1. Biological Molecules Flashcards
1
Q
Water is a ___ molecule
A
Polar/dipolar
2
Q
Explain why water is a polar/dipolar molecule
A
- Pairs of electrons slightly more attracted to oxygen: more protons in its nucleus
- Oxygen has slightly negative charge, hydrogen has slightly positive charge
3
Q
What type of bonds form between water molecules?
A
Hydrogen bonds
4
Q
What property of water do hydrogen bonds cause?
A
Cohesion
5
Q
Define hydrogen bonds
A
Weak forces of attraction between a slightly negative and slightly positive group
6
Q
Water is a ___ for all polar molecules
A
Solvent
7
Q
Why is it biologically important for molecules to be able to dissolve in water?
A
- Many molecules that are transported around living things are dissolved in water (e.g. in blood)
- All metabolic reactions in living things happen in solution
8
Q
What will dissolve in water?
A
- All polar molecules (e.g. glucose)
- All ions
- All ionic molecules
9
Q
What won’t dissolve in water (give an example)?
A
Fats (e.g. oils) because they are non-polar
10
Q
Water has a ___ specific heat capacity
A
high
11
Q
What does having a high specific heat capacity mean?
A
Water absorbs/loses a relatively large amount of energy before changing temperature
12
Q
Because of its high specific capacity, water acts as a ___
A
buffer against sudden temperature fluctuations/changes
13
Q
Biological importance of water having a high specific heat capacity
A
- Important for homeostasis - easier to regulate internal temperature because living organisms are mostly water (enzyme activity!)
- Important for organisms that live in water (aquatic environments have a more stable temp)
14
Q
Water and latent heat of vaporisation
A
Water has a high latent heat of vaporisation
15
Q
Latent heat of vaporisation is…
A
the amount of energy absorbed before something turns into vapour
16
Q
Biological significance of water having a high latent heat of vaporisation
A
Can act as a coolant (eg sweat) with little loss of water through evaporation
17
Q
Why does water have a high latent heat of vaporisation
A
Hydrogen bonds need to be broken - this requires energy
18
Q
Why does water have a high specific heat capacity
A
Hydrogen bonds
19
Q
Water will stick to other polar molecules - this is known as
A
Adhesion
20
Q
Why is cohesion important in plants?
A
Water column doesn’t break up when water is pulled up the xylem in the transpiration stream - continuous
21
Q
When does water show surface tension
A
At an air-water surface due to the cohesion between water molecules
22
Q
What does surface tension do
A
Makes a solid-like surface, explaining why pond skaters can walk on water
23
Q
Condensation reaction
A
Two monomers joining together to form a polymer and water
24
Q
Hydrolysis reaction
A
A polymer splitting up into monomers - water required as a reactant
25
What do monosaccharides and disaccharides have in common?
They are sugars: sweet-tasting and very soluble
26
What general property do polysaccharides share?
Insoluble in water
27
How can monosaccharides form disaccharides and polysaccharides?
Through condensation reactions
28
Examples of monosaccharides
```
Glucose
Fructose
Galactose
Deoxyribose
Ribose
```
29
General formula of monosaccharides
(CH2O)subscript n
30
What is meant by a hexose sugar?
Has 6 carbons
31
Maltose =
glucose + glucose
32
Sucrose =
glucose + fructose
33
Lactose =
glucose + galactose
34
What type of bond forms between the two glucose molecules in maltose?
1-4 glycosidic bond
35
What type of glucose is used in maltose?
Alpha glucose
36
Are all monosaccharides reducing sugars?
Yes
37
Are all disaccharides reducing sugars?
No - only some are!
38
What is the test for reducing sugars?
Benedict's solution
39
What do reducing sugars act as?
Reducing agents (they donate electrons)
40
The blue colour in Benedict's solution is due to...
Cu2+ ions
| They are soluble
41
The red colour in Benedict's solution is due to...
Cu1+ ions
| They are insoluble
42
Test for non-reducing sugars
1. Negative Benedict's result
2. Hydrolyse sample to split into monosaccharides: add HCl, heat in water bath, neutralise with hydrogencarbonate
2. OR add an enzyme
3. Repeat Benedict's test - if brick red there is non-reducing sugar
43
Benedict's solution practical main point
The colour and density of any precipitate formed with Benedict's solution can be used to indicate the concentration of reducing sugar present in a sample
44
What does a colorimeter measure
Percentage transmission (% of light that passes through the solution) and percentage absorbance (% of light that doesn't get through)
45
Polymers of alpha glucose
Starch & glycogen
46
Polymers of beta glucose
Cellulose
47
Most glucose molecules join via...
1-4 glycosidic bonds, forming a helical chain
48
What's good about a helical chain
It can coil so it's more compact
49
How do polymers of glucose become branched?
1-6 glycosidic bonds
50
Describe starch (storage polysaccharide? structure?)
1. Storage polysaccharide in plants
2. Polymer wound into a tight coil
3. Mix of branched (amylopectin) and unbranched (amylose) chains
51
Starch properties
1. Large & insoluble - doesn't affect water potential, doesn't easily diffuse out of cells
2. Helix - compact, lots of glucose can be stored in a small space
3. Branched - many ends so can be broken down rapidly
52
Glycogen is...
A more highly branched polymer of alpha glucose
53
Advantages of a more highly branched molecule
More compact and can be broken down even more rapidly (animals are more likely to suddenly need a lot of energy)
54
Cellulose structure
* Long straight chains held close to each other by hydrogen bonds
* Strong & rigid overall structure
* Every other glucose molecule is flipped so no helix - only long straight chains
55
Where is cellulose found
Storage polysaccharide in plant cell walls
56
Groups of cellulose molecules form...
Microfibrils, which are then arranged in parallel groups which form cellulose fibres
57
What are cellulose fibres like?
Rigid and strong - giving cell walls their strength
58
What are lipids made of
Carbon, hydrogen and oxygen but proportionally less oxygen than carbs
59
Are lipids soluble in water?
No - they are non-polar and hydrophobic
60
What are lipids soluble in?
Organic solvents e.g. ethanol
61
Opposite of hydrophobic
Hydrophilic
62
Most important groups of lipids are...
Triglycerides - includes all fats and oils
63
Other types of fats include...
Cholesterol, phospholipids, waxes
64
Four different roles of lipids in living organisms
1. Source of energy (often used as an energy store) - lipids have more energy per gram than carbs
2. Insulation - poor conductor of heat
3. Protection (around organs esp those outside the ribcage)
4. Waterproofing - it's hydrophobic!
65
What is a triglyceride molecule made up of?
3 fatty acids and 1 glycerol molecule
66
What does the "n" in fatty acid structural diagrams mean?
Number of repeats (of CH2 units)
67
What reaction forms a triglyceride?
Condensation
68
What bonds form in a triglyceride after condensation?
Ester bonds
69
What 3 properties make triglycerides a good energy storage molecule?
1. Triglycerides have many energy-storing C-H bonds. This makes then an excellent source of energy.
2. They are also very energy dense (lots of energy per gram) which makes them a good energy store.
3. Being non polar also means they are insoluble - a useful property in a storage molecule.
70
Lipids vs. glycogen as energy stores
* Glucose can be used immediately in respiration - faster, short-term energy store. More readily available energy. Can be used in aerobic and anaerobic respiration.
* Lipids can only be used in aerobic respiration - energy is less readily available.
71
Difference between saturated & unsaturated fatty acid
Saturated has single bonds only & straight chain & tend to be solid @ room temp, unsaturated contains C=C double bonds (and wherever there is a double bond there's a kink in the chain) & tend to be liquid @ room temp
72
Monounsaturated vs polyunsaturated
Monounsaturated: one C=C double bond
Polyunsaturated: many C=C double bonds
73
Why are unsaturated fats more likely to be liquid @ room temperature?
There are kinks in the chain so it's harder to pack the fatty acid chains into a regular arrangement
74
Phospholipid structure vs triglyceride
A fatty acid has been replaced by a phosphate group (so two fatty acids, one glycerol, one phosphate group)
75
The head of a phospholipid molecule is...
hydrophilic
76
The tail of a phospholipid is...
hydrophobic
77
What do we call a molecule that is part hydrophilic and part hydrophobic?
Amphipathic
78
What happens when a phospholipid is in water?
Forms a micelle (see Notion for diagram)
79
Describe chemical test for lipids (emulsion test)
1. Mix sample with ethanol - lipid is dissolved
2. Add water - any previously dissolved lipid in ethanol will come out of solution, forming tiny lipid droplets
3. The droplets give a white milky appearance
80
Proteins are made of _____ which are joined together by _____
Amino acids; Peptide bonds
81
Some proteins contain which element?
Sulphur
82
What elements are all proteins made of?
C, H, O, N
83
Examples of proteins
1. Keratin & collagen: found in skin, hair, nails & connective tissue
2. Actin & myosin: found in muscles
3. Enzymes
4. Haemoglobin
5. SOME hormones (e.g. insulin)
6. Antibodies are made of a protein called immunoglobin
84
Keratin and collagen are examples of...
Structural proteins
85
Is immunoglobin soluble or insoluble?
Soluble
86
Are enzymes soluble or insoluble?
Soluble
87
What are the three parts of an amino acid?
Amino group
R group
Carboxyl group
88
Is amino group acidic or basic?
Basic
89
Is carboxyl group acidic or basic?
Acidic
90
Define primary structure of a protein
The order of amino acids in the polypeptide chain (chain of amino acids)
91
Why is primary structure significant?
* It determines the final shape and properties of the molecule
* A mistake in the order can lead to a change in the molecule's shape and properties, and therefore stop it carrying out its function
92
Define tertiary structure of a protein
The way in which the polypeptide is further twisted and folded to make a 3D shape
93
What bonds hold secondary structure of a protein in place?
Hydrogen bonds between the N-H (slightly positive) group on one amino acid and the C=O (slightly negative) group on another
93
Two types of secondary structure
Alpha helix
| Beta pleated sheet
94
What bonds hold the tertiary structure in place?
Disulphide bridges, ionic bonds and hydrogen bonds between the R groups
95
What R groups/amino acids do disulphide bonds form between?
Ones with sulphur in them (i.e. cysteine R groups and methionine R groups)
96
Where are ionic bonds in a tertiary structure found?
They form between R groups that are charged
97
Where are hydrogen bonds in a tertiary structure found?
Weak bonds between R groups with a slight charge
98
What is quaternary structure?
When some proteins made up of several polypeptide chains, each with their own tertiary structure, join together to make one larger protein
99
Examples of proteins with quaternary structure
Haemoglobin - made of 4 polypeptides joined together
100
Some proteins with a quaternary structure might also have...
Prosthetic groups - non-protein parts of the molecule (e.g. in haemoglobin it's Fe)
101
Biuret test for proteins
1. Add NaOH
2. Add 1% CuSO4 drop by drop
3. Allow mixture to stand for 5 min: positive result is blue to violet
102
Role of phospholipids
What cell membranes are made of - forms barrier between cell interior & exterior
103
Globular vs fibrous proteins: what type?
Globular: usually metabolic (i.e involved in chemical reactions in the body)
Fibrous: structural
104
Globular vs fibrous proteins: solubility
Globular: soluble in water
Fibrous: insoluble in water
105
Globular vs fibrous proteins: primary structure
Globular: irregular & specific
Fibrous: repetitive sequences
106
Globular vs fibrous proteins: easy/hard to denature?
Globular: unstable so relatively easy to denature
Fibrous: stable so much harder to denature
107
Examples of globular proteins
Enzymes
Haemoglobin
Hormones
108
Examples of fibrous proteins
Keratin
Collagen
Actin
Myosin
