2.3 Flashcards
Carbohydrates are made of…
C, H and O (‘carbo’ – contains carbon ; ‘hydrate’ – contains H and O)
carbohydrates are composed of
Carbohydrates are composed of recurring monomers called monosaccharides (which typically form ring structures)
monosaccharides may be linked together by…
These monosaccharides may be linked together via condensation reactions (water is formed as a by-product)
- Two monosaccharide monomers may be joined via a glycosidic linkage to form a disaccharide
- Many monosaccharide monomers may be joined via glycosidic linkages to form polysaccharides
Examples of Carbohydrates:
monosaccharides, disaccharides, polysaccharides
Monosaccharides example
Monosaccharides (one sugar unit) are typically sweet-tasting and function as an immediate energy source for cells
Examples of monosaccharides include glucose, galactose and fructose
Disaccharides example
Disaccharides (two sugar units) are small enough to be soluble in water and commonly function as a transport form
Examples of disaccharides include lactose, maltose and sucrose
Polysaccharides example
Polysaccharides (many sugar units) may be used for energy storage or cell structure, and also play a role in cell recognition
Examples of polysaccharides include cellulose, glycogen and starch
Polysaccharides are…
carbohydrate polymers comprised of many (hundreds to thousands) monosaccharide monomers
- The type of polymer formed depends on the monosaccharide subunits involved and the bonding arrangement between them
- Three key polymers can be made from glucose monosaccharides – cellulose, starch (in plants) and glycogen (in animals)
Cellulose
Cellulose is a structural polysaccharide that is found in the cell wall of plants
It is a linear molecule composed of β-glucose subunits (bound in a 1-4 arrangement)
Because it is composed of β-glucose, it is indigestible for most animals (lack the enzyme required to break it down)
- Ruminants (e.g. cows) may digest cellulose due to the presence of helpful bacteria in a specialised stomach
- Caecotrophs (e.g. rabbits) will re-ingest specialised faeces that contain digested cellulose (broken down in the caecum)
Starch
Starch is an energy storage polysaccharide found in plants
It is composed of α-glucose subunits (bound in a 1-4 arrangement) and exists in one of two forms – amylose or amylopectin
- Amylose is a linear (helical) molecule while amylopectin is branched (contains additional 1-6 linkages)
- Amylose is harder to digest and less soluble, however, as it takes up less space, is the preferred storage form in plants
Glycogen
Glycogen is an energy storage polysaccharide formed in the liver in animals
It is composed of α-glucose subunits linked together by both 1-4 linkages and 1-6 linkages (branching)
- It is akin to amylopectin in plants, but is more highly branched (1-6 linkages occur every ~10 subunits as opposed to ~20)
Fatty acids can be…
saturated, monounsaturated or polyunsaturated
fatty acids are
Fatty acids are long hydrocarbon chains that are found in certain types of lipids (triglycerides & phospholipids)
- Fatty acids may differ in the length of the hydrocarbon chain (typically 4 – 24 carbons) and in the number of double bonds
saturated fatty acids
Fatty acids that possess no double bonds are saturated (have maximum number of H atoms)
- Saturated fatty acids are linear in structure, originate from animal sources (i.e. fats) and are typically solid at room temperatures
unsaturated fatty acids
Fatty acids with double bonds are unsaturated – either monounsaturated (1 double bond) or polyunsaturated (>1 double bond)
- Unsaturated fatty acids are bent in structure, originate from plant sources (i.e. oils) and are typically liquid at room temperatures
unsaturated fatty acids may occur in two distinct structural configurations
cis and trans isomers
cis
Cis: The hydrogen atoms attached to the carbon double bond are on the same side
trans
Trans: The hydrogen atoms attached to the carbon double bond are on different sides
trans fatty acids…
- Trans fatty acids do not commonly occur in nature and are typically produced by an industrial process called - hydrogenation
- Trans fatty acids are generally linear in structure (despite being unsaturated) and are usually solid at room temperature
Triglycerides
Triglycerides are the largest class of lipids and function primarily as long-term energy storage molecules - Animals tend to store triglycerides as fats (solid), while plants tend to store triglycerides as oils (liquid)
triglycerides are formed when…
Triglycerides are formed when condensation reactions occur between one glycerol and three fatty acids
- The hydroxyl groups of glycerol combine with the carboxyl groups of the fatty acids to form an ester linkage
This condensation reaction results in the formation of three molecules of water
Triglycerides can be either…
saturated or unsaturated, depending on the composition of the fatty acid chains
types of fats
Whilst all types of fats consumed as part of dietary intake will cause adverse health effects if taken in excessive amounts, some types of fats are associated with increased health risks
- The mix of fats in the diet influences the level of cholesterol in the bloodstream
- Saturated fats and trans fats raise blood cholesterol levels, while (cis) unsaturated fats lower blood cholesterol levels
Regulating Blood Cholesterol Levels
Fats and cholesterol cannot dissolve in blood and are consequently packaged with proteins (to form lipoproteins) for transport
- Low density lipoproteins (LDL) carry cholesterol from the liver to the rest of the body
- High density lipoproteins (HDL) scavenge excess cholesterol and carry it back to the liver for disposal