Biological molecules

Question 1

What are the roles of iron ions?

Answer 1

-Form part of the ham group in haemoglobin.
-Haemoglobin binds to oxygen in roc and aids the transport of oxygen to respiring tissues.

Question 2

What are the roles of phosphate ions?

Answer 2

-Joins nucleotides in phosphodiester bonds.
-Used in atp synthesis
-Affects osmosis/water potential
-Hydrophillic/water soluble part of phospholipid bilayer.
-Posphorylates other compounds to make them more reactive.

Question 3

What are the roles of sodium ions?

Answer 3

-Affects osmosis/water potential
-Involved in the co transport of glucose.
-Sodium moved out by the na-k pump
- Creates concentration gradient of sodium

Question 4

How can high sodium concentrations affect blood volume?

Answer 4

-Sodium ions lower the water potential of blood/ make the water potential of blood more negative.
-Water moves into blood by osmosis from cells/tissues.
-Increases blood volume.

Question 5

How is an ATP molecule formed from its component molecules?

Answer 5

• Composed of adenine, ribose/pentose, 3 phosphates
• ATP synthase used
• Condensation reaction.

Question 6

Give an equation for ATP hydrolysis using pi as ATP hydrolase.

Answer 6

ATP + pi -> ADP + H2O

Question 7

How is ATP a suitable energy source for cells?

Answer 7

• Releases relatively small/ manageable amounts of energy, little energy lost as heat.
• Releases energy instantaneously, energy readily available.
• Phosphorylates other compounds, making them more reactive.
• Can be rapidly re-sythesised
  -Doesnt move out of cells.

Question 8

How is ATP resythesised in cells?

Answer 8

-From ADP and phosphate
-Using ATP synthase
- During respiration / photosynthesis.

Question 9

How is ATP hydrolysis used in cells?

Answer 9

• For other reactions/ named processes ( mitosis, ribosome synthesis, protein synthesis )
• For phosphorylation of other compounds to make them more reactive.

Question 10

State five properties of water.

Answer 10

Metabolite, solvent, high specific heat capacity, high latent heat of vaporisation, cohesion (accept hydrogen bonding).

Question 11

Explain the role of water as a metabolite.

Answer 11

A metabolite in hydrolysis/condensation/photosynthesis,respiration

Question 12

Explain the role of water as a solvent

Answer 12

-Allows metabolic reactions to occur(e.g. in the cytoplasm of cells)
-Allows the transport of substances (translocation)

Question 13

Explain the property of ‘high specific heat capacity’ for water.

Answer 13

• Buffers changes in temperature
• Useful as it makes it an ideal aquatic habitat, buffers temperature change in cells

Question 14

Explain the property of a ‘high latent heat of vaporistation’ for water.

Answer 14

-Provides a cooling effect- on animals and plants, as well it evaporates it takes lots of energy with it.

Question 15

Explain the property of ‘cohesion’ in water.

Answer 15

• Creates surface tension, supporting smaller organisms
• Supports columns of water in plants (e.g. transpiration stream, translocation.)

Question 16

Describe how you would test for the presence of lipid in a liquid food sample.

Answer 16

-If not a liquid, crush and add distilled water
- Add ethanol and shake.
-Then add water and shake again.
- Observe a milky/white emulsion.(ignore cloudy, reject precipitate)

Question 17

Describe how you would test for the presence of lipids on a solid food sample

Answer 17

-Dissolve in ethanol, add water.
-White emulsion shows the presence of a lipid.

Question 18

Describe how a triglyceride molecule is formed

Answer 18

• ONE glycerol and THREE fatty acids
• Condensation reaction leads to the removal of THREE molecules of water.
• Three ester bonds formed.

Question 19

Describe how an ester bond is formed in a phospholipid molecule.

Answer 19

-Condensation reaction / loss of water
-Between glycerol and fatty acid

Question 20

Describe the chemical reactions involved in the conversion of polymers to monomers and monomers to polymers.
Give two named examples of polymers and their associated monomers to illustrate your answer.

Answer 20

-A condensation reaction joins monomers together and forms a (chemical) bond and releases water
-A hydrolysis reaction breaks a (chemical) bond between monomers and uses water
-nucleotide and polynucleotide, DNA or RNA
- Alpha glucose and starch/glycogen
- Beta glucose and cellulose.
-Reference to a correct bond within a named polymer- e.g. glycosidic, peptide etc.

Question 21

Describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst.

Answer 21

-Substrate binds to the active site of an enzyme
-Enzyme-substrate complex forms
-Active site changes shape slightly so it is complimentary to the substrate
OR
-Active site changes shape slightly so distorting/breaking bonds in the substrate
-Reduces activation energy.

Question 22

A competitive inhibitor decreases the rate of an enzyme-controlled reaction.
Explain how.

Answer 22

-Inhibitor has a similar shape to substrate
-Fits/binds to the active site
-Prevents/reduces enzyme-substrate complex from forming

Question 23

When bread becomes stale, the structure of some of the starch is changed. This changed starch is called retrograded starch.
Scientists have suggested retrograded starch is a competitive inhibitor of amylase in the small intestine.
Assuming the scientists are correct, suggest how eating stale bread could help to reduce weight gain.

Answer 23

-Less hydrolysis of starch
-To maltose
-So less absorption of glucose

Question 24

Describe how the structure of a protein depends on the amino acids it contains.

Answer 24

-Structure is determined by relative position of Amino acid/ R group interactions
-Primary structure is the sequence of amino acids
-Secondary structure is formed by hydrogen bonding between amino acids (accept alpha helix/beta pleated sheet)
-Tertiary structure is formed by interactions between the R groups forming ionic bonds, hydrogen bonds, and disulphide bridges.
-Creates active site in enzymes and creates complementary/ specific shapes in antibodies/carrier proteins/receptor molecules.
-Quarternary structure formed by interactions between polypeptides.

Question 25

Describe how amino acids join to form a polypeptide so there is always NH2 at one end and COOH at the other end.

Answer 25

-One amine/NH2 group joins to a carboxyl/COOH group to form a peptide bond -So in chain there is a free amine/NH2 group at one end and a free carboxyl/COOH group at the other OR -Each amino acid is orientated in the same direction in the chain

Question 26

Explain how the active site of an enzyme causes a high rate of reaction

Answer 26

-Lowers activation energy -Induced fit causes active site (of enzyme) to change shape -So enzyme-substrate complex causes bonds to form/break

Question 27

Describe a biochemical test to confirm the presence of protein in a solution.

Answer 27

-Add biuret reagent -Positive result purple/lilac/violet /mauve;

Question 28

Describe three ways in which all dipeptides are similar and one way in which they might differ.

Answer 28

Similarities -The type of amino acids they contain -Amine (NH2 or NH3) group at end -Carboxyl (COOH or COO-) group at end -All contain C and H and N and O Differences -Variable/different R group(s);

Question 29

Describe how a non-competitive inhibitor can reduce the rate of an enzyme-controlled reaction.

Answer 29

-Attaches to the enzyme at a site other than the active site (Accept ‘attaches to allosteric/inhibitor site’) -Changes shape of the active site OR -Changes tertiary structure of enzyme -So active site and substrate no longer complementary so less/no substrate can fit/bind

Question 30

Describe how a peptide bond is formed between two amino acids to form a dipeptide.

Answer 30

-Condensation (reaction) / loss of water -Between amine / NH2 and carboxyl / COOH

Question 31

The secondary structure of a polypeptide is produced by bonds between amino acids. Describe how.

Answer 31

-Hydrogen bonds -Between NH group of one amino acid and C=O group of another OR Forming β pleated sheets / α helix

Question 32

Two proteins have the same number and type of amino acids but different tertiary structures. Explain why.

Answer 32

-Different sequence of amino acids OR -Different primary structure -Forms ionic / hydrogen / disulfide bonds in different places

Question 33

Formation of an enzyme-substrate complex increases the rate of reaction. Explain how.

Answer 33

-Reduces activation energy -Due to bending bonds OR -Without enzyme, very few substrates have sufficient energy for reaction

Question 34

The genetic code is described as degenerate. What is meant by this?

Answer 34

-More than one codon codes for a single amino acid -If a table is provided, use an example

Question 35

Describe a biochemical test to show that raffinose solution contains a non-reducing sugar.

Answer 35

-Heat with acid and neutralise -Heat with benedicts solution -Brick red precipitate/colour.

Question 36

A precipitate is produced in a positive result for reducing sugar in a Benedict’s test. A precipitate is solid matter suspended in solution. A student carried out the Benedict’s test. Suggest a method, other than using a colorimeter, that this student could use to measure the quantity of reducing sugar in a solution.

Answer 36

-Filter and dry (the precipitate) -Find mass/ weight using balance

Question 37

What is a monomer?

Answer 37

-Unit/molecule from which larger molecules/ polymers are made.

Question 38

Lactulose is a disaccharide formed from one molecule of galactose and one molecule of fructose. Other than both being disaccharides, give one similarity and one difference between the structures of lactulose and lactose.

Answer 38

-Both contain galactose / a glycosidic bond -Lactulose contains fructose, whereas lactose contains glucose

Question 39

Glycogen and cellulose are both carbohydrates. Describe two differences between the structure of a cellulose molecule and a glycogen molecule.

Answer 39

-Cellulose is made up of β-glucose monomers and glycogen is made up of α-glucose monomers - Cellulose molecule has straight chain and glycogen is branched - Cellulose molecule has straight chain and glycogen is coiled - Glycogen has 1,4- and 1,6- glycosidic bonds and cellulose has 1,4- glycosidic bonds

Question 40

Starch is a carbohydrate often stored in plant cells. Describe and explain two features of starch that make it a good storage molecule.

Answer 40

-Insoluble in water so doesn’t affect water potential -Branched / coiled / (α-)helix, so makes molecule compact OR Branched / coiled / (α-)helix so can fit many molecules in small area - Polymer of (α-)glucose so provides glucose for respiration -Branched / more ends for fast breakdown / enzyme action -Large molecule, so can’t cross the cell membrane and doesn't move out of cells.

Question 41

Describe the structure of glycogen.

Answer 41

-Polysaccharide of alpha glucose -Joined by glycosidic bonds OR Branched structure

Question 42

Name the type of chemical bond that joins the two monomers to form maltose.

Answer 42

Glycosidic

Question 43

Explain the difference in the structure of the starch molecule and the cellulose molecule

Answer 43

-Starch formed from alpha glucose but cellulose formed from beta glucose -Position of hydrogen and hydroxyl groups on carbon atom 1 inverted.

Question 44

Explain three ways in which starch molecules are adapted for their function in plant cells.

Answer 44

-Insolouble so it doesn't effect water potential -Helical so it is compact -Large molecule so it cannot leave the cell

Question 45

Explain how cellulose molecules are adapted for their function in plant cells.

Answer 45

-Long and straight chains -Become linked together by many hydrogen bonds to form fibrils -Provide strength to cell wall.