Biological Molecules

Question 1

What is a monosaccharide?

Answer 1

A carbohydrate containing a single sugar molecule. Monosaccharides act as monmers for longer chain polysaccharides.

Question 2

What is A disaccharide?

Answer 2

A carbohydrate containing 2 sugar molecules joined by a glycosidic bond during a condensation reaction.

Question 3

What is a polysaccharide?

Answer 3

A carbohydrate made from multiple monosccharide monomers.

Question 4

What are the 3 main monosaccharides?

Answer 4

Glucose
Fructose
Galactose

Question 5

What are the 3 main disaccharides?

Answer 5

Maltose (2 Alpha glucose molecules)
Sucrose (1 Alpha glucose molecule and 1 fructose molecule)
Lactose (1 Alpha glucose molecule and 1 galactose molecule)

Question 6

What are the 3 main polysaccharides?

Answer 6

Starch (Polymer of Alpha glucose)
Glycogen (Polymer of Alpha glucose)
Cellulose (Polymer of Beta glucose)

Question 7

What is the test for reducing sugars (glucose, fructose, galactose, lactose and maltose)?

Answer 7

Benedicts test:
1. Crush or grind sample and mix strongly with water
2. Add Benedict’s reagent
3. Boil
4. A positive result is indicated by a clour change from blue to brick red (A semi-quantitative result gives a colour change from blue to green, yellow or brick red depending on concentration)

Question 8

What is the test for non reducing sugars (sucrose)?

Answer 8

Following a negative result for reducing sugars:
1. Add hydrochloric acid
2. Boil
(This hydrolyses Sucrose into glucose and Fructose)
3.Add sodium hydrogen carbonate to neutralise
4.Repeat Benedict’s test. A positive result indicates the presence of reducing sugars in the original sample.

Question 9

What is the structure of starch?

Answer 9

Starch is composed of 2 components - amylose and amylopectin (both polymers of alpha glucose):
Amylose - a long unbranched chain of alpha glucose that is tightly coiled allwing many glucose molecules to be stored in a small space

Amylopectin - a highly branched chain of alpha glucose. This provides a higher surface area allowing enzymes to quickly release sugars for respiration

Question 10

What is the structure of glycogen?

Answer 10

Highly branched structure of alpha glucose allowing enzymes to quickly release sugars for respiration.

Question 11

What is the structure of cellulose?

Answer 11

Long unbranched chain of beta glucose called microfibrils. As the hydroxyl groups on beta glucose molecules have different orientations, every second beta glucose molecule ust be inverted in order for a glycosidic bond to form. There are hydrogen bonds between microfibrils providing strength and rigidty to the cell wall.

Question 12

What are the 2 main lipid molecules?

Answer 12

Triglycerides and Phospholipids

Question 13

What is the structure of a triglyceride?

Answer 13

Consists of a glycerol molecule bonded to 3 fatty acid tails via ester bonds formed in a condensation reaction

Question 14

What is the structure of a phospholipid?

Answer 14

Consists of a hydrophilic phosphate head bonded to a glycerol molecule via a phosphodiester bond. The Glycerol molecule is bonded to 2 fatty acid tails via ester bonds.

Question 15

What is the difference betwenn saturated fatty acids and unsaturated fatty acids?

Answer 15

Saturated fats have no carbon - carbon double bond. This gives them a higher melting point and so are typically solid at room temperature. Unsaturated fats have at least 1 carbon - carbon double bond. This gives them a lower melting point and so are typically liquid at room temperature. The carbon - carbon double bond creates a kink in the structure which provides fluidity in the phospholipid bilayer of cell membranes.

Question 16

Why do phospholipid molecules form a bilayer in cell membranes?

Answer 16

The hyrophilic phosphate heads are attracted to the aqueous solutions on either side of the membrane and thus face both outsied and inside the cell. The hydrophobic tails are repelled by the aqueous solution either side of the membrane and thus occur between the hydrophilic heads.

Question 17

What are the 3 main nucleic acid?

Answer 17

DNA (Deoxyribose nucleic acid)
RNA (Ribonucelic acid)
ATP (Adenosine triphosphate)

Question 18

What is the monomer of nucelic acids?

Answer 18

Nucleotides

Question 19

What is the structure of a DNA nucleotide?

Answer 19

Consists of a phosphate head bonded to a deoxyribose molecule which is bonded to a nitrogen containing organic base ( either adenine, thymine, cytosine or guanine)

Question 20

What is the structure of a RNA nucleotide?

Answer 20

Consists of a phosphate group bonded to a ribose molecule which is bonded to a nitrogen containing organic base ( adenine, uracil cytosine or guanine).

Question 21

What is the structur of ATP?

Answer 21

Consists of an adenine base bonded to a ribose molecule bonded to 3 phosphate groups.

Question 22

What is the structure of a DNA molecule?

Answer 22

Nucleotides running antiparallel with hydrogen bonds between complementary base pairs on opposite nucleotides. There are phosphodiester bonds between adjacent nucleotides on the same strand.

Question 23

Describe the process of DNA replication?

Answer 23

1. DNA helicase breaks hydrogen bonds between complemeentary base pairs on opposite nucleotides. This results in the DNA double helix unwiding, exposing the bases on either strand.
2. Free nucelotides bind to the exposed bases on each strand of the unwound DNA molecule via hydrogen bonds
3. DNA polymerase joins the nucelotides together with phosphodiester bonds to form 2 identical DNA molecules.

This process is described as semi conservative as each new DNA molecule contains one template strand and 1 replicated strand.

Question 24

How did Meselsohn and Stahl prove that DNA replication was semi conservative?

Answer 24

DNA grown in Nitrogen 14 was less dense and thus when the DNA is centrifuged it forms a band close to the tops. DNA grown in Nitrogen 15 is more dense and thus forms a band close to a bottom. When bacteria grown in Nitrogen 15 was placed in Nitrogen 14 and grown for 1 generation, the DNA was centrifuged which formed a band in the middle proving the DNA molecules contained 1 strand of light DNA and 1 strand of heavy DNA.

Question 25

How does ATP release energy?

Answer 25

When it is hydrolysed, forming ADP and inorganic phosphate

Question 26

Why is ATP a good source of energy?

Answer 26

The unstable bonds between phosphate groups allow energy to be released immediately in one reaction. It releases less energy per molecule than glucose and is thus more manageable.

Question 27

What are the properties of water and why are they useful?

Answer 27

High specific heat capacity - Lots of energy is required to heat a given mass of water due to the hydrogen bonds. Therefore it acts as a buffer against sudden temperature change.

Cohesive - Due to hydrogen bonds, water us cohesive allowing it to be pulled upwards through a tube such as xylem. Water’s cohesive property also provides surface tension. This force is strong enough to support small organisms like pond skaters

High Latent heat of vaporisation - this means lots of energy is required to evaporat3e a given mass of water. This makes evaporation of water an effective method of cooling as heat is used to evaporate water.

Question 28

What are some uses of water?

Answer 28

1. Hydrolysing complex molecules
2. Photosynthesis
3. Aqueous solutions for chemical reactions
4. As a solvent for gases, waste products, inorganic ions, polar molecules
5. Hydrostatic skeletons (as water cannot be easily compressed)

Question 29

What is the structure of an amino acid?

Answer 29

Consists of an amine group, a carboxyl group and an R group.

Question 30

How is a peptide bond formed?

Answer 30

A condensation reaction between the carboxyl group of one amino acid and the amine group of another

Question 31

What are the different structure of proteins?

Answer 31

Primary - Sequence of amino acids

Secondary - Amino acids form localised hydrogen bonds forming either an alpha helix or beta pleated sheet

Tertiary - Disulfide bridges form between amino acids in the polypeptide. This provides the proteins 3D shape.

Quaternary - Containing multiple polypeptides

Question 32

What is the test for proteins?

Answer 32

Biurets Test:
1. Crush or grind sample
2. Add Biuret’s reagent
3. A positive result is indicated by a colour change from blue to purple

Question 33

What is an enzyme?

Answer 33

A globular protein which act as catalysts by lowering the activation energy of a reaction

Question 34

What is the induced fit model?

Answer 34

1. The active site and substrate are almost complementary
2. Interactions between the substrate and active site alter the tertiary structure of the enzyme so the shape of the active site so that it becomes complementary to the substrate
3. The substrate binds to the active site, forming an enzyme-substrate complex, and is hydrolysed

Question 35

What factors affect enzyme activity?

Answer 35

Temperature, pH, enzyme and substrate concentration, presence of inhibitors

Question 36

What is the difference between a competitive inhibitor and non competitive inhibitor?

Answer 36

Competitive inhibitor - Has a similar shape to the substrate and thus binds to the active site instead of the substrate. This prevents an enzyme-substrate complex from forming. Increasing substrate concentration decreases the affect of competitive inhibitors

Non competitive inhibitors - Bind to the allosteric site of an enzyme, temporarily changing the tertiary structure so that the enyme and active site are no longer complementary and an enzyme substrate complex can’t form. Increasing substrate concentration has no affect on the affect of non competitive enzymes.