proteins and proteins as enzymes Flashcards
what are enzymes
biological catalysts
what type of protein are enxymes
globular
metabolic pathways
controlled by enzymes in a biochemical cascade of reactions
virtually every metabolic reaction is catalysed by an enzyme
intra vs extracellular
active inside or outside the cell
how do extracellular enzymes catalyse reactions outside cells
secreted by cells
monomer of proteisn
amino acids
bond formed between amino ocids
peptide bond
formed when a hydroxide is lost from carboxyl group and hydrogen of another lost from amine group
releases water
condensation
3 groups in amino acids
amino group
carboxyl
repeat chain
dipeptides are
formed by two amino acids
polypeptides are
formed by many amino acids
four levels of protein structure
primary
secondsary
tertiary
quaternary
primary structure
sequence of amino acids bonded by peptide bonds
DNA determines the sequence of amino acids
secondary structure how does it occur
occurs when a weak negatively charged nitrogen and oxygen atoms interact with the weak positive hydrogen atoms - forming hydrogen bonds (because they are coiled/ sheets)
when does an alpha helix occur
hydrogen bonds form between every fourth peptide bond
beta pleated sheet occurs when
protein folds so that 2 parts of the polypeptide are parallel
allowing hydrogen bonds to form between the parallel chains
how to break hydrogen bonds
high temperatures and PH changes
what does secondary structure only refer to
the formation of hydrogen bonds
how does tertiary structure occur
additional bonds form between the R groups
additional bonds are
hydrogen
disulphide
ionic
weak hydrophobic interactions
how do Quaternary structures occur
proteins that have more than one polypeptide chain working together as a macro molecule
disulphide bonds
strong covelant
form between cystine repeat groups
strongest in proteins but less frequent
how top break disulphide bridges
broken by reduction
ionic bonds
between positive amine and negative carboxyl groups
stronger than hydrogen bonds but less frequent
hydrophobic interactions how do they form
form between non polar R groups
biuret test for proteins
sample is treated with sodium to make it alkaline
copper sulphate (blue) added to sample
or scrap both steps and add biurets which already has those in
colour goes from blue to lilac
might need white tile as subtle colour change
only shows as present if there is two or more peptide bonds present - only works in polypeptides
globular proteins structure
spherical
compact
soluble in water
often have prosthetic group eg haemoglobin
why are globular proteins soluble
non polar groups orient away from surroundings
polar groups orient twoards surroundings
importance of soluble globular proteins
can be easily transported around organisms and be involved in metabolic reactions
friborous proteins
long strands of polypeptide chains
insoluble
strong and suitable for structural roles eg. collagen
how enzymes work (catabolic)
active site is complomentary to substrate
substrate binds to active site
active site morphs around substrate
enxyme substrate complec formed
substrate is broken into two products
anabolic enzyme reaction
2 substrate enters active site
one substrate product formed
how do enzymes work
provide an alternate path of lower activation energy allowing more products to be formed
how could you measure enzyme activity
oxygen measured in gas syringe
amylase in spotting tile - blue-black iodine solution
affect of temperature on rate
lower temperatures slow reactions down less KE - less e-S formation
enzyme and substrate collide with less energy so less likely to create bonds
higher temps increase KE
Enzyme begins to denature - hydrogen bonds in the enzyme begin to break apart
tertiary structure (active site) of enzyme breaks apart
substrate can no longer bind
effect of PH on rate
acidic or alkali solutions denature enzymes
hydrogen and ionic bonds are broken apart by excess OH / H+
alters active site shape
denatured
to measure effect of pH
use buffer solutions with different pHs
they maintain this pH even during reaction
PH equation
pH = -log₁₀ [H⁺]
Rate: Enzyme Concentration
more enzymes = more active sites available
more likelyhood of e-s
if substrate is infinite then =rate increases linearly
if finite then it will level out as all substrates used up
Rate: Substrate Concentration
the more substrate , the more reaction
enzyme is limiting factor
active sites become saturated
and any more substrate will not increase rate
