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MECH U3/4 > Amino acids > Flashcards

Amino acids Flashcards

1
Q

What are proteins used for in living things? (4)

A
  • enzymes that catalyse specific biochemical reactions
  • hormones that control biological processes
  • structural components in cell membranes, muscles, hair, feathers and spider silk
  • transportation of substances across cell membranes or around the body; for example, many proteins form channels in cell membranes
  • antibody molecules of immune system
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2
Q

How many amino acids make up proteins in the human body?

A

20

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3
Q

What are the functional groups that every amino acid has? (3)

A

amino functional group (—NH₂), a carboxyl functional group, (—COOH) and a hydrogen atom attached to central carbon, called α-carbon (alpha-carbon)

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4
Q

How many proteins can humans synthesis?

A

11 of 20 amino acids

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5
Q

How are the other 9 proteins gained?

A

Proteins sustain bodily functions, other nine amino acids (isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine and histidine (in infants)) provided directly though proteins you eat.

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6
Q

What are essential amino acids?

A

9 amino acids that cannot be synthesised humanly.

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7
Q

Why are essential amino acids important?

A

As the human body does not store amino acids, so a balanced intake of protein is required each day.

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8
Q

What happens if there is a lack of amino acid in a person’s diet?

A

serious diseases can occur such as kwashiorkor, which is characterised by low overall protein intake, it is thought the lack of sulfur-containing amino acids crystiene and methionine

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9
Q

Are side chains polar or non-polar in proteins?

A

Side chain may be:
non-polar (eg. —CH₃ in alanine and —CH(CH₃)₂ in valine)
polar (eg. —CH₂COOH in aspartic acid and —CH₂OH in serine)

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10
Q

What can side chains behave as in proteins?

A 
The side chain may also include functional groups that can behave as:
proton donors (eg. —CH₂COOH in aspartic acid contains an acidic carboxyl group)
proton acceptors (eg. —CH₂CH₂CH₂CH₂NH₂ in lysine contains a basic amino group)
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11
Q

Which of 9 essential amino acids be found in Legumes?

A

Methionine

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12
Q

Which of 9 essential amino acids be found in Soyabeans?

A

Methionine

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13
Q

Which of 9 essential amino acids be found in Corn?

A

Lysine, tryptophan

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14
Q

Which of 9 essential amino acids be found in Nuts?

A

Methionine

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15
Q

Which of 9 essential amino acids be found in Wheat?

A

Lysine

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16
Q

Why can amino acids form hydrogen bonds with water molecules?

A

as they contain polar amino and carboxyl functional groups

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17
Q

What happens when amino acids react with water? (2)

A
  • NH₂ group can act as a base, accepting a proton to become a -NH₃⁺ group
  • COOH group can act as an acid, donating a proton to become a -COO⁻ group
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18
Q

What is a zwitterion?

A

a molecule that contains positive and negative charges but has no overall charge.

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19
Q

As a result of an amino acid reacting with water what is formed?

A

As a result of amino acid molecule in an aqueous solution may be in the form ⁺HN-CH(R)-COO⁻

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20
Q

Why do pure crystalline amino acids have relatively high melting points?

A

due to the zwitterion being present in the solid state, meaning amino acids are held together by ionic bonds in solid state.

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21
Q

How can different forms of an amino acids be in equilibrium?

A

Dual acidic and basic nature of amino acids

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22
Q

Why are they called α-amino acids (2-amino acids)?

A

because the amino group and carbon atom of the carboxyl group are attached to same carbon atom

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23
Q

What is the general formula for amino acids used to produce proteins in the body?

A

H₂N-CH(R)-COOH

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24
Q

What are the two simplest amino acids?

A

glycerine and alanine

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25
Q

How does a intermediate pH (5-7) affect amino acids?

A

the zwitterion ⁺HN-CH(R)-COO⁻ is most abundant

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26
Q

How does a low pH affect amino acids?

A

⁺H₃N-CH(R)-COO⁻ is most abundant. The H₃O⁺ ions in solution can react with amino acid according to the equation: ⁺H₃N-CH(R)-COO⁻(aq) + H₃O⁺(aq) ⇄ ⁺H₃N-CH(R)-COOH + H₂O. If concentration of H₃O⁺ is very high (due to low pH solution) the position of this equilibrium lies well to the right.

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27
Q

What side components are required for dispersion forces occur in amino acids?

A

Any non-polar group

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28
Q

How does a high pH affect amino acids?

A

Anion H₂N-CH(R)-COO⁻ is most abundant. The OH⁻ ions in solution can react with the amino acid according to the equation: ⁺H₃N-CH(R)-COO⁻(aq) + OH- ⇄ H₂N-CH(R)-COO⁻ +H₂O
If concentration of OH- is very high (solution of high pH) position of equilibrium lies well to the right.

29
Q

What is occurs in a condensation polymerisation?

A

A carboxyl group and amino group form a amide functional group (-CONH-) linking two molecules and water is also formed

30
Q

Why is condensation easy for α-amino acids?

A

because α-amino acids contain both amino functional group and carboxyl group they can undergo condensation together.

31
Q

What are peptide links?

A

When two amino acids react an amide group is formed that links the molecule together

32
Q

What are peptide bonds?

A

bond between carbon and nitrogen atoms in amide group

33
Q

What are dipeptide?

A

Two amino acid molecules react together

34
Q

What is a tripeptide?

A

Three amino acids react together

35
Q

What is a polypeptide?

A

Polymer made from many amino acids

36
Q

What are primary structure of protein?

A

number, type and sequence of amino acid units in a protein

37
Q

How is the protein named?

A

By convention, the sequence is written from left to right, starting from the N-terminal amino acid and ending with the C-terminal amino acid.

38
Q

What are secondary structure of proteins?

A

Coiling and pleating of sections of protein molecule, highly ordered segments, stabilised by hydrogen bonds.

39
Q

What forms at regular intervals?

A

Hydrogen bonds between the polar -NH group in one peptide link and the polar -C=o group in another peptide link form at regular intervals

40
Q

What is α-helix?

A

Spiral shapes

41
Q

What is β-pleated sheets?

A

sections line up parallel to each other

42
Q

How is the helical structure of keratin created?

A

from extensive hydrogen bonding between peptide links in the polypeptide chain, the hydrogen bonds make the molecule coil into the shape.

43
Q

How are hydrogen bonds created in the helical structure of keratin?

A

from the attraction between the partial positive charge on the H of -NH group in a peptide link with a partial negative charge on the O of a -C=O group of a peptide link with a link, four amino acid units along the chain.

44
Q

Why is proline unlikely to exist in an α-helix structure?

A

Due to its ring structure, proline’s structure is too rigid to allow it to form part of a helix.

45
Q

Why is glycine unlikely to exist in an α-helix structure?

A

only has a hydrogen atom for its R group means that it introduces too much flexibility and reduces the stability of the α-helix structure

46
Q

How is a β-pleated sheets structure created?

A

Hydrogen bonds form between peptide links to produce regions where two or more parts of the polypeptide chains line up parallel to each other, because of the repeating structure of the backbone, hydrogen bonds can form at regular intervals, stabilising the protein structure.

47
Q

What is the repeating structure of the backbone of β-pleated sheets?

A

-N-C-C-N-C-C-N-C-C-

48
Q

Why is silk a β-pleated sheet?

A

As the chain contains mainly amino acids glycine, alanine and serine. At every second R group is H, with only small side groups, sections of protein molecule can line up closely, enabling hydrogen bonds to form between these adjacent sections.

49
Q

What form is the amino acid present in when there is a low pH?

A

Cationic form

50
Q

What form is the amino acid present in when there is a high pH?

A

Anodic form

51
Q

What are tertiary structures?

A

Overall three-dimensional shape adopted by a protein molecule. Three dimensional folding of its secondary structures (α-helix and β-pleated sheet)

52
Q

What mostly influences the three-dimensional shape of the molecule? and why?

A

side chains of the amino acid units making up the polypeptide chain. Side chains can interact with each other in a number of ways, causing the protein to fold into it three-dimensional shape.

53
Q

How do relatively side chains affect the amino acid?

A

As side chains can be relatively large, they can contain polar/non-polar functional groups or become charged, acidic or basic depending on the pH of their surroundings.

54
Q

What happens when amino acids have hydrophobic chains?

A

the chain is non-polar which causes the chain to tend to fold towards the interior of protein molecules, away from contact with water molecules

55
Q

What are the five types of attractions that are important in protein folding?

A

Hydrogen bonds, dipole-dipole interactions, ionic interactions, covalent cross-links, dispersion forces

56
Q

What side components are required for hydrogen bonds occur in amino acids?

A

Contains -O-H, -N-H or -C=O

57
Q

What side components are required for dipole-dipole occur in amino acids?

A

Any polar group such as those containing -S-H, -O-H or -N-H

58
Q

What side components are required for ionic interactions occur in amino acids?

A

Contains -NH₃⁺ and another group that contains -COO-

59
Q

What side components are required for covalent cross-links occur in amino acids?

A

Cysteine side groups react to form a disulfide bridge (-S-S-)

60
Q

What are polymers?

A

Polymers are very large molecules that consist of thousands of small repetitive units (called monomers) linked by covalent bonds

61
Q

Explain how a single change in a protein’s primary structure could cause such dramatically different results .

A

Enzymes depend on its three-dimensional shape. The tertiary structure results from a combination of hydrogen bonding, electrostatic attraction between polar groups and disulfide linkages. If the wrong amino acid is introduced into the chain, these bonds may not form and the tertiary structure may be distorted. In some instances, the enzyme becomes inactive, depending upon how the tertiary structure is altered.

62
Q

Which mutilation will have the greatest effect on the tertiary structure, instead of having leucine, either isoleucine or serine.

A

Leucine with serine would have greater effect as serine is polar amino acid with a side chain capable of forming hydrogen bonds with other amino acid side chains. While Isoleucine and leucine are both non-polar amino acid side chains therefore form similar strength interactions with nearby amino acid side chains.

63
Q

The amid links that form between amino acids are integral to both the primary and secondary structure of a protein. Explain this statement.

A

amino acid are joined together by amide groups, formed between carboxyl and amino groups on two amino acids. Therefore they are integral to the primary structure as they link the sequence of amino acids together. The secondary structure of protein also depends on the amide groups, as as hydrogen bonds form between oxygen in C=O of one amide group and hydrogen in the N-H of another amide group, which help stabilise the a-helices and B-sheets that make up the secondary structure.

64
Q

What happens when the temperature is too high?

A

the increased kinetic energy of the polypeptide chains of the enzyme breaks some of the bonds between side chains of the amino acid units.

65
Q

Which structure is affected by different pH and high temperatures?

A

the tertiary structure, as the dimensional specific shape is disrupted. The primary structure of the protein, the covalently bonded sequence of amino acids, remains intact

66
Q

True or False: A mutation that causes one amino acid in a protein to be exchanged will always result in a loss of protein function.

A

A mutation will not necessarily cause a loss in protein function. If the mutation is far away from the active site of the protein, then its activity may not be affected at all. Similarly, if the mutation results in exchanging an amino acid with similar characteristics, then it may not have a large effect on the protein’s secondary and tertiary structure. Eg. exchanging aspartic acid for glutamic acid may not have a large impact on the protein.

67
Q

Lipase function best at a temperature of approx. 25-35C. Explain why a temperature higher than this range can result in the loss of enzyme function.

A

Increased temperature would disrupt the bonding in the various intermolecular forces involved in secondary and tertiary structures. This would weaken/destroy these structures (denature enzyme) resulting in loss of shape and function of enzyme.

68
Q

Why did the anode increase in mass?

A

Pb(s) lead is converted to PbSO4 so the extra mass is due to the sulfate ion in the lead(II) sulfate solid

MECH U3/4 (8 decks)

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