b1.1 carbohydrates and lipids Flashcards
what are the chemical properties of carbon?
each carbon atom can form 4 covalent bonds
carbon is contained in nucleic acids, carbohydrates, lipids and proteins
carbon can form rings (nucleic acids), branched and unbranched molecules
what are monomers, polymers and macromolecules?
monomers are the smaller subunits from which larger molecules are made. polymers are molecules made up from a large number of monomers in a chain. the process by which monomers join to form polymers is called polymerisation.
macromolecules are very large molecules. polymers can be macromolecules, but not all polymers are macromolecules.
what is a condensation reaction?
polymers are formed during condensation reactions. a condensation reaction occurs when molecules combine together, forming covalent bonds and resulting in polymers. water is removed as part of the reaction.
what is a hydrolysis reaction?
polymers often need to be broken down into their monomers. the reaction that allows this to occur is a hydrolysis reaction. in hydrolysis of macromolecules, covalent bonds are broken when water is added.
what are the functions of carbohydrates?
carbs make up 10% of the organic matter in a cell. functions include:
- energy source (released from glucose during respiration)
- energy store (starch & glycogen)
- structural (cellulose)
some form parts of larger molecules (nucleic acids, glycolipids)
what are the properties of monosaccharides?
monosaccharides can join together via condensation reactions. the new chemical bond that forms between two monosaccharides is known as a glycosidic bond.
monosaccharides have the general formula Cn H2n On.
monosaccharide properties include:
1. soluble in water
2. sweet
3. form crystals
4. chemically stable
5. yields high levels of energy when broken down
there are different types of monosaccharides formed from molecules with varying numbers of carbon atoms, eg:
- triose 3c
- pentose 5c
- hexose 6c
what is alpha glucose?
C₆H₁₂O₆ - tends to occur as ring structure as it is more stable than linear
what is beta glucose?
the same as alpha glucose, however there is a slight difference in the structure. the hydroxyl group at carbon 1 is above the plane of the ring (instead of above it).
a-glucose and b-glucose have very different properties due to these structural differences.
different shaped forms of the same molecule are called isomers.
what are disaccharides?
disaccharides are :
- soluble
- sweet tasting
- forms crystals
examples are:
- glucose + glucose = maltose
- glucose + fructose = sucrose
- glucose + galactose = lactose
how are disaccharides formed?
disaccharides are formed when two monosaccharides are joined together by a glycosidic bond (covalent).
the reaction involves the formation of a water molecule.
the glycosidic bond forms at carbon 1 of the first glucose molecule and carbon 4 of the second - called a 1,4-glycosidic bond. many of these bonds results in an unbranched chain.
carbon 1 can also form a glycosidic bond with carbon 6, which results in side branches
what is amylose?
amylose consists of thousands of a-glucose molecules, all bonded together by 1,4-glycosidic bonds through condensation reactions. it has unbranched, straight chains.
amylose chains coil into a spring due to ring structure of glucose and 1,4 linkage. this makes it compact and ideal for storage.
starch is a mixture of amylose and amylopectin molecules
what is amylopectin?
amylopectin consists of a-glucose molecules in a branched chain, bonded by 1,4 and 1,6 glycosidic bonds.
starch is a mixture of amylose and amylopectin molecules
what is glycogen?
glycogen is a polymer of a-glucose moelcules. it has a similar structure to starch, but has shorter chains with lots of branches.
it is found in animals (liver and muscle cells) and can be hydrolysed into glucose molecules - therefore is an energy storage molecule.
due to shorter chains, it can be hydrolysed quicker and so releases energy quicker than starch - often called animal starch. it is insoluble
what is cellulose?
cellulose is a polysaccharide of b-glucose molecules bonded together by condensation reactions. the chains are straight and long (unlike chains of a-glucose molecules, which are coiled and often branched). the chains are strong, which means cellulose has a structural function in plants.
the b-glucose, the hydroxyl group on c1 is angled upwards and the hydroxyl group on c4 is angled downwards. to bring these groups together and allow a condensation reaction to occur, each b-glucose added to the chain must be inverted in relation to the previous one.
what are glycoproteins?
carbohydrates and polypeptides can combine to make structures called glycoproteins, which form part of the structure of cell surface membranes. they act as receptor molecules in processes such as cell recognition and identification, and receptors for cell signalling molecules.
how do glycoproteins dictate blood type?
glycoproteins can act as antigens which can identify cells as either ‘self’ or ‘non self’. a person’s blood type is determined by the glycoprotein antigens on the surface of their red blood cells. the presence of antibodies within an individual can create an interaction with the glycoproteins if blood of the wrong type enters their body. this can cause fatal issues during blood transfusions if the incorrect blood type is given.
why are lipids hydrophobic?
lipid macromolecules contain carbon, hydrogen and oxygen atoms. the structure of lipids affects their solubility. lipids contain hydrocarbon molecules which contain many non-polar covalent bonds, meaning that lipids are insoluble in water.
what is the structure of a triglyceride?
three fatty acids join to one glycerol molecule to form a triglyceride. triglycerides are formed by a process known as esterification. an ester bond forms when the hydroxyl group of a glycerol molecule bonds with the carboxyl group of a fatty acid. the formation of an ester bond is a condensation reaction.
what is the structure of a phospholipid?
phospholipids are also formed from glycerol and fatty acids. they contain two fatty acids bonded to a glycerol molecule and a phosphate ion. phospholipids are said to be amphipathic, meaning they have both hydrophobic and hydrophilic regions.
what are saturated fatty acids?
in saturated fatty acids, the bonds between the carbon atoms in the hydrocarbon tail are all single bonds. saturated fatty acids are straight molecules, meaning that lipid molecules containing them are able to pack tightly together. this increases their melting point and causes them to be solid at room temperature.
what are unsaturated fatty acids?
in unsaturated fatty acids, the bonds between the carbon atoms in the hydrocarbon tail are not all single bonds. these double bonds can cause the hydrocarbon tail of unsaturated fatty acids to kink, or bend, meaning they are not as straight as saturated fatty acids.
what are the different types of unsaturated fatty acid?
a fatty acid with one carbon double bond is known as a monounsaturated fatty acid. in some unsaturated fatty acids, there are many carbon double bonds - these are known as polyunsaturated fatty acids.
why are lipids used for energy storage?
the hydrolysis of triglycerides releases glycerol and fatty acids, which can form useful respiratory substrates. lipids are energy dense in comparison to carbohydrates and are insoluble, meaning they aren’t transported round the body easily and remain in their storage cells. when lipids are respired a lot of water is produced. these features make lipids ideal for long term energy storage.
why are lipids used for thermal insulation?
in animals, lipids are stored in adipose tissue. fat is stored in adipose cells, which are specialised to contain large globules of fat. adipose tissue can be used as a thermal insulator in animals that live in particularly cold environments. in many plants, seeds have evolved to store fats to provide energy for a growing seedling plant.
how do phospholipid layers form?
when placed in water, the hydrophilic phosphate heads of phospholipids orient themselves towards the water and the hydrophobic hydrocarbon tails orient themselves away from the water, causing them to form a phospholipid monolayer. when phospholipids are mixed with water, two layered structures known as phospholipid bilayers can form.
how does the phospholipid bilayer act as a barrier?
the amphipathic nature of phospholipids mean that the phospholipid bilayer acts as a barrier to most water soluble substances. this means that water soluble molecules such as sugars, amino acids and proteins cannot leak out of the cell and unwanted water soluble molecules cannot get in.
what lipids can cross the phospholipid bilayer?
small, non polar molecules (such as oxygen and carbon dioxide) are soluble in the lipid bilayer and can therefore easily cross cell membranes to be utilised by the cell. other larger molecules can also enter the cell across the lipid bilayer, such as steroid hormones (which contain cholesterol). the hydrocarbon region of cholesterol is non polar, allowing it to cross lipid bilayers.
oestradiol and testosterone are two examples of steroid hormones formed from cholesterol. due to their lipid structure, they can cross the lipid bilayer and can readily travel into and out of cells and nuclei.
