BY1: Biochemistry

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Carbohydrates: Monosaccharides

-Relatively small molecules that make up the building blocks to the larger carbohydrates.
-Have the general formula: (Cn2O)n
-Glucose exists in two isomers:

-The only difference between these molecules are the rotation of the OH group.
Monosaccharides have two functions: 
-Used as a source of energy in respiration, C-H bonds are broken to release energy. (ATP)
-They act as building blocls to polysaccharides such as starch, gylcogen and cellulose. 

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Carbohydrates: Disaccharides

-These consist of two monosaccharides linked together with the formation of a gycocidic bonds and the elimination of water; a condensation reaction.

-Glucose and fructose = sucrose.
-Glucose and galactose = lactose.

-These are used for storage and transport. 

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Testing For Sugars

-Testing for glucose by adding the solution in a water bath:

-Some disaccharides, are non-reducing sugars and must first be broken down by HCl, to form a monosaccharides. 

-This test is qualative or at best, semi-quantative; so estimations are required. 

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Carbohydrates: Polysaccharides-Starch

Starch
-It is a storage unit as it is insoluble, so it doesn't affect osmotic pressure.
-It is also a compact molecule and can be stored in small spaces.
-Made up of many a-glucose held together in an alpha helix, and consists of amylose (linear) and amylopectin (branched); and form 1-4 bonds. 

-To test for starch add iodine and a blue-black colour will appear for positive.

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Carbohydrates: Polysaccharides-Cellulose

-This is a structural polysaccharide, and the most abundant organic molecule.
-They consist of many long parallel chains of b-glucose units, the chain has adjacent glucose molecules rotated by 180 degrees; allowing H bonds to form.
-These form microfibrils, which then form bundles - fibres.
-They are strong, and permeable; so they allow water to pass through.

 

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Carbohydrates: Polysaccharides-Chitin

-A polysaccharide found in insects' exoskeletons. 
-Similar to cellulose but with additional amino acids.
-Waterproof and lightweight.

 

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Carbohydrates: Polysaccharides-Chitin

-A polysaccharide found in insects' exoskeletons. 
-Similar to cellulose but with additional amino acids.
-Waterproof and lightweight.

 

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Lipids

-These contain less oxygen in general.
-They are non-polar and insoluble in water.
-Formed by the combination of one glycerol molecule and three fatty acids.
-They are formed by a condensation reaction, known as an ester bond.
-The glycerol molecule is always the same, but many fatty acids.

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Lipids: Properties/Roles

-The differences in the properties of fats and oils come from the fatty acid variation.
-C=C is unsaturated, and no C=C is saturated; the first of which is better for you. 
-Insoluble in water, but soluble in organic solvents such as alcohols. 

Lipids are important because:
-They play an important part in the structure of the plasma membrane.
-Lipids are an exellent energy reserve, because they have more C-H bonds than carbs.
-When stored under skin, it acts against heat loss.
-Protection; fat is stored around delicate organs
-Triglycerides produce a lot of metabollic water, important for desert animals.
-Waterproofing; fats are water insoluble and important in insects/plants where the waxy cuticle reduces water loss.

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Phospholipids

-A special kind of lipid that has one end which is soluble in water.
-This is because one fatty acid is replaced by a polar phosphate group.
-These are important in the formation of the plasma membrane in cells.

-The lipid part is non-polar and is described as the hydrophobic part.
-The phosphate group is polar and dissolves in water, hydrophillic. 

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Proteins

-These also contain Nitrogen.
-Are large compounds made up of amino acids, specific shape to each chain of 20.
All amino acids have the same basic structure:
-An amino group: -NH2.
-A carboxylic group: -COOH.
-But each amino acid has a different R group.

-The formation of a peptide bond is a condensation reaction, forming a dipeptide. 
-To test for protein, a biuret test must be undertaken; showing a purple colour. 

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Protein Structure

Primary Structure
-This is the sequence of amino acids in a polypeptide chain, up to 20 amino acids.

Secondary Structure
-The shape that the polypeptide chain forms as a result of H bonding:
-Can form an a-helix, or less commonly a b-pleated sheet.

Teriary Structure
-The a-helix folds and twists to give a more complex, compact shape.
-Held together by disulphide, ionic and hydrogen bonds.

Quaternary Structure
-The comination of two or more tertiary structure with the addition of a non-protein group such as Haem in haemoglobin. 

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Globular And Fibrous Proteins

Fibrous:
-Structural functions.
-Consist of polpeptides in parallel chains or sheets with cross-links.
-Insoluble, tough and strong; such as collagen - stable, single fibre.

Globular:
-Variety of functions such as enzymes, antibodies and hormones.
-Compact and spherical.
-Soluble in water.
-E.g. haemoglobin. 

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Water

Water As A Solvent
-Water is an excellent solvent because it is polar, and so attracts ions and other polar molecules.
-This allows chemical reactions to take place, acting as a transport medium.

Thermal Properties
-Water has a high specific heat, due to H bonds; preventing large fluctuation in temperature.
-Allowing for stable environments and enzymes to work properly.
-Water has a high latent heat, so this aids in the evaporative cooling of an animal.

Cohesion And Surface Tension
-Water is a polar molecule, so H bonds are formed; holding all H2O molecules together in a strong lattice, aiding in the xylem tissue.
-Had the second highest surface tension of any liquid, meaning insects can 'glide' on it.

-Ice is less dense than water, and thus floats; producing survival of organisms underneath.
-Water is transparent so aquatic plants can photosynethesise. 

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Inorganic Ions

-Magnesium is an important component of chlorophyll, so crucial for photosynthesis.
-Iron makes up haemoglobin, which is important in transport of O2.
-Phosphate ions make up nucleotides, and the phospholipid bilayer.
-Calcium, is an important structural component of bones and teeth. 

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