Biological molecules

Question 1

Hydrogen bonds in water

Answer 1

• Oxygen attracts the electrons towards itself, becoming slightly negative
• The hydrogen molecules become slightly positive
• Hydrogen bonds form between slightly negative oxygens and slightly positive hydrogens

Question 2

Hydrogen bonds and properties of water

Answer 2

• good solvent, as can interact with other polar/charged molecules due to hydrogen bonds
• cohesive, as hydrogen bonds stick water molecules together
• density: ice is less dense as hydrogen bonds form a lattice
• high specific heat capacity, as lots of energy is needed to raise the temperature of water
• liquid across a variety of temperatures

Question 3

Importance of properties of water (6)

Answer 3

• good solvent: metabolic processes rely on chemical reactions occurring in solution
• liquid: good transport medium for transporting materials around organisms
• cohesive: creates surface tension as a habitat and prevents columns of water breaking
• freezing at lower density: water below is insulated (whole lake won’t freeze), provides a habitat
• thermal stability: large bodies of water have fairly constant temperatures, evaporation can cool surfaces
• metabolic: takes part in chemical processes

Question 4

Structure of amino acids

Answer 4

H H O amino group (NH2)
N C C acid group (COOH)
H R OH R group

Question 5

Forming peptide bonds

Answer 5

OH (from acid group) and H (from amino group) form water in a condensation reaction. End up with a peptide bond of:
l
C=O
 l
N-H
 l

Question 6

Breaking peptide bonds

Answer 6

Hydrolysis reaction. OH from water goes to C=O (bonds to carbon), H from water goes to N-H

Question 7

Primary structure

Answer 7

The sequence of amino acids in a polypeptide/protein

Question 8

Secondary structure

Answer 8

Coiling and pleating (alpha helix and beta pleated sheets) of parts of the polypeptide molecules. Held together by hydrogen bonds between carbon-nitrogen backbone (C=O—-H-N) not between R-groups.

Question 9

Tertiary structure

Answer 9

Overall 3D structure of the final polypeptide/protein molecule. Held together by: disulfide bonds, ionic bonds, hydrogen bonds, hydrophobic and hydrophilic interactions. Hydrophobic R-groups will be held together with water excluded; hydrophilic groups will be on the outside

Question 10

Quaternary structure

Answer 10

More than one polypeptide subunit joined together. Protein formed can’t function if not all subunits are present.

Question 11

Haemoglobin as a protein

Answer 11

• 4 polypeptide subunits
• 1 prosthetic group on each chain: a haem group with Fe2+ ion
• Globular protein: vital tertiary structure
• Soluble in water
• Wide range of amino acids in primary structure
• Many alpha helix structures

Question 12

Collagen molecule as a protein

Answer 12

• Fibrous protein
• Insoluble in water
• Not much variety in amino acids: 35% is glycine
• No prosthetic groups
• Many left-handed helix structures

Question 13

Structure of collagen fibres

Answer 13

• Collagen molecules form staggered cross links with adjacent collagen molecules
• This makes collagen fibril
• Many fibrils together become collagen fibres.

Question 14

Function of haemoglobin

Answer 14

Carry oxygen from lungs to tissues.

Question 15

Function of collagen

Answer 15

Provide mechanical strength:

• in walls of arteries (no blood bursting from walls)
• tendons of collagen connecting skeletal muscle to bone (muscles can pull bones)
• makes up bones (with other stuff, e.g. calcium phosphate to harden them)
• Cartilage and connective tissue

Question 16

Structure of alpha glucose

Answer 16

Hexagonal ring, C1, C2, C3, C4, C5, O. C1,2,3,4 have an H and an OH group attached. C5 has C(6)H2OH attached and H. In alpha glucose, the H on C1 is above the plane of the paper (the OH is below the plane of the ring)

Question 17

Alpha and beta glucose

Answer 17

In alpha glucose, C1 has H above plane of ring and OH below plane of ring. In beta glucose, C1 has OH above plane of ring and H below plane of ring

Question 18

Forming a glycosidic bond

Answer 18

OH of C1 and H from OH of C4 make a water molecule. The O left on C4 forms the glycosidic bond between C1 and C4. This is a condensation reaction

Question 19

Breaking a glycosidic bond

Answer 19

OH of a water molecule goes to C1, H of a water molecule binds with the O of the glycosidic bond and forms an OH group on C4. Hydrolysis reaction

Question 20

alpha glucose + alpha glucose ->

Answer 20

Maltose, a sweet, soluble disaccharide sugar. Forms a glycosidic bond in a condensation reaction

Question 21

Carbohydrates

Answer 21

Group of molecules containing carbon, hydrogen and oxygen in the ration C(n)(H2O)(n)

Question 22

Making amylose

Answer 22

Many glycosidic bonds form between many alpha glucoses, forming a long chain of amylose - a polysaccharide.

Question 23

Starch

Answer 23

Made of amylose and branched amylopectin (when C1 - C6 bond forms). Energy-storage molecule for plants. Stored in chloroplasts and in membrane bound starch grains. Can be broken down into glucose molecules for respiration. Insoluble, so doesn’t effect water potential.

Question 24

Amylose

Answer 24

Long chain of many alpha glucoses glycosidically bonded together. Long chain coils up into a compact molecule; iodine can become trapped in the coils of the spring, causing iodine in potassium iodide change colour (starch test)

Question 25

Glycogen

Answer 25

The energy-storage molecule in animals. Made of alpha glucose subunits that can be broken down to release glucose for respiration. Glycogen has more branches than starch, making it more compact. Insoluble, so doesn't effect water potential. As animals are more active, more branches means glucose can be released quicker.

Question 26

Cellulose

Answer 26

Polymer with beta glucose monomers. Makes long, straight chains, with alternating orientations of beta glucose monomers. OH groups form hydrogen bonds forming cross links. 60-70 chains forms a microfibril. They form macrofibrils. They are very strong, and embedded in pectins (a sort of glue) to form plant cell walls. Structure allows easy passage of water, provides strength to cells (no burst, support plant), change shape e.g. in guard cells.

Question 27

Structure of a triglyceride

Answer 27

A glycerol molecule bonded to 3 fatty acid molecules: H l H-C-O-C=O (and a fatty acid chain attached to the C) l H-C-O-C=O (and a fatty acid chain attached to the C) l H-C-O-C=O (and a fatty acid chain attached to the C) l H The O-C=O bond is an ester bond. Made by COOH group of a fatty acid reacting with OH on glycerol. H of glycerol is lost, OH of fatty acid is lost

Question 28

Structure of glycerol

Answer 28

``` H l H-C-OH l H-C-OH l H-C-OH l H ```

Question 29

Structure of a phospholipid

Answer 29

``` H l H-C-O-phosphate group l H-C-O-C=O (and a fatty acid chain attached to the C) l H-C-O-C=O (and a fatty acid chain attached to the C) l H ```

Question 30

Structure and function of triglycerides

Answer 30

- Glycerol and 3 fatty acids - Compact energy store, insoluble so no effect water potential - stored as fat, also an insulator and protector

Question 31

Structure and function of phospholipids

Answer 31

- Glycerol and 2 fatty acids and a phosphate group - A hydrophilic and hydrophobic molecule for a cell surface membrane - Phosphate group may have carbohydrates attached involved in cell signalling

Question 32

Structure and function of cholesterol

Answer 32

- 4 carbon-based ring structures joined together - Thin, small, hydrophobic molecule that fits into the lipid bilayer giving strength and stability - Forms steroid hormones

Question 33

Testing for proteins

Answer 33

Adding biuret reagent to a sample. Biuret reagent contains sodium hydroxide and copper sulfate. Colour change is observed from pale blue to lilac

Question 34

Testing for reducing sugars

Answer 34

Heat with benedict's solution (alkaline copper sulfate). Colour change from blue to orange-red precipitate

Question 35

Reducing sugars

Answer 35

All monosaccharides and many dissaccharides. Can give an electron to other molecules

Question 36

Testing for non-reducing sugars

Answer 36

E.g. sucrose. First, test for reducing sugars. Only if negative: boil with hydrochloric acid (splitting non-reducing sugars into reducing sugars, e.g. sucrose -> glucose and fructose), cool solution and neutralise it with sodium hydrogencarbonate solution/sodium carbonate solution. Carry out reducing sugar test again, if positive, non-reducing sugars are present

Question 37

Testing for starch

Answer 37

Add iodine in potassium iodide solution. Colour change from yellow-brown to blue-black

Question 38

Testing for lipids

Answer 38

Mix sample with ethanol, dissolving lipids present. Pour liquid into water in a test tube. Emulsion will form if a lipid is present (comes out of solution)

Question 39

Measuring concentration of glucose in a solution

Answer 39

Carry out a benedict's test to get an orange-red precipitate. Filter out precipitate, can see how much benedict's solution is left. Use a colorimeter to measure how much light can pass through - lots will if there is lots of glucose as a lot of benedict's solution has been used. Make a calibration curve with known concentrations of glucose, then read off what concentration you have. BE CAREFUL OF PERCENTAGE TRANSMISSION/PERCENTAGE ABSORPTION!!!