AQA Biology - Biological Molecules

Define a monomer?

~ one of many small molecules that combine to form a larger one known as a polymer

Define a polymer?

~ large molecule made up of repeating smaller molecules(monomer)

4 examples of monomers?

~ Monosaccharides- Glucose, galactose
~ Nucleotides
~ amino acid
~ fatty acid or glycerol

Define a hydroylsis reaction?

~ the breaking down of large molecules into smaller ones by the addition of water molecules

Define a condensation reaction?

~ chemical process in which 2 molecules are combine to form to form more complex one with the elimination of a simple substance usually water. polymers are form through this reaction.

Define monosaccharides?

~ A monomer of carbohydrates

Define dissacharides?

~ A molecule that is made up of two monosaccharides

Define polysaccharides?

~ A molecule formed from more than two monosaccharides

Draw a Beta glucose?

Draw alpha glucose?

What type of sugar is a glucose?

~ Hexose sugar

What is a Sucrose made up of?

~ Fructose & Glucose

What is Maltose made up of?

~ Glucose & Glucose

What is Lactose made up of?

~ Glucose & Galactose

Draw a condensation reaction between 2 alpha glucoses?

Describe the structure of amylose?

~ Long, unbranched chains of α-glucose
~ Angles of glyosidic bonds makes it a coiled structure - this makes it compact and good for storage
~ Amylose is insoluble so does not effect water potential
~ Contain 1-4 glyosidic bonds

Describe the structure of amylopectin

~ Long, unbranched chains of α-glucose
~ Has side branches which allows enzyme to hydrolyse bonds more easily - glucose is released quickly
~ Amylopectin is insoluble so does not effect water potential inside a cell
~ Contain 1-4 glyosidic bonds
~ Branches with 1-6 glyosidic bonds

Function of amylopectin & amylase?

~ Cells get energy from glucose
~ Plants store excess glucose as starch - when glucose is needed the starch is broken down

Draw amylopectin & amylase?

Structure and function of Glycogen?

~ shorter , unbranched chains of α-glucose
~ highly unbrached chains amylopectin
~ Very compact molecule so good for storage
~ Glycogen is insoluble so does not effect water potential inside a cell
~ Smaller chains of 1-4 glyosidic bonds
functions:
Loads of side branches means that glucose can be released quickly to provide energy
~ Way excess glucose is stored in animals
storage for excess sugar in liver

Function of Glycogen?

storage for excess sugar in liver

Describe the structure of cellulose?

~ Long, unbranched chains of β-glucose
~ Glyosidic bonds makes a straight chained molecule
~ Cellulose chains are linked together by hydrogen bonds - forming microfibrils
~ Microfibrils are further bunched together to form macrofibrils

Function of cellulose?

~ The strong macrofibrils means cellulose provides structural support for cells - cell walls for cells are turgid

Biochemical test for a reducing sugar?

~ Add benedicts reagent and heat it in a water bath
~ Positive result will form a brick red precipitate

Biochemical test for a non-reducing sugar?

If test for reducing is negative then do this:
~ Add dilute hydrochloric acid to the sample and heat it in a water bath - to break non-reducing sugars down into monosaccharides
~ Neutralise with sodium hydrocarbonate
~ Carry out Benedict's test

What is a reducing sugar?

~ All monosaccharides
~ Some disaccharides - Maltose & Lactose

What is a non-reducing sugar?

~ Some disaccharides like sucrose

How to evaluate the concentration of reducing sugar?

~ Filter the solution and weigh the precipitate
~ Remove the precipitate and use a colorimeter to measure the absorbance of light of remaining solution - Each colour of precipitate lets a certain amount of light through

Describe the test for starch (E.g. amylopectin & amylose)?

~ Add iodine dissolved in potassium iodide solution to the sample
~ Positive result means it will go from browny-orange to a blue-black colour

Describe the structure of triglycerides?

~ Have one molecule of glycerol with 3 fatty acids attached
~ Fatty acids made of hydrocarbons
~ The tails are hydrophobic so makes triglycerides insoluble

How does a monosaccharide form?

~ Joined by a condensation reaction forming a glyosidic bond
~ A molecule of water is released

Draw a triglyceride - simple version?

What is the general structure of a fatty acid?

Draw A triglyceride - complex version?

Describe the differences between a saturated and unsaturated fatty acid?

~ Saturated fatty acids don't have any double bonds between their carbon atoms while a unsaturated does

Draw a saturated and unsaturated fatty acid?

How is a triglyceride formed?

~ By a condensation reaction between fatty acids and a glycerol
~ Ester bond is formed and a molecule of water is removed

Draw the condensation reaction of the formation of a triglyceride?

Draw a diagram of a phospholipid?

Where are the hydrophobic & hydrophilic regions on a phospholipid?

~ Hydrophobic fatty acid tail
~ Hydrophilic phosphate group

Describe the test for lipids?

Called the emulsion test
~ Shake the test substance with ethanol and then pour into water
~ Any lipids present will show up as a white emulsion
~ The greater the presence of emulsion means more lipids present

Relate the structure of triglycerides to their function?

~ Mainly used a energy storage molecules - good because they have long hydrocarbon tails which contain lots of chemical energy. When broken down they release twice as much energy as carbohydrates
~ They are insoluble in water so do not effect water potential - which causes water to enter by osmosis - As triglycerides bundle into insoluble droplets as the tails are hydrophobic

Draw a insoluble triglyceride droplet?

Relate the structure of a phospholipid to its function?

~ Make up a bilayer of cell membranes controlling what enters and leaves cell - As the tails are hydrophobic so point inwards and the heads a hydrophilic so point into water.
~ So allows membrane to be a barrier as water-soluble substances can't easily pass through

Draw the general structure of a amino acid?

How many different types of amino acids are there?

~ Only 20 different types

Define polypeptide?

~ A molecule formed from more than 2 amino acids bonded by peptide bonds

Bonds in carbohydrates?

~ Glyosidic bonds

Bonds in Lipids?

~ Ester bonds

Bonds in proteins?

~ Peptide bonds

Define dipeptide?

~ A molecule formed from two amino acids

Define protein?

~ Proteins are large macromolecules consisting of more than one amino acid chain

Define Peptide?

~ Short chains of more than two amino acids bonded in a chain

Draw the formation of dipeptides from amino acids?

~ Reaction not revisible

Describe how dipeptides are formed?

~ Amino acids are linked by condensation reactions to form dipeptides
~ Forming a peptide bond and a molecule of water

Describe the primary structure of a protein and name the bonds?

~ A sequence of amino acids in a polypeptide chain
~ Contains peptide bonds

Draw the primary structure of a protein?

Describe the secondary structure of a protein and name the bonds?

~ Hydrogen bonds form between amino acids
~ This makes primary structure automatically coil up into a α-helix or fold into a β-pleated sheet

Draw a β-pleated sheet and α-helix?

Describe the tertiary structure of a protein and name the bond involved?

~ Amino acid chain is coiled or folded further
~ Hydrogen bonds, Ionic bonds and disulphide bridges form
~ Disulphide bridges form where two molecules of cytosine come very close and their sulphur atoms bond
~ Hydrophobic interactions form between non-polar R groups
~ Made of single polypeptide chain

Draw the structure of a tertiary protein?

Describe the quaternary structure of a protein and name the bonds involved?

~ Made up of several polypeptide chains bonded together
~ Quaternary structure depends on primary structures
~ Examples of bonds: Hydrogen bonding and Disulphide bonds

Draw a quaternary structure of a protein?

Overall sequence of shapes formed in a protein?

Relate the structure of proteins to their function?

~ Enzymes - spherical due to tight folding of polypeptide chain. They are soluble and often used in metabolic processes
~ Antibodies - made up of 2 light and 2 heavy polypeptide chains. Have a variable region where the amino acid sequence greatly varies
~ Transport proteins - Channel proteins contain hydrophobic and hydrophilic amino acids causing it to fold up into a channel
~ Structural proteins - are physically strong as consist of long polypeptide chains parallel with each other, with cross-links between them.

Describe the structure of Collagen?

~ Has 3 polypeptide chains coiled around each other in a triple helix with cross-link which are covalent bonds makes it strong
~ Every 3rd amino acid is glycine
~ Used in supportive tissue

Describe the biurets test?

~ Solution must be alkaline so add few drops of sodium hydroxide
~ Add some Copper(II) sulphate
~ If the solution turns purple then a protein is present, no proteins it will stay blue

What do enzymes do?

~ Lower the activation energy of a reaction in metabolic reactions

Describe the induced-fit model?

~ Substrate collides with active site
~ The tertiary structure of the active site is able to combine with complementary substrates
~ The active site changes to fit more closely around the substrate - held in position by oppositely charged R-groups
~ Enzyme-substrate complex forms
~ Change in shape puts strain on the bonds, weakening them, so lowers the activation energy
~ Enzyme-product complex forms and the substrate no longer fits so is released

How come the enzyme binds to the substrate?

~ Because the tertiary shape of the active site is complementary to the shape of the substrate
~ So can form a enzyme substrate-complex

Why does a enzyme-substrate complex lower activation energy?

~ Being close together reduces any repulsion between the molecules allowing them to bond more easily
~ Active site puts strain on the bond

Explain why enzymes are so specific?

~ Because only one complementary substrate will fit into the active site.
~ Each enzyme has a different tertiary structure which is determined by primary structure so has a different shaped active site
~ If substrate does not match the shape a enzyme substrate complex will not form

Methods of measuring enzyme activity?

~ How fast product is made
~ How fast substrate is broken down

Annotate a graph about how temperature effects the rate of a enzyme controlled reaction?

Explain how temperature effects the rate of a enzyme controlled reaction?

~ More heat means increase kinetic energy, so molecules move faster
~ Substrate is more likely to collide with enzyme and more energy involved in each collision so more likely to be above activation energy
~ Very high temperatures makes the enzyme's molecules vibrate more - vibrations break weaker ionic and hydrogen bonds
~ Tertiary structure changes so enzyme is denatured

Annotate a graph about how pH effects the rate of a enzyme controlled reaction?

Explain how pH effects the rate of a enzyme controlled reaction?

~ All enzymes have a optimum pH value
~ Above and below the optimum OH- and H+ ions can disrupt ionic and hydrogen bonds that hold tertiary structure
~ Tertiary structure changes - enzyme denatures

Annotate a graph about how Enzyme concentration effects the rate of a enzyme controlled reaction?

Explain how Enzyme concentration effects the rate of a enzyme controlled reaction?

~ The more enzymes there are the more likely it is for a substrate molecule to collide - forming a enzyme substrate-complex
~ If the amount of substrate is limited, there comes a point where all the active sites are full

Explan how Substrate concentration effects the rate of a enzyme controlled reaction?

~ More substrate is more likely to collide with the active site - more enzyme substrate-complexes form
~ Reaches a 'saturation point' where all the active sites are full so graph levels off

Describe the action of a competitive inhibitor?

~ Have a similar shape to the substrate
~ They compete with the substrate to bind with the active site
~ They block the active site so no enzyme substrate complexes can form

Describe the action of a non-competitive inhibitor

~ Molecules that bind away from the active site at the allosteric site
~ Distorts the active shape so substrate is no longer complementary to the active site

Annotate a graph about how Non-competitive inhibitors effects the rate of a enzyme controlled reaction?

Annotate a graph about how Competitive inhibitors effects the rate of a enzyme controlled reaction?

Annotate a graph about how Substrate concentration effects the rate of a enzyme controlled reaction?

Explain how the enzyme model of reactions changed over time?

~ The enzyme and substrate do not have to fit together in the first place
~ As evidence showed that the enzyme-substrate complex did not form until the active site slightly changed - this locks substrate even more tightly and explains why it lowers activation energy

What is a extracellular reaction and give a example?

~ Reactions that take place outside the cells
~ Salivary Amylase in the digestive system

What is a intracellular reaction and give a example?

~ Reactions that take place inside the cells
~ Examples : Catalase, peroxidase, RNA / DNA Polymerase and ATP synthase

What do enzymes do to make you special?

~ Enzymes determine the structure and function of cells and the whole organism

What are important molecules that carry information?

~ Deoxyribonucleic acid
~ Ribonucleic acid

What are ribosomes made of?

~ RNA and protiens

What are RNA and DNA polymers of?

~ Polymers of nucleotides

Draw and label a DNA nucleotide?

~ DNA - deoxyribose sugar
~ RNA - Ribose sugar

What bond does a condensation reaction between two nucleotides form?

~ Phosphodiester bond

Describe the structure of a DNA molecule?

~ Two anti-parallel polynucleotide stands
~ Held together by Hydrogen bonds between specific complementary bases

Draw a single DNA strand?

Describe the structure of RNA?

~ Shorter than DNA strands
~ Have a ribose sugar
~ Uracil replaces thymine
~ Single stranded linear polynucleotide strand

Why did scientist doubt that DNA carried the genetic code?

~ Because of the relative simplicity of the molecule
~ Some people said it must be proteins because they are much more chemically varied

Describe the differences between RNA and DNA?

Draw a DNA Molecule?