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Biological Molecules Flashcards

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1
Q

What does macromolecule mean?

A
  • A large biological molecule
  • Three types or macromolecules in living organisms: polysaccharides, proteins (polypeptides) and nucleic acids (polynucleotides)
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2
Q

What are polymers?

A
  • They are giant molecules made up of repeating monomers which are similar or identical to each other, joined together in a chain
  • Examples of biological polymers are polysaccharides, proteins and nucleic acids
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3
Q

What is the general formula for carbohydrates?

A

Cx(H20)y

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4
Q

What are the three main groups of carbohydrates?

A

monosaccharides, disaccharides and polysaccharides

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5
Q

What is a monomer?

A
  • It is a relatively simples molecule which is used as a basic building block for the synthesis of a polymer
  • Many monomers are joined together to make the polymer, usually by condensation reactions
  • Common examples of molecules used as monomers are monosaccharides, amino acids and nucleotides
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6
Q

What is a monosaccharide? What are some examples?

A
  1. Is a molecule consisting of a single sugar unit with the general formula (CH2O)n
    - Monosaccharides are sugars
    - General formula: (CH2O)n and consist of a single sugar molecule
    - The main types of monosaccharides, if they are classified according to the number of carbon atoms in each molecule are:
  2. Trioses (3C) e.g. Aldomiose
  3. Pentoses (5C) e.g. ribose (DNA!) and deoxyribose
  4. Hexoses (6C) e.g. glucose, fructose (sucrose when these two join) and galactose
    - Monosaccharides are used as a source of energy in respiration and are important building blocks for large molecules e.g. glucose used to make starch
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7
Q

What is a disaccharide? What is maltose? What is sucrose? What is lactose?

A
  1. Is a sugar molecule consisting of two monosaccharides joined together by a glycosidic bond
    - They are sugars
    - The three most common:
  2. Maltose (glucose + glucose)
  3. Sucrose (glucose + fructose)
  4. Lactose (glucose +galactose)
    - The joining of two monosaccharides takes place by a condensation reaction
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8
Q

What is a polysaccharide?

A
  1. Is a polymer whose subunits are monosaccharides joined together by glycosidic bonds
    - The final molecule may be several thousand monosaccharide units long
    - The most important polysaccharides are starch, glycogen and cellulose, all of which are polymers of glucose
    - Polysaccharides are NOT sugars
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9
Q

Describe the ring structure of alpha glucose

A

The hydroxyl group, -OH, on carbon atom 1 is below the plane of the ring

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10
Q

Describe the ring structure of beta glucose

A

The hydroxyl group, -OH, on carbon atom 1 is above the plane of the ring

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11
Q

Why is there a ring structure?

A

The chain of carbon atoms e.g. in pentoses and hexoses, is long enough to close euro on itself to form a more stable ring structure
E.G. When glucose forms a ring, carbon atom number 1 joins to the oxygen on carbon atom number 5. The ring therefore contains oxygen, and carbon atom number 6 is not part of the ring

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12
Q

What is the difference between the molecular formula and the structural formula?

A

-The molecular formula show the number of each element in a compound and the structural formula shows the arrangements of atoms, using a diagram (CHECK)

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13
Q

What happens during a condensation reaction?

A
  1. For each condensation reaction, two hydroxyl groups each from a monosaccharide, line up alongside each other
  2. One combines with a hydrogen atom from the other to form a water molecule
  3. This results in a glycosidic bond forming between the two molecules, holding them together and forming a disaccharide
    - Monosaccharides bind together in condensation reactions to form glycosidic linkages
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14
Q

What is the reverse of the condensation reaction?

A
  1. The addition of water, called hydrolysis
    - This takes place during the digestion of disaccharides and polysaccharides when they are broken down to monosaccharides
    - Also happens in non-reducing sugar test
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15
Q

What is starch made up of?

A

Starch is a mixture of amylose and amylopectin

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16
Q

How is amylose made?

A
  1. Amylose is made by condensations between alpha glucose molecules
  2. In this way a long, unbranching chain of several thousand 1,4 linked glucose molecules is built up
    (they are linked between carbon atoms 1 and 4 of successive glucose units)
  3. The chains are curved and coil up into helical structures, making the final molecule more compact
    -The spirals are held in shape by hydrogen bonds
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17
Q

How is amylopectin made?

A
  1. Made of many 1,4 linked alpha glucose molecules
  2. But the chains are shorter than in amylose and branch out to the sides
  3. The branches are formed by 1,6 linkages
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18
Q

Where is starch found?

A
  • Mixtures of amylose and amylopectin molecules build up into relatively large starch grains, which are commonly found in:
    1. Chloroplasts
    2. In storage organs such as potato tubers and the seeds of cereals and legumes
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19
Q

What is glycogen made up of? What is it used for?

A
  1. Glycogen is made of chains of 1,4 linked alpha glucose with 1,6 linkages forming branches
    - Glycogen molecules tend to be even more branched than amylopectin molecules
    - Glycogen molecules clump together to form granules, which are visible in liver cells and muscle cells, where they form an energy reserve, therefore glycogen is the storage polysaccharide in animals and fungi
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20
Q

What is a test for reducing sugars?

A
  1. Add Benedict’s reagent to solution
  2. Place in water bath for 5 mins
  3. If a reducing sugar is present, the solution will gradually turn to a red-brown precipitate as the insoluble copper (I) oxide forms a precipitate
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21
Q

What is a reducing sugar?

A
  1. These carry out reduction and so are oxidised during the process
  2. The reducing sugars include all monosaccharides, such as glucose, and some disaccharides such as maltose. The only common non-reducing sugar is sucrose
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22
Q

How would you find out the concentration of an unknown sugar solution?

A
  1. Carry out Benedict’s test (explained in other flashcard)
  2. Using Benedict’s in excess means that the intensity of the red colour is releated to the concentration of the reducing sugar
  3. Therefore you can then estimate the concentration using colour standards, made by comparing the colour against the colours obtained in tests done with reducing sugar solutions of known concentration
    - You could also measure the time taken for the colour to change
    - Alternatively, you can use a colorimeter to measure subtle differences in colour precisely
    - Semi-quantitive colorimetry
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23
Q

What is the test for a non-reducing sugar?

A
  1. Heat the sugar solution with hydrochloric acid, this will break the disaccharide into its two monosaccharide constituents (hydrolysis) and these are reducing sugars
  2. Add an alkali e.g. NAOH to neutralise the solution since Benedict’s reagent needs alkaline conditions to work
  3. Add Benedict’s, heat, look for colour change
  4. If solution goes brick red now and it did not before, then there is a non-reducing sugar present. If there is still no colour change, then there is no sugar of any kind present
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24
Q

How do you test for the presence of starch?

A
  1. Iodine solution is orange-brown
  2. Add a drop of iodine solution to the solid or liquid substance to be tested (it is actually potassium iodide solution)
  3. A blue-black colour is quickly produced if starch is present
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25
Q

How do you test for protein?

A
  1. Add biuret reagent to solution
  2. (No heating is needed) A purple colour indicates that protein is present (initially blue) and the colour develops slowly over several minutes
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26
Q

How do you test for lipids?

A
  • Emulsion test
    1. Substance is shaken vigorously with some absolute ethanol
    2. This allows any lipids in the substance to dissolve in the ethanol
    3. The ethanol is then poured into a tube containing water
    4. If lipid is present, a cloudy white suspension is formed
27
Q

What are properties common to all monosaccharides?

A
  1. All dissolve in water
  2. Sweet tasting
  3. All form crystals
28
Q

What is starch used for?

A
  1. Starch is the storage polysaccharide in plants
29
Q

What are some functions of monosaccharides and disaccharides?

A
  1. Good sources of energy, and can be used in respiration, in which the energy they contain is sued to make ATP
  2. They are soluble and so they are the form in which carbohydrates are transported through an organism’s body. In animals, glucose is transported dissolved in blood plasma. In plants, sucrose is transported in phloem sap (carbs are transported as glucose in animals, but as sucrose in plants!)
30
Q

What is the structure of cellulose?

A
  1. Polymer of beta glucose with 1,4 glycosidic bonds
  2. As a result adjacent glucose molecules in the chain are upside down in relation to one another
  3. The chains stay straight and so many hydrogen bonds, which are individually weak, form that an enormous strength is produced (beta 1,4 linked glucose molecules in a long straight chains held together by hydrogen bonds)
  4. Between 60 and 70 cellulose molecules become tightly cross-linked to form MICROFIBRILS
  5. Microfibrils ar ein turn elf together in bundles called FIBRES by hydrogen bonding
31
Q

What is the function of cellulose?

A
  1. Structural role as mechanically strong molecule
  2. Very high tensile strength (cellulose fibres) and this makes it possible for the cell to withstand the large pressures that develop within it as a result of osmosis , without it cells would burst when in a dilute solution
  3. These pressures also help provide support for the plant by making tissues rigid and are responsible for cell expansion during growth
  4. Cellulose fibres are freely permeable, allowing water and solutes to reach or leave the cell surface membrane
    - Cellulose cell walls of plant cells
    - (Is most abundant structural polysaccharide in nature?)
32
Q

What are phospholipids?

A
  1. One end is soluble in water because one of the three fatty acid molecules is replaced by a phosphate group, which is polar and can therefore dissolve in water
  2. The phosphate group is hydrophilic and thus the head is two whilst the two remaining tails are hydrophobic
  3. This allows the molecules to form a membrane around a cell, where the hydrophilic heads lie in the watery solutions on the outside of the membrane, and the hydrophobic tails form a layer that is impermeable to hydrophilic structures
    - Phospholipid bilayer of all cell membranes
33
Q

What is a glyceride? What are lipids?

A

-It is an ester (a chemical produced from the reaction between an alcohol and an acid) formed by a fatty acid combining with the alcohol glycerol
-Lipids are a diverse group of chemicals that dissolve in organic solvents such as alcohol but not in water. They include fatty acids, triglycerides, phospholipids, glycolipids and cholesterol
(Much less oxygen in lipids compared to carbohydrates?)

34
Q

What is a triglyceride?

A
  1. Glycerol has three hydroxyl groups
  2. Each one is able to undergo a condensation reaction with a fatty acid
  3. When a triglyceride is made, the final molecule contains three fatty acids tails attached three ester bonds to a glycerol. The tails can vary in length depending on the fatty aids used
    - Broken up by lipase into fatty acids and glycerol
35
Q

What is an unsaturated fatty acid and a saturated fatty acid?

A
  1. When the hydrocarbon tails contain double bonded carbons, and so do not contain the maximum possible amount of hydrogen they are called unsaturated fatty acids and thus unsaturated lipids (usually plant lipids and occur as oils and lower melting point than saturated - tend to be liquids)
  2. No double bonds mean saturated fatty acid and thus saturated lipid (animal lipids often and occur as fats - tend to be solids)
    - If there is more than one double bond, the fatty acid or lipid is described as polyunsaturated; if there is only one it is monounsaturated
36
Q

What is the role of triglycerides?

A
  1. Insulator against loss of heat and relatively low density so useful for buoyancy (aquatic animals living in cold environment e.g. whales)
  2. Energy storage compounds in plants animal and fungi and insoluble. They contain more energy per gram than polysaccharides, so can store more energy in less mass. In mammals, s cores of triglycerides often build up beneath the skin in the form of adipose tissue. the cells in adipose tissue contain oil droplets made up of triglycerides
  3. Metabolic source of water, when oxidised in respiration they are converted to carbon dioxide and water (desert animals)
37
Q

Describe the general structure of amino acids

A
  • Central carbon atom which is bonded to an AMINE group (NH2), and a CARBOXYLIC acid group (-COOH) and the their component that is always bonded to the carbon atom is a HYDROGEN atom
  • R group is what changes depending on amino acid (if just hydrogen then called glycine
  • 20 different amino acids
38
Q

What happens when two amino acids bond together? What type of reaction is this?

A
  1. One amino acids loses a hydroxyl (-OH) group from its carboxylic acid group
  2. The other loses a hydrogen atom from its amine group
  3. This leaves a carbon atom of the first amino acid free to bond with the nitrogen atom of the second. The link is called a PEPTIDE bond
  4. The oxygen and two hydrogen atoms removed from the amino acids form a water molecules
    - Condensation reaction (breaking part is called hydrolysis)
39
Q

What is it called when two amino acids bond together?

A
  • The new molecule formed, made up of two linked amino acids is called a dipeptide
  • A molecule made up of many amino acids linked together by peptide bonds is called a polypeptide (an example of a macromolecule and polymer)
  • A complete protein molecule may contain just one polypeptide chain, or it may have two or more chains which interact with each other
40
Q

What is the primary structure of a protein?

A
  1. Is the sequence of amino acids in a polypeptide or protein
    - Enormous number of different possible primary structures
41
Q

What is the secondary structure of a protein?

A
  1. Is the structure of a protein molecule resulting from the regular coiling or filing of the chain of amino acids, e.g. an alpha helix or beta pleated sheet
    - Hydrogen bonds between the amino acids; form these shapes
    - These structures are easily broken by high temperatures and pH changes
    - In diagrams alpha helices can be represented as coils or cylinder, beta sheets as arrows and random coils as ribbons
42
Q

What is the tertiary structure of a protein?

A
  1. Is the compact structure of a protein molecule resulting from the three-dimensional coiling of the already-folded chain of amino acids
43
Q

What are the four types of bond which help to keep folded proteins in there precise shapes? What do they bond to?

A
  1. Hydrogen bonds can form between a wide variety of R groups (weakest? of them?)
  2. Disulphide bonds are very strong snd form between two cysteine molecules which contain sulphur atoms (strongest? of them?)
  3. Ionic bonds form between R groups groups containing amine and carboxyl groups
  4. Hydrophobic interactions occur between R groups which are non-polar, or hydrophobic
44
Q

What is the quaternary structure of a protein?

A
  1. Is the three-dimensional arrangement of two or more polypeptides, or of a polypeptide and a non-protein component such as haem, in a protein molecule
    - Multiple polypeptides joined by non-covalent interactions
45
Q

What is a globular protein?

A

A protein whose molecules curl up into a ‘ball’ shape such as myoglobin or haemoglobin which is then soluble

46
Q

What is a fibrous protein?

A

Protein molecules form long strands and are not usually soluble in water and most have structural roles

47
Q

Describe the structure of haemoglobin

A
  1. Globular protein
  2. Made up of four polypeptide chains, and each chain is itself is a protein, globin
  3. Two of the haemoglobin chains, called alpha chains, are made from alpha globin and the other two chains, called beta chains, are made from beta globin
  4. Haemoglobin molecule is nearly spherical with hydrophobic R groups pointing towards the centre of the molecule (important in holding it in its correct 3D shape), and their hydrophilic ones pointing outwards (important in painting its solubility)
48
Q

What is the haem group?

A
  1. Each polypeptide chain of haemoglobin contains a haem group, which is not made of amino acids (a prosthetic group)
  2. One oxygen molecule (O2) can bind to with each iron atom
  3. Therefore a complete haemoglobin molecule, with four haem groups can carry four oxygen molecules at a time (eight oxygen atoms)
    - The haem group is responsible for the colour of haemoglobin, if the iron atoms are combined with oxygen the molecule is known as oxyhaemoglobin and is bright red, if not, the colour is purplish
49
Q

What is the function of haemoglobin?

A
  1. An oxygen carrying pigment found in red blood cells

2. The iron is important

50
Q

What is the role of collagen?

A
  1. Insoluble fibrous protein found in the skin, tendons, cartilage, bones, teeth and the walls of blood vessels
  2. Important structural protein in animals
  3. It is flexible but has a high tensile strength as so can withstand large pulling forces without stretching or breaking e.g. in human Achilles tendon
    - Allows arteries to withstand high pressure of blood being pumped from the heart
    - Form tendons (connections between muscle and bone)
    - Constituent of bone
    - Form cartilage and connective tissue
    - Cosmetic treatments
51
Q

Describe the structure of a collagen molecule

A
  1. Collagen molecule consists of three polypeptide chains, each in the shape of a helix
  2. These three helical polypeptides are wound around each other, forming a three stranded ‘role’ or ‘triple helix’
  3. These three strands are held together with hydrogen bonds and some covalent bonds
  4. Each complete three stranded molecule of collagen interacts with other collagen molecules running parallel to it
  5. Covalent bonds form between the R groups of amino acids lying next to each other
  6. These cross links hold many collagen molecules side by side forming fibrils
52
Q

Describe the structure of a collagen fibre

A
  1. The ends of the parallel molecules are staggered; if they were not, there would be a weak spot running right across the collagen fibril
  2. Finally, many fibrils lie alongside each other, forming strong bundles called fibres
53
Q

How is collagen organised in the body?

A
  • Collagen fibres line up according to the forces they must withstand
    1. In tendons they line up in parallel bundles along the length of the tendon, the direction of tension
    2. In skin, they may form layers, with the fibres running in different directions in the different layers, like cellulose in cell walls. In this way, they resist tensile (pulling) forces from many directions
54
Q

How does hydrogen bonding occur between water molecules?

A
  1. The electrons in a water molecule are not shared completely equally
    - Oxygen atom gets slightly more (delta minus)
    - Hydrogen atoms get slight less (delta plus)
  2. This unequal distribution of charge is called a dipole
  3. The negatively charged oxygen of one molecule is attracted to a positively charged hydrogen of another and this attraction is called a hydrogen bond
  4. A hydrogen bond is much weaker than a covalent bond and written using dotted line
55
Q

How is water important as a solvent?

A
  1. Solvent for ions and polar molecules because the water molecules are attracted to the ions and polar molecules and therefore collect around them and separate them
56
Q

What happens to an insoluble molecule in water

A

Non-polar molecules e.g. lipids would tend to be pushed together by the water, since the water molecules are attracted to each other
-This is important for example in hydrophobic interactions in protein structure and in membrane structure and it increase the stability of these structures

57
Q

What is the specific heat capacity of something?

A
  • The heat capacity of a substance is the amount of heat required to raise its temperature by a given amount
  • Specific heat capacity of water his the amount of heat energy required to raise the temperature of 1kg of water by 1 degrees Celsius
58
Q

Why does water have a high specific heat capacity?

A
  1. The hydrogen bonds that tend to make water molecules stick to each other make it more difficult for the molecules to move about freely
  2. For the temperature of a liquid to be raised the molecules must gain energy and consequently move about more rapidly
  3. Therefore the bond must be broken to look free movement and so more energy is needed to raise the temperature of water than wold be the case if there were no hydrogen bonds
59
Q

Why is water’s high specific heat capacity important?

A
  1. It makes water more resistant to changes in temperature
  2. This means that the temperature within cells and within the bodies of organisms tends to be more constant than that of the air around them and so biochemical reactions (enzymes) operate at relatively constant rates and are less likely to be adversely affected by extremes of temp.
  3. Large bodies of water e.g. lakes and oceans are slow to change temperature as environmental temperature changes and as a result they provide more stable habitats for aquatic organisms
60
Q

What is the latent heat of vaporisation?

A

Is a measure of heat energy needed to vaporise a liquid

61
Q

Why does water have a high latent heat of vaporisation?

A
  1. Consequence of its high heat capacity
  2. Since the water molecules tend to stick to each other by hydrogen bonds, large amounts of energy are needed for vaporisation to occur, because hydrogen bonds have to be broken before molecules can escape as a gas
  3. The energy transferred to water molecules during vaporisation results in a corresponding loss of energy from their surroundings, which therefore cool down
62
Q

Why is water’s high latent heat of vaporisation important?

A
  1. Organisms can use evaporation as a cooling mechanism, as in sweating or panting in mammals.
  2. A large amount of heat energy can be lost for relatively little loss of water reducing the risk of dehydration
  3. It can also be important in cooling leaves during transpiration
    - The reverse is true when water changes from liquid to solid ice. This time the water molecules must lose a relatively large amount of energy, making it less likely the water will freeze. This is an advantage for aquatic organism and makes it less likely that their bodies will freeze
63
Q

What makes water a good place for photosynthetic organisms to live?

A
  1. Good solvent/polar
  2. Transparent
  3. Liquid over a whole range of temperatures
  4. High specific heat capacity
  5. High latent heat of vaporisation
  6. Ice is less dense than liquid
  7. Low viscosity

Z A level Biology (15 decks)

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