Chapter 2: Chemistry and Cells

Properties of water

 1) Water is a good solvent - many chemicals dissolve in it. A chemical that dissolves is called a solute.

2) Cohesive - molecules stick together with hydrogen bonds, so small animals can walk on water.

3) Water expands when it freezes - so ice floats.
Water is most dense at 4o C ( 39o F ). This means that in cold climates lakes and the ocean have a relatively thin layer of ice floating on top of the water, so fish and other organisms can survive under the ice.

Organic chemistry

Element : a substance that cannot be broken down by chemical reaction eg carbon, gold.
Everything in the universe is made of 92 different elements. Living things contain a maximum of 25 elements.

Important biological elements : 
The following four are the most important, making up over 95% of the body:	
	Carbon          C               Oxygen          O	
	Hydrogen        H               Nitrogen        N	

Most of the rest of the body is made up of the next group:
	Calcium         Ca              Phosphorus      P
	Potassium       K               Sulfur          S
Compound - two or more elements joined by chemical bonds
eg salt, water, plastic.

Atom - the smallest unit of an element.
An atom consists of three different types of particle, shown below:
Particle        Location        Charge
Proton          Nucleus            + 1
Neutron         Nucleus              0
Electron        Shells             - 1
Atomic number = Number of Protons per atom.
Atomic number also equals the number of electrons. Example : Carbon has atomic number of 6 so it has 6 protons and 6 electrons.

Atomic mass, or mass number = Number of Protons + Neutrons.
To find the number of neutrons in an atom you subtract the atomic number from the atomic mass.
Example: carbon with atomic mass 14 has 8 neutrons (14 minus 6 )

Acids, bases and pH

Acid - a substance that gives off hydrogen ions ( H+ )
- eg hydrochloric acid ( HCl )

Base ( alkali ) - a substance that absorbs hydrogen ions
- eg sodium hydroxide ( NaOH )

pH scale measures how acid, or basic, a chemical is (Fig 2.6)

pH 0 - 4    is a strong acid
pH 4 - 6.9  is a weak acid
pH 7.0      is neutral ( not acid or base )
pH 7.1 - 10 is a weak base 
pH 10 - 14  is a strong base
Examples :
Stomach acid : pH 2, Soda pH 3, Coffee pH 5, Seawater pH 8, drain cleaner pH 13

Macromolecules

1). Carbohydrates contain C , H and O.
Carbohydrates are made of simple sugars called monosaccharides (Fig 2.10)
such as glucose ( C6H12O6 ).

Disaccharides consist of 2 monosaccharides joined together
such as Maltose or brewing sugar ( 2 glucose ) and Sucrose or table sugar ( glucose + fructose ).

Polysaccharides are made of many monosaccharides. Examples:
starch ( energy storage in plants )
glycogen ( energy storage in animals )
cellulose ( cell walls in plants )
chitin ( hard outer layer of insects ).


 2). Lipids
 Lipids contain C , H , and O. They do not dissolve in water. Lipids can be fats, phospholipids, or steroids.

A) Fats ( triglycerides ) Fig 2.12. They are made of glycerol and 3 fatty acids. Fats are used for energy storage and insulation

B) Phospholipids
These are made of glycerol, 2 fatty acids and phosphate. Part of the molecule is hydrophobic (keeps away from water), part is hydrophilic (dissolves well). Phospholipids make up most of the cell membrane.

C) Steroids
Steroids are made of 4 rings of carbon. They form sex hormones eg estrogen, testosterone. Animals often need small amounts of steroids in their diet eg cholesterol.


 3). Proteins
 contain C , H , O and N.

Proteins are made of amino acids joined together. There are 20 different amino acids. The order of amino acids in a protein is important.

Proteins are found in cell membranes, blood, hair, enzymes and muscles.
Protein powders are often sold like vitamins as nutritional supplements, however protein deficiency is almost unknown in this country, so you do not need these supplements.

 4). Nucleic acids
 contain C , H , O , N and P. They are made of nucleotides, ( phosphate, sugar and base ). Fig 2.13.

DNA ( Deoxyribonucleic acid )
DNA has deoxyribose as the sugar.
4 bases :  Adenine     Thymine	
           Guanine     Cytosine
bases pair up and join with hydrogen bonds to form a double helix.
The code on DNA carries information the cell needs to make proteins. Closely related animals have similar DNA. Humans and primates have very similar DNA
A new study will trace human migrations by looking at DNA. DNA study

RNA ( ribonucleic acid )
RNA has ribose as the sugar.Rna has 4 bases: with Uracil instead of Thymine.

RNA is a single strand. RNA moves from the nucleus of the cell to the cytoplasm to allow the cell to make proteins ( mRNA : messenger RNA ).
New RNA drugs could be very useful, for example to reduce heart attack risk. RNA drugs

Cells
 All living things are made of cells. Cells are microscopic they were first discovered in 1665.

1) Prokaryotic cells - are only in bacteria. Fig 2.15
Prokaryotic cells are small, and have no nucleus or organelles

2) Eukaryotic cells - in plants, fungi, animals
Eukaryotic cells are larger, and have specialized organelles.

The Cell
Cells consist of : membrane, nucleus and cytoplasm.

Membranes separate cells from their surroundings. Membranes are made of phospholipid and protein.
Membranes are selectively permeable : they only let some chemicals through.

Nucleus: Table 2.1
It contains DNA arranged in chromosomes.The nucleus is surrounded by nuclear membrane which has pores. The nucleolus produces ribosomes

Cytoplasm : the area outside the nucleus. It contains many organelles which are listed below:

1). Ribosomes : contain RNA
use RNA to produce proteins.

2). ER (Endoplasmic reticulum)

Rough ER : series of membranes with ribosomes
produces new membrane

Smooth ER : membranes without ribosome
produces lipids
detoxifies chemicals ( in the liver )

3). Golgi body or Golgi apparatus
packages and ships off chemicals

4). Lysosomes : produced by Golgi body.
Lysosomes contain digestive enzymes to digest :
a) food brought in by phagocytosis (when a cell pulls food in through the cell membrane).
b) old organelles

5). Vacuoles : Fig 2.16
typically found in plants : storage vacuoles hold water, minerals, poison

6). Mitochondria
smooth outer membrane, folded inner membrane
break down food to produce ATP ( energy)

7). Chloroplasts : only found in plants
contain chlorophyll
carry out photosynthesis to produce carbohydrate

8). Cytoskeleton
controls the shape, and movement, of the cell
consists of microtubules and microfilaments

Microtubules : made of the protein tubulin
form cilia and flagella to help single cells swim around.
Clean debris from the lungs.

Microfilaments : made of the protein actin
cause muscle movement in animals

9 ). Cell wall : only in plants.
made of cellulose
stops the cell from bursting and helps support trees.

 Last edited March 2009 by David Byres, dbyres@fccj.edu