AQA A level Biology
Amino Acid - correct answerOnly different and specific in the R group. The R group represents a side
chain from the central 'alpha' carbon and can be anything from a simple hydrogen atom to a more
complex ring structure. The R group defines the amino acid.
Glycine is the only amino acid that does not contain carbon.
20 amino acids make up all living things.
Amylopectin (75%) - correct answer- Long, branched chain of alpha glucose
-Side branches allow the enzymes to break down the molecule to get at the glycosidic bonds easily. This
means glucose can be released quickly.
-The molecule is branches at 1-4 glycosidic bonds and 1-6 glycosidic bonds.
-Highly branched means it can be easily digested by enzymes to produce glucose for respiration for ATP
production due to the large surface area.
Amylose (25%) - correct answer- Long unbranched chain of alpha glucose, linked by a 1-4 glycosidic
bond.
- Hydrogen bonds give it a coiled, spiral structure so it is therefore very compact.
-Hydroxyl groups project into the middle. They form hydrogen bonds with each other which stabilises
the spiral.
Iodine detects this as it gets stuck inside the spiral and forms an iodine starch complex.
Benedict's Test for Reducing Sugars - correct answer1.Add Benedict's reagent
2.Bring to Boil
3.Forms a brick red precipitate if positive.
To find how much sugar there is, filter the solution and weigh the precipitate
Biuret Test - correct answerCrush and add distilled water to make the sample a solution.
Add sodium hydroxide to make the solution alkaline.
Add copper (II) sulphate solution.
, If there is protein the colour will change from blue to violet.
Bonds - correct answerShape is maintained by:
Hydrogen bonds are involved in all levels of the structure and are weak.
Hydrophobic interaction are between the non polar sections of the protein and are strong.
Disulphide bonds are the strongest and most important types of bond in proteins. They occur between
two cysteine amino acids.
Cellulose - correct answer-Long, unbranched chains of beta glucose. When beta molecules bond, every
other molecule is inverted 180 degrees, forming straight cellulose chains, linked by 1,2 glycosidic bonds.
-Chains become linked together by many hydrogen bonds to form microfibrils (many hydrogen bonds
provides strength and stability). These stack to form fibrils.
-Used in the cell wall of plants.
-Provides strength and rigidity to cell wall as it can resist turgid pressure from water, stopping the cell
from bursting.
Condensation Reactions - correct answerForming a chemical bond between monomers and releasing a
molecule of water.
Dipeptide and Peptide Formation - correct answerAmino acids are linked by condensation reactions to
form dipeptides and polypeptides.
-1 molecule of water is released during the reaction.
-Peptide bonds are formed.
-Hydrolysis is breaking down a polypeptide into an amino acid through the addition of water.
Disaccharides - correct answerA disaccharide forms when two monosaccharides join together through a
condensation reaction. This forms a glycosidic bond.
Glucose + Glucose = maltose
Glucose + Fructose = sucrose
Glucose + Galactose = lactose.
Amino Acid - correct answerOnly different and specific in the R group. The R group represents a side
chain from the central 'alpha' carbon and can be anything from a simple hydrogen atom to a more
complex ring structure. The R group defines the amino acid.
Glycine is the only amino acid that does not contain carbon.
20 amino acids make up all living things.
Amylopectin (75%) - correct answer- Long, branched chain of alpha glucose
-Side branches allow the enzymes to break down the molecule to get at the glycosidic bonds easily. This
means glucose can be released quickly.
-The molecule is branches at 1-4 glycosidic bonds and 1-6 glycosidic bonds.
-Highly branched means it can be easily digested by enzymes to produce glucose for respiration for ATP
production due to the large surface area.
Amylose (25%) - correct answer- Long unbranched chain of alpha glucose, linked by a 1-4 glycosidic
bond.
- Hydrogen bonds give it a coiled, spiral structure so it is therefore very compact.
-Hydroxyl groups project into the middle. They form hydrogen bonds with each other which stabilises
the spiral.
Iodine detects this as it gets stuck inside the spiral and forms an iodine starch complex.
Benedict's Test for Reducing Sugars - correct answer1.Add Benedict's reagent
2.Bring to Boil
3.Forms a brick red precipitate if positive.
To find how much sugar there is, filter the solution and weigh the precipitate
Biuret Test - correct answerCrush and add distilled water to make the sample a solution.
Add sodium hydroxide to make the solution alkaline.
Add copper (II) sulphate solution.
, If there is protein the colour will change from blue to violet.
Bonds - correct answerShape is maintained by:
Hydrogen bonds are involved in all levels of the structure and are weak.
Hydrophobic interaction are between the non polar sections of the protein and are strong.
Disulphide bonds are the strongest and most important types of bond in proteins. They occur between
two cysteine amino acids.
Cellulose - correct answer-Long, unbranched chains of beta glucose. When beta molecules bond, every
other molecule is inverted 180 degrees, forming straight cellulose chains, linked by 1,2 glycosidic bonds.
-Chains become linked together by many hydrogen bonds to form microfibrils (many hydrogen bonds
provides strength and stability). These stack to form fibrils.
-Used in the cell wall of plants.
-Provides strength and rigidity to cell wall as it can resist turgid pressure from water, stopping the cell
from bursting.
Condensation Reactions - correct answerForming a chemical bond between monomers and releasing a
molecule of water.
Dipeptide and Peptide Formation - correct answerAmino acids are linked by condensation reactions to
form dipeptides and polypeptides.
-1 molecule of water is released during the reaction.
-Peptide bonds are formed.
-Hydrolysis is breaking down a polypeptide into an amino acid through the addition of water.
Disaccharides - correct answerA disaccharide forms when two monosaccharides join together through a
condensation reaction. This forms a glycosidic bond.
Glucose + Glucose = maltose
Glucose + Fructose = sucrose
Glucose + Galactose = lactose.
