BM: Proteins Flashcards

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1
Q

What are the monomers of proteins?

A

Amino acids

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2
Q

What are amino acids?

A

The monomer unit which combine to form polypeptides.

Polypeptides then combine to form proteins.

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3
Q

What is formed when two amino acids join?

A

A dipeptide

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4
Q

What is formed when more than two amino acids join together?

A

Polypeptides.

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5
Q

What are proteins made up?

A

One or more polypeptides.

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6
Q

What is the general structure of an amino acid?

A
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7
Q

How many amino acids have been discovered?

How many of these are naturally occuring.

A

About 100 have been identified.

20 of which naturally occur in all living organisms - this provides evidence for evolution.

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8
Q

What is the only difference between the 20 naturally reoccuring amino acids?

A

The ‘R’ variable group.

Glycine is the only amino acid that doesn’t have carbon in its R group. It consists of just one hydrogen atom.

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9
Q

What bond is formed by the joing of two amino acids?

A

A peptide bond.

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10
Q

Draw a condensation reaction between two amino acids:

A
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11
Q

How do amino acids join together?

A

Through condensation reactions.

A water molecule is released and a peptide bond forms.

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12
Q

How many structural levels do all proteins have?

How many can some larger proteins have?

A

All have 3 levels - primary, secondary and tertiary.

Some have 4 levels - an additional quaternary structure.

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13
Q

Through what process can many amino acids join together?

A

Polymerisation.

This results in the formation of a polypeptide.

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14
Q

What forms the primary structure of a protein?

A

The sequence of amino acids in the polypeptide chain.

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15
Q

What determines the sequencing of amino acids in the primary structure of a protein?

A

DNA.

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16
Q

What determines the ultimate shape and function of a protein?

A

The primary structure.

A change in sequencing of amino acids results in bonds forming in different places, and the protein folding differently.

This changes its shape which is very specific to its function.

17
Q

What causes hydrogen bonds to form in the secondary structure of the protein?

A
  • Linked amino acids contain both -NH and -C=O groups on either side of peptide bond.
  • H of -NH group has an overall positive charge.
  • O of -C=O group has an overall negative charge.
  • Therefore, a weak hydrogen bond is formed between them.
18
Q

Describe the secondary structure of a protein:

A
  • Hydrogen bonds form between amino acids in chain.
  • Therefore, chain becomes a 3D shape by either:
    • Coiling into an alpha helix
    • Folding into a beta pleated sheet.
19
Q

Draw a diagram illustrating the difference between an alpha helix and a beta pleated sheet:

A
20
Q

What bonds are there within the primary structure of a protein?

A

Peptide

21
Q

What bonds are there within the secondary structure of a protein?

A

Hydrogen

22
Q

What bonds are there within the tertiary structure of a protein?

A
  • Disulfide - fairly strong and not easily broken
  • Hydrogen - numerous but easily broken
  • Ionic - formed between carboxyl and amino groups not involved in peptide bond - weaker than disulfide and broken by changes in pH.
23
Q

Describe the tertiary structure of a protein:

A
  • Polypeptide chain is coiled or folded further.
  • More bonds form between different parts of the chain, such as ionic and hydrogen.
  • Disulfide bridges form.
  • Can result in final 3D structure.
24
Q

How do disulfide bridges form?

A

When two molecules of the amino acid cysteine come close together - sulfur atom in one molecule bonds to sulfur atom in another.

25
Q

What is important in determining how a protein functions?

A

Its 3D structure - this is distinctive allowing it to recognise, and be recognised by, other molecules.

This is first determined by the sequencing of amino acids.

26
Q

Describe the quaternary structure of some proteins:

A
  • Two or more polypeptide chains joining together.
  • Sometimes, there may also be a non-protein group associated with the molecule.
    • Eg, the haem group in haemoglobin.
27
Q

Give examples of proteins that have a quaternary structure:

A
  • Haemoglobin
  • Insulin
  • Collagen
28
Q

Draw a diagram to illustrate the structural levels of a protein:

A
29
Q

Name 4 different examples of proteins:

A
  1. Enzymes
  2. Antibodies
  3. Transport proteins
  4. Structural proteins
30
Q

Explain the structure of enzymes:

A

Usually roughly spherical due to tight folding of polypeptide chains.

31
Q

Describe the structure of antibodies:

A

Two light polypeptide chains and two heavy polypeptide chains bonded together, with a variable region so they can be highly specific.

32
Q

Describe the structure of transport proteins:

A

Hydrophobic amino acids and hydrophilic amino acids are both present, causing the protein to fold up and form a channel.

33
Q

Describe the structure of structural proteins:

A

Long polypeptide chains lying parallel to each other with cross-links between them, making them very strong.

34
Q

What is the test for proteins?

A

Biuret test

35
Q

What does the biurets test detect?

A

The presence of a peptide bond.

36
Q

How would you perform the Biuret test?

A
  1. Place sample in test tube.
  2. Add an equal volume of sodium hydroxide solution at room temperature, to make the solution alkaline.
  3. Add a few drops of very dilute (0.05%) copper (II) sulfate solution.
37
Q

What are the possible results of the Biuret test?

A

Positive = solution turns purple

Negative = solution remains blue

The colours are pale, so you will need to look carefully.