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A-Level Biology > Proteins, Enzymes and Digestion > Flashcards

Proteins, Enzymes and Digestion Flashcards

1
Q

What are the different functions of proteins?

A

Structural
Signalling
Catalysts
Transport

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2
Q

Draw the chemical structure of an amino acid

A
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3
Q

How are dipeptides formed?

A

A condensation reaction occurs between the carboxyl group of one amino acid and the amine group of the other.

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4
Q

What is the bond between two amino acids called?

A

Peptide bond

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5
Q

What is the primary structure of a protein?

A

The sequence of amino acids linked together to form a polypeptide chain

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6
Q

What is the secondary structure of a protein?

A

The initial folding of a polypeptide into an alpha helix or a Beta pleated sheet due to hydrogen bonding

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7
Q

What is the secondary structure of a protein determined by?

A

The sequence of its amino acids, or primary structure

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8
Q

What is the tertiary structure of a protein?

A

Further folding of polypeptide into a 3D Shape, held together by hydrogen bonds, disulfide bonds and ionic bonds

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9
Q

What is the tertiary structure of a protein determined by?

A

Its secondary structure, and therefore its primary structure

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10
Q

Two protein have the exact same number and type of amino acids, but have different tertiary structures. Explain why.

A
  • Different sequence of amino acids
  • Different primary structure
  • Primary determines secondary, which determines tertiary
  • Different primary means different initial folding, and also different further folding, so different tertiary structure
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11
Q

What is the quaternary structure of a protein?

A

Multiple polypeptides bonded together

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12
Q

What is the prosthetic group of a protein?

A

Non-protein-based molecule that aids function of the protein. The prosthetic group of haemoglobin is Iron.

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13
Q

What is the biuret test for protein?

A
  1. Add sample to distilled water and biuret solution (grind in water if sample is solid)
  2. Shake, then leave upright for 5 minutes and observe the colour
  3. Colour change from blue to violet indicates a positive result. The result will only be positive if the amino acids are joined together by peptide bonds. Free amino acids will not produce a positive result.
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14
Q

What type of bonds does biuret reagent test for the presence of?

A

Peptide

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15
Q

What colour will biuret reagent be in a solution of free amino acids?

A

Blue, because biuret tests for peptide bonds.

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16
Q

What colour does biuret change from and what colour indicates a positive result?

A

Blue to purple

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17
Q

What is an enzyme?

A

Enzymes are protein catalysts that lowers activation energy without being used up, by forming enzyme substrate complexes

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18
Q

How do enzymes work in catabolic reactions?

A

Enzymes form an enzyme substrate complex which strains the bonds, making them easier to break and lowering the activation energy

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19
Q

How do enzymes work in anabolic reactions?

A

Enzymes bond to both substrates, bringing them closer together, lowering the activation energy

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20
Q

Describe the lock and key model of enzyme action

A

The substrate is complementary to the enzyme site and fits like a key in a lock

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21
Q

Describe the induced fit model of enzyme action

A
  1. Before the reaction, the enzyme active site is not complementary to the substrate
  2. The shape of the active site changes as the enzyme substrate complex forms
  3. This stresses the bonds or brings substrates together
    4.Lowering activation energy
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22
Q

What are the factors that effect the rate of enzyme catalyzed reaction?

A

Temperature
pH
Enzyme concentration
Substrate concentration
Inhibitors – competitive and non-competitive

23
Q

How does temperature affect the rate of enzyme catalyzed reactions?

A
  1. As temperature increases molecules have more kinetic energy and vibrate more. There are more collisions and more particles with sufficient energy, so more E-S complexes are formed.
  2. As temperature exceeds the optimum, molecules vibrate and break internal bonds which changes the active site.
24
Q

How does pH affect the rate of enzyme catalyzed reactions?

A
  1. Increasing/Decreasing the pH away from the optimum will cause the enzyme to denature and decrease the rate of reaction.
  2. This is because the OH- or H+ will interact with hydrogen and ionic bonds which changes the tertiary structure of the protein and therefore the shape of the active site.
25
Q

How does enzyme concentration affect the rate of enzyme catalyzed reactions?

A
  1. As enzyme concentration increases rate increases as there are more active sites for substrates to react with
  2. Providing there is an unlimited amount of substrate the rate will keep increasing
  3. However, in practice there is never an unlimited amount of substrate so eventually the rate will level off.
26
Q

How does substrate concentration affect the rate of enzyme catalyzed reactions?

A
  1. As substrate concentration increases rate increases as there are more substrates for enzymes to react with
  2. Once all the active sites are filled, the rate will stop, and enzyme concentration becomes the limiting factor
  3. At this point, increasing substrate concentration will have no effect on rate
27
Q

What are competitive inhibitors and how do they affect the rate of enzyme catalyzed reaction?

A
  • Molecules with a similar shape to the substrate.
  • They bind to active sites and prevent E-S complexes forming.
  • Eventually, competitive inhibitors will leave the active site, so presence of competitive inhibitors only decreases rate.
28
Q

What are non-competitive inhibitors and how do they affect the rate of enzyme catalyzed reaction?

A
  • Molecules that attach to the allosteric binding site of an enzyme and permanently changes the tertiary structure of the active site permanently.
  • Reaction slows and does not complete
29
Q

Name 3 membrane bound enzymes

A

maltase, sucrase, lactase, dipeptidase

30
Q

What are the benefits of having membrane bound enzymes?

A

Allows the enzymes to be reused. If they weren’t membrane bound, we would be excreting enzymes all the time, so having membrane bound enzymes saves us from remaking enzymes all the time

31
Q

What is the product of Maltose digestion?

A

2x alpha glucose

32
Q

What bonds are broken in order to digest maltose?

A

Alpha 1,4 glycosidic

33
Q

Which enzyme digests sucrose, where is it made, and where does it act?

A

Sucrase, made in the ileum lining, Acts in the ileum

34
Q

What is the product of Sucrose digestion?

A

Alpha glucose and fructose

35
Q

Which enzyme digests lactose, where is it made, and where does it act?

A

Lactase, made in the ileum lining, acts in the ileum

36
Q

Which enzyme digests proteins by breaking inner peptide bonds, where is it made, and where does it act?

A

Endopeptidase, made in the stomach and pancreas, acts in the stomach and ileum

37
Q

What is the product of protein digestion by endopeptidase?

A

Smaller polypeptides

38
Q

What type of bonds are broken when proteins/dipeptides are digested?

A

Peptide

39
Q

What is digestion?

A

The hydrolysis of large insoluble food molecules into smaller soluble food molecules that can be absorbed into the blood

40
Q

Describe how monoglycerides and fatty acids are absorbed into the blood

A
  1. Lipase breaks triglycerides into monoglycerides and fatty acids
  2. Lipid soluble micelles can diffuse straight through cell membrane
  3. Triglycerides are reformed at the smooth endoplasmic reticulum
  4. Fatty globules and proteins combine at the Golgi apparatus to form chylomicrons
  5. Chylomicrons are released by exocytosis
  6. Chylomicron passes to lymphatic vessel and then into the bloodstream
41
Q

Which enzyme digests proteins by breaking peptide bonds on the end of polypeptides, where is it made, and where does it act?

A

Exopeptidase, made in the stomach and pancreas, acts in the stomach

42
Q

What is the product of protein digestion by exopeptidase?

A

Amino acids, dipeptides

43
Q

Which enzyme digests dipeptides, where is it made, and where does it act?

A

Dipeptidases, made in the ileum lining, acts in the ileum

44
Q

What is the product of dipeptide digestion?

A

Amino acids

45
Q

Which enzyme digests lipids, where is it made, and where does it act?

A

Lipase, Made in the ileum lining or the pancreas, acts in the ileum

46
Q

What is the product of lipid digestion?

A

2x fatty acids and a monoglyceride

47
Q

What type of bonds are broken when lipids are digested?

A

Ester

48
Q

What are the benefits of having both endo and exopeptidase?

A

Having both endo and exopeptidase allows digestion of proteins to be much quicker as endopeptidase can break polypeptides into smaller chains giving exopeptidase more chains to work on. This allows lots of dipeptides to be left for the protease dipeptidase to break down into amino acids.

49
Q

What is the emulsification of fats?

A

Breaking down of fats into small droplets in presence of bile
salts.

50
Q

What is the product of emulsification of fats and what does it contain?

A

The smaller fat droplets are called micelles, and they contain monoglycerides and fatty acids.

51
Q

What are the advantages of micelle formation?

A
  1. Droplets increase surface area for lipase action
  2. So faster hydrolysis of triglycerides
  3. Micelles carry fatty acids and glycerol/monoglycerides through membrane to intestine epithelial cell
52
Q

Describe the structure of the ileum and explain how it aids function

A
  1. Walls are folded into villi which increases surface area for faster absorption
  2. Walls are 1 cell thick, shorter diffusion distance for faster absorption
  3. Epithelial cells have microvilli, increases surface area for faster absorption
  4. Many capillaries, rich blood supply maintains concentration gradient
  5. Muscles in villi so they can move from side to side, maintains diffusion gradient by moving contents of lumen
53
Q

Describe how glucose/amino acids are absorbed into the blood

A
  1. Sodium ions removed (from epithelial cells) by active transport via a sodium potassium carrier protein
  2. Into the blood
  3. Maintaining low concentration of Na+ in the epithelial cell
  4. Glucose/Amino Acids moves in with sodium
  5. Via a carrier protein that carries out co-transport
  6. Glucose/Amino acids moves into the blood
  7. By facilitated diffusion

A-Level Biology (5 decks)

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