2.1.4 - Enzymes (set A - Enzyme Action)

Question 1

Why are enzymes important?

Answer 1

Most of the processes necessary to life involve chemical reactions which need to happen very fast - they would demand very high temperatures and pressures which are not possible in living cells (would damage them)

• catalysts provide an alternate reaction pathway

Question 2

What are enzymes?

Answer 2

Globular proteins which act as biological catalysts for intra and extracellular reactions - interact with substrate molecules forming an enzyme-substrate complex which lowers activation energy for metabolic reactions

Question 3

Explain the role of enzymes?

Answer 3

Enzymes catalyse anabolic (building up) reactions and catabolic (breaking down) reactions - overall important for growth (forming tissues ext) and releasing energy

Question 4

Explain why temperature and pressure increases enzyme action?

Answer 4

Molecules in a solution move and collide randomly - they need to collide in the right origination to form an enzyme substrate complex, increasing temperature and pressure increases the likelihood of more successful collisions (therefore rate of reactions)

Question 5

Outline the meaning of enzyme specificity?

Answer 5

Enzymes are specific to only one substrate and only that substrate fits into the enzyme active site and forms an enzyme-substrate complex

• each enzyme only catalyses one biochemical reaction

Question 6

Outline enzymes affect on activation energy?

Answer 6

Energy needs to be supplied to start most reactions - sometimes the activation energy is too large, so enzymes help the molecules collide more successfully, reducing energy required for reaction to start

Question 7

Give the two hypotheses for how enzymes lower activation energy?

Answer 7

• lock and key theory
• induced-fit hypothesis

Question 8

Outline the lock and key theory?

Answer 8

Tertiary structure on enzyme has complementary shape for a specific substrate (active site), only specific substrate fits into enzymes active site - forms an enzyme-substrate complex lowers activation energy, substrate react forming the products which are then released due to weak bonds

• enzyme is unchanged and free to form another complex

Question 9

Outline in depth the binding of the enzyme-substrate complex - with focus on the lock and key hypothesis?

Answer 9

Substrate held in way that the complementary atom-groups are close enough to react - R-groups of amino acid within enzymes active site also interact with the substrate

• forms temporary bonds - which put strain on the bonds within the substrate, helps the reaction

Question 10

Outline the induced-fit hypothesis?

Answer 10

Modified versions of lock and key

Idea AS changes slightly not completely complementary

initial interaction between the enzyme and substrate is relatively weak - however interactions rapidly induce changes in the enzyme’s tertiary structure that strengthen binding, putting strain on the substrate molecule

Weakens bonds in substrate, lowering the activation energy for reaction

Question 11

explain how activation energy is lowered, explain with focus on the induced-fit?

Answer 11

Initial interaction between enzyme and substrate is relatively weak - weak interactions rapidly induce changes in enzymes tertiary structure - puts strain on the substrate molecule

• weakens bonds in the substrate, lowering activation energy

Question 12

Outline what intracellular enzymes are - give an example of an enzyme that catalyses intracellular reactions?

Answer 12

Enzymes which act within cells

• catalase - catalyses decomposition of hydrogen peroxide into water and oxygen (found in plants and animals)

Question 13

Outline what extracellular enzymes are - give an example of an enzyme that catalyses extracellular reactions?

Answer 13

Enzymes which work outside the cell that made them - released by the cell to break down large nutrient molecules into smaller molecules (process of digestion) which can enter cell
through the cell-surface membrane

• eg amylase and trypsin (involved in human digestion)

Question 14

Give 2 examples of enzyme that catalyse extracellular reaction, state location they function?

Answer 14

• amylase - carbohydrate catalyses digestion of starch to maltose (in saliva and small intestine lumen)
• trypsin - type of protease (breaks down protein) catalyses hydrolysis of peptide bonds (in small intestine lumen)

Question 15

Outline the digestion of starch?

Answer 15

1) Starch polymers partially broken down into maltose (disaccharide) reaction catalysed by amylase (produce in salivary glands and pancreas)

2) maltose broken down into glucose (monosaccharide) - enzyme maltase present in small intestine catalyses the reaction

Question 16

Give the names of both enzymes involved in the digestion of starch state where they are produced?

Answer 16

• amylase -produced in the salivary gland and pancreas - released into saliva in the mouth and in pancreatic juice in small intestines
• maltase - present in small intestines

Question 17

Outline the digestion of proteins?

Answer 17

Trypsin is a type of protease which catalyses the digestion of proteins into smaller peptides - can be further broken down into amino acids by other protease

• amino acids than absorbed into cells lining the digestive system and then absorbed into the bloodstream

Question 18

Explain where trypsin is produced and where it acts?

Answer 18

Produced in pancreas - where its released with pancreatic juice into the small intestine to act on proteins