WJEC AS Biology Unit 1.1 - Chemical Elements are Joined Together to Form Biological Compunds

The key elements present as inorganic ions in living organisms

• Magnesium (Mg²⁺)

• Iron (Fe²⁺)

• Calcium (Ca²⁺)

• Phosphate (PO₄^3-)

Magnesium (Mg²⁺) ion function

• Constituent of chlorophyll and is therefore essential for photosynthesis. Plants without Mg in their soil cannot make chlorophyll and so the leaves are yellow, a condition known as chlorosis.

• Mammals need magnesium for their bones. Bound to calcium and phosphorus in the skeleton

Magnesium (Mg²⁺) ion location

• Constituent of chlorophyll

• In soil

• Bones in mammals

Iron (Fe²⁺) ion function

• Constituent of haemoglobin in the blood of animals, which transports oxygen in red blood cells.

• In plants = for growth and development

Iron (Fe²⁺) ion location

In animals = haemoglobin

Calcium (Ca²⁺) ion function

• strengthening tissues

• In mammals; bones and teeth

• In plants; main components in structure, rigidity and strength of plant cell walls

• Contributes to release of hormones and neuro-transmitters

Calcium (Ca²⁺) ion location

Structural component of bones and teeth in mammals and is a component of plant cell walls,

Structural component of bones and teeth in mammals

Component plant cell walls, providing strength

Phosphate (PO₄^3-) ion function

• Making biological molecules; nucleic acids such as DNA and RNA, nucleotides such as ATP, constituent of phospholipids in biological membranes.

Phosphate (PO₄^3-) ion location

• nucleic acids, e.g. DNA/RNA

• nucleotides, e.g. ATP (energy carrier)

• Phospholipids (main component of plasma membranes)

Organic molecules

• Molecules that have a high proportion of carbon atoms

• Excludes simple oxides of carbon, e.g. CO₂

• Includes carbohydrates, proteins, lipids and nucleic acids

Inorganic molecules

• Molecules/ions that have no more than one carbon atom

• Includes simple oxides of carbon, e.g. CO₂

Water - Polarity

• Polar molecule (separated charges)

• Dipole (positively charged end (hydrogen) and a negatively charged end (oxygen) but no overall charge

Water - Ability for form hydrogen bonds

• When two water molecules are in close contact the opposing charges attract each other, forming a hydrogen bond.

• Form between the positively charge on the hydrogen atom of one molecule and the negative charge on an oxygen atom of another.

• Individually, the hydrogen bonds are weaker, but together, the large number of them present in water form a lattice framework = strong + difficult to seperate —> wide range of physical properties vital to life

Water - Surface tension

• High surface tension at ordinary temperatures

• Cohesion between the water molecules at the surface produces surface tension so that, e.g. the body of an insect, such as a pond skater, is supported

Water - Solvent

• Water molecules = dipoles

• Positive and negative charged components of the molecule attract other charged particles, such as ions, and other polar molecules, such as glucose.

• The ions and polar molecules can then dissolve in water, so chemical reactions take place in solution

• Acts as a transport medium, e.g. plasma in blood, xylem/phloem.

• Non-polar molecules, such as lipids, do not dissolve in water

Water - Specific heat capacity

• High specific heat capacity

• Large amount of heat energy is needed to raise its temperature

• Hydrogen bonds between the water molecules restrict their movement, resisting an increase in kinetic energy —> resisting an increase in temperature

• Prevents large fluctuations in water temperature (keeps aquatic habitats stable, organisms therefore don’t have to adapt to the extremes of temperature)

• Allows enzymes within cells to work efficiently

Water - Latent heat of vaporisation

• High latent heat of vaporisation

• A lot of heat energy is required to change water from liquid to vapour

• Process of evaporation transfers heat energy and is an effective way of cooling the body through sweating, panting, etc.

• Important in temperature control, where heat is used to vaporise water from sweat on the skin or from a leaf’s surface

• At the water evaporates, the body/surface cools

Water - Metabolite

• Used in many biochemical reactions as a reactant

• In hydrolysis and photosynthesis as a reactant

• In condensation reactions and aerobic respiration, where water is a product

Water - Transport medium

• Acts as a transport medium

• Animals = in blood, where plasma transports dissolved substances

• Plants = minerals dissolved in water are transported from root to leaves via xylem, and sucrose and amino acids in the phloem

Water - Chemical reactions

• Solvent and metabolite

• Transport of ions and polar molecules allows chemical reactions to take place when particles or molecules meet

Water - Cohesion

• Attraction of water molecules for each other, seen as hydrogen bonds, resulting from the dipole structure of the water molecule

• Individually, hydrogen bonds = weak, but because there are many of them, the molecules stick together in a lattice. This sticking together is called cohesion

• Allowed columns of water to be drawn up xylem vessels in plants

Water - Transparency

• Transparent, allowing light to pass through

• Lets aquatic organisms to photosynthesise effectively

Water - Density

• Denser than air

• Provides a habitat support and buoyancy

• Ice is less dense than water as hydrogen bonds hold the molecules further apart than they are in the liquid

• Ice = good insulator, prevents heat loss

Dipole

A polar molecule, with a positive and a negative charge, separated by a very small distance

Hydrogen bond

• The weak attractive force between the partial positive charge of a hydrogen atom of one molecule and a partial negative charge on another atom, usually oxygen or nitrogen

Carbohydrates

• organic compounds which contain the elements carbon, hydrogen and oxygen

• The basic unit = a monosaccharide

Monosaccharides

• Small organic molecules

• General formula C_n(H₂O)_n

• Names are determined by the number of carbon atoms in the molecule

• Building blocks for the larger carbohydrates

• The carbon atoms within them make a ring when the sugar is dissolved in water, and they can alter their binding to make straight chains, with the rings and chains in equilibrium

Monosaccharides - properties

• Can easily dissolve in water —> sweet tasting solutions

• Cannot be broken down into simpler sugars - single monomer sugars

Monosaccharides - function

• source of energy in respiration (carbon-hydrogen and carbon-carbon bonds are broken to release energy, which is transferred to make ATP)

• building blocks for larger molecules (e.g. glucose is used to make polysaccharides starch, glycogen and cellulose)

• intermediates in reactions (e.g. trioses, are intermediates in the reactions of respiration and photosynthesis)

• constituents of nucleotides (e.g. deoxyribose in DNA, ribose in RNA, ATP and ADP)

What happens when two monosaccharides join together

• Condensation reaction

• Join from one carbon to the other, water is formed as a bi product

• Forms a disaccharide

Examples of Monosaccharides

• Triose

• Pentose

• Hexose sugars

Glucose structure

Glucose properties

• Sweet in taste

• Polar compound that readily dissolves in water

• Reducing sugar that gives positive Benedict’s test

• Cannot undergo hydrolysis

Glucose function

• energy source

• storage

• synthesis (e.g. synthesis of carbohydrates)

• regulation of blood sugar levels

• organ function

Triose structure

• C₃H₆O₃

Triose properties

• Monosaccharide containing three carbon atoms

• Example; (glyceraldehyde)

Triose function

• important in metabolism. Triose sugars are intermediates in the reactions of respiration and photosynthesis

Pentose structure

C₅H₁₀O₅

Pentose properties

• Monosaccharide containing 5 carbon atoms

• Examples; ribose and deoxyribose

Pentose function

• Constituents of nucleotides, e.g. deoxyribose in DNA, ribose in RNA, ATP and ADP

Hexose structure

C₆H₁₂O₆

Hexose properties

• Monosaccharide containing 6 carbon atoms

• Examples; alpha-glucose, beta-glucose, fructose and galactose

Hexose function

• Glucose is a hexose sugar

• Glucose is a source of energy in respiration (carbon-hydrogen and carbon-carbon bonds are broken to release energy, which is transferred to make ATP)

Disaccharides

• Composed of two monosaccharide units bonded together with the formation of a glycosidic bond and the elimination of water

• This is an example of a condensation reaction

Disaccharide structure

• General formula; C₁₂H₂₂O₁₁

• Linked by glycosidic bonds in the alpha or beta orientation

Disaccharide properties

• Polar compounds

• Readily soluble in water due to hydrogen bonding

• Sweet in taste

• Cannot diffuse through cellular membranes

• Formed by condensation reactions, broken down by hydrolysis

Disaccharide function

• Energy source

• Body breaks them down into monosaccharides for absorption

• Transport

• Storage

• Bodily function

• Blood glucose regulation

• Biological structure

Examples of Disaccharides

• sucrose

• lactose

• maltose

Sucrose structure

• Made up of a glucose and a fructose molecule joined together by a glycosidic bond

• This glycosidic bond is formed between the carbon 1 of glucose and the carbon 2 of fructose. It is formed between the functional groups of the two molecules

• The fructose molecule has a beta orientation while the glucose molecule has alpha orientation

Sucrose’s component disaccharide

• glucose + fructose

Sucrose properties

• Sweeter than glucose

• Soluble in water

• White crystalline solid in appearance

• Non-reducing sugar

Sucrose function

A product of photosynthesis which is transported in phloem of flowering plants

Lactose structure

• Made up of glucose and galactose molecules attached via a glycosidic bond

• A C1-C4 glycosidic bond as it attaches the first carbon of glucose to the fourth of galactose

• Both the glucose and galactose molecules have alpha orientation in lactose

Lactose’s component disaccharide

• glucose + galactose

Lactose properties

• Soluble in water, but its solubility is less than sucrose

• Less sweet than sucrose

Lactose function

Found in mammalian milk

Maltose structure

• Disaccharide made up of two subunits of glucose

• Both glucose molecules are attach via a 1-4 glycosidic bond

• This bond attaches the carbon 1 of one glucose molecule to the carbon 4 of the second glucose molecule

• Both glucose molecules have alpha orientation

Maltose’s component disaccharide

• Alpha- glucose + Alpha-glucose

Maltose properties

• Reducing sugar

• Soluble in water

• Sweet in taste

• Upon hydrolysis, it yields two glucose molecules

Maltose function

• In germinating seeds

Polysaccharides

• Large, complex polymers

• Formed from very large numbers of monosaccharide units, which are their monomers, linked by glycosidic bonds formed by condensation reactions

Examples of Polysaccharides

• starch

• glycogen

• cellulose

• chitin

Starch properties

• Compact structure of helical amylose and branched amylopectin make it energy dense

• Insoluble in water

• Additional units of glucose can be easily added to numerous ends or removed by hydrolysis

• Not osmotically active as insoluble in water + chemically unreactive

Starch function

• storage of glucose units + therefore storage of energy in plant cells. Can be stored in tubers like potatoes

• Broken down releasing glucose units. The glucose units are used in respiration to produce ATP

Starch structure

• Made of two polysaccharide components; amylose and amylopectin

• Amylose; Polymer of alpha-glucose linked by alpha-1, 4-glycosidic bonds. Molecules can be thousands of residues/units long. Coils into a helix. Unbranched structure.

• Amylopectin; Polymer of alpha-glucose monomers with a branched structure. Units of glucose within a chain are joined by alpha-1, 4-glycosidic bonds, branches formed by alpha-1, 6-glycosidic bonds, every 25-30 residues. Molecules can be up to million units of glucose.

• The branched amylopectin and helical amylose form a compact structure.

Starch’s adaptations for function

• Compact structure —> energy dense and an ideal to store lots of glucose units, and therefore energy, in a small volume

• Glucose = an important respiratory substrate

• Molecules of glucose can be easily added, allowing quick storage, or hydrolysed from the ends releasing glucose quickly for respiration.

• Insoluble in water so does not affect the osmotic balance of cells.

Glycogen properties

• Compact structure and high energy density

• Many branches create many ends meaning many glucose units can be added (by condensation reactions) and units removed quickly (by hydrolysis reactions)

• Insoluble in water/low solubility in water

Glycogen function

• Glucose store in humans and therefore energy store. Particularly found in the liver and the muscles.

• Plays an important role in regulating blood sugar levels in the blood; excess glucose can be added to the numerous ends of glycogen, reducing blood sugar quickly or removed from numerous ends to release glucose into the blood, raising blood sugar levels quickly.

Glycogen structure

• Polymer of alpha-glucose

• The units of glucose are within chains. Units are connected by alpha-1, 4-glycosidic bonds.

• Has many branches

• Branches formed by alpha-1, 6-glycosidic bonds

• The branches are every 8 to 12 units

Glycogen’s adaptations for function

• Compact structure + high energy density —> ideal energy store as a lot of energy can be stored in a small volume

• Storage of glucose as glycogen in the liver plays an important role in regulating blood sugar levels. Many branches create ends, so lots of glucose units can be added quickly and removed quickly, allowed blood sugar levels to be reduced quickly or raised quickly

• Low solubility means it is cosmetically inert and therefore does not affect osmosis in cells

Cellulose properties

• High tensile strength

• Rigid

• Insoluble in water, soluble in organic solvents

• Cellulose fibres are freely permeable, because there are spaces between the fibres. Water and its solutes can penetrate through these spaces in the cell walls, to the cell membrane

Cellulose function

• Major component of cell walls. Cell walls are rigid which maintains the shape and supports the cells

• Energy source for animals

Cellulose structure

• Polymer of beta-glucose

• Units joined by beta-1, 4-glycosidic bonds

• The beta-linkage rotates the adjacent monomers 180 degrees to each other, resulting in long and straight chains

• Hydrogen bonds form between parallel chains

• Chains are highly cross linked

• Many chains are linked via hydrogen bonding to form a microfibrils

• The microfibrils come together to form stronger fibres

• Fibres form layers (laminar structure).

• Layers arranged at different angles to each other, providing additional rigidity

• Calcium is also involved in forming cross bridges, providing strength

Cellulose adaptations for function

• Rigid and so when the cell contents push against the cell wall, turgor pressure is generated

• This supports the shape of the cell wall and makes them form (turgid). Without it they become floppy/flaccid

Chitin properties

• High tensil strength

• Rigidity

• Waterproof

Chitin function

• In insects, it forms the exoskeleton

• In fungi, chitin is found in the cell wall

Chitin structure

• Made of beta-glucose units, joined by beta-1, 4-glycosidic bonds

• Beta glycosidic bonds cause the adjacent monomers to be twisted 180 degrees to each other, forming straight chains

• Hydrogen bonds age able to form between the chains —> makes chitin strong and gives it high tensile strength and rigidity

• Some -OH groups of the glucose units are replaced by nitrogen-containing acetylamine groups

• These groups contribute towards the hydrogen bonding between the chains, adding to its tensile strength

• These form microfibrils and fibres, with the fibres being arranged in groups at opposing angles, all adding to its rigidity and strength

Chitin’s adaptations for function

• Rigid + therefore provides a tough, rigid exoskeleton that gives shape and supports the insect’s body

• Insects tend to live in dry/arid habitats; because the chitin is water proof, it reduces loss of water by evaporation, preventing desiccation, allowing the insect to survive dry conditions

• In fungi, it is found in the cell wall; because it is rigid, it generates turf or pressure when the cell contents push against the cell wall. This gives the fungal cells shape and support. It also prevents too much water entering and resulting in osmotic lysis of the cell

Structural isomer

• Molecules that have the same molecular formula but different structural formulae

Alpha structural isomerism in _glucose

AT CARBON 1;

• -OH below

• -H above

This therefore affects the bond between the unit sugars in disaccharides and polysaccharides. Same chemical formula as beta-glucose; C6H12O6

Beta structural isomerism in glucose

AT CARBON 1;

• -OH above

• -H below

This therefore affects the bond between the unit sugars in disaccharides and polysaccharides. Same chemical formula as alpha-glucose; C6H12O6

Polymers

• A large molecule comprising repeated units, monomers, bonded together

Monomers

• Single repeating units of a polymer

Polymerisation of glucose into storage and structural carbohydrates

• Formed from very large numbers of monosaccharide units, which are their monomers, linked by glycosidic bonds

Polymerisation of glucose into starch

• Several simple and soluble molecules of glucose age put together to form a complex, insoluble molecule of starch

Polymerisation of glucose into glycogen

• Glycogenesis

• Several simple and soluble molecules of glucose are put together to form a complex, insoluble molecule of glycogen

Polymerisation of glucose into cellulose

• several simple and soluble molecules of glucose are put together to form a complex, insoluble molecule of cellulose

Polymerisation of glucose into chitin

• Several simple and soluble molecules of glucose are put together to form a complex, insoluble molecule of chitin

Lipids

• Contain Carbon, Hydrogen and Oxygen

• In proportion to carbon and hydrogen, contain much less oxygen

• Non-polar compounds —> insoluble in water, soluble in organic solvents

Lipid structure

• Most lipids are triglycerides which are made of glycerol and three fatty acids

• Others are phospholipids which are made of a hydrophilic phosphate group, glycerol and two fatty acids

Lipid function

• Good source of energy (high yield per gram)

• Phospholipids; biological membranes and electrical insulation

• Triglycerides; energy reserves in plants and animals as lipids contain more carbon-hydrogen bonds than carbohydrates, thermal insulation, protection of organs, produce metabolic water when oxidised

• Waxes; reduce water loss

Lipid properties

• Differences in properties come from variations in the fatty acids

• Can exist as fats or oils

• Insoluble in water because they are non-polar

• Store a lot of energy

• Poor conductors of heat

Lipid adaptations for function

• High yield of energy per gram (when oxidised/used in respiration) due to compact structure

• Insoluble in water so does not affect osmosis

Triglycerides

• Formed by the combination of one glycerol molecule and three molecules of fatty acids

• Glycerol molecule is always the same but the fatty acid component varies

• The fatty acids join to glycerol by condensation reactions, where by three molecules of water are removed and ester bonds are formed between the glycerol and fatty acids, forming a triglyceride

Triglyceride structure

Triglyceride function

• Insulation

• Energy store/source

• Protection

Triglyceride properties

• Non-polar —> insoluble in water —> don’t affect osmosis within cells

Triglyceride location

• Body fat under skin/around organs

Triglyceride adaptations for function

• High yield of energy per gram (when oxidised/used in respiration) due to compact structure

• Insoluble in water so does not affect osmosis

Phospholipids

• One end of each molecule is soluble in water

• Consists of hydrophilic phosphate group, glycerol and two hydrophobic fatty acid tails