biological molecules (chap 3) -olevel pure bio

what are carbohydrates

• organic molecules made of elements carbon, hydrogen and oxygen

• ratio of hydrogen to oxygen is always 2:1

• has a fixed proportion of C1:H2:O1

what are monosaccharides

• simple sugars

• basic unit of a carbohydrate

• small enough to pass through cell membranes

examples of monosaccharides

• glucose (found in plants and animals)

• fructose (mainly found in plants)

what are polysaccharides

• double sugars

• formed when 2 single sugars are joined together

• can be split into 2 single sugar molecules in the presence of an enzyme

examples of polysaccharides

-maltose

-sucrose

what are the 3 types of complex carbohydrates

• starch

• cellulose

• glycogen

starch: role, occurrence and what it is

• several thousand glucose molecules joined together

• storage form of carbohydrates in plants

• can be digested to form glucose to provide energy for cell activities.

• found in the storage organs of plants

cellulose: what it is, role, and where its found

• many glucose molecules joined together but bonded differently from starch

• role: cellulose cell walls protect plant cells from damage or bursting

• serves as dietary fibre that prevents constipation as it cannot be digested in our intestines

• found in cell walls of plants

glycogen: what it is, role, and where its found

• branched molecule of many glucose molecules

• storage form of carbs in mammals

• when needed, it is digested to glucose to provide energy for cell activities

• stored in liver and muscle of mammals

why is glycogen and starch suitable as storage materials of glucose

• insoluble in water

• they are large molecules that cannot diffuse through cell membranes

• easily hydrolysed to glucose when needed

• made of molecules that have compact shapes so they occupy less space

function of carbohydrates

• provide energy for cell activities

• form supporting structures (eg cell wall)

• for conversion into other organic compounds (eg amino acids and fats)

• formation of DNA

• synthesises lubricants (eg mucus)

• synthesises nectar in flowers

what are fats

• organic molecules made of carbon, hydrogen, oxygen

• significantly higher amount of hydrogen to oxygen than carbs

• no fixed proportion

function of fats

• source and store of energy

• acts as an insulating material to prevent excessive heat loss

• solvent for fat soluble vitamins and some hormones

• form cell membranes

• help reduce water loss from skin surface

what are proteins

organic molecules made of carbon, hydrogen, oxygen and nitrogen

traces of sulfur may sometimes also be found in proteins

what are amino acids

basic building blocks of protein

how are polypeptides formed

peptide bonds link up amino acids to form polypeptide

how are proteins formed

2 or more polypeptide chains to form 3D molecule which is protein.

functions of protein

synthesis of

• new protoplasm for growth and repair of worn out cells

• enzymes and hormones

• antibodies

how to carry out Biuret’s test and what it is tests for

• tests for proteins

• add 2cm3 of biurets solution to 2cm3 of food sample to a clean test tube. shake well and allow mixture to stand for 5 minutes

• blue — no proteins

• purple — protein present

how to carry out iodine test and what it tests for

• tests for presence of starch

• add a few drops of iodine to a food sample

• brown — no starch

• blue-black — starch

how to carry out ethanol emulsion test and what it is for

• used to test for presence of fats

• add 2cm3 of ethanol to 2cm3 of food sample to a clean test tube. shake contents vigorously. add 2cm3 of water into test tube and shake mixture.

• cloudy mixture — presence of fats

• clear mixture — no fats

how to carry out benedict’s test and what it is used to test

• used to test for reducing sugars (glucose, fructose, maltose)

• add 2cm3 of benedict’s solution to 2cm3 of food sample in a test tube. shake the mixture. heat the contents in a boiling water bath for 2-3 minutes.

• red — green -presence of reducing sugars

• blue — no reducing sugar