Lipids & Proteins & Enzymes Flashcards
Triglycerides and Phospholipids are types of what?
Lipids
What is a triglyceride made up of?
One glycerol molecule and three fatty acids attached.
What makes a triglyceride insoluble in water?
The fatty acid tails are hydrophobic meaning they repel water.
What are saturated and unsaturated fatty acids
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
Describe the formation of a triglyceride.
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.
What are the lipids found in cell membranes?
Phospholipids.
Describe the structure of a phospholipid.
A glycerol molecule, two fatty acids and a phosphate group which acts as the hydrophilic head meaning it attracts water.
How are the hydrophilic head and hydrophobic tail important to make up cell membranes?
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.
How is a triglyceride related to its function?
• 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.
Describe the test for lipids.
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.
What is an Ester bond and where is it found?
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.
What are the lipids found in cell membranes?
Phospholipids
What is the monomer of a protein?
Amino acids.
What is a dipeptide?
Formed when two amino acids are joined together
Describe the structure of an amino acid.
Carboxyl group (COOH)
Amino group (H2H)
R group
What is the bond between amino acids?
Peptide bond.
What is the only difference between the amino acid structures
What makes up the R group.
Name 3 functions of proteins
Enzymes (like role in metabolism - breaking down food molecules)
Transport proteins (channel proteins in cell membranes to transport molecules)
Structural proteins
Antibodies
Test for proteins
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.
Describe the primary structure of a protein.
Sequence of amino acids in the polypeptide chain.
Describe the secondary structure of a protein.
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.
Describe the tertiary structure of a protein.
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.
Describe the quaternary structure of a protein.
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.
Describe how a dipeptide is formed
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.
Describe the induced fit model of enzyme action.
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.
What is an enzyme
Speed up chemical reactions by acting as biological catalysts. They are proteins with a 3D structure.
What is an E-S complex?
(enzyme-substrate complex.)
When a substrate interacts with an enzyme’s active site it forms an E-S complex.
Explain how a change in the amino acid sequence of any enzyme may prevent it from functioning properly
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.
How do the E-S complexes lower the activation energy?
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
What does the lock and key model show?
The substrate fits into an enzyme in the same way a key fits into a lock.
Explain how a competitive inhibitor works.
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.
Explain how a non competitive inhibitor works.
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.
What factors affect enzyme activity?
Temperature
pH
Enzyme concentration
Substrate concentration
Inhibitors.
How does temperature affect enzyme activity?
When the temperature is increased more heat means more kinetic energy some molecules collide more and so the number of ES complexes is increased.
What happens when the temperature gets too high in an enzyme controlled reaction?
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.
How does pH affect enzyme activity?
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.
How does enzyme concentration affect the rate of reaction?
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.
How does substrate concentration affect the rate of reaction?
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 .
What is a non-competitive inhibitor?
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.
State four roles of lipids
Insulate organisms, provide energy, form membranes and water proofing.
Test for starch
Add iodine. If starch is present, the iodine will turn from brown/yellow to blue/black.
Test for reducing sugars
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.
Test for non-reducing sugars.
(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
How is a phospholipid different to a triglyceride?
Only 2 fatty acids compared to 3. Also has a phosphate group (head)
How is a phospholipid similar to a triglyceride?
Both have fatty acids and one glycerol molecule.
Describe how phospholipids can form a bilayer arrangement.
Hydrophilic head points outwards and hydrophobic tail points inwards
What is the difference between primary and secondary structure of a protein?
Primary is the sequence of amino acids compared to the shape in which the chain forms due to hydrogen bonds.
One role that phospholipids have in a cell
Make up cell membranes
OR
Hydrophobic regions act as a barrier to water-soluble substances
One function of triglycerides and how this related to one of their properties
One function is they are energy storage molecules and the long hydrocarbon tails contain lots of chemicals energy to release
Why do lipids give an emulsion is positive in the emulsion test?
They cannot dissolve in water so if they are present they form an emulsion
Explain the shape of an enzyme curve that is gradually increasing to optimum temp and then decreasing.
• 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
