carbohydrates and lipids

week 1 ctb

macromolecules

• large carbon containing molecules

nucleic acid functions (DNA and RNA)

• information storage

• transmission

protein functions

• enzymatic catalysis

• antibodies

• hormonal signalling

• structural proteins

• contractile proteins

• gas transport

carbohydrate functions

• energy source

lipids functions

• energy source

• membrane components

• hormonal signalling

carbohydrates

• general molecular formula: [C(H₂0)]_n

• classified according to monomer number:

monosaccharide: 1 monomeric unit

disaccharide: 2 monomeric unit

oligosaccharide: 3-10 units

polysaccharide: >10 units

monosaccharides

• names ending in ‘ose’

• classified by chemical structure

triose (3)

tetrose (4)

pentose (5)

hexose (6)

• isomer: same atoms, bonded to each other in different 3D arrangement

• longer chain ones form cyclic molecules

important monosaccharides

• trioses: dihyroxyacetone phosphate and glyceraldehyde 3 phosphate are important intermediates in energy metabolism

• pentoses: ribose and deoxyribose are crucial components of RNA and DNA respectively

important disaccharides

• disaccharides are formed by reaction from two monosaccharides (eliminates water, forms glycosidic bond)

important poly/oligosaccharides

• starch obtained in in diet from plant sources

• cellulose

• glycogen (obtained from plant sources)

• dextrin (breakdown product of starch and glycogen, branched oligomer of glucose)

lipids

3 main types of biologically important lipids:

1. fatty acids

2. triglycerides (triacylglycerols)

3. cholesterol

fatty acids

• fatty chains are hydrocarbon chains of various lengths 

• saturated or unsaturated

• unsaturated have at least one C=C double bond

• join to glycerol to form triglycerides

cis vs trans fatty acids

• cis or trans describes a form of isomerism at double bonds (around which there is no rotation) and applies to unsaturated fatty acids

• either isomer can be incorporated into triglycerides and modified lipids

• cis fatty acids pack next to each other less closely than trans ones, so they cause membranes to be more fluid

modified lipids

• phospholipids consist of phosphate group attached to fatty acid chains via glycerol/ sphingosine which itself contains a long hydrocarbon chain

• glycolipids consist of carb element (oligosaccharide) attached to one or more fatty acid chains directly or via glycerol/sphingosine

• both important for cell membrane

ketone bodies

• small, 4 carbon water soluble fatty acids formed by liver during fasting, where they become important energy substrates for brain

• acetoacetic acid, beta hydroxybutyic acid and acetone are the main ketone bodies

• excess formation of ketone bodies in T1DM result in dangerously high concs in blood

roles of lipids

• fuels/substrates for energy metabolism for cells (fatty acids, ketone bodies)

• energy storage (triglycerides)

• transport between tissues (cholesterol esters, triglycerides)

• structural components of cell membranes (phospholipids, cholesterol)

• chemical messengers (steroids, diglycerides)

energy release

• energy is released from organic molecules by oxidation reactions

• oxidation = loss of electrons, gain of oxygen atoms

• opposite = reduction

lipoproteins

• lipids are transported through aqeous environments such as blood plasma in structures called lipoproteins

• they have a hydrophobic core containing:

triglycerides

esters

• hydrophilic surface containing:

phospholipids

free proteins

apolipoproteins

• separated by ultracentrifugation and classified according to densities

• lipoprotein lipase releases fatty acids from chylomicrons and VLDLs into tissues

chylomicrons: highest triglycerides, lowest cholesterol

• deliver dietary (exogenous) triglycerides into peripheral tissues

VLDL: high triglycerides, low cholsterol

• deliver endogenous triglycerides to peripheral tissues

LDL: low triglycerides, highest cholesterol

• deliver cholesterol to peripheral tissues and to liver

HDL: lowest triglycerides, high cholesterol

• deliver cholesterol from peripheral tissues to liver for elimination