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Option Chemistry > Proteins and Enzymes > Flashcards

Proteins and Enzymes Flashcards

1
Q

List some functions of proteins

A
  • enzymes
  • collagen
  • antibodies
  • structural protein for hair
  • transport molecule (ex: hemoglobin)
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2
Q

What are the monomers of proteins

A

amino acids

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3
Q

Outline the chemical composition of an amino acid

A
  • amine group (NH2)
  • carboxyl group (COOH)
  • side chain (R)
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4
Q

What is the name of the bond formed in proteins

A

peptide bond or amine link

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5
Q

Outline the primary structure of proteins

A

the sequence of amino acids held by peptide bonds

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6
Q

Outline the secondary structure of proteins

A

the folding of the polypeptide result of hydrogen bond occurring between the amine and carboxyl group, creating alpha-helix or beta-pleated

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7
Q

What is the difference between alpha-helix and beta-pleated in proteins

A
  • alpha-helix: intramolecular
  • beta-pleated: H bonding between the sheets/chains (intermolecular)
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8
Q

Outline the tertiary structure of proteins

A

the further folding of the secondary structure, due to the interactions between the R’ groups to form a specific 3D shape (H bonds, disulfide, LDFs)

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9
Q

Describe the different types of interactions between the R groups

A
  • hydrogen bonds (between OH and N/polar side chains)
  • ionic bonds (between charged side chains)
  • LDFs (between non-polar side chains), - disulfide links (between cysteine side chains)
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10
Q

Outline the quaternary structure of proteins

A

the interactions between polypeptide chains

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11
Q

What are the chemical properties of amino acids

A
  • they are amphoteric
  • they exist as zwitterions, anions and cations
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12
Q

Why can amino acids act as amphoteric

A
  • they have a carboxylic group (acidic) and amine group (basic)
  • enables them to react with both acids and bases
  • they can donate and accept protons
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13
Q

Define zwitterion

A
  • electrically neutral molecule with a positive and negative charged groups
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14
Q

Explain what happens when an amino acid is in low pH

A
  • the amine group reacts with the H+ to form a cation
  • amino acid acts as a base
  • the COO- gains an H+
  • NH3+CH2COOH
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15
Q

Explain what happens when an amino acid is in high pH

A
  • the carboxylic group reacts with the OH- to form an anion
  • amino acid acts as an acid
  • NH3+ loses an H+
  • NH2CH2COO-
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16
Q

Outline the features of fibrous protein

A
  • long and narrow
  • structural role
  • insoluble
  • more sensitive to heat and pH
  • irregular sequence of amino acids
  • ex: collagen and jeratine
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17
Q

Outline the features of globular proteins

A
  • spherical
  • functional role (catalyst&transport)
  • soluble
  • less sensitive to pH and heat
  • repetitive sequence of amino acids
  • ex: hemoglobin & insulin
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18
Q

Outline the zwitterion of an amino acid

A

NH3+CH2COO-

19
Q

What is the equation that represents an amino acid acting as a base

A

NH3+CH2COO- + H+ ⇋ NH3+CH2COOH

20
Q

What is the equation that represents an amino acid acting as an acid

A

NH3+CH2COO- ⇋ NH2CH2COO-

21
Q

What is the isoelectric point

A

the pH at which the amino acid has no overall charge (becomes zwitterions)

22
Q

What are the factors that affect the isoelectric point of an amino acid

A
  • An acidic R’ group (an additional COOH) leads to a lower isoelectric point
  • A basic R’ group (an additional NH2) leads to a higher isoelectric point
23
Q

What is the relationship between pH and the type of ion formed

A
  • At a pH higher than the isoelectric point, a cation will form
  • At a pH lower than the isoelectric point, an anion will form
24
Q

Explain the melting point of amino acids in terms of zwitterions

A
  • amino acids have higher melting than compounds of similar size
  • strong electrostatic force of attraction between the oppositely charged groups
  • also depends on the IMFs of the R’ group (more IMFs – higher melting point)
25
Q

Explain the solubility of amino acids in terms of zwitterions

A
  • A zwitterion is more soluble in water when its pH is further from the isoelectric point
  • more polar R’ group = more soluble
26
Q

Determine the number of different tripeptides that can be made from twenty different amino acids

A

20^3 = 8000

27
Q

Why are amino acids insoluble in organic solvents

A

Without strong attractions between solvent and amino acid, there won’t be enough energy released to pull the ionic lattice apart.

28
Q

Define an enzyme

A

Enzymes are globular proteins that act as biological catalysts, increasing the rate of the reaction without being used up in the process

29
Q

How do enzymes speed the rate of a reaction

A

they provide an alternative pathway with a lower activation energy

30
Q

How do enzymes catalyse a reaction

A

1) The complementary substrate binds to the active site and forms an enzyme-substrate complex
2) The bonds formed between the enzyme and the substrate weaken (ex: LDFs, hydrogen bonds, ionic, dipole-dipole), which distorts the shape of the enzyme’s active site
3) The substrate breaks into products and the products are released

31
Q

Define denaturation

A

the loss of the tertiary structure which leads to a change in the active site and the substrate can no longer bind to it

32
Q

What factors affect the conformation of an enzyme

A
  • temperature
  • pH
  • heavy metal ions
33
Q

What are the characteristics of enzymes?

A
  • highly specific to their substrate
  • globular proteins
  • not altered in a reaction
  • sensitive to changes in temperature and pH
  • provide an alternative pathway with lower activation energy (acts as a catalyst)
34
Q

Outline how temperature affects enzymes

A
  • increase in temp. → increases enzyme activity (more frequent collisions)
  • very high temp. will denature the enzyme because the heat causes vibrations in the enzyme and breaks the bonds which maintain the tertiary structure of the enzyme
  • substrate cannot bind to enzyme
35
Q

Outline how pH affects enzymes

A
  • Large deviations in pH will lead to denaturation
  • it alters the charge on -COO- (acidic) and -NH3+ (basic) groups in polypeptide
  • tertiary structure is disrupted and substrate cannot bind to enzyme
36
Q

Outline how heavy metal ions affect enzymes

A
  • heavy metals ions will react with sulfhydryl groups (replacing the H atom with a heavy metal ion)
  • this changes the tertiary structure of the enzyme (a type of inhibition)
37
Q

What is the function of chromatography

A

it is used to separate a mixture of amino acid

38
Q

Explain how chromatography works

A

the amino acids will travel at different speeds with the solvent depending on how soluble their R’ group is in water

39
Q

What is the Rf formula

A

distance moved by solute divided by distance moved by solvent

40
Q

Explain how gel electrophoresis works

A

they separate amino acids according to their charge and the shape and size.

41
Q

What happens when the pH is equal to the isoelectric point of the amino acid (gel electrophoresis)

A

amino acids will not move as they carry no net charge

42
Q

What happens when the pH is greater than the isoelectric point of the amino acid (gel electrophoresis)

A
  • An amino acid is negatively charged
  • move to the positively charged size
43
Q

What happens when the pH is lower than the isoelectric point of the amino acid (gel electrophoresis)

A
  • An amino acid is positively charged
  • move to the negatively charged size
44
Q

What does the optimum point in a temperature/pH graph represent

A
  • the highest frequency of successful collisions between substrate and enzyme’s active site
  • best ability for the active site to bind to the substrate

Option Chemistry (10 decks)

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