Arsenate poisoning. Arsenate (AsO43-) closely resembles Pi in structure and reactivity. In the reaction catalyzed by glyceraldehyde 3-phosphate dehydrogenase, arsenate can replace phosphate in attacking the energy-rich thioester intermediate. The product of this reaction, 1-arseno-3-phosphoglycerate, is unstable. It and other acyl arsenates are rapidly and spontaneously hydrolyzed.
Glycolysis proceeds in the presence of arsenate, but the ATP normally formed in the conversion of 1,3-bisphosphoglycerate into 3-phosphoglycerate is lost. Thus, arsenate uncouples oxidation and phosphorylation by forming a highly labile acyl arsenate
Glycolysis literally means “splitting sugars.” In glycolysis, glucose (a six carbon sugar) is split into two molecules of a three-carbon sugar. Glycolysis yields two molecules of ATP (free energy containing molecule), two molecules of pyruvic acid and two “high energy” electron carrying molecules of NADH. Glycolysis can occur with or without oxygen. In the presence of oxygen, glycolysis is the first stage of cellular respiration. Without oxygen, glycolysis allows cells to make small amounts of ATP. This process is called fermentation.
10 Steps of Glycolysis
The enzyme hexokinase phosphorylates (adds a phosphate group to) glucose in the cell’s cytoplasm. In the process, a phosphate group from ATP is transferred to glucose producing glucose 6-phosphate.
Glucose (C6H12O6) + hexokinase + ATP → ADP + Glucose 6-phosphate (C6H11O6P1)
The enzyme phosphoglucoisomerase converts glucose 6-phosphate into its isomer fructose 6-phosphate. Isomers have the same molecular formula, but the atoms of each molecule are arranged differently.
Glucose 6-phosphate (C6H11O6P1) + Phosphoglucoisomerase → Fructose 6-phosphate (C6H11O6P1)
The enzyme phosphofructokinase uses another ATP molecule to transfer a phosphate group to fructose 6-phosphate to form fructose 1, 6-bisphosphate.
Fructose 6-phosphate (C6H11O6P1) + phosphofructokinase + ATP → ADP + Fructose 1, 6-bisphosphate (C6H10O6P2)
The enzyme aldolase splits fructose 1, 6-bisphosphate into two sugars that are isomers of each other. These two sugars are dihydroxyacetone phosphate and glyceraldehyde phosphate.
Fructose 1, 6-bisphosphate (C6H10O6P2) + aldolase → Dihydroxyacetone phosphate (C3H5O3P1) + Glyceraldehyde phosphate (C3H5O3P1)
The enzyme triose phosphate isomerase rapidly inter-converts the molecules dihydroxyacetone phosphate and glyceraldehyde phosphate. Glyceraldehyde phosphate is removed as soon as it is formed to be used in the next step of glycolysis.
Dihydroxyacetone phosphate (C3H5O3P1) → Glyceraldehyde phosphate (C3H5O3P1)
Net result for steps 4 and 5: Fructose 1, 6-bisphosphate (C6H10O6P2) ↔ 2 molecules of Glyceraldehyde phosphate (C3H5O3P1)
The enzyme triose phosphate dehydrogenase serves two functions in this step. First the enzyme transfers a hydrogen (H–) from glyceraldehyde phosphate to the oxidizing agent nicotinamide adenine dinucleotide (NAD+) to form NADH. Next triose phosphate dehydrogenase adds a phosphate (P) from the cytosol to the oxidized glyceraldehyde phosphate to form 1, 3-bisphosphoglycerate. This occurs for both molecules of glyceraldehyde phosphate produced in step 5.
A. Triose phosphate dehydrogenase + 2 H– + 2 NAD+ → 2 NADH + 2 H+
B. Triose phosphate dehydrogenase + 2 P + 2 glyceraldehyde phosphate (C3H5O3P1) → 2 molecules of 1,3-bisphosphoglycerate (C3H4O4P2)
The enzyme phosphoglycerokinase transfers a P from 1,3-bisphosphoglycerate to a molecule of ADP to form ATP. This happens for each molecule of 1,3-bisphosphoglycerate. The process yields two 3-phosphoglycerate molecules and two ATP molecules.
2 molecules of 1,3-bisphoshoglycerate (C3H4O4P2) + phosphoglycerokinase + 2 ADP → 2 molecules of 3-phosphoglycerate (C3H5O4P1) + 2 ATP
The enzyme phosphoglyceromutase relocates the P from 3-phosphoglycerate from the third carbon to the second carbon to form 2-phosphoglycerate.
2 molecules of 3-Phosphoglycerate (C3H5O4P1) + phosphoglyceromutase → 2 molecules of 2-Phosphoglycerate (C3H5O4P1)
The enzyme enolase removes a molecule of water from 2-phosphoglycerate to form phosphoenolpyruvic acid (PEP). This happens for each molecule of 2-phosphoglycerate.
2 molecules of 2-Phosphoglycerate (C3H5O4P1) + enolase → 2 molecules of phosphoenolpyruvic acid (PEP) (C3H3O3P1)
The enzyme pyruvate kinase transfers a P from PEP to ADP to form pyruvic acid and ATP. This happens for each molecule of PEP. This reaction yields 2 molecules of pyruvic acid and 2 ATP molecules.
2 molecules of PEP (C3H3O3P1) + pyruvate kinase + 2 ADP → 2 molecules of pyruvic acid (C3H4O3) + 2 ATP
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heyy yall 🙂 Heres a second youtube video, this one is on the topic of glycolysis.
A detailed description of the process/ stages of glycolysis was given. To me this video was very informative and captured my attention by the illustrations that was used in aid of describing this complex process. Follwing this is a summary of what I learnt.
In glycolysis, one molecule of glucose is converted to 3 carbon molecules. Anet gain of energy is captured by ATP and NADH. In eukaryotes, the end product pyruvated is imported into the mitochondria where it feeds into the Citric Acid Cycle and Electron Transport Chain. Glycolysis involves 10 steps. In the 1st 3steps, energy in the form of ATP is invested and in steps 4 and 5 it allows it to be split into 2 small molecules. The last five steps breaks it down ATP and NADH.The 10 steps were then explained one by one and the reactions taking place were seen. Hope you hav fun looking at this as much i did 🙂
Enzymes are Globular proteins that catalyse or speed up a metabolic reaction.
The existence of enzymes has been known for well over a century. Some of the earliest studies were performed in 1835 by the Swedish chemist Jon Jakob Berzelius who termed their chemical action catalytic. It was not until 1926, however, that the first enzyme was obtained in pure form, a feat accomplished by James B. Sumner of Cornell University. Sumner was able to isolate and crystallize the enzyme urease from the jack bean. His work was to earn him the 1947 Nobel Prize.
Chemical properties of enzymes
A coenzyme – a non-protein organic substance which is loosely attached to the protein part.
A prosthetic group – an organic substance which is firmly attached to the protein or apoenzyme portion.
Specificity of Enzymes
One of the properties of enzymes that makes them so important as diagnostic and research tools is the specificity they exhibit relative to the reactions they catalyze. A few enzymes exhibit absolute specificity; that is, they will catalyze only one particular reaction. Other enzymes will be specific for a particular type of chemical bond or functional group. In general, there are four distinct types of specificity:
Absolute specificity – the enzyme will catalyze only one reaction.
Group specificity – the enzyme will act only on molecules that have specific functional groups, such as amino, phosphate and methyl groups.
Linkage specificity – the enzyme will act on a particular type of chemical bond regardless of the rest of the molecular structure.
Stereochemical specificity – the enzyme will act on a particular steric or optical isomer.
Though enzymes exhibit great degrees of specificity, cofactors may serve many apoenzymes.
Most enzymes end in ‘ase’ however,enzymes can be classified by the kind of chemical reaction catalyzed. For example:
- Addition or removal of water
- Hydrolases – these include carbohydrases, nucleases and proteases
- Hydrases such as fumarase and enolase
- Transfer of electrons
- Transfer of a radical
- Transglycosidases – of monosaccharides
- Transphosphorylases and phosphomutases – of a phosphate group
- Transaminases – of amino group
- Transmethylases – of a methyl group
- Transacetylases – of an acetyl group
- Splitting or forming a C-C bond
- Changing geometry or structure of a molecule
- Joining two molecules through hydrolysis of pyrophosphate bond in ATP or other tri-phosphate
Remember as previously stated above, enzymes are catalysts and increase the speed of a chemical reaction without themselves undergoing any permanent chemical change. They are neither used up in the reaction nor do they appear as reaction products.
The basic enzymatic reaction can be represented as follows
E represents the enzyme catalyzing the reaction
S the substrate, the substance being changed
P the product of the reaction.
- Energy levels
Lock and key Hypothesis or Induced fit Model
This compares the active site (place where the chemical reactions occur) to represent the keyhole and the substrate being the key. When the right substrate entered the active site, catalysis occurred because the substrate was perfectly complementary to the active site. This model described some enzymes, but not all. For others, binding leads to conformational, or shape changes, in the enzyme active site to enhance the bond breakage and formation required to reach the transition state. In both models, the active site provides the tightest fit for the transition state, and the substrate is drawn into the transition state configuration as a result.
Several factors affect the rate at which enzymatic reactions proceed. These are:
The presence of any inhibitors or activators
Enzymes have an optimum temperature – this is the temperature at which they work most rapidly. Below the optimum temperature, increasing temperature will increase the rate of the reaction. This is because temperature increases the kinetic energy of the system, effectively increasing the number of collisions between the substrate and the enzyme’s active site. Temperatures above the optimum will lead to denaturation This occurs because the hydrogen bonds and disulphide bridges which maintain the shape of the active site are broken. Thus, enzyme substrate complexes can no longer be formed.
As with temperature, similarly if pH increases or decreases much beyond this optimum, the ionisation of groups at the active site and on the substrate may change, effectively slowing or preventing the formation of the enzyme substrate complex. At extreme pH, the bonds which maintain the tertiary structure are disrupted and hence the enzyme is irreversibly denatured.
- Enzyme concentration
Normally reactions are catalysed by enzyme concentrations which are much lower than substrate concentrations. Thus as the rate of the enzyme concentration is increased , so will the rate of the enzyme reaction. If the substrate concentrations is at a high level and other conditions are optimum then the rate of reaction is proportional to the enzyme concentration.
- Substrate concentration
At low substrate concentration the reaction proceeds slowly. This is because there are not enough substrate molecules to occupy all of the active sites on the enzyme. As substrate concentration increases, the rate increases because there are more enzyme substrate complexes formed. At point x, however, increasing the substrate concentration will have no further effect on the rate of reaction. This is because all of the enzyme’s active sites are now occupied by substrate molecules – increasing the substrate concentration further will have no effect, because no more enzyme substrate complexes can form. The rate of reaction now depends on the turnover rate of the enzyme, i.e. the number of substrate molecules transformed by one molecule of enzyme per second.
Inhibitors slow down the rate of reaction. As such, they are an essential form of cellular control, allowing enzyme reaction rate to be slowed when necessary. Some enzymes are inhibited by the end product of the reaction they catalyse.
there are two types of reversible inhibitors:
- competitive reversible inhibitors
- non-competitive inhibitors
Irreversible inhibitors bind covalently and permanently to the enzyme, preventing normal enzyme function.
So that’s it for enzymes, I’m not sure if i forgot anything but i really enjoyed doing this topic.
this is definitely one of the interesting topics in biochemistry that caught my attention like no other!
Here’s my wordle that was done on both cells and carbohydrates ^_^
Heyy guys ,its week2 and we just started carbohydrates. Honestly I don’t really like this topic, never did I always got confused when it comes to identifying and drawing the structures some of these compounds. However so far based on how our lecturer Mr.Matthew is teaching, I think I’ve understood most of it. So here’s the thing loll I’m going to try to explain what I’ve learnt sooo far and hopefully this will be of some benefit to us both.
During the 1st week of biochem lectures we discussed the cell , its organelles such as Golgi apparatus, chloroplast, lysosomes, peroxisomes, glyoxysomes, mitochondria, nucleus the proteasome and endoplasmic reticulum. The structure and function of these organelles were also described . Here’s a summary of what i learnt 🙂
The Cell is the fundamental unit of life and every living organism is composed of them. Modern cell Theory states that :
- all living matter is composed of cells;
- all new cells arise from other cells;
- all metabolic reactions of an organism takes place in the cell;
cells contain hereditay information of organisms of which they are a part and this is passed from parent to daughter cell
Their Cell size is restricted by :
- the surface area to volume ratio, which must be as large as possible to allow exchange of metabolic substances.
- the capacity of the nucleus to excercise control over the rest of the cell.
|Eukaryotic Cell||Prokaryotic Cell|
|Number of chromosomes:||More than one||One–but not true chromosome: Plasmids|
|Cell Type:||Usually multicellular||
|True Membrane bound Nucleus:||Present||Absent|
|Example:||Animals and Plants||Bacteria and Archaea
|Genetic Recombination:||Meiosis and fusion of gametes||Partial, undirectional transfers DNA|
|Lysosomes and peroxisomes:||Present||Absent|
|Microtubules:||Present||Absent or rare
|Cytoskeleton:||Present||May be absent
|DNA wrapping on proteins.:||Eukaryotes wrap their DNA aroundproteins called histones.||Multiple proteins act together to fold and condense prokaryotic DNA. Folded DNA is then organized into a variety of conformations that are supercoiled and wound around tetramers of the HU protein.
|Chloroplasts:||Present (in plants)||Absent; chlorophyll scattered in the cytoplasm|
|Flagella:||Microscopic in size; membrane bound; usually arranged as nine doublets surrounding two singlets||Submicroscopic in size, composed of only one fiber|
|Permeability of Nuclear Membrane:||Selective||not present|
|Plasma membrane with steriod:||Yes||Usually no|
|Cell wall:||Only in plant cells and fungi (chemically simpler)
|Usually chemically complexed|
The Endosymbiosis Theory
The theory of Endosymbiosis explains the origin of chloroplasts and mitochondria and their double membranes.This concept postulates that chloroplasts and mitochondria are the result of years of evolution initiated by the endocytosis of bacteria and blue-green algae.
According to this theory, blue green algae and bacteria were not digested; they became symbiotic instead. Endocytosis is when a substance gains entry into a cell without passing through its cell membrane.