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Biology A level > Proteins > Flashcards

Proteins Flashcards

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1
Q

What percent of the body is protein?

A

18%

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2
Q

What elements do proteins contain?

A

All- Carbon, Hydrogen, Oxygen, Nitrogen, many- phosphorous, some have sulphur

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3
Q

Why can proteins have so many different functions?

A

There is a great variety in structure

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4
Q

What are polypeptides made up from?

A

Monomers called amino acids joined together

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5
Q

What does a folded polypeptide form?

A

Final protein

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6
Q

How many types of amino acids are there?

A

20

9-essential
5-non essential
6- conditionally essential( growing children)

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7
Q

What’s different about each different amino acid?

A

Has a different R group, giving it different properties

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8
Q

How to draw an amino acid?

A

Linear structure in middle= N-C-C

At the left N bonded to 2 hydrogens

Centre C, bonded to the R group above, and a hydrogen bellow

The right Carbon is double bonded to an oxygen above, and a hydroxide bellow

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9
Q

What group is on the left of the amino acid )NH2)

A

The amine group

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10
Q

What group is on the right of the amino acid? (COOH)

A

Carboxyl group

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11
Q

How can the R groups differ?

A

Hydrophobic or Hydrophilic

Acidic or Basic

Charged or not charged

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12
Q

Which amino acid contains sulphur in it’s R group?

A

Cysteine

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13
Q

What is the stationary phase in thin layer chromatography?

A

Thin layer of silica gel, applied to thin glass or metal sheet

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14
Q

What is the mobile phase in thin layer chromatography?

A

The organic solvent

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15
Q

What does the mobile phase do?

A

Picks up the amino acids and moves through the stationary phase separating out the amino acids

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16
Q

Why do different amino acids travel at different speeds in thin layer chromatography?

A
  • Their ability to make hydrogen bonds with the silica gel (stationary phase)
  • Their solubility in the solvent (Mobile phase)
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17
Q

Method for thin layer chromatography?

A

Draw pencil line on chromatography plate 2 cm from bottom

For each amino acid mixture in solution, put on line with capillary tube equally spaced from each other, dry and spot again

Plate is put in jar, with no more than 1 cm of solvent at bottom, jar is closed

Plate removed from solvent when it reaches 2 cm from top mark this to show the solvent front

Plate is then sprayed with ninhydrin spray, this reacts with aminos turning them purple/brown

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18
Q

How do you work out the RF value of an amino acid?

A

RF= Distance travelled by component/ distance travelled by solvent front

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19
Q

How are amino acids joined together?

A

Condensation reaction

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20
Q

How are amino acids separated?

A

Hydrolysis reaction

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21
Q

How is a peptide bond formed?

A

When 2 amino acids are chemically bonded together, a covalent bond forms between the Nitrogen of the amine group of one amino acid, and the carbon of the carboxyl group of another, one molecule of water is lost

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22
Q

Which enzyme carries out the condensation reaction in amino acids?

A

Peptidyl transferase, found in the ribosome

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23
Q

What’s a dipeptide?

A

2 amino acids bonded together by a peptide bond

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24
Q

What’s the biuret test?

A

sample mixed with equal amount of 10% sodium hydroxide solution
1% copper sulfate solution is added until solution turns blue
Solution left to stand for 5 minutes if lilac colour appears protein is present

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25
Q

What is done for the biuret test, if it’s difficult to see a colour change?

A

2 reagents mixed together to form biuret reagent, which is then layered on top of the solution, so reaction can be seen at the top

26
Q

Why is Sodium hydroxide hazardous?

A

Corrosive

so dangerous for eyes

27
Q

Why is copper sulphate hazardous?

A

Harmful if swallowed

dangerous for the environment

28
Q

How does biuret reagent work?

A

Indicates the presence of peptide bonds
Cu2+ ions are reduced to CU+ ions, these form a complex with the nitrogen component in the peptide bond in alkaline conditions
Therefore the blue of the copper sulphate turns lilac

29
Q

What’s the primary structure?

A

The sequence of amino acids in a polypeptide- determines the final shape of the protein

30
Q

What’s the secondary structure?

A

The folding a coiling caused by Hydrogen bonding between Nitrogen, Hydrogen and Oxygen of nearby amino acids

31
Q

What’s formed in secondary structure when hydrogen bonds pull the polypeptide chain into coils?

A

Alpha helix

32
Q

What’s formed in secondary structure when polypeptide chains lie parallel in sheets held together by hydrogen bonds?

A

Beta pleated sheet

33
Q

What’s tertiary structure?

A

Further folding of secondary structure, by bonds and interactions between R groups

34
Q

4 types of bonding which can occur in tertiary structure?

A

Hydrogen bonds, hydrophobic interaction, disulphide bonds, ionic bonds

35
Q

Which amino acid allows disulphide bonds?

A

Cysteine

36
Q

What’s the quaternary structure?

A

The level of structure where 2 or more polypeptide subunits are bonded together
(subunits can be identical or different)

37
Q

What are globular proteins?

A

Soluble in water
Have metabolic roles
Eg. Haemoglobin, enzymes and antibodies

38
Q

What are fibrous proteins?

A
  • Usually insoluble
  • Structural roles
  • Eg. Collagen, Keratin and silk, Elastin
39
Q

What’s the quaternary structure of haemoglobin?

A

2 alpha polypeptides
2 beta polypeptides
4 heme prosthetic groups

40
Q

Why is haemoglobin a globular protein?

A

Ball shaped
Hydrophilic groups towards exterior therefore soluble
Hydrophobic groups towards interior

41
Q

Where is haemoglobin located?

A

Red blood cells

42
Q

What’s haemoglobin’s role?

A

Transport oxygen from the lungs to released in the tissues

43
Q

How does haemoglobin transport oxygen?

A

One oxygen molecule can bind to the iron in each of the 4 heme groups

44
Q

Why is the haem located in the centre of each subunit in haemoglobin?

A

So it’s protected from being oxidised and destroyed by the oxygen it transports

45
Q

What does insulin do?

A

A hormone involved in blood glucose regulation

46
Q

How is insulin transported?

A

In the blood so needs to be soluble

47
Q

How do hormones create a reaction?

A

Fit into specifically shaped receptors protein on cell surface membranes

48
Q

What is catalase?

A

An enzyme which catalyses reactions
It’s specific to a particular reaction
Hydrogen peroxide is the substrate
Has 4 heme prosthetic groups

49
Q

Why is hydrogen peroxide found in the body?

A

Common by-product of metabolism, it’s damaging to cells and organelles

50
Q

How does catalase help the breakdown of hydrogen peroxide?

A

Fe +2 ions allows catalase to interact with hydrogen peroxide, and speed up it’s breakdown, water and oxygen are produced

51
Q

Features of fibrous proteins?

A

High proportion of hydrophobic r groups
Not folded into complex 3D shapes
Limited amount of amino acids also with small R groups
Repetitive amino acid structure, leads to organised structure

52
Q

Where do you find Keratin?

A

Hair, skin and nails

53
Q

Where do you find Elastin?

A

Walls of blood vessels, alveoli

54
Q

Where do you find collagen?

A

Skin, tendons, ligaments, nervous tissue

55
Q

Keratins bonding?

A

Large proportion of sulphur containing cysteine, so many strong disulphide bonds, so strong, inflexible and insoluble

56
Q

What is elastin made up of?

A

Many stretchy molecules called tropoelastin essential as arteries need to expand and return to their original size

57
Q

Collagens structure?

A

Each polypeptide chain is 1000 amino acids long, each molecule is made of three polypeptide chains twisted round each other
Every 3rd amino acid is glycine
Each collagen molecule cross links with 2 other collagen molecules to form fibrils
Many fibrils are joined together to form a collagen fibre

58
Q

Explain the denaturation of a protein?

A

When a protein is heated there will be an increase in thermal energy

Therefore there will be an increase in kinetic energy affecting the atoms within the protein molecule.

This means that the atoms within the bonds of the tertiary structure (Disulfide bonds, ionic bonds, hydrogen bonds, and hydrophobic interactions), will start to vibrate more, and therefore start to break.

The weakest bonds will break first (hydrogen bonds, and hydrophilic and hydrophobic interactions), and the strong covalent disulfide bonds will break last.

As the bonds break, the tertiary structure will begin to unwind, and therefore losing its shape.

59
Q

Why is the shape of the tertiary structure essential in proteins?

A

There are receptor proteins in the plasma membrane, whose function depends on the shape of the tertiary structure, and therefore the tertiary structure

In enzymes the tertiary structure is important because if the shape of the active site alters, the substrate no longer fits. Meaning the enzyme won’t work anymore.

60
Q

What’s a prosthetic group?

A

a non-protein group forming part of or combined with a protein.

61
Q

What’s a conjugated protein?

A

protein that functions in interaction with other (non-polypeptide) chemical groups attached by covalent bonding or weak interactions

Biology A level (19 decks)

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