biological molecules Flashcards
carbohydrates, lipids and proteins + bio practical
1
Q
What are biological molecules?
A
- critically important molecules needed for organisms to survive.
- contain carbon atoms arranged in rings or chains.
2
Q
What are the types of biological molecules?
A
- Carbohydrates
- Lipids
- Proteins
- Nucleic Acids (y4)
3
Q
What are monomers?
A
the building blocks that form polymers.
LIPIDS are not polymers.
4
Q
What are monosaccharides?
A
Simplest forms of carbohydrates, cannot be broken down further.
5
Q
Give examples of common monosaccharides.
A
- Glucose
- Fructose
- Galactose
same general formula: C₆H₁₂O₆
6
Q
List properties of monosaccharides.
A
- Sweet-tasting
- Soluble in water
- Able to lower water potential of solutions
7
Q
What are disaccharides?
A
- Formed by two monosaccharides
- Joined through a glycosidic (covalent) bond.
8
Q
Name common types of disaccharides.
A
- Maltose (glucose + glucose)
- Lactose (glucose + galactose)
- Sucrose (glucose + fructose)
9
Q
What are polysaccharides?
A
- consist of many monosaccharides joined together.
10
Q
What are the two main types of polysaccharides?
A
- Storage polysaccharides (starch, glycogen)
- Structural polysaccharides (cellulose)
11
Q
What is starch?
A
- storage polysaccharide
- formed from glucose molecules
- mainly found in plants
- in long straight chains or branched chains
12
Q
What is glycogen?
A
- storage polysaccharide
- found in animals, stored in the liver and muscles
- formed from glucose molecules
- joined up in highly branched chains
impt: MORE branched than starch.
13
Q
Why are starch and glycogen suitable as storage materials?
A
- Insoluble in water, do not affect water potential in cells
- Too large to diffuse through cell membranes –> stay in cells
- Compact shapes occupy lesser space than individual glucose molecules
- Easily broken down into glucose when needed
14
Q
What are the key characteristics of cellulose?
*cellulose: a structural polysaccharide.
A
- formed from glucose molecules bonded differently compared to starch
- insoluble in water
15
Q
What is Benedict’s test?
hint: define reducing sugars
A
- test for presence of reducing sugar: all monosaccharides + some disaccharides
- sucrose is the only common non-reducing sugar
- using Benedict’s solution
16
Q
What are the steps in Benedict’s test?
A
1) add an equal volume of Benedict’s solution to food solution.
2) shake the mixture
3) place the test tube in a boiling water bath and wait for max. 5 mins
4) observe precipitate formation/colour changes
start boiling the water before step 1!
17
Q
What are the steps in the iodine test?
A
- Place food substance on white tile. Chop up if needed.
- add 2-3 drops of dilute iodine solution.
- observe colour changes.
18
Q
What is the general formula of carbohydrates?
A
(CH₂O)ₙ
ONLY carbohydrates have 1:2:1 CHO ratio
19
Q
what is a lipid?
A
- organic compounds containing much less O than C and H
- insoluble in water but soluble in organic solvents (e.g. alcohol/acetone)
NOT a polymer + fatty acids/glycerol are not monomers.
20
Q
composition of a triglyceride
A
- 3 fatty acid molecules
- 1 glycerol molecule
21
Q
what is a fatty acid?
A
- long hydrocarbon chain
- contains carboxyl group (COOH)
- hydrocarbon chain may be unsaturated (contain carbon-carbon double bond) or saturated (no C=C bond)
- hydrophobic
saturated = max. hydrogen = max. no of carbon available for bonding = no C=C bond
22
Q
bond between fatty acid and glycerol
A
ester bond
23
Q
difference between oils & fats?
A
- oils have unsaturated fatty acids while fats have saturated fatty acids
- oils have shorter fatty acid chains than fats
- oils have a lower melting point, molecular weight & density than fats
fats: solid at r.t.p, oils: liquid at r.t.p
24
Q
explain difference in density between oils and fats
A
- oils LESS DENSE than fats (oil is liquid while fat is solid at r.t.p)
- fat –> contains saturated fatty acids –> packed closely together at r.t.p –> solid formed
- oil –> contains unsaturated fatty acids –> unable to pack closely due to kink/bend in fatty acid chains (due to C=C bond) –> liquid formed
oils & fats are triglycerides
25
properties of triglycerides
- classified as **oils or fats**
- compact & **insoluble in water** --> **do not affect water potential** in cells
26
steps for biuret test
1. using a syringe, add 2cm3 of food solution to a clean test tube
2. add **1cm3 sodium hydroxide** to the test tube
3. shake thoroughly
4. add **1% CuSO4 solution, drop by drop**, shaking mixture after each drop
5. observe for colour changes
## Footnote
drop by drop is impt as too much CuSO4 may cover up a positive (violet-coloured) result
27
observation/conclusion phrases for biuret test
| hint: proteins
* **violet colouration** was observed: protein is present
* solution **remained blue**: protein is absent
28
observation/conclusion phrases for iodine test
| hint: starch
* **blue-black colouration** was observed: starch is present
* solution **remained brown**: starch is absent
29
steps for ethanol emulsion test
| ETHANOL IS **FLAMMABLE**, keep away from flames
1. using a syringe, add 2cm3 of food solution to a clean test tube
2. add **2cm3 of ethanol** to the test tube
3. shake thoroughly
4. pour the mixture into another test tube **containing 2cm3 of deionised water**
5. observe for colour changes/emulsion formation
30
observation/conclusion phrases for ethanol emulsion test
a **white emulsion** was formed: fat is present
solution **remained colourless**: fat is absent
31
observations/conclusions for benedict's test
* solution **remained blue** --> **absence** of reducing sugar
* **green/yellow precipitate** was formed --> **low concentration** of reducing sugar is present
* **orange precipitate** was formed --> **moderate concentration** of reducing sugar is present
* **brick-red precipitate** was formed --> **large concentration** of reducing sugar is present
32
why are triglycerides good energy stores?
- contain **greater no. of C-H bonds** compared to carbohydrates -> for the **same mass**, triglyceride yields **twice the energy** of carbohydrates
OR
for **half the mass**, yields the **same amt. of energy** -> **lightweight** energy source good for seeds dispersed by wind/animals that rely on speed/fly
33
name 3 functions of triglycerides
| besides energy storage
1. heat insulator --> fats **conduct heat slowly**
2. keeps aquatic mammals buoyant --> **less dense** than water
3. protective layer around vital organs --> fats **absorb shock**
4. **metabolic water** (water produced from respiration)--> breakdown of triglycerides **releases 2x as much water** as breakdown of carbohydrates due to **more hydrogen atoms**
5. solvent for fat-soluble vitamins
6. insulates nerve cells in form of myelin sheath
34
components of phospholipids
* 2 fatty acid molecules
* 1 phosphate group
* 1 glycerol molecule
35
how do different components in a phospholipid react to water?
* phosphate group is **hydrophilic**, attracted to water molecules --> phosphate group **faces exterior aqueous environment** （intracellular and extracellular fluid)
* fatty acids are **hydrophobic**, repelled by water molecules --> fatty acids **face inside** of phospholipid bilayer
36
function of phospholipids
major component of biological **membranes**
37
elements that make up proteins
C, H, O, N, (S)
38
properties of proteins
* **unique 3D shape** that gives proteins **unique functions**-> once shape is lost, protein is **denatured**
* polymers made up of monomers (amino acids)
39
general structure of amino acids
* 1 central carbon atom bonded to (at least) 4 groups:
1. NH2 (amino group)
2. COOH (carboxyl group)
3. H (hydrogen atom)
4. R (variable group/side chain)
| amino: H-N-H, carboxyl: O=C-OH
## Footnote
R group influences property/function of amino acid
40
how are polypeptides & proteins formed + bonded?
* amino acids joined in chains
* bonded by **peptide bond**
* polypeptide chain folds into protein with unique 3D shape
41
functions of proteins
* synthesize new cells
* transport proteins
* structural proteins
* defence of body (antibodies are proteins, fight infections)
* biological catalysts (enzymes)
* chemical messengers (hormones e.g. insulin)
42
name 3 points of comparison for biological molecules
1. made up of which **elements**? (similarity/difference)
2. building blocks (for lipids)/monomers (usu. difference)
3. presence of **bonds** (usu. difference)
4. H:O ratio (if comparing this, one molecule must be carbohydrate) (**2:1** for carbs, **no fixed ratio** for proteins/lipids)
