B1.1 Carbohydrates and lipids

production of macromolecules

condensation reactions that link monomers to form a polymer

monomer

smallest repeating unit

polymer

a long continious chain of monomers

digestion of polymers

polymers break down into monomers by hydrolysis reaction

alpha glucose

beta glucose

glucose (monosaccharide) properties

• small and soluble → can be readily transported, dissolved in blood plasma, selectively reabsorbed in tubule

• chemically stable → can be stored in cells, converted to starch/glycogen so it doesn’t affect osmosis

• releases large amount of energy when oxidise → used in respiration

alpha glucose condensation reaction

• glucose + glucose →

• glucose + fructose →

• glucose + galactose →

• maltose

• sucrose

• lactose

polysaccharisdes

• polymers made of simple sugar monomers joined by glycosidic bonds

• do not dissolve or taste sweet

• energy storage molecules within cells

starch

• monomer: alpha glucose

• storage carbohydrate in plants

• metabolically un-reactive and insoluble - does not affect osmosis

• easy to add or remove glucose molecules to

• made of amylose and amylopectin

amylopectin

• polymer of glucose

• 1,4 and 1,6 glycosidic bonds, branches (hydrolysed rapidly)

amylose

• polymer of glucose

• 1,4 glycosidic bonds

• helical shape

glycogen

• monomer: alpha glucose

• bacteria, fungi and animals store glycogen instead of starch

• highly branched (more so than amylopectin)

• 1,4 and 1,6 glycosidic bonds

• stored in human liver and muscles

• can be hydrolysed to break glucose molecules off to be used in respiration

• easy to add or remove extra glucose molecules to starch

cellulose

• monomer: beta glucose

• glucose monomers in un-branched long straight chains

• parallel chains held together in fibres by hydrogen bonds

• orientation of glucose molecules alternates

• bundles of cross linked chains are called microfibrils

• indigestible, gives the muscles of the gut something to push against and therefore prevents constipation

• found in plant cell walls, enormous tensile strength so provides structural support

starch and glucose

compact and coiled → lots of storage, carbohydrates can fit in the cell - needed for respiration

glycoproteins

a protein molecule with a carbohydrate chain attached

glycolipids

a lipid molecule with a carbohydrate chain attached

role of glycoproteins

• used in cell recognition

• cells in the body can be recognised as self or non-self by glycoproteins on the cell membrane

ABO glycoproteins on red blood cells

• red blood cells have glycoproteins (antigens) on their cell membranes

• ABO antigens are involved in cell-cell recognition during blood transfusions and organ transplants and must match between the donor and recipient

• Type A → A antigens, B antibodies, can receive A and O, cannot receive A or AB

• Type B → B antigens, A antibodies, can receive B and O, cannot receive B or AB

• Type AB → A and B antigens, no antibodies, can receive A, B, AB and O (universal recipient)

• Type O → no antigens, A and B antibodies, can only receive O (universal donor)

lipids

• insoluble in water, non polar and hydrophobic molecules

• soluble in organic solvents such as ethanol

triglyceride

made of one glycerol and three fatty acid molecules in a condensation reaction

glycerol

fatty acid

phospholipid

• amphipathic molecules (both hydrophobic and hydrophilic in nature)

• hydrophilic phosphate heads

• hydrophobic fatty acid tails

• naturally form continuous bilayers in water

saturated fatty acids

• no C=C double bonds

• saturated with hydrogen

• straight chained

• can be tightly packed - high melting point

mono-unsaturated fatty acid

• one C=C double bond

• slightly bent chain

poly-unsaturated fatty acid

• more than one C=C double bonds

• bent/kinky chain

• loosely packed/cannot be tightly packed - lower melting point

cis unsaturated fatty acids

• cis configuration means adjacent hydrogen atoms are on the same side of double bond

• causes the chain to bend and restrict freedom

• loosely packed and liquid at room temperature (vegetable oil)

trans unsaturated fatty acids

• trans configuration means hydrogen atoms are bound to opposite sides of double bond

• do not bend as much, shape is similar to straight saturated fatty acids

• can be closely packed, usually solid at room temperature (margarine)

function of lipids in living organisms

• phospholipids as main component of cell membranes

• steroids involved in hormonal signalling

• fats in animals as heat insulators

• sphingolipids in myelin sheath as electrical insulators

• triglycerides form tissue around key internal organs for protection against injury

• triglycerides used in long term energy storage

lipid as energy store

• stored in specialised groups of cells called adipose tissue

• adipose tissue is located immediately under the skin and also around organs

• lipids are chemically stable molecules

• the amount of energy released in cell respiration per gram of lipids is double that for carbohydrates

• contribute less to body mass than carbohydrates, critical for active animals (bats)

steroids

• non-polar/hydrophobic, can pass through phospholipid bilayer

• are a different group of lipids

• all have similar 4 ring structure

• e.g. oestradiol, testosterone