Biological Molecules

What kinds of bonds occur in carbohydrates

Glycosidic bonds between hydroxyl and hydrogen

What is an isomer

A compound with the same chemical formula but a different arrangement of atoms

What are glucose's isomers - add a structural difference

• Alpha-glucose: OH at C1 is below the plane of the ring

• Beta-glucose: OH at C1 is above the plane of the ring

Whats the difference between a hexose, triose and pentose monosaccharide

• Hexose - contains 6 carbon atoms

• Pentose - contains 5 carbon atoms

• Triose - contains 3 carbon atoms

How is a disaccharide formed?

• two monosaccharides join together

• condensation reaction takes place

• glycosidic bond is formed

• water is released

How is glucose adapted for its role

• small and soluble so can dissolve and be transported easily

• low reactivity

How is a polysaccharide formed?

• two monosaccharides join where a condensation reaction takes place

• A glycosidic bond is formed

• A molecule of water is released each time

• Many more condensation reactions take place until a long chain is produced

Describe the structure of amylose (starch)

• long chain of a-glucose

• has 1,4-alpha glycosidic bonds

• coiled/helical shape

• compact, allows large amount packed in small space

• unbranched

Describe the structure of amylopectin (starch)

• long chains of a-glucose

• 1,4-alpha glycosidic bonds

• branches formed by 1,6-alpha glycosidic bonds

• coiled shape

• more compact, allows large amount packed in small space

What is the advantage of having branches?

• many accessible ends

• allows rapid release of glucose

Describe the structure of glycogen

• long chains of a-glucose

• 1,4-alpha glycosidic bonds

• HIGHLY branched - VERY compact

• branches formed by 1,6-alpha glycosidic bonds

• accessible ends

• smaller chains than amylopectin → less coiled

Describe the structure of cellulose

• long, straight chains of beta-glucose molecules

• b-glucose joined by 1,4 glycosidic links

• unbranched

• molecules invert alternatively by 180° (prevent coiling)

What are cellulose microfibrils?

• parallel cellulose chains that become cross linked by

• hydrogen bonds in between chains which provides strength (cross links)

Why are polysaccharides good sources of energy? (a-glucose for last)

• compact - more energy stored in small space

• can hold glucose in large chains - doesnt diffuse out of cell

• can be (un)branched

• insoluble in water - no impact on water potential of a cell

• easily hydrolysed to a-glucose when energy is needed

What are the properties of water?

• Polar

• High SHC

• High latent heat of evaporation

• Cohesive

• Ice has low density

• Good solvent

Explain waters polarity

• shared negative H electrons are pulled towards O atom

• so other ends of H atoms have slight positive charge

• unshared E-s on O atom give a slight negative charge

How are water molecules held together

• delta negative O atoms attract the delta positive H atoms of other water molecules

• this attraction = hydrogen bonding

Why is a high SHC good for water?

• water doesn’t experience rapid temperature changes

• living organisms have a stable temperature - for optimal enzyme reactions

Why is a high LH of evaporation good for water

• good cooling property for mammals

• eg when sweat evaporates, it cools surface of skin

Why is cohesion good for water

• water molecules stick together as they’re polar so there’s a great attraction

• helps water flow → useful to transport substances

• provides surface tension

How is the structure of ice different to liquid water?

• water molecules held further apart as each molecule forms 4 hydrogen bonds

• this forms a lattice shape

Why is low density good for ice

• ice forms insulating layer over water

• ice on top provides habitat

• animals underneath dont freeze and can still move

What is the benefit of water being a good solvent for living organisms

• ions can dissolve in water

• can be transported up the xylem in plants

• the plant can absorb mineral ions for growth and survival

What is the structure of an amino acid

• has amine group

• has carboxyl group

• has variable ‘R’ group

• has hydrogen

What bonds occur in proteins

Peptide bonds between amine and carboxyl 

What is meant by primary protein structure

• sequence of amino acids

• determined by order of nucleotides in DNA

What is meant by secondary protein structure

• initial folding of amino acids

• folds into alpha-helix or / and beta-pleated sheet

What is meant by tertiary structure

• further folding of proteins to give it a 3D shape

• gains a function

• structure determined by the R group

What is meant by quaternary structure

• clustering of several polypeptide chains to give a final specific shape

Describe structure of a globular protein

• spherical

• has specific shapes

• soluble

• external hydrophilic R group

• irregular arrangement

Describe structure of haemoglobin

• spherical globular protein

• specific shape

• made up of 4 polypeptides (2X alpha 2X beta)

• functional; transports O2

• cofactor; prosthetic group HAEM Fe2+

• has external hydrophillic R group

Describe the structure of a fibrous protein

• form fibres; linear

• regular and repetitive structure

• structural

• insoluble

Describe the structure of collagen

• forms fibrils→ fibrous protein

• structural; provides support

• repeating structure of Gly-Pro-Ala

• 3 polypeptides → coiled

• chains are cross linked by hydrogen bonding

• peptide bonds between AAs

• insoluble - external hydrophobic R group

What is a beta pleated sheet?

• secondary protein structure which has hydrogen bonds between R groups

• sheet folds over itself

What is an alpha helix?

• secondary protein structure that has a coiled shape

• hydrogen bonds between R groups

What is a disulfide bond

• bond between 2 sulfur atoms

• aa has S atom on its R group

What is an ionic bond

• forms between an R group with full -charge and one with full +charge

• bond can be broken by a change in pH

What bonds occur in lipids? HYDROPHOBIC!

ester bonds between hydrogen and hydroxyl

What is the structure of a lipid

• has glycerol

• has fatty acids - not identical so there are no monomers

What is the structure of fatty acids? 

• long hydrocarbon tails 

• saturated FAC: no double carbon bond, saturated with H atoms, long straight chains

• unsaturated FAC: double carbon bond, less H atoms, kinked chain

What are unsaturated fatty acids?

• oils

• liquid at room temp

What are saturated fatty acids

• animal fats

• solid at room temp

What is the structure of a triglyceride and how is it made

• 1 glycerol + THREE fatty acids 

• condensation reaction where X3 H2O lost

• 3 ester bonds formed

What is the function of triglycerides?

• energy storage

• insulation

• provide buoyancy for aquatic animals

What is the structure of a phospholipid? 

• has glycerol

• has 2 fatty acid tails which are hydrophobic; nonpolar

• its third fatty acid replaced by phosphate head; hydrophillic 

• 2 ester bonds

Whats the difference between phospholipid and triglyceride

• phospholipid has a phosphate head which replaces the 3rd fatty acid

What is the sructure of cholestrol - STEROL

• lipid not made from glycerol & fatty acids

• has 4 carbon rings

• small hydrophobic molecule

• sits between hydrophobic tails in bilayer

What are the functions of cholestrol

• regulates fluidity in the membrane

• making vitamin D

• steroid hormone

Describe the similarities of haemoglobin and collagen

• more than one polypeptide chain

• have quaternary structure

• aa chains with peptide bonds

• disulfide, ionic, hydrogen bonds

Role of H+ ions

• affects pH - acidic

• important in photosynthesis and respiration reactions

Role of Ca2+ ions

• transmission of nerve impulses 

• bone and enamel structure

Role of Na+ ions

• generating nerve impulses

• regulating water potential

Role of K+ ions

• allow reabsorption of water in kidneys

• opening of the stomata 

Role of NH4+ ions

• absorbed by soil in plants as a source of nitrogen

• deamination of proteins

Role of NO3- ions

• absorbed by plants as a source of nitrogen

• used for growth and repair in plants

Role of HCO3- ions

• transport CO2 in blood

• acts as a buffer to maintain pH

Role of Cl- ions

• maintain pH balance

• acts as cofactor for amylase

Role of PO4 3- 

• component of cell membrane - phospholipids

• component of ATP and nucleic acids

Role of OH- ions

• affects pH of substances - alkali

Which chemical elements make up the biological molecules?

• carbs & lipids: C, H, O

• proteins: C, H, O, N, S

• nucleic acids: C, H, O, P

What is a conjugated protein

• globular protein with a prosthetic group

• such as Fe2+

• attached by covalent bonds