AQA Alevel biology - biological molecules

what are monomers ?

Monomers are the smaller units from which larger molecules are made.

what are polymers ?

Polymers are molecules made from a large number of monomers joined together.

what does a condensation reaction do ?

A condensation reaction joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water.

what does a hydrolysis reaction do ?

A hydrolysis reaction breaks a chemical bond between two molecules and involves the use of a water molecule.

what is a monosaccharide ?

Monosaccharides are the monomers from which larger carbohydrates are made. A single monomer.

what are the examples of monomers ?

Glucose, galactose and fructose

what is a disaccharide ?

Disaccharides are formed by the condensation of two monosaccharides

What bond forms between monosaccharides ?

glycosidic bond

what are the disaccharides and what 2 monosaccharides do they consist of ?

• Maltose - glucose + glucose

• Sucrose - glucose + fructose

• Lactose - glucose + galactose

what is the alpha glucose isomer look like ?

what does the beta glucose isomer look like ?

what is a polysaccharide ?

Polysaccharides are formed by the condensation of many glucose units

what are the polysaccharides of alpha glucose ?

glycogen and starch

what is a polysaccharide of beta glucose ?

cellulose

what is the structure of glycogen ?

• 1,4 or 1,6 glycosidic bonds

• large number of side branches

• large but compact

• insoluble

why is having a large number of branches important ?

energy can be released quickly as enzymes can simultaneously act on the branches

why is important to be compact ?

so you can fit more , increasing amount of energy

why is it important to be insoluble ?

It doesnt affect the water potential and cannot diffuse out of the cell

what is the structure of amylose ?

• unbranched

• 1,4 glycosidic bonds

• coiled (very compact )

what is the structure of amylopectin ?

• many side branches

• 1,4 + 1,6 glycosidic bonds

what is the method for reducing sugars ?

• Add equal volumes (e.g., 2 cm³) of the food sample test solution and Benedict's reagent into a test tube.

• Place the test tube into a boiling water bath.

• Heat the mixture for 5 minutes

what is a positive result for reducing sugars ?

Blue turns into Brick Red

what is the test for non-reducing sugars ?

• erform Benedict's test: Test a sample first. If it stays blue, reducing sugars are absent.

• Acid Hydrolysis: Add 2 cm³ of the fresh sample and an equal volume of dilute hydrochloric acid (HCl) to a new test tube.

• Heat: Place the tube in a boiling water bath for 5 minutes to break glycosidic bonds.

• Neutralise: Add sodium hydrocarbonate (NaHCO₃) or sodium hydroxide (NaOH) until the solution stops fizzing. Benedict's reagent requires alkaline conditions to work.

• Re-test: Add equal volume Benedict's reagent. Heat in a boiling water bath for 5 minutes.

• Observe: A color change to green, yellow, orange, or brick-red confirms non-reducing sugars.

what is the test for starch ?

• Prepare Sample: Add 2 cm³ of your liquid food sample (or a solid piece of food) into a test tube or onto a spotting tile.

• Add a few drops of iodine

• positive result : orange to blue-black

what are triglycerides made of ?

Triglycerides are formed by the condensation of one molecule of glycerol and three molecules of fatty acid.

what type of bond is formed between a glycerol and fatty acid ?

A condensation reaction between glycerol and a fatty acid (RCOOH) forms an ester bond.

what is substituted in a phospholipid from a triglyceride ?

In phospholipids, one of the fatty acids of a triglyceride is substituted by a phosphate-containing group.

what makes an unsaturated fatty acid different to a saturated fatty acid ?

Unsaturated has a carbon-carbon double bond. Therefore they are liquids at room temp

what are the properties of triglycerides and why are they important ?

• large and non-polar so they are insoluble in water and thus do not affect water potential

• low mass to energy ratio so a lot of energy can be stored n a small volume

• high ratio of hydrogen - oxygen atoms

what is the structure of a phospholipid ?

• hydrophilic head and hydrophobic tail creates a bilayer and makes the cell polar

• glycerol , phosphate and 2 fatty acids

what is the method of the emulsion test ?

• add the sample to test tube

• add ethanol

• shake the test tube

• then add water and shake again

• positive result is a milky white emulsion

what is the general structure of an amino acid ?

where NH₂ represents an amine group, COOH represents a carboxyl group and R represents a side chain

what bond forms between 2 amino acids ?

A condensation reaction between two amino acids forms a peptide bond.

what is a dipeptide ?

• Dipeptides are formed by the condensation of two amino acids.

what is a polypeptide ?

• Polypeptides are formed by the condensation of many amino acids.

what is the primary structure of proteins ?

Sequence of amino acids joined by peptide bonds

what is the secondary structure of proteins ?

the shape that the amino acid chain makes - either beta pleated or alpha helix

what is the tertiary structure of proteins ?

• the 3D shape of the protein by further twisting and folding

• held together by disulphide bridges , hydrogen bonds and ionic bonds

what is the Quaternary structure of proteins ?

2 or more polypeptide chains

what is the method for testing for proteins ?

• add biuret to sample

• positive result is purple

how do enzymes work ?

lower the activation energy without being used up themselves

what is the induced fit model ?

When the active site slightly alters to fit the substrate

what is the lock and key model ?

the active site and substrate are perfectly complementary

how does enzyme activity change with temperature ?

An increase in temperature increases the rate of reaction as kinetic energy increases up to the optimum

how does pH change the rate of reaction ?

it increases rate of reaction up tp optimum where it denatures thereafter

how does enzyme concentration affect rate of reaction ?

It increases until substrate conc becomes the limiting factor

how does substrate concentration effect rate of reaction ?

It increases until enzyme conc becomes the limiting factor

how is DNA and RNA used to carry info ?

DNA holds genetic information and RNA transfers genetic information from DNA to the ribosomes.

what are ribosomes made of ?

RNA and proteins

what are the components of DNA ?

• The components of a DNA nucleotide are deoxyribose, a phosphate group and one of the organic bases adenine, cytosine, guanine or thymine.

what are the components of RNA ?

• The components of an RNA nucleotide are ribose, a phosphate group and one of the organic bases adenine, cytosine, guanine or uracil.

what bond is formed between nucleotides ?

• A condensation reaction between two nucleotides forms a phosphodiester bond.

what is the structure of DNA ?

A DNA molecule is a double helix with two polynucleotide chains held together by hydrogen bonds between specific complementary base pairs.

what is the structure of RNA ?

An RNA molecule is a relatively short, single stranded polynucleotide chain.

why is DNA stable ?

• Phosphodiester backbone protects the more chemically reactive nitrogen containing bases inside the double helix

• Hydrogen bonds between bases

what is the process of semi - conservative replication in DNA ?

• DNA helicase causes the DNA helix to unwind.

• DNA helicase breaks the hydrogen bonds between the complementary base pairs.

• This separates the two strands, leaving both strands to act as templates

• Free DNA nucleotides align alongside the exposed template strands.

• They attach via complementary base pairing.

• Adenine pairs with Thymine and Cytosine pairs with Guanine

• DNA polymerase joins the new nucleotides together in a condensation reaction.

• This forms phosphodiester bonds to create the new sugar-phosphate backbone.

• Each new DNA molecule retains one original (parental) strand and one new strand.

what is the structure of ATP ?

A single molecule of adenosine triphosphate (ATP) is a nucleotide derivative and is formed from a molecule of ribose, a molecule of adenine and three phosphate groups.

how does ATP release energy ?

ATP is hydrolysed with the help of ATP hydrolase to form ADP and a phosphate molecule

how is ATP produced ?

ATP Synthase catalyses the condensation reaction of ADP and inorganic phosphate

what happens to the inorganic phosphate in ATP ?

Can be used to phosphorylate other compounds , making them more reactive

what are the properties of ATP ?

• its an immediate source of energy

What are the properties of water ?

• is a metabolite in many metabolic reactions, including condensation and hydrolysis reactions

• is an important solvent in which metabolic reactions occur

• has a relatively high heat capacity, buffering changes in temperature

• has a relatively large latent heat of vaporisation, providing a cooling effect with little loss of water through evaporation

• has strong cohesion between water molecules; this supports columns of water in the tube-like transport cells of plants and produces surface tension where water meets air.

what is the role of hydrogen ions ?

determine the pH of substances such as blood

what is the role of iron ions ?

a component of haemoglobin

what is the role of sodium ions ?

involved in the co-transport of glucose and amino acid ions

what is the role of phosphate ions ?

a component of DNA and ATP