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A level Chemistry > Unit 4.7 - Amino acids, peptides and proteins > Flashcards

Unit 4.7 - Amino acids, peptides and proteins Flashcards

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1
Q

What are amino acids?

A

Carbon compounds which contain two functional groups:
An amino (amine) group - NH2
A carboxylic acid group - COOH

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2
Q

Two functional groups of an amino acid

A

-NH2 (amine)
-COOH (carboxylic acid)

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3
Q

Most common group of amino acids

A

2-amino acids (alpha amino acids)

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4
Q

Describe a 2-amino acid

A

Both functional groups are attached to the same carbon atom

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5
Q

Why is the 2-amino acid the most common group?

A

It’s the type of amino acid most commonly found in nature and is the building block from which proteins are made

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6
Q

Type of amino most commonly found in nature and from which proteins are made?

A

2-amino acids/alpha amino acids

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7
Q

H2NCH2COOH

A

Aminoethanoic acid (glycine)

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8
Q

Aminoethanoic acid (glycine) formula

A

H2NCH2COOH

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9
Q

CH3CH(NH2)COOH

A

2-aminopropanoic acid (alanine)

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10
Q

2-aminopropanoic acid (alanine) formula

A

CH3CH(NH2)COOH

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11
Q

C6H5CH2CH(NH2)COOH

A

Phenylalanine

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12
Q

Phenylalaline formula

A

C6H5CH2CH(NH2)COOH

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13
Q

HOCH2CH(NH2)COOH

A

Serine

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14
Q

Serine formula

A

HOCH2CH(NH2)COOH

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15
Q

What may X be in the 2-amino acid structure?

A

A wide variety of groups, each making a different amino acid

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16
Q

What do all 2-amino acids have except for Aminoethanoic?

A

A chiral centre on the 2-carbon

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17
Q

Only 2-amino acid without a chiral centre on the 2-carbon atom

A

Aminoethanoic

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18
Q

Chiral centre

A

Has 4 different groups or atoms attaches to the carbon atom and forms optical isomers

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19
Q

What type of amino acids all have a chiral centre (except for amino ethanoic)

A

2-amino acids

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20
Q

Describe the optical isomers of 2-aminopropanoic acid

A

Have the same structural and molecular formula, but have different spatial arrangement of atoms. Same chemical and physical properties but rotate plane polarised light in opposite directions. The two isomers are known as enantiomers.

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21
Q

What do most naturally occurring materials have?

A

Chirality

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22
Q

What type of materials do most of them have chirality?

A

Naturally occurring ones

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23
Q

Amphoteric behaviour

A

Can react as both an acid and a base

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24
Q

Describe amino acids at room temperature

A

White crystalline solids

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25
Q

Describe amino acids solubility in water and in non-polar solvents

A

Readily soluble

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26
Q

Describe the melting point of amino acids compared to alkanes of similar molar mass

A

Fairly high

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27
Q

What type of compound are the properties of the solubility and melting points of amino acids typical of?

A

An ionic compound, not a covalent compound

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28
Q

What type of forces predominate in the solid of an amino acid?

A

Ionic

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29
Q

How do we explain the high melting points and solubility of amino acids?

A

Talk about the Ionic bonds, they do not form hydrogen bonds

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30
Q

How do amino acids exist?

A

As internal salts known as zwitterions

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31
Q

What are zwitterions?

A

Hybrids - how amino acids exist as internal salts

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32
Q

What type of form is the zwitterion form of an amino acid?

A

Ionic

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33
Q

Where is the ionic form of amino acids found?

A

Also in aqueous solution

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34
Q

Is an aqueous solution of an amino acid acidic or basic and why?

A

Neutral since the basic and acidic properties cancel one another out since the amino acid is in its ionic (zwitterion) form

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35
Q

Equilibrium of the amino acid amino ethanoic acid in aqueous solution

A

NH2CH2COO- —><— NH3+CH2COO- —><— NH3+CH2COOH

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36
Q

What does an aqueous solution of amino acids contain?

A

Zwitterions

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37
Q

When does the compound of an amino acid exist as the zwitterion itself?

A

At a certain pH

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38
Q

What does the compound of an amino acid exist as at a certain pH?

A

The zwitterion

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39
Q

What does the isoelectronic point vary with?

A

Depending on the amino acid

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40
Q

Isoelectronic point

A

The pH at which the compounds exist as the zwitterion itself

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41
Q

The pH at which the compounds exist as the zwitterion itself

A

Isoelectronic point

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42
Q

What is essentially happening to a zwitterion when acid is added?

A

It becomes protonated

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43
Q

What is essentially happening to a zwitterion when alkali is added?

A

It’s deprotonated

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44
Q

What happens when acid is added to a zwitterion?

A

Free acid forms

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45
Q

Describe a free acid

A

Both protonated

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46
Q

What forms when alkali is added to a zwitterion?

A

Free amine

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47
Q

Describe a free amine

A

Neither protonated

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48
Q

What forms when acid is added to a free amine?

A

Zwitterion

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49
Q

What forms when alkali is added to a free acid?

A

Zwitterion

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50
Q

What happens when an amino acid is reacted with HCl?

A

A dipeptide is formed

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51
Q

How is a dipeptide formed?

A

If an amino acid is reacted with HCl

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52
Q

Dipeptide

A

2 amino acids bonded together

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53
Q

2 amino acids bonded together

A

Dipeptide

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54
Q

Peptide link

A

Forms when the amino group from one amino acid reacts with the carboxylic acid group from another amino acid

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55
Q

Which groups of 2 amino acids react to form a peptide link?

A

The amino group from one, the carboxylic acid group from the other

56
Q

What is eliminated during the formation of a peptide link?

A

Water

57
Q

What type of reaction is the formation of a peptide link?

A

Condensation

58
Q

What is a peptide link essentially?

A

An amide link

59
Q

How many dipeptides would be possible if we were to mix 2 amino acids?

A

4

60
Q

Explain what proteins are

A

Complex molecules derived from amino acids in condensation reactions

61
Q

From what type of reactions do proteins form?

A

Condensation reactions

62
Q

What do proteins make up?

A

A significant amount of living tissue - muscles, skin, hair

63
Q

Why does the body require a constant supply of protein?

A

For growth, replacement of old protein and for metabolic reactions in the body

64
Q

How are proteins formed in the body?

A

By reactions between 2-amino acids

65
Q

How are the amino acids needed for growth obtained?

A

From proteins in the diet

66
Q

What catalyse the formation of proteins?

A

Enzymes - protease enzymes

67
Q

Basic link between amino acids

A

The peptide (amide) link

68
Q

Dipeptide

A

2 amino acids

69
Q

Tripeptide

A

3 amino acids

70
Q

Polypeptide

A

Many amino acids

71
Q

What is a protein essentially?

A

A polypeptide containing between 200 and 60,000 amino acids in a chain

72
Q

How many polypeptides are proteins made up of?

A

One or more

73
Q

Haemoglobin

A

A globular protein containing 4 polypeptide chains

74
Q

How many amino acids are there in the body required for the formation of proteins?

A

20

75
Q

How do we obtain the proteins needed?

A

The body produces some of them, others can only be obtained from plant material

76
Q

How are proteins similar?

A

Chemically

77
Q

Even though proteins are chemically similar, what’s different?

A

They show a wide variety of functions, reflecting the immense number of combinations

78
Q

What reflects the immense number of combinations of amino acids to form proteins?

A

The wide variety of functions they have

79
Q

4 main type of protein structure

A

Primary
Secondary
Tertiary
Quaternary

80
Q

Primary protein structure

A

Describes the sequence in which the amino acids are arranged

81
Q

What does a particular protein have?

A

A sequence of amino acids unique to itself

82
Q

What can enzymes do to a polyptide chain?

A

Can hydrolyse protein at particular peptide links in the chain

83
Q

How do identify the amino acids in a protein?

A

Enzymes can hydrolyse proteins at particular peptide links in the chain
The sequence of amino acids in the protein is found
The peptide and subsequently the amino acids in the protein can be identified by chromatography

84
Q

What type of bonding do proteins have within the structure?

A

Hydrogen bonding

85
Q

Where is the hydrogen bond formed in a secondary protein structure?

A

Between the H atoms bonded to the nitrogen and the O atoms on the carbonyl group

86
Q

What happen in the secondary protein structure when hydrogen bonds form within the structure?

A

The chain folds into a spiral

87
Q

Secondary protein structure

A

The shape (conformation) of the spiral formed when hydrogen bonding occurs within the structure

88
Q

2 types of secondary protein structure

A

Alpha helix
Beta pleated sheet

89
Q

Alpha helix

A

The structure coils up into a helical shape. Typically, eighteen amino acids make five coils

90
Q

Beta pleated sheet

A

The hydrogen bonds can form predominantly between adjacent protein molecules, resulting in a pleated sheet structure extending over 3-10 amino acids

91
Q

Describe the secondary structure of a protein

A

Short-range three-dimensional shape (covering a small number of adjacent amino acids) and is generally either an alpha helix or a beta pleated sheet

92
Q

How is the tertiary protein structure formed?

A

Amino acids in some parts of the protein react with the different amino acids in the protein

93
Q

Describe the tertiary protein structure

A

The spiral can be folded back on itself in a loop by bonds between sulfur atoms, which are found in some amino acids (e.g - cystine)

94
Q

Type of amino acids example where bonds occur between sulphur atoms

A

Cystine

95
Q

What is the secondary structure of a protein due to?

A

Hydorgen bonding between adjacent chains

96
Q

Hydorgen bonding in silk

A

Between chains

97
Q

Hydrogen bonding in wool

A

Within the chain

98
Q

Quaternary protein structure

A

The way in which different polypeptide chains come together to form the final protein structure

99
Q

Final 3D conformation of a protein

A

Quaternary structure

100
Q

What do proteins with more than one polypeptide chain have to do?

A

Undergo additional folding to form the quaternary structure

101
Q

Explain how the quaternary structure of a protein forms

A

Various bonds join together the polypeptide chains. Different polypeptide chains coming together to form the final protein are typically bonded together either via hydrogen bonds, covalent bonds or ionic bonds.

102
Q

Types of bonding in quaternary structure

A

Hydrogen, covalent, ionic

103
Q

Diners

A

Proteins made up of two polypeptide chains

104
Q

Trimers

A

Proteins made up of three polypeptide chains

105
Q

Tetramers

A

Proteins made up of four polypeptide chains

106
Q

Proteins made up of four polypeptide chains

A

Tetramers

107
Q

Proteins made up of 3 polypeptide chains

A

Trimers

108
Q

What are enzymes?

A

Proteins

109
Q

What are enzymes composed of?

A

Polymers that act as natural catalysts to regulate the speed of many chemical reactions involved in the metabolism of living organisms

110
Q

Categories of enzymes

A

Hydrolysis
Oxidising
Reducing

111
Q

What does the classification of an enzyme depend on?

A

The type of reaction they control

112
Q

Example of enzymes that control many different reactions + explain

A

Pepsin and trypsin
Bring about the digestion of meat

113
Q

Example of enzymes that are specific and only accelerate one reaction + explain

A

Urease
Breaks down urea

114
Q

Why are enzymes useful?

A

They’re very efficient
Minute quantities can accomplish at low temperatures and mild conditions what would require violent reagents and high temperatures by ordinary chemical means

115
Q

What are enzymes being designed to replace?

A

Transition metal catalysts

116
Q

What do the kinetics of enzyme reaction differ from?

A

Those os simple inorganic reactions

117
Q

What is each enzyme selectively specific for?

A

The substance in which it causes a reaction

118
Q

When are enzymes most effective?

A

At a temperature particular to them

119
Q

Why don’t we just increase the temperature of enzyme catalysed reactions?

A

Although an increase in temperature may accelerate a reaction, enzymes are unstable when heated

120
Q

What does alcoholic fermentation depend on?

A

The action of enzymes that are synthesised by the yeasts and bacteria used in the production process

121
Q

How are the medical uses of enzymes illustrated?

A

By research into L-asparaginase, which is thought to be a potent weapon for the treatment of leukemia

122
Q

Types of enzymes used in laundry and their mode of action

A

Amylases, lipases, proteases
Removing stains from clothes caused by starch, fats and proteins

123
Q

Types of enzymes used in brewing and their mode of action

A

Amylases, glucanases, proteases, zymases
Hydrolysing polysaccharides and proteins into smaller molecules

124
Q

Types of enzymes used in dairy and their mode of action

A

Rennin
Hydrolysing protein in cheese making

125
Q

How come amino acids are amphoteric?

A

They contain a basic NH2 group and an acidic COOH group

126
Q

What type of catalysts are enzymes?

A

Biological

127
Q

Zwitterion

A

A dipole form of an amino acid where the carbonic group loses a proton, becoming a COO- and the amino group gains a proton to become NH3+

128
Q

What type of reaction would hydrolysis be to an amino acid?

A

Decomposition

129
Q

What happens when acid is added to a zwitterion?

A

Everything can can be protonated will be

130
Q

What happens when alkali is added to a zwitterion?

A

Everything that can be deprotonated will be

131
Q

What might we have to do to make amino acid questions easier?

A

Rearrange the amino acid

132
Q

What does “heated with concentrated sulphuric acid” imply and what does this mean?

A

Hydrolysis of the protein
Amino acids form

133
Q

What does a question involving “alcohol in the presence of a small amount of concentrated sulphuric acid mean is happening?

A

Esterification

134
Q

Why do amino acids have stronger melting temperatures than other acids?

A

They exist as zwitterions, so they have a strong ionic character and so stronger forces between the molecules than other acids and thus a higher melting point

135
Q

When can we only form one dipeptide?

A

When it’s formed from two molecules of the same acid

136
Q

When can we not form a zwitterion?

A

When there’s no acidic hydrogen in the carboxylic acid group

137
Q

Why do zwitterion forms of molecules have high melting temperatures?

A

Strong ionic character and strong forces between molecules

A level Chemistry (39 decks)

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