Bio molecules

Question 1

Monomers

Answer 1

1. Glucose
2. Glycerol
3. Fatty acid
4. Amino acids

Question 2

Structure and function of glucose

Answer 2

S:
- C6H12O6
- alpha glucose: Hydroxyl group on carbon-1 projecting below the ring
- beta glucose: Hydroxyl group on carbon-1 projecting above the ring

F:
- Monomers of polysacharrides

• Acts as a substrate for the production of energy in the form of adenosine triphosphate (ATP)

Question 3

Structure and function of glycerol

Answer 3

S:
- An alcohol, which has 3 carbon, each attached to a hydroxyl (-OH) group

F:
- Monomers of lipids

Question 4

Structure and function of fatty acid

Answer 4

S:
- Consists of a hydrophobic hydrocarbon chain and hydrophilic carboxyl group

• General formula: R-COOH, where R is the hydrocarbon chain
• Saturated fatty acids: contains carbon-carbon single bonds
• Unsaturated fatty acids: contains carbon-carbon double bond, resulting in kinks that prevent the tight packing of fatty acid chains

F:
- Monomers of lipids

Question 5

Structure and function of amino acids

Answer 5

S:
Central carbon atom bonded to:
- hydrogen atom
- basic amino (-NH2) group
- acidic carboxyl (-COOH) group
- R group/side chain which is unique to each amino acid

Uncharged R group -> amino acid is non-polar/polar

Charged R group -> amino acid is basic/acidic

F:
- Monomers of proteins

Question 6

Formation and breakage of glycosidic bonds (between monosaccharides)

Answer 6

Formation:
- Formed by condensation reaction between 2 monosaccharides with the removal of 1 molecule of H2O

Breakage:
- Broken by hydrolysis reaction between 2 monosaccharides, with the addition of 1 molecule of H2O, to form a hydroxyl group on each monosaccharide

Question 7

Formation and breakage of ester bonds (between fatty acid and glycerol)

Answer 7

Formation:
- Formed by condensation reaction between hydroxyl group of glycerol and carboxyl group of fatty acid, with the removal of 3 molecules of H2O

Breakage:
- Broken by hydrolysis with the addition of 3 molecules of H2O, to form a hydroxyl group on a glycerol and a carboxyl group on the fatty acid

Question 8

Formation and breakage of peptide bonds (between amino acids)

Answer 8

Formation:
- Formed between the carboxyl group of one amino acid and the amino group of another in a condensation reaction, with the removal of one molecule of water

Breakage:
-Broken between two amino acids during hydrolysis reaction with the addition of one molecule of water, to form the amino group and the carboxyl group on two different amino acids

Question 9

Polysaccharides

Answer 9

1. Starch
2. Glycogen
3. Cellulose

Question 10

Lipids

Answer 10

1. Triglycerides
2. Phospholipids
3. Cholesterol

Question 11

Properties of starch

Answer 11

1. Large and thus insoluble in water, exerts no osmotic effect on cells when stored in large amounts
2. Large and thus unable to diffuse out of cells
3. Fold into compact shaped, hence large amounts can be stored within the cell
4. Easily hydrolysed into glucose when glucose is needed for metabolic reactions

Question 12

Properties of glycogen

Answer 12

1. Large and thus insoluble in water, exerts no osmotic effect on cells when stored in large amounts
2. Large and thus unable to diffuse out of cells
3. Fold into compact shaped, hence large amounts can be stored within the cell
4. Easily hydrolysed into glucose when glucose is needed for metabolic reactions

Question 13

Properties of cellulose

Answer 13

1. Unbranched polymer
2. Form straight chains, which is ideal for formation of strong fibers

Question 14

Structure and function of starch

Answer 14

S:
- Alpha glucose
- Amylose and amylopectin fit together to form a complex three-dimensional structure in which the amylose helices are entangled in the branches of the amylopectin molecules
- Amylose:
1. Consists of several thousand alpha glucose residues
2. Linked by alpha-1,4-glycosidic bonds
3. Unbranched chain polymer
4. Coils into a helical, compact structure stabilized by hydrogen bonds

Amylopectin:
1. Consists of several thousand alpha glucose residues
2. Linked by alpha-1,4-glycosidic bonds
3. Branched chain polymer
4. Coils into a helical, compact structure stabilized by hydrogen bonds

F:
1. Main energy storage molecule in plants
2. Accumulates to form starch grains in chloroplasts of plant cells
3. Compact structure allows more glucose molecules to be stored in a small volume within the cell
4. Easily hydrolysed into glucose, when required by cells, for use in respiration to produce ATP

Question 15

Structure and function of glycogen

Answer 15

S:
1. Consists of alpha-glucose residues
2. Linked by alpha-1,4-glycosidic bonds and alpha-1,6-glycosidic bonds where branch point occurs
3. More extensive branching as compared to amylopectin which results in a more compact structure
4. Coils into a helical compact structure stabilized by hydrogen bonds

F:
1. Main energy storage molecule in animals
2. Accumulates to form glycogen granules in liver and muscle cells
3. Compact structure allows more glucose molecules to be stored in a small volume within the cell
4. Easily hydrolysed into glucose, when required by cells, for use in respiration to produce ATP

Question 16

Structure and function of cellulose

Answer 16

S:
1. Consists of beta-glucose residues
2. Linked by beta-1,4-glycosidic bonds
3. Unbranched chain polymer
4. Straight chains of beta-glucose run parallel to each other with numerous hydrogen bonds
5. Adjacent glucose molecules are rotated 180 degrees with respect to each other
6. Macrofibrils of successive layers are interwoven and are embedded in a gel-like matrix, thus having high tensile strength

F:
1. Main component of cellulose cell wall of plants for structural support
2. Large intermolecular spaces between microfibrils cause the cell wall to be permeable because they allow free movement of molecules in and out of the cell

Question 17

Properties of phospholipids

Answer 17

1. Amphipathic because contain a hydrophilic phosphate head and 2 hydrophobic fatty acid chains

Thus, head of molecule is soluble in water but the tails are insoluble in water

Question 17

Properties of triglycerides

Answer 17

1. Insoluble in water, soluble in organic solvents
2. Less dense than water and hence floats on the surface of water
3. Can be classified as oils and fats
4. The more saturated the triglyceride is, the higher the melting point of the triglycerides

Question 18

Properties of cholesterol

Answer 18

1. Insoluble in water because non-polar
2. Soluble in organic solvents

Question 19

Structure and function of triglycerides

Answer 19

S:
1. Consists of 1 glycerol molecule bonded to 3 fatty acid chains in a condensation reaction
2. Fatty acid is made up of a hydrophobic hydrocarbon chain and a hydrophilic carboxyl group

F:
1. Energy storage because can be used to produce energy in the form of ATP
2. Heat insulation because poor conductor of heat
3. Protection from shock and physical impact
4. Buoyancy

Question 20

Structure and function of phospholipids

Answer 20

S:
1. Consists of 1 glycerol, 2 fatty acid chains, 1 phosphate group

F:
1. Forms the basic structure of the cell surface membrane and the internal membranes of cells called the phospholipid bilayer
2. Arrangement of phospholipid in the form of a bilayer allows it to form a barrier in an aqueous environment
3. Can associate with hydrophilic oligosaccharides to form glycolipids which help in cell-cell recognition and cell-cell adhesion

Question 21

Structure and function of cholesterol

Answer 21

S:
1. Hydrophilic region interacts with hydrophilic phosphate heads of phospholipid molecules
2. Hydrophobic region interacts with hydrophobic fatty acid tails of the phospholipid bilayer
3. Cholesterol is interspersed among the bilayer to hinder the close packing of phospholipids

F:
1. Regulates membrane fluidity
2. Maintains mechanical stability
3. Prevents leakage of small polar molecules

Question 22

Structure of proteins

Answer 22

1. Primary
2. Secondary
3. Tertiary
4. Quartenary

Question 23

Primary structure

Answer 23

Types of bonds involved:
- Peptide bonds formed between carboxyl group of one amino acid and amino group of another amino acid

Primary structure is the specific number and sequence of amino acids joined by peptide bonds in a polypeptide chain

Sequence:
- Every protein molecule has a unique sequence of amino acids which is determined by the base sequence of DNA
- The unique sequence of amino acids with its side chains of different chemical and physical properties determines the three-dimensional conformation of the protein

Number:
- Every polypeptide possess a carboxyl terminus (C-terminus) and amino terminus (N-terminus)
- The possible amino acid residues in a polypeptide chain can be of any number and arrangement of the 20 common amino acids

Question 24

Secondary structure

Answer 24

Types of bonds involved: - Hydrogen bonds formed between N-H group in a peptide bond of one amino acid and C=O group group in a peptide bond of another amino acid Secondary structure is the repeated coiling and folding of a polypeptide chain, maintained by hydrogen bonds formed between peptide bonds Alpha-helix 1. Unbranched polypeptide chain tightly coiled into a spiral 2. Each turn of a helix consists of 3.6 amino acids 3. Held by intra-chain H-bond between N-H group in a peptide bond of one amino acid and C=O group in a peptide bond of another amino acid, four amino acids away 4. Structurally strong and inelastic (cannot be stretched) but flexible (can be bent) eg. hair, nails Beta-pleated sheets 1. Extended adjacent regions of a single polypeptide chain arranged in a parallel manner 2. “Pleated” appearance arises from the tetrahedral chemical bonding of alpha-carbon atoms 3. Held together by H bonds between N-H group in a peptide bond of one amino acid and C=O group in a peptide bond of an adjacent amino acid of the same chain 4. Very stable and rigid, high tensile strength (cannot be stretched) eg. silk, fibroin protein

Question 25

Tertiary structure

Answer 25

Types of bonds involved: - Hydrogen bonds between an electronegative atom and a hydrogen atom bonded to another electronegative atom (FON) (between 2 peptide bonds/ between peptide bond and R group/ between 2 R groups) - Ionic bonds between positively and negatively charged R groups - Disulfide bonds between sulphydryl (-SH) groups of two neighbouring cysteine R groups - Hydrophobic interactions between nonpolar R groups Tertiary structure is the compact unique three-dimensional conformation due to further coiling and folding of the secondary structure Tertiary structure is the compact unique three-dimensional conformation due to further coiling and folding of the secondary structure

Question 26

Quaternary structure

Answer 26

Types of bonds involved: Involves inter-chain interactions: - H-bond - Ionic - Disulfide - Hydrophobic interactions Involves intra-chain interaction seen in pri, sec, ter structures: - Peptide - H-bond - Ionic - Disulfide - Hydrophobic interactions Quaternary structure is when more than one polypeptide chains are held together by hydrogen bonds, ionic bonds, sulfide bonds and hydrophobic interactions between R groups of different polypeptide chains

Question 27

Proteins

Answer 27

1. Haemoglobin 2. Collagen 3. G-protein linked receptor 4. Intrinsic

Question 28

Structure and function of haemoglobin

Answer 28

S: Polypeptide chains: - 2 identical alpha-chains of 141 amino acids - 2 identical beta-chains of 146 amino acids - each p chain coiled into alpha-helices then folded into spherical shape (no beta-pleated sheets) - 4 polypeptide chains held by hydrophobic interactions, ionic bonds and hydrogen bonds Haem group: - Fe2+ binds to O2 reversibly - Each haem group resides in hydrophobic pocket in the tertiary structure of a polypeptide chain - 1 haemoglobin, 4 polypeptide chains, 4 haem groups, 4 O2 S to F: 1. Hydrophobic amino acids in the interior of the protein and hydrophilic amino acids found at the exterior surface of the protein… …allows the haemoglobin to be soluble, to take part in chemical reactions 2. The haem group is held in the hydrophobic pocket of the polypeptide chain… …allows the haemoglobin to bind reversibly to oxygen and transport oxygen to the rest of the body 3. Quaternary structure, of 4 subunits, held by weak bonds such as hydrophobic interactions, ionic bonds, hydrogen bonds… …allows cooperative binding of oxygen to haemoglobin …binding of one O2 molecule to one subunit results in a conformation change of the adjacent subunits in the haemoglobin molecule, making it easier for another O2 molecule to bind with the other haem groups in the molecule -> increases rate of uptake of O2 by haemoglobin 4. Haemoglobin is a globular protein and is folded into a spherical shape… …allows the protein to be compact and many haemoglobin molecules to be dissolved in the cytoplasm of a rbc

Question 29

Structure and function of collagen

Answer 29

S: Structural unit of collagen: Tropocollagen - comprises 3 polypeptide chains wound around each other to form a triple helix Each p chain: - 1050 amino acid residues - repeated triplet seq of Gly-Proline-Hydroxyproline - proline and hydroxyproline is bulky and relatively inflexible - coiled into a helix S to F: 1. Every 3rd amino acid residue is a glycine -> allows each helical chain to make a turn every 3 residues and intertwine around 2 other chains to form the tropocollagen (only glycine is small enough to fit into the centre)... …allows the structure to be compact 2. 3 helical chains are held together by hydrogen bonds forming tropocollagen… …allows the structure to be relatively rigid 3. Hydrophobic amino acids found at exterior surface of collagen… …allows collagen to be insoluble and metabolically inactive, thus resistant to chemical changes 4. Many triple helices lie parallel in a staggered pattern to form fibrils with covalent bonds between neighbouring triple helix chains. Fibrils unite to form fibers… …allows collagen to have high tensile strength, thus resistant to stretching

Question 30

Structure and function of G-protein linked receptor

Answer 30

S: - Each GPLR is closely associated with a G protein, a protein that binds to GTP/GDP - G protein consists of 3 subunits - Galpha, Gbeta, Gy - Galpha subunit binds to GDP/GTP - GTP is an energy molecule similar to ATP S to F: 1. A single polypeptide chain with 7 hydrophobic transmembrane alpha-helices… …allows the protein to be embedded within the cell membrane by forming hydrophobic interactions with the fatty acid chains of the phospholipid bilayer 2. Extracellular amino terminus and specific loops between the helices… …allows the protein to have an extracellular ligand-binding site 3. Intracellular carboxyl terminus and specific loops between the helices… …allows the protein to have an intracellular G protein-binding site

Question 31

Structure and function of intrinsic protein

Answer 31

S: - Unilateral (embedded in monolayer) - Transmembrane (embedded in bilayer) S to F: 1. Embedded in hydrophobic core of phospholipid bilayer... ...Hydrophobic region forms hydrophobic interactions with the hydrophobic fatty acid tails of the phospholipid bilayer Hydrophilic region forms hydrogen bonds with aqueous medium and hydrophilic phosphate head of the phospholipid molecules

Question 32

Defn. Denaturation

Answer 32

The loss of the specific 3-dimensional conformation of a protein molecule. This involves the breakage of bonds maintaining the protein structure, resulting in the protein losing its biological function.

Question 33

Factors causing denaturation and bonds involved

Answer 33

1. Temp. - hydrophobic interactions & hydrogen bonds & ionic bonds 2. pH - hydrogen bonds & ionic bonds 3. Heavy metal ions - ionic bonds 4. Reducing/ oxidising agents - Disulfide bonds 5. Organic solvents and detergents - hydrophobic interactions and hydrogen bonds

Question 34

Temp. causing denaturation

Answer 34

1. High temperature increases kinetic energy and causes atoms in protein to vibrate 2. therefore, disrupting the weak hydrophobic interactions, hydrogen bonds and ionic bonds

Question 35

pH causing denaturation

Answer 35

1. Drastic change in pH affects charged and polar R-groups and disrupts ionic bonds and hydrogen bonds of proteins

Question 36

Heavy metal ions causing denaturation

Answer 36

1. Heavy metal ions are positively charged and form strong bonds with negatively charged carboxyl R-groups of proteins, disrupting ionic bonds

Question 36

Reducing/oxidising agents causing denaturation

Answer 36

1. Disrupts disulfide bonds formed between cysteine, thus causing proteins to lose their 3-dimensional conformation

Question 37

Organic solvents and detergents causing denaturation

Answer 37

1. Disrupts hydrogen bonding and hydrophobic interactions of proteins