This section delves deeper into the structure and function of carbohydrates a level Biology, focusing on the complex polysaccharides starch, glycogen, and cellulose. It provides detailed information about their structures and properties, which is crucial for understanding AQA A Level Biology Biological Molecules exam questions.

The structure of starch is explained as being composed of two components: amylose and amylopectin. Amylose is described as a long, straight chain of alpha-glucose molecules that forms a coiled structure. Amylopectin, on the other hand, is a straight chain of alpha-glucose with side branches, connected by 1,6-glycosidic bonds.

Glycogen's structure is similarly detailed, consisting of a straight chain of alpha-glucose molecules connected by 1,4-glycosidic bonds, with side branches formed by 1,6-glycosidic bonds.

The guide then discusses the properties of starch and glycogen as energy stores. Their insolubility is highlighted as an important feature, preventing them from affecting cell water potential or diffusing out of cells. The coiled and branched structures are noted for their compactness, allowing more to fit into a cell. The branched nature also facilitates easy glucose removal from the ends.

Cellulose structure is described in detail, emphasizing its role in plant cell walls. The guide explains how beta-glucose molecules are arranged in straight chains, with alternating molecules rotated 180 degrees. These chains are cross-linked by hydrogen bonds to form microfibrils, which in turn form macrofibrils.

The section concludes with information on testing methods for various carbohydrates, including the iodine test for starch and Benedict's test for reducing and non-reducing sugars.

Vocabulary: Microfibrils - Thin threads of cellulose molecules that are cross-linked to form the structure of plant cell walls.

Example: The iodine test for starch results in a blue-black color change when starch is present.

Definition: Glycosidic bond - A type of covalent bond that joins a carbohydrate molecule to another group, which may or may not be another carbohydrate.

Highlight: The branched structure of starch and glycogen allows for more efficient storage and easier access to glucose molecules for energy release.

Quote: "Cellulose used to form Cell Wall in Plants, made out of many beta glucose"

This section provides an in-depth look at protein structure and function, which is a crucial component of biological molecules A level AQA curriculum. It covers the different levels of protein structure and introduces important concepts for AQA A Level Biology Biological Molecules flashcards.

The guide begins by distinguishing between two types of proteins: globular and fibrous. Globular proteins are described as soluble proteins with a specific 3D shape, with examples including enzymes, hormones, antibodies, and hemoglobin. Fibrous proteins are characterized as strong, insoluble, and inflexible materials, with collagen and keratin given as examples.

The building blocks of proteins, amino acids, are introduced. The guide provides a detailed description of the amino acid structure, including the central carbon atom, carboxyl group $COOH$, amine group $NH2$, hydrogen, and the variable R group. It explains that different amino acids are distinguished by their unique R groups.

The formation of peptide bonds through condensation reactions between amino acids is explained, leading to the creation of dipeptides and eventually polypeptides.

The four levels of protein structure are defined:

1. Primary structure: The sequence of amino acids in a polypeptide chain, held together by peptide bonds.
2. Secondary structure: The coiling of the primary structure to form a helix, stabilized by hydrogen bonds.
3. Tertiary structure: Further folding of the secondary structure to create the final 3D shape, held together by various bonds including hydrogen, ionic, and disulfide bonds.
4. Quaternary structure: Proteins composed of more than one polypeptide chain.

Examples of proteins with quaternary structure are provided, including collagen $3 chains$, antibodies $3 chains$, and hemoglobin $4 chains$.

The structure of collagen is described in detail, emphasizing its role as a strong material used in tendons, ligaments, and connective tissues. Its primary structure is noted to be mainly composed of glycine, the simplest amino acid, which allows for tight coiling in the secondary and tertiary structures.

The section concludes with a description of the biuret test for proteins, which results in a purple color change.

Vocabulary: Peptide bond - A covalent bond formed between the carboxyl group of one amino acid and the amino group of another, resulting in the release of a water molecule.

Example: Hemoglobin, a protein with quaternary structure, is composed of four polypeptide chains.

Definition: Tertiary structure - The final three-dimensional shape of a protein, resulting from further folding of the secondary structure and stabilized by various types of bonds.

Highlight: The presence of glycine in collagen's primary structure allows for tight coiling, contributing to its strength as a structural protein.

Quote: "Structure of collagen? strong material, used to build tendons/ligaments/connective tissues"

This section provides a comprehensive overview of biological molecules, with a focus on carbohydrates and proteins. It covers their basic structures, functions, and classifications, which are essential components of the AQA A Level Biology Biological Molecules curriculum.

Biological molecules are defined as molecules made and used by living organisms. The guide lists examples such as carbohydrates, proteins, lipids, DNA, ATP, water, and inorganic ions. It then delves into the functions of carbohydrates, highlighting their roles as energy sources, energy stores, and structural components.

The building blocks of carbohydrates, monosaccharides, are introduced with examples like glucose, galactose, and fructose. The guide explains the formula for monosaccharides $C6H12O6$ and distinguishes between alpha and beta glucose.

The formation of more complex carbohydrates through condensation reactions is described, introducing the concept of glycosidic bonds. Examples of disaccharides and their formulas are provided, along with an explanation of how polymers are separated through hydrolysis.

Polysaccharides are defined and examples such as starch, glycogen, and cellulose are given, along with their functions and structures.

The section on proteins introduces globular and fibrous proteins, their characteristics, and examples. It explains that amino acids are the building blocks of proteins and describes their basic structure.

Vocabulary: Monosaccharides - The simplest form of carbohydrates, serving as the building blocks for more complex carbohydrate molecules.

Example: Glucose is a monosaccharide that serves as an energy source in respiration.

Definition: Condensation reaction - A chemical reaction in which two molecules combine to form a larger molecule, releasing a water molecule in the process.

Highlight: The difference between alpha and beta glucose lies in the position of the OH group on Carbon 1: in alpha glucose, it's on the bottom, while in beta glucose, it's on the top.

Quote: "What are biological molecules? molecules made and used by living organisms e.g. Carbohydrates, Proteins, Lipids, DNA, ATP, Water, Inorganic Ions"