A LEVEL BIO - Biological Molecules

Biological Molecules

The variety of life is extensive but all living things share the same biological molecules.

Monomer

Simple, basic, molecular unit from which larger molecules/polymers are made from. E.g monosaccharides, amino acids, nucleotides.

Polymer

Large, complex molecule made up of repeating monomers joined together. E.g starch, glycogen, cellulose, polypeptide (protein), DNA, RNA.

Condensation Reaction

Joins two monomers together, forming a chemical bond and eliminating a water molecule.

Hydrolysis Reaction

Separates two monomers, breaking a chemical bond and requiring the addition of a water molecule.

Carbohydrates

Contain carbon, hydrogen and oxygen, serving functions such as energy, storage, and strength.

Monosaccharides

Simplest sugars, monomers from which larger carbohydrates are made. 3 examples all have formula C6H12O6.

Glucose

A monosaccharide that exists in alpha and beta forms, with the OH group inverted on carbon 1.

Fructose

A monosaccharide that is one of the simplest sugars.

Galactose

A monosaccharide that is one of the simplest sugars.

Disaccharides

Forms when two monosaccharides join together by a condensation reaction forming a glycosidic bond.

Maltose

A disaccharide formed from glucose + glucose.

Sucrose

A disaccharide formed from glucose + fructose.

Lactose

A disaccharide formed from glucose + galactose.

Lactulose

A disaccharide formed from galactose + fructose.

Polysaccharides

Formed when more than 2 monosaccharides join together via condensation reaction.

Starch

A polysaccharide found in many parts of a plant, especially in seeds and storage organs, and is a major energy source.

Glycogen

Main storage of energy in animals, stored in muscle and liver cells.

Cellulose

Provides structural strength in the cell walls of plants due to its strength from hydrogen bonds between microfibrils.

Test for Sugars - Benedict's

Method for reducing sugars with a positive result showing a color change from blue to green, yellow, orange, or brick red.

Positive result for reducing sugar

blue to brick red, green or yellow

Can donate electrons

Refers to substances that can reduce other compounds.

Glucose, fructose, galactose, maltose, lactose

Examples of reducing sugars.

Benedict's reagent

Contains copper II sulfate and is used to test for reducing sugars.

Method for non-reducing sugars

If negative from first test, needs hydrolysis into monosaccharides.

Positive result for reducing sugars

Color change from blue to brick red.

Cannot donate electrons

Refers to substances that do not reduce other compounds.

Hydrolysis

The process of breaking down sucrose into monosaccharides using hydrochloric acid.

Test for starch

Involves adding iodine in potassium-iodide solution to the sample.

Positive result for starch test

Color change from orange to blue/black.

Lipids

Organic compounds that contain elements C, H, and O.

Triglycerides structure

1 molecule of glycerol attached to 3 fatty acids.

Formation of triglycerides

Involves a condensation reaction releasing a water molecule.

Function of triglycerides

Mainly used as storage molecules.

Properties of triglycerides

Insoluble in water due to hydrophobic fatty acid tails.

Phospholipids structure

1 glycerol, 1 phosphate group, and 2 fatty acid tails.

Amphipathic

Refers to molecules that have both hydrophobic and hydrophilic regions.

Function of phospholipids

Mainly form phospholipid bilayers and micelles.

Fatty acids

Composed of a carboxyl group (COOH) and a hydrocarbon tail.

Saturated fatty acids

Contain no double bonds and are saturated with hydrogen.

Unsaturated fatty acids

Contain C=C double bonds which cause the chain to kink.

Test for lipids

Involves adding ethanol to the sample followed by water.

Positive result for lipid test

Formation of a white/milky emulsion.

Hazards of ethanol

Ethanol is flammable; do not test near open flames.

Proteins

Composed of monomers called amino acids.

Amino acid structure

Contains NH2 (amine group), COOH (carboxyl group), and R (variable group).

Dipeptide formation

Occurs through a condensation reaction between amino acids.

Primary structure of proteins

The sequence of amino acids in a polypeptide chain.

Secondary structure of proteins

Formed by hydrogen bonds between amino acids, resulting in alpha helix or beta pleated sheet.

Tertiary Structure of Proteins

Further conformational change of the secondary structure, coiled or folded further, leads to additional bonds forming between the R groups (side chains).

Hydrogen Bonds

These are between R groups.

Disulphide Bridges

Only occurs between cysteine amino acids.

Ionic Bonds

Occurs between charged R groups.

Hydrophobic Interactions

Between non-polar R groups.

Quaternary Structure of Proteins

The way polypeptide chains are assembled, stabilized with hydrogen bonds, ionic bonds, and disulfide bridges.

Homodimer

Same polypeptide chains involved.

Heterodimer

Different polypeptide chains involved.

Primary Structure

The sequence of amino acids determined by the genetic code.

Enzyme Reaction

A change in DNA base sequence can affect an enzyme reaction.

Base Sequence

Determines sequence of amino acids in polypeptide chain/primary structure.

3 Bases

Code for one amino acid.

Active Site

The shape of a protein determines its function.

Globular Proteins

Soluble, R group folded in molecule.

Fibrous Proteins

Insoluble, R group exposed.

Biuret Test

Test for proteins; positive result is blue to purple.

Enzymes

Biological catalysts that speed up the rate of a chemical reaction.

Intracellular Reactions

Reactions inside cells.

Extracellular Reactions

Reactions outside cells.

Lock and Key Model

Active site fixed shape; substrate is complementary to active site.

Induced Fit Model

Active site of enzyme is not completely complementary to substrate.

Enzyme Specificity

Only catalyse one reaction as only one substrate is complementary to the active site.

Factors Affecting Enzyme Activity

Temperature, pH, enzyme concentration, substrate concentration, competitive inhibitors, non-competitive inhibitors.

Temperature Effect on Enzymes

As temperature increases, particles vibrate more as they have more kinetic energy and move faster.

Temperature

As temperature increases, particles vibrate more as they have more kinetic energy and move faster, leading to more likely collisions to form enzyme-substrate complexes.

Optimum temperature

Rate increases up to the optimum temperature; if temperature continues to increase past the optimum, vibrations cause hydrogen bonds to break, leading to enzyme denaturation.

pH

All enzymes have an optimum pH (usually pH7 but pH2 optimum for pepsin) and denature above and below this due to H+ and OH- ions altering the hydrogen and ionic bonds.

Enzyme concentration

Increasing enzyme concentration increases the rate of reaction as more enzymes are available for collisions with substrates.

Substrate concentration

Increasing substrate concentration increases the rate of reaction up to a saturation point where all enzyme active sites are in use.

Saturation point

The point at which increasing substrate concentration has no further effect as all enzyme active sites are occupied.

Initial rate

The highest rate of reaction observed at the beginning before substrate concentration decreases over time.

Competitive inhibitors

Competitive inhibitors have a similar shape to the substrate and compete for binding to the enzyme, reducing the formation of enzyme-substrate complexes.

Effect of competitive inhibitors

Increasing competitive inhibitors reduces the rate as they occupy active sites, but increasing substrate concentration can reduce their effect.

Non-competitive inhibitors

Non-competitive inhibitors bind away from the active site, causing a permanent conformational change in the active site, preventing substrate binding.

Effect of non-competitive inhibitors

Increasing substrate concentration has no effect on non-competitive inhibitors as they do not compete and alter the shape of the active sites.

DNA

Stores genetic information and is the hereditary material responsible for passing genetic material from cell to cell across generations.

Base pairs in DNA

3.2 billion base pairs in DNA of a typical mammalian cell provide an infinite variety of sequences, contributing to genetic diversity.

RNA

Transfers genetic information from DNA to ribosomes to make proteins (translation).

Nucleotide structure

Composed of a phosphate group, a pentose sugar (deoxyribose or ribose), and a nitrogenous base (A, T, C, G, U).

Polynucleotide formation

Formed by a condensation reaction between a phosphate group and pentose sugar, creating a phosphodiester bond.

Sugar-phosphate backbone

The structure formed by the joining of pentose sugars and phosphate groups in a chain.

DNA structure

Consists of a double helix structure with two separate polynucleotide strands wound around each other, held by hydrogen bonds between bases.

Pentose sugar in DNA

The pentose sugar in nucleotides of DNA is deoxyribose.

Nitrogenous bases in DNA

The nitrogenous bases in DNA are adenine, thymine, cytosine, and guanine.

Double stranded

Both strands can act as templates for semi-conservative replication.

Weak hydrogen bonds between bases

Can be unzipped for replication.

Complementary base pairing

Accurate replication as free nucleotides complementary exposed bases, reduce chance of mutation.

Many hydrogen bonds between bases

Stable / strong molecule.

Double helix with sugar phosphate backbone

Protects bases / H bonds/ degeneration of molecule.

Long molecule

Store lots of (genetic) information (that codes for polypeptides).

Double helix (coiled)

Compact, store a lot in a small space.