Biological Molecules

Question 1

Monomers

Answer 1

Small units from which large molecules are made from

Question 2

Polymers

Answer 2

Molecules made from a large number of monomers joined together

Question 3

Glycosidic bond

Answer 3

• C–O–C link
• between two sugar molecules formed by a condensation reaction
• it is a covalent bond

Question 4

Condensation reaction

Answer 4

• A reaction that joins two molecules together
• with the formation of a chemical bond
• involves the elimination of a molecule of water

Question 5

Hydrolysis reaction

Answer 5

• A reaction that breaks a chemical bond
• between two molecules
• involves the use of a water molecule

Question 6

Describe the structure of DNA and the structure of a chromosome (6)

Answer 6

1. Polymer of nucleotides
2. DNA consists of deoxyribose, sugar, phosphate group and a nitrogenous base
3. Phosphodiester bonds between nucleotides
4. Hydrogen bonds between adenine, thymine and cytosine, guanine
5. Double helix held by hydrogen bonds
6. Associated with protein called histones

Question 7

Describe how a quaternary protein is formed from its monomers.
Do not include the process of translation in your answer. (5)

Answer 7

1. Amino acids are joined together by peptide bonds
2. By condensation reaction
3. Folding of the polypeptide chain and hydrogen binding results in the secondary structure
4. Tertiary structure is formed by R group interactions
5. Quaternary structure contains more than 1 polypeptide chains joined together

Question 8

Chitin is a polysaccharide. The chitin monomer is a B-glucose molecule with one OH group replaced by an NHCOCH, group. NHCOCH can be represented by N(Ac).
Chitin has a similar structure to cellulose.
Use Figure 1 to describe three ways the structure of chitin is similar to the structure of cellulose. {3}

Answer 8

1. Both has beta glucose
2. Joined together by glycosidic bonds (inverted 180)
3. Forms straight/ unbranched chains

Question 9

Suggest how the production of a protein with one amino acid missing may lead to a genetic disorder such as Ellis-van Creveld syndrome. (2)

Answer 9

1. Change in tertiary structure/
   active site;
2. (So) faulty/non-functional protein
   /enzyme;

Question 10

Describe the structure of a protein (5)

Answer 10

1. Polymer of amino acids;
2. Joined by peptide bonds;
3. Formed by condensation;
4. Primary structure is order of amino acids;
5. Secondary structure is folding of polypeptide chain due to hydrogen bonding;
   Accept alpha helix / pleated sheet
6. Tertiary structure is 3-D folding due to hydrogen bonding and ionic / disulfide bonds;
7. Quaternary structure is two or more polypeptide chains;

Question 11

Describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule. (3)

Answer 11

1. Condensation (reaction)/loss of water;
2. (Between) phosphate and deoxyribose;
3. (Catalysed by) DNA polymerase;

Question 12

Describe how monomers join to form the primary structure of a protein

Answer 12

1. Condensation reaction between amino acids;
2. (Forming) peptide bonds;
3. Creating (specific) sequence/order of amino acids;

Question 13

Explain how DNA replicates

Answer 13

• hydrogen bonds broken by DNA helicase
• semi-conservative replication / both strands used (as templates);
• nucleotides line up;
  complementary / specific base pairing / A and T / C and G;
• by DNA polymerase;

Question 14

Bacteria produce enzymes which cause food to decay. Explain how vinegar, which is acidic, can prevent the action of bacterial enzymes in some preserved foods. (3)

Answer 14

• (bacterial) active site/enzymes/proteins denatured / tertiary 3D structure disrupted/changed;
• (ionic) bonds broken; (reject peptide bonds) (ignore other bonds)
• no enzyme substrate complex formed / substrate no longer fits;

Question 15

Explain why triglycerides are not considered to be polymers. (1)

Answer 15

Not made of monomers

Question 16

Suggest why the water potential of apple juice decreases when apple are stored

Answer 16

Starch is hydrolysed
Maltose is soluble

Question 17

State how enzymes help reactions to proceed quickly at lower temperatures.

Answer 17

Lower/reduce activation energy (needed to start
a reaction

Question 18

What is an enzyme?

Answer 18

-Protein, biological catalyst
-lowers activation energy

Question 19

Describe how, after the parent DNA strands separated, the second strand of DNA in region Y was formed

Answer 19

• semi conservation replication
• complementary pairing
• hydrogen bonding of nucleotides
• condensation reaction
  -DNA polymerase

Question 20

Test for reducing and non reducing sugars

Answer 20

1. Add Benedict’s solution (blue) to sample
2. Heat in a boiling water bath
3. Positive result = green / yellow / orange / red precipitate

Question 21

test for non-reducing sugars (sucrose)

Answer 21

1. Do Benedict’s test and stays blue / negative
2. Heat in a boiling water bath with acid (to hydrolyse into reducing sugars)
3. Neutralise with alkali (eg. sodium bicarbonate)
4. Heat in a boiling water bath with Benedict’s solution
5. Positive result = green / yellow / orange / red precipitate

Question 22

Test for starch

Answer 22

1. Add iodine dissolved in potassium iodide (orange / brown) and shake / stir
2. Positive result = blue-black

Question 23

Suggest a method to measure the quantity of sugar in a solution

Answer 23

● Carry out Benedict’s test as above, then filter and dry precipitate
● Find mass / weight

Question 24

Test for lipids

Answer 24

Add ethanol & water: white emulsion

Question 25

Test for protein

Answer 25

add biuret, turns purple

Question 26

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

Answer 26

1. Substrate binds to active site 2. Active site changes shape so it is complementary to substrate 3. Reduces activation energy

Question 27

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

Answer 27

1. Different sequence of amino acids OR Different primary structure 2. Forms ionic / hydrogen / disulfide bonds in different places