Biological molecules

Question 1

What are the three types of bonding present in biological molecules?

Answer 1

Covalent bonding - two atoms sharing an outer electron.
Ionic bonding - ions with opposite charges attracting each other through electrostatic attraction. This is weaker than covalent bonding.
Hydrogen bonding - the electrons within a molecule are not evenly distributed, so they stay in one area making that area negatively charged. This makes a molecule polarized. The negative region of one atom is electrostatically attracted to the positive region of another. Individually, these are weak, but they can be strong collectively.

Question 2

What is a monomer?

Answer 2

A monomer is an individual sub units that make up a polymer.

Question 3

What is a polymer?

Answer 3

A polymer is many repeating units of sub units called monomers.

Question 4

What is polymerization?

Answer 4

The process where many monomers link together to create a chain, known as a polymer.

Question 5

What is a condensation reaction?

Answer 5

A condensation reaction occurs when during polymerization, sub units are joined together and a water molecule is formed.

Question 6

What is hydrolysis?

Answer 6

The reaction where a polymer is broken down through the addition of water into its constituent sub unit monomers.

Question 7

What is the metabolism?

Answer 7

All the chemical reactions that occur in a living organism.

Question 8

What is a mole and the Avogadro’s constant?

Answer 8

A mole of a substance contain the same amount of particles as the Mr amount of grams of that substance would have.

Question 9

What is the atomic number and the mass number?

Answer 9

The atomic number is the number of protons in an atom. The mass number is the number of protons and neutrons in an atom.

Question 10

What is an isotope?

Answer 10

An isotope is a type of atom with the same number of protons, but different number of neutrons. Therefore, the atomic number stays the same but the mass number changes.

Question 11

What are monosaccharides?

Answer 11

Simple sugars that are the building blocks of all sugars.

Question 12

What are the four monosaccharides?

Answer 12

Alpha-glucose, Beta-glucose, galactose and fructose.

Question 13

What is an isomer?

Answer 13

A compound that has the same formula but a different atom arrangement.

Question 14

Describe the atom arrangement of the two isomers of glucose.

Answer 14

Alpha glucose - a hexagon with one oxygen and 5 other carbons. The top two arms are H and the bottom two arms are OH.
Beta glucose - a hexagon with one oxygen and 5 other carbons. The left arms are H on top and OH on bottom. The right arms are OH on top and H on the bottom.

Question 15

What is a disaccharide and how does it form?

Answer 15

A disaccharide is when two monosaccharides join together. They are joined together by a condensation reaction, where a glycosidic bond is formed and a water molecule is released.

Question 16

What happens when water is added to a disaccharide in the right conditions?

Answer 16

A hydrolysis reaction occurs and the glycosidic bond is broken down to form the two constituent monosachharides.

Question 17

What are the three disaccharides and what are their monomers?

Answer 17

Maltose - two alpha-glucose.
Lactose - one alpha-glucose and one galactose
Sucrose - one alpha-glucose and one fructose

Question 18

What type of glycosidic bond occurs in disaccharide?

Answer 18

A 1,4 glycosidic bond.

Question 19

What are reducing sugars?
Name the examples.

Answer 19

Reducing sugars are sugars that can donate electrons (reduce) to other chemicals, in this case Benedict’s reagent. The examples are all monosaccharides and some disaccharides (maltose and lactose).

Question 20

What are non-reducing sugars?
Name the example.

Answer 20

Do not reduce other chemicals, so would not change the color of Benedict’s solution when heated with it. The example is the disaccharide sucrose.

Question 21

What is benedict’s reagent?

Answer 21

It is copper sulfate. When heated with reducing sugars it becomes a red solution of copper oxide.

Question 22

Name the process of testing for reducing sugars.

Answer 22

1. Add 2cm of the sample into a test tube. If not already liquid, grind up with water.
2. Add an equal amount of Benedict’s Reagent and heat up in a water bath.
3. If reducing sugar is present, the solution will turn from blue to (in order of concentration) green, yellow, orange and brick-red.

Question 23

Name the process of testing for non-reducing sugars.

Answer 23

1. Add 2cm of sample into a test tube. If not already liquid, grind up with water.
2. Add an equal amount of Benedict’s Reagent and heat up in a water bath.
3. If no color change occurs, no reducing sugar is present.
4. Add another 2cm sample into a different test tube with 2cm of hydrochloric acid and heat in a water bath. The HCL will hydrolyze the disaccharide into its constituent monosaccharides (which are reducing).
5. Add sodium hydrogen carbonate to neutralize the solution. This is because benedict’s reagent does not work in acidic conditions. Use a pH paper to check the solution is alkaline.
6. Re-test the new sample with Benedict’s solution. If a non-reducing sugar was present before, the solution will now turn orange-brown, as it has been hydrolyzed to a reducing sugar.

Question 24

What are polysaccharides?

Answer 24

Polysaccharides are formed when more than two monosaccharides are joined together by condensation reactions. They are very long molecules and are insoluble, making them good for storage. Some are used for strength and not just for storage, though (such as cellulose).

Question 25

What is starch and how is it formed?

Answer 25

Starch is a polysaccharide found in the form of grains or granules in plants. It is made up of many alpha-glucose monomers joined up by condensation reactions to make glycosidic bonds. It is the major energy source in most diets.

Question 26

What are the two main chains of starch?

Answer 26

1. Amylose is unbranched. The angles of the hydrogen bonds make it coiled, so it is compact and suitable for storage in small spaces. 2.Amylopectin is branched. Its side branches means it has many ends for enzymes to work on and break down the glycosidic bonds so glucose can be released quickly.

Question 27

Describe the structure of starch and how this aids its function.

Answer 27

Insoluble - does not affect osmosis or water potential of the cell. Large and insoluble - does not diffuse out of cells. Compact - can be stored in small spaces. Branched from many ends - enzymes can work simultaneously to work faster. Releases alpha-glucose - used for energy/respiration.

Question 28

How do you test for starch?

Answer 28

1. Add sample in a test tube. 2. Add iodine dissolved in potassium iodide to the test sample. 3. If starch is present, the sample will turn from brown-orange to blue-black.

Question 29

What is glycogen, how is it formed and what is its structure?

Answer 29

Glycogen is another polysaccharide made out of alpha-glucose molecules. However, unlike starch, it is stored in animals and not plants in the form of granules in the muscles and liver. It has the same structure as starch however is has many more branches. This is so enzymes can break it down faster as animals require energy a lot more and faster than plants due to having a higher metabolic rate and respiratory date due to them being more active.

Question 30

What is cellulose and how is it formed?

Answer 30

Cellulose is a polysaccharide made out long, unbranched, straight chains of beta-glucose molecules joined by glycosidic bonds. These straight chains form hydrogen bonds between parallel cellulose chains, which form cross-link bonds to make microfibrils. The strong microfibrils means that cellulose can provide strength to a plant cell.

Question 31

Explain the structure of cellulose.

Answer 31

Long, straight, unbranched chains. Parallel to each other and form cross-links of hydrogen bonds which makes them strong. These molecules link to make microfibrils, which link together again to make fibers, which again increase strength.

Question 32

What are lipids?

Answer 32

Lipids are not polymers and are made out of hydrogen, carbon and oxygen. They are insoluble in water, but soluble in organic solutes such as acetone and alcohol.

Question 33

What are the roles of lipids?

Answer 33

Source of energy - when oxidized they release twice the amount of energy and valuable water. Waterproofing - lipids are insoluble in water so many plants and insects produce waxy, lipid cuticles that conserve water. Insulation - fats are slow conductors of heat and when they are stored under the skin they can insulate the body's heat. They also act as electric insulators around the nerve cells in the myelin sheath. Protection - fats are often stored around delicate organs, such as around the liver.

Question 34

What are triglycerides?

Answer 34

Triglycerides are a type of lipids that are made out of 3 fatty acids and one glycerol molecule. Each fatty acid is joined to the glycerol by an ester bond through condensation reactions. When hydrolyzed, the triglyceride becomes three fatty acids and a glycerol molecule. Fatty acids have a hydrocarbon tail, which are hydrophobic, making fatty acids insoluble in water.

Question 35

What are fatty acids?

Answer 35

All fatty acids consist of a carboxyl group and a hydrocarbon tail, which varies. There are two types of fatty acids, saturated and unsaturated.

Question 36

What is the difference between the two types of fatty acids?

Answer 36

Saturated acids - have no c=c double bonds between their carbon atoms. The fatty acid is 'saturated' in hydrogen. Unsaturated acids - have a c=c double bond between their carbon atoms.

Question 37

Explain the structure and properties of triglycerides.

Answer 37

High energy source - they have long hydrocarbon chains which release a lot of energy when broken down. Insoluble in water- this is because they are large, non-polar molecules, so they do not affect the water potential of the atom. Low mass to energy ratio - they can store a lot of energy is a small mass. High ratio of hydrogen to carbon atoms, so they can release a lot of water when oxidized useful for animals in dry areas. Hydrophobic fatty acids so they face inwards, shielding themselves from water.

Question 38

What are phospholipids and what are they made out of?

Answer 38

These are the lipids found in the cell membranes. They have the same structure as a triglyceride except one of the fatty acids is replaced with a phosphate group. The phosphate group is hydrophilic, and the hydrocarbon tail is hydrophobic. Phospholipids are polar, meaning their phosphate heads are hydrophilic and face close to the water, whereas the hydrocarbon tails are hydrophobic and are as far away from the water as possible.

Question 39

What are the structure and properties of phospholipids?

Answer 39

Polar molecule so they can form a bilayer in an aqueous solution, such as in the cell membrane. This forms a hydrophobic barrier between the inside and the outside of the cell. The center is hydrophobic, so substances cannot pass through it, making the membrane a barrier to these substances. The hydrophilic phosphate heads help to hold at the surface of the membrane. The phospholipid structure allows them to form a glycolipid with carbohydrates in the cell membrane.

Question 40

Describe the test for lipids.

Answer 40

1. Take a dry and grease-free test tube. 2. Add ethanol to the sample. 3. Shake. 4. Add water and gently shake. 5. If lipid present, a white, milky emulsion is present. 6. As a control, repeat with just water and the solution should be clear.

Question 41

What are proteins?

Answer 41

Proteins are large molecules made from polypeptides, which are made up of amino acids. There are 20 amino acids.

Question 42

What is a dipeptide?

Answer 42

A dipeptide is made when two amino acids are joint through a condensation reactions, forming a peptide bond.

Question 43

What is a polypeptide?

Answer 43

When more than two amino acids join together together.

Question 44

Describe the structure of an amino acid.

Answer 44

Every amino acid has a central carbon to which is attached to four different chemical groups: 1. A hydrogen. 2. An amine group (NH2) 3. A carboxyl group (COOH) 4. A variable group (R).

Question 45

How does a peptide bond form?

Answer 45

A peptide bond occurs when hydrogens from one amine group of an amino acid bond with an oxygen from the carboxyl group of another amino acid, through a condensation reaction (water is formed).

Question 46

What are the four levels of the structure of protein.

Answer 46

Primary structure, secondary structure, tertiary structure and quaternary structure.

Question 47

Describe what the primary structure is.

Answer 47

Primary structure of a protein is the sequence of the amino acids that make up the polypeptide through polymerization (condensation of a series of amino acids). There are 20 amino acids, therefore many sequences. The sequence of amino acids determines the tertiary structure of the protein. A single change of amino acid can lead to change of tertiary structure and function of the protein.

Question 48

Describe what secondary structure is.

Answer 48

Once a polypeptide forms, hydrogen bonds form between the hydrogen of amine groups and oxygens of carboxyl groups. This causes the polypeptide to coil and fold into a 3D shape, forming either an alpha helix shape or a beta pleated sheet.

Question 49

Describe what tertiary structure is.

Answer 49

The coiled or folded polypeptides can fold and coil even further. This occurs from hydrogen bonds (weak), ionic bonds (stronger) and disulfide bridges(strong). If the protein is only made of one polypeptide, the tertiary structure determines its final shape (and function), which allows it to recognize or be recognized by other molecules. However, this is determined by the sequence (primary).

Question 50

Describe what quaternary structure is.

Answer 50

Quaternary structure occurs when the protein is made out of several polypeptide chains. These are assembled by bonds and determine the final 3D shape of a protein which has multiple polypeptide chains.

Question 51

Name proteins in living organisms which have different shapes for this function.

Answer 51

Enzymes - specific to substrates. Antibodies - specific to antigens. Transport proteins - have hydrophilic and hydrophobic amino acids to produce channels. Structural proteins - strong polypeptide chains joint by cross-links to parallel chains to coil together, causing support and strength (e.g. collagen is 3 tightly coiled polypeptide chains).

Question 52

What's the test for proteins?

Answer 52

1. Add the solution into a test tube, if not liquid grind with water. 2. Add sodium hydroxide to make alkaline. 3. Add biuret solution. 4. If protein present, it will turn from blue to purple.

Question 53

What are enzymes?

Answer 53

Enzymes are proteins that work as biological catalysts to speed up reactions without being chemically changed themselves. They can occur intracellular (in cells) or extracellular (outside of cells).

Question 54

Why are enzymes highly specific?

Answer 54

They have active sites which depend on their tertiary structure. The active site is complementary to a substrate.

Question 55

What is the activation energy?

Answer 55

The certain amount of energy that needs to be supplied for the reaction to take place. The particles must collide with sufficient energy to react. This means the products must have a lower energy level than the reactants.

Question 56

How do enzymes speed up the rate of reactions?

Answer 56

They lower the activation energy, meaning less energy needs to be supplied (for example, a lower temperature is required) for the reaction to take place. This occurs when the enzyme binds to its complementary substrate molecule to form enzyme-substrate complexes.

Question 57

What are the two ways in which enzymes work?

Answer 57

They need to lower the activation energy. Once the enzyme binds to the substrate it does one of two things: 1. If two substrate molecules need to bond, the enzyme binds to them both and holds them closer so they can bind regardless of any repulsion. 2. If it is catalyzing the breakdown of a reaction, it will bind to the substrate and put strains on the bonds, weakening them so they can break more easily.

Question 58

What is the lock and key model?

Answer 58

The early idea that enzymes had an active site which has a complementary substrate and they fit together (like a lock and key) to create enzyme-substrate complexes.

Question 59

What is the induced fit model?

Answer 59

Scientists figured out that once the enzyme binds to the substrate with the right shape, it molds the active site of the enzyme to form a functional active site. As it changes shape, the enzyme puts strains on the substrate's bonds, lowering the activation energy to break the bond. This makes enzymes very specific. Any change to the enzyme's environment changes its active site change. Colliding with the substrate is a change in the environment, therefore changes its active site shape.

Question 60

What decides an enzyme's properties?

Answer 60

An enzyme's tertiary structure, which determines the enzyme's shape and therefore its active site and its function. Tertiary structure can be affected by temperature and ph. It also depends on the primary structure. Primary structure can only be affected if there is a mutation in the genes, as genes are what decides the amino acids sequence.

Question 61

What are the two ways to measure the rate of a reaction?

Answer 61

There are two main ways: 1. Measure how much product is formed over time. As the reaction goes on, more product is formed until it is all formed. 2. Measure how much reactant is broken down. As the reaction goes on, more reactant is broken down until it is all broken down.

Question 62

How does the rate of enzyme action change?

Answer 62

At the start, there is a lot of substrate. This means there is a higher chance of it colliding with an enzyme and forming an enzyme-substrate complex. As the substrate is broken down, there are less substrates and more products. Therefore, the rate slows as there are less substrates to meet enzymes and the products get in the way. Eventually, the substrates are all broken down and the rate stops.

Question 63

How do you measure the rate of change on a graph?

Answer 63

Find the gradient by drawing a tangent.

Question 64

How does increasing temperature change the rate?

Answer 64

As temperature is increased, there is more kinetic energy. This means the particles are moving faster and therefore more likely to collide and form enzyme-substrate complexes. Furthermore, more molecules will collide with sufficient energy and reach the activation energy to react, therefore the rate increases. However, if temperature gets too high, the enzyme will begin to vibrate, which will break hydrogen bonds. This can change the tertiary structure so the enzyme will not work as well, until it has changes too much and will not form e-s complexes anymore, so it is said to be denatured.

Question 65

Why would increasing the body's temperature not be beneficial for speeding reactions?

Answer 65

Although it would raise the metabolic rate slightly, it will be offset by the additional energy (food) required to increase the temperature. Furthermore, other proteins that are not enzymes could denature. Finally, any other increase in the body's temperature (such as from illnesses) would cause the enzymes to denature.

Question 66

How does PH affect enzyme action?

Answer 66

All enzymes have an optimum PH value. It is usually 7, however some enzymes such as pepsin in the stomach work best at acidic conditions such as PH 2. The H+ and OH- in the acid or alkalis can disrupt with the hydrogen or ionic bonds in enzymes which hold the tertiary structure together. A change in PH can alter the amino acids which hold the active sites, which will change the enzyme's shape, so it becomes denatured.

Question 67

Why does PH fluctuating in living organisms not denature the enzymes?

Answer 67

It only occurs in small amounts, therefore it would only reduce the enzyme's activity for a while, not denature them.