5 Differences between Viroids and Prions

Both Viroids and Prions are strict intracellular, sub cellular infectious agents, always requires a living host for replication.

Viroids are the smallest known infectious agents, discovered by T.O. Diener. The first discovered is Potato spindle Tuber Viroid (PSTV).

Prions are infectious misfolded protein particles discovered by Stanley Prusiner in 1982. 

Viroids vs Prions

Viroids (virus like)

Prions (infectious protein)

Infectious RNA particles without protein coat

Infectious protein particles

1971, T.O.  Diener discovered PSTV

Discovered by Stanley B Prusiner, 1982

Chemical nature: Always small circular ss RNA molecule

~5-10 times smaller than the smallest DNA and RNA viral genomes.  PSTV consist of 359 nucleotides (246 to 463 nucleotide)

PrPC (prion protein cellular) has  209 amino acids present on nerve cell surface has neuro protective function.

PrPsc(prion protein scrapie) protein highy stable structure with beta sheets accumulates within nerve cells and ultimately kill neurons

Viroid replication proceeds through an RNA-based rolling-circle mechanism using RNA polymerase II of host

PrPSc molecule binds to a single PrPC molecule and catalyzes its conversion into PrPSc

Heterodimer model & Fibril Model  

Infects only plants

 

Infects only animals but presence reported in plants causing nuerodegenerative disease.

Examples: Potato spindle tuber viroids (PSTV) (1st viroid discovered)

Tomato plant macho viroid (TPMVd)

Avocado sunblotch viroid (ASBVd)

Peach latent mosaic viroid (PLMVd) 

Bovine spongiform encephalopathy (BSE)—"mad cow disease", Scrapie in sheep. Human prion diseases Creutzfeldt–Jakob disease (CJD), Kuru disease

Learn More Virus vs Viroid

Both Viroids and Prions are strict intracellular, sub cellular infectious agents, always requires a living host for replication.

Viroids are the smallest known infectious agents, discovered by T.O. Diener. The first discovered is Potato spindle Tuber Viroid (PSTV).

Prions are infectious misfolded protein particles discovered by Stanley Prusiner in 1982. 

Viroids vs Prions

Viroids (virus like)

Prions (infectious protein)

Infectious RNA particles without protein coat

Infectious protein particles

1971, T.O.  Diener discovered PSTV

Discovered by Stanley B Prusiner, 1982

Chemical nature: Always small circular ss RNA molecule

~5-10 times smaller than the smallest DNA and RNA viral genomes.  PSTV consist of 359 nucleotides (246 to 463 nucleotide)

PrPC (prion protein cellular) has  209 amino acids present on nerve cell surface has neuro protective function.

PrPsc(prion protein scrapie) protein highy stable structure with beta sheets accumulates within nerve cells and ultimately kill neurons

Viroid replication proceeds through an RNA-based rolling-circle mechanism using RNA polymerase II of host

PrPSc molecule binds to a single PrPC molecule and catalyzes its conversion into PrPSc

Heterodimer model & Fibril Model  

Infects only plants

 

Infects only animals but presence reported in plants causing nuerodegenerative disease.

Examples: Potato spindle tuber viroids (PSTV) (1st viroid discovered)

Tomato plant macho viroid (TPMVd)

Avocado sunblotch viroid (ASBVd)

Peach latent mosaic viroid (PLMVd) 

Bovine spongiform encephalopathy (BSE)—"mad cow disease", Scrapie in sheep. Human prion diseases Creutzfeldt–Jakob disease (CJD), Kuru disease

Learn More Virus vs Viroid

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Definition of Trophic Cascade? Top down vs Bottom up Trophic Cascade

What is a Trophic Cascade? Top down vs Bottom up Trophic Cascade

Trophic cascade is an ecological phenomenon that has significant effect on the overall structure and stability of an ecosystem.The term trophic cascade was coined by the famous American ecologist Robert Paine.

Definition of trophic cascade

Trophic cascade is an indirect effect by predators that changes biomass, abundance or productivity of a population, community at successively lower trophic levels or trophic level across more than one link in a food chain.

These are powerful indirect interactions that can control the entire ecosystem.

The most common type of trophic cascade is three level trophic cascade that involves three trophic levels or feeding levels.

Top down Trophic cascade

Top down vs Bottom up Trophic Cascade

Here the predators influence the abundance or biomass of a population at lower trophic levels.

Take this example. In the above figure, the tiger population (predator) has direct effect on the abundance of prey population. By controlling the prey population the predator indirectly influences the abundance or productivity at the producer level. This type of indirect influence at lower trophic levels by predators is termed as Top down trophic cascade.

Bottom up Trophic cascade

Here the Space or nutrients influence the abundance or biomass of a population at higher trophic levels.

In the above figure, lack of space or nutrients may lead to poor productivity at the producer level (amount of grass, no of fruits etc). This limits the number of prey population that will influence the number of predators. This type of indirect influence on higher trophic levels by lack of space or nutrients is termed as bottom up trophic cascade.

What is a Trophic Cascade? Top down vs Bottom up Trophic Cascade

Trophic cascade is an ecological phenomenon that has significant effect on the overall structure and stability of an ecosystem.The term trophic cascade was coined by the famous American ecologist Robert Paine.

Definition of trophic cascade

Trophic cascade is an indirect effect by predators that changes biomass, abundance or productivity of a population, community at successively lower trophic levels or trophic level across more than one link in a food chain.

These are powerful indirect interactions that can control the entire ecosystem.

The most common type of trophic cascade is three level trophic cascade that involves three trophic levels or feeding levels.

Top down Trophic cascade

Top down vs Bottom up Trophic Cascade

Here the predators influence the abundance or biomass of a population at lower trophic levels.

Take this example. In the above figure, the tiger population (predator) has direct effect on the abundance of prey population. By controlling the prey population the predator indirectly influences the abundance or productivity at the producer level. This type of indirect influence at lower trophic levels by predators is termed as Top down trophic cascade.

Bottom up Trophic cascade

Here the Space or nutrients influence the abundance or biomass of a population at higher trophic levels.

In the above figure, lack of space or nutrients may lead to poor productivity at the producer level (amount of grass, no of fruits etc). This limits the number of prey population that will influence the number of predators. This type of indirect influence on higher trophic levels by lack of space or nutrients is termed as bottom up trophic cascade.

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10 Differences between Positive sense RNA Viruses and Negative sense ss RNA Viruses

Based on the sense or polarity of the genome, single stranded RNA viruses are of two types.
Differences between Positive sense RNA Viruses and Negative sense ss RNA Viruses
1. Positive Sense RNA viruses (+ssRNA virus) or PSV
2. Negative Sense ss RNA viruses (-ssRNA virus) or NSV
Positive sense RNA viruses (PSV)
Negative sense ss RNA viruses (NSV)
Genetic Material is positive sense ssRNA
Genetic Material is Negative sense ssRNA
Virus with +ssRNA genome can be translated directly to make viral proteins  by host ribosome
Virus with -ssRNA genome cannot be translated directly to make viral proteins.
‘translation ready genome’
Not ‘translational ready genome’
Viral genome acts like cellular mRNA. ssRNA has 5’cap and poly A tail for recognition by eukaryotic host ribosme.
Negative ssRNA is  complementary to mRNA

Genetic material is infectious inside the host
Genetic material is not infectious inside the host. It It should be converted to +ss RNA by viral RNA dependent RNA polymerase (RdRP) for viral protein synthesis inside host.
+ve ssRNA viruses belong to Group IV in the Baltimore classification.
-ve  sense ssRNA viruses belong to Group V in the Baltimore classification.
The genome  usually contains relatively few genes, including an RdRP.
Negative-sense single-stranded RNA viruses have complex genomic sequences, cell cycles, and mode of replication
Most common type of plant viruses and more abundant
Less abundant compared to +ve ssRNA viruses and more infectious
Examples: SARS CoV-2, Rhino viruses, Dengue virus, MERS corona virus.
Examples: Influenza virus, Ebola virus, Hanta virus, Rabies virus, Mumps virus
Based on the sense or polarity of the genome, single stranded RNA viruses are of two types.
Differences between Positive sense RNA Viruses and Negative sense ss RNA Viruses
1. Positive Sense RNA viruses (+ssRNA virus) or PSV
2. Negative Sense ss RNA viruses (-ssRNA virus) or NSV
Positive sense RNA viruses (PSV)
Negative sense ss RNA viruses (NSV)
Genetic Material is positive sense ssRNA
Genetic Material is Negative sense ssRNA
Virus with +ssRNA genome can be translated directly to make viral proteins  by host ribosome
Virus with -ssRNA genome cannot be translated directly to make viral proteins.
‘translation ready genome’
Not ‘translational ready genome’
Viral genome acts like cellular mRNA. ssRNA has 5’cap and poly A tail for recognition by eukaryotic host ribosme.
Negative ssRNA is  complementary to mRNA

Genetic material is infectious inside the host
Genetic material is not infectious inside the host. It It should be converted to +ss RNA by viral RNA dependent RNA polymerase (RdRP) for viral protein synthesis inside host.
+ve ssRNA viruses belong to Group IV in the Baltimore classification.
-ve  sense ssRNA viruses belong to Group V in the Baltimore classification.
The genome  usually contains relatively few genes, including an RdRP.
Negative-sense single-stranded RNA viruses have complex genomic sequences, cell cycles, and mode of replication
Most common type of plant viruses and more abundant
Less abundant compared to +ve ssRNA viruses and more infectious
Examples: SARS CoV-2, Rhino viruses, Dengue virus, MERS corona virus.
Examples: Influenza virus, Ebola virus, Hanta virus, Rabies virus, Mumps virus
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Difference between Coronavirus and COVID-19

Corona Virus vs COVID-19
Corona Virus
Corona virus is a family of virus that causes diseases in mammals and birds.
According to World Health Organization (WHO), in humans, several coronaviruses are known to cause respiratory infections ranging from the common cold to more severe diseases such as Middle East Respiratory Syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS).
Difference between Coronavirus and COVID-19
Some examples include
a) Coronaviruses causing mild symptoms of common cold
  • Human coronavirus OC43 (HCoV-OC43), Human coronavirus HKU1, Human coronavirus NL63 (HCoV-NL63, New Haven coronavirus), Human coronavirus 229E (HCoV-229E)

b) Coronaviruses causing severe respiratory infections including Pneumonia
  • Middle East respiratory syndrome-related coronavirus (MERS-CoV)
  • Severe acute respiratory syndrome coronavirus (SARS-CoV)
  • COVID-19
Structure: Enveloped positive sense RNA viruses with nucleocapsid of helical symmetry
Why the name “corona”?
The most prominent feature of coronaviruses is the club-shape spike projections emanating from the surface of the virion. These spikes are a defining feature of the virion and give them the appearance of a solar corona under two-dimensional transmission electron microscopy (TEM), prompting the name, coronaviruses. (Latin corona meaning “crown or halo”)
COVID-19
  • COVID 19 Is the infectious disease caused by newly discovered corona virus, first identified at Wuhan, China in December 2019
  • February 11, 2020 WHO announced an official name  COVID-19, ‘CO’ stands for ‘CORONA,’ ‘VI’ for ‘VIrus,’ and ‘D’ for Disease
  • Formerly, this disease was called as “2019 novel coronavirus” or “2019-nCoV”
Symptoms of Covid-19 include
  • fever, tiredness, and dry cough. Some patients may have aches and pains, nasal congestion, runny nose, sore throat or diarrhea. These symptoms are usually mild and begin gradually.
Transmission of disease: 
  • People can catch COVID-19 from others who have the virus, through respiratory droplets or through infected surfaces
Preventive measures:
  • Regularly and thoroughly clean your hands with an alcohol-based hand rub or wash them with soap and water.
  • Maintain at least 1 meter (3 feet) distance between yourself and anyone who is coughing or sneezing.
  • Avoid touching eyes, nose and mouth as infected surfaces can spread the disease
  • Cover your mouth and nose with your bent elbow or tissue when you cough or sneeze. Then dispose of the used tissue immediately.
  • Avoid direct contact with animals and surfaces in contact with animals
  • Stay home if you feel unwell. If you have a fever, cough and difficulty in breathing, seek medical attention immediately.
For more updates and answers on COVID-19 visit: 
Reference:
Zhu, N., Zhang, D., Wang, W., Li, X., Yang, B., Song, J., ... & Niu, P. (2020). A novel coronavirus from patients with pneumonia in China, 2019. New England Journal of Medicine.
Fehr, A. R., & Perlman, S. (2015). Coronaviruses: an overview of their replication and pathogenesis. In Coronaviruses (pp. 1-23). Humana Press, New York, NY.
Corona Virus vs COVID-19
Corona Virus
Corona virus is a family of virus that causes diseases in mammals and birds.
According to World Health Organization (WHO), in humans, several coronaviruses are known to cause respiratory infections ranging from the common cold to more severe diseases such as Middle East Respiratory Syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS).
Difference between Coronavirus and COVID-19
Some examples include
a) Coronaviruses causing mild symptoms of common cold
  • Human coronavirus OC43 (HCoV-OC43), Human coronavirus HKU1, Human coronavirus NL63 (HCoV-NL63, New Haven coronavirus), Human coronavirus 229E (HCoV-229E)

b) Coronaviruses causing severe respiratory infections including Pneumonia
  • Middle East respiratory syndrome-related coronavirus (MERS-CoV)
  • Severe acute respiratory syndrome coronavirus (SARS-CoV)
  • COVID-19
Structure: Enveloped positive sense RNA viruses with nucleocapsid of helical symmetry
Why the name “corona”?
The most prominent feature of coronaviruses is the club-shape spike projections emanating from the surface of the virion. These spikes are a defining feature of the virion and give them the appearance of a solar corona under two-dimensional transmission electron microscopy (TEM), prompting the name, coronaviruses. (Latin corona meaning “crown or halo”)
COVID-19
  • COVID 19 Is the infectious disease caused by newly discovered corona virus, first identified at Wuhan, China in December 2019
  • February 11, 2020 WHO announced an official name  COVID-19, ‘CO’ stands for ‘CORONA,’ ‘VI’ for ‘VIrus,’ and ‘D’ for Disease
  • Formerly, this disease was called as “2019 novel coronavirus” or “2019-nCoV”
Symptoms of Covid-19 include
  • fever, tiredness, and dry cough. Some patients may have aches and pains, nasal congestion, runny nose, sore throat or diarrhea. These symptoms are usually mild and begin gradually.
Transmission of disease: 
  • People can catch COVID-19 from others who have the virus, through respiratory droplets or through infected surfaces
Preventive measures:
  • Regularly and thoroughly clean your hands with an alcohol-based hand rub or wash them with soap and water.
  • Maintain at least 1 meter (3 feet) distance between yourself and anyone who is coughing or sneezing.
  • Avoid touching eyes, nose and mouth as infected surfaces can spread the disease
  • Cover your mouth and nose with your bent elbow or tissue when you cough or sneeze. Then dispose of the used tissue immediately.
  • Avoid direct contact with animals and surfaces in contact with animals
  • Stay home if you feel unwell. If you have a fever, cough and difficulty in breathing, seek medical attention immediately.
For more updates and answers on COVID-19 visit: 
Reference:
Zhu, N., Zhang, D., Wang, W., Li, X., Yang, B., Song, J., ... & Niu, P. (2020). A novel coronavirus from patients with pneumonia in China, 2019. New England Journal of Medicine.
Fehr, A. R., & Perlman, S. (2015). Coronaviruses: an overview of their replication and pathogenesis. In Coronaviruses (pp. 1-23). Humana Press, New York, NY.
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Difference between Cell Theory and Modern Cell Theory

Cell Theory 1839
Proposed by Theodor Schwann (1810–1882) and Matthias Jakob Schleiden (1804–1881)
1. All living organisms are composed of one or more cells.
2. The cell is the basic structural and functional unit of all living things.
Difference between Cell Theory and Modern Cell Theory
The third tenet was proposed by Rudolf Virchow, a German Pathologist (1821–1902) in 1855
3. Cells arise from pre-existing cells “Omnis cellula e cellula” (by cell division; mitosis or meiosis; not derived from spontaneous generation)
Background:
Schleiden in 1838, German botanist, found out cell as the basic unit of plant structure.
Theodor Schwann, a German physiologist in 1839 defined cell as the basic unit of animal structure also. In 1839, they together proposed the two statements of the present cell theory.

Modern Cell Theory
The knowledge of the advancement in the field of molecular biology, biochemistry, etc. is considered to make the following additions to the above classical cell theory
 Modern Cell Theorystatements
4. Cells contain heredity information in their DNA. This information is passed to new cells by cell division.
5. All cells have the same basic chemical composition.
6. Energy flow (Metabolism and biochemistry) occurs within cells.
The other major contributors to the Cell Theory are Robert Hooke; who coined the tern “cell” and Antonie van Leeuwenhoek; who was the first one to observe living organisms under his own microscope.
Cell Theory 1839
Proposed by Theodor Schwann (1810–1882) and Matthias Jakob Schleiden (1804–1881)
1. All living organisms are composed of one or more cells.
2. The cell is the basic structural and functional unit of all living things.
Difference between Cell Theory and Modern Cell Theory
The third tenet was proposed by Rudolf Virchow, a German Pathologist (1821–1902) in 1855
3. Cells arise from pre-existing cells “Omnis cellula e cellula” (by cell division; mitosis or meiosis; not derived from spontaneous generation)
Background:
Schleiden in 1838, German botanist, found out cell as the basic unit of plant structure.
Theodor Schwann, a German physiologist in 1839 defined cell as the basic unit of animal structure also. In 1839, they together proposed the two statements of the present cell theory.

Modern Cell Theory
The knowledge of the advancement in the field of molecular biology, biochemistry, etc. is considered to make the following additions to the above classical cell theory
 Modern Cell Theorystatements
4. Cells contain heredity information in their DNA. This information is passed to new cells by cell division.
5. All cells have the same basic chemical composition.
6. Energy flow (Metabolism and biochemistry) occurs within cells.
The other major contributors to the Cell Theory are Robert Hooke; who coined the tern “cell” and Antonie van Leeuwenhoek; who was the first one to observe living organisms under his own microscope.
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10 Differences between chemiosmosis in Cellular Respiration and Photosynthesis

Chemiosmosis in Cellular Respiration vs chemiosmosis in Photosynthesis
Chemiosmotic Hypothesis was proposed by Peter Mitchell 1961. He was awarded the Nobel Prize for Chemistry in 1978. This process is occurring during cellular respiration and photosynthesis.
Chemiosmotic Theory states that Electron transport and ATP synthesis are coupled by a proton gradient across the inner mitochondrial membrane.
Peter Mitchell proposed this theory to explain ATP synthesis during cellular respiration
See simple step wise explanation on
Chemiosmosis in Cellular Respiration
Chemiosmosis in Photosynthesis
Chemiosmosis in Cellular Respiration occurs in all living cells.
Chemiosmosis in photosynthesis occurs only in green plants and cyanobacteria
Chemiosmosis occurs during Electron transport chain of cellular respiration
Chemiosmosis occurs during Light dependent reaction of photosynthesis
The organelle involved is Mitochondrion
The organelle involved is Chloroplast
The exact site of chemiosmosis is Mitochondrial inner membrane (cristae)
The exact site of chemiosmosis is thylakoid membrane of chloroplast
Electron flows through electron carriers located in the Mitochondrial inner membrane
Electron flows through electron carriers located in the Thylakoid membrane of chloroplast
Proton gradient formation occurs across the mitochondrial inner membrane
Proton gradient formation occurs across thylakoid membrane
Proton (H+) is pumped from matrix into the intermembrane space of mitochondria using energy derived from electron flow
Proton (H+) is pumped from stroma into the thylakoid lumen or thylakoid space using energy derived from electron flow
ATP synthesis occurs towards the matrix side
as ATP synthase is oriented towards matrix side
ATP synthesis occurs towards the stromal side as ATP synthase is oriented towards stromal side
Transforms chemical energy or bond energy form food to ATP
Transforms light energy into chemical energy in the form of ATP
ATP synthesized is used to drive all cellular activities
ATP synthesized is used to fix carbondioxide to carbohydrates during light independent reaction of photosynthesis
Chemiosmosis in Cellular Respiration vs chemiosmosis in Photosynthesis
Chemiosmotic Hypothesis was proposed by Peter Mitchell 1961. He was awarded the Nobel Prize for Chemistry in 1978. This process is occurring during cellular respiration and photosynthesis.
Chemiosmotic Theory states that Electron transport and ATP synthesis are coupled by a proton gradient across the inner mitochondrial membrane.
Peter Mitchell proposed this theory to explain ATP synthesis during cellular respiration
See simple step wise explanation on
Chemiosmosis in Cellular Respiration
Chemiosmosis in Photosynthesis
Chemiosmosis in Cellular Respiration occurs in all living cells.
Chemiosmosis in photosynthesis occurs only in green plants and cyanobacteria
Chemiosmosis occurs during Electron transport chain of cellular respiration
Chemiosmosis occurs during Light dependent reaction of photosynthesis
The organelle involved is Mitochondrion
The organelle involved is Chloroplast
The exact site of chemiosmosis is Mitochondrial inner membrane (cristae)
The exact site of chemiosmosis is thylakoid membrane of chloroplast
Electron flows through electron carriers located in the Mitochondrial inner membrane
Electron flows through electron carriers located in the Thylakoid membrane of chloroplast
Proton gradient formation occurs across the mitochondrial inner membrane
Proton gradient formation occurs across thylakoid membrane
Proton (H+) is pumped from matrix into the intermembrane space of mitochondria using energy derived from electron flow
Proton (H+) is pumped from stroma into the thylakoid lumen or thylakoid space using energy derived from electron flow
ATP synthesis occurs towards the matrix side
as ATP synthase is oriented towards matrix side
ATP synthesis occurs towards the stromal side as ATP synthase is oriented towards stromal side
Transforms chemical energy or bond energy form food to ATP
Transforms light energy into chemical energy in the form of ATP
ATP synthesized is used to drive all cellular activities
ATP synthesized is used to fix carbondioxide to carbohydrates during light independent reaction of photosynthesis
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5 Differences between Proteinogenic Amino Acid and Non-proteinogenic amino acids

Proteinogenic vs Non-proteinogenic amino acids
Proteins are nitrogen containing bio molecules made up of amino acids joined by peptide bond.
An amino acids consists of a central α carbon atom joined by 4 groups namely Hydrogen (H), amino group (–NH2), carboxyl group (-COOH) and side group (R-group).
Proteinogenic amino acids are “protein forming amino acids where as non-proteinogenic amino acids not naturally incorporated into proteins
 Proteinogenic Amino Acid vs Non-proteinogenic amino acids
Proteinogenic amino acids
Non-proteinogenic aminoacids
Proteinogenic amino acids are those which are naturally encoded in the genetic code of any organism
Non-coded or non-proteinogenic amino acids are those not naturally encoded or found in the genetic code of any organism.
Natural amino acids incorporated into proteins during translation
Amino acids not incorporated into proteins during translation
Protein forming amino acids or amino acids that are natural constituents of proteins
Not Protein forming amino acids or amino acids that are not naturally incorporated into proteins
Coded amino acids or proteinogenic amino acids are those which are naturally encoded in the genetic code of any organism
Non-coded or non-proteinogenic amino acids are those not naturally encoded or found in the genetic code of any organism.
Examples: In Eukaryotes all 21 amino
acids including selenocysteine are  proteinogenic. (Glycine, alanine, valine etc)
Ornithine, citruline, Gamma-Aminobutyric Acid (GABA) etc
Forms all proteins that carry out different activities of the cell like enzymes, hormones like insulin.
They are often intermediates in biosynthesis with specific physiological functions.
For example GABA is a neurotransmitter that blocks impulses between nerve cells in the brain.
Proteinogenic vs Non-proteinogenic amino acids
Proteins are nitrogen containing bio molecules made up of amino acids joined by peptide bond.
An amino acids consists of a central α carbon atom joined by 4 groups namely Hydrogen (H), amino group (–NH2), carboxyl group (-COOH) and side group (R-group).
Proteinogenic amino acids are “protein forming amino acids where as non-proteinogenic amino acids not naturally incorporated into proteins
 Proteinogenic Amino Acid vs Non-proteinogenic amino acids
Proteinogenic amino acids
Non-proteinogenic aminoacids
Proteinogenic amino acids are those which are naturally encoded in the genetic code of any organism
Non-coded or non-proteinogenic amino acids are those not naturally encoded or found in the genetic code of any organism.
Natural amino acids incorporated into proteins during translation
Amino acids not incorporated into proteins during translation
Protein forming amino acids or amino acids that are natural constituents of proteins
Not Protein forming amino acids or amino acids that are not naturally incorporated into proteins
Coded amino acids or proteinogenic amino acids are those which are naturally encoded in the genetic code of any organism
Non-coded or non-proteinogenic amino acids are those not naturally encoded or found in the genetic code of any organism.
Examples: In Eukaryotes all 21 amino
acids including selenocysteine are  proteinogenic. (Glycine, alanine, valine etc)
Ornithine, citruline, Gamma-Aminobutyric Acid (GABA) etc
Forms all proteins that carry out different activities of the cell like enzymes, hormones like insulin.
They are often intermediates in biosynthesis with specific physiological functions.
For example GABA is a neurotransmitter that blocks impulses between nerve cells in the brain.
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10 Difference between Hexokinase and Glucokinase

Both Hexokinase and Glucokinase are enzymes catalyzing the phophorylation of Glucose to Glucose-6-phosphate using ATP. During the reaction, one ATP molecule is cleaved to ADP and the phosphate thus released is added to glucose. Hexokinase and Glucokinae are isoenzymes with same catalytic activity but have different physical properties and site of action. Glucokinase is also called as human hexokinase IV, hexokinase D etc
10 Difference Hexokinase vs Glucokinase
Hexokinase
Glucokinase (Hexokinase D)
Present in all tissues except the liver and the Beta cells of pancreas
Present in liver and Beta cells of pancreas
Acts upon many hexoses such as fructose, galactose including glucose
The only substrate is D-glucose
Hexokinase is one of the regulatory enzymes of glycolysis
Glucokinase plays a central role as a glucose sensor in the regulation of glucose homeostasis.
Hexokinase has high Km value that is high affinity for the substrate glucose
Glucokinase has high Km value that means low affinity for the substrate
The maximum reaction rate (Vmax) of hexokinase is low that means it gets saturated quickly by increasing glucose concentration
The maximum reaction rate (Vmax) of glucokinase is quite high, thus can handle larger glucose load resulting in a rapid conversion of glucose into usable energy.
Hexokinase is active even at low glucose levels
Glucokinase is active only at high glucose levels in liver
Is not inducible (*constitutive enzyme)
Is induced by glucose and insulin
Hexokinase is an allosteric enzyme with **allosteric site for regulation of enzyme activity
Glucokinase is not an allosteric enzyme
Feedback inhibition of hexokinase by
glucose 6 phosphate (product)
No direct feedback inhibition; not inhibited by glucose-6-phosphate
*Constitutive enzymes are always produced in constant amounts without regard to the physiological demand or the concentration of the substrate.
**Allosteric site: is the site other than the active site where effector molecule binds and regulated enzyme activity. This type of regulation is called allosteric regulation.
Both Hexokinase and Glucokinase are enzymes catalyzing the phophorylation of Glucose to Glucose-6-phosphate using ATP. During the reaction, one ATP molecule is cleaved to ADP and the phosphate thus released is added to glucose. Hexokinase and Glucokinae are isoenzymes with same catalytic activity but have different physical properties and site of action. Glucokinase is also called as human hexokinase IV, hexokinase D etc
10 Difference Hexokinase vs Glucokinase
Hexokinase
Glucokinase (Hexokinase D)
Present in all tissues except the liver and the Beta cells of pancreas
Present in liver and Beta cells of pancreas
Acts upon many hexoses such as fructose, galactose including glucose
The only substrate is D-glucose
Hexokinase is one of the regulatory enzymes of glycolysis
Glucokinase plays a central role as a glucose sensor in the regulation of glucose homeostasis.
Hexokinase has high Km value that is high affinity for the substrate glucose
Glucokinase has high Km value that means low affinity for the substrate
The maximum reaction rate (Vmax) of hexokinase is low that means it gets saturated quickly by increasing glucose concentration
The maximum reaction rate (Vmax) of glucokinase is quite high, thus can handle larger glucose load resulting in a rapid conversion of glucose into usable energy.
Hexokinase is active even at low glucose levels
Glucokinase is active only at high glucose levels in liver
Is not inducible (*constitutive enzyme)
Is induced by glucose and insulin
Hexokinase is an allosteric enzyme with **allosteric site for regulation of enzyme activity
Glucokinase is not an allosteric enzyme
Feedback inhibition of hexokinase by
glucose 6 phosphate (product)
No direct feedback inhibition; not inhibited by glucose-6-phosphate
*Constitutive enzymes are always produced in constant amounts without regard to the physiological demand or the concentration of the substrate.
**Allosteric site: is the site other than the active site where effector molecule binds and regulated enzyme activity. This type of regulation is called allosteric regulation.
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