Biological Molecules Flashcards
1
Q
Describe the chemical reactions involved in the conversion of polymers to monomers and monomers to polymers with examples.
A
- A condensation reaction joins monomers together
- and forms a chemical bond
- and releases water
- A hydrolysis reaction breaks a chemical bond between monomers together
- and uses water
- Examples:
- Amino acid and polypeptide, enzyme, antibody
- Nucleotide and polynucleotide (DNA,RNA)
- Alpha glucose and starch/glycogen
- Beta glucose and cellulose
2
Q
What is a monomer?
A
A small repeating unit
from which larger polymers are made
3
Q
Raffinose is a trisaccharide of 3 monosaccharides:
galactose = C6H12O6
glucose = C6H12O6
fructose = C6H12O6
Give the number of carbon atoms, hydrogen atoms and oxygen atoms in a molecule of raffinose.
A
Carbon atoms = 18
Hydrogen atoms = 32
Oxygen atoms = 16
This is because 2 water molecules are removed in the condensation reaction between these monosaccharides so 4 H and 2 O are removed.
4
Q
Describe a biochemical test to show that a solution contains a non-reducing sugar.
A
- Heat with acid and neutralise
- Heat with Benedict’s solution
- Red precipitate present
5
Q
What is a precipitate?
A
Solid matter suspended in solution
6
Q
Suggest a method to measure the quantity of reducing sugar in a solution.
A
- Colorimeter
- Filter and dry the precipitate
- Find mass
7
Q
Why does the use of a colorimeter improve the repeatability?
A
- Quantitative
- Colour change is subjective
- Standardises the method
8
Q
Lactulose is a disaccharide formed from one molecule of galactose and one molecule of fructose. Give one similarity and one difference between the structures of lactulose and lactose.
A
S: -Both contain galactose
-Both contain a glycosidic bond
D: -Lactulose contains fructose, whereas lactose contains glucose
9
Q
Describe 2 differences between the structures of a cellulose molecule and a glycogen molecule.
A
- Cellulose is made up of beta-glucose and glycogen is made up of alpha-glucose
- Cellulose has straight chain and glycogen is branched
- Cellulose has straight chain and glycogen is coiled
- Glycogen has 1,4- and 1,6- glycosidic bonds and cellulose only has 1,4- glycosidic bonds
10
Q
Describe and explain 2 features of starch that make it a good storage molecule.
A
- Insoluble in water so, doesnt affect water potential
- Branches/coiled in alpha helix so makes molecule compact
- Polymer of alpha glucose so provides glucose for respiration
- Branched/more ends for fast enzyme action
- Large molecule so cant cross the cell membrane
11
Q
What test shows the presence of starch?
A
Iodine/potassium iodide test
12
Q
Describe the structure of glycogen.
A
- Polysaccharide alpha glucose
- Branched structure
- Joined by glycosidic bonds
13
Q
Suggest how glycogen acts as a source of energy.
A
- Hydrolysed to glucose
- Glucose used in respiration
14
Q
Name the monomers from which a maltose molecule is made.
A
Glucose and glucose
15
Q
Name the type of chemical bond that joins the two monomers to form maltose.
A
Glycosidic bond (alpha 1,4-)
16
Q
Explain the difference between the structures of starch molecules and cellulose molecules.
A
- Starch formed from alpha-glucose but cellulose formed from beta-glucose
- Position of hydrogen and hydroxyl group on carbon atom 1 inverted
17
Q
Explain one way on which starch molecules are adapted for their function in plant cells.
A
- Insoluble, doesnt affect water potential
- Helical, compact
- Large molecule, cannot leave cell
18
Q
Explain how cellulose molecules are adapted for their function in plant cells.
A
- Long and straight chains
- Become linked together by many hydrogen bonds to form fibrils
- Provide strength to cell wall
19
Q
The general structure of a fatty acid is RCOOH.
Name the group represented by COOH.
A
Carboxyl
20
Q
What is meant by an unsaturated R group.
A
Double bond between carbons C=C
21
Q
Describe how you would test for the presence of a lipid in a liquid sample of food.
A
- Add ethanol
- Shake
- Add water
- White/milky emulsion present
22
Q
Describe how a triglyceride molecules is formed.
A
- 1 glycerol and 3 fatty acids
- Condensation reactions and removal of 3 molecules of water
- Ester bonds formed
23
Q
Describe how an ester bond is formed in a phospholipid molecule.
A
- Condensation reaction
- Loss of water
- Between glycerol and fatty acids
24
Q
Describe how you would test a piece of food for the presence of lipid.
A
- Dissolve in alcohol
- Add water
- White emulsion shows presence of lipid
25
Describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst.
1. Substrate binds to active site
2. Active site changes shape so it is complementary to substrate
3. Reduces activation energy
26
Suggest and explain a procedure to stop reactions between inorganic phosphate and ATP synthase.
1. -Boil/add strong acid/alkali
-Denatures ATP synthase
2. -Put in freezer
-Lowers the kinetic energy so no enzyme-substrate complexes form
3. -Add high concentration of inhibitor
- Enzyme-substrate complexes do not form
27
How does a competitive inhibitor decreases the rate or an enzyme-controlled reaction?
- Inhibitor similar shape to substrate
- Binds to active site
- Reduces enzyme-substrate complexes forming
28
When bread becomes stale, the structure is some of the starch is changed and becomes a competitive inhibitor of amylase in the small intestine.
Suggest how eating stale bread could help to reduce weight gain.
- Less hydrolysis of starch
- To maltose
- So less absorption of glucose
- More egested statch
29
Describe how the structure of a protein depends on the amino acid it contains.
- Structure is determined by relative position of amino acid/R group
- Primary structure is sequence of amino acids
- Secondary structure formed by hydrogen bondings between amino acids
- Tertiary structure formed by interactions between R groups
(hydrogen, ionic, disulphide bonds)
- Creates active site in enzymes/complementary shapes in antibodies/carriers proteins/receptors
- Quaternary structure formed by bonds between more than 1 polypeptide
30
Describe how amino acids join to form a polypeptide so there is always NH2 at one end and COOH at the other end.
1. One amine/NH2 group joins to a carboxyl group/COOH to form a peptide bond
2. So in the chain there is a free NH2 group at one end and a free COOH at the other
31
Explain how the active site of an enzyme causes a high rate of reaction.
- Lowers activation energy
- Induced fit causes active site of enzyme to change shape
- Enzyme-substrate complex causes bonds to form/break
32
Describe a biochemical test to confirm the presence of protein in a solution.
1. Add biuret reagent (sodium hydroxide and copper sulphate)
2. Positive result = purple
33
What is a dipeptide?
2 amino acids joined by a peptide bond
34
Describe two ways in which all dipeptides are similar and one way in which they might differ.
S: -Amine/NH2 group at end
-Carboxyl/COOH group at end
-Two R groups
-All contain C, H, N, and O
D: -Variable/different R groups
35
Describe how a non-competitive inhibitor can reduce the rate of an enzyme-controlled reaction.
- Attaches to the enzyme at a site other than the active site
- Changes shape of the active site/tertiary structure
- Active site no longer complementary so less substrate can bind
36
Describe how a peptide bond is formed between 2 amino acids to form a dipeptide.
- Condensation reaction
- Between amine and carboxyl group
37
Describe how the secondary structure of a polypeptide is produced by bonds between amino acids.
- Hydrogen bonds
- Between NH group of one amino acids and C=O group
- Forming beta-pleated sheets or alpha helix
38
Explain why two proteins could have the same number and type of amino acids but different tertiary strictures.
- Different sequence of amino acids
- Forms ionic/hydrogen/disulphide bonds in different places
39
Explain how the formation of an enzyme-substrate complex increases the rate of reaction.
-Reduces activation energy
-Due to bending/weakening bonds
-Without enzyme, very fee substrates have sufficient energy for reaction
40
The generic code is describes as degenerate.
What is meant by this?
More than one codon codes for a single amino acid
41
A high concentration of sodium in the blood can affect blood volume and cause hypertension.
Suggest how high sodium concentration in medicines could affect blood volume.
1. Sodium ions lower the water potential of blood
2. Water would move into the blood by osmosis from tissue fluid
3. Increases the blood volume
42
Describe the roles of iron ions.
Haemoglobin binds/associates with oxygen to load it
43
Describe the roles of sodium ions.
1. -Co-transport of glucose/amino acids into cells
-Because sodium moved out by active transport in Na — K pump
-Creates a sodium concentration gradient
2.Affects water potential/osmosis
44
Describe the roles of phosphate ions.
1. Affects osmosis/water potential
2. Joins nucleotides in phosphodiester bonds in backbone of DNA/RNA
3. Used in/to produce ATP
4. Phosphorylates other compounds making them more reactive
5. Hydrophilic/water soluble part of phospholipid bilayer
45
Explain 5 properties that make water important for organisms.
1. A metabolite in condensation/hydrolysis/ photosynthesis/respiration
2. A solvent so metabolic reactions can occur
A solvent so allows transport of substances
3. High specific heat capacity so buffers changes in temperature
4. Large latent heat of vaporisation so provides a cooling effect
5. Cohesion between water molecules supports columns of water in plants
6. Cohesion (hydrogen bonding) so produces surface tension supporting small organisms
7. Transparent so allows light penetration for photosynthesis in aquatic habitat
46
State and explain the property of water that helps to prevent temperature increases in a cell.
-High specific heat capacity
-Buffers changes in temperature increases
-As its takes a lot of energy to change temperature due to hydrogen bonding between molecules
47
High specific heat capacity
Buffers changes in temperature
48
Give two properties of water that are important in the cytoplasm of cells.
1. Polar molecule
Acts as a universal solvent
2. Universal solvent
Metabolic reactions occur faster in solution
3. Reactive
Takes place in hydrolysis/condensation reactions
49
Describe how an ATP molecule is formed from its component molecules.
- Adenine, ribose, 3 phosphates
- Condensation reaction
- Formed by ATP synthase
50
Name the two products of ATP hydrolysis.
1. Adenosine disphosphate
2. Inorganic phosphate
51
Equation which represents the reaction catalysed by ATP synthase.
ADP + Pi -> ATP + H2O
52
A new antibiotic is safe to use in humans because it does not inhibit the ATP synthase found in human cells. Suggest why human ATP synthase is not inhibited and bacterial synthase is inhibited.
1. Human ATP synthase has a different tertiary structure/ active site to bacterial ATP synthase
2. Antibiotic cannot enter human cells/mitochondria
3. Antibiotic not complementary to human ATP synthase
53
Give two ways in which ATP is a suitable energy source for cells to use.
1. Releases relatively small amount on energy/ little energy lost as heat
2. Releases energy instantaneously
3. Phosphorylates other compounds, making them more reactive
4. Can be rapidly re-synthesised
5. Is mot lost from/does not cells
54
Cells constantly hydrolyse ATP to provide energy.
Describe how ATP is re-synthesised in cells.
- From ADP and phosphate
- By ATP synthase
- During respiration/photosynthesis
55
Give two ways in which the hydrolysis of ATP is used in cells.
1. To provide energy for other reactions
2. To add phosphate to other substances and make them more reactive/change their shape
56
Lactose is formed by a reaction between glucose and galactose, both of which have the chemical formula C6H12O6.
What is the chemical formula for lactose?
C12H22O11
57
Carbohydrates, such as starch, are made from monosaccharides joined together.
Which bond joins monosaccharides together?
Glycosidic
58
What can occur during condensation of carbohydrates?
A disaccharide is produced from monosaccharides
59
What occurs when sucrose is broken down to monosaccharides?
Hydrolysis, releasing reducing sugars and using water
60
A sample of milk is tested with Benedict’s solution. After boiling, a yellow colour is observed.
What conclusion can be made?
Reducing sugars are present
61
Which carbohydrate gives a brick red colour when boiled with Benedict’s solution?
Fructose
62
Tests were performed on samples from a mixture of biological molecules.
When iodine in potassium iodide solution was added to a sample, the mixture turned black.
When the biuret test was carried out on another sample, the mixture turned purple.
Which biological molecules were in the mixture?
Amylase and starch
63
An unknown solution of a single sugar was tested.
After Benedict’s test fir reducing sugars, the colour observed was blue.
After Benedict’s test for non-reducing sugars, the colour observed was brick red.
Sucrose
64
The structure of phospholipids includes the following:
1 - polar phosphate heads
2 - hydrophobic fatty acid chains
3 - saturated fatty acid chains
Which of these are essential for the formation of a phospholipid bilayer in a cell-surface membrane?
1 and 2
65
Which formula of fatty acids represents a saturated fatty acid?
1 - palmitic acid, C15H31COOH
2 - oleic acid, C17H33COOH
3 - linoleic acid C17H31COOH
Only 1
66
In unsaturated lipid molecules, where are double bonds located?
Within fatty acids only
67
68
Which level of organisation of a haemoglobin molecule is coded by a DNA molecule?
Primary structure
69
A peptide bond is formed between 2 amino acids.
Which groups form the peptide bond?
H2N and COOH
70
Which statements about a peptide bond are correct?
1 - it joins two monomers that are always identical to each other
2 - it contains four different atoms
3 - it can be broken down by the addition of water at room temperature
4 - it is important in the primary structure of proteins
2 and 4 only
