Biological Molecules - Chapter 1 and 2 Flashcards
1
Q
State the definition of a polar/polarised molecule.
A
A molecule with an uneven distribution of charge.
2
Q
State the definition of a monomer.
A
One of the many small molecules that combine to form a larger one (polymer).
3
Q
State the definition of a polymer.
A
Large molecule made up of repeating smaller molecules (monomers).
4
Q
What is a condensation reaction?
A
A reaction in which molecules are combined and water is produced.
5
Q
What is a hydrolysis reaction?
A
A reaction in which molecules are broken down through the addition of water.
6
Q
State the definition of ‘metabolism’.
A
All the chemical processes that take place in living organisms.
7
Q
Give an example of a monomer.
A
Monosaccharides, amino acids, nucleotides.
8
Q
Monosaccharides are made up of what three elements?
A
Carbon, hydrogen and oxygen.
9
Q
Give an example of a monosaccharide.
A
Glucose (alpha or beta), Galactose and Fructose.
10
Q
What is a reducing sugar?
A
A sugar that can donate electrons to (or reduce) another chemical.
11
Q
If a student was to use Benedict’s reagent in an experiment, what would they be testing for?
What would be the steps involved?
A
Test for reducing sugars.
- Add 2cm3 of food sample to a test tube (liquid form).
- Add an equal voume of Benedict’s reagent.
- Heat the mixture in a boiling water bath (5 mins).
If reducing sugar is present, the soultion will turn a brick orange/red colour.
12
Q
Glucose + Glucose =
A
Maltose.
13
Q
Glucose + Fructose =
A
Sucrose.
14
Q
Glucose + Galactose =
A
Lactose.
15
Q
What is the bond called when two monosaccharides combine to form a disaccharide?
A
Glycosidic bond.
16
Q
What is the difference in the molecular arrangement of alpha and beta glucose?
A
Alpha glucose = OH group below.
Beta glucose = OH group above.
17
Q
What is the test for non-reducing sugars?
State the steps involved.
A
Benedict’s test.
1. The solution should remain blue after completing the Benedict’s test to test for reducing sugars.
2. Add another 2cm3 of the food sample to 2cm3 of dilute HCl acid in a test tube.
(The dilute HCl will hydrolyse any disaccharide present)
3. Place the test tube in a boiling water bath (5 mins).
4. Slowly add sodium hydrocarbonate to the test tube - neutralises dilute HCl.
5. Re-test the resulting solution by heating 2cm3 of Benedict’s reagent in a boiling water bath (5 mins).
6. Soultion will turn brick orange/red if non-reducing sugars are present (reducing sugars are produced during hydrolysis).
18
Q
List three polysaccharides.
A
Starch, glycogen and cellulose.
19
Q
How does a person test for starch in a food sample?
State the steps involved.
A
Iodine test.
- Add 2cm3 of food sample into a test tube.
- Add 2 drops of iodine solution (potassium iodide).
- The presence of starch is indicated by a colour change from yellow to blue/black.
20
Q
What monosaccharide is starch made up from?
A
Alpha glucose.
21
Q
Are the chains of starch branched or unbranched?
A
Both.
Branched - amylopectin.
Unbranched - amylose (would into a tight coil, making the molecule compact).
22
Q
How is starch’s structure suited for its function?
A
- It is insoluble - does not affect water potential.
- It is large and insoluble - does not diffuse out of cells.
- It is compact - a lot can be stored in a small space.
- When hydrolysed it forms alpha glucose - readily used in respiration.
- Branched - enzymes can act simultaneously on the branched ends, meaning glucose monomers are quickly released.
23
Q
In what cell is starch found?
A
Plant cells - in the form of small grains.
24
Q
In what cells is glycogen found?
A
Animal and bacteria cells.
25
What monosaccharide is glycogen made up from?
Alpha glucose.
26
How is glycogen's structure suited for its function?
1. Insoluble - does not affect water potential.
2. Insoluble - does not diffuse out of cells.
3. Compact - a lot can be stored in a small spaced.
4. More highly branched than starch - enzymes can act simultaneously on the branched ends, meaning glucose monomers are quickly released.
27
Why does glycogen need to be more highly branched than starch? (3 marks)
Glucose is quickly released from the branches.
Having more branches releases more glucose which is used in respiration.
This is important as animals have a higher metabolic rate and therefore respiratory rate than plants because they are more active.
28
What monosaccharide is cellulose made up from?
Beta glucose.
29
Does cellulose have branched or unbranched chains?
Straight, unbranched chains.
30
How does cellulose prevent the plant cell wall from bursting?
Cellulose exerts an inward pressure, stopping the influx of water. This makes plant cells turgid.
31
How is cellulose's structure suited for its function?
1. Made from beta glucose - forms long, straight unbranched chains.
2. Chains run parallel to one another and are cross linked by hydrogen bonds - adds collective strength.
3. Grouped to form microfibrils which in turn are grouped to form fibres - provides more strength.
32
What 3 components make up a lipid?
Carbon, hydrogen and oxygen.
33
How do phospholipids contribute to the cell membrane?
Phospholipids contribute to the flexibility of membranes and the transfer of lipid-soluble substances across them.
34
How do lipids provide a source of energy?
When oxidised, lipids produce both energy and water.
35
Why are lipids good molecules for waterproofing?
Lipids are insoluble and therefore useful in waterproofing.
36
Give an example of when lipids help to waterproof an organism/plant.
Both insects and plants have waxy lipid cuticles.
37
How to lipids contribute to insulation?
Fats are slow conductors of heat and so help to retain body heat.
Lipids act as electrical insulators around the myelin sheath.
38
Give an example of when a lipid is used for protection in the human body.
Fats are stored around delicate organs, such as the kidney.
39
State which two molecules (and how many) are used to produce a triglyceride.
3 fatty acids and 1 glycerol.
40
What bond is formed between a fatty acid and a glycerol molecule?
Ester bond.
41
Why is it beneficial that triglycerides have a high ratio of carbon-hydrogen bonds to carbon atoms?
Carbon-hydrogen bonds store energy and so having a highr atio makes triglycerides an excellent enery source.
42
Why is it beneficial that triglycerides have a low mass to energy ratio?
This makes triglycerides a good energy storage molecule because a lot can be stored in a small volume.
43
Why is it beneficial for triglycerides to be large, insoluble and non-polar?
Triglycerides do not affect the water potential of the cell and have no osmotic effect.
44
What is the imporance of triglycerides having a high ratio of hydrogen to oxygen atoms?
Triglycerides release water when oxidised and therefore provide an important source of water.
45
List the components that make up a phospholipid.
Phosphate molecule, glycerol, 2 fatty acids.
46
How does the hydrophilic head of the phospholipid interact with water?
The hydrophilic head is attracted to water, but does not interact with fat.
47
How does the hydrophobic tail of the phospholipid interact with water?
The hydrophobic tai orients itself away from water, but mixes readily with fat.
48
What is the benefit of phospholipids being polar molecules?
In an aqueous environment, phospholipids form a bilayer within cell-surface membranes.
49
How do phospholipids contribute to helping cell recognition?
The phospholipid structure allows them to form glycolipids by combining carbohydrates within the cell-surface membrane. Glycolipids are important in cell recognition.
50
What is the name of the test used to test for lipids?
| State the steps involved.
The emulsion test.
1. Add 2cm3 of sample to a dry test tube.
2. Add 5cm3 of ethanol.
3. Shake the tube to dissolve any lipid in the sample.
4. Add 5cm3 of water and shake gently.
5. A cloudy white emulsion should form, indicating the presence of a lipid.
Use water as a control instead of the sample being tested.
51
Amino acids are combined to form what?
A protein.
52
How many amino acids occur in all living organisms?
20
53
An amino acid has a centraol carbon attached to what 4 different chemical groups?
1. Amino group (NH2)
2. Carboxyl group (COOH)
3. Hydogen atom (H)
4. R (side) group - each amino acid has a different R group.
54
What bond links two amino acids?
Peptide bond.
55
What forms the primary structure of a protein?
The sequence of amino acids in a polypeptide chain.
56
What does the primary structure of a protein determine?
The shape and function of the protein.
57
What occurs in order to create the secondary structure of a protein?
State the two forms in which a protein can be presented.
The NH2 group and COOH group form hydrogen bonds, causing the polypeptide chain to be twisted into a 3D shape.
1. Alpha-helix.
2. Beta-pleated sheet.
58
The tertiary structure of a protein is maintained by what three bonds?
List them in strength order (strongest to weakest).
Disulfide bridges, ionic bonds and hydrogen bonds.
59
What addition turns a protein from its tertiary structure to its quaternary structure?
```
Polypeptide chains are linked together.
Prosthetic groups (such as the iron-containing haem group) may also be added to the protein.
```
60
State the test used in order to test for proteins.
| List the steps taken in order to obtain a result.
Biuret test.
1. Place the sample in a test tube.
2. Add an equal volme of sodium hydroxide solution (at room temperature).
3. Add a few drops of dilute copper (II) sulfate solution and mix gently.
4. A purple colouration indicated the presence of peptide bonds and hence protein.
61
What is an enzyme?
An enzyme is a globular protein that acts as a biological catalyst.
62
How do enzymes work?
Enzymes work by lowering the activation energy level, enabling processes to occur faster than what they normally would. Enzymes do not undergo permanent changes.
63
What is an active site?
A specific region of the enzyme that is functional. The active site forms a small depression in which the substrate binds with.
64
When a substrate binds with the active site, what is formed?
An enzyme-substrate (E-S) complex.
65
Name the two models that have been proposed to describe the interaction between enzymes and substartes.
1. Lock and Key Model
| 2. Induced fit Model
66
Describe the process that the induced fit model proposes.
1. The enzyme has a flexible, complementary active site that moulds itself around the substrate.
2. This produces an enzyme-substrate complex.
3. As the enzyme changes its shape, it puts a strain on the substrate.
4. This strain disorts a particular bond(s) in the substrate, lowering the activation energy required to break the bond.
67
State a limitation of the lock and key model.
The enzyme (lock) is considereed to be a rigid structure.
68
What factors affect enzyme action?
Temperature, pH, enzyme concentration and substrate concentration.
69
How does temperature affect enzyme action?
A rise in temperature increases kinetic energy which means that molecules will collide with one another more often. Therefore, more enzyme-substrate complexes will be formed.
When temperatures rise too high, the bonds in the enzyme begin to break and eventually the enzyme denatures.
70
What does it mean if an enzyme is said to be denatured?
The enzyme becomes so disrupted that it stops working all together. Denaturation is a permanent change, so the enzyme never functions again.
71
How does pH affect the way enzymes work?
A change in pH alters the charge on the amino acids, making up the active site. As a result E-S complexes cannot be formed.
If the change in pH is significant, the active site shape will change as the bonds maintaining the enzyme's tertiary structure will break.
72
How does enzyme concentration affect enzyme action?
As long as there is an excess of substrate, an increase in the amount of enzyme leads to a proportionate increase in the rate of reaction.
If however, the substrate is limiting, then any increase in the enzyme concentration will have no effect on the rate of reaction.
73
How does substrate concentration affect enzyme action?
As the concentration of substrate is increased, more active sites will become filled until eventually they all become filled. After this, despite increasing the substrate concentration, the rate of reaction will not increase.
74
List the two type of enzyme inhibitors.
1. Compeitive inhibitor.
| 2. Non-competitive inhibitor.
75
Describe how competitive inhibitors function.
1. Competitive inhibitors have a molecular shape similar to the substrate.
2. This allows them to occupy the active site of an enzyme.
3. They therefore compete with the substrate for the avaliable active sites.
76
Describe how non-competitive inhibitors function.
1. Non-competitive inhibitors attach themsleves to the enzyme at a binding site (allosteric site) that is not the active site.
2. This changes the shape of the active site and so the substrate cannot bind to the active site and the enzyme cannot function properly.
77
State two well-known polynucleotides.
1. DNA (deoxyribonucleic acid).
| 2. RNA (ribonucleic acid).
78
What three components are nucleotides made up of?
1. Pentose sugar.
2. Phosphate group.
3. Nitrogen-containing organic base (adenine, thymine, cytosine, guanine and uracil).
79
What bond forms between two nucleotides after a condensation reaction?
Phosphodiester bond.
80
What organic base can occur in RNA and not DNA?
Uracil (replaces thymine).
81
Name the three scientists that helped to understand the structure of DNA.
James Watson.
Francis Crick.
Rosalind Franklin.
82
How does the structure of DNA keep the molecule stable?
1. The phosphodiester backbone protects the more chemically reactive organic bases inside the double helix.
2. Hydrogen bonds link the organic base pairs, forming bridges.
83
How many hydrogen bonds form between Guanine and Cytosine?
3
84
How many hydrogen bonds form between Thymine and Adenine?
2
85
List a benefit of a DNA molecule being stable.
The stability of the molecule ensures that information and genes pass from generation to generation without change - rarely does it mutate.
86
What is the benefit of DNA being joined by hydrogen bonds?
Hydrogen bonds are easily broken, allowing the DNA strands to seperate during DNA replication and protein synthesis.
87
Base pairing has what benefit for DNA?
base pairing leads to DNA being able to replicate and transfer information as mRNA.
88
Describe what nuclear division is.
Nuclear division is the process by which the nucleus divides. There are two types - mitosis and meiosis.
89
What is Cytokinesis?
The process after nuclear division by which the whole cell divides.
90
What are the four requirements needed for semi-conservative replication to take place?
1. 4 types of nucleotide - thymine, adenine, guanine and cytosine.
2. Both strands of DNA must ars as a template.
3. Enzyme DNA Polymerase must be present.
4. A source of chemical energy must be avaliable to drive the process.
91
Explain the process of semi-conservative replication. (5 marks)
1. DNA helicase breaks hydrogen bonds linking base pairs.
2. Double helix unwinds and seperates into two strands.
3. Each polynucleotide strand then acts as a template strand and complementary free nucleotides bind by specific base pairing.
4. Nucleotides are joined together in a condensation reaction by the enzyme DNA Polymerase.
5. Each of the new DNA molecules contains half new and half original DNA.
92
What did the conservative DNA model suggest?
The original DNA molecule remained in tact and that a seperate daughter DNA molecule was built from entirely new material.
93
What three components make up an ATP molecule?
Adenine, ribose and phosphates.
94
What gives ATP its low activation energy level?
The bonds between the three phosphate groups are unstable.
95
State the hydrolysis reaction of ATP.
ATP + Water → ADP + Pi + Energy
96
What enzyme catalyses the hydrolysis of ATP?
ATP Hydrolase (ATPase).
97
The synthesis of ADP and Pi is catalysed by what enzyme?
ATP Synthase.
98
The synthesis of ATP occurs in what three ways?
1. In chlorophyll-containing plant cells during photosynthesis (photophosphorylation).
2. In plant and animal cells during respiration (oxidative phosphorylation).
3. In plant and animal cells when phosphate groups are transferred from donor molecules to ADP (substrate-level phosphorylation).
99
Why is ATP a better immediate source of energy compared to glucose? (2 marks)
1. Each ATP molecule releases less energy than each glucose molecule - reactions are smaller and more manageable.
2. The hydrolysis of ATP is a single reaction whereas the breakdown of glucose occurs in a series of reactions.
100
How is ATP used during metabolic processes?
ATP provides the energy needed to build up macromolecules from their base units.
101
How is ATP used during movement?
ATP provides the energy for muscle contraction.
102
How does ATP facilitate active transport?
ATP provides the energy to change the shape of carrier proteins in the plasma membranes.
103
How is ATP used during secretion?
ATP is needed to form the lysosomes necessary for the secretion of cell products.
104
How does the hydrolysis of ATP activate other molecules?
The inorganic phosphate released during the hydrolysis of ATP can be used to phosphorylate other compounds and make them more reactive.
105
What properties make water a dipolar molecule?
The oxygen atom has a slight negative charge, while the hydrogen atoms have a slight positive charge.
106
The attractive force between opposite poles in water is called what?
Hydrogen bond.
107
Hydrogen bonds help water molecules to what?
Stick together.
108
Why is the boiling point of water higher than expected?
As water molecules stick together, it takes more energy to seperate them than what would be needed if they did not bond together.
109
Why does water have a high specific heat capacity?
It takes more energy to heat a given mass of water because of its hydrogen bonds.
110
Why is water a good temperature - stable aquatic environment for an organism?
The high specific heat capacity of water buffers against sudden temperature changes.
111
Hydrogen bonding between water molecules means that it requires a lot of energy to evaporate 1g of water. This is called what?
Latent heat of vapourisation.
112
Explain what cohesion is and how cohesive properties affect water.
The tendancy of molecules to stick together.
| Water has large cohesive forces allowing it to be pulled up through a tube (e.g. xylem vessel).
113
What is surface tension and how does it benefit water?
When water molecules meet the air they tend to be pulled back into the body of water rather than escaping it.
The water surface acts like a skin and can support organisms such as pond skaters.
114
How is water used in metabolism? (3 marks)
1. Water is used to hydrolyse complex molecules.
2. Chemical reactions take place in an aqueous medium.
3. Water is a major material in photosynthesis.
115
If water readily dissolves other substances, it is said to be a what?
Solvent.
116
Why is the evaporation of water important to an organism?
The evaporation cools organisms and allows them to control their body temperature.
117
As water is not eaily compressed, what can it provide?
Support - e.g. the hydrostatic skeleton of animals and turgor pressure of plants.
118
Why is it beneficial that water is transparent? (2 seperate points)
1. Aquatic plants can photosynthesise.
| 2. Light rays can penetrate the jelly-like fluid that fills the eye and so can reach the retina.
119
What role do iron ions have in the body?
Iron ions are found in haemoglobin where they play a role in the transport of oxygen.
120
What role do phosphate ions have in the body? (2 roles)
1. Phosphate ions form a structural role in DNA molecules.
| 2. And a role in storing energy in ATP molecules.
121
What role do hydrogen ions have in the body?
Hydrogen ions are important in determining the pH of solutions and therefore the functioning enzymes.
122
What role do sodium ions have in the body?
Sodium ions are important in the transport of glucose and amino acids across plasma membranes (co-transport).
