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UGA / Biology / BCMB 3100 / What is hexokinase?

What is hexokinase?

What is hexokinase?

Description

School: University of Georgia
Department: Biology
Course: Intro to Biochem and Molecular Bio
Professor: Wood sabatini
Term: Fall 2016
Tags:
Cost: 25
Name: Quiz 7 Study Guide- Sabitini
Description: I gave a detailed description of each step of glycolysis according to what he told us we needed to know, as well as completed all of the quiz review questions using the powerpoint and book as reference. Everything you need!
Uploaded: 09/26/2016
9 Pages 8 Views 13 Unlocks
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1. *Hexokinase:*


What is hexokinase?



a. Phosphoryl transfer  

b. Example of allosteric inhibition  

c. Regulated negatively by Glc-6P. If later steps slow down, Glc-6P  builds up and stops glucose from becoming phosphorylated and  entering cell  

d. Allows your liver to respond to different levels of glucose  e. Requires Mg2+ or other divalent metal to work- as do all kinases* f. *inhibition of phosphofructokinase leads to inhibition of  hexokinase


What is phosphoglucose isomerase?



2. Phosphoglucose isomerase:

a. Isomerization of glucose 6-phosphate into fructose 6-phosphate  is the conversion of an aldose to a ketose We also discuss several other topics like reduction of status differences

b. Crucial b/c only 3-C molecules are metabolized, and fructose is  readily cleaved into 3-C but glucose is not  

3. *Phosphofructokinase:*

a. Phosphoryl transfer  


What is phosphofructokinase?



b. The most important regulatory enzyme (pacemaker) for  glycolysis. Irreversible. First irreversible reaction; the committed step

c. High levels of ATP allosterically inhibit this enzyme by reducing  its affinity for fructose 6-phosphate. AMP competes for binding  site and does not inhibit, so activity of enzyme increases when  ATP/AMP ratio is low

d. Decrease in pH also inhibits by inhibiting ATP (ex: lactic acid protects muscle from damage that would occur if there were too  much acid)

e. In liver, PFK is inhibited by citrate. High citrate means we are  forming enough energy, and glycolysis can stop now.  

f. *inhibition of phosphofructokinase leads to inhibition of  hexokinase Don't forget about the age old question of history 101 study guide

4. Aldolase:

a. Aldol cleavage  

b. Cleaves 6-C fructose at the 3-4 bond to yield two 3-C triose  phosphates

Don't forget about the age old question of what does the suffix otomy mean

5. Triose Phosphate Isomerase:

a. Isomerization between the two 3-C products  

b. Dihydroxyacetone phosphate is not in a usable form for  glycolysis, so this enzyme allows for easy conversion to the  usable form, glyceraldehyde 3-phosphate. Ketosealdose  conversion.

STAGE 2 OF  GLYCOLYSIS

6. Glyceraldehyde 3-phosphate dehydrogenase

a. Phosphorylation coupled to oxidation  If you want to learn more check out biol 322 concordia

b. Produces NADH- glycolysis will stop unless it is re-oxidized to  NAD+ by e- transport chain or lactate dehydrogenase

c. Product has higher phosphor-transfer potential than ATP  d. Considered the high energy producing step of glycolysis  

7. Phosphoglycerate Kinase: We also discuss several other topics like pcb 3043 fiu

a. Phosphoryl transfer  

b. First ATP-generating step  

c. Substrate-level phosphorylation because the P donor, 1,3-BPG, is  a kinase substrate with a high phosphoryl-transfer potential

8. Phosphoglycerate mutase:

a. Phosphoryl shift rearrangement: shifts position of the phosphoryl  group  

We also discuss several other topics like What is marketing?

9. Enolase

a. Dehydration  

b. Elevates the transfer potential of the phosphoryl group through  formation of the enol phosphate PEP

10. *Pyruvate  Kinase:*

a. Phosphoryl transfer  

b. Irreversible transfer of phosphoryl group from PEP to ADP to  form ATP

c. ATP allosterically inhibits this enzyme to decrease rate of  glycolysis when energy of the cell is high  

= Regulatory Step  = Type of reaction  

QUIZ REVIEW QUESTIONS  

1. What properties of ATP make it an especially effective phosphoryl-transfer-potential compound (thus an energy-rich  molecule) 

Explain the source of Gibbs free energy when ATP reacts with water. 

The standard free energy of ATP hydrolysis depends on the difference in free  energies of the products and reactants:

1) Electrostatic Repulsion: Repulsion between the 4 negative charges on  ATP repel each other is reduced when ATP is hydrolyzed  

2) Resonance Stabilization: Pi has the highest resonance stabilization  

out of any of the phosphates in ATP  

3) Increase in Entropy: Entropy of products is greater after hydrolysis  4) Stabilization due to hydrolysis: water binds ADP and Pi , reducing the favorability of the reverse reaction- the synthesis of ATP

2. Understand why ATP is the energy molecule in the cell 

ATP has a phosphoryl-transfer potential that is intermediate among the  biologically important phosphorylated molecules. The intermediate position  of ATP allows it to function most effectively as carrier of phosphoryl groups: it can receive a phosphate as ADP from higher energy transfer groups or  donate phosphate to lower energy groups.  

3. Understand how ATP can power reactions that would otherwise  not take place 

ATP is an energy coupling agent. A thermodynamically unfavorable reaction  can become favorable by coupling it with the hydrolysis of ATP. 

4. Understand ways a metabolic pathway is regulated. Which is  favored and why? 

1) Catalytic Activity: favored because it is the fastest mechanism and  uses feedback inhibition to prevent unnecessary accumulation of  metabolic intermediates. Reversible. Allosteric control.  

2) Amounts of enzymes are controlled: change rate of transcription to  control production of enzymes  

3) Regulating Accessibility of Substrates- Transfer of substrates from one  compartment of a cell to another. Compartmentalization segregates  opposed reactions.  

5. Understand the steps of glycolysis. Including the metabolic  irreversible ones 

and the ATP generating steps

6. Why does NADH build up inhibit glycolysis, and how is this  prevented? 

NADH inhibits glycolysis through product inhibition in step 6. Glycolysis can  only continue if NADH is re-oxidized to NAD+ through the electron transport  chain or lactic acid fermentation.  

7. Structures of key disaccharides

Maltose (a-glucose + b-glucose) Lactose (b-galactose  + a-glucose) 

Sucrose (a-glucose + b-fructose) Cellobiose (b-glucose  

+ b-glucose) chitin? 

8. What are starch,  

glycogen, cellulose and  

Starch is the polymer of glucose in plants, and glycogen is the polymer of  glucose found in animals. Most of the glucose in starch and glycogen are  alpha-1,4 linkages, but glycogen has more branching chains formed by alpha 1,6 linkages than starch does. They are both open helices, which explains  why they function as energy stores. Cellulose is the major polymer of beta 1,4 glucose linkages in plant cell walls. The beta linkages result in long,  straight chains with high tensile strength. Chitin has a similar makeup to  cellulose, but the N-acetyl substituent allows for even more H-bonding and  an even more rigid structure. It is found in the exoskeletons of insects and is  the second most abundant organic compound on earth.

CHITIN CELLULOSE

STARCH/ GLYCOGEN

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