key area 2.1 - metabolic pathways

Question 1

metabolism

Answer 1

• sun of all the biochemical reactions occurring within a living organism

Question 2

metabolic pathway

Answer 2

• integrated and controlled pathways of enzyme catalysed reactions within a cell
• these can be reversible, irreversible or there may be alternative routes

Question 3

anabolic pathways

Answer 3

• type of pathway that brings about the build up of large molecules from smaller molecules
• usually requires energy
• eg protein synthesis

Question 4

catabolic pathways

Answer 4

• type of pathway that bring about the break down of complex molecules to simpler ones
• usually releases energy
• eg protein => amino acids

Question 5

alternative routes

Answer 5

• steps in a metabolic pathway that allow regular steps to be bypassed

Question 6

structure of plasma membrane

Answer 6

• made of bilayer of phospholipids and proteins which are on the surface and embedded within the membrane
• phospholipids are in constant motion making membranes flexible
• known as fluid mosaic model

Question 7

roles of proteins in plasma membrane

Answer 7

• pores
• protein pumps
• enzymes

Question 8

protein pore

Answer 8

• proteins in a membrane which allow certain molecules to move across the membrane by passive diffusion
• makes membranes selectively permeable

Question 9

active transport

Answer 9

• movement of molecules or ions through a cell membrane from a region of lower concentration to a region of higher concentration
• requires energy as it goes against concentration gradient

Question 10

protein pump

Answer 10

• proteins in a membrane which actively pump molecules against the concentration gradient by active transport
• requires energy

Question 11

diffusion

Answer 11

• movement of molecules or ions from the region of high concentration to a region of lower concentration down the concentration gradient
• requires no energy

Question 12

enzyme

Answer 12

• protein made by living cells that act as a biological catalyst
• some proteins in the membrane catalyse steps within cellular metabolic processes

Question 13

activation energy

Answer 13

• energy required to initiate a reaction called its activation energy
• substrate must overcome an energy barrier before reaction can begin
• enzymes reduce the activation energy needed for a reaction to occur

Question 14

induced fit

Answer 14

• the active site of an enzyme changes shape to form the substrate more closely, increasing the rate of reaction

Question 15

affinity

Answer 15

• degree of chemical attraction between reactant molecules
• active site has high affinity for the substrate molecules
• product moves away from active site as it has low affinity for the active site

Question 16

substrate concentration

Answer 16

• maximum rate at which any enzyme catalysed reaction can proceed depends on concentration of substrate molecules
• an increase in substrate concentration drives the reaction in the direction of the end product and increase the rate of the reaction

Question 17

competitive inhibitors

Answer 17

• competitive inhibitors are a similar shape to the substrate and bind to active site of enzyme, preventing substrate from binding
• reduces rate of reaction
• can be revered by increasing substrate concentration (increases the chance of the substrate binding to enzyme rather than inhibitor)

Question 18

non-competitive inhibitors

Answer 18

• non competitive inhibitors have different structure from substrate so don’t fit into active site
• they bind to the enzyme at an allosteric site (don’t need to know name)
• shape of active site is changed so substrate can no longer bind to enzyme and reaction is not catalysed
• cannot be reversed and increasing substrate concentration doesn’t work since inhibitors are not competing with substrate

Question 19

feedback inhibition

Answer 19

• the end product of a metabolic pathway acts as an inhibitor (non competitive) to an enzyme earlier in the pathway
• this blocks the pathway and prevents any further synthesis of the end product
• occurs when end product in the metabolic plateau reaches a critical concentration

Question 20

transition state

Answer 20

• state of reactant molecules that have absorbed enough energy to break the binds and allow the reaction to occur