1A - Biological Molecules

Question 1

What are polymers?

Answer 1

They are large, complex molecules composed of long chains of monomers joined.
Most carbohydrates, proteins and nucleic acids.

Question 2

What are monomers and examples?

Answer 2

They’re small, basic molecular units.
Eg. Monosaccharides, amino acids, and nucleotides.

Question 3

What are carbohydrates?

Answer 3

They’re made up of monosaccarides (eg. Glucose, galactose, fructose)
And only contain the elements C, H and O.

Question 4

What is glucose - its sugar type, and structure?
(Including isomers)

Answer 4

Glucose = hexose sugar (monosaccharide with six C atoms in a molecule)

Isomers are molecules with same molecular formula
But atoms connected different order.
There are two isomers of glucose (alpha and beta)

(diagrams on notes NO. 1)

Question 5

What are condensation reactions?

Answer 5

When two molecules join forming new chemical bond -
Water molecule released when bond’s formed.

Monosaccharides join by condensation reactions.
Glycosidic bonds form between them, when water is released.
Disaccharides are formed when two monosaccharides join.

Question 6

What’s an example of condensation reactions?
AND Which monosaccharides make which disaccharides?

Answer 6

Eg. Two alpha glucose molecules join
By a glycosidic bond, forming maltose
(diagram NO. 2)

α glucose + α glucose = maltose
glucose + fructose = sucrose
glucose + galactose = lactose

Question 7

What are hydrolysis reactions

Answer 7

Polymers get broken down into monomers by hydrolysis reactions.

These reactions break the chemical bond between monomers
using a water molecule.
—> opposite of condensation reaction.

Eg. Carbohydrates break into their monosaccharides by hydrolysis…
(diagram NO. 3)

Question 8

What’s the general term for most mono and disaccharides?

Answer 8

Sugar is the general term for most of them.
All sugars can be classified as reducing or non-reducing

The Benedict test tests for sugars, differing depending on type of sugar you test for.

Question 9

How to test for reducing sugars?

Answer 9

This includes all monosaccharides (glucose)
And some disaccharides (maltose, lactose)

• add Benedict’s reagent (blue) to sample; use excess so all sugar reacts.
• Heat in water bath that’s boiling
• if test’s positive, coloured precipitate is formed.
  From blue to red.

The higher conc of reducing sugar, the further colour change.
A more accurate way to compare conc = filter and weigh

Question 10

How to test non reducing sugars?

Answer 10

When Benedict’s test’s negative, there may still be non reducing sugar.
(Eg. Sucrose) You must break it down into monosaccharides.

1. Get new sample of solution
2. Add dilute HCl and gently heat in water bath
3. Neutralise solution with sodium hydrogen carbonate
4. Repeat Benedict’s test with this neutralised solution.

If negative stays blue, so has no non/reducing sugar whatsoever

Question 11

What’s a polysaccharide?

Answer 11

They are formed when more than two monosaccharides join by condensation reactions
Eg. Lots of Alpha Glucose molecules join by
glycosidic bonds to form amylose

Some include starch, cellulose and glycogen.

Question 12

Structure and function of starch?

Answer 12

Plants store excess glucose as starch (cells —> energy from glucose)
- when plant needs more glucose for energy
- breaks down starch to release glucose

Starch is a mixture of two polysaccharides of α-glucose
Amylose
• long unbranched chain
• coiled structure makes molecule compact, take up less space so fits

amylopectin.
• long branched chain, allowing enzymes that break molecule down
Getting to glycosidic bonds easily, so glucose can release faster
• long so doesn’t move out cell membrane

• insoluble
Doesn’t affect water potential
not causing water to enter cells via osmosis (would make swell)
—> good for storage

• glucose polymer
Can be used as respiratory substrate

Question 13

What’s test for starch

Answer 13

Add iodine dissolved in potassium iodide solution
If starch, changes from brown-orange to blue-black

Question 14

What is function and structure of glycogen

Answer 14

Animal cells get energy from glucose,
Storing excess as glycogen - another polysaccharide of α-glucose

Structure is similar to amylopectin
—> but has more side branches off of it and short
— so stored glucose can be released quicker

— also very compact coiled molecule = good for storage
— glucose polymer
— insoluble

Question 15

Structure and function of cellulose?

Answer 15

MAJOR COMPONENT of cell walls in plants

Made of long unbranched chains of β-glucose
—> when they bond = form straight cellulose chains

these cellulose chains linked by hydrogen bonds
To form strong fibres called microfibrils
—> so cellulose can provide structural support in cells

Hydrogen bonds are only strong in large numbers

Question 16

Difference between beta and alpha glucose

Answer 16

Beta glucose has OH at top/O at bottom
Alpha has OH at bottom/O at top

To form glycosidic bond, every glucose rotate by 180°
As it’s β.

Question 17

Which are mono,di and polysaccharides?

Answer 17

Mono..
- glucose
- galactose
- fructose

Di…
- lactose
- maltose
- sucrose

Poly..
- cellulose
- starch
- glycogen

Question 18

How is calorimetry used to determine conc of glucose solution?

Answer 18

1. Quantitative Benedict’s reagent (diff to normal Benedict’s)
   Is heated with glucose (initial blue colour lost; red precipitate isn’t produced)
2. Use a calorimeter to measure light absorbance
   Of solution after quantitative Benedict’s test
3. Higher glucose concentration, the more paler solution
   So decreasing absorbance of light of solution (more is transmitted)

Question 19

How are triglycerides formed

Answer 19

By condensation reactions (between OHs on each molecule)

Fatty acids attach to glycerol
When ester bonds are formed, water is released (condensation)
Happens twice more to form triglycerides

Question 20

What are triglycerides

Answer 20

Triglycerides have one molecule of glycerol
with three fatty acids branching off, attached to it
..

Fatty acid molecules have long ‘tails’ of hydrocarbons
—> these tails are hydrophobic (repel water molecules)
- and the tails make lipids insoluble in water

• All fatty acids have same basic structure
• But the hydrocarbon tail varies

Fatty acids structure are -COOH groups
With R (representing hydrocarbon tail) attached to C

Question 21

What does it mean if fatty acids are saturated or unsaturated

Answer 21

These are the 2 kinds of fatty acids.
The difference is in their hydrocarbon tails (R group)

• saturated (solid at room temp packed close)
They don’t have double bonds between C atoms
The fatty acid is saturated with hydrogen

• unsaturated (liquid room temp)
Have at least one double bond
Between carbons wch cause chain to kink.
- can be monounsaturated or polyunsaturated

Question 22

What are phospholipids (other type of lipid)

Answer 22

These are the lipids found in cell membranes
—> similar to triglycerides but one fatty acid molecule is replaced
By a phosphate group

The phosphate group is hydrophilic (attracts water)
Fatty acid tails are hydrophobic
This is important in cell membrane…

Question 23

How do triglycerides lipids structures link to their functions?

Answer 23

• Triglycerides
Mainly used as energy storage molecules because
- long hydrocarbon tails of fatty acids contain lots of chemical energy
Lots of energy released when broken down
Because of the tails, lipids have double the energy per gram as carbohydrates

..

• insoluble so don’t affect water potential
  Of cells and cause water osmosis (swells cells)

Triglycerides clump together as insoluble droplets in cells
As fatty acid tails = hydrophobic
Tails face inwards shielding themselves from water with glycerol heads

Question 24

How do phospholipids lipids structures link to their functions?

Answer 24

They make up the bilayer of cell membranes
Cell membranes control what enters and leaves cells

•heads are hydrophilic and tails, hydrophobic
- so form a double layer with heads facing out to water (on either side)

•centre of bilayer is hydrophobic so water soluble substances
- can’t easily pass through
- membrane acts like a barrier to those substances