definition of carbohydrates
= organic molecules made up of elements carbon, hydrogen and oxygen (ratio of atoms H:O = 2:1)
definition of double sugars
= formed when 2 single sugars are joined together
what is maltose made of?
2 glucose molecules bonded together
what is sucrose made of?
1 glucose molecule and 1 fructose molecules joined together
definition of polysaccharides/complex carbohydrates
= macromolecules/polymers made up of many similar molecules of single sugars/monosaccharides joined together to form a large molecule
why are glycogen and starch suitable as storage materials in cells?
- molecules are large and insoluble in water, so they do not change the water potential in
the cells - they are large molecules that cannot diffuse through cell membranes, so
they will not be lost from the cell - they can easily be hydrolised to glucose when needed, for
example, in tissue respiration - their molecules have compact shapes, so they occupy less space
than all the individual glucose molecules that make up a glycogen or
starch molecule
why are carbohydrates needed?
- as a substrate for respiration, to provide energy for cell activities;
- to form supporting structures, for example, cell walls in plants
- to be converted into other organic compounds such as amino acids and fats.
- for the formation of nucleic acids, for example, DNA;
- to synthesise lubricants e.g. mucus, which consists of a
carbohydrate and a protein - to synthesize the nectar in some flowers
definition of fats
= a type of lipid
= like carbohydrates, are organic molecules made up of the elements carbon, hydrogen and
oxygen
*but unlike carbohydrates, fats contain much less oxygen in proportion to hydrogen
functions of fats
- a concentrated source and a long-term storage of energy as they release more than twice as much energy as carbohydrates
- a suitable long-term storage material because fats have a higher energy value compared to
carbohydrates - an insulating material that prevents excessive heat loss
e.g. animals such as seals have a thick layer of fat (blubber) beneath the skin, which helps to
reduce loss of body heat - a solvent for fat-soluble vitamins and many other vital substances such as hormones
- an essential part of cells, especially in cell membranes
- a way to reduce water loss from the skin surface
-> glands in the skin secrete an oily substance
-> reduces rate of heat loss from skin
-> forms a thin layer over the skin surface, reducing the rate of evaporation of water
definition of protein
= organic molecules made up of the elements carbon, hydrogen, oxygen and nitrogen
(sulfur may also be present)
-> always present in all cells
-> their molecules are the largest and most complicated of all the food substances
-> commonly found in the meat of animals
what are proteins used for?
- synthesis of new cytoplasm, for growth and repair
of worn-out body cells; - synthesis of enzymes and some hormones; and
- formation of antibodies to combat diseases
primary protein structure
long chain of amino acids joined in a linear manner
secondary protein structure
develops when either part or all of the polypeptide chain becomes coiled to produce an a-helix or it becomes folded into b-sheets
tertiary protein structure
precise 3D shape with compact structure unique to the protein
-> when molecule is further folded and held in a particular complex shape
quaternary protein structure
precise 3D shape
-> when 2 or more polypeptides become held together, forming a complex biologically active molecule
