Zellbiologie

Zwitterions: Positive and negative charge on the same molecule. Amino acids exist in this form at physiological
pH ( about 7.4)

There 20 naturally occurring amino acids which can be linked together by peptide bonds. The
bond is mace between the amide-nitrogen and the carbonyl oxygen.

Only one way to link amino acids together – peptide bond

Amino acids/proteins act as: enzymes (catalysts), metabolic
intermediates, carriers of energy and waste products and hormones.

(chemistry) describing a molecule, such as a detergent, which has both hydrophobic and hydrophilic groups.

Proteins Functions: Enzymes, storage proteins, signal proteins, structural proteins, receptor proteins, transport proteins, motor proteins and gene regulatory proteins.

Proteins Primary structure: Amino acid sequence --> stabilised only by covalent peptide bonds

Protein Secondary structure: Folding of the polypeptide structure (hydrophilic side chains on the outside),
usually as α-helix and/or β-sheet(parallel/antiparallel) --> stabilised by non-covalent bonds such as hydrogen bonds of the
peptide backbone

Proteins Tertiary structure: Folding of separate elements of the secondary structure --> stabilised by non-
covalent interactions between the side chains of the amino acids and covalent disulphide bonds.

Proteins Quaternary structure: Assemblies of several subunits to a complex protein --> stabilised by covalent
and non-covalent bonds.

Identical polypeptide chains: homodimers, homooligomers
Different polypeptide chains: heterodimers, heterooligomers

• resonance between the amide-nitrogen and the carbonyl-oxygen affects that the peptide bond is planar and fixed.
• rotations around the α-carbon atom are possible.
• the side chains at the α-C of neighbouring amino acids determine the flexibility
• protein folding is independent of this flexibility.

Two or more atoms come very close together and share one or more electrons, which defines
spatial arrangement and three-dimensional structure. Double (or triple) bonds change the geometry and inhibit
free rotation

Hydrogen Bonds: Occur between molecules with partial positive or negative charges with a differential electron
distribution between the atoms (polar molecules).

Monosaccharides: They have a general formula of (CH 2 O)n where n is between 3 and 6. They consist of 2 or
more OH groups and are called aldose if they contain an aldehyde group and ketose, if they contain a ketone
group.

• containing aldehyde group: aldose
• containing ketone group: ketose
• ring formation in aqueous solution

Isomers: Same chemical formula, different structure.

Di-/Polysaccharides: Consist of two or several monosaccharides, which are linked together. The linkage is
“produced” by a condensation reaction and destroyed by hydrolysis.

Cellulose: The major structural component of plants. It is a long polymer made of cellobiose (a disaccharide
made of two glucose molecules). Humans can’t digest cellulose because we don’t have the enzyme cellulase.

cellobiose: glucose-β-1,4-glucose

Lactose: It is made up of galactose linked to glucose. The galactose can be converted to glucose by the human
body only if the enzyme lactase is present.

lactose: galactose β 1,4 glucose

Sucrose: A very common natural sweetener made up of glucose and fructose. Our body can synthesise all the
different sugars needed from glucose and it can also produce the glucose itself in many different ways.

sucrose: glucose α 1,2 fructose

Glycogen: Branched polysaccharide which is used for energy storage (in humans/animals)