Cellular Chemistry
Organic compounds are found in living things.
There are four main types of organic compounds (macromolecules):
Carbohydrates (energy and structural)
Lipids (energy storage)
Proteins - (chain of amino acids)
Nucleic acids - (hereditary information) DNA and RNA
also, ATP - the main energy "currency" for cells.
Carbohydrates, such as glucose, are a source of energy and are used as structural materials in organisms.
Monosaccharides are the single-sugar building blocks of carbohydrates.
Glucose - C6H12O6
Fructose
Disaccharides - two joined monosaccharides
Sucrose (table sugar) = glucose + fructose
Polysaccharides - storage for the energy in sugars
Starch (plants) and glycogen (animals) or cellulose (plant structure)
Lipids are non-polar molecules that are not soluble in water
Fats - store energy
Phospholipids - form the lipid bilayer of cell membranes
Steroids - Sterol (plants) and cholesterol (animals)
Waxes
Others - chlorophyll and similar light-absorbing pigments
More on Fats
- Typically, 3 fatty acids bonded to a glycerol molecule
- Glycerol is an alcohol with three carbon atoms
- Fatty acids are long chains of carbon with hydrogens
- These bonds hold lots of energy!
Saturated fatty acids - all carbon atoms have two hydrogens, and the last carbon has 3. Most animal fats, solid at room temperature.
Unsaturated fatty acids - some carbons are linked by double covalent bonds. Most plant oils and fish oils.
Hydrogenated vegetable oils - naturally unsaturated oils that have been artificially saturated with hydrogen atoms. This makes margarine and vegetable shortening solid at room temperature.
Proteins are chains of amino acids. They tend to bend and fold.
Some proteins called enzymes by promoting chemical reactions.
Others have structural functions:
collagen (most abundant in your body) - skin, ligaments, tendons and bones
Antibodies - defend against infection
Muscle contraction
Hemoglobin - carries oxygen in the blood
Nucleic acids are long chains of nucleotides that carry hereditary information.
Nucleotides have three parts - phosphate group, a sugar, and a nitrogenous base.
DNA - deoxyribonucleic acid - has two strands of nucleotides that spiral around each other, held together by hydrogen bonds.
Chromosomes consist of very long strands of DNA.
RNA is made of a single strand of nucleotides, and functions in the manufacturing of proteins.
Energy and Chemical Reactions
Energy is the ability to move or change matter. It can be stored or released by chemical reactions.
Chemical reactions are summarized by the following:
Reactants Products
Chemical reactions absorb or release energy
Metabolism is the term that describes the sum of all chemical reactions within an organism.
Activation Energy is needed to start a chemical reaction.
Enzymes help biochemical reactions occur.
Enzymes speed up metabolic reactions by lowering energy barriers (pp. 96-97,FIGURES 6.12and6.13)
Enzymes, which are proteins, are biological catalysts. They speed up reactions by lowering activation energy (EA), allowing bonds to break at moderate temperatures.
Enzymes are substrate specific (pp. 97-98,FIGURE 6.14) Each type of enzyme has a unique active site that combines specifically with its substrate, the reactant molecule on which it acts. The enzyme changes shape slightly when it binds the substrate (induced fit).
Web/CD Activity6D:How Enzymes Work
The active site is an enzyme’s catalytic center (pp. 98-99,FIGURE 6.15) The active site can lower activation energy by orienting substrates correctly, straining their bonds, and providing a microenvironment that favors the reaction.
A cell’s physical and chemical environment affects enzyme activity (pp. 99-101,FIGURES 6.16and6.17) As proteins, enzymes are sensitive to conditions that influence their three-dimensional structure. Each has an optimal temperature and pH. Cofactors are metal ions or molecules required for some enzymes to function. Coenzymes are organic cofactors. Inhibitors reduce enzyme function. A competitive inhibitor binds to the active site, while a noncompetitive inhibitor binds to a different site on the enzyme.
Web/CD Case Study in the Process of Science: How Is the Rate of Enzyme Catalysis Measured?
Enzymes help organisms maintain homeostasis. Without them, reactions could not happen quickly enough to sustain life.
In your body, blood carries CO2 to your lungs. There it reacts with water to form carbonic acid, H2CO3. The reverse happens in your lungs and the CO2 is released and exhaled.
Without an enzyme, only about 200 molecules of carbonic acid would be produced in one hour. With carbonic anhydrase, an enzyme, more than 600,000 molecules are formed each second!
Enzymes affect specific substances, called substrates.
The enzyme amylase acts on starch to produce glucose.
The enzyme catalase breaks down hydrogen peroxide (H2O2), a toxin formed in cells, into H2O and O2.
An enzyme's shape determines its activity. They are usually large proteins with many folds, which form pockets called active sites.
It affects the substrate in a 3-step process:
- When an enzyme first attaches, the enzyme's shape changes slightly for a better fit for the substrate.
- At an active site, the enzyme and substrate act in a way that reduces the activation energy of the reaction.
- The reaction is complete when the products have formed. The enzyme is ready to catalyze further reactions.
Why do some laundry detergents contain enzymes?
These enzymes are purified by mutant bacteria that can withstand the heat and alkalinity of the clothes washer.
Factors affecting enzyme activity include:
Temperature range;
pH range;