3.1.3 Biochemical Reactions in Cells are Controlled by Enzymes Flashcards
Enzymes can affect ______ and _____ in organisms
Enzymes can affect structures and functions in organisms
Enzymes are highly specific due to their ____ _______
tertiary structure
Explain how forming an enzyme-substrate complex lowers activation energy
- If 2 substrate molecules need to be joined:
- Being attached to the enzyme holds them close together = reducing any repulsion between molecules
- ∴ they bond more easily
- If enzyme is catalysing a breakdown reaction:
- Fitting into the active site puts a strain on bonds in substrate
- ∴ substrate molecule breaks up more easily
How is a substrate molecule held within an active site?
By bonds that form temporarily between amino acids of active site and groups on substrate molecules
Describe the ‘lock and key’ model
Where substrate fits into enzyme in the same way a key fits into a lock
What is the problem with the ‘lock and key’ model?
Too simplistic = enzyme-substrate complex actually CHANGES shape slightly to complete the fit
What model is better than the ‘lock and key’ model?
‘Induced Fit’ Model
Why do enzymes only bond to one particular substrate?
∵ substrate has to be right shape (complementary) to fit active site & has to make active site CHANGE SHAPE
Why are enzymes very specific?
∵ only one complementary substrate will fit into their active site
Each enzyme has a different tertiary structure ∴ …
It has a different shaped active site
How might a mutation in a gene affect the stucture of an enzyme?
- Primary structure is determined by gene
- If mutation occurs in gene = could change tertiary structure of enzyme produced
How can a change in the primary structure affect an enzyme?
- Sequence of amino acids changes
- Bonds form in different places as it alters hydrogen, disulfide, ionic bonds
- Tertiary structure changes
Describe how tertiary structure of a protein determines the shape of an active site (3)
- Primary structure: unique sequence of amino acids
- Different arrangement of R groups determine how it’ll fold into the secondary structure & then tertiary structure
- Tertiary structure determines 3D shape & shape of active site
Explain in terms of primary structure why an enzyme is usually specific to one substrate (4)
- Primary structure: unique sequence of amino acids
- Different arrangement of R groups determine how it’ll fold into the secondary structure & then tertiary structure
- Tertiary structure = specific 3D shape & active site is apart of this shape (made up of around 10 amino acids)
- Certain R groups will be exposed that allow substrate to bind
Explain why increasing the temperature increases rate of reaction (enzyme activity)?
- More heat = more kinetic energy so molecules move faster
- ∴ enzymes more likely to collide with substrate molecules
- Energy of collisions increase = collisions more likely to result in reaction (be successful)
- More enzyme-substrate complexes form
What happens to the rate of reaction when the temperature is too low (enzyme activity)?
- Little kinetic energy = little movement
- Substate won’t collide with active site = rate of reaction decreases
- Less enzyme-substrate complexes form
Explain what happens to enzymes when they get too hot
- Lots of kinetic energy = enzymes vibrate too much
- This breaks some of bonds (e.g. weaker hydrogen/ionic) that hold enzyme in shape
- Changes in tertiary structure
- Active site changes shape
- Enzyme substrate complex can’t form
- Enzyme = denatured
What happens when an enzyme is placed in a solution that is above or below its optimum pH?
- H+ and OH- ions found in acids/alkalis form extra/break ionic & hydrogen bonds that hold enzyme’s tertiary structure
- Active site change shape ∴ enzyme = denatured
- (Happens ∵ ions can bind to any negatively charged R groups active site)
Describe and explain how increasing the substrate concentration affects the rate of a reaction
- Increases rate of reaction
- ∵ More substrate molecules = more collisions between substrate & enzymes = more enzyme substrate complexes
- BUT up to a ‘saturation’ point where it then levels off
- ∵ active sites are full
If the substrate concentration decreases with time then the rate of reaction will…
decrease over time