U2 Metabolic pathways Flashcards
What is metabolism?
All of the chemical reactions that take place inside living cells
Unicellular and multicellular organisms must control their metabolisms in order to survive
examples of Metabolic reactions
respiration
protein synthesis
photosynthesis
starch synthesis
What are metabolic pathways?
a series of chemical reactions which take place within a cell involving several enzymes
The products of one reaction will become the substrate of the next
What can metabolic pathways have?
reversible steps
irreversible steps
alternative routes
Catabolic metabolic pathway?
Involves breaking down (degrading) large molecules into smaller ones
Releases energy
Anabolic metabolic pathways
Involves building up (synthesising) large molecules from smaller ones
requires energy
What is the cell membrane made up of?
Phospholipid molecules
proteins
(external surface membrane
protein molecule
channel protein
phospholipid bilayer)
In what ways can materials pass through the membrane?
diffusion
osmosis
active transport (pump mechanism)
What functions can proteins in the plasma membrane have?
protein pores (diffusion)
pumps (active transport)
enzymes (atp synthase)
these are embedded in the phospholipid membranes
What are metabolic pathways controlled by!
the presence or absence of particular enzymes (embedded in the cell membrane which catalyse the steps in metabolic pathways)
What are the 3 reasons that enzymes are essential in to metabolic pathways?
They speed up chemical reactions
They remain unchanged after the reaction so can be used again
They lower the activation energy required to carry out the reaction
When does induced fit occur?
When the active site changes shape to better fit the substrate after the substrate binds.
The active site of an enzyme is flexible and dynamic. When a substrate enters the active site, the shape of the active site changes slightly making it fit exactly (induced fit)
What is affinity?
Attraction
Why do substrate molecules bind readily to the active site
They have a high affinity for the active site
What affinity do products have?
Low affinity, allowing them to leave the active site and leaving the active site free to catalyse another reaction
What is enzyme action affected by?
pH and temperature
They also require an adequate supply of substrate. If the substrate concentration is too low, the rate of reaction is low. This improves as the substrate concentration increases.
What drives a sequence of reactions in a particular direction?
Some metabolic reactions are reversible
-The presence of a substrate
-Removal of a products
What are inhibitors?
Substances which can slow down the rate of an enzyme and they are split into 2 main groups:
-competitive inhibitors
-non-competitive inhibitors
Competitive inhibitors
Have a similar shape to that of the substrate and so they also fit the enzymes active substrate
If the inhibitor joins the enzyme, this prevents the substrate from doing so, and so this therefore reduces the number of substrate molecules being used by the enzyme (reduced rate of reaction in presence of inhibitor)
How is the effect of a competitive inhibitor reversed?
By increasing the substrate conconcentration
with more substrate molecules present, there is a higher chance that the active site will be occupied by a substrate molecule rather than the inhibitor
At high substrate conc., the inhibitor is out-competed by the substrate and the maximum rate of reaction is achieved
Non-competitive inhibitors
Doesn’t interfere with the active site
It binds to another part of the enzyme but results in the shape of the enzyme being altered so changes the shape of the active site
Substrate can now no longer let fit the enzyme’s active site and therefore the reaction cannot take place
(no inhibitor: maximum rate of reaction achieved at high substrate concentration
with inhibitor: max reaction rate never achieved)
Can the effect of a non-competitive inhibitor be reversed by increasing substrate concentration?
no
Examples of non-competitive inhibitors
heavy metals like lead, silver, etc
What is end product feedback inhibition
Another way in which a metabolic pathway can be regulated (saves energy/end-product only produced when required)
As the concentration of the end product builds up to a critical level, some of the product binds to an earlier enzyme in the pathway and blocks this enzyme’s action (inhibits enzyme)
This prevents (unnecessary) synthesis of the end-product
What 3 things play a part controlling metabolic pathways?
Competitive inhibition
Non-competitive inhibition
Feedback inhibition
