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Chapter 11
P222
Organic Chemistry – the chemistry of carbon and carbon compounds
About 65% of the human body is water. Of the remainder, 91% is only
four elements: carbon, oxygen, nitrogen, and hydrogen. Carbon is the
largest fraction at 53%.
Carbon has four electrons in its outer level, and can share one or more
electrons to make covalent bonds with itself, or as many as four other
elements.
Carbon molecules come in 3 basic forms: straight chains, branching
chains, and rings.
Benzene C6H6
Glucose C6H12O6
Valine C5H11NO2
Rings and chains can be combined in the same molecule.
P223: 4 Types Biological Molecules in plants and animals
Carbohydrates- energy-rich sugars and starches. Mainly composed of
carbon, hydrogen, and oxygen, in a ratio of 1:2:1
Proteins – large molecules found in animal and plant tissues. Skin and
muscle tissue are composed mostly of protein. A single protein may have
several thousand atoms
Fats – energy-rich hydrocarbon chain molecules, nonpolar, does not
dissolve in water. Cholesterol is a fat that is needed by cells, but high
cholesterol may lead to heart disease.
Nucleic Acids – Biological molecules such as DNA that have the ability to
store the genetic code. DNA is a huge molecule with millions of
individual atoms.
P224: Carbohydrates
Plant cells use energy from the sun to build carbohydrates from carbon
dioxide and water. Animal cells consume carbohydrates and extract the
energy by breaking the carbohydrates into smaller molecules.
Carbohydrates are classified as either sugars or starches. Sugars break
down quickly in the body, releasing energy within a short time of being
eaten. Glucose is smallest sugar and is dissolved directly into the
bloodstream.
Starches are long chains of simple sugars joined together to make natural
polymers. Starches are larger molecules, so they are slower to break
down in the body and can provide energy for a longer time than sugars.
Cellulose is the primary molecule in plant fibers, including wood. The
long-chain molecules of cellulose are what give wood its strength. Like
starch, cellulose is made from chains of thousands of glucose molecules.
However, in cellulose, alternate glucose units are inverted. This is what
makes cellulose strong and difficult for animals to digest.
P225 Photosynthesis
Occurs mostly in plants and some types of bacteria.
Photosynthesis is the foundation of the food chain on Earth. Bottom of
food chain is producers, plants that take energy from the sun and convert
it to chemical energy in glucose. Animals (including humans) ultimately
get energy from photosynthesis because we eat plants, or eat other
animals that eat plants.
Photosynthesis also produces the oxygen in our atmosphere. Oxygen is a
common element, but is usually trapped by rocks and minerals like
calcium carbonate (CaCO₃).
P226 Respiration
The digestive system breaks food down into molecules the body can use.
Proteins are split into amino acids, carbohydrates are reduced to simple
sugars, fats are split into glycerol and fatty acids. Nutrients are then
absorbed into the blood and transported to all the cells of the body.
Cellular respiration – the reactions in cells that release energy from
glucose.
This process breaks down glucose into water and carbon dioxide again,
extracting energy in the process. The glucose and oxygen are used up,
and carbon dioxide and water are produced – almost the reverse of
photosynthesis.
ATP Cycle – each cell converts the energy in glucose into chemical energy
stored in molecules of ATP like a battery - then distributes energy to
where it is needed. One molecule of glucose is used to convert a
maximum of 36 to 38 molecules of ADP to ATP. Cells use the energy by
converting the ATP back into ADP and the cycle starts over.
Phosphorus is a critical part of the ADP-ATP cycle.
P227 Water
Liquid water is essential to life. Most chemical reactions that sustain life
only work in solution. 3 important characteristics of water that make it
essential:
Water is a good solvent: In order to have a chemical reaction, molecules
must be able to move around and contact each other.
Liquid over a wide temperature range: virtually all living organisms on
Earth are most active between the freezing and boiling point of water.
High specific heat: takes a lot of energy to raise the temp a small amount
– this helps living organisms maintain a stable body temp even when
outside temps fluctuate
Macromolecule – really big molecule made up of thousands or millions of
atoms
11.2 p 229 Fats (lipids)
Fats are high-energy molecules that plants and animals use to store
energy in reserve for longer periods. Oils are fats that are liquid at room
temperature.
Saturated fat – a fat molecule in which each carbon is bonded with 2
hydrogen atoms.
Unsaturated fat – a fat molecule that has less hydrogen atoms than a
saturated fat.
Chemical processing of some food adds some hydrogen to unsaturated
fats in a process called hydrogenation. Partially hydrogenated fats have a
longer shelf-life, however, research is showing they are unhealthy.
P230 Proteins – basic building blocks of cells and all parts of animals:
muscle, skin, blood, internal organs
Amino acids – organic molecules that are the building blocks of proteins.
Virtually all proteins found in animals are made from only 20 different
amino acids. Many fit together like a lock and key. This is one reason
why proteins that do the same function in one organism do not work in
another organism.
Food supplies new proteins that a body needs to live and grow. Digestion
breaks down protein into amino acids. Cells reassemble the amino acids
into new proteins suitable for the body’s needs.
P231 Enzymes – special proteins that are catalysts for chemical reactions
in living things.
Thousands of chemical reactions are going on in your body EACH
SECOND.
Sugar does not turn into water and carbon dioxide by itself. Outside the
body, this reaction would need a flame. How does the body do this at a
lower temperature?
Enzymes allow your body to initiate chemical reactions at low
temperature and to control the rate of reactions.
Catalyst – a chemical that allows a reaction to have a much lower
activation energy than it normally would
The body controls the rate of reactions by regulating the amount of
enzymes produced. When a cell needs more energy, it produces more
enzymes to break down glucose. Without those enzymes, glucose
molecules stay together and store their energy.
P234 Vitamins – Most chemicals required for life can be synthesized by
your own body. However, there are certain chemicals necessary for life
that the human body does not make.
Vitamin C – ascorbic acid is required for your brain and nervous system,
and to transfer energy (ADP/ATP). It must be supplied daily through
food.
Vitamin D – calciferols – not a true vitamin since it can be made by your
skin when cholesterol reacts with ultraviolet light. Sunscreens block UV
rays from the skin and can result in vitamin D deficiency, so it is added to
foods such as milk. A severe deficiency softens bones (rickets or
osteomalacia)
B Vitamins – must be obtained from food. They work to maintain healthy
skin and muscle, nervous system, cell growth and division
B-1: thiamine
B-2: riboflavin (aka vitamin G)
B-3: niacin (aka vitamin P)
B-5: pantothenic acid
B-6: pyridoxine
B-7: biotin (aka vitamin H)
B-9: folic acid (aka vitamin M)
B-12: cyanocobalamin
Folate: especially important during periods of rapid cell division and
growth, such as infancy, needed to make DNA and RNA, and to make red
blood cells.
------------------------------------------------------------P 232 DNA and nucleic acids
Protein synthesis – using the information in DNA to assemble proteins
from amino acids
Cells must continually create the proteins they need from amino acids.
DNA molecule is put together like a twisted ladder (double helix)
Each side of the ladder is made of 5-carbon sugars called deoxyribose and
phosphate groups. The nitrogen bases are paired in the center of the
ladder.
4 Nitrogen Bases:
Adenine pairs with Thymine
Guanine pairs with Cytosine
The assembly instructions for building a protein are coded in the
sequence of nitrogen bases ON ONE SIDE of the ladder
Example:
TAA – GCT – AGG – GCT – GGG – GGC – TAA
Start – alanine – argenine – alanine – glycine – glycine – stop
(5 amino acids)
TTT – phenylalanine
TTA - Leucine
ATG – Methionine
TAA – start/stop
GCT – Alanine
CCC – Proline
GTT – Valine
ACA - Threonine
GGT – Glycine
GGC – Glycine
AGG – Argenine
ACT - Serine
P233 DNA
Mutation – change in the sequence of base pairs in DNA that may be
passed on to successive generations
The DNA molecule is able to make exact replicas of itself. Enzymes split
the DNA molecule down the center. Each half of the molecule contains a
complementary code of nitrogen bases. Since guanine only pairs with
cytosine, and adenine only pairs with thymine, each half of the molecule
contains the complete genetic info for how to make proteins.
Enzymes called polymerases move along the unzipped DNA molecule
rebuilding the nitrogen bases on each side. More enzymes rebuild the
sugar and phosphate backbone on top of the completed nitrogen bases.
Another set of enzymes compares the old and new DNA strands for
errors and corrects them by replacing nitrogen bases where necessary.
There is less than one error out of every billion base pairs.