1
Q
What are carbohydrates primarily composed of?
A
Carbon, hydrogen, and oxygen
Carbohydrates follow the general formula (CH₂O)n.
2
Q
What is a monomer of carbohydrates called?
A
Monosaccharide
3
Q
What is the general formula for monosaccharides?
A
(CH₂O)n
4
Q
Name three examples of monosaccharides.
A
- Glucose
- Galactose
- Fructose
5
Q
How many isomers does glucose have?
A
Two: alpha and beta
6
Q
What is a reducing sugar?
A
A sugar that can donate electrons to another chemical
7
Q
What is the purpose of Benedict’s reagent?
A
To test for reducing sugars
8
Q
What forms when a reducing sugar reacts with Benedict’s reagent?
A
An insoluble red precipitate of copper(I) oxide
9
Q
Describe the steps of the Benedict’s Test.
A
- Add 2 cm³ of the food sample to a test tube
- Add an equal volume of Benedict’s reagent
- Heat the mixture in a gently boiling water bath for 5 minutes
10
Q
Fill in the blank: A reducing sugar can _______ another chemical.
A
reduce
11
Q
True or False: Maltose is a reducing sugar.
A
True
12
Q
What are disaccharides?
A
Pairs of monosaccharides
Examples include maltose (glucose + glucose), lactose (glucose + galactose), and sucrose (glucose + fructose).
13
Q
What happens when monosaccharides join?
A
A molecule of water is removed in a condensation reaction, forming a glycosidic bond.
This process connects monosaccharides to form disaccharides.
14
Q
What is hydrolysis in the context of disaccharides?
A
The addition of water to a disaccharide that breaks the glycosidic bond, releasing monosaccharides.
This reaction is the reverse of the condensation reaction.
15
Q
Define polysaccharides.
A
Polymers formed from the joining of many monosaccharides by glycosidic bonds.
They are large, insoluble molecules suitable for storage.
16
Q
What role do some polysaccharides like cellulose play?
A
Provide structural support to plant cells.
Cellulose is not used for storage.
17
Q
What are the characteristics of fructose?
A
Very soluble, main sugar in fruits, sweeter than glucose.
Fructose is a monosaccharide.
18
Q
How does galactose compare to glucose in terms of solubility?
A
Galactose is not as soluble as glucose.
It plays an important role in the production of glycolipids and glycoproteins.
19
Q
List the characteristics of sugars.
A
- Sweet taste
- Low molecular mass
- Soluble in water
- Used for energy
Sugars are typically simple carbohydrates.
20
Q
What are the characteristics of non-sugars?
A
- Non-sweet taste
- Insoluble in water
- High molecular mass
- Important role in storage and structure
Non-sugars include complex carbohydrates.
21
Q
Structure of starch
A
- Made up of chains of a-glucose monosaccharides linked by glycosidic bonds that are formed by condensation reactions
- these chains can be branched or unbranched
-> the un branched chain is wound into a coil (helix) which makes the molecule compact
22
Q
The pairs of monosaccharides
A
- glucose + glucose -> maltose
- glucose + fructose -> sucrose
- glucose + galactose -> lactose
23
Q
How the properties of starch help it
A
- insoluble -> doesn’t affect water potential so water isn’t drawn into the cell by osmosis
- large -> can’t diffuse out of cells
- coiled ->compact, lots can be stored in small space
- when hydrolysed is form a-glucose -> easily transported and readily used in respiration
- branded form has many ends -> enzymes can act simultaneously (large SA for hydrolysis back to glucose)
24
Q
Why does glycogen have more branches than starch
A
Because animals have a higher metabolic rate than plants and so higher respiratory rate
25
Where is glycogen found
In bacteria and animals
26
Where is glycogen stored in animals
In small granules mainly in muscles and liver
27
Properties of glycogen
- insoluble
- compact
- large
- more branched than starch -> enzymes can easily hydrolyse glycosidic bonds to rapidly release glucose
- hydrolysis releases alpha-glucose monomers -> readily used in respiration
28
What monomers are cellulose made of
B-glucose
29
Structure of cellulose
- instead of coiled chain like starch it forms straight, long unbranched chains
-> these run parallel to each other which allows H2 bonds to form cross-linkages
-> individually the H2 bonds are weak but collectively very strong
- the cellulose molecules are grouped to form microfibrils
- cellulose also prevents the cell from bursting as water enters by osmosis
30
Properties of cellulose
- Made from B-glucose -> to form long straight unbranched chains - provide rigidity to cell wall
- Chains run parallel to one another -> are cross-linked by H2 bonds that add collective strength
- Grouped to form microfibrils -> provides more strength
31
What are lipids primarily composed of?
Carbon, hydrogen, and oxygen
## Footnote
Lipids have a high proportion of carbon and hydrogen relative to oxygen.
32
Are lipids soluble in water?
No, they are insoluble in water
## Footnote
Lipids are soluble in organic solvents like alcohol and acetone.
33
What are the main groups of lipids?
* Triglycerides (fats and oils)
* Phospholipids
34
What role do phospholipids play in cellular membranes?
Contribute to the flexibility of membranes and transfer of lipid-soluble substances across them.
35
What is one source of energy in the body?
Lipids
36
What function do lipids serve in waterproofing?
Insoluble in water
37
How do fats contribute to insulation?
Fats are poor conductors of heat and act as electrical insulators in the myelin sheath around nerve cells.
38
What protective role do lipids have in the body?
Fat is often stored around organs.
39
What are triglycerides formed from?
3 fatty acids and 1 glycerol
40
What type of reaction forms ester bonds between fatty acids and glycerol?
Condensation reaction
41
What products are formed from the hydrolysis of a triglyceride?
Glycerol and 3 fatty acids
42
Fill in the blank: A triglyceride is composed of _____ fatty acids and one glycerol.
3
43
True or False: Hydrolysis of triglycerides results in the formation of water.
True
44
5 roles of lipids
- flexibility of membranes + transfer of lipid-soluble substances across them
- source of energy
- waterproofing
- insulation
- protection
45
What is the primary component that varies among different fats and oils?
Variations in the fatty acids
## Footnote
There are over 70 different fatty acids, each contributing to the properties of fats and oils.
46
What functional group is present in all fatty acids?
Carboxyl (-COOH) group
## Footnote
This group is attached to a hydrocarbon chain in fatty acids.
47
What characterizes a saturated fatty acid?
No C double bonds in the hydrocarbon chain
## Footnote
Saturated fatty acids are solid at room temperature.
48
What defines a monounsaturated fatty acid?
Presence of a single double bond
## Footnote
This type of fatty acid has one double bond in its hydrocarbon chain.
49
How is a polyunsaturated fatty acid characterized?
More than one double bond present
## Footnote
Polyunsaturated fatty acids tend to be liquid at room temperature.
50
What effect do double bonds have on the structure of fatty acids?
Cause the molecule to bend
## Footnote
This bending prevents tight packing, making them liquid at room temperature.
51
What is a significant property of triglycerides related to energy?
High ratio of energy-storing C-H bonds to C atoms
## Footnote
This makes triglycerides an excellent source of energy.
52
What is the mass-to-energy ratio of triglycerides?
Low mass to energy ratio
## Footnote
This allows for more energy to be stored in a smaller volume.
53
Why are triglycerides considered good storage molecules?
They can store more energy in a small volume
## Footnote
This reduces the mass animals have to carry.
54
What is the solubility of triglycerides in water?
Insoluble in water
## Footnote
This characteristic prevents them from affecting water potential.
55
What is the ratio of H:O atoms in triglycerides, and what does it provide?
High ratio of H:O atoms; provides a source of water when oxidized
## Footnote
This is important for energy metabolism in animals.
56
What are phospholipids?
Lipids similar to lipids but one fatty acid is replaced by a phosphate molecule
## Footnote
Phospholipids are essential components of cell membranes.
57
What is the hydrophilic part of a phospholipid called?
Hydrophilic head
## Footnote
The hydrophilic head attracts water.
58
What is the hydrophobic part of a phospholipid called?
Hydrophobic tail
## Footnote
The hydrophobic tail repels water and mixes readily with fat.
59
What characteristic of phospholipids allows them to form a bilayer in an aqueous environment?
Their polar nature
## Footnote
The hydrophilic heads orient towards water while the hydrophobic tails orient away.
60
What structure do phospholipids create within cell-surface membranes?
A bilayer
## Footnote
This bilayer forms a hydrophobic barrier between the outside and inside of a cell.
61
How do hydrophilic heads behave in relation to water?
They are attracted to water
## Footnote
This allows them to hold at the surface of the cell-surface membrane.
62
What role do glycolipids play in cell membranes?
They are important in cell recognition
## Footnote
Glycolipids are formed by the combination of phospholipids with carbohydrates.
63
Fill in the blank: Phospholipids have a _______ head and a _______ tail.
hydrophilic; hydrophobic
## Footnote
This dual nature is crucial for their function in membranes.
64
Why are saturated fats more unhealthy
Because they are densely compacted
65
What are the monomers of proteins
Amino acids
66
How is a dipeptide formed
When 2 amino acids join
67
How is a polypeptide formed
When more than 2 amino acids join
68
What makes up proteins
1 or more polypeptides
69
What makes up amino acids
- a carboxyl group (-COOH)
- an amine or amino group (-NH2)
- an R group (variable side group)
- a H
70
What differentiates amino acids
What makes up their R group
-> 20 different amino acids
71
Why is glycine special
It’s the only amino acid with no C in its side group -> it’s R group is just 1 hydrogen atom
72
What is a condensation reaction
A condensation reaction joins 2 molecules together with the formation of a chemical bond and involves the elimination of a molecule of water
73
Hydrolysis
A hydrolysis reaction breaks a chemical bond between two molecules and involves the use of a water molecule
74
How are polypeptides formed
When amino acids link together by condensation reactions
-> a molecule of water is released and the bonds formed between amino acids are called peptide bonds
(The reverse happens in digestion)
75
The 4 protein structural levels
- primary structure
- secondary structure
- tertiary structure
- quaternary structure
76
Primary structure of proteins and
The sequence of amino acids in the polypeptide chains
-> determines its shape and function
77
Secondary structure of proteins
The polypeptide chain doesn’t stay flat and straight - hydrogen bonds form between the amino acids in the chain
-> this makes it coil into an alpha helix or fold into a beta pleated sheet
78
Tertiary structure of proteins
When the coiled or folded chain is coiled or folded even more, more bonds form:
• Disulfide bridges - fairly strong and so not easily broken
• Ionic bonds - formed between any carboxyl and amino groups that aren’t involved in forming peptide bonds
-> weaker than disulfide bonds and easily broken by changes in pH
• Hydrogen bonds - numerous but easily broken
- for single polypeptide chain proteins this structure forms their final 3D structure
79
Quaternary structure of proteins
Some proteins are made of several different polypeptide chains held together by bonds
-> this structure is the way these chains are assembled
-> for proteins formed from multiple polypeptide chains this is the final 3D structure
80
2 types of proteins
• Fibrous proteins (eg collagen) - have structural functions
• Globular proteins (eg enzymes, haemoglobin) - carry out metabolic function
81
Protein Functions
- enzymes
- antibodies
- transport proteins
- structural proteins
82
Proteins as enzymes
- usually spherical shape due to tight folding of polypeptide chains
- soluble + often have roles in metabolism
83
Proteins as antibodies
- involved in immune response
- made up of 2 light polypeptide chains + 2 heavy ones bonded together
- have variable regions -> the amino sequence in the regions vary a lot
84
Proteins as transport proteins
E.g. channel proteins are present in cell membranes
-> contain hydrophobic + hydrophilic amino acids which cause the protein to fold up and forms channel
-> they transport molecules and ions across membranes
85
Proteins as structural proteins
- strong with long polypeptide chains parallel to each other with cross-links
- includes keratin (in hair + nails) and collagen (in connective tissue)
86
Biuret test
- solution needs to be alkaline so add a few drops of NaOH solution
- then add copper (II) sulfate solution
-> if protein is present it will turn purple from blue
87
What is activation energy
The minimum amount of energy required for a reaction to take place
88
What does an enzyme do
Lower the activation energy and so speeds up to reaction without being used up
89
Explain why the quaternary structures of collagen makes it a suitable molecule for a tendon
It’s made up of 3 polypeptide chains wound together making it strong in the direction of pull of the tendon
90
How do the cross-linkages between the amino acids of polypeptide chains increase the strength and stability of a carbon fibre
Prevents the individual polypeptide chains sliding past each other
91
Explain why this arrangement of collagen molecule is necessary for efficient functioning of a tendon
The junctions between the adjacent molecules are weak and if they joined back where it started they could easily break
92
Globular proteins
- have spherical shape
- soluble in water
- tend to have a biochemical function over a structural one
- all enzymes are globular proteins
93
What reactions do enzymes catalyse
Both anabolic (building up) and catabolic (breaking down) reactions
94
Where does enzyme action occur
Both intracellularly (eg DNA replication) and extracellularly (eg digestion)
95
Lock and key model
Substrate is perfectly complimentary to active site of enzyme then substrate breaks into product molecules
-> substrates only fits 1 active site (fixed shape)
96
Limitation of lock and key model
Rigid structure instead of flexible
97
Induced fit theory
- Substrate molecule isn’t exact shape of the enzyme’s active site
- enzyme molecule changes shape slightly as the substrate molecule binds with the active site
- enzyme then resumes original shape and active site is free to accept another pair of substrate molecules
98
What does the induced fit theory propose
That the active site forms as the enzyme and substrate interact
99
How do enzymes cause activation energy to decrease
The enzyme is flexible and can mould itself around the substrate -> as it changes shape, it puts **strain** on the substrate molecule which **distorts** a particular bond(s) in the substrate causing the **activation energy** needed to break the bond to decrease
100
Factors that affect enzyme action
- temp
-pH
-substrate conc
- enzyme conc
101
Effect of temp on enzymes
- Increase in kinetic energy so molecules collide more frequently (RoR increase)
- eventually denatures as the weak H bonds break and tertiary structure unravels
-> active site distorts so its not complimentary to the substrate
102
Effect of pH on enzymes
- A change alters the charges on the amino acids that make up the active site
- they denature due to weak H bonds breaking which distorts the active site
- this makes it not complimentary to the substrate
103
Effect of substrate conc in enzymes
The number of substrate exceeds the number of enzymes
104
Effect of enzyme conc on enzymes
The number of enzymes exceeds the number of substrates conc
105
What are inhibitors
Substances that interfere with enzyme activity
106
Competitive inhibitor
- molecular shape similar to substrate
-> so they compete for the active site with the normal substrate
- if the normal substrate conc is increased the effect of the inhibitor is reduced
107
Non-competitive inhibitor
- Attach to a site on the enzyme which isn’t the active site
-> this leads to a change in the shape of the active site so the substrate can no longer occupy it
- as the substrate and inhibitor aren’t competing for the same site an increase in substrate conc doesn’t decrease the effect of the inhibitor
108
What is an inorganic ion
An ion that doesn’t contain carbon
109
What are inorganic ions used for
Central to the structure and metabolism or all living organisms, participating in metabolic reactions and combining with organic molecules to form complex molecules
110
Cation
A positive ion
111
Anion
A negative ion
112
Sodium (Na+)
- Generating nerve impulses
- Muscle contraction
- Co-transport of glucose and AAs
- in plants, its involved in maintaining cell turgid + in opening and closing the stomata
113
Potassium (K+)
- Generating nerve impulses
- Muscle contraction
- Regulating fluid balance
- in plants, it’s involved in controlling stomata opening via guard cells
114
Ammonium (NH4+)
Source of nitrogen for plants
115
Iron (Fe3+/Fe2+)
Bind to oxygen within haemoglobin
116
Hydrogen (H+)
- Determines the pH of solutions
- Used in photosynthesis reactions
117
Calcium (Ca2+)
- Nerve impulse transmission
- Muscle contraction
- Cofactor for enzymes
- in plants, it’s a component of the cell wall
118
Hydrogen carbonate (HCO3-)
Maintains blood pH
119
Chloride (Cl-)
- Maintains blood pH in gas exchange
- Cofactor for amylase enzyme
120
Nitrate (NO3-)
- important source of nitrogen for plants
BUT anaimls obtain their nitrogen by eating other organisms
- nitrogen is a component of amino acids and nucleotides
121
Phosphate (PO4 3-)
- component of phospholipids, nucleotides and ATP
- bonds store energy in ATP
122
Hydroxide (OH-)
Determines the pH of solutions
123
ATP
Adenosine Triphosphate
124
Structure of ATP
A phosphorylated macromolecule w/ 3 parts:
• adenine - a nitrogen-containing organic base
• ribose - a sugar molecule w/a 5 carbon ring structure (pentose) which all else is attached to
• phosphates - a chain of 3 phosphate groups
125
What does adenine and ribose make
Adenosine
126
What does adenine, ribose and 1 phosphate group make
Adenosine monophosphate (AMP)
127
What does adenine, ribose and 2 phosphate groups make
Adenosine diphosphate (ADP)
128
What does adenine, ribose and 3 phosphate groups make
Adenosine triphosphate (ATP)
129
What is ATP also
A nucleotide
130
What is significant about the phosphate groups in ATP
The bonds between them are unstable and so have a low activation energy, meaning they can be easily broken to release lots of energy
131
How is ATP converted to ADP
Water is used in a hydrolysis reaction and the reaction is catalysed by the enzyme **ATP hydrolase** to break the bonds between the 2nd + 3rd phosphate groups
132
How is ADP converted back to ATP
Energy can be used to add an inorganic phosphate to ADP to reform ATP -> this condensation reaction is catalysed by ATP synthase
133
When does the synthesis of ATP from ADP occur
- in chlorophyll-containing plant cells during photosynthesis (photophosphorylation)
- in plants and animal cells during respiration (oxidative phosphorylation)
- in plant and animals cells when phosphate groups are transferred from donor molecules to ADP (substrate-level phosphorylation)
134
Why is ATP a better immediate energy source than glucose
- the hydrolysis of ADP to ATP is a single reaction whereas the breakdown of glucose is a lot of reaction and so energy release is slower
- each ATP molecule release less energy than each glucose molecule
-> therefore they are more manageable quantities
135
What organelle makes ATP and when
Mitochondria during aerobic respiration
136
Role of ATP in metabolic processes
ATP provides the energy needed to build up macromolecules from their basic units eg AA to polypeptides
137
Role of ATP in movement
ATP provides energy for muscle contraction
138
Role of ATP in active transport
ATP provides the energy to change the shape of carrier proteins in plasma membranes -> allows ions/molecules to be moved against a conc gradient
139
Role of ATP in secretion
ATP needed to form lysosomes necessary
-> in lysosomes enzymes are secreted
140
Role of ATP in activation molecules
Inorganic phosphate released during hydrolysis of ATP can be used to phosphorylate other compounds in order to make them more reactive
-> lowering the activation energy in enzyme-catalysed reactions
141
Why is ATP sometimes referred to as an immediate energy source
The phosphate bonds are unstable so it’s quick
142
Explain how ATP can make an enzyme catalysed reaction take place more readily
Lowers the activation energy -> the inorganic phosphate
143
3 roles of ATP in plant cells
- photosynthesis
- respiration
- when phosphate groups are transferred from donor molecules to ATP
- metabolism
gene expression
144
Why is water dipolar
The oxygen atom has a slight -ve charge whisky the hydrogen atoms have a slight +ve charge
145
Hydrogen bonding in water
The attractive force between the opposite charges is called a hydrogen bond
146
Water as a metabolite
Water is involved in many chemical reactions inside organisms.
These reactions include:
- Hydrolysis reactions - These use water to break down complex molecules.
- Condensation reactions - These release water to join molecules together.
- Photosynthesis - This uses water as a raw material.
147
Water as a solvent
Readily dissolves other substances:
- Most biological reactions take place in solution - e.g. in the cytoplasm of eukaryotes and prokaryotes
- Dissolved substances can be transported around the body - e.g. ions can be transported in the blood plasma
148
Water with high heat capacity
- The many hydrogen bonds between water molecules can absorb a lot of energy before being broken, so it takes a lot of energy to break the hydrogen bonds and heat the water
149
Water with a large latent heat of vaporisation
- A lot of energy needed to break hydrogen bonding between water molecules -> requires lots of energy to evaporate 1g of water
- Can use evaporation of water as a method of cooling without losing too much water.
-> when water evaporates from the surface of the skin, it takes heat energy away from the surface, cooling the organism down
150
Water as cohesive
- tendency of water molecules to stick together
- hydrogen bonds -> gives it large cohesive forces which allow water to be pulled up through a tube (eg xylem vessel)
- water polar -> +ve hydrogen -ve oxygen
- surface tension
151
Describe how the properties of water allow a tree to survive
- a metabolite
- the water molecules stick together due to hydrogen bonding so waters bp is high (it buffers them against sudden temp changes)
- water has large cohesive forces which allow it to be pulled up through the xylem so it can replace water that’s been evaporated in the leaf
- it’s a major raw material in photosynthesis helping it to produce glucose
- solvent -> can help transport mineral ions
152
Describe how the properties of water allows humans to survive
- evaporation of water eg sweat helps cooling as body heat is used to evaporate the water due to a lot of latent heat of vaporisation -> uses a lot of heat energy so cools you down removing heat
- used in hydrolysis
- produced in condensation reactions
- dissolves in wastes like urea
- can evaporate which helps control temp -> prevents enzymes denaturing - acts as a temp buffer
- not easily compressive so provides support eg the skeleton
153
What does RNA stand for
Ribonucleic acid
154
What does DNA stand for
Deoxyribonucleic acid
155
What does each nucleotide consist of
Phosphate group
Deoxyribose (pentose sugar)
Organic base
156
What is the polymer made from the nucleotide monomers
DNA
157
Double helix structure
- adenine always bonds with thymine
- guanine always bonds with cytosine
- bases held together by hydrogen bonds
- complementary base pairing
- order of letters makes DNA code
158
What are pyrimidines
Single ring bases - C and T
159
What are purines
Double ring bases - A and G
160
What joins A and T
2 hydrogen bonds
161
What joins C and G
3 hydrogen bonds
162
What does more GC mean in DNA and why
Means it is more stable and harder to split up as they form a base pair with 3 hydrogen bonds opposed to the 2 hydrogen bonds between AT
163
How is a polynucleotide made
The phosphate bonds to the C of the deoxyribose sugar in a condensation reaction forming a phosphodiester bond which joins adjacent nucleotides together
164
RNA structure
- contains A, C and G but U (uracil) instead of T
- the sugar is ribose not deoxyribose
- it’s a single strand not double
- different types: mRNA, tRNA, rRNA
165
Name the 4 bases found in DNA and the bonds formed between them
Adenine, Guanine, Thymine, Cytosine
Hydrogen bonds
166
Which molecules make up the backbone of a polynucleotide
Phosphate and deoxyribose
167
What are the 3 differences between DNA and RNA
- RNA contains uracil not thymine
- RNA has ribose sugar not deoxyribose
- RNA is single strand not double
168
What is the structure of ATP
Adenine, ribose and 3 phosphate groups
169
What does the hydrolysis of ATP produce
ADP
170
Give the equation for the formation of ATP
ADP + inorganic phosphate -> ATP + water
171
How is DNA stable
- the phosphodiester backbones protects the more chemically reactive organic base
- hydrogen bonds link the organic bases
172
Function of DNA
It’s the hereditary material that passes on genetic material from generation to generation
173
DNA adaptations for its function
- very stable
- only hydrogen bonds join the 2 strands -> can separate during DNA replication and protein synthesis
- very large -> so carries a lot of genetic info
- the base pairs are within the sugar-phosphate backbones -> so the genetic info is protected
174
Five key properties of water
1. It is a metabolite (e.g. in condensation and hydrolysis reactions).
2. An important solvent in reactions.
3. Has a high heat capacity, it buffers temperature.
4. Has a high latent heat of vaporisation, providing a cooling effect with loss of water
5. Has strong cohesion between water molecules; this supports water columns and provides surface tension
175
Role of iron ions
Haemoglobin binds/associates with oxygen
OR
Haemoglobin transports/loads oxygen;
176
Role of sodium ions
- Co-transport of glucose/amino acids (into cells);
(Because) sodium moved out by active transport/Na - K pump;
- Creates a sodium concentration/diffusion gradient;
- Affects osmosis/water potential;
177
Role of phosphate ions
1. Affects osmosis/water potential;
2. Joins nucleotides/in phosphodiester bond/in backbone of
DNA/RNA/in nucleotides:
3. Used in/to produce ATP;
4. Phosphorylates other compounds (usually) making them more reactive;
10. Hydrophilic/water soluble part of phospholipid bilayer/membrane;
178
What are the biological molecules
- Carbohydrates
- Proteins
- Lipids
- Nucleic acids
179
What are the monomers of the biological molecules
- Monosaccharides
- Amino acids
- Nucleotides
180
What elements do the biological molecules contain
- Carbohydrates: carbon (C), hydrogen (H), and oxygen (O).
- Lipids: carbon (C), hydrogen (H), and oxygen (O).
- Proteins: carbon (C), hydrogen (H), oxygen (O), and nitrogen (N).
- Nucleic acids: carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and phosphorus (P).
181
Roles of carbohydrates
1. **Energy supply for cells** - This is the main role of carbohydrates.
2. **Energy storage** - Sugars can be stored as complex carbohydrates (e.g. starch or glycogen).
3. **Structural components** - Cellulose and chitin are used in cell walls.
4. **Cellular recognition** - Glycoproteins help cells identify each other and communicate.
5. **Building blocks for biological molecules** - Deoxyribose and ribose can be used to make nucleic acids.
182
Main function of the different types of carbohydrates
Monosaccharides - energy source
Disaccharides - transport form
Polysaccharides - storage form
183
Hexose sugars
- glucose
- fructose
- galactose
184
Pentose sugars
- ribose
- deoxyribose
185
What features of glucose help it as an energy source
1. It is soluble - The hydroxyl groups can form hydrogen bonds with water, so it can be transported around organisms.
2. Its bonds store lots of energy - This energy is released when the bonds are broken.
186
What bonds make up starch
alpha-glucose monomer joined via 1-4 and 1-6 glycosidic bonds
187
What bonds make up glycogen
alpha-glucose monomers joined via 1-4 and 1-6 glycosidic bonds
188
Quantitative methods to determine concentration of reducing sugars
- Use a colorimeter to measure the absorbance of each solution.
- Filter the solution and weigh the precipitate.
189
Test for non-reducing sugars
1. Carry out the test for reducing sugars, and if the result is negative (turns blue), continue with the next steps.
2. Add 2 cm3 of the food sample to 2 cm3 of dilute hydrochloric acid.
3. Heat the mixture in a gently boiling water bath for 5 minutes (the acid will hydrolyse disaccharides into monosaccharides).
4. Neutralise the mixture by adding sodium hydrogencarbonate solution.
5. Retest this mixture using the test for reducing sugars.
6. If non-reducing sugars were present at the start, the mixture will now change from a blue solution to a brick red precipitate.
190
Testing for starch
1. Place 2 cm3 of your food sample into a test tube.
2. Add a couple of drops of iodine solution and shake.
3. If starch is present, the solution will turn from orange to blue-black.
191
Test for lipids
1. Place your food sample in a test tube.
2. Add 2 cm3 of ethanol.
3. Shake.
4. Add 2 cm3 of distilled water.
5. If lipids are present, a milky white emulsion will appear.
192
Features that allows triglycerides to store energy efficiently
1. Long hydrocarbon tails - Their many carbon-hydrogen bonds can be broken to release energy.
2. Low mass to energy ratio - Lots of energy can be stored in a small volume.
3. Insoluble - They do not affect the water potential of cells as they are large and non-polar.
4. High ratio of hydrogen to oxygen atoms - Triglycerides will release water when oxidised.
193
Roles of proteins in living organisms
1. Enzymes - These proteins are used to breakdown and synthesise molecules.
2. Antibodies - These proteins are involved in the immune response.
3. Transport - Some proteins can move molecules or ions across membranes.
4. Structural components - Proteins like keratin and collagen are used to create strong fibres.
5. Hormones - Some of these are proteins that act as chemical messengers in the body.
6. Muscle contraction - Muscles are made up of proteins.
194
More about the bonds in protein's tertiary structure
1. Hydrogen bonds - These are individually weak but provide strength in large numbers.
2. Ionic bonds - These form between positive and negative R groups.
3. Disulfide bridges - These form between R groups that contain sulphur (such as cysteine).
4. Hydrophobic and hydrophilic interactions - These are weak interactions between polar and non-polar R groups.
195
Differences between intracellular enzymes and extracellular enzymes:
1. Intracellular enzymes - These act within the cells that produce them.
2. Extracellular enzymes - These act outside the cells that produce them, and are secreted.
196
What happens when enzymes bind substrates
1. Enzymes have unique tertiary structures which determine the shape of their active site.
-> this shape is complementary to the substrate
2. The substrate binds to the active site to form an enzyme-substrate complex
3. Temporary bonds form between the R groups within the active site and the substrate
-> these bonds lower the activation energy to help break down the substrate into products
4. The products are released from the active site, leaving the enzyme free to be used again.
197
Description of temperature and enzyme graph
1. As temperature increases, the rate of reaction increases.
2. The maximum rate is reached at the optimum temperature.
3. As temperature increases past the optimum, the rate of reaction decreases until the reaction stops.
198
Explanation of temperature and enzyme graph
1. The molecules have more kinetic energy, causing more collisions and enzyme-substrate complexes.
2. The optimum temperature is the temperature this enzyme works fastest at.
3. Too much kinetic energy causes the active site to change shape and the enzyme denatures.
199
Explanation of pH and enzyme graph
1. In acidic conditions, H+ ions break ionic/hydrogen bonds and denature enzymes.
2. The optimum pH is the pH the enzyme works fastest at.
3. In alkaline conditions, OH- ions break ionic bonds or hydrogen bonds and denature enzymes.
200
Description of pH and enzyme graph
1. Below the optimum pH, the rate of reaction is low or zero.
2. The maximum rate of reaction is reached at the optimum pH.
3. Above the optimum pH, the rate of reaction is low or zero.
201
Explanation of substrate conc and enzyme graph
1. There are more substrate molecules to form more enzyme-substrate complexes.
2. This is the saturation point, which is when all active sites are occupied by a substrate and enzyme concentration becomes the limiting factor.
202
Description of substrate conc and enzyme grpah
1. As the substrate concentration increases, the rate of reaction increases.
2. As the substrate concentration increases further, the rate of reaction plateaus (levels off).
203
Explanation of enzyme conc graph
1. There are more enzyme molecules to form more enzyme-substrate complexes.
2. All substrate molecules available are being acted upon and substrate concentration becomes the limiting factor.
204
Description of enzyme conc graph
1. As the enzyme concentration increases, the rate of reaction increases.
2. As the enzyme concentration increases further, the rate of reaction plateaus (levels off).
205
Reversible vs irreversible inhibitors
- Reversible inhibitors - These form weak bonds (e.g. hydrogen or ionic) with the enzyme.
- Irreversible inhibitors - These form strong bonds (e.g. covalent) with the enzyme.
206
Watson and Crick
found out the structure of DNA
207
DNA vs RNA role
DNA: contains the instructions needed to make proteins
RNA: uses information from DNA to synthesise proteins
208
The following features allow ATP to work well as an immediate energy source:
1. The hydrolysis of ATP releases a small amount of energy, meaning little energy is lost as heat.
2. ATP is broken down in one step, meaning energy is released quickly.
3. ATP is rapidly re-synthesised so that ATP is always readily available.
4. The inorganic phosphate from ATP hydrolysis can phosphorylate other compounds, which makes them more reactive.
5. The bonds between the phosphate groups are unstable, have a low activation energy and are easily broken.
6. ATP is soluble, so it can easily be transported around cells.
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210
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Examples of condensation reactions
•Formation of glycosidic bonds in carbohydrates.
•Formation of peptide bonds in proteins.
• Formation of phosphodiester bonds in nucleic acids.
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Examples of hydrolysis reactions
•Breaking starch into maltose using amylase (glycosidic bond hydrolysis).
•Breaking proteins into amino acids using proteases (peptide bond hydrolysis).
•Removing fatty acids from glycerol in triglycerides using lipases (ester bond hydrolysis).
213
Explain how biological polymers are formed and broken down. (2 marks)
Biological polymers are formed by condensation reactions, where many monomers join together, forming covalent bonds and producing water.
Conversely, biological polymers are broken down by hydrolysis reactions, where water is added to break the covalent bonds between monomers.
214
Contrast the structure of monosaccharides and polysaccharides (3 marks).
• Monosaccharides are individual monomers.
• Polysaccharides are made of many, repeating monosaccharides.
• Joined by glycosidic bonds.
• Formed in condensation reactions.
215
Hexoses
α-glucose (used in energy storage and respiration)
β-glucose (used in structural molecules like cellulose)
Fructose (found in fruits, an alternative energy source)
Galactose (part of lactose, important in milk digestion)
216
Pentoses
Ribose (used to make nucleic acids: RNA)
Deoxyribose (used to make nucleic acids: DNA)
217
Contrast the structure of monosaccharides and polysaccharides (3)
• monosaccharides are individual monomers
• polysaccharides are made of many repeating monosaccharides
• joined by glycosidic bonds
• formed in condensation reactions
218
Examples of hexoses
• a glucose
• beta glucose
• fructose
• galactose
219
Examples of pentoses
Ribose
Deoxyribose
220
Structure of glucose
• both Alpha and beta have 6 carbon atoms
• Alpha and beta glucose are isomers of each other
• the carbons are numbered starting clockwise from the O in the ring
• the difference between Alpha and beta glucose is the position of the hydroxyl group on carbon 1
221
Monosaccharide definition
The monomer of carbohydrates containing carbon, hydrogen, and oxygen in a ratio of (CH2O)n
222
Disaccharide definition
Carbohydrates forms when two monosaccharides join via a glycosidic bond
223
What glucose is maltose made out of
2 Alpha glucose
224
Why do lipids form an emulsion in the emulsion test
Lipids are insoluble in water but soluble in ethanol -> when mixed with water, lipid droplets disperse, forming a white emulsion
225
The Benedict’s test is considered…
Semi quantitative becuase it provides an approximate indication of the concentration of reducing sugars in a sample rather than an exact numerical value
226
To quantify the concentration of reducing sugar present you could:
1. Filter the precipitate and dry it
2. Weigh the precipitate
3. The greater the mass of precipitate, the greater the concentration of reducing sugars
Bio Alevel
flashcards
Decks in class (12)
# Cards
-
Cells165
-
Biological Molecules226
-
Exam Questions111
-
Exchange128
-
Genetic Information, Variation And Relationships117
-
Mass Transport134
-
Immunology86
-
Energy Transfers In And Between Organisms124
-
Genetic Info, Variation And Relationships Between Organisms 293
-
Genetics, Populations, Evolution And Ecosystems84
-
Changikg Conditilns251
-
Control Of Gene Expression228
