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A-level biology > AS - Unit 2 - Biological molecules > Flashcards

AS - Unit 2 - Biological molecules Flashcards

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1
Q

What are the important roles of calcium ions in living organisms?

A

Nerve impulse transmission

Muscle contraction

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2
Q

What are the important roles of sodium ions in living organisms?

A

Nerve impulse transmission

Kidney function

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3
Q

What are the important roles of potassium ions in living organisms?

A

Nerve impulse transmission

Stomata opening

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4
Q

What are the important roles of hydrogen ions in living organisms?

A

Catalysing reactions

pH determination

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5
Q

What is the role of ammonium ions in living organisms?

A

Production of nitrate ions by bacteria

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6
Q

What is the role of nitrate ions in living organisms?

A

Nitrogen supply to plants for amino acid and protein formation

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7
Q

What is the role of hydrogen carbonate ions in living organisms?

A

Maintenance of blood pH

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8
Q

What is the role of chloride ions in living organisms?

A

To balance the positive charge of sodium and potassium ions in cells

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9
Q

What is the role of phosphate ions in living organisms?

A

Cell membrane formation
Nucleic acid and ATP formation
Bone formation

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10
Q

What is the role of hydroxide ions in living organisms?

A

Catalysis of reactions

pH determination

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11
Q

What are the 4 biological molecules?

A

Carbohydrates
Lipids
Proteins
Nucleic acids

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12
Q

Give some characteristics of water

A

High boiling point
Solid state less dense than liquid state
Molecules are attracted to each other so moves as one (cohesion)
Water molecules are attracted to other things (adhesion)
Polar so acts as a solvent
Strong surface tension

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13
Q

Name three monosaccharides

A

Glucose
Fructose
Ribose

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14
Q

Name two disaccharides

A

Lactose

Sucrose

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15
Q

Name three polysaccharides

A

Glycogen
Cellulose
Starch

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16
Q

What are the two types of glucose

A

Alpha glucose

Beta glucose

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17
Q

What is the chemical formula for glucose?

A

C6H12O6

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18
Q

Where is the OH group in alpha glucose?

A

Below the plane

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19
Q

Where is the OH group in beta glucose?

A

Above the plane

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20
Q

Which way do you label and number the carbon atoms in glucose?

A

Clock wise

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21
Q

What is the bond called that forms between two glucose molecules?

A

Glycosidic bond

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22
Q

What reaction does glucose undergo to produce a disaccharide and form a glycosidic bond?

A

Condensation reaction

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23
Q

When two alpha glucose molecules join together which type of bond do they form and what is the name of the disaccharide formed?

A

1,4-glycosidic bond

Maltose

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24
Q

What are the two kinds of starch?

A

Amylose

Amylopectin

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25
Q

What type of glucose makes up starch?

A

Alpha glucose

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26
Q

Describe amylose

A

Alpha glucose bonded together by 1,4-glycosidic bonds
Angle of bond means long chain of glucose twists to form helix
Helix further stabilized by hydrogen bonds within the molecule
Polysaccharide becomes more compact
Less soluble with H bonds

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27
Q

Describe amylopectin

A

Branches coming off main chain
1,6-glycosidic bonds formed for branches
Branched units approx every 25 glucose subunits

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28
Q

What type of glucose is glycogen made out of?

A

Alpha

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29
Q

What’s the difference between glycogen and amylopectin?

A

Glycogen forms more branches than amylopectin meaning it is more compact and less space is needed for it to be stored
More branches means more free ends where glucose can be added or removed
Speeds up processes of storing or releasing glucose molecules required by the cell

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30
Q

What type of reaction occurs when glucose is removed from glycogen and starch?

A

Hydrolysis

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31
Q

What type of glucose is in cellulose?

A

Beta glucose

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32
Q

How do beta glucose molecules join together to form cellulose?

A

Each successive beta glucose molecule is flipped so the OH molecules are next to each other to form glycosidic bonds

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33
Q

How is cellulose formed from the polysaccharide?

A

Long chains of cellulose make hydrogen bonds with each other to form microfibrils
The microfibrils form together to form microfibrils
These combine to form fibres

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34
Q

Give some properties of cellulose

A

Strong
Insoluble
Used to make new cell walls
Important part of our diets
Hard to break down into glucose molecules
Formed the fiber part of our diet which is necessary for a functioning digestive system

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35
Q

What sugars are known as reducing sugars??

A

Monosaccharides and disaccharides
E.g. Maltose
E.g. Lactose

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36
Q

What test do you use for reducing sugars?

A

Benedicts test

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37
Q

How do you perform a benedicts test?

A

Place sample in test tube, in liquid form
Add equal amount of benedicts reagent
Heat mixture gently in a boiling water bath for five minutes
If a brick red color is produced it is a positive result
Meaning there is a reducing sugar in the solution
E.g. Mono or disaccharide

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38
Q

How do you test for non reducing sugars?

A

Also the benedicts test however you should get a negative result originally
Go back and boil with original solution with HCl then carry out the benedicts test again and this time you should get a positive result

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39
Q

What test do you carry out for starch and how does it work?

A

Iodine test
A few drops of iodine dissolved in potassium iodide solution are mixed with a sample
If the solution changes color from yellow/brown to purple/black then starch is present in the sample

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40
Q

Why are lipids not soluble in water?

A

They are non polar, so they don’t form hydrogen bonds with water, therefore not soluble

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41
Q

How are triglycerides formed?

A

Combining one glycerol molecule with three fatty acids

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42
Q

How do you add fatty acids to a glycerol molecule?

A

The OH groups on both the glycerol and the fatty acid will interact, in a condensation reaction three H2O molecules are formed, these are called ester bonds.

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43
Q

What is a risk factor?

A

A factor than increases your chance of developing a particular disease

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44
Q

What is metabolism?

A

The sum total of all the biochemical reactions taking place in the cells of an organism

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45
Q

Give an example of a carbohydrate as an energy source

A

Release of glucose during respiration

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46
Q

Give an example of a carbohydrate as an energy store

A

Starch

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47
Q

Give an example of a carbohydrate as a structure

A

Cellulose

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48
Q

Give the word equation for respiration

A

Glucose + oxygen —> carbon dioxide + water + energy that is used to form ATP

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49
Q

Animals and plant cells have enzymes which can only break down which type of glucose?

A

Alpha

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50
Q

Alpha glucose + alpha glucose = ?

A

Maltose

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51
Q

Maltose + maltose + maltose + maltose etc =

A

Amylose

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52
Q

What structure does Beta glucose take on when reacted in a condensation reaction?

A

A long straight chain

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53
Q

Where is cellulose only found?

A

In plants

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54
Q

How is each cellulose chain connected to all the other cellulose chains?

A

By hydrogen bonding

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55
Q

Explain the larger structure of cellulose?

A

The beta glucose chains are all hydrogen bonded to each other to produce a tightly packed fibril, the fibrils join together to create a microfibril then these microfibrils all join together to create a macrofibril. This is also known as fibre which is what keeps your digestive system moving as it carries everything out.

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56
Q

What is cellulose?

A

A carbohydrate polymer made by bonding many beta glucose molecules together in long chains

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57
Q

What does the polysaccharide chitin do?

A

Forms the exoskeleton of insects

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58
Q

What does the polysaccharide peptidoglycan do?

A

The basis of cell walls found around most bacterial cells

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59
Q

Give two examples of monosaccharides

A

Glucose

Deoxyribose

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60
Q

What is the role of glucose?

A

To provide energy via respiration

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61
Q

What is the role of deoxyribose?

A

Part of DNA - information molecule

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62
Q

Give an example of a disaccharide

A

Maltose

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63
Q

What is the role of maltose?

A

Obtained when starch is broken down in hydrolysis reactions

can be split further to glucose for respiration

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64
Q

Give three polysaccharides

A

Starch
Glycogen
Cellulose

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65
Q

Give the roles of starch and glycogen

A

Energy storage carbohydrates
Starch in plants
Glycogen in animals and fungi

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66
Q

What is the role of cellulose?

A

Structural

Found only in plants, where it forms cell walls

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67
Q

What are the characteristics of glucose?

A

Small, soluble, sweet and crystalline

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68
Q

What are the characteristics of maltose?

A

Small, soluble, sweet, and crystalline

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69
Q

What are the characteristics of starch and glycogen?

A

Large molecules of many alpha glucose molecules joined by condensation reaction. Insoluble in water. Forms grains/ granules

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70
Q

What are the characteristics of cellulose?

A

Large molecules of many beta glucose molecules joined by condensation reactions. Insoluble in water very strong

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71
Q

What is the monomer of a protein?

A

An amino acid

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72
Q

Give 5 functions of proteins

A 
Structural components e.g. muscle and bone
Membrane carriers and pores 
All enzymes are proteins
Many hormones are proteins
Antibodies are proteins
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73
Q

When amino acids are joined together which part of the molecules makes up the ‘backbone’?

A

The NCC part

NCCNCCNCCNCCNCC (a protein polymer backbone)

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74
Q

How many different types of amino acid are there?

A

20

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75
Q

What part of the amino acid determines the differences between them?

A

The R group

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76
Q

What does the body do when it has excess amino acids it doesn’t need?

A

The amino group is removed (deamination), in mammals this takes place in the liver. The amino groups removed are converted to a substance called urea and removed in the urine

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77
Q

What bond is formed between two amino acids and what is the process called that joins them?

A

Peptide bond

Condensation reaction

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78
Q

What is the primary structure of a protein?

A

The primary structure of a protein is given by the specific sequence of amino acids that make up the protein

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79
Q

What is the name for the structure when two amino acids are joined together?

A

A dipeptide

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80
Q

Where are proteins synthesised?

A

In the cell on the ribosomes

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81
Q

Which enzyme breaks down peptide bonds in proteins?

A

Protease

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82
Q

Give two examples of where protease is used in the body

A

Hormone regulation - hormones need to be broken down so the effects aren’t permanent
Ageing - young skin contains lots of the protein collagen. Older skin cannot rebuild it as easily

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83
Q

What is the secondary structure of a protein?

A

The coiling and pleating of parts of the polypeptide molecules

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84
Q

What is the tertiary structure of a protein?

A

The overall 3D structure of the final polypeptide or protein molecule, when the coils and pleats themselves coil and pleat

85
Q

What determines the sequence of proteins?

A

DNA

86
Q

To avoid tangling and breaking of amino acids chains what happens to the structure?

A

It pleats and folds as it is made, the pleats and folds are held in place by numerous hydrogen bonds, once the whole chain is complete the coils and pleats come together in a specific way to form a specific three-dimensional shape

87
Q

How many amino acids are there per 10 turns of the coil in an alpha helix?

A

36

88
Q

How often to hydrogen bonds form in an alpha helix?

A

H bonds form between one amino acid and the one four places along the chain

89
Q

What are the 4 different types of bonds which stabilise the tertiary structure of a protein?

A

Disulfide bonds
Ionic bonds
Hydrogen bonds
Hydrophilic and hydrophobic interrations

90
Q

What happens to the tertiary structure of a protein if it is heated up?

A

The molecules vibrates
Breaks some of the bonds holding the tertiary structure in place
If enough heat applied, whole tertiary structure unravels and the protein no longer functions
Process is called denaturation

91
Q

What two categories do tertiary proteins fall into?

A

Globular proteins

Fibrous proteins

92
Q

Give some properties of globular proteins

A 
Roll up to form balls
Usually soluble
Usually have metabolic roles
E.g. enzymes found in all organisms
e.g. plasma proteins and antibodies found in the blood of mammals
93
Q

Give some properties of fibrous proteins

A

Form fibres
Usually insoluble
Structural roles
e.g. collagen found in bone and cartilage.
e.g. keratin found in fingernails and hair

94
Q

What is the quaternary structure of a protein?

A

Some proteins are made up of more than one polypeptide subunit, or a polypeptide and an inorganic component

95
Q

Give two examples of quaternary proteins

A

Haemoglobin

Insulin

96
Q

What is haemoglobin?

A

A globular transport protein

97
Q

What is collagen?

A

A fibrous structural protein

98
Q

What does the quaternary structure of haemoglobin consist of?

A

Four polypeptide subunits
Two are alpha helix
Two are beta chains

99
Q

What is the function of haemoglobin?

A

To carry oxygen from the lungs to the tissues. It binds oxygen in the lungs and releases it in the tissues.

100
Q

Which part of the haemoglobin molecule is responsible for the colour?

A

The Fe+ ion.

Haemoglobin (purple-red) + oxygen = oxyhaemoglobin (bright red)

101
Q

How much oxygen can haemoglobin take up?

A

An oxygen molecules can bind to the iron in the haem group.

One complete haemoglobin molecule can bind up to four oxygen molecules

102
Q

Explain the significance of a prosthetic group

A

It is not made up of amino acids but in an essential part of the molecule. Prosthetic groups are found in a number of proteins

103
Q

How is collagen so strong?

A

The collagen molecules form covalent bonds called cross-links with other collagen molecules next to it.
The cross links that form are staggered along the collagen molecules, adding to the strength of the molecule. This results in a structure called a collagen fibril, many fibrils together form a collagen fibre

104
Q

What is the function of collagen?

A

A layer of collagen prevents blood that is being pumped from the heart at high pressure from bursting the walls
Tendons connect skeletal muscles to the bones, tendons are mostly collagen, and form a strong connection that allows muscles to pull bones for movement
Bones are formed from collagen and reinforced with materials such as calcium phosphate to make them hard
Cartilage and connective tissue are also made of collagen
Cosmetic treatments using collagen are becoming increasingly popular

105
Q

Give some properties of haemoglobin

A

Globular protein
Soluble in water
Wide range of amino acid constituents in primary structure
Contains prosthetic group - haem
Much of the molecule is wound into alpha helix structures

106
Q

Give some properties of collagen

A

Fibrous protein
Insoluble in water
Approx 35% of the molecule’s primary structure is one type of amino acid (glycine)
Does not have a prosthetic group
Much of the molecule consists of left-handed helix structures

107
Q

What are lipids?

A

A diverse group of chemicals that dissolve in organic solvents, such as alcohol, but not in water. They include fatty acids, triglycerides and cholesterol

108
Q

At room temperature, what is a solid lipid called?

A

A fat

109
Q

What is a liquid lipid called?

A

Oil

110
Q

Give 6 functions of lipids

A

A source of energy - can be respired to release energy to generate ATP
Energy storage - lipids are stored in adipose cells in ‘fat stores’
All biological membranes are made from lipids
Insulation
Protection - e.g. the surface of plant leaves is protected against drying out by a layer of lipid
Some hormones are lipids

111
Q

Explain the structure of a fatty acid

A

An acid group on the end, with a hydrocarbon chain on the end. The hydrocarbon chain can be anything from 2 to 20 carbons long.

112
Q

What are the two different types of fatty acid?

A

Saturated and unsaturated

113
Q

What makes a polyunsaturated fatty acid?

A

A fatty acid with two or more C=C double bonds

114
Q

What is a triglyceride?

A

A molecules consisting of one glycerol molecule bonded to three fatty acid molecules. All fatty acid molecules are joined to glycerol molecules in a condensation reaction. An ester bond is formed between the OH on the glycerol and the OH on the fatty acid molecule

115
Q

Give a property of a triglyceride

A

The fatty acid tails are hydrophobic meaning the triglyceride doesn’t mix well with water

116
Q

What is a phospholipid?

A

Essentially a triglyceride however one fatty acid is changed out for a phosphate group

117
Q

Where are phospholipids generally found?

A

Cell membranes

118
Q

How can animals make sure their fluid membrane remains fluid?

A

Animals in low temperature climates can increase the number of unsaturated fatty acids in their phospholipid molecules. So despite the low temperatures their membranes remain fluid

119
Q

How does respiration of a lipid compare to the respiration of a carbohydrate?

A

Respiration of one gram of lipid gives out about twice as much energy as the respiration of one gram of carbohydrate.

120
Q

What makes a triglyceride an excellent energy-storage molecule?

A

Lipids are insoluble in water, they can be stored in a compact way and they do not affect the water potential of the cell contents.

121
Q

How much water is given out by respiration of a lipid compared to the respiration of a carbohydrate?

A

Lipid respiration gives out a great deal more water than the respiration of carbohydrates. This metabolic water is vital to the survival of some organisms

122
Q

What is cholesterol and where is it found?

A

A class of lipid, it is found in call biological molecules

123
Q

Which steroid hormones and one vitamin are made from cholesterol?

A

Testosterone, oestrogen and vitamin D

124
Q

What allows steroid hormones to pass through membranes easily?

A

They are made from cholesterol with a lipid nature meaning they can pass through the phospholipid bilayer in order to reach their target receptor.

125
Q

Give two examples of how excess cholesterol in the body is unhealthy

A

In bile, cholesterol can stick together to form lumps called gallstones
In blood, cholesterol can be deposited in the inner linings of blood vessels causing atherosclerosis, which can result in a number of circulatory problems

126
Q

What is a hydrogen bond?

A

A weak interaction that can occur whenever molecules contain a slightly negatively charged atom bonded to a slightly positively charged hydrogen

127
Q

Explain what water is like in liquid form

A

The molecules form hydrogen bonds with each other, forming a network which allows the molecules to move around, continually making and breaking hydrogen bonds as they do so. This makes it much more difficult for water molecules to escape to liquid to become gas.

128
Q

What happens to the bonds in water as it goes from liquid to solid form?

A

More hydrogen bonds form, and they do not break easily. As water becomes more solid the hydrogen bonds formed hold the structure in a semi-crystalline form. This form is less dense than liquid water so ice forms on the surface of water as it cools

129
Q

How does ice help to keep living organisms alive in water?

A

Ice floats on liquid water, insulating the water below. This allows living organisms to survive the winter, and even to live under the ice

130
Q

Why does water appear spherical on a waxy surface like a leaf?

A

The hydrogen bonds pull water molecules in at the surface. It is basically the water molecules sticking together, this is called cohesion.

131
Q

How does water act as a solvent?

A

The substance to be dissolved (the solute) has slightly negative and slightly positive parts. These will interact with water molecules
The water molecules cluster around the slightly charged parts of the solute molecule
This keeps the solute molecules apart so they are dissolved
Once in solution, molecules can move around and react with other molecules. This is the basis of most metabolic reactions, which take place in solution in the cytoplasm
Ions are charged particles that also dissolve very easily because water molecules can cluster around them and separate them

132
Q

What properties of water make it an ideal transport medium in living organisms?

A

Water remains liquid over a large temperature range and can act as a solvent for many chemicals

133
Q

What is the importance of water being used as a solvent and give an example?

A

Metabolic processes in all organisms rely on chemicals being able to react together in solution.
e.g. 70-95% of cytoplasm is water. Dissolved chemicals take part in processes such as respiration and photosynthesis in living organisms

134
Q

What is the importance of water being in liquid form and give an example?

A

The movement of materials around organisms, both in cell and on a larger scale in multicellular organisms, requires a liquid transport medium
e.g. Blood in animals and the vascular tissues in plants use water as a liquid transport medium

135
Q

What is the importance of cohesion in water and give an example?

A

Water molecules stick to each other creating surface tension at the water surface. Cohesion also makes long, thin water columns very strong and difficult to break

e. g. Transport of water in the xylem relies on water molecules sticking to each other as they are pulled up the xylem in the transport stream
e. g. some small organisms make use of surface tension to ‘walk on water’

136
Q

What is the importance of being able to freeze water and give an example?

A

Water freezes, forming ice on the surface. Water beneath the surface becomes insulated and less likely to freeze

e. g. Organisms such as polar bears live in an environment of floating ice packs
e. g. Lakes tend not to freeze completely, so aquatic organisms are not killed as temperatures fall

137
Q

What is the importance of waters’ thermal stability and give an example?

A

Large bodies of water have fairly constant temperatures. Evaporation of water can cool surfaces by removing heat

e. g. Oceans provide a relatively stable environment in terms of temperature
e. g. many land-based organisms use evaporation as a cooling mechanism, for example in panting or sweating

138
Q

What is the importance of water in metabolic processes and give an example?

A

Water takes part as a reactant in some chemical processes

e.g. Water molecules are used in hydrolysis reactions an in the process of photosynthesis

139
Q

What are the two forms of nucleic acids?

A

DNA and RNA

140
Q

What are nucleotides?

A

The monomers of all nucleic acids. Each nucleotide is formed by bonding together a phosphate group, a sugar molecule and a nitrogenous base

141
Q

What are the five possible bases for nucleic acids?

A 
Adenine
Thymine
Guanine
Cytosine
Uracil
142
Q

What is the ‘backbone’ of DNA?

A

Repeating sugar-phosphate chain

143
Q

Which nitrogenous bases are purines?

A

Adenine

Guanine

144
Q

Which nitrogenous bases are pyrimidines?

A

Thymine
Uracil
Cytosine

145
Q

Which base pairs go together?

A

Adenine and Thymine

Guanine and Cytosine

146
Q

How many hydrogen bonds do adenine and thymine form?

A

2

147
Q

How many hydrogen bonds do guanine and cytosine form?

A

3

148
Q

What has to happen in order to make a new copy of a DNA molecule?

A

Double helix untwisted
Hydrogen bonds between bases broken apart to ‘unzip’ DNA - exposes the bases
Free DNA nucleotides hydrogen-bonded onto the exposed bases according to base pairing rules
Covalent bonds are formed between phosphate of one nucleotide and the sugar of the next to seal the backbone

149
Q

How is DNA replication described?

A

As semi-conservative replication

150
Q

What is DNA?

A

A stable polynucleotide molecule. It acts as an information store because the bases projecting from the backbone act as a coded sequence. Organisms differ in their DNA only because they contain different sequences of bases in the DNA

151
Q

How is the structure of DNA ideal for its function?

A

The sequence of bases is an example of information storage. The information is in the form of codes to build proteins
The molecules are long, so a large amount of information can be stored
Base-pairing rules mean that complimentary strands of information can be replicated
Double helix structure gives the molecules stability
Hydrogen bonds allow easy unzipping for copying and reading information

152
Q

Give 4 ways that RNA is different to DNA

A

The sugar molecules that makes up the nucleotides is ribose
Nitrogenous base uracil is found instead of thymine
Polynucleotide chain is usually single stranded
Three forms of RNA molecule exist

153
Q

In RNA which base pair matches with Adenine?

A

Uracil

154
Q

What are the three forms of RNA?

A

Messenger RNA
Ribosomal RNA
Transfer RNA

155
Q

What is messenger RNA?

A

It is made as a strand complimentary to one strand of a DNA molecule (the template strand) - it is therefore a copy of the other DNA strand (the coding strand) of the double helix

156
Q

Where is ribosomal RNA found?

A

In the ribosomes

157
Q

What is the role of transfer RNA?

A

It carries amino acids to the ribosomes, where they are bonded together to form polypeptides

158
Q

What is a gene?

A

A length of DNA (part of a DNA molecule) that codes for one (or more) polypeptides. Each gene occupies a specific place on a chromosome. Different versions of the same gene are called alleles

159
Q

Give 7 steps of protein synthesis

A
  1. The sequences of bases on DNA makes up codes for particular protein molecules. They code for the sequence of amino acids in the protein
  2. The sequence is exposed by splitting the hydrogen bonds that hold the double helix together
  3. RNA nucleotides form a complimentary strand (mRNA). This mRNA molecule is a copy of the DNA coding strand
  4. mRNA peels away from the DNA and leaves the nucleus through a nuclear pore
  5. mRNA attaches to a ribosome
  6. tRNA molecules bring amino acids to the ribosome in the correct order, according to the base sequence on the mRNA
  7. Amino acids are joined together by peptide bonds to give a protein with a specific primary structure
160
Q

Give 5 ways that enzymes are similar

A

Globular proteins - generally soluble in water
Act as catalysts
Specific
Globular structure contains a ‘pocket’ or cleft area called an active site
Activity is affected by temperature and pH

161
Q

What is a catalyst?

A

A molecule or element that speeds up a chemical reaction but does not get used up in the reaction, at the end of the reaction the catalyst remains unchanged

162
Q

What does the enzyme lactase do?

A

The breakdown of milk sugar, lactose, into glucose and galactose monomers. Lactose-intolerant individuals do not produce lactase and suffer stomach cramps, bloating and diarrhoea if they take in milk products

163
Q

What does the enzyme catalase do?

A

Breaks down hydrogen peroxide to water and oxygen gas.

Almost all organisms produce catalase because hydrogen peroxide is a toxic by-product of some metabolic reactions

164
Q

What does the enzyme ribulose bisphosphate carboxylase (rubisco) do?

A

Catalyses the binding of carbon dioxide to a molecule called ribulose bisphosphate

165
Q

What does the enzyme ATP-ase do?

A

Breaks down ATP to produce ADP and a phosphate group. Reaction releases a small amount of energy that is used to drive energy requiring processes such as active transport

166
Q

What does the enzyme glycogen synthetase do?

A

Builds up glycogen by catalysing the joining together of glucose molecules

167
Q

What do extracellular enzymes do?

A

They catalyse reactions outside of the cell

168
Q

What do intracellular enzmymes do?

A

They catalyse reactions inside the cell

169
Q

How are endotherms able to live almost anywhere on the globe?

A

They are able to maintain their own body temperature independently of the environment.
Regulating body temperature means that enzymes can function at near-optimum temperature inside the organism

170
Q

Why do endotherms need a greater food supply?

A

They can regulate their own body temperature, at the cost of it requiring very high amounts of energy.

171
Q

What is a heterotroph?

A

An organism that obtains its nutrients by consuming other organisms

172
Q

What is activation energy?

A

The amount of energy that must be applied for a reaction to proceed.

173
Q

What do enzymes do to activation energy?

A

They lower the amount of activation energy needed to allow a reaction to proceed

174
Q

What are the two theories on how substrates fit into the active site of an enzyme?

A

Lock and key

Induced-fit

175
Q

Explain the induced-fit hypothesis

A

As a substrate molecule collides with an enzyme’s active site, the enzyme molecule changes shape slightly
This makes the active site fit more closely around the substrate
The substrate is held in place because oppositely charged groups on the substrate and the active site are found near to each other
This is called the enzyme-substrate complex
This change in enzyme shape put strain on the substrate and destabilises it so the reaction occurs more easily
Produces a product and is now called an enzyme-product complex
Products formed no longer fit into active site and they move away
Enzyme is now able to catalyse the same reaction with another substrate molecule

176
Q

How can you increase the number of collisions with enzyme and substrate?

A

Increasing the temperature increases the kinetic energy, reaching the activation energy so more collisions will occur
Increasing the concentration will increase the changes of collisions

177
Q

How does heat affect enzymes?

A

Applying heat doesn’t only make the molecules move faster it also makes them vibrate which puts a strain on the bonds that hold the molecules together
In enzymes this vibration breaks the weaker bonds such as hydrogen bonds and ionic bonds
These weaker bonds are responsible for the tertiary structure that maintains the shape of the active site
The rate of reaction will decrease
If enough bonds are broken, the tertiary structure will unravel and the enzyme will stop working

178
Q

What is denaturation?

A

It changes the structure of an enzyme such that it cannot function and its function cannot be restored

179
Q

How does increasing the temperature of a reaction affect the rate of reaction regarding enzymes?

A

Increasing the temperature increases the rate of reaction at first, but as the temperature increases further, the rate of reaction decreases. Eventually the enzyme will stop working

180
Q

What is pH?

A

A measure of the hydrogen ion concentration, with values for pH ranging from 1 to 14

181
Q

How does pH affect enzymes?

A

pH is the concentration of H+ ions in a solution, these H+ ions can interfere with the hydrogen bonds and ionic bonds in the tertiary structure of an enzyme.
So changes in pH can cause changes to the structure of an enzyme’s active site.

182
Q

What is optimum pH?

A

The pH value at which the rate of an enzyme-controlled reaction is at its maximum. Each enzyme has a specific optimum pH

183
Q

How are pepsin and trypsin examples of how ezmyes are effected by pH and location?

A

Pepsin has an optimum pH of 2 whereas trypsin has an optimum pH of around 7
Pepsin is found in the stomach which has a low acidity, and therefore needs enzymes which work in an optimum of a low pH e.g. 2
Trypsin is found in the small intestine where the average pH is 7

184
Q

Why is it important to keep a steady pH?

A

Changes to pH, altering the concentration of H+ ions even slightly result in a fall in the reaction rate because the shape of the enzyme molecule is disrupted and so the shape of the active site is changed

185
Q

How does increasing the substrate affect the rate of reaction?

A

Increased substrate concentration leads to increased rate of reaction initially
However the rate of reaction levels off at a constant rate when all enzymes present are working at their maximum rate

186
Q

What is a limiting factor?

A

If all other conditions are kept constant, increasing the concentration of that factor alone will increase the reaction rate

187
Q

What is an enzyme inhibitor?

A

Any substance or molecule that slows down the rate of an enzyme-controlled reaction by affecting the enzmye molecule in some way

188
Q

What is a competitive inhibitor?

A

Competitive inhibitors have a similar shape to that of the substrate molecules.
This means they occupy the active site, creating enzyme-inhibitor complexes, the enzyme is no longer catalysing the reaction, preventing the substrate from entering the active site and therefore slowing the rate of reaction

189
Q

What does the level of enzyme inhibition depend on?

A

The concentrations of inhibitor and substrate
If there is a really high concentration of inhibitor and a low concentration of substrate the rate of reaction will be extremely low

190
Q

What is a non-competitive inhibitor?

A

Non-competitive inhibitors do not compete with substrate molecules for a place in the active site.
Instead, they attach to the enzyme molecules in a region away from the active site. This distorts the enzymes, which changes the tertiary structure and thus, the active site.

191
Q

How do competitive and non-competitive enzyme reaction graphs differ?

A

Competitive:
Without inhibitor the graph increases at a constant rate then levels off
With inhibitor the graph increases at a slower but still constant rate then levels off at the same level but slightly later than with no inhibitor
Non-competitive:
Without inhibitor the graph increases at a constant rate then levels off
With inhibitor the graph increases slightly then stays levelled off low down. The two graph lines do not meet or touch. The level of inhibition is controlled by the number of inhibitor molecules present

192
Q

Which inhibitors are permanent and which are non-permanent?

A

Most competitive inhibitors do not bind permanently to the active site. They bind for a short period then leave.
Many non-competitive inhibitors bind permanently to enzyme molecules. The inhibition is not reversible.

193
Q

What is a cofactor?

A

Any substance that must be present to ensure enzyme-controlled reaction take place at the appropriate rate.

194
Q

What are coenzymes?

A

Small, organic, non-protein molecules that bind for a short period to the active site.
They often bind just before or as the reaction is taking place .
They take part in the reaction and like the substrate they are changed in some way however unlike the substrate they are recycled back to take part in the reaction again

195
Q

What is a prosthetic group?

A

A coenzyme that is a permanent part of an enzyme molecule.
They are also found in other protein molecules
They are vital to the function of the enzyme molecule and contribute to the final 3D shape, and to other properties of the molecule, including its charge

196
Q

What is a biosensor?

A

It uses enzyme-controlled reaction to detect the presence of substances in a highly sensitive and specific way. If the substance is present, the enzyme-controlled reaction takes place. The biosensor has a mechanism for revealing whether product is made

197
Q

How can alcohol be both a poison and a drug?

A

It can over time be poisonous to the liver, however if Ethylene glycol (antifreeze) is ingested by a human alcohol is given to the patient as it is a competitive inhibitor for alcohol dehydrogenase (the enzyme which can break both things down).
This alcohol inhibition reduces the rate of production of oxalic acid (the harmful product of the breakdown of ethylene glycol) allowing the ethylene gylcol to be excreted harmlessly

198
Q

What is a variable?

A

Any factor that may change and therefore affect the reaction rate.

199
Q

How can you test the reaction rate of the enzyme catalase?

A

Catalase breaks down hydrogen peroxide into water and oxygen gas
You can measure the rate of reaction by measuring the amount of oxygen gas produced

200
Q

How can you keep temperature constant while carrying out an investigation? Give reasoning

A

Usually by using a water bath with a thermostat to keep the temperature constant
If you can use a water bath a polystyrene cup can provide insulation to keep the temperature as constant as possible.
This is because, room temperature is too variable. Fluctuations in temperature will affect the enzyme-controlled reaction so readings taken will not reflect the action of the independent variable being tested

201
Q

How can you keep enzyme concentration constant while carrying out an investigation? Give reasoning

A
  1. Use accurately measured volumes of enzyme solution. This is because the reaction rate depends on the concentration of enzyme molecules
  2. If you are using enzyme in living tissue, accurate measurements of the mass of tissue is important. This is because in all living tissue you must assume that all pieces of tissue contain the same number of enzyme molecules
  3. If you are using whole pieces of tissue, you must keep the surface area of the tissue constant as well as the mass. This is because the number of enzyme molecules in contact with substrate molecules will affect the reaction rate
202
Q

How can you control substrate concentration while carrying out an investigation?

A

Use accurately measured volume or mass of substrate

This is because reaction rate depends on the concentration of substrate molecules

203
Q

How can you control the pH value while carrying out an investigation?

A

Use pH buffers - solutions that maintain pH at a set level by keeping the H+ concentration in solution constant
This is because reaction rate depends on the pH because of it effects on the shape of the active site of the enzyme

204
Q

What are the two main ways of measuring reaction rate?

A

Start the reaction then measure the concentration of product after a fixed period
Monitor the reaction by taking readings of product formation at a number of time intervals

205
Q

How can you calculate reaction rate?

A

Reaction rate = 1/time

206
Q

How do you test for the effect of pH on enzyme activity?

A

Cut wells into an agar plate using a cork borer
Into each well place the same volume of one of a range of pH duffer solutions
Place identical volume of a stock amylase solution into each well except one
To that well add an equal volume of distilled water as a control
Incubate for 24hrs in a dry oven at 35 degrees C
During this time amylase will diffuse through the agar
and catalyse the conversion of starch to maltose
Flood the plate with iodie solution and rinse with water
(iodine indicates the presence of starch by turning blue-black)
Measure the diameter of the cleared zone - this gives a measure of how much substrate has been turned into product

207
Q

How can you test the effect of termperature of the enzyme catalase?

A

Catalase is present in the cells of potato tubers, where it catalyses the breakdown of hydrogen peroxide to water and oxygen gas
take samples of potato tissue using cork borer, then slice into discs of equal thickness
Place equal number of discs on each of seven test tubes
Place one in each of a range of water baths at 20, 30, 40, 50, 60, 70 and 80 degrees C
Place equal volume of pH7 buffer and hydrogen peroxide solution to each of the seven test tubes and place one in each water bath
Allow to equilibriate
Taking each in turn, add peroxide/buffer mixture to potato discs then fix stopper and side arm into the tube close the clip
Time how long in seconds it takes for the water bubble in the side arm tube to move 5cm along the tube

208
Q

What is an anomalous result?

A

One that looks out of place with other results or readings

209
Q

What is a turnover number?

A

The number of reactions an enzyme molecule can catalyse in one second. In catalase, the turnover number is up to 200 000

A-level biology (18 decks)

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