Biological Molecules Flashcards
Water, Carbohydrates, Fats and Oils, Proteins, Food chemical tests
1
Q
What are monomers?
A
They are individual units that are joined together to form a polymer
2
Q
What are polymers?
A
They are large molecules composed of repeating structural units
3
Q
What are carbohydrates?
A
They are compounds that contain carbon, hydrogen and oxygen
4
Q
What are some examples of monosaccharides?
A
Glucose, Fructose, Galactose and Ribose
5
Q
What are some examples of disaccharides?
A
Sucrose, Maltose, Lactose
6
Q
What are some examples of polysaccharides?
A
Starch/Cellulose, Glycogen
7
Q
What are some properties of monsaccharides?
A
- They are soluble in water because of their hydroxyl group that forms hydrogen bonds when reacted with water
- They are crystalline and sweet tasting
8
Q
What is Glucose?
A
It is a hexose monosaccharide with the chemical formula C6H12O6
9
Q
Draw the structure of glucose molecule
A
https://www.geeksforgeeks.org/glucose-chemical-formula-structure-properties-uses-sample-questions/
10
Q
What is the difference between Alpha glucose and Beta glucose?
A
The position of the hydroxyl group on carbon 1 on alpha glucose is at the bottom of the ring while the hydroxyl group on carbon 1 on beta is on top of the ring
11
Q
Draw an α glucose and a β glucose
A
https://www.alamy.com/chemical-structure-of-alpha-d-glucose-and-beta-d-glucose-chemical-formula-of-d-glucose-and-d-glucose-compound-d-glucose-anatomy-image438297490.html
12
Q
What is Ribose?
A
It is a pentose monosaccharide
13
Q
Draw the structure of ribose
A
https://stock.adobe.com/uk/images/chemical-structure-of-ribose-c5h10o5/515960430
14
Q
How are Disaccharides formed?
A
Disaccharides are formed when two monosaccharides chemically react together
15
Q
What is a glycosidic bond?
A
It is the bond between two glucose molecules(1), the hydroxyl group on carbon 1(1) on one of the molecules and carbon 4 on the other(1) interacts in a condensation reaction(1) forming an oxygen bridge
16
Q
Describe the formation of maltose
A
Maltose is formed when two α glucose molecules chemically react and the hydroxyl on carbon 1 of one of the molecules reacts with the hydroxyl on carbon 4 of the other molecule in a condensation reaction which forms water
17
Q
Draw the structure of maltose
A
https://byjus.com/jee/maltose-structure/
18
Q
Formation of Sucrose
A
α glucose + fructose
19
Q
Formation of Lactose
A
β glucose + galactose
20
Q
What is Starch?
A
It is a glucose storage molecule in plants
21
Q
What is starch made up of?
A
Amylose + Amylopectin
22
Q
What is the structure of amylose?
A
- It is a polymer made up of α glucose chains
- The α glucose chains have a 1,4 glycosidic bond
- The chain then twists into a compact helix with hydrogen bonds between the molecules
23
Q
What is the structure of amylopectin?
A
- It is also a polymer made up of α glucose chains
- The α glucose chains also have a 1,4 glycosidic bond
- Amylopectin has a branched chain which is connected to the main chain by a 1,6 glycosidic bond
24
Q
How does the structure of starch relate to its function?
A
- Due to the helix structure of amylose, starch can hold more glucose molecules for its size
- It also makes it compact and insoluble so it doesn’t allow water to enter the cell by osmosis
- Due to the branched chains in amylopection, enzymes can rapidly break down starch to release glucose for respiration
25
What is glycogen?
It is an ideal glucose storage molecule in animals
26
What is the structure of glycogen?
1. It is also a polymer of α glucose molecules which are joined together by a 1,4 glycosidic bond
2. It also has branches which are connected to the main chain by a 1,6 glycosidic bond
3. It has more branches than amylopectin which means enzymes can quickly convert glycogen to release glucose for respiration
27
How does the structure of glycogen relate to its function?
1. It is insoluble in water and so it doesn't allow water to enter the cell by osmosis
2. It is also a big molecule so it can't diffuse out of the cell.
28
What is the structure of cellulose?
1. It is a polymer of beta glucose
2. The second glucose molecule is flipped 180° so that the OH on the carbon 4 is close enough to react in a condensation reaction , which forms a glycosidic bond with the OH on carbon 1 on the first β glucose molecule
3. The rotation of molecules then forms a straight chain molecule with hydrogen bonds between individual glucose molecules.
29
Draw the structure of cellulose
https://theory.labster.com/cellulose/
30
How does the structure of cellulose relate to its function? (4 marks)
Cellulose is a straight chain molecule(1) with many hydrogen bonds between the individual chains(1) and staggered ends(1). This confers strength to the fibres.(1)
31
Explain why β glucose when polymerised, leads to the production of cellulose instead of starch (6 marks)
In β glucose, the OH group on carbon 1 is above the ring(1), so alternate glucose molecule is flipped 180°(1) so the OH group on carbon 1 and 4 are close enough to react(1) in a condensation reaction(1) forming a β1,4 glycosidic bond(1). The rotation of molecules produces a straight chain molecule(1)
32
What are the function of lipids?
1. Main energy source
2. Provides insulation
3. Protects the organs like kidney
4. They are a major structure of the membrane e.g cells or mitochondria membrane
33
What are the types of lipids?
1. Triglycerides
2. Phospholipids
34
What are triglycerides?
They are non-polar molecules which means they do not dissolve in water (hydrophobic)
35
What is the structure of a triglyceride?
It is made up of 1 glycerol + 3 fatty acid molecules
36
What are fatty acids?
It is a long chain of hydrocarbon with a carboxyl group at the end (-COOH)
37
Types of fatty acids
Saturated and Unsaturated fatty acids
38
What are saturated fatty acids?
They are fatty acid chains that have no double bonds between the carbon atoms.
39
What are unsaturated fatty acids?
They are fatty acid chains that have double bonds between the carbon atoms
40
What does the presence of double bonds do to the fatty acid chain?
The presence of double bonds causes the chain to kink or bend and they therefore cannot pack closely together. This makes them liquid at room temperature
41
Describe the formation of a triglyceride
It is formed when one glycerol molecule reacts with 3 fatty acid molecules and the OH on the glycerol reacts with the OH on the fatty acids in a condensation reaction to form 3 water molecules
42
Draw the structure of a triglyceride
https://pressbooks.calstate.edu/nutritionandfitness/chapter/6-1-triglycerides-and-fatty-acids/
43
What bonds is formed when the OH on the glycerol reacts with the OH on the fatty acids?
Ester bonds are formed and the process is called esterification.
44
Describe the hydrolysis reaction of a triglyceride?
It involves 3 water molecules being used to break the triglyceride into 1 glycerol and 3 fatty acid molecules.
45
What is the structure of a phospholipid?
It is made up of a phosphate group + a glycerol molecule and 2 fatty acids
46
Explain how phospholipid molecules arrange themselves in cell membranes and relate this to their structure (3 marks)
They arrange themselves in a phospholipid bilayer (1) with fatty acid tails facing towards each other(1) and the phosphate group facing outwards towards the water because of their hydrophilic nature. This is because the fatty acid tails are hydrophobic, forcing them to face inwards away from the water (1)
47
Structure of cholesterol
It has a hydrocarbon ring structure attached to a hydrocarbon tail. The ring structure has a polar hydroxyl group attached to it making it hydrophilic.
48
How does cholesterol having a flattened shape relate to its function? (2 marks)
The flattened shape allows the cholesterol molecule to fit in between the phospholipids, causing the phospholipids to pack together more tightly (1) which makes the membrane less fluid and more rigid (1)
49
Function of cholesterol
Used in the liver to produce bile
Used as a starting point for hormones
Used to make vitamin D
Controls the fluidity of cell membrane
50
What is the monomer that makes up proteins?
Amino acids
51
What is the general structure of an amino acid?
https://www.savemyexams.com/a-level/biology/aqa/17/revision-notes/1-biological-molecules/1-3-biological-molecules-proteins/1-3-1-amino-acids--the-peptide-bond/
52
Describe the formation of a peptide bond?
A peptide bond is formed when the OH on the carboxyl of one amino acid reacts in a condensation reaction with the H on the amine group of another amino acid to form a water molecule
53
What are polypeptides?
It is a long chain of at least 30 amino acids (or more) that are joined together by peptide bonds
54
What are proteins?
It is a polypeptide that has folded into a complex, 3D shape
55
What are the levels of protein structure?
Primary
Secondary
Tertiary
Quaternary
56
What is the primary level of protein structure?
It is the sequence of amino acids in the polypeptide.
57
What is the secondary level of protein structure?
It is the folding of the polypeptide chain into either α helix or β pleated sheets
58
What is the tertiary structure of protein structure?
It is the folding of a polypeptide chain into its final 3D shape
59
What is the role of the R groups interaction in the formation of tertiary structure?
The R groups on amino acid can interact within a protein molecule and this determines the shape of the molecule
60
What is the quaternary level of protein structure?
It is when two or more polypeptides join together to form one big molecule
61
What is the role of the R groups interaction in the formation of quaternary structure?
The R groups can interact between protein molecules and this holds molecules together
62
What are the 4 bonds that the R groups can form?
Disulphide bonds
Hydrogen bonding
Hydrophobic and hydrophilic interactions
Ionic bonds
63
How is a disulphide bond formed?
It is formed when 2 sulphur atoms from 2 cysteine molecules form a covalent bond
64
Features of a disulphide bond?
1. Relatively strong
2. It's not broken by changes in pH or temperature
65
How is an ionic bond formed?
It is formed from oppositely charged R groups
66
Features of an ionic bond?
They are broken by changes in pH
67
How are hydrogen bonds formed within the structure of secondary proteins?
It forms when the negative charges on the oxygen(on the carboxyl) attracts the positive charge on the hydrogen (on the amine group)
68
Features of hydrogen bonds?
1. They are weak bonds
2. They are easily broken by changes in pH and high temperatures
69
Compare and contrast the role of R-group interactions in the formation of tertiary and quaternary structures of proteins. (6 marks)
R groups on amino acids interact (1). In a tertiary structure, the R groups interact WITHIN a protein molecule(1) which determines the shape of the protein (1). In quaternary structures, the R groups interact BETWEEN the protein molecules(1) and this holds the molecules together(1). Both structures involved the same interactions(1) e.g. ionic bonds, disulphide bonds, hydrogen bonds and hydrophobic and hydrophilic interactions.
70
What are the two ways protein are classified?
1 Their structure- globular and fibrous proteins
2. Their compositions- simple and conjugated
71
What are some features of globular proteins?
1. They are soluble in water.
2. They are spherical in shape and compact
72
Why are globular proteins soluble in water?
This is because the hydrophilic R-groups are outside of the protein which interacts with water, while the hydrophobic R-groups hide at the center of the protein away from water or the aqueous environment in the cytoplasm
73
What are the 3 examples of globular proteins?
Haemoglobin
Insulin (a hormone)
Catalase (an enzyme)
74
What is a simple protein?
It is a protein that does not have non-protein parts.
75
What are conjugated proteins?
They are globular proteins that contain non protein parts called prosthetic groups
76
What is haemoglobin?
It is a globular protein that has 4 polypeptide subunits (2 α helices and 2 β pleated sheets)
77
Where is it found and its functions?
It is found in red blood cells and its function is to reversibly bind to oxygen and transport it to body tissues where needed
78
Describe the structure of haemoglobin
1. It has 4 polypeptide subunits
2. Each subunit has a prosthetic "haem" group which contains a Fe2+ ion which is where oxygen binds to
This means that one molecule of haemoglobin can bind to 4 oxygen molecules
79
Equation of haemoglobin with oxygen
Haemoglobin+oxygen➡oxyhaemoglobin
Hb + 4O2⇌HbO8
80
Describe the structure of insulin
1. It is a globular protein and also a hormone
2. It has 2 polypeptide chains which are linked together by disulphide bonds
81
Function of insulin
It plays a role in blood glucose regulation
82
Why is the shape of a hormone important for its function?
The shape is important because hormones have to fit into specific receptors on cell- surface membranes to have their effect
83
Describe the structure of catalase?
1. It is a globular protein and also an enzyme
2. It is a quaternary protein that has 4 polypeptide subunits
3. Each subunit has a haem group with contains iron II oxide that catalyzes the breakdown of hydrogen peroxide
84
What are some features of fibrous proteins?
1. They play structural roles eg in bones, or in walls of arteries
2. They are insoluble because they contain large amounts of hydrophobic R groups amino acids
3. They form long rope-like molecules
85
Examples of fibrous proteins
Collagen
Elastin
Keratin
86
What is collagen?
It is a connective tissue found in skins, tendons and ligaments.
87
Describe the structure of collagen
(YOU DON'T HAVE TO KNOW THIS)
The polypeptide chains wrap tightly around each other to form three helix
In the polypeptide chain, every 3rd amino acid is glycine which has a hydrogen atom as its R group. This allows the polypeptide chains to warp tightly with hydrogen bonds between the polypeptide chain
88
What is keratin?
It is a fibrous protein that is found in nails, hairs and skin
89
Describe the structure of keratin
(YOU DO NOT NEED TO KNOW THIS)
It contains a large amount of cysteine amino acid which results in many strong disulphide bonds forming strong, inflexible and insoluble materials.
90
What is elastin?
It is a fibrous protein found in the walls of blood vessels(arteries) and in the alveoli of lungs
91
Function of elastin
It is very elastic and so it allows the structures to expand and return to their normal shape
92
What are the two types of inorganic ions?
Cations and anions
93
What are inorganic ions?
They are charged particles that are not part of a larger organic molecule
94
Describe the food test of proteins
1. Make your food sample
2. Add biuret solution and shake
POSITIVE RESULT- If protein is present then the solution will change from blue to purple
95
What are cations?
Cations are positively charged ions
96
What are anions?
Anions are negatively charged ions
97
Examples of cations
Calcium ions- Ca2+
Sodium ions- Na+
Potassium ions- K+
Hydrogen ions- H+
Ammonium ions- NH4+
98
Function of Ca2+ ions?
1. Acts as a cofactor for many enzymes
2. It is important for bone formation
99
Function of Na+ ions?
100
Examples of anions
Nitrate ions - NO3-
Phosphate ions- PO3-4
Hydroxide ions- OH-
Hydrogencarbonate ions- HCO-3
Chloride ions- Cl-
101
Describe the food test for starch?
1. Make your food sample
2. Add iodine solution that has been dissolved in potassium iodide and mix
POSITIVE RESULT- if starch is present, the solution will change from orange to blue-black
102
Describe the food test for REDUCING SUGARS
1. Make your food sample
2. Add benedict's solution and gently heat it in a water bath
POSITIVE RESULT- If reducing sugars are present, the sample will change from blue to either green, yellow, red or brick red depending on the concentration of the RS
103
Describe the food test for lipids
1. Make your food sample but this time DO NOT FILTER IT
2. Add ethanol, water and then shake it
POSITIVE RESULT- If lipids are present, then a white emulsion layer will form
104
Describe the test for NON-REDUCING sugars?
1. Make your food sample
2. Carry out the benedict's test and this will give a negative result
3. Add concentrated HCl and this is added to break the glycosidic bonds between the monosaccharides releasing them
4. Add an alkali to neutralize the acid eg sodium carbonate or sodium hydroxide
5. Carry out the benedict's test again and this will give a positive result
105
What is the purpose of carrying out a benedict's test first?
To prove that it is a non reducing sugar
106
Why do we neutralize the acid?
We do this because Benedict's solution doesn't work in acidic conditions
107
How can test strips be used to quantify concentration of glucose?
The strips are dipped in a test solution and change colour if glucose is present. The colour change can be compared to a chart to give an indication of the concentration of glucose present
108
When can test strips be useful?
They can be useful for testing a person's urine for glucose which could indicate they have diabetes
