
potatoes. When we eat breads, potatoes, and cakes, we convert it to glucose. These don’t
break down to glucose as easily, so they tend to get stored and are only broken down
when there is not enough glucose available.
c) CELLULOSE is only found in plant cell walls, and gives plant stems
and leaves their firmness. Our body is unable to break down this substance, so it just
passes through our digestive tract. That is what is referred to as eating fiber. It helps a
person who has constipation. You may have heard the term cellulite referring to fat.
However, there is no such thing; it is just regular fat, which we’ll talk about now. Some
companies made up the term and said their cream can dissolve it: NO!
2. LIPIDS differ from carbohydrates in that they don’t dissolve in water.
a) FATS AND OILS: Fats are animal lipids, and oils are plant lipids.
When we ingest (eat) oils, we convert them to fats.
Function of fats
a) Fats are for long-term energy storage.
b) They also insulate against heat loss
c) Fat forms protective cushions around organs.
1) SATURATED FATTY ACIDS are solid at room temperature,
like butter and lard.
2) UNSATURATED FATTY ACIDS are liquid at room temperature,
such as vegetable oils
b) STEROIDS are lipids that have a very different structure than fats.
Steroids are formed from cholesterol, which is found in the cell
membranes of our body. An example of steroids that our body makes is
estrogen and testosterone.
3. PROTEINS are molecules that make up most of our body. Our hair, nails,
tissues, ligaments, cartilage, bone, tendons, muscles, and organs are made of
proteins. Other proteins we have are enzymes, which function to speed up metabolic
reactions and break down larger molecules into smaller ones. In order to understand
what a protein is, we have to talk about AA’s.
a) AMINO ACIDS are the building blocks of protein. They are tiny
carbon molecules, made of just a carbon atom and a few other atoms. There are
only about 12 types of amino acids. They are like beads on a necklace. How they
are arranged on the string determines the type of necklace. Each bead is an amino
acid, and the whole necklace is the protein. A bunch of the same types of
necklaces (proteins) woven together makes up our tissues.
b) NUCLEIC ACIDS are the types of proteins that make up DNA,
which makes up our genes. GENES store information about how to replicate,
including how to arrange the amino acids in the new cell to form the proper
proteins for the body. When a person has a genetic defect, it is because the
nucleic acids are not in the exact right order. Sometimes, just one amino acid in
the wrong order will cause death in a person before they are born.
c) ATP is a type of protein that provides all the energy to cells. When food
is broken down to glucose for energy, ATP is what is released, which is the actual
energy molecule. The more ATP that is produced, the more energy we have.
When we inhale oxygen, it is used in a process called respiration, which produces
ATP for energy. That is why we breathe. Just remember that ATP is an energy
molecule.
This information will be useful in understanding proper nutrition when we get to that
section. In the meantime, now that you understand what these molecules are, next we’ll
talk about what a typical cell in our body looks like.
CELL STRUCTURE AND FUNCTION
The fundamental units that make up all living things are called cells.
When cells cluster together and perform the same function, they are called tissues.
When tissues cluster together and perform the same function, they are called organs.
Organs cluster together to form organ systems, which result in the total organism.
Every cell has three things in common:
1. Metabolic functions (using up oxygen and sugars). The sum of all of the
chemical reactions that occur in a cell collectively are called metabolism.
2. Responds to its environment
3. Capable of maintaining homeostasis within itself and within the body.
HOMEOSTASIS is maintaining a balanced internal environment, such as
temperature, pH, glucose levels, etc.
The average cell (if there is such a thing) contains the following:
CELL ORGANIZATION
1. ORGANELLES: miniature organs that carry out particular functions.
2. RIBOSOMES: Little factories that make proteins out of amino acids.
3. CYTOPLASM: Jelly-like stuff in the cell around the organelles.
Contains the following:
a. Mostly water
b. Things dissolved in water (sugars like glucose, and energy molecules =ATP)
c. Cytoskeleton: made up of long protein fibers that extend throughout cytoplasm.
Function of cytoskeleton:
1) Maintains cell shape
2) Movement (such as muscle cell contraction, organelles within
the cell, or the cell itself moving around).
ORGANELLES
1. PLASMA MEMBRANE: Surrounds the entire cell.
Functions of the Plasma Membrane:
a. Selective movement of materials into and out of cell
b. communication with other cells and the environment
2. NUCLEUS: Usually the largest structure in a cell.
Functions of the nucleus:
a. Stores DNA (genetic material that makes up chromosomes). Our genes
are on the chromosomes)
3. MITOCHONDRIA
Cells have hundreds of mitochondria.
Function of mitochondria is to make ATP (energy molecules).
NOTE: Mitochondria must have OXYGEN to convert nutrients to ATP for energy.
4. ROUGH ENDOPLASMIC RETICULUM (endoplasmic = within cytoplasm;
reticulum = network; rough = surface of membrane covered with ribosomes.
Function of RER is to make proteins:
5. GOLGI COMPLEX
This is a complex system of membranous channels and saccules continuous with the
plasma membrane. Function of Golgi complex:
a. Packages the proteins made by the RER and sends them where they
need to go (like a UPS center!)
6. SMOOTH ENDOPLASMIC RETICULUM (no ribosomes)
Function of SER
a. Involved in metabolism (making use of carbohydrates (sugars) and lipids (fats).
b. Stores calcium (necessary for every cell)
c. Detoxifies harmful substances (alcohol, drugs, etc)
i. NOTE: in CSI, when they suspect poisoning, they first look at the SER
in the liver.
7. VESICLES: a sphere of membrane with something in it. Many types:
a. LYSOSOMES: contains digestive enzymes to dissolve bacteria.
b. TRANSPORT VESICLES: when material needs to move from RER to
Golgi complex, or from Golgi complex to cell membrane, etc.
c. STORAGE VESICLES
8. CILIA AND FLAGELLA
Some cells have hair-like structures that move the cell (sperm cell has flagella)
Others move mucous along the top of the cell (when you cough up mucous)
SUMMERY OF CELL FUNCTION
Each cell is near a blood vessel, which gives the cell nutrients it needs and takes products
out of the cell to distribute to the rest of the body. The nucleus has DNA which tells the
ribosomes what kind of proteins to make at the moment. The ribosomes get the amino
acids from the bloodsteam and build the protein molecule. The protein is taken to the
golgi complex, where it is packaged and sent to a storage vesicle. The cytoskeleton fibers
move the vesicle to the plasma membrane where it is released from the cell and picked up
by the bloodstream and taken to where it is needed in the body. The bloodstream drops
off sugars to the cell, which are taken to the mitochondria to be broken down into ATP,
which is the energy molecule used to fuel all the functions of the cell.
Cellular (aerobic) respiration is a process whereby cells use oxygen, produce carbon
dioxide, produce energy, and form ATP.
The rate of cell division is close to the rate of cell death. 200 billion red blood cells die
every day, so 200 billion red blood cells have to be made every day. Too few = anemia;
too many is also a problem.
Body needs to do two things:
1. Control the rate of cell division
2. Control the rate of cell death