Amino Acids: Disposal of Nitrogen. Flashcards
What is the chemical formula for ammonia?
NH3.
What is the chemical formula for ammonium?
NH4+.
What kind of food products are amino acids found?
In proteins.
Why do amino acids differ from other dietary foods?
Because they contain nitrogen which cannot be stored in the body.
What does the metabolism of amino acids require?
For nitrogen to disposed of in a non toxic way.
What can aminos acids be used to make?
Proteins.
Energy.
Specialised products.
How many essential amino acids are there?
10 essential amino acids.
Where do we obtain our essential amino acids from?
From the diet.
How many non essential amino acids are there?
10 non-essential amino acids.
What does the body use dietary proteins for?
To synthesise body proteins.
They can also be used to make specialised products.
They can be used as a source of energy.
What specialised products does the body use proteins to make?
Heme.
Neurotransmitters.
Nucleotides.
Can amino acids be used as precursors for gluconeogenesis?
Yes.
What is the most common amino acid that is used as a precursor for gluconeogenesis?
Alanine.
How can alanine be used to form pyruvate?
It is converted to a keto acid and then to pyruvate.
How much of a standard American diet comes from protein?
Around 20%.
What element does the metabolism of amino acids produce?
Nitrogen.
Can nitrogen be stored in the body?
No.
Why is nitrogen not stored in the body?
Because it can easily form ammonia which is very toxic, especially to the nervous system.
Are the proteins that make up the body ever degraded?
Yes.
An adult human will turnover how many grams of protein per day?
Around 400g.
What happens to the proteins that are turned over by the body?
They are combined with dietary proteins and are broken down to create a pool of amino acids.
What percentage of turned over amino acids are recycled by the body?
Around 80%.
What are the amino acids that are recycled by the body used for?
To synthesise proteins.
Energy production.
To specialised products.
What is very important to maintain in protein degradation and synthesis?
Balance.
This is called nitrogen balance.
Do all proteins have the same lifetime?
No.
Different proteins have different life spans, some can last for years and others for days or even minutes.
How many signals do are used for protein degradation?
3 signals.
What do the signals for protein degradation depend on?
The structural aspect of the protein.
Post translational modification.
What are the 3 signals for protein degradation?
Oxidation.
PEST sequences.
Ubiquitination.
What is the oxidation signal for protein degradation?
It is a generic signal that occurs if the protein has been damaged by oxidation and needs to be destroyed.
What is the PEST signal for protein degradation?
Many proteins have sequences containing 4 amino acids that form the acronym PEST in their primary structures.
These proteins have a very short half-life as their sequences are a signal for the body to destroy the protein.
What amino acids make up the PEST sequence used for protein degradation?
Proline Glutamate Serine Threonine
What is the ubiquitination signal used for protein degradation?
It is a mechanism where cellular proteins are tagged with a small protein called ubiquitin.
What happens to cellular proteins that are tagged with ubiquitin?
They enter a special organelle called a proteasome and the protein will be degraded.
Are enzymes destroyed by ubiquitination?
Yes.
Enzymes such HMG-CoA are de-activated by ubiquitination.
What are the macronutrients that make up our diet?
Carbohydrates.
Proteins.
Fats.
What is the caloric contribution of each of the macronutrients from the diet?
Carbs. 4 kcal/gram.
Protein. 4 kcal/gram.
Fat. 9 kcal/gram.
Alcohol. 7 kcal/gram.
What micronutrients are consumed in the diet?
Essential fatty acids.
Essential amino acids.
Vitamins.
Minerals.
What % of the diet do carbs, fats and proteins make up in a standard diet?
Carbs. 50%.
Proteins. 20%.
Fats. 10%.
What molecules make up carbohydrates?
Polysaccharides. (Starch).
Disaccharides. (Sucrose and lactose).
Monosaccharides. (Glucose, fructose, galactose).
What molecules make up proteins?
Proteins.
Amino acids.
What molecules make up fats?
Triacylglycerol.
Fatty acids (90%).
Phospholipids.
Cholesterol.
What are the major catabolic pathways that involve carbohydrates?
Glycolysis.
Pyruvate dehydrogenase.
TCA cycle.
What are the major catabolic pathways that involve fats?
Beta oxidation.
How much energy will the body take from food?
It will take all the energy it needs and will store the rest.
What forms will the body use to store energy?
Fats.
Glycogen.
Proteins.
What happens to the fats glycogen and proteins that are stored in the body?
They are stored until their energy needs to be released.
How much fat does the average human body have and how much energy does the body store in fat?
15 Kg of stored fat = 135,000 Kcal.
How much protein does the average human body have and how much energy does the body store as protein?
6 Kg of stored protein = 24,000 Kcal.
How much glycogen does the average human body have and how much energy does the body store as glycogen?
0.2 Kg of stored glycogen = 800 Kcal.
Which stored form of energy can be created straight to energy?
Fats can be converted directly to energy via beta oxidation.
What must glycogen and amino acids be converted to before they can give energy?
Protein must be converted to amino acids.
Glycogen must be converted to glucose.
What is the glucose that is made in the fasting state used to power?
Certain tissues that cannot run on fatty acids such as the brain and red blood cells.
Will nitrogen containing molecules ever be stored in the body?
Nitrogen containing molecules will never be stored in the body.
What are excess amino acids used for?
For protein synthesis, energy or specialised products.
What is the protein input and output in an adult?
The input of proteins is equal to the output of proteins.
Will any humans have a positive nitrogen balance?
Children have a positive nitrogen balance as they take in more than they excrete.
Why do children need to eat more nitrogen than they excrete?
Because of the increased protein synthesis that is involved in growth.
What is a negative nitrogen balance usually caused by?
A larger output than input.
A negative nitrogen balance is usually caused by what?
Trauma which causes stress hormones to degrade amino acids in muscle leading to a loss of nitrogen.
Or by inadequate consumption dietary protein.
What is the worst type of negative nitrogen balance?
The lack of an essential amino acid.
What will the lack of an essential amino acid result in?
If 1 essential amino acid is missing then a protein cannot be synthesised.
What will diets that are low in protein result in?
A deficiency of essential amino acids which results in a breakdown of tissue protein.
What will a long term low protein diet cause?
Kwashiorkor syndrome.
What are the symptoms of Kwashikor syndrome?
The distended belly that is seen in famine victims.
What effects does Kwashikor syndrome have on the body?
The body cannot recycle its proteins so it will begin to excrete them leading to loss of muscle.
How does the body deal with amino acids that are obtained in a high protein diet?
The ammonia is removed and excreted.
The carbon skeleton is stored as fat or converted to glucose.
What enzyme will break down proteins in the stomach?
A protease enzyme called pepsin.
What does pepsin break proteins down to?
To form smaller peptides and amino acids.
What must happen to large proteins before they can be broken down?
They must be hydrolysed.
Does the digestion of proteins occur in the small intestine?
Yes.
How do the enzymes that break down proteins in the small intestine enter the small intestine?
As zymogens.
Where are the zymogens that are secreted into the small intestine made?
In the pancreas.
What are the active enzymes that break down proteins called?
Trypsin and chymotrypsin.
What enzyme found in in the intestinal mucosal cells will also help to break down proteins?
An enzyme called amino-peptidase.
How is trypsin activated from its zymogen form of trypsinogen?
Enteropeptidase cleaves trypsinogen to form trypsin
What process is used to activate trypsin from trypsinogen?
Proteolytic cleavage.
What is responsible for activating all of the zymogens other than trypsin?
Trypsin perform proteolytic cleavage on the other zymogens to activate them.
What is the zymogen pepsinogen activated to?
Pepsin.
What is the zymogen chymotrypsinogen activated to?
Chymotrypsin.
What is the zymogen proelastase activated to?
Elastase.
What is the zymogen procarboxypeptidases activated to?
Carboxypeptidases.
What do proteins form once they have been broken down in the small intestine?
Free amino acids or dipeptides.
What parts of a digested protein will cross into the intestinal epithelial cell?
Free amino acids and dipeptides.
What happens to dipeptides once they enter the intestinal epithelial cell?
They are cleaved to amino acids by amino peptidase.
What happens to the individual amino acids once they enter the intestinal mucosal cell?
They enter the bloodstream.
What is the only component of dietary proteins that enters the bloodstream?
The individual amino acids.
Where are the individual amino acids that enter the bloodstream taken to?
The liver.
What happens to the amino acids in the blood once they reach the liver?
They are metabolised or are released back into circulation.
What must amino acids form so that they can be used for energy?
Either a carbon skeleton or a keto-acid.
The formation of a carbon skeleton or keto acid from an amino acid involves the removal of what from the amino acid?
The removal of the amino group from the amino acid.
