Biological molecules

whats a monosaccharide?

Sweet tasting soluble substanves that have the general formula {CH2O}n where n can equal 3-7. E.g glucose, fructose,galactose.

Why is life based on carbon?

-carbon can readily form bonds with other carbon atoms

-this creates a backbone for other atoms to bond to

This leads to different ypes and sizes of carbon based molecules

Carbon containing molecules are all organic

What is a monomer?

A single unit that joins together to make a long chain.

What is. Long chain of monomers called?

Polymers

What are the two isomers of glucose?

Alpha and beta

What is a reducing sugar

Monosaccharides or disaccharides that transfer electrons to chemicals e.g. benedict’s reagent

What is the test for reducing sugars?

• add 2cm3 of food sample in a test tube. Grind up with water if not in liquid forms

• Add equal amounts of benedicts reagent

• Heat up in water bath for 5 min until a insoluble red precipitate is formed

What are the different results according to the concentration of reducing sugars?

Red→orange→yellow→green→blue

High to none concentration

What is a disaccharide?

A pair of monosaccharides joined together by a glycosidic bond in a condensation reaction because water is produced.

What are examples of disaccharides?

Glucose and glucose join to make maltose

Glucose and fructose join to make sucrose

Glucose and galactose join to make lactose

What is hydrolysis?

Water is added to disaccharides causing to break the glycosidic bond so it breaks down into monosaccharides.

What is the test for non reducing sugars

• ad 2cm3 of food sample with 2cm3 of benedicts reagent in atest tube and filter. Grind food with water if not liquid.

• Heat up i water bath for 5 minutes. If colour doesnt change reducing sugars are not present

• Add 2cm3 of food sample and 2cm3 of dilute hydrochloric acid in a separate test tube AND HEAT IN WATER BATH so that disaccharides are broken down into monosaccharides - hydrolised

• Slowly add sodium hydrogencarbonate to neutralise hydrocholic acid. Test with ph paper to make sure solution is alkaline.

• Add 2cm3 of benedicts reagent.Heat final solution in water bath for 5 min. If colour changes to orange brown/brick red, reducing sugars are present.

What are polysacharides?

Monosaccharides joined together in a long chain by glycosidic bonds through a condensation reaction.

They are very large molecules so are insoluble so easy to store.

Glycogen and starch are formed by the condensation of alpha glucse.

Cellulose are formed by the condensation of beta glucose

Why are disaccharides known as non reducing sugars?

They don’t change the colour of benedict’s reagent when heated up in a water bath.

What is the test for starch?

Add 2cm3 of sample into test tube

Add 2 drops of iodine in test tube and shake/stir.

Colour turns yellow to blue black if theres a presence o starch.

What is starch made up of?

Starch is made up of chains of alpha glucose monosaccharides linked by glycosidic bond formed by condensation reactions.

What is the structure of starch?

Chains maybe unbranched o branched. The unbrnched chins is wound in to a tight coil that makes the molecule very compact.

Why is starch’s structure suitable for energy storage?

Insoluble - doesn’t affect water potential ,so water not draw out by osmosis doesn’t diffuse out of cells.

Compact - lots of energy stored in small space

Easily hydrolysed- forms alpha glucose , which is easier to transport and to be used in respiration

Branched ends can attach to enzymes to break it down to glucose very quickly.

What is glycogen

Known as animal starch - found in animals and bacteria but never in plants

Stored as small granules in muscle and liver cells

What is the structure of glycogen

Chains of alpha glucose

Shorter chians but more highly branched.

Why does its structure suits it for storage.

Insoluble - doesnt affect water potential and cnat diffuse out.

Compact - lots of it stored in small space

Highly branched so more enzymes can break it down to glucose for respiration.

What is cellulose?

Chains of beta glucose used in plant cells.

Whats the structure of cellulose

Straight parallel chains that re interlinked by hydrogen bonds , adding strength. The sheer amount of molecules gives them strength.

What are grouped cellulose called?

Microfibrils that also grouped together to form fibres

What characteristics do all lipids share?

They are carbohydrates

The proportions of oxygen to carbon to hydrogen is smaller than in carbohydrates

Insoluble in water

Soluble in alcohol

What are the roles of lipids in the cell membranes

When oxidised they provide lots of energy.

Insoluble in water - waterproofing leaves with waxy cuticles and oily secretion on skin in mammals.

Insulations - retain body heat when fat is tored under body. Covers myelein sheath in nerve cells, acts as electrical insulators

Protection - fat stored around delicate organs like the kidney.

What are triglycerides?

3 fatty acids bonded with a glycerol through condensation reaction. Each fatty acid forms an ester bond with glycerol.

Whats the difference between saturated and unsaturated?

Saturated- has many hydrogen bonds as possible and no double bonds. Straight chians.

Unsaturated - has double bonds so doesnt have the maximum amount of hydrogen bonds. Has kinks in the chain that causes it bend. This prevents it from being compact, so liquid at room temp.

Structure of triglycerides related to their properties

Lots of carbon and hydrogen bonds so can store more energy

Compact- lots of energy stored in small spaces

Large and insoluble so doesn’t affect water potential.

High ratio of hydrogen to oxygen atoms, so when oxidised it relases water so good water source.

What phospholipids

Two fatty acids bonded with glycerol and phosphate group through condensation reaction . Each fatty acid has an ester bond with glycerol.

Fatty acids are hydrophobic and the phosphate group id hydrophillic.

Structure of phosopholipids

The hydrophillic head position themselves so they are closer to the water as possible

The hydrophobic tail positions themselves so that they are further away from the water.

The two and are polar so they are polar molecules.

Structure pf phospholipids related to their properties

Polar molecules forming a bilayer between the cell surface membranes so that a hydrophobic barrier formes between the inside and outside of a cell

Hydrophillic heads help to hold at the surface of the cell surface membrane

The structure allows them to form glycolipids by combioning with carbohydrates within cell surface membrane. Glycolipids are important in cell recognition

Test for lipids - emulsion test

2cm3 of sample in grease free tube and add 5cm3 of ethanol

Shake tube to dissolve lipid in sample

Add 5cm3 of water and shake gently

Milky white emulsion shows presence of lipid

As control, repeat using water instead of sample, result should be clear.

Polypeptides

Polypeptides are a polymer made up of monomers called amino acids

how are peptide bonds formed

Amino acids joined together by a condensation reaction, removing a water molecule. The peptide bond can be broken by hydrolysis to give amino acid monomers

Primary structure of proteins - polypeptides

The sequence of amino acids in a polypeptide chain forms the primary chain forms the primary structure of any protein - the site sequence is determined by DNA

A change in the sequence changes its functions and shape

Proteins are made up of many of polypeptide bonds

Secondary structure of proteins

The sequence of amino acids causes parts of a protein molecule to bend in a alpha helix shapes or fold into beta pleated sheets

Hydrogen bonds holds the structure - H of NH has a positive charge and O of C- - O has a negative charge

Tertiary structure

Further folding of secondary structure to forms a unique 3D shape

Held by ionic, hydrogen and disuphide bonds

The ionic and disulphide bonds forms between R groups of different amino acids

Quaternary structure

Protein made up of more than one polypeptide chain

Test for proteins

Biuret test

Substance in test tube and equal amounts of sodium hydroxide at room temp

Add few drops dilute copper sulfate and mix gently

Colour turns purple, detecting peptide bonds so proteins present

what happens to the bonds when enzyme is denatured

Bonds holding tertiary and secondary structure in shape break and unique 3D shape is lost

Enzymes will have a different shape of active site and carrier proteins will have a different binding site

A change in amino acid sequence does what to tertiary and secondary structures

Ionic or disuphide or hydrogen bonds are formed somewhere else so different 3D shapes are formed

How does enzymes denature

Too high a temperature

Too high or low pH

What are enzymes

Globular proteins that acts as biological catalysts, increase the rate of reaction without being used up.

What conditions must be needed for a reaction to take place

Reactant molecules must have minimum amount of energy to start reaction - activation energy

Energy of products must be less than substrates

What does enzymes do activation energy

Reduce activation energy, so lower temperatures needed to start reaction.

How do enzymes work?

The enzyme binds to the substrate by its active site, creating an enzyme substrate complex.

What are active sites

Small key residues that bind to substrates. The rest of the protein is needed to maintain these residues in position.

Induced fit model.

Active site changes shape when it comes close to the substrate, in order to bind. As it changes shape, it puts a strain on the substrate molecules so that the bonds are distorted and so lowers temperature.

What evidence supports the induced fit model

Molecules could bind to enzymes at sites other than the active site, altering the activity and shape of the enzyme.

So structure was flexible not rigid

Cofactors

Non protein substances recruited by enzymes before they can catalyse a reaction.

What are two types of cofactors

Activators - inorganic groups that are permanently bonded to the enzyme and so are a type of prosthetic group, eg. iron zinc copper

Co enzymes - organic molecules that bind temporarily to the enzyme , transferring a chemical group needed for the reaction e.g vitamin C , ATP

turnover number

number of substrate molecules transformed per minute by one enzyme molecules.

Inhibitor

Molecules that reduce the rate of an enzymes controlled reaction.

Competitive inhibitors

Fits into the active site, so have a similar shape to substrates,

Forms an enzyme inhibitor complex.

Blocks access to substrates molecules, reducing rate of reaction.

Non competitive inhibitors

Don’t bind to active site, binds on the enzyme molecule, so changes shape of enzyme

How can competitive and non competitive inhibitors be overcome?

Competitive inhibitors can be overcome by increasing substrate concentration.

Increasing substrate concentration doesn’t overcome non competitive inhibitors.

Why is enzyme inhibition important

Important for regulating metabolic pathways.

Process of End product inhibition

The end product often acts as a regulator of the metabolic pathway.

When the amount of end product is high it binds non competitively to an enzyme in the pathway, blocking further production of end products.

When amount of end product falls, inhibition ends and the pathway restarts.

What is an example of end product inhibition

Synthesis of ATP is regulated this way, with ATP acting as the inhibitor.

Uses of inhibitors

Natural poisons e.g cyanide

Biocides used in food industry, medicine