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Biology > Pack 4 - Proteins, Enzymes and Digestion > Flashcards

Pack 4 - Proteins, Enzymes and Digestion Flashcards

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1
Q

Why are proteins such an important molecule in the body?

A

The large amount of diversity in the shapes of different proteins.

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2
Q

What type of molecule is the monomer of a protein?

A

Amino acids

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3
Q

What is a single chain of amino acids called?

A

A polypeptide chain

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4
Q

How many naturally occurring amino acids are there?

A

20

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5
Q

The same 20 amino acids appear in all living organisms.

What does this provide indirect evidence for?

A

Evolution

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6
Q

Draw the structure of an amino acid and name the four groups.

A 
R
             |
 H₂N--- C ----COOH
             |
            H
• Amino group (H₂N)
• Carboxyl group (COOH)
• Hydrogen atom (H)
• R - group (unique to each different amino acid)
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7
Q

What is the name of the bond formed between two amino acids and what are the products?

A
  • A peptide bond

* Dipeptide + water

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8
Q

What type of reaction is the formation of a peptide bond? Between which two groups is it formed?

A

Condensation - amino and carboxyl groups.

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9
Q

What is the name of the reaction which breaks the bond between two amino acids called? What other molecules is needed?

A

Hydrolysis - addition of water

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10
Q

What is the process of joining many amino acids together called? What is the resulting chain called?

A

Polymerisation, Polypeptide chain

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11
Q

Define the primary structure of proteins.

A

The order and number of amino acids in a polypeptide chain.

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12
Q

How many different proteins can be made with 4 amino acids?

A

20⁴ = 160 000

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13
Q

How does a proteins primary structure affect its function?

A

The primary structure determines, ultimately, a proteins shape. Changing one amino acid could change a proteins shape and therefore its function.

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14
Q

What is a protein?

A

One or more polypeptide chain forming a molecule.

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15
Q

Define and explain the secondary structure of proteins, in terms of molecules and shape.

A
  • -NH group has slight positive charge.
  • -C=O group has a slight negative charge.
  • Hydrogen bonds form between these two groups.
  • This causes the polypeptide chain to twist and form a 3D α-helix or a β-pleated sheet.
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16
Q 
Name the bonds involved in:
 • primary  
 • secondary
 • tertiary 
 • quaternary
structure of proteins.
A
  • Primary - peptide bonds
  • Secondary - H-bonds
  • Tertiary - H-bonds, disulphide bonds, ionic bonds
  • Quaternary - H-bonds, disulphide bonds, ionic bonds
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17
Q

Define tertiary structure. What bonds are involved?

A

α-helices and β-pleated sheets are twisted and folded even more to give a complex and specific 3D structure to a protein. H-bonds are formed. Ionic bonds are formed between free -NH and -C=O groups. Disulphide bridges (covalent).

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18
Q

Why is tertiary structure important? What determines tertiary structure?

A

The unique 3D shape of a protein allows it to carry out a specific function and be recognised. The primary structure determines where the bonds are formed between different amino acids.

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19
Q

Define quaternary structure. What bonds are involved?

A

The combination of more than 1 polypeptide chain. H-bonds, disulphide bridges, ionic bonds.

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20
Q

What is the name for a non protein group that is associated with a protein. Give an example.

A

A prosthetic group. The haem group in haemoglobin.

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21
Q

Describe the biuret test.

A
  • Add an equal volume of sodium hydroxide to the sample.
  • Add a few drops of very dilute copper sulphate solution (burets reagent)
  • Turns blue to purple.
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22
Q

What is a fibrous protein? Give an example.

A

Long polypeptide chains that run parallel. Cross bridges increase strength. e.g. collagen.

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23
Q

What is an enzyme?

A

Biological catalyst. Protein.

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24
Q

How does an enzyme speed up the rate of reaction.

A

Decreasing the activation energy required.

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25
Q

What is the advantage of enzymes in the body.

A

Speeds up rate of reaction as less energy is required. Therefore reactions can take place at a lower temperature.

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26
Q

What is the name of the molecule formed when a substrate binds to the active site of an enzyme?

A

Enzyme-substrate complex.

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27
Q

Explain the induced fit model in 4 steps.

A
  • As the substrate binds to the enzyme the enzyme shape changes.
  • This changes the shape of the active site where the enzyme can bind.
  • This puts a strain on the substrate and therefore distorts certain bond(s) and breaks them.
  • The products are released.
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28
Q

Give two ways you can measure the rate of enzyme reaction. Give an example for each.

A
  • Measuring the rate of production of a PRODUCT. e.g. volume of oxygen produced in a certain amount of time due to the enzyme catalase acting on hydrogen peroxide.
  • Measuring the rate of disappearance of a substrate. e.g. concentration of starch when it is acted upon by amylase.
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29
Q

Describe why the rate of reaction in a set solution of substrate and enzyme decreases over time.

A
  • Initially there is a high concentration of substrate so ES complexes are formed easily.
  • As substrate concentration decreases fewer ES complexes are formed so therefore the rate decreases.
  • Until there is no substrate left.
30
Q

How would you describe the relationship between the shape of the substrate and the active site?

A

Complementary. NOT the same.

31
Q

Describe the effect of temperature on the rate of reactions due to enzymes.

A
  • As temperature increases so does the kinetic energy of molecules.
  • This results in more collisions and more ES complexes being formed and therefore more products being formed.
  • However, as temperature passes the optimum temperature the rate of reaction decreases because high temperatures change the shape of the active site and bonds begin to break (ionic and hydrogen). The enzyme denatures.
  • Fewer ES complexes are formed and the rate of reaction therefore decreases until no ES complexes can be formed.
32
Q

Describe the effect of pH on the rate of reactions due to enzymes.

A
  • Each enzyme has an optimum pH.
  • If the pH increases OH⁻ ions react with positively charged groups which changes the shape of the enzyme and the active site denaturing it.
  • If the pH decreases H⁺ ions react with negatively charged groups which changes the shape of the enzyme and the active site denaturing it.
33
Q

Describe the effect of substrate concentration on the rate of reactions due to enzymes.

A
  • Increasing substrate concentration is proportional to the rate of reaction because more ES complexes can be formed and more product produced.
  • This is true until enzyme concentration becomes the limiting factor. The addition of more substrate has no effect because there are not enough enzymes to bind to the substrate.
34
Q

Describe the effect of enzyme concentration on the rate of reactions due to enzymes.

A
  • Increasing enzyme concentration is proportional to the rate of reaction because more ES complexes can be formed and more product produced.
  • This is true until substrate concentration becomes the limiting factor. The addition of more enzymes has no effect because there is not enough substrate to bind to these enzymes.
35
Q

What is it called when adding more substrate doesn’t increase the rate of reaction?

A

Vmax value. Maximum rate of reaction. All enzymes are being used.

36
Q

What is a competitive inhibitor?

A
  • Competitive inhibitors have a shape similar to the shape of the substrate molecule.
  • There binding is temporary.
37
Q

What is a non-competitive inhibitor?

A
  • They attach to a binding site other than the active site

* They change the shape of the active site so the substrate cannot bind.

38
Q

What is the difference between endopeptidases and exopeptidases?

A

Endopeptidases hydrolyse the peptide bonds within peptide chains.

Exopeptidases hydrolyse the peptide bonds at the end of peptide chains.

39
Q

What is a dipeptidase and where are they found?

A

An enzyme that hydrolyses the peptide bond between the two amino acids in a dipeptide.

They are found in the cell membrane of epithelial cells.

40
Q

Where is amylase produced?

A

Salivary glands

Pancreas

41
Q

Where is maltose found?

A

The cell membrane of epithelial cells in the ileum.

42
Q

What does amylase hydrolyse starch into?

A

Maltose

43
Q

Describe the passage of food through (what organs) the digestive system.

A
  • Oesophagus
  • Stomach
  • Ileum
  • Large intestine
  • Rectum
44
Q

What is the role of the stomach?

A
  • Store and digest food.

* Especially proteins.

45
Q

What is the role of the ileum?

A
  • To digest food further.
  • Large surface area for absorption molecules into the bloodstream.
  • Ileum walls produce enzymes.
46
Q

What is the role of the large intestine?

A

To absorb water.

47
Q

What is the role of the salivary glands?

A

• To secret amylase containing saliva into the mouth.

48
Q

What is the role of the pancreas? (what enzymes)

A

• Produces pancreatic juice containing: proteases, lipase and amylase.

49
Q

What are the two stages of digestion?

A
  1. Physical breakdown

2. Chemical breakdown

50
Q

What is the purpose of physical breakdown and in what two ways does this mainly occur?

A
  • To increase surface area.

* Teeth and stomach walls.

51
Q

What is chemical digestion?

A

The hydrolysis of large insoluble molecules into smaller soluble ones.

52
Q

Describe the digestion of starch and where it occurs. (pH)

A
  • Salivary amylase (pH 7 - due to mineral salts) into maltose.
  • Stomach acid denatures amylase.
  • Ileum - pancreatic amylase. Alkaline salts - pH7
  • Epithelial lining of the ileum produces maltase. (Not released into the ileum).
53
Q

Where are Sucrase and Lactase found.

A

The membrane of epithelial cells.

54
Q

What is a membrane bound disaccharidase. Give three examples.

A
  • An enzyme bound to a membrane (not secreted) that hydrolyses disaccharides.
  • Maltase, sucrase and lactase.
55
Q

What does lipase hydrolyse a triglyceride into?

A
  • Two fatty acids

* A monoglyceride

56
Q

What is a micelle?

A

A tiny droplet of lipids

57
Q

What is the role of bile salts?

A

To split lipids into micelles.

58
Q

Where are bile salts produced?

A

The liver

59
Q

What is emulsification?

A

The formation of micelles using bile salts.

60
Q

What three types peptidases hydrolyse proteins.

A
  • Endopeptidases
  • Exopeptidase
  • Dipeptidases
61
Q

What is the role of endopeptidases and exopeptidases? What molecule is produced by exopeptidase?

A
  • Endo - hydrolyse the peptide bond between amino acids in the centre of the peptide molecule.
  • Exo - hydrolyse the peptide bond on the terminal amino acids of a peptide molecule.

Dipeptidases

62
Q

What enzyme breaks down dipeptides and into what molecules?

A
  • Dipeptidases

* 2 amino acids

63
Q

How is the surface area of the ileum increased?

A

Villi

64
Q

How is the surface area of ileum epithelial cells increased?

A

Microvilli

65
Q

How do villi increase the efficiency of absorption?

A
  • Increased surface area. (SA)
  • Thin walled (DD)
  • Muscles that move and mix contents of the lumen (CG)
  • Well supplied with capillaries. (CG)
66
Q

Why do villi need to have a good blood supply?

A

So the blood can carry away absorbed molecules and hence maintain a concentration gradient.

67
Q

At what point do micelles break down into monoglycerides and fatty acids?

A

When they come in contact with the Epithelial cells of the ileum.

68
Q

What happens to monoglycerides and fatty acids when micelles break down?

A

They diffuse across the cell surface membrane of the epithelial cells.

69
Q

What happens to monoglycerides and fatty acids once inside the cell?

A

They are transported to the endoplasmic reticulum where they are recombined to form triglycerides.

70
Q

What happens to triglycerides formed in the ER? What structure is formed?

A

They are associated with cholesterol and lipoproteins to form Chylomicrons in the Golgi apparatus.

71
Q

What are Chylomicrons and what happens to them?

A

Special particles adapted for the transport of lipids. They move out of epithelial cells by exocytosis. They then enter lymphatic capillaries called lacteals. Then they pass into the blood stream. They are then hydrolysed in the endothelial cells of capillaries and pass into cells.

Biology (18 decks)

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