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OCR Biology > 2.2 - Biological Molecules > Flashcards

2.2 - Biological Molecules Flashcards

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1
Q

What are the main elements that make up living matter?

A

Carbon (C)
Oxygen (O)
Hydrogen (H)
Nitrogen (N)

Phosphorus (P) and Sulfur (S) also have very important roles

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2
Q

How many bonds can a carbon atom form?

A

4

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3
Q

How many bonds can a nitrogen atom form?

A

3

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4
Q

How many bonds can an oxygen atom form?

A

2

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5
Q

How many bonds can a hydrogen atom form?

A

1

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6
Q

What is a molecule?

A

A collection of 2 or more atoms held together by chemical bonds

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7
Q

What is an ion?

A

An atom or molecule that has gained or lost electrons, and so it has a net charge.

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8
Q

What is a cation?

A

Where an atom or molecule loses one or more electrons and has a net positive charge

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9
Q

What is an anion?

A

Where an atom or molecule gains one or more electrons and has a net negative charge

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11
Q

What is a covalent bond?

A

When two atoms share a pair of electrons. The shared pair occupies the outer shell of the atom.

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13
Q

What is an ionic bond?

A

The electrostatic bond between a cation and an anion. This occurs when one atom ‘donates’ electrons to another atom. The donor becomes a cation, and the receiver becomes an anion.

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14
Q

What is an electrolyte?

A

Ions in a solution

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15
Q

What are calcium ions [Ca2+] used for?

A

Nerve impulse transmission

Muscle contraction

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16
Q

What are sodium ions [Na+] used for?

A

Nerve impulse transmission

Kidney function

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17
Q

What are potassium ions [K+] used for?

A

Nerve impulse transmissions

Stomatal opening

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18
Q

What are hydrogen ions [H+] used for?

A

Catalysis of reactions

pH determination

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19
Q

What are ammonium ions [NH4]+ used for?

A

Production of nitrate ions by bacteria

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20
Q

What are nitrate ions [NO3]- used for?

A

Nitrogen supply to plants for amino acid production

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21
Q

What are hydrogen carbonate ions [HCO3]- ions used for?

A

Maintenance of blood pH

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22
Q

What are chloride ions [Cl]- ions used for?

A

Balance positive charge of some ions (eg sodium, potassium) in cells

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23
Q

What are phosphate ions [PO4]3- used for?

A

Cell membrane formation

Nucleic acid and ATP formation

Bone formation

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24
Q

What are hydroxide ions [OH]- ions used for?

A

Catalysis of reactions

pH determination

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25
Q

What elements are present in carbohydrates?

A

Carbon, hydrogen, oxygen

Usually in ratio 1:2:1

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26
Q

What elements are present in lipids?

A

Carbon, hydrogen and oxygen

Phosphorus if it is a phospholipid

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27
Q

What is a polymer?

A

A molecule that is a long chain linking multiple individual molecules (monomers) in a repeating pattern

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28
Q

What elements are present in proteins?

A

Carbon, hydrogen, oxygen, nitrogen and sulphur

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29
Q

What elements are present in nucleic acids?

A

Carbon, hydrogen, oxygen, nitrogen and phosphorus

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30
Q

What is a monomer?

A

An individual subunit that is repeated in a polymer

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31
Q

What is the monomer of a carbohydrate?

A

A sugar (saccharide)

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32
Q

What is the monomer of a protein?

A

Amino acids

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33
Q

What is a polar molecule?

A

A covalently bonded molecule with regions of positivity and regions of negativity.

This occurs due to the unequal sharing of electrons between atoms as a result of different levels of electronegativity.

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34
Q

Describe the distribution of electrons in a polar molecule.

A

In a covalent bond, if the two atoms involved have different levels of electronegativity , the electrons will s
spend more time closer to one atom than another.

The atom with the greater share of electrons will be slightly negative, whereas other atom with less electrons will be slightly positive.

If the molecule is not symmetrical, and there is a clear positive and negative end, the molecule is polar.

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35
Q

Is an O-H bond polar?

A

Yes: the O is slightly negative and the H is slightly positive.

Many organic molecules contain O-H bonds (called hydroxyl groups), and are therefore slightly polar

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36
Q

What makes water a polar molecule?

A

Water contains 2 O-H bonds, which are negative.

The oxygen is slightly negative, and the the 2 hydrogens are slightly positive

Water isn’t symmetrical

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37
Q

What is a macromolecule?

A

a ‘giant molecule’

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38
Q

What are the 3 main types of macromolecules in living organisms?

A

Polysaccharides
Polypeptides
Polynucleotides

These are all also examples of polymers

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39
Q

Describe the features of making a polymer

A
  • it is a condensation reaction (adding monomers to create a polymer)
  • water molecules are released
  • new covalent bonds formed
  • larger molecule (polymer) is formed
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40
Q

Describe the features of breaking a polymer

A
  • hydrolysis reaction (breaking polymers into monomers)
  • water molecule added
  • covalent bond broken
  • smaller molecules (monomers) formed
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41
Q

Why is water (H2O) liquid at room temperature, whereas other simple covalent molecules such as CO2, CH4 and NH3 are gasses?

A

Because water has polar molecules, there are many hydrogen bonds between the molecules. Even though these are quite weak, the large number of them results in water being packed close together, making it a liquid.

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42
Q

What is a hydrogen bond?

A

An intermolecular bond where a slightly positive hydrogen atom in one molecule is attracted to a slightly negative atom in another molecule.

In water, the hydrogen atoms in one molecule are attracted to the negative oxygen atom in another molecule

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43
Q

What are the properties of water?

A

Due to polarity:

  • liquid at biological temperatures
  • high latent heat
  • good solvent
  • high specific heat capacity
  • high surface tension
  • most dense at 4 degrees celsius
  • capillary action

also useful as a reactant

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44
Q

What does water having high latent heat mean?

A
  • it takes a lot of energy to change the physical state of water
  • it is unlikely to change state
  • its a stable environment to live in as it is less likely to evaporate or freeze than other liquids
  • evaporation of water takes a lot of energy, so it can be used as a cooling mechanism ( eg panting/sweating)
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45
Q

What does water being liquid at biological temperatures mean?

A
  • organisms can interact with it, live in/on it, use it as a solvent etc which they couldn’t if it were a gas
  • as a liquid, it is incompressible.
    therefore, it can be used as support - eg turgor pressure in plants and hydrostatic skeletons (eg in worms)
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46
Q

What does water being a good solvent mean?

A
  • as a solvent of polar molecules, water can dissolve most biological molecules (except lipds)
  • reactions can therefore easily take place in water (eg respiration), so organisms can use water as the basis of their cytoplasm
  • in multiclellular organisms, it can be used as a transport medium (eg it is the base of plasma and xylem fluid (minerals dissolved in water)
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47
Q

What does water having a high specific heat capacity mean?

A
  • it takes a lot of energy to change the temperature of water therefore it is a stable environment to live in
  • internal body temperatures are less likely to change
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48
Q

What does water having a high surface tension mean?

A
  • hydrogen bonds form thin film on top of the water as the bonds between the water molecules are stronger than the intermolecular bonds between the water and air molecules
  • this allows organisms to live on the surface of the water eg pond skaters
  • it is also important in capillary action
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49
Q

What does water having capillary properties mean?

A
  • the cohesive properties of water mean that it moves in one mass as the molecules are attracted to each other (cohesion)
  • it also has adhesive properties - the water molecules are attracted to other materials if they are polar or ionic.
  • this means water can travel up a narrow tube, even if it is against gravity
  • this is how the xylem transports water up the plant, from the roots to the shoots
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50
Q

What does water being most dense at 4 degrees celsius mean?

A
  • ice (solid water) is less dense than liquid water as hydrogen bonds fix the positions of the molecules further apart than the average distance when in liquid state, meaning the ice is less dense.
  • this means the ice floats on top of water.
  • this insulates the lower levels of a body of water so that the entire body doesn’t freeze
  • ice provides a habitat for penguins, polar bears etc
    it sets up currents in the water which circulates nutrients (particularly in the sea)
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51
Q

What does water being a good reactant mean?

A
  • it is used in hydrolysis reactions to split macromolecules into smaller units by adding water
  • it is a source of ydrogen for reactions of photosynthesis
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52
Q

What is cohesion?

A

Attraction between the same type of molecule (eg water and water)

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53
Q

What is adhesion?

A

Attraction between two different types of molecules (eg water and the side of a glass)

54
Q

What is the general formula of a carbohydrate?

A

Cx(H2O)y

55
Q

What is a carbohydrate?

A

Also known as a saccharide or sugar.

Made of carbon, oxygen, hydrogen

56
Q

What is a monosaccharide?

A
  • a single sugar unit
  • water soluble
  • single sugar
  • taste sweet
  • general formula Cx(H2O)x
  • classified according to number of carbon atoms (eg 6 carbons = hexose monosaccharide)
  • names end in -ose eg glucose, fructose
57
Q

Roles of monosaccharides

A
  • energy source for respiration (esp glucose) due to large number of C-H groups which are easily oxidised to yield a lot of energy
  • building blocks (monomers) for larger molecules ie polysaccharides
58
Q

Properties of glucose

A
  • a hexose monosaccharide - has 6 carbons
  • formula C6H12O6
  • Has two isomers, alpha glucose and beta glucose. these have important biological consequences in starch, glycogen and cellulose
  • fructose and galactose have same molecular formula but different structural formula
  • polar and soluble in water due to hydrogen bonds formed between hydroxyl groups and water molecules
  • solubility is important as glucose is dissolved in cytosol of cell
59
Q

What is the difference between alpha and beta glucose?

A
  • alpha glucose has hydroxyl group above carbon 1

- beta glucose has hydroxyl group below carbon 1

60
Q

Properties of ribose

A
  • pentose sugar
  • molecular formula C5H10O5
  • component of RNA, ATP and NAD
61
Q

Properties of deoxyribose

A
  • an oxygen has been removed from ribose
  • molecular formula C5H10O4
  • component of DNA
62
Q

What is a disaccharide?

A
  • when two monosaccharide residues joined together (called residue as some of monosaccharide has been lost)
  • joined by condensation reaction
  • sugars
  • dissolve easily in water
  • taste sweet
  • contain a glycosidic bond
63
Q

What is a condensation reaction of monosaccharides

A
  • two hydroxyl groups (OH) link together
  • the O from one and OH from another creates water
  • water is produced
  • a glycosidic bond is formed (oxygen bridge)
  • successive additions of monosaccharides produce polysaccharides
64
Q

1) alpha glucose + alpha glucose = A
2) glucose + B = sucrose
3) glucose + C = lactose

A

1) maltose
2) fructose
3) galactose

65
Q

Describe the removal of monosaccharides

A
  • a hydrolysis reaction
  • addition of water
  • breakdown of polysaccharides/disaccharides into monosaccharides
  • happens in digestion
  • catalysed by enzyme amylase
66
Q

What is a 1,4 glycosidic bond?

A

When carbon 1 of one saccharide joins to a carbon 4 of another saccharide

67
Q

What is a polysaccharide?

A
  • many monosaccharides bonded together by condensation reactions, forming glycosidic bonds
  • polymers
  • macromolecules
  • inert and insoluble
  • not sweet
68
Q

Why isn’t glucose good for storage?

A
  • it is reactive and soluble

- therefore it is stored as a polysaccharide until needed

69
Q

a) How is glucose stored in plants?
b) How is glucose stored in animals?
c) what other polysaccharide does glucose form and what is it used for?

A

a) Starch
b) Glycogen
c) cellulose, used for cell walls in plants

70
Q

What are the properties of starch?

A
  • grains in plant cells
  • large enough to be seen with light microscope
  • carbohydrate store in plants
  • large; cannot escape through membranes
  • insoluble; can be stored in large quantities without affecting water potential of cells
  • compact; can be stored easily within cells
  • branched molecules: the more branching, the more efficient the release of glucose by hydrolysis
71
Q

What is the composition of starch?

A

Made up of 2 polysaccharides of alpha glucose - amylose (20%) and amylopectin (80%)

72
Q

Describe amylose

A
  • 20% of starch
  • long, unbranched chains of alpha glucose units
  • linked via 1,4 glycosidic bonds
  • chains curve into helix due to hydrogen bonds making a compact molecule
  • like maltose
  • less space to store each kJ
73
Q

Describe amylopectin

A
  • 80% of starch
  • has 1-4 glycosidic bonds between alpha glucose molecules as well as 1-6 glycosidic bonds, resulting in branched structure.
  • 1-6 glycosidic bonds occur approximately every 25 glucose subunits
74
Q

How to test for starch

A
  • test with iodine solution at room temp
  • blue/black with starch
  • deep blue with amylose
  • red-purple with amylopectin

iodine forms a complex with starch in between the helix shapes to form blue-black solution

75
Q

What are the properties of glycogen?

A
  • granules in animal cells
  • carbohydrate store in animals
  • large; cannot escape through membranes
  • insoluble; can be stored in large quantities without affecting water potential of cells
  • compact; can be stored easily within cells
  • branched molecules: the more branching, the more efficient the release of glucose by hydrolysis
76
Q

Describe glycogen

A
  • similar to amylopectin but with shorter chains and more highly branched, making it more compact. This is important as animals are more mobile than plants
  • has 1-4 glycosidic bonds between alpha glucose molecules as well as 1-6 glycosidic bonds, resulting in branched structure.
  • branched structure means glucose molecules can easily be added or removed
  • mainly stored in muscles and liver as granules
  • shorter chains means it hydrolyses more readily
77
Q

What is cellulose?

A
  • polymer of beta glucose
  • straight, unbranched chains due to beta glucose residues alternating in orientation - one up, next one flipped down
  • straight chains mean they can pack closely together
  • 60-70 cellulose molecules become tightly cross - linked to make microfibrils
  • microfibrils held together in bundles called fibres
  • typically, cell walls have several layers of fibres running in different directions, which increases strength.
  • other molecules cross-link the fibres, forming a glue-like matrix
  • fibres have a high tensile strength which prevents cell walls from bursting (turger pressure).
78
Q

What are the properties of cellulose?

A
  • found in cell walls of plants
  • provides strong and permeable cell wall
  • have a structural role due to mechanical strength due to bonding
  • insoluble; structure of cell wall not affected by water
  • exposed OH groups; exposed hydroxyl groups on all directions allow hydrogen bonding to create a string 3D lattice
  • straight chains (microfibrils); create a strong, permeable, flexible mesh of interwoven strands
  • not brittle
  • fully permeable
79
Q

What are the properties of glucose?

A
  • found in all living cells
  • main substrate for respiration
  • small; passes through membrane easily and has high energy value
  • soluble; transported easily through fluids
  • reactive - forms polymers easily
80
Q

What is a reducing sugar?

A
  • all monosaccharides
  • some disaccharides (eg maltose, lactose)
  • they can donate electrons, or reduce another molecule or chemical
81
Q

How do you test for reducing sugars?

A

Benedict’s test
Use Benedict’s Reagent (alkaline solution of copper(II) sulfate)
1) place sample in test tube. if not in liquid form, grind up or blend in water.
2) add equal volume of benedicts reagent
3) heat mixture gently in a boiling water bath for 5 mins.

82
Q

How do you test for non-reducing sugars?

A

Benedicts test
Use Benedict’s Reagent (alkaline solution of copper(II) sulfate)
1) test for reducing sugars first. If result is negative, move on to test for non-reducing sugars
2) place fresh sample in test tube. if not in liquid form, grind up or blend in water.
3) boil sample in dilute hydrochloric acid. This will hydrolyse the non-reducing sugar (eg sucrose) into reducing sugars (eg glucose and fructose)
4) add equal volume of benedicts reagent
5) heat mixture gently in a boiling water bath for 5 mins.

83
Q

What is a positive result for Benedict’s test?

A

Reducing sugars will react with reagent. Cu2+ ions will be reduced (gain electrons) from the reducing sugars, turning them into brick red Cu+ ions. When it is warmed, a brick-red precipitate is formed, indicating a positive result
The more reducing sugar present, the more precipitate formed and the less blue Cu2+ ions left in solution. The colour of the solution will depend on the ratio of precipitate to solution. This makes the test qualitative.

  • green = low concentration of reducing sugar
  • yellow/amber = medium concentration of reducing sugar
  • red = high concentration of reducing sugar
84
Q

What are lipids?

A
  • commonly known as fats and oils
  • contain the elements carbon, oxygen, hydrogen
  • generally, fats are solid at room temperature and oils are liquid at room temperature
  • macromolecules
85
Q

Are lipids polar? What affect does this have on the properties if them?

A

No, they are non polar.
This means they are hydrophobic and are not soluble in water.
immiscible - doesn’t form a homogenous mixture when mixed

86
Q

What is a triglyceride?

A

A lipid made by combining one glycerol molecule with three fatty acids

glycerol + 3 fatty acids -> triglyceride + water

87
Q

Describe triglyceride fats

A
  • animal origin
  • mainly saturated
  • high levels are more likely to contribute to cardiovascular disease
  • eg butter, lard
88
Q

Describe triglyceride oils

A
  • plant origin
  • mainly unsaturated
  • tend to be more healthy than saturated fats
  • eg olive oil, rapeseed oil
89
Q

What is the structure of glycerol?

A

C3H8O3
Type of alcohol
Contains 3 hydroxyl groups

90
Q

What are fatty acids?

A

Carboxylic acid - have a carboxyl group (-COOH) with hydrocarbon chain attached
Can be saturated or unsaturated

91
Q

How are triglycerides formed?

A

glycerol + 3 fatty acids -> triglyceride + water
reaction called esterification (type of condensation reaction)
hydroxyl groups between the glycerol and fatty acid react, leading to the formation of 3 water molecules.
The bond between the glycerol and the fatty acid is an ester bond

92
Q

How would you break down a triglyceride?

A

Addition of water molecules to reverse the reaction that formed the triglyceride
This is known as hydrolysis

93
Q

What is a saturated fatty acid?

A
  • no double bonds between carbon atoms (C=C )
  • they form the maximum number of binds with hydrogen atoms (‘saturated’ with hydrogen)
  • solid at room temperature as they are straight chains and easier to pack close together
94
Q

What is an unsaturated fatty acid?

A
  • contains some C=C bonds
  • therefore, less H atoms than with saturated fatty acids
  • if only one, it is monounsaturated. If 2 or more C=C bonds, it is polyunsaturated.
  • the C=C bonds cause the fatty acid to kink or bend. This means they cannot be packed as closely together.
  • As a result, they have a much lower melting and boiling point, and are often liquid at room temperature
95
Q

Roles and properties of triglycerides

A
  • energy store and energy source when respired - more C-H bonds
  • thermal insulation - poor conductors of heat
  • buoyancy - less dense than water
  • protection of internal organs - around most organs, takes impacts, low melting point so not restrictive
  • source of water - can be a source of water when respired
96
Q

What are phospholipids?

A

Modified triglycerides containing the element phosphorus along with carbon, hydrogen and oxygen..
Inorganic phosphate ions can be found in cytoplasm of every cell
The phosphate ions are negatively charged, and are therefore soluble in water
One of the fatty acids in a triglyceride is replaced with a phosphate group to make a phospholipid

97
Q

Similarities and differences between a phospholipid and triglyceride

A

Similarities:
- both have glycerol
- both contain ester bonds between glycerol and fatty acids
Differences:
- phospholipids contain phosphate group
- phospholipids have 2 fatty acids rather than 3
-phospholipids have a charged, hydrophilic head and non-polar, hydrophobic fatty acid tail. However, triglycerides are entirely non-polar and hydrophobic.

98
Q

How to phosphates interact with water?

A
  • they form a thin layer on the surface of the water with the hydrophilic phosphate head in the water and the hydrophobic fatty acid tail sticking out of the water. Because of this, they are called surface active agents or surfactants for short
  • they also form structures based on a two layered sheet formation (a bilayer) with all the hydrophobic tails pointing inwards and all the hydrophilic heads sticking out. This is called a phospholipid bilayer
99
Q

What are the main functions of phospholipids?

A
  • the phospholipid bilayer forms cell membranes. They are able to separate the aqueous environment cells usually exist in and the aqueous cytosol within the cell.
  • they also make up the myelin sheath on neurones as they are good insulators.
100
Q

What are steroid/sterols?

A

Sterols/steroid alcohols are another type of lipid. They arent fats or oild, and have little in common with them structurally.

  • they are complex alcohol molecules based on a 4 carbon ring structure with a hydroxyl group at one end.
  • they have dual hydrophilic/phobic properties like phospholipids - most of the molecule is non-polar, but the O-H group is
101
Q

How can you test for lipids?

A

Emulsion test

1) mix sample woth ethanol - this dissolves any lipids present. shake
2) pour liquid into another clean test tube containing water
3) if lipids are present, a cloudy white emulsion will form - the lipid comes out of ethanol solution and becomes dispersed as tiny droplets in water

102
Q

What is cholesterol?

A
  • a sterol
  • the body manufactures it primarily in liver and intestines
  • it becomes positioned between the phospholipids with hydroxyl groups at the periphery of the membrane . This adds stability to the cell membranes and regulates their fluidity by keeping membranes fluid at low temperatures and stopping them becoming too fluid at high temperatures
103
Q

What are the uses of cholesterol?

A
  • cell membranes
  • needed to make some hormones eg testosterone, oestrogen
  • Vitamin D, and bile are also manufactured with cholesterol
  • Vit D can be stored if excess is removed, whereas Vit B/C are water soluble and just excreted out.
104
Q

What is a peptide?

A

Polymers that are made up of amino acids, which are the monomers

105
Q

What is a protein?

A

Consist of one or more polypeptides arranged as complex macromolecules.
They have specific biological functions.
All proteins contain the elements carbon, hydrogen, oxygen and nitrogen

106
Q

What are the functions of protein?

A
  • structural component- muscle, bones, hair etc
  • carriers and pores
  • enzymes
  • hormones
  • antibodies
107
Q

How are amino acids sourced?

A

In plants:
- are able to manufacture the amino acids they need
- require nitrates to do so
In animals:
- must take in as part of diet
- 20 amino acids common in polypeptides
- 5 = non essential as body can make them
- 9 are essential and can only be obtained by consumption in diet
- 6 conditionally essential as only needed by infants and children

108
Q

What is the basic structure of an amino acid?

A

One Nitrogen bonded to 2 hydrogens (amine group). This is bonded to a carbon, which is bonded to a hydrogen, an R group (could be anything), and another carbon. This last carbon has a double bond to an oxygen and a single bond to another oxygen. That oxygen is bonded to a hydrogen (hydroxyl group)

109
Q

Describe the synthesis of peptides

A
  • the hydroxyl group of the carboxyl in one amino acid reacts with a hydrogen atom in the amine group of another, producing a water molecule
  • this means that this is a type of condensation reaction
  • the bond between the amino acids is a peptide bond (between a carbon atom and a nitrogen) which is covalent
  • two amino acids = dipeptide, multiple = polypeptide
  • reaction catalysed by enzyme peptidyl transferase, present in ribosomes
  • can be broken down by hydrolysis
  • protease enzymes catalyse breakdown of polypeptides
  • proteins arent just broken down during digestion
  • amino acids in di and polypeptides aee known as residues
110
Q

What are the properties of an R group in an amino acid?

A

CAN be

  • big
  • positively charged
  • negatively charged
  • acidic
  • basic
  • hydrophobic
  • hydrophilic
  • include sulphur
  • ring structures
111
Q

What are the different levels of structure in a protein?

A

primary
secondary
tertiary
quaternary

112
Q

What are the features of the primary structure of a protein?

A
  • given by the specific sequence of amino acids that make up the polypeptide (determined by the DENA sequence)
  • there are many different possibilities of amino acid sequences
  • only bonds involved in primary structure are peptide bonds
113
Q

What are the features of the secondary structure of a protein?

A
  • coiling/folding of primary structure in specific areas
  • held in place by hydrogen bonds, which give stability due to quantity
  • two types of secondary structure - alpha helix (a coil shape) and beta pleated sheet (folded)
  • is determined by the R group on the specific amono acids
  • some regions of primary structure do not have secondary structure
114
Q

What are the features of the tertiary structure of a protein?

A
  • the folding of the protein into its final shape
  • held in place by intermolecular bonds and interactions with watery cell environment
  • determined by the R groups of amino acids
  • causes protein to have 3D shape vital to its speific function
115
Q

What are the different interactions/intermolecular bonds that determine the tertiary structure of a protein?

A

Possible intermolecular bonds:

  • disulphide bonds: always formed when 2 cystine are close enough to react. covalent and strongest of bonds. Formed between 2 sulphurs in R groups of different amino acids.
  • ionic bonds - stronger than hydrogen bonds, form between oppositely charged R groups
  • hydrogen bonds - weakest of all bonds

Interactions with watery cell environment:

  • hydrophobic regions will turn to the inside of the protein
  • hydrophilic reactions will turn to the outside of the protein
116
Q

What are the features of the quaternary structure of a protein?

A
  • more than one polypeptide chain combined to form the functional protein and/or the addition of a non-protein component (prosthetic group)
  • enzymes often have two identical subunits whereas hormones usually have 2 different polypeptides
117
Q

How do you test for proteins?

A

Biuret test
1) add sample to test tube. mix with biuret reagent (mic of copper(II) sulphate and an alkali)
2) mix and let stand for 5 mins
if proteins are present, peptide bonds will form a violet coloured complex with copper ions in alkaline solutions.

118
Q

What is a globular protein?

A
  • 3D spherical shape which is specific to the type of protein
  • sequence of amino acids are much more varied than fibrous proteins
  • are therefore much more susceptible to temperature and pH changes
  • soluble in water as hydrophobic R groups turn to inside and hydrophilic R groups move to outside
119
Q

what is denaturation?

A
  • the breakdown of the tertiary structure of a protein

- occurs due to high temperatures, some chemicals or pH changes interfering with the intermolecular bonds

120
Q

Describe the properties of insulin

A
  • a globular protein
  • a hormone involved in the regulation of blood glucose concentration
  • very small so transported quickly
  • a hormone so must be soluble so that it can be transported via bloodstream
  • moves quickly through blood and is easily captured by glycoprotein receptors on cell surface for cell signalling
121
Q

What is a conjugated protein?

A
  • globular proteins that contain a prosthetic group (non protein component)
  • there are different types of prosthetic groups - lipids or carbohydrates can join proteins to become lipoproteins or glycoproteins
  • metal ions and molecules derived from vitamins can also form prosthetic groups
122
Q

Describe the properties of haemoglobin

A
  • conjugated protein
  • red pigment inside red blood cells
  • transports oxygen in blood
  • has 4 polypeptides, 2 alpha and 2 beta subunits
  • each subunit contains a haem group (contains an Fe2+ ion) which can reversibly bind to an oxygen molecule
  • each molecule can bind to 4 oxygen molecules
123
Q

Describe the properties of catalase

A
  • conjugated protein
  • an enzyme, which catalyse reactions
  • contains 4 prosthetic haem groups
  • breaks down hydrogen peroxide (H2O2), which is a common byproduct of metabolism but harmful to proteins
124
Q

What are fibrous proteins?

A
  • formed from long molecules
  • insoluble due to large number of hydrophobic r groups - useful as you don’t want hem to react or be carried around the body
  • form long chains that run parallel to each other
  • have an elongated shape (not folded into 3D shapes like globular proteins)
  • chains linked by cross bridges - strong
  • very stable molecules
  • can be flexible
  • high proportion of molecules primary structure is one type of amino acid - very repetitive structure
  • have a structural function - make up tendons, skin, hair, etc. sometimes used for support
125
Q

Describe the structure of collagen

A
  • a structural, fibrous, insoluble, linear and strong protein
  • 3 uniform polypeptide chains. these are coiled and each coil held together with hydrogen bonds.
  • the three coiled chains lie close together because of the high proportion of glycine in them (one every 3 amino acids). These form hydrogen bonds
  • 3 coiled chains are wound tightly together to form a triple helix, which is also stabilised by H-bonds between the chains for more strength (and other bonds too)
  • triple helix is a collagen molecule
  • each collagen molecule forms covalent bonds (cross links) with other collagen molecules for even ore strength
  • many molecules form a fibril. the ends of the molecules are staggered to avoid weak points
  • many collagen fibrils join together to form a collagen fibre
  • in some tissues, there are many fibres in a bundle
126
Q

What is collagen used for?

A

structure in

  • walls of arteries
  • tendons
  • ligaments
  • bones (with addition of calcium phosphate)
  • cartilage and connective tissue
  • cosmetic treatments eg lip filler
127
Q

Describe the properties of keratin

A
  • fibrous protein
  • rich in cysteine - lots of disulphide bonds making it very strong
  • often inflexible and used where strength and hardness needed eg nails, hair, claws, hoofs, horns, scales, fur and feathers
  • provides mechanical protection - resistant to forces
  • impermeable barrier to infection
  • waterproof
128
Q

Describe the properties of elastin

A
  • fibrous protein
  • strong and extensible due to cross linking and coiling
  • made of many stretchy molecules called tropoelastin
  • used wherever the ability to stretch and recoil is needed eg walls of blood vessels, alveoli of lungs, skin, bladder

OCR Biology (25 decks)

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