3.1 - BIOLOGICAL MOLECULES Flashcards
what is a monomer?
a smaller, repeating unit from which larger molecules (polymers) are made
what are polymers? (1)
large molecules made up of long chains of monomers joined together
state three examples of monomers (3)
- monosaccharides (monomers of carbohydrates)
- amino acids (monomers of proteins)
- nucleotides (monomers of DNA and RNA)
state three examples of polymers (3)
- carbohydrates (polymers of monosaccharides)
- proteins (polymers of amino acids)
- DNA and RNA (polymers of nucleotides)
what does organic mean? how is all life on earth similar? what does this provide evidence for?
- organic means when something contains the element carbon
- all biological molecules contain carbon because carbon atoms can regularly form four strong covalent bonds which makes the compounds stable as these bonds require a lot of energy to break them
- all life on earth is carbon-based
- this provides indirect evidence for evolution
- living organisms have great variety amongst them, but despite this, the biochemical basis of life is similar for all living things
what is polymerisation (2)
this is any process in which monomers chemically combine to produce a polymer
what is a condensation reaction (2)
- a condensation reaction joins two molecules together with the formation of a chemical bond
- it involves the elimination (release) of a water molecule
what is a hydrolysis reaction (2)
- a hydrolysis reaction breaks a chemical bond between two molecules
- it involves the use of a water molecule
define metabolism. what are its two pathways? (3)
metabolism: the sum of all the chemical reactions taking place in the body
anabolic pathway: building up molecules
catabolic pathway: breaking down molecules
what is a covalent bond? (2)
- when atoms share a pair of electrons in their outer shells
- non-metal + non-metal
what is an ionic bond? (2)
- this is electrostatic attraction between ions with opposite charges
- metal + non-metal
what is a hydrogen bond? (2)
this is a type of bond that involves weak forces between two polar molecules
what is a polar molecule? (2)
- a molecule with an uneven distribution of charge (e.g. one side is positively charged, the other side is negatively charged)
- the electrons in the molecule are not evenly distributed, they spend more time at a certain position (they are polarised)
what is a glycosidic bond? (2)
- this bond is formed when two monosaccharides are joined together through a condensation reaction.
- these bonds can also form between two different carbohydrate molecules
what are monosaccharides? what are their characteristics? (+ examples)
- monosaccharides are the monomers from which larger carbohydrates are made
- monosaccharides are sweet-tasting soluble substances
examples:
- glucose
- galactose
- fructose
what is the general formula for a monosaccharide? (1)
the general formula of a monosaccharide is (CH2O)n where ‘n’ can be any number between 2 and 7
what are disaccharides? (+ examples)
- disaccharides are formed by the condensation of two monosaccharides
- also known as dimers
examples:
- maltose
- sucrose
- lactose
what is an isomer? what are the two isomers of glucose? (2)
- molecules with the same molecular formula as each other but with the atoms connected in differing ways
- the two isomers of glucose are alpha-glucose and beta-glucose
what three elements do carbohydrates consist of? (3)
- carbon
- hydrogen
- oxygen
what is a polysaccharide? (+ examples)
- polysaccharides are formed by the condensation of many glucose units
examples:
- glycogen
- starch
- cellulose
how is cellulose formed? (1)
by the condensation of beta-glucose
how are glycogen and starch formed? (1)
by the condensation of alpha-glucose
what is a peptide bond? how is it formed? (1)
a condensation reaction between two amino acids forms a peptide bond
explain the two different types of glycosidic bonds. what does this allow to happen? (4)
1-4 glycosidic bond:
- a covalent bond between carbon 1 of one molecule and carbon 4 of another molecule
1-6 glycosidic bond:
- a covalent bond between carbon 1 of one molecule and carbon 6 of another molecule
these bonds allow different shapes to be formed, including branched chains
what is starch? what is it composed of? (2)
- starch is made up of two main components: amylopectin and amylose (both made up of alpha-glucose units)
- starch is insoluble in water, so doesn’t affect osmotic water potential
what is a hexose sugar? (1)
a monosaccharide with six carbon atoms in each molecule
explain what type of sugar glucose is (2)
- glucose is a hexose sugar
- hexose means it consists of 6 carbon atoms in each molecule
describe the chemical reactions involved in the conversion of polymers to monomers and monomers to polymers, provide two examples. (5)
- a condensation reaction joins monomers together and forms a chemical bond, this releases water
- a hydrolysis reactions breaks a chemical bond between monomers, this uses water
- amino acids can be condensed to produce proteins
- the glycosidic bonds in starch can be hydrolysed to produce alpha glucose
- mentioning of bonds
describe a biochemical test to show a solution contains a non-reducing sugar (3)
- heat new sample in water bath with an acid (HCl) and neutralise (using sodium hydrogen carbonate)
- heat with Benedict’s reagent
- if sugar is present, red precipitate will form (or colour change will take place)
suggest a method to measure the quantity of reducing sugar in a solution (2)
- filter and dry the precipitate after filtration
- find the mass
describe two differences between the structure of a cellulose molecule and a glycogen molecule (2)
any two from:
difference 1:
- cellulose is made up of beta-glucose but glycogen is made of alpha-glucose
difference 2:
- cellulose molecule has a straight chain but glycogen is branched/coiled
difference 3:
- cellulose only has 1,4 glycosidic bonds, glycogen has 1,4 and 1,6 glycosidic bonds
describe and explain two features of starch that make it a good storage molecule (2)
any two from:
- insoluble in water, so it doesn’t affect water potential
- branched, so many molecules can fit on one area
- polymer of (alpha) glucose so it provides glucose for respiration
- branched, allows enzyme action to occur faster
- large molecule, so can’t cross cell membrane
suggest how glycogen acts as a source of energy (2)
- can be hydrolysed into glucose
- glucose used in respiration (DO NOT SAY produces energy)
describe structure of glycogen (2)
- polymer of alpha-glucose
- branched structure OR joined by glycosidic bonds
explain one way starch molecules are adapted for their function in plant cells (2)
any one of the following:
- insoluble, doesn’t affect water potential
- helical (spiral), so it is compact
- large molecule, it cannot leave the cell
explain how cellulose molecules are adapted for their function in plant cells (3)
- long, straight chains
- become linked together by many hydrogen bonds to form fibrils
- provides strength to cell wall
how do you test for reducing sugars? (3)
- add sample to test tube (if not in liquid form, grind it up)
- then add equal volume of benedict’s solution
- heat in water bath for 5 minutes
- if reducing sugar is present, a colour change from blue to green, yellow, orange or red will be seen OR red precipitate will form (solid particles suspended in the solution)
how do you test for proteins? (3)
- add equal amount of sodium hydroxide to equal amount of sample
- add a few drops of copper(II) sulphate solution and mix gently
- protein is present if colour change from blue to purple occurs
1 & 2 can also be “add biuret solution”
how do you test for starch? (3)
- add potassium iodide to sample
- if starch is present a colour change from brown-orange to blue-black will occur
how do you test for lipids if the sample is liquid? (3)
- mix sample with ethanol then add water
- shake it
- if it turns milky (NOT cloudy), lipid is present
what is the structure and function of amylopectin?
structure:
- made of alpha-glucose units joined together by 1,4 glycosidic bonds
- highly branched, this facilitates rapid glucose release
function:
- branched structure makes it easier for enzymes to reach the glycosidic bonds
- so energy can be released quickly from glucose molecules (sustained energy)
what is the function and structure of amylose?
structure:
- composed of alpha-glucose units linked by 1,4 glycosidic bonds
- long, linear, unbranched, coiled, cylinder-like
function:
- compact structure is ideal for glucose storage in plants
what is the function and structure of cellulose?
structure:
- composed of beta-glucose units linked by 1,4 glycosidic bonds, this forms straight cellulose chains
- these chains are linked together by hydrogen bonds to form strong fibres called microfibrils
- this results in cellulose being a long, linear, straight molecule
function:
- the fibre formation provides structural support in plant cell walls
- rigid and insoluble so it provides support, preventing cell from bursting due to high water pressure
- NOT used as energy storage molecule
what is the structure and function of glycogen?
glycogen is the primary energy storage molecule in animals and some fungi.
structure:
- alpha-glucose units linked by 1,4 glycosidic bonds and 1,6 glycosidic bonds at branch points
- it is compact (so ideal for energy storage)
function:
- excess glucose is stored as glycogen in animals (mainly in the liver and muscle)
- because it can be rapidly broken down into glucose (due to branched structure)
- does not disrupt osmotic balance
what is a non-reducing sugar? give examples
a non-reducing sugar is a sugar that cannot donate an electron to another molecule
examples:
- all polysaccharides and some disaccharides:
- sucrose
- starch
- glycogen
- cellulose
what is a reducing sugar? give examples
a reducing sugar is a sugar than can donate an electron to another molecule
examples:
- all monosaccharides and some disaccharides:
- glucose
- galactose
- fructose
- maltose
- lactose
what are the 3 functions of lipids? (3)
- to protect muscles
- to keep warm
- store as fat
what is a lipid? what elements do they consist of? what are the two types of lipids?
- lipids are macromolecules
- all lipids contain carbon, hydrogen and oxygen but some can also contain other elements
- the two types of lipids are: triglycerides and phospholipids
how is a triglyceride formed? (3)
- one glycerol molecule and 3 fatty acid molecules join together in a condensation reaction (esterification)
- this results in the removal of three water molecules
- the bonds formed between the glycerol and fatty acids are called ester bonds
how is a phospholipid formed? (3)
- 1 molecule of glycerol joins to 2 fatty acid molecules and one molecule of phosphate in a condensation reaction
- this releases
what is an ester bond?
a bond between an alcohol and an acid (glycerol and fatty acid)
what is a saturated lipid? (2)
these lipids don’t have any double bonds between their carbon atoms
what is an unsaturated lipid? (4)
these lipids do contain double bonds between two carbons, which results in the formation of a kink
- double bond causes a bend to form in the molecule, therefore can not be tightly packed and so are liquid at room temperature
monounsaturated = only one double bond present
polyunsaturated = more than one double bond present
what is an R group? give an example. (2)
a variable group
- in lipids this is the hydrocarbon tail
what is a lipid called if it is solid at room temperature?
it is referred to as fat
what is a lipid called if it is liquid at room temperature? what type of fatty acid is more likely to be a liquid at room temperate?
- it is referred to as an oil
- unsaturated fatty acids are more likely to be liquid at room temperature
describe how one molecule of maltose is formed (3)
- made from two molecules of glucose (alpha)
- joined by a condensation reaction which forms a glycosidic bond
- this releases one molecule of water
describe how one molecule of sucrose is formed (3)
- made from one molecule of glucose (alpha) and one molecule of fructose
- joined by a condensation reaction which forms a glycosidic bond
- this releases one molecule of water
describe how one molecule of lactose is formed (3)
- made from one molecule of glucose (alpha) and one molecule of galactose
- joined by a condensation reaction which forms a glycosidic bond
- this releases one molecule of water
how do you test for lipids if the sample is solid? (3)
- dissolve in alcohol, then water
- shake it
- if it turns milky (NOT cloudy), lipid is present
how is a dipeptide formed? (2)
condensation reaction between the amine group of one amino acid and the carboxyl group of another amino acid
