Samenvatting
CELBIOLOGIE
Nathalie Ridderhof
,Chapter 5: Biological macromolecules and lipids
Large molecules can be sorted in 4 main classes:
- Carbohydrates
- Lipids
- Proteins
- Nucleic acids
Macromolecules:
A giant molecule formed by the joining of smaller molecules, usually by a dehydration
reaction. Polysaccharides, proteins and nucleic acids are macromolecules.
5.1
Macromolecules are polymers, built from monomers.
- Polymer; A long molecule consisting of many similar or identical monomers linked
together by covalent bonds.
- Monomers; The subunit that serves as the building block of a polymer.
Enzymes:
A macromolecule serving as a catalyst. They speed up the chemical reaction. Most enzymes
are proteins.
• Dehydration reaction: A reaction in which two molecules are covalently bonded to
each other with the loss of a water molecule.
- One monomer provides a hydroxyl group (-oh)
- The other provides a hydrogen (-H)
• Hydrolysis: The bond between monomers is broken by the addition of a water
molecule. Hydrogen from water is being attached to one monomer and de hydroxyl
group is attached to the other monomer.
5.2 - Carbohydrates serve as fuel and building material.
Carbohydrates:
A sugar (mono-saccharide) or one of its dimers (disaccharides) or polymers
(polysaccharides).
Sugars:
- Aldose (aldehyde sugar)
- Ketose (ketone sugar)
Cellular respiration, cells extract energy from glucose molecules by breaking them down in a
series of reactions.
• Disaccharide consist of two monosaccharides joined by a glycosidic linkage, a
covalent bond formed between two monosaccharides by a dehydration reaction.
, - Disaccharides must be broken down to monosaccharides to be used for energy by
organisms.
- Lactose-intolerance is a condition in humans who lack lactase, The enzyme that
breaks down lactose.
Polysaccharides;
- Hydrolyzed as needed to provide sugar for cells.
- Serve as building material for structures that protect the cell or the whole organism.
Storage polysaccharides:
- Plants store Starch; a polymer of glucose monomers, granules within plastids. (stored
energy)
- The simplest form of starch, amylose, is unbranched.
- Animals store a polysaccharide called glycogen, a polymer of glucose that is more
extensively branched. Mainly in liver and muscle cells.
- Hydrolysis of glycogen in these cells releases glucose when the demand for sugar
increases.
Structural polysaccharides:
- The polysaccharide called cellulose is a major component of the tough walls that
enclose plant cells.
- Cellulose; polymer of glucose with 1-4 glycosidic linkages.
, • Enzymes that digest starch by hydrolyzing it’s a-linkages are unable to hydrolyze the
b-linkages of cellulose because of the different shapes.
Chitin:
Structural polysaccharide, consisting of amino sugar monomers found in many fungal cell
walls and in the exoskeletons of all arthropods ( insects, spiders, etc.)
5.3 – Lipids are a diverse group of hydrophobic molecules
Lipids;
Any of a group of large biological molecules, including fats, phospholipids, and steroids, that
mix poorly, if at all, with water.
Fats;
- Are not polymers
- Fat; three fatty acid molecules are each joined to glycerol by an ester linkage, a bond
formed by a dehydration reaction between a hydroxyl-group and a carboxyl-group.
Also called a triacyl-glycerol.
- Glycerol is a alcohol; bears a hydroxyl-group
- Fatty acid; A carboxylic acid with a long carbon chain. C-H bonds in this fatty acid are
the reason that they are hydrophobic.
• Saturated fatty acid; connected by single bonds.
• Unsaturated fatty acid; connected by one or more double bonds.
A diet rich in saturated fats → atherosclerosis
Deposits called plaques develop within the walls of blood vessels, causing inward bulges
(uitstulpingen) that disturb the blood flow and reduce the resilience (veerkracht) of the
blood vessels.