Metabolic Stores Flashcards
How are carbohydrates stored in the body?
as glycogen mainly in liver and muscle
How much glycogen is stored in the body?
For about 3-5 hours of moderate exercise
What is glycogen?
A branched glucose polymer
When glycogen is broken down what is it converted into?
most is converted directly to glucose-6-P without consuming ATP
Why is converting glucose-6-P in the bloodstream for use in cells a shit idea?
Glucose-6-P cannot easily pass through the cell membrane
What happens when glucose is required in an area of the body that doesn’t have any?
Glucose is transported there and then phosphorylated after entering the cell, using ATP
After glycogen stores run out during extended periods of exercise/starvation what fuel does the body use?
Lipids
Why are lipids important?
weight-for weight, triglycerides (= triacylglycerols) can produce about six times as much energy as
glycogen
What is fat stored as?
Much is stored as triglycerides (=triacylglycerols)
What are triglycerides (=triacylglycerols)?
esters of glycerol and fatty acids
What’s an ester?
chemical compound derived from an acid (organic or inorganic) in which at least one –OH (hydroxyl) group is replaced by an –O–alkyl (alkoxy) group
What is a triglyceride?
a triacyl glycerol
esters in which three molecules of one or more different fatty acids are linked to the alcohol glycerol
How are esters named?
according to the fatty acid components; e.g., tristearin contains three molecules of stearic acid, and oleodistearin, one of oleic acid and two of stearic acid
What are fatty acids linked to to begin lipolysis?
Coenzyme A
What occurs to fatty acids that are linked to coenzyme A?
they are oxidized and 2-carbon fragments cleaved off (as acetyl-CoA)
How may the breakdown of fatty acids by coenzyme A generate ATP?
Although no ATP is generated directly by this process, hydrogen and electrons removed during fatty acid oxidation are passed along the respiratory chain, so indirectly producing ATP
What releases fatty acids and glycerol?
Adipose tissue
Where in the body are fatty acids and glycerol metabolised?
The liver
What does the breakdown of fatty acids lead to?
the formation of chemicals known as ketone bodies
What are the main ketone bodies in the body?
acetoacetate, 3-hydroxybutyrate
and acetone
Why are ketone bodies made?
Ketone bodies are made because acetyl-CoA formed in the breakdown of fatty acids cannot enter the citric acid cycle since oxaloacetate becomes depleted because the liver converts it to pyruvate to produce glucose (gluconeogenesis)
Acetyl-CoA, therefore, is converted to ketone bodies
What is a way to identify if there are a significant number ketone bodies present in a patient?
Ketone bodies smell fruity, so they
can often be smelled on the breath of people who have been fasting for some time
Under what circumstances on the metabolic level are ketone bodies produced?
Formed in the liver when Acetyl CoA production exceeds the needs of the citric acid cycle
Discuss proteins in the metabolism
Amino acids produced by the breakdown of dietary proteins can be incorporated into new proteins
However, amino acids not needed to make new proteins cannot be stored, so they are used as metabolic fuel
Some amino acids can be deaminated, yielding NH4 + a keto acid
that are intermediates of the glycolytic pathway or of the citric acid cycle
Why are excess amino acids used as fuel or broken down for use as intermediates?
They cannot be stored
Why are only some excess amino acids broken down for use as intermediates and others not?
Some amino acids cannot release their amino groups as NH4+
What occurs to excess amino acids that cannot release their amino groups as NH4+?
they have to pass their amino group to a keto acid (mainly
alpha-ketoglutarate) in the process known as transamination
(A new amino acid and a new ketogenic acid are formed, its literally only a change in the R groups functionally)
What occurs to the ketogenic acid formed as a result of transamination? (and resulting amino acid)
The resulting keto acid can then be fed into glycolysis or the citric acid cycle (as pyruvate, acetyl-CoA, a-ketoglutarate or oxaloacetate), while the resulting amino acid can then be deaminated and used similarly
What occurs to the NH4+ released when amino acids release their amino groups?
It is converted into urea
Why is NH4+ converted into urea instead of just hanging about?
The NH4+ which is formed is very toxic, so the body rapidly converts it to urea, which is far less toxic
What two reactions occur to convert amino acids to provide fuel molecules? (and another reaction to do with these)
Transamination (AA + KA -> KA + AA) Oxidative deamination (AA(glutamic acid) -> NH3 +KA)
Also I guess CO2 is combined with NH3 (ammonia) to produce urea
What is anabolism?
Synthesis of more complex molecules
What is gluconeogenesis?
Formation of glucose from non carbohydrate sources
What is the difference between gluconeogenesis and just doing glycolysis backwards?
Some enzymes are different:
- Pyruvate carboxylase (mitochondria)
- Phosphoenol pyruvate carboxykinase (PEPCK) (mito + cyto)
- Glucose 6-phosphatase (G6-Pase) (endoplasmic reticulum)
What are the enzymes present in gluconeogenesis?
- Pyruvate carboxylase (mitochondria)
- Phosphoenol pyruvate carboxykinase (PEPCK) (mito + cyto)
- Glucose 6-phosphatase (G6-Pase) (endoplasmic reticulum)
What molecules found in cells can feed into the pathway of gluconeogenesis?
Glycerol (from triglycerides) and the
carbon backbone of amino acids
Where does the bulk of gluconeogenesis occur?
The liver
Give an example of an anabolic reaction
Lipid synthesis
What is the process of lipid synthesis?
1 - Glycerol can be made from glucose through glycolysis
2 - Two-carbon acyl units from acetyl coenzyme A are linked together by fatty acid synthesise to form fatty acids
3 - One glycerol plus 3 fatty acids makes a triglyceride
Where is fatty acid synthetase (essential for reaction of Acetyl CoA and acyl unit to form fatty acid) found in the cell?
In the cytoplasm
Provide a brief summary of the strengths and weaknesses of fatty acids v glycerol
Although fats are efficient for storage, they are not used as effectively as fuel as carbohydrate
What is an issue arising from the use of less efficient fatty acids for fuel?
energy production cannot be as high when we are using lipids as fuel rather than carbohydrate
What do athletes do to get around the lacking efficiency of lipid fuel?
endurance athletes carbohydrate (carbo) load by eating foods like pasta before an event
How are amino acids sourced in the body?
Some amino acids must be provided in the diet, while others can be made by transferring amino groups to keto acids
How are amino acids incorporated into proteins that we eat?
the normal way (DNA, mRNA, tRNA and ribosomal RNA……………)
What is the largest potential source of external protein by tissue type?
Muscle
What fuel(s) does the brain use?
Normally glucose is the only fuel the brain can use
How much glucose does the brain use?
Brain accounts for about 60% of all glucose used by the body (approx 120 g per day)
Where does the brain get its fuel?
It cannot store glucose or glycogen, so needs a constant supply in the blood
In times of starvation it can use ketone bodies (mainly acetoacetate and 3-hydroxybutyrate) formed in other tissues
Why can the brain not use fatty acids as fuel?
Because a special barrier (blood-brain barrier) that protects the brain from other potentially dangerous chemicals prevents fatty acids getting into brain tissue
What fuel(s) do the skeletal muscle use?
Muscle can use glucose, fatty acids and ketone bodies
Resting muscle mainly uses fatty acids as fuel
Where does the muscle get its fuel?
Muscle differs from brain in having large glycogen reserves (3⁄4 of body glycogen)
In muscle, glucose-6-P is formed from glycogen
-Like brain, muscle cannot convert this to glucose, so neither tissue can export glucose
Which can export glucose to the body: the brain or the skeletal muscle?
neither
What occurs to the metabolic process in the skeletal muscle during activity?
When muscle is active the rate of glycolysis far outpaces the citric acid cycle
Therefore, pyruvate must be converted to lactate
The lactate passes into the blood and to the liver, where it is converted back to glucose
What occurs when muscle protein is being broken down?
many amino acids pass their amino group to pyruvate (transamination) to form alanine
Alanine enters the blood and in the liver can be converted to back to pyruvate, which is used to synthesize glucose
So, this shows that the liver takes some of the metabolic burden away from muscle
What is fat (adipose) tissue made of?
Adipocytes, each of which has a fat droplet that occupies most of the cell
What is the main function of the fat (adipose) tissue?
To synthesize and store triglycerides (=triacylglycerols) and release fatty acids and glycerol in times of need
What determines the rate at which fatty acids are esterified?
Availability of glucose
What may effect the activity of the lipase that hydrolyses triglycerides?
Hormones
What cool vascular system ensures the liver has access to nutrients absorbed by the gut?
The hepatic portal system
When fuel supplies are available what does the liver do?
Synthesizes fatty acids, esterifies them and then secretes them into the blood as very low density lipoprotein (VLDL)
In fasting what does the liver do?
Generates ketone bodies for use in other tissues
What functions does the liver have relevant to the fuelling of other systems?
The liver can readily store and release glucose and can make new glucose (gluconeogenesis) from lactate, alanine and glycerol in the diet or released by other tissues
Where is pyruvate carboxylase found in the cell?
In the mitochondria
Where is phosphoenol pyruvate carboxykinase (PEPCK) found in the cell?
In the mitochondria and cytoplasm
Where is glucose 6-phosphatase (G6-Pase) found in the cell?
In the endoplasmic reticulum
