Carbohydrates and Lipids PDF

CARBOHYDRATES AND LIPIDS Carbohydrates - Saccharid - Sugars Function Quick energy (sugars) Energy storage (starches) Structure (Cellulose- cell wall in plants and...

CARBOHYDRATES AND LIPIDS Carbohydrates - Saccharid - Sugars Function Quick energy (sugars) Energy storage (starches) Structure (Cellulose- cell wall in plants and glycogen) Molecule Structure: made of oxygen, hydrogen and carbon Ratio 1:2:1 C:H:O (CH2O)n Examples: C6H12O6 glucose Types Monosaccharides: Monosaccharides are sugars that consist of a single sub-unit (monomer) Ring structure Chain structure Ring structure of monosaccharides Glucose (6 carbon) hexose D- Ribose (5 carbon) Pentose Glucose Soluble, dissolved in plasma Stable molecule, useful for food storage Osmotic problems, so is store as glycogen or starch Substrate for cell respiration https://www.youtube.com/watch?v=Dgf8FQWb7V0 Disaccharides: Pairs of monosaccharides are linked together by condensation to form disaccharides. Glucose, galactose and fructose are monosaccharides that are commonly used to make disaccharides: glucose + glucose maltose + H 2O glucose + galactose lactose + H 2O glucose + fructose sucrose + H 2O Maltose Condensation Polymerisation; Glucose to Malto se Lactose https://www.youtube.com/watch?v=SZdz1yiAO5U Sucrose Polysaccharides The polysaccharides cellulose, glycogen and starch are all composed of glucose. The basic linkage between the glucose subunits is a glycosidic bond from C 1 of a glucose to C4 of the next, but some polysaccharides also have some 1,6 glycosidic bonds, giving them a branched structure. Cellulose Unbranched polymer of - β-glucose. The orientation of the glucose units alternates(up-down-up and so on), which makes the polymers straight rather than curved, and allows groups of cellulose molecules to be arranged in parallel with hydrogen bonds forming cross links. These structures are cellulose microfibrils. They have enormous tensile strength and are the basis of plant cell walls. Cell wall Cellulose Starch Polymer of -α-glucose All of the glucose subunits in the same orientation, giving the polymer a helical shape. There are two forms of starch: amylose has only 1,4 linkages so is unbranched, whereas amylopectin has some 1,6 linkages so is a branched molecule (below). Used by plants to store glucose in an insoluble form. By making the molecule branched it is possible to load or unload glucose more rapidly as there are more points on starch molecules to which glucose can be added or detached. Amylopectin Glycogen is similar in structure to amylopectin it is a branched polymer of α-glucose. There are more 1,6 linkages than in amylopectin so it is more branched. Glycogen is used by mammals to store glucose in liver and muscle cells. Because glycogen is insoluble, large amounts can be stored whereas if glucose was stored it would cause water to enter the cells by osmosis and there would be a danger of them bursting. Role of glycoproteins in cell–cell recognition Glycoproteins are composed of polypeptides with carbohydrate attached. They are a component of plasma membranes in animal cells and are positioned with the attached carbohydrate facing outwards. By displaying distinctive glycoproteins, cells allow other cells to recognize them. The glycoprotein on the surface of one cell is recognized by receptors on the surface of another cell. Cell-to-cell recognition helps with the organization of tissues and can also allow foreign cells or infected body cells to be identified and destroyed. The ABO antigens in red blood cells are an example of glycoproteins providing the means of cell–cell recognition. ABO glycoproteins Red blood cells have glycoproteins in their membranes that do not have a known function, but that affect blood transfusion. Any of three possible types of oligosaccharide can be present on the glycoprotein. The oligosaccharides are called O, A and B. One or two of these types of glycoprotein are present in every person’s blood, but not all three. If blood containing glycoprotein A is transfused into a person who does not produce it themself, the blood will be rejected. Similarly, blood containing glycoprotein B is rejected if a person does not produce it themself. However, glycoprotein O does not cause rejection problems, because it has the same structure as A and B with one monosaccharide less, so is not recognized as foreign. LIPIDS - FATS Key components in cells (cell membrane) Made of C, O and H Insoluble in water (hydrophobic) dissolve in non-polar solvents.Ethanol, toluene and propanone (acetone) Triglycerides Triglycerides are made from three fatty acids and one glycerol by condensation reactions so they have three hydrocarbon tails. Fats and oils are triglycerides. https://www.youtube.com/watch?v=55oCUwxKpsk Carboxylic acid group Types of fatty acids: saturated and unsaturated Saturated all of the carbon atoms in the chain are connected by single covalent bonds so the number of hydrogen atoms bonded to the carbons cannot be increased. Unsaturated fatty acids contain one or more double bonds between carbon atoms in the chain, so more hydrogen could be bonded to the carbons if a double bond was replaced by a single bond. Monounsaturated: only one double bond. Polyunsaturated: two or more double bonds Types of unsaturated fatty acids Cis unsaturated: hydrogen atoms are Trans unsaturated: hydrogen atoms are bonded to carbon atoms on the same side of bonded to carbon atoms on opposite sides of a double bond. a double bond. Triglycerides Phospholipids Phospholipids are similar to triglycerides but only have two fatty acids linked to glycerol, with a phosphate group instead of the third fatty acid. Phospholipids are only partly hydrophobic and form the basis of membranes. Steroids Steroids: all have a similar structure of our used rings in their molecule. Cholesterol Progesterone Estrogen Testosterone https://www.youtube.com/watch?v=69-eGO7XDfU Lipids and health In fact the mass advantage of lipids is even greater because fats form pure droplets in cells with no water associated, whereas each gram of glycogen is associated with about two grams of water, so lipids are actually six times more efficient in the amount of energy that can be stored per gram of body mass This is important for animals such as birds and bats that fly. HEALTH RISKS OF TRANS-FATS AND SATURATED FATTY ACIDS Trans-fats are mostly artificially produced but Saturated fatty acids occur naturally in animal their use is now banned in some countries. fats and some vegetable oils. There is a positive correlation between A positive correlation has been found between amounts of trans- fat consumed and rates of saturated fatty acid intake and rates of CHD in coronary heart disease (CHD). many research programs, but there are populations that do not have the correlation, In patients who died from CHD, fatty deposits in such as the Maasai of Kenya that have a diet of the diseased arteries have been found to foods rich in saturated fats yet CHD is very rare. contain high concentrations of trans-fats, which gives more evidence of a causal link. It is possible that the actual cause of CHD is not saturated at itself but another actor correlated with saturated fat intake, such as low amounts of dietary fiber.