the biochemGazettE: Enzymes

Refelection party: thinking-face Well, what to say about enzymes their pretty freakin awesome. So this wasn’t my first tango with enzymes knew the basic like what they do and how they bind and stuff, but well we went a little further, I will admit I missed a class an was lost as……….but after catching up on the JM Enzyme 2 and 3 vid I am confident to say I have grasped what i needs to know. Although those Linweaver beark plots were pretty tricky and the new types of inhibition uncompetitve and mixed the latter being more difficult…all in all twas good. So this here post gonna be what’s new to me and what gave me head. So what do we know Enzymes are globular proteins, they are biological catalysts that speed up chemical reactions by lower the activation energy, offering a alternate pathway with lower activation energy. The saga of enzyme and substrate….NaruHina forever XD 2081 Enzymes are highly specific, well this was recently learned, there are four types of specificity Absolute specificity– where the enzyme is only catalyzes uno reaction. Group specificity- only works on a molecules with a specific functional group. Linkage specificity– only catalyzes a certain bond, no matter what the molecule. Steriochemical specificity– works only on certain isomers. Well we know there are 2 main hypotheses on how enzymes work and they are as follows 1 (1)

2 (1)

There are various things that affect enzyme catalysed reaction they are [S], [E], temperature, pH and inhibitors. In [S], as the substrate conc. increases rate of reaction increases until, it plateau’s off, this is because there are more substrate molecules present than free active sites, thus they have to wait, this is referred to as enzyme SATURATION. 512px-Michaelis-Menten_saturation_curve_of_an_enzyme_reaction_LARGE.svg In [E],  it is similar to the Michaelius-Menten curve fro [S], as enzyme con increases say in a reaction where there is more substrate the rate of reaction increases. In temperature effect on rate of reaction, it has three effects,

  • it increases the frequency of collisions between enzyme and substrate molecules, thus increasing probability of product formation
  • it increases the amount of substrate molecule with energy greater than the activation energy.
  • it increases the kinetic energy within that causes the bonds holding the enzyme together to vibrate too much and eventually break, this is a cooperartive process, the enzyme active site unfolds due to loss of tertiary structure leading to DENATURATION. This occurs after the optimum temp. has been surpassed.

tempactivity

There a certain optimum pH levels particular enzymes operate most efficiently at based on based on the ionization present either acidic or basic. Therefore if there is a change in the pH that favours the ionization present the rate of reaction increases but if their is one in opposition the rate of reaction decreases, basically denaturation occurs.

ph_opt

Inhibitors…….hmmmm… they be like the Espada’s to the enzymes. They diminsh the velocity of a enzyme catalysed reaction.

espada-SV Alright some things I does forget some small things what is Vmax and Km? Vmax- the maximum initial velocity of the enzyme catalysed reaction under the given conditions. Km-is a measure of enzyme affinity to the substrate large Km- low affinity, small Km-high affinty. It is also 1/2 the Vmax.   Competitive inhibitors, are like their names they compete for the active site, thus their shape must be similar to to substrate. Competitive inhibitors also affect Vmax and Km. The effect on Vmax is reversed by increasing [S]. However in Km it is increased.     Image19     Non-competitive inhibitors, don’t bind to the active site but to some place other than the active site to either the ES-complex or the free enzyme, preventing catalysis. It causes the active site to change, thus substrate can’t bind. 514px-Lineweaver-Burke_plot_non-competitive_inhibition.svg   As seen it has no effect on Km but decreases apparent Vmax.   Uncompetitive inhibitors, only bind to the ES complex at a different site from the active site. It decreases both Km and Vmax by the same amount. REhNAyWfPZ3Wfy2p6w2wIw_m   Mixed inhibitors, is similar to the non-competitive inhibitor as it binds to either the free enzyme or ES complex but not at the active site. But, it has different effects on Vmax and Km. Vmax is always decreased, whereas Km is either decreased or increased. In addition there is Residual activity in the ESI-complex where you still get products formed. mix_inh1350347366893   Allosteric inhibitors, possess more than one active site, and show cooperative binding to the substrate. When one substrate binds to one active site a conformational change is induced in the enzyme that changes the affinity in the other active sites. Effectors-regulate these enzymes, bind to other site, Homotrophic and Heterotrophic Effectors. Homotrophic- substrate is the effector can be positive or negative. eg haemoglobin Hetertrophic- a product inhibits it’s formation eg PFK-1 and citrate.   FINALLY FINISHED! So enzymes Sayanora…ohhh wait don’t I have to remember you for exams…. school_rumble_1_2   References: BiochemJm. “Enzymes 1, 2 and 3”.http://www.youtube.com/watch?v=qcA57r2gBL8

http://www.youtube.com/watch?v=FPKAJlgMCbE

http://www.youtube.com/watch?v=nXaQyj5Vlpk

Virtualchem book. “Enzymes” http://www.elmhurst.edu/~chm/vchembook/571lockkey.html

 

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