Biological molecules: Water and carbohydrates

How do hydrogen bonds form between water molecules?

Water is polar; slightly -ve oxygen atom and slightly +ve hydrogen atoms are attracted

Are hydrogen bonds weak or strong

Weak individually, strong in large numbers

Why are hydrogen bonds constantly breaking and reforming

Hydrogen bonds are weak when only few of them

Properties of water

Excellent solvent; transport medium; high SHC; high LHE; less dense as solid; high surface tension

Describe water’s high SHC

Hydrogen bonds can absorb lots of e; takes lots of e to heat up water; so suitable habitat; maintain optimum temp within cells

Describe water’s high LHE

Takes lots of e to overcome hydrogen bonds; lots of heat lost when little water evaporates; so good for thermoregulation, transpiration

Describe water’s cohesion

Polar molecules; large number of H bonds collectively strong; highly cohesive; chain of water molecules pulled up; allows for transpiration stream; transport medium e.g. blood

Describe water’s solubility

Polar; -ve O end attracted to +ve ions; +ve H end attracted to -ve ions; so good solvent

Name 4 roles of water which relate to its properties

Solvent; transport medium; coolant; habitat

Name physical properties of water which support life

Ice is less dense; cohesion and adhesion; surface tension; solvent; transparent

How does ice being less dense support life

Floats so habitat e.g. polar bears; freezes bottom up so water below is insulated

Describe how surface tension of water supports life

Allows for movement on water surface e.g. pond skaters

How does water’s role as a solvent support life

Medium for chemical reaction; transport of dissolved substances e.g. glucose in blood, ions in transpiration stream

What is a macromolecule

Very large molecule

What is a monomer

A single unit e.g. monosaccharide, amino acid

What is a polymer

Chains of monomers connected to one another

Polymer vs macromolecule

Polymer: made up of identical monomers repeated; macromolecule: any group of monomers

What do condensation reactions usually make

Polymers

What kind of reaction turns monomers into polymers usually

Condensation

Why is a condensation reaction called that

Molecule of water is released

How would you break down a polymer back into monomers

Hydrolysis reaction

What is a hydrolysis reaction

Water molecules break down bonds between monomers in polymers, turn back into monomers

Glycosidic bond

-O-

Peptide bond

O=C-N-H

Ester bond

C-O-C=O

What kind of covalent bonds are formed to make proteins

Peptide

What kind of covalent bonds formed for carbohydrates

Glycosidic

What kind of covalent bonds formed for lipids

Ester bonds

Example of a hexose monosaccharide

Glucose

2 isomers of glucose

α-glucose, β-glucose

Chemical elements in carbohydrates

C,H,O

Chemical elements in lipids

C,H,O

Chemical elements in proteins

C,H,O,N,S

Chemical elements in nucleic acid

C,H,O,N,P

Difference between α-glucose and β-glucose

α-glucose has OH on c1 below ring; β-glucose has OH on c1 above ring

What is C5 bonded to on a glucose molecule

CH2OH on top; H on bottom

What is C2 bonded to in a glucose molecule

H on top; OH on bottom

What is in the top right of the hexagon of a glucose molecule

O atom

Polysaccharides containing only α-glucose

Starch, glycogen

Polysaccharide containing only β-glucose

Cellulose

What is difference between hexose and pentose sugars

Hexose has 6 C, pentose 5 C

Example of pentose sugars

Ribose, deoxyribose

Ribose vs deoxyribose

Deoxyribose has C2 bonded to 2 H atoms, ribose has C2 bonded to H on top and OH on bottom

Ribose structure

Deoxyribose structure

How are glucose molecules joined together (what kind of bonds)

Glycosidic bonds

What is produced when a glycosidic bond is formed between glucose molecules

Polysaccharide + Water molecule

Properties of starch

Insoluble; mixture of amylose and amylopectin

What is starch used for

Main energy storage material in plants

What kind(s) of glucose does amylose contain

α-glucose

What kind(s) of glucose does amylopectin contain

α-glucose

How does insolubility of starch relate to its function

Won’t cause water to enter cell by osmosis

Describe structure of amylose

Unbranched helix chain; stabilised by h bonds within molecule

What kind of bonds are in amylose

α-1,4 glycosidic bonds

Describe how structure of amylose relates to its function

Angles of 1,4 glycosidic bonds => compact coiled structure; more can fit in small space; so good for storage

Describe bonds in amylopectin

In long chain: α-1, 4 glycosidic bonds; when branching off: α-1,6 glycosidic bonds

Describe structure of amylopectin

Long, branched chain of α-glucose

How does structure of amylopectin relate to its function

Enzymes which break it down can access glycosidic bonds more easily; so glucose can be released easily

What is glycogens main function

Main energy storage in animals

Glycogen vs amylopectin

Glycogen

How does glycogen’s structure relate to its function

Compact so good for storing lots of glucose; more branches for enzymes to easily access glycosidic bonds

What kind of bonds are in glycogen

α-1,4 and 1,6 glycosidic bonds

Describe structure of cellulose

Long unbranched straight chains of β-glucose linked together by many hydrogen bonds to form strong fibres

How does structure of cellulose relate to its function

Strong fibres due to many hydrogen bonds provide structural support for plants

What is sucrose made of

A-glucose and fructose

What is maltose made out of

Alpha-glucose and alpha-glucose

What is lactose made up of

Glucose and galactose

How are fructose, galactose and glucose similar/different

Same molecular structure, different structural formula

What is a carbonyl group

C=O

What is a carboxyl group

OH

What is a reducing sugar

A sugar which can donate electrons (Can be oxidised)

Examples of reducing sugars

All monosaccharides; some disaccharides (maltose)

What is a non-reducing sugar

A sugar which cannot donate electrons (cannot be oxidised)

Which part of a sugar gets oxidised

Carbonyl group C=O loses O

How does Benedict’s test work

Sugar reduces soluble copper sulphate to insoluble copper oxide

What colour is copper (i) oxide formed in Benedict’s test

Brick-red

What is Benedict’s solution

Blue solution containing copper (I) sulfate ions

Is Benedict’s test quantitative or qualitative

Semi-quantitative; degree of colour change gives approximate indication of how much reducing sugar is present; not exact

Examples of non-reducing sugars

Sucrose

Test for non-reducing sugars

Add HCl; water bath; neutralise with sodium hydrogencarbonate (use indicator to identify when); add a little more to make slightly alkaline; then do Benedict’s

How does test for non-reducing sugars work

Acid hydrolyses glycosidic bonds; resulting monosaccharides will able to reduce the copper sulphate

How do you test for starch

Iodine test - add a few drops of orange/brown iodine in potassium iodide solution

How does iodine test work

Iodide ions interact with centre of starch molecules; resulting complex has blue-black colour

Why is iodine put in potassium iodide solution for starch test

Iodine is insoluble in water