Lipids & Proteins & Enzymes

Question 1

Triglycerides and Phospholipids are types of what?

Answer 1

Lipids

Question 2

What is a triglyceride made up of?

Answer 2

One glycerol molecule and three fatty acids attached.

Question 3

What makes a triglyceride insoluble in water?

Answer 3

The fatty acid tails are hydrophobic meaning they repel water.

Question 4

What are saturated and unsaturated fatty acids

Answer 4

Saturated = don’t have double bonds between carbon atoms.
Unsaturated = do have double bonds between carbon atoms. It means there are fewer hydrogen atoms and the chain may bend easier

Question 5

Describe the formation of a triglyceride.

Answer 5

The carboxyl group on the fatty acid reacts with the hydroxyl group on the glycerol to form 3 ester bonds and three water molecules released from a condensation reaction.

Question 6

What are the lipids found in cell membranes?

Answer 6

Phospholipids.

Question 7

Describe the structure of a phospholipid.

Answer 7

A glycerol molecule, two fatty acids and a phosphate group which acts as the hydrophilic head meaning it attracts water.

Question 8

How are the hydrophilic head and hydrophobic tail important to make up cell membranes?

Answer 8

They form a bilayer with the head facing out to the water. The centre is hydrophobic so water-soluble substances can’t pass through. The membrane acts as a barrier to those substances.

Question 9

How is a triglyceride related to its function?

Answer 9

• the long hydrocarbon tail contains lots of energy so when broken down, releases lots of energy. This makes them good for their function of energy storage molecules.
• insoluble in water so don’t affect water potential of the cell and cause water to enter by osmosis.

Question 10

Describe the test for lipids.

Answer 10

Emulsion test -
Add ethanol to the sample and then add water and shake for a minute
Milky white emulsion on top of the ethanol/water solution is a positive result.

Question 11

What is an Ester bond and where is it found?

Answer 11

An ester bond is the bond between fats after a water molecule is released. It is found between the hydroxyl group of glycerol and the carboxyl group of fatty acid.

Question 12

What are the lipids found in cell membranes?

Answer 12

Phospholipids

Question 13

What is the monomer of a protein?

Answer 13

Amino acids.

Question 14

What is a dipeptide?

Answer 14

Formed when two amino acids are joined together

Question 15

Describe the structure of an amino acid.

Answer 15

Carboxyl group (COOH)
Amino group (H2H)
R group

Question 16

What is the bond between amino acids?

Answer 16

Peptide bond.

Question 17

What is the only difference between the amino acid structures

Answer 17

What makes up the R group.

Question 18

Name 3 functions of proteins

Answer 18

Enzymes (like role in metabolism - breaking down food molecules)
Transport proteins (channel proteins in cell membranes to transport molecules)
Structural proteins
Antibodies

Question 19

Test for proteins

Answer 19

Biurets test. Add biurets reagent to sample and then shake and leave at room temp.
Blue indicates no protein (normal colour)
Positive result is a purple colour.

Question 20

Describe the primary structure of a protein.

Answer 20

Sequence of amino acids in the polypeptide chain joined together by peptide bonds

Question 21

Describe the secondary structure of a protein.

Answer 21

Polypeptide chain is held in a spiral shape. Hydrogen bonds form between the amino acids. Coils into an alpha helix/fold into beta pleated sheet.

Question 22

Describe the tertiary structure of a protein.

Answer 22

Further folding of the polypeptide chain into a 3D structure. Hydrogen and ionic bonds form between the chains. Disulfide bridges form too. This is the proteins final 3-D structure if it’s only a single polypeptide chain protein.

Question 23

Describe the quaternary structure of a protein.

Answer 23

Several polypeptide chains held together by bonds. They form functional proteins. (E.g haemoglobin,insulin.) this is the final 3-D structure if the protein is made from more than one polypeptide chain.

Question 24

Describe how a dipeptide is formed

Answer 24

A peptide bond forms between the carboxyl group of one amino acid and the amino group on the other amino acid. A molecule of water is released and the condensation reaction takes place.

Question 25

Describe the induced fit model of enzyme action.

Answer 25

New evidence suggests the shape of the active site is not exactly complementary to the substrate. When the substrate collides with the enzyme, the active site undergoes a slight change in its shape to allow a better fit between the active site and substrate, forming an E-S complex.

Question 26

What is an enzyme

Answer 26

Speed up chemical reactions by acting as biological catalysts. They are proteins with a 3D structure.

Question 27

What is an E-S complex?

Answer 27

(enzyme-substrate complex.) When a substrate interacts with an enzyme’s active site it forms an E-S complex.

Question 28

Explain how a change in the amino acid sequence of any enzyme may prevent it from functioning properly

Answer 28

A change in the amino acid sequence of an enzyme may alter its tertiary structure. This changes the shape of the active site so that the substrate can’t bind to it.

Question 29

How do the E-S complexes lower the activation energy?

Answer 29

The enzyme holds the two substrate molecules close together, reducing any repulsion between the molecules so they can bond more easily Or: If the enzyme is catalysing a breakdown reaction, fitting into the active site puts a strain on bonds in the substrate so the substrate molecule breaks up more easily

Question 30

What does the lock and key model show?

Answer 30

The substrate fits into an enzyme in the same way a key fits into a lock.

Question 31

Explain how a competitive inhibitor works.

Answer 31

Competitive inhibitor molecules have a similar shape to the substrate molecules. They compete with the substrate molecules to bind to the active site of an enzyme. when an inhibitor molecule is bound to the active site it blocks the substrate molecule from binding so no ES complexes are formed.

Question 32

Explain how a non competitive inhibitor works.

Answer 32

Non-competitive inhibitor molecules blind enzymes away from their active site. this breaks up some hydrogen bonds and forms incorrect ones in the tertiary structure changing the shape of the active site. This means the substrate molecule can no longer fit in, and no E-S complexes are formed.

Question 33

What factors affect enzyme activity?

Answer 33

Temperature pH Enzyme concentration Substrate concentration Inhibitors.

Question 34

How does temperature affect enzyme activity?

Answer 34

When the temperature is increased more heat means more kinetic energy some molecules collide more and so the number of ES complexes is increased.

Question 35

What happens when the temperature gets too high in an enzyme controlled reaction?

Answer 35

Bonds that maintain the tertiary structure are broken, the active site changes shape and the substrate and enzyme can no longer fit together at this point the enzyme is denatured.

Question 36

How does pH affect enzyme activity?

Answer 36

All enzymes have an optimum level. Above or below this level, bonds can be disrupted so tertiary structure changes so active site changes shape so enzyme is denatured.

Question 37

How does enzyme concentration affect the rate of reaction?

Answer 37

Increasing enzyme concentration increases the number of active sites available so more ES complexes can form. Rate of reaction will increase until the amount of substrate becomes the limiting factor as there are more enzymes than substrate.

Question 38

How does substrate concentration affect the rate of reaction?

Answer 38

The higher the substrate concentration, the faster the reaction. This is because more substrate molecules means a collision between substrate and enzyme is more likely and so more active sites will be used. Eventually, when all active sites are used, an increase in substrate concentration has no further effect. A decrease in substrate concentration will decrease the rate of reaction .

Question 39

What is a non-competitive inhibitor?

Answer 39

When a molecule attaches to a site on the enzyme away from the active site and causes the active site to change shape so it is no longer complementary to the substrate shape.

Question 40

State four roles of lipids

Answer 40

Insulate organisms, provide energy, form membranes and water proofing.

Question 41

Test for starch

Answer 41

Add iodine. If starch is present, the iodine will turn from brown/yellow to blue/black.

Question 42

Test for reducing sugars

Answer 42

Add Benedict’s reagent to the sample. Heat in a boiling water bath The solution will remain blue if not present Colour of precipitate indicates amount of sugar present. Brick red is strong, yellow is low, orange is moderate.

Question 43

Test for non-reducing sugars.

Answer 43

(Used if the reducing test is negative) Add dilute hydrochloric acid and heat in a water bath to break bonds Add an alkali to neutralise Add Benedict’s reagent to sample Heat in a boiling water bath Results will be brick red for high, orange for moderate

Question 44

How is a phospholipid different to a triglyceride?

Answer 44

Only 2 fatty acids compared to 3. Also has a phosphate group (head)

Question 45

How is a phospholipid similar to a triglyceride?

Answer 45

Both have fatty acids and one glycerol molecule.

Question 46

Describe how phospholipids can form a bilayer arrangement.

Answer 46

Hydrophilic head points outwards and hydrophobic tail points inwards

Question 47

What is the difference between primary and secondary structure of a protein?

Answer 47

Primary is the sequence of amino acids compared to the shape in which the chain forms due to hydrogen bonds.

Question 48

One role that phospholipids have in a cell

Answer 48

Make up cell membranes OR Hydrophobic regions act as a barrier to water-soluble substances

Question 49

One function of triglycerides and how this related to one of their properties

Answer 49

One function is they are energy storage molecules and the long hydrocarbon tails contain lots of chemicals energy to release

Question 50

Why do lipids give an emulsion is positive in the emulsion test?

Answer 50

They cannot dissolve in water so if they are present they form an emulsion

Question 51

Explain the shape of an enzyme curve that is gradually increasing to optimum temp and then decreasing.

Answer 51

• At low temperatures, the rate of reaction is slow as kinetic energy of enzyme and substrate is slow so less collisions. • Optimum temperature has high rate of reaction because of more kinetic energy so more successful collisions between enzyme and substrate •rate of reaction decreases as enzyme starts to denature because temperatures are too high

Question 52

What are unsaturated fatty acids and how does their fluidity change?

Answer 52

They are fatty acid chains that have a double carbon bond(s) so it has fewer hydrogen bonds and may bend easier, increasing fluidity