Biological Molecules

Question 1

What are the long chains of monomer sub units called?

What process is this called?

Answer 1

Polymers

Polymerisation

Question 2

What is the reaction called when each time a new sub-unit is attached, a molecule of water is formed?

Answer 2

Condensation reaction

Question 3

What is it called when water molecules are used to break the bonds that link the sub-units of a polymer?

Answer 3

Hydrolysis reaction

Question 4

What is a molar solution?

Answer 4

A solution that contains one mole of solute in each litre of solution.

Question 5

What are some examples of monomers?

Answer 5

Monosaccharides, amino acids and nucleotides

Question 6

Pattern of sugars joining (saccharides)

Answer 6

A single monomer is a monosaccharide -
two monosaccharides = disaccharide
many monosaccharides = polysaccharide

Question 7

What are examples of monosaccharides?

isomers?

Answer 7

glucose, galactose, fructose

glucose has alpha and beta glucose isomers

Question 8

Test for reducing sugars

Answer 8

Add 2cm^3 of food sample to test tube. grind if not in liquid form.
Add equal volume of Benedicts reagent.
Heat in gently boiling water for five minutes.
If it turns orange brown, then reducing sugar present

Question 9

Disaccharides made from monosaccharides joining

What are these reactions called and what are the bonds called?

Answer 9

glucose + glucose = maltose
glucose + fructose = sucrose
glucose + galactose = lactose
Condensation reaction and glycosidic bond

Question 10

Test for non reducing sugars

Answer 10

start with sample in liquid form
do reducing sugar test first and if no colour change, then non reducing sugar may be present.
Boil the food sample with dilute hydrochloric acid, HCl hydrolyses any disaccharide present into monosaccharides.
Neutralise with some sodium hydrogencarbonate solution.
Test with pH paper to check that the solution is akaline
Heat with 2 cm^3 Benedicts in gently boiling water for 5 mins.
Will turn orange brown, shows non reducing sugar was present, not reducing sugar

Question 11

What are advantages of polysaccharides?

Examples of polysaccharides?

Answer 11

Very large molecules so insoluble - suitable for storage
When hydrolysed, broken down into disaccharides and monosaccharides.
Cellulose
Starch

Question 12

Test for starch

Answer 12

2cm^3 of sample into test tube
Two drops of iodine solution and shake
Colour change to blue-black

Question 13

Advantages and roles of starch

Where is it found?

Answer 13

insoluble - doesn’t affect water potential, water is not drawn into cells by osmosis
large and insoluble - does not diffuse out of cells
compact - a lot can be stored in a small space
when hydrolysed, forms alpha glucose, easily transported and readily used in respiration
branched form has many ends, glucose monomers can be released very rapidly.
in plant cells, never in animal cells

Question 14

Advantages and roles of glycogen

Where is it found?

Answer 14

insoluble - does not tend to draw in water into cells by osmosis
insoluble - does not diffuse out of cells
compact - lot can be stored in small space
more highly branched than starch - rapdily broken down to glucose monomers and this is useful as animals have higher metabolic rate + respiratory rate
Found in animals and bateria but never in plant cells

Question 15

Features of cellulose

What is the main role of cellulose?

Answer 15

made of beta glucose - form straight, unbranched chains
cellulose molecular chains run parallel to each other and are cross linked by hydrogen bonds which add collective strength
molecules grouped to form microfibrils - in turn grouped to form fibres - provides more strength.
provides rigidity in plant cell walls, to prevent it from bursting as water enters through osmosis

Question 16

What are lipids soluble and insoluble in?

Answer 16

Soluble in organic solvents (such as alcohols and acetone)

Insoluble in water

Question 17

What are the two main groups of lipids?

Answer 17

Phospholipids and triglycerides

Question 18

What are four roles of phospholipids?

Answer 18

Source of energy- when oxidised, provide more than twice the energy as the same mass of carbohydrates
Waterproofing- insoluble in water
Insulation- fats are slow conductors of heat + electrical insulators in myelin sheath
Protection- fat usually stored around delicate organs

Question 19

What are triglycerides and how are they formed?

Answer 19

Three fatty acids combined with glycerol.
Fatty acids form an ester bond with glycerol in a condensation reaction
Hydrolysis of triglyceride produces glycerol and three fatty acids

Question 20

Explain what it means for triglycerides to be saturated, mono-unsaturated and polyunsaturated

Answer 20

Saturated- no carbon-carbon double bonds
Mono-unsaturated- single double bond
Polyunsaturated- more than one double bond present

Question 21

4 ways the structure of triglycerides are related to their properties

Answer 21

• high ratio of energy-storing- carbon-hydrogen bonds to carbon atoms so excellent source of energy
• low mass to energy ratio - good storage molecule
• large, non-polar molecules - insoluble in water, and so does not affect osmosis in cells or their water potential
• high ratio of hydrogen to oxygen atoms - release water when oxidised, important water source for organisms in dry environment

Question 22

What is the structure of a phospholipid and what do these features do? (two parts)
Is a phospholipid polar or non polar?

Answer 22

similar to triglyceride- one fatty acid replaced with by a phosphate molecule
phosphate makes up hydrophilic head
fatty acids make up hydrophobic tail
Polar

Question 23

How does the structure of a phosphlipid relate to its function?

Answer 23

Polar, along with hydrophilic phosphate + hydrophobic fatty acid forms a bilayer within cell surface membrane (in an aqueous environment)
Can form glycolipids, which are important in cell recognition

Question 24

Test for lipids

WHAT IS THE KEY WORD TO USE IN EXAM QUESTION ANSWERS?

Answer 24

Take completely empty, grease-free tube
Add 5cm^3 of ethanol to 2cm^3 sample
Shake tube thoroughly to dissolve any lipid present
Add 5cm^3 water and shake gently
A cloudy-white colour indicates lipid present
AN EMULSION IS MADE
As a control, repeat with water instead of sample

Question 25

If amino acids= monomer then what is the polymer?

Answer 25

Polypeptide

Question 26

What are the four different components of an amino acid?

Answer 26

Amino group Carboxyl group hydrogen atom R (side) group

Question 27

What is it called when two amino acid monomers join? What is this reaction called? What is the name of the bond formed? What is this bond between?

Answer 27

Dipeptide is formed Condensation reaction Peptide bond between carbon atom of one and nitrogen group of another

Question 28

What is a primary protein? | What does it determine?

Answer 28

It is a sequence of amino acids in a polypeptide chain. It determines the ultimate shape and hence the protein’s function. If there is a change in just a single amino acid in the primary structure, then it can lead to a change in the protein.

Question 29

What is the secondary structure of proteins?

Answer 29

When amino acids readily form weak hydrogen bonds, and are twisted into a 3D shape of an alpha helix

Question 30

What is the tertiary structure of proteins? What are the three different bonds? Why is the 3D structure important?

Answer 30

When alpha helix of secondary protein structure is twisted and folded to become more complex and specific. Disulfide bonds- fairly strong, not easily broken Ionic bonds- weaker than disulfide bonds, easily broken by changes in pH Hydrogen bonds- numerous but easily broken Makes each protein distinct and is key for function

Question 31

What is the quaternary structure of a protein?

Answer 31

A number of individual polypeptide chains linked in various ways. Can also have a prosthetic group attached.

Question 32

Test for proteins

Answer 32

Sample in test tube Add equal volume of NaOH at rtp Add a few drops of Biuret reagent (very dilute copper(II) sulfate) Mix gently If protein present, blue to violet (purple)

Question 33

What are enzymes?

Answer 33

Globular proteins that act as catalysts. | They lower the activation energy level and provide an alternative pathway

Question 34

How do enzymes work in terms of structure?

Answer 34

Enzymes have an active site. The molecule that the enzyme acts on is called the substrate. This fits neatly into this depression- called the enzyme-substrate complex.

Question 35

What is the induced fit model of enzyme activity?

Answer 35

The active site forms as the enzyme and substrate interact. Enzyme is flexible and can mould itself around the substrate. The very act of colliding with its substrate is a change to the enzyme’s environment and so it’s changes shape.

Question 36

What are four factors that affect enzyme action? | Explain what they do and how:

Answer 36

Temperature - rise increases kinetic energy, RoR increases, temp rise also breaks bonds and enzyme changes shape - denaturation pH - each enzyme has an optimum pH, if it goes above then likely to be denatured, a change in pH alters the charges on amino acids that make up the active site of the enzyme Enzyme concentration - if substrate is limiting, then increase in enzyme conc. will have no effect on RoR Substrate concentration - RoR increases in proportion with conc. of substrate. as more substrate is added, the active sites gradually get filled, until the point that all of them are working as fast as they can.

Question 37

What are competitive inhibitors?

Answer 37

Have a molecular shape similar to that of the substrate. They are then able to occupy the active site of an enzyme. Blocks the substrate from joining. If the substrate conc. is increased, the effect of the inhibitor is reduced.

Question 38

What is a non-competitive inhibitor?

Answer 38

They attach themselves to the enzyme at a binding site which is not the active site. Alters the shape of the enzyme and the active site, and a substrate molecule can no longer occupy it. An increase in substrate conc. does not decrease the effect of the inhibitor.