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12 Cards in this Set

  • Front
  • Back
What are the four main classes of biomolecule and their main function?
• Carbohydrates: respiratory substrate (short term).

• Nucleic acids: encode genetic information.

• Fatty acids: respiratory substrate (long-term).

• Amino acids: form proteins.
What are some other biomolecules that are less common?
• Cholesterol/steroid hormones.

• Vitamins.

• Co-factors.

• Xenobiotics.
Carbohydrates
Overview:
• General formula (CH2O)n, highly soluble due to polar and hydrophilic nature.

• Act as an energy source and use for energy storage, part of cell wall (in bacteria) and important for protein function (as they are often glycosylated).

Nomenclature:
• Based on number of carbon atoms: triose=3 (DHAP, glyceraldehyde), pentose=5 (ribose), hexose=6 (glucose, fructose).
• Aldoses have a terminal C=O group - they are aldehydes - as opposed to ketoses.
• Optical isomers possible, in humans D-isomers are used.

Structure:
• <1% are in the linear form, most being found as a ring - where an OH group bonds with the anomeric carbon (found in carbonyl group) to release water.
• Alpha and beta forms possible - depending on which position the hydroxyl group attached to the anomeric carbon is found (up or down). In solution the two forms freely interconvert (in a monosaccharide).

Polymer formation:
• Monosaccharides are single 'units', such as glucose and galactose. Disaccharides are two units joined together (by a glycosidic bond), such as sucrose and lactose. Polysaccharides consists of many monosaccharides, such as glycogen and starch.
• Glycosidic bonds are formed in a condensation reaction, mediated by glycosyltransferase.
• If the anomeric carbon is not attached to another residue, the molecule is a 'reducing sugar'.
Describe the structure and function of glycogen.
• Linear glucose polymer - α(1->4) glycosidic links - with α(1->6) branches.
• Digestion: α-amylase causes random hydrolysis of internal α(1->4) links in saliva and pancreas, to give a mixture of mono- and disaccharides. Finally, maltose produces single units for absorption by intestinal cells.
What causes lactose intolerance?
• Disruption of lactase/ß-galactosidase, causing increased digestion of the substate by bacteria in the large intestine. This leads to bloating and diarrhoea.
Nucleic acids
Overview:
• Polymer of nucleotides - which are units consisting of a pentose sugar, phosphate and nitrogenous base - that stores genetic information (DNA) and converts it into proteins (RNA).

Examples:
• DNA: long polymer of nucleotides (A, C, G, T) with a backbone of alternating sugar/phosphate molecules. Complementary strand runs antiparallel and bound via hydrogen bonding between bases. Helical structure with bases extending inwards perpendicular to helical axis.

• RNA: single stranded polymer of nucleotides (A, C, G, U). Can be classed as messenger, ribosomal or transfer RNA - see theme two.

• ATP: major intracellular 'currency' of energy - hydrolysis of high-energy phosphate bonds between phosphate is exergonic. Structure is pentose sugar bound to adenine (A) and three phosphate groups.
Lipids
• Triacylglycerols are hydrophobic ester of three fatty acids and glycerol, acts as an energy store and stored in adipose tissue.

• Fatty acids are long chain aliphatic carboxylic acids, with a general structure of CH3(CH2)nCOOH. They are metabolised the ß-oxidation pathway to yield ATP (see theme four). Can be saturated, with only C-C single bonds (e.g. palmitic acid 16:0); unsaturated, with a single C=C double bond (e.g. oleic acid 18:1) or polyunsaturated, with many C=C double bonds (e.g. linoleic acid18:2.

• Cell membranes are composed of a phospholipid bilayer - the phospholipid being a glycerol attached to two fatty acids and an alcohol group (e.g. choline). Therefore, they are amphipathic - with a polar 'head' and non-polar 'tail' and spontaneously form a bilayer in an aqueous environment.
Cholesterol
• A steroid, obtained through diet and endogenous synthesis. Has a multi-ring structure and is important for membrane fluidity.

• It is an important precursor for steroid hormone synthesis (e.g. testosterone, oestrogen, cortisol).
Proteins/Amino Acids
Amino acids:
• General structure of central alpha carbon bound to amino and carboxyl groups and a variable 'R' chain. There are 20 'natural' amino acids that are used as building blocks for protein synthesis. They are water soluble and electri...
Amino acids:
• General structure of central alpha carbon bound to amino and carboxyl groups and a variable 'R' chain. There are 20 'natural' amino acids that are used as building blocks for protein synthesis. They are water soluble and electrically charged at physiological pH.

• Can be sorted into four categories: positively charged, negatively charged, polar uncharged and non-polar uncharged (see table)

• You must learn the three letter and one letter abbreviations!

• Amino acids can be used to synthesise neurotransmitters: tyrosine->noradrenaline, dopamine; histidine->histamine; tryptophan-> serotonin.

Proteins:
• Polymers of amino acids, joined by peptide bonds.

• Proteins=life, basically.

• Hydrolysis only by specialised enzymes.
pKa of side groups
• A measure of how 'keen' side chains are to give up their protons.

• At physiological pH alpha carboxyl and amino groups are both ionised - the former having a pKa of 2.3, the latter of 9.8.

• As these are groups are involved in the peptide bond this is not important for proteins - only the pKa of side groups count.
What causes phenylketonuria (PKU)?
• Defective phenylalanine hydroxylase (Phe-->Tyr). Reduced tyrosine leads to reduced dopamine and melanin production and an increase in Phe by-products, such as phenylacetate.
What causes albinism?
• Defective tyrosinase, which usually converts tyrosine to melanin.