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Lipids

Lipids

  • Lipids have a much lower proportion of water than other molecules such as Carbohydrates.
  • insoluble
  • Long carbon chains
  • They are made from two molecules: Lipids can exist as fats, oils and waxes.
    • Fats and oils are very similar in structure (triglycerides).
  • At room temperature, fats are solids and oils are liquids.
    • Fats are of animal origin, while oils tend to be found in plants.
  • Waxes have a different structure (esters of fatty acids with long chain alcohols) and can be found in both animals and plants.
  • They are a diverse group of:
    • Fats
    • Phospholipids
    • Steroids
  • They do not form polymers, they have large molecules (unlike proteins and carbohydrates which are polymers)
  • They have a greater ratio of Oxygen and hydrogen than H2O
  • Lipids perform many functions, such as:
  1. Storage – lipids are non-polar and so are insoluble in water.
  2. High-energy store – they have a high proportion of H atoms relative to O atoms and so yield more energy than the same mass of carbohydrate.
  3. Production of metabolic water – some water is produced as a final result of respiration.
  4. Thermal insulation – fat conducts heat very slowly so having a layer under the skin keeps metabolic heat in.
  5. Electrical insulation – the myelin sheath around axons prevents ion leakage.
  6. Waterproofing – waxy cuticles are useful, for example, to prevent excess evaporation from the surface of a leaf.
  7. Hormone production – steroid hormones. Oestrogen requires lipids for its formation, as do other substances such as plant growth hormones.
  8. Buoyancy – as lipids float on water, they can have a role in maintaining buoyancy in organisms.

Testing for Lipids: Emulsion Test

Equipment

  • A clean test tube
  • 2cm3 of the sample being tested
  • 5cm3 Ethanol
  • 5cm3 water

Method

  1. Put 2cm3 of the sample being tested into the test tube
  2. Add 5cm3 of ethanol to the test tube
  3. Add 5cm3 of water and shake the mixture gently
  4. For a control, use water as the sample in a new test tube. Repeat instructions.

Result

If the solution turns cloudy white, this indicates lipids are present.

Carbohydrates

Carbohydrates

Carbohydrates

Monosaccharide:

  • Monosaccharides are the monomers which make up carbohydrates
  • Most Simple sugar
  • They have the same number of carbon + oxygen

e.g. Glucose is C6H12O6

  • They have the general formula of (CH2O)n
  • White Crystalline solids
  • Soluble
  • The 3 monosaccharides are Glucose, Fructose and Galactose
  • Glyosidic bonds between each monomer formed under a condensation reaction

Monosaccharide to Disaccharide

Monosaccharide

Disaccharide

Glucose + Glucose

Maltose

Glucose + Fructose

Sucrose

Glucose + Galactose

Lactose

Starch

  • An Alpha-helix structure
  • Insoluble and is compact
  • No impact of water potential (osmotically inactive)
  • It is the main plant storage of sugar
  • Made of

Cellulose

  • Polymer of β-glucose
  • Each monomer is inverted to the previous monomer
  • Different chains are held with hydrogen bonds
  • These chains run parallel with hydrogen bonds between the chains to form microfibrils.
  • Cellulose is what makes up the structure of a plant cell

Glycogen

  • Similar to amylopectin
  • α-glucose polymer with 1,4 bonds with some 1,6 branches
  • Highly branched structure
  • Can be broken down quickly to glucose when needed
  • Reflects the high metabolic rate demand for energy in animals

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Water

Water

Properties of Water

  • 2 atoms of hydrogen are covalently bonded to a molecule of oxygen, water is a polar molecule. There are weak hydrogen bonds between each water molecule and it has a high heat capacity.
  • Water has a large latent heat of vaporisation (Energy required to convert it to as gas)
  • Water has strong cohesion between other water molecules
  • Water is a metabolite (required) in many metabolic reactions

Specific Heat Capacity

  • The heat required to raise 1kg of water by 1 degree Celsius.
  • Water has a large heat capacity, and therefore can absorb large amounts of heat energy before temperature increases
  • In animals, water is used as a ‘heat buffer’ which maintains an internal body temperature (homeostasis)
  • In aquatic animals, it also helps them live in a constant temperature environment

Large Latent Heat of vaporisation

  • Water has a high boiling point
  • When a mammal sweats, it evaporates using a lot of energy and can therefore taking that energy away and therefore the mammal loses heat efficiently
  • Water molecules that have evaporated and the energy lost is the latent heat

Strong Cohesion

  • Due to water being polar, water molecules have a strong polarity meaning that water molecules are attracted to each other, and form hydrogen bonds between each molecule; therefore hydrogen bonds help hold water together
  • In plants, water moves up the xylem as a continuous stream. This allows water to reach the top of trees
  • Water cohesion leads to surface tension making water behave if there is a skin which allows for pond skaters for example

Water Solvent

  • Transportation of molecules (Gases such as Oand CO2 and waste product such as NHand urea) are dissolved in water before being moved around the body
  • Inorganic ions are small hydrophilic molecules such as amino acids, monosaccharides and ATP can also be absorbed into water.
  • Enzymes that require a solution
  • Metabolic reactions occur inside each cell in the cytoplasm which contains water

Metabolite

  • Water molecules can also be involved in chemical process e.g. hydrolysis is used in digestion and condensation used in synthesis

 

The Roles of water in living Organisms:

  • High specific heat capacity allows for a ‘heat buffer’ so there are no massive heat fluctuations as well as allowing for a constant sea temperature in aquatic animals.
  • High latent heat allows for energy to be lost through sweating which allows for heat to be lost, cooling the animal down
  • Cohesion allows for water to be moved up plants
  • Water is a solvent absorbing molecules to be transported around the body
  • Use in metabolism, water is used to break complex molecules in hydrolysis reactions or break down molecules in condensation reactions
  • Water is used in synthesis

 

Inhibitors

Inhibitors

An Enzyme Inhibitor interferes with an enzyme on a temporary or permanent basis causing it to reduce the rate of reaction of an enzyme catalysed reaction.

Nonspecific Inhibitors

  • Non Specific Inhibitors  are those that affect all enzymes under the same conditions, this usually is the result of physical or chemical changes causing the enzyme to denature.
  • Examples of Nonspecific Inhibitors:
    • Low/High temperature
    • Extreme Low/High pH

Competitive Inhibitors

  • Competitive Inhibitors compete with substrates for positions at the enzymes active site.
  • They usually have a shape close to the substrate. The inhibitor blocks the site for other enzymes to attach.
  • The result slows down the reaction, rather than stops it.

Non Competitive Inhibitors

  • Non-competitive inhibitors do not compete with the substrate, it binds to the allosteric site.
  • As a result the active site of the enzyme changes.
  • Thus, the substrate cannot bond to it. If the non-competitive inhibitor releases, then the enzyme restores back to normal.
  • It slows the reaction down rather than stops it.

ATP

ATP

  • ATP is a phosphorylated molecule made up of 3 parts:
    • Adenine: A nitrogen containing Organic base
    • Ribose: A sugar molecule with a 5-carbon ring structure (pentose sugar) acting as a backbone
    • Phosphate A chain of three phosphate groups
  • ATP is a nucleotide, it has strong bonds between the phosphates, therefore providing large amounts of energy when these bonds are broke.

Formation of a ATP synthase (or phosphorylation)

  • ATP + H2O -> ADP + P (+ energy)
  • Adenosine Water Adenosine Phosphorus
  • Triphosphate diphosphate
  • Water is required to breakdown the ATP molecules requiring the Enzyme ATPase (or ATP Hydrolase), thus being a hydrolysis reaction.
  • In phosphorylation, the adding of phosphate to ADP to create ATP
  • There are 3 forms:
    Oxidative phosphorylation
    Occurs in the membrane of mitochondria during aerobic respiration and provides the process of the electron transport chain
  • Phosphorylation
    Occurs in the thylakoid membrane in the chloroplast of plants only
  • Substrate-level phosphorylation
    Occurs when phosphate groups are transferred from donor molecules to ADP to make ATP (e.g. in glycolysis)

ATP vs Glucose

  • ATP is more immediate than glucose as hydrolysis reactions are quick
    ATP to ADP is a single reaction, thus quicker however less energy is produced. ATP is more suitable for tasks that require a quick response in energy, however not in massive yields.
    Glucose is a complex reaction, therefore slower, however produces far more energy

Which reactions require ATP?

  • Metabolic process
  • Movement (muscle contractions)
  • Active transport
  • Secretion
  • Activation of molecules
  • Bioluminescence
ATP and Energy
ATP

ATP and Energy

ATP is a phosphorylated molecule made up of 3 parts:

  • Adenine: A nitrogen containing Organic base
  • Ribose: A sugar molecule with a 5-carbon ring structure (pentose sugar) acting as a backbone
  • Phosphate A chain of three phosphate group

ATP is a nucleotide, it has strong bonds between the phosphates, therefore providing large amounts of energy when these bonds are broke. (albeit small in comparison to glucose)

Formation of a ATP synthase (or phosphorylation) 

ATP                 +             H2O                        ->                      ADP                 +             P          (+ energy)

Adenosine                         Water                                           Adenosine                    Phosphorus

Triphosphate                                                                           diphosphate

Water is required to breakdown the ATP molecules requiring the Enzyme ATPase (or ATP Hydrolase), thus being a hydrolysis reaction.

In phosphorylation, the adding of phosphate to ADP to create ATP

  • There are 3 forms:
  • Oxidative phosphorylation

Occurs in the membrane of mitochondria during aerobic respiration and provides the process of the electron transport chain

  • Phosphorylation

Occurs in the thylakoid membrane in the chloroplast of plants only

  • Substrate-level phosphorylation

Occurs when phosphate groups are transferred from donor molecules to ADP to make ATP (e.g. in glycolysis)

ATP vs Glucose

  • ATP is more immediate than glucose as hydrolysis reactions are quick
  • ATP to ADP is a single reaction, thus quicker however less energy is produced. ATP is more suitable for tasks that require a quick response in energy, however not in massive yields.
  • Glucose is a complex reaction, therefore slower, however produces far more energy

Which reactions require ATP?

  • Metabolic process
  • Movement (muscle contractions)
  • Active transport
  • Secretion
  • Activation of molecules
  • Bioluminescence

ATP is a phosphorylated molecule made up of 3 parts:

  • Adenine: A nitrogen containing Organic base
  • Ribose: A sugar molecule with a 5-carbon ring structure (pentose sugar) acting as a backbone
  • Phosphate A chain of three phosphate groups

 

ATP is a nucleotide, it has strong bonds between the phosphates, therefore providing large amounts of energy when these bonds are broke.

 

ATP properties:

  • ATP stores a small unit of energy which is both suitable for the reactions which requires it as well as minimal energy is wasted as heat
  • ATP is a small soluble molecule and therefore can easily be transported around the cell
  • The ATP molecule is easily hydrolysed and so energy release is fast
  • ATP is a simple molecule to reform
  • ATP allows for other molecules to become more reactive as it can transfer one of its phosphate groups to them in phosphorylation
  • ATP does not leave the cell it is produced in

 

 

 

 

 

 

Triglycerides
Triglycerides

Triglycerides

 

Triglycerides

  • Triglycerides are made up of 3 fatty acid chains attached to a glycerol molecule
  • They are bonded by an ester bond formed through condensation reactions
Triglycerides diagram

Triglycerides diagram

Triglycerides are formed under condensation reactions between Glycerol (C3H8O3) and fatty acids. The result of this reaction is a water molecule that forms one part of the triglyceride, with 3 forming together though an ester bond.

Saturated: C-C

Unsaturated: C=C

Saturated Fatty Acids

  • Every Carbon atom is bonded to as many hydrogen atoms as possible, no more can be added hence they are “saturated with hydrogens”
  • Triglycerides consisting of saturated fatty acids can pack together to form solid fats at room temperature
  • Carbon chains are straight with no kinks
  • Mainly food in animals and dairy products contain saturated fats

Unsaturated Fats

  • Triglycerides consistent of a “kink” in its chain at the double bond point.
  • They do not pack together easily, and form liquid oils at room temperature
  • The more double bonds, the more kinks it will have in the chain
  • Double bonds introduce a definite “kink” in the carbon atom chain
  • Not every carbon atom are bonded to as many hydrogen atoms as it could be – hence unsaturated (with hydrogen) there are double bonds
  • Mainly found in vegetable oils, nuts and fish

Triglycerides are lipids that are an important source of energy for the body. Triglycerides are broken down and reassembled in the body.

Enzymes
Enzyme

Enzymes

Enzymes

Enzymes are made up of proteins, they are biological catalysts.

They increase the rate of metabolic reactions. Nearly all of the reactions in the body use an enzyme, when a reaction involving an Enzyme occurs, a Substrate is turned into a Product. The Substrate can be one or more molecules. The Active Site of an Enzyme is Complementary to the Substrate it catalyses.

They are soluble in water to hydrophilic side group

They very large molecules, but only small parts of the molecules act as the catalyst

Enzymes are specific are specific to one type of reaction Enzymes. All enzymes are Globular Proteins with a specific Tertiary Shape. The rest of the Enzyme is much larger and is involved in maintaining the specific shape of the Enzyme.

Enzymes in respiration

Hydrogen peroxide is a product of respiration, enzymes are required to break down this as it is harmful

Hydrogen Peroxide         ->             Water                                +             Oxygen

                         4H2O2                                                                      4H2O                                     2O2

The use of catalase is used to break down Hydrogen peroxide down into water and oxygen

a) Measure 25 cm3 of hydrogen peroxide solution into each of three conical flasks.

b) At the same time, add a small piece of liver to the first flask, a small piece of potato to the second flask, and a small piece of celery to the third flask.

c) Hold a glowing splint in the neck of each flask.

d) Note the time taken before each glowing splint is re-lit by the evolved oxygen.

e) Dispose of all mixtures into the bucket or bin provided.

 

Extracellularly and intracellularly

Extracellularly are enzymes that is secreted by a cell and functions outside of that cell. Many enzymes secreted in digestion are extracellularly such as amylase or pepsin.

Intracellularly are enzymes that functions within the cell in which it was produced

DNA replication is intracellularly

All reactions require energy before they can start.  It is shown as activation energy.  This starts in breaking bonds of the reactants: enzymes lower this activation energy. This creates a transition state between enzymes and substances that are more stable.

Lock and Key Theory

Active sites are a small area with a specific shape to the substrate of the substance. The shape of the Active Sites of Enzymes are exactly complementary to the shape of the Substrate.

Enzymes that bonds with the correct substrate form enzyme substrate complex. The enzyme will catalyse the reaction, and the products, together with the enzyme, will form an Enzyme-Product Complex. According to this model, it is possible for an enzyme to catalyse a reverse reaction.

 

Structure

Structure

 

Induced Fit Theory

The active site is not the exact size of the substrate, but change shape in the presence of a specific substrate to become Complementary.

As the substrate moves closer to the enzyme it is ‘moulded’ around the substrate. This tight envelope of the substrate forms enzyme substrate complexes. When a substrate molecule collides with an enzyme, if its composition is specifically correct, the shape of the enzyme’s Active Site will change so that the substrate fits into it and an Enzyme-Substrate Complex can form. The reaction is then catalysed and an Enzyme-Product Complex forms.

Structure

Structure

Enzyme actions

For enzymes to work they require:

  • Physical contact with substrate
  • Must have correct shaped active sites

Measuring Enzyme action

  • Rate of the formation of products

 

Structure

Formation

 

  • Rate of Disappearance

Structure

 As the enzyme reacts with the substrate of the molecule, the mass of the substrate decreases as the amount of product increases over time

Graph 1 shows that at the beginning there is lots of substrate, when these substrates bond to the active sites the reaction begins. This process occurs rapidly causing amount of product to rise quickly and the amount of reactant to fall too, as shown in graph 2. The curve levels of nearer the end as a result of the amount of substrates was reducing. The decreased concentration of substrates causes the drop off of amount of product produced, this is the result of the enzyme finding it harder to find a substrate molecule that haven’t been reacted yet as well as products of previous reactions being in the way.

Rate of enzyme actions

  • Temperature

Lower temperatures means there is less kinetic energy in the molecules, so fewer successful collisions occur.

Optimum temperature for enzymes is the maximum amount of kinetic energy, thus successful collisions, before the enzyme begins to denature to excessive heat.

At high temperature there is an increase in kinetic energy and heat which causes the breakdown of hydrogen bonds, denaturing the tertiary structure of the active site and enzyme shape. At first enzymes fit less easily, therefore there is a slower rate of reaction.

Structure

pH

Only extreme pH causes denaturing

pH affects the amino acids of the enzyme as it changes the charge of them. This causes different molecules to bond to it, as a result the active site is different. This alters the tertiary structure.

Fluctuations in internal pH of small amounts does little however

Structure

Concentration of Enzymes

Low enzyme concentration means there are fewer active sites occupied. This means more active sites are available.

Increased enzymes concentration means more active sites available and the reaction can produced at a faster rate due to more successful collisions

Eventually increasing the enzyme concentration beyond a point means that there are too many enzymes to substrate.

 

Structure

Structure

 

  • Substrate Concentration

Low substrate concentration means there are fewer substrate sites occupied. This means more substrates are available.

Increased substrate concentration means more substrates available and the reaction can produced at a faster rate due to more successful collisions

Eventually increasing the substrate concentration beyond a point means that there are too many substrate to enzymes

Structure

Tests for Reducing Sugars
Test for Reducing Sugars

Tests for Reducing Sugars

What are Reducing Sugars?

sugar that serves as a reducing agent due to its free aldehyde or ketone functional groups in its molecular structure. Disaccharides are hydrolysed to their constituent monosaccharides when boiled in dilute hydrochloric acid.

The monosaccharide products of hydrolysis are reducing sugars i.e. have the aldehyde functional group and can reduce copper in the presence of alkali producing the colour changes. Examples are glucose, fructose, lactose, arabinose and maltose.

Biochemical test for Reducing Sugars: Benedict’s test

The principal reagent in Benedict’s Test for Reducing Sugars is Benedict’s Solution which contains:

  • Copper(II) Sulphate
  • Sodium Hydrogen Carbonate (NaHCO₃)
  • Sodium Citrate

Equipment:

  • 2cm3 of food sample (must be in liquidated form)
  • 2cm3 of benedict reagent (per sample)
  • Beaker
  • Clean, grease free test tube
  • Kettle/hot water source
  • mortar and pestle

Method:

A liquid food sample does not need prior preparation except dilution if viscous or concentrated.

For a solid sample prepare a test solution by crushing the food in a mortar and pestle, and adding a moderate amount of distilled water. Decant the suspension to remove large particles. Use the decanted liquid as the test solution.

  1. Add 2 cm3 of the sample solution to a test tube.
  2. Add 1 cm3 of dilute hydrochloric acid and boil for one minute.
  3. Allow the tube to cool and then neutralize the acid with Sodium Hydrogen Carbonate (NaHCO₃).
  4. Leave the test tube in a boiling water bath for about 5 minutes, or until the colour of the mixture does not change.
  5. Observe the colour changes during that time as well as the final colour.
  6. To prepare a control, repeat the steps using 2 cm3 of distilled water instead of sample solution.

Results:

Observation Interpretation
No Colour Change (Blue) No non-reducing sugars present
Green Trace amounts of non-reducing sugars present
Yellow Low amounts of reducing sugars present
Orange Moderate amounts of reducing sugars present
Brick Red Large amounts of non-reducing sugars present

 

The blue copper(II) ions from copper(II) sulphate in Benedict’s Reagent are reduced to red copper(I) ions by the aldehyde groups in the reducing sugars. This accounts for the colour changes observed.

The red copper(I) oxide formed is insoluble in water and is precipitated out of solution. This accounts for the precipitate formed.

As the concentration of reducing sugar increases, the nearer the final colour is to brick-red and the greater the precipitate formed.

Amino Acids
Amino Acids

Amino Acids

Amino Acids
Amino acid is a monomer.
chain of amino acids form polypeptides/dipeptides

Different amino acid have different R groups attached to them. The amino acid carboxyl group stays the same.
here are 20 amino acids naturally incorporated proteins:
Valine, Leucine, Alanine, Arginine, Proline, Cysteine, Threonine, Methionine, Histidine,
Glutamine, Lysine, Aspartic acid, Glutamic Acid, Serine, Phenylalanine, Tyrosine, Tryptophan, Asparagine, Glycine,
There are 8 amino acids which must be consumed through foods:
Histidine, Lysine, BCAAS (Branched Chain amino acid), Phenylalanine, Methionine
Dipeptides are formed by 2 amino acids in a condensation reactions.