2 - Energy and Metabolism Flashcards
ATP is comprised of:
Adenine
Ribose
Three Phosphate Radicals
90% of the carbohydrates utilized by the body are used to:
create ATP
Once fructose and galactose are reabsorbed, what happens to them?
They are converted to glucose in the liver
How does glucose get through the cell membrane?
It cannot easily diffuse. It’s molecular weight is prohibitive.
Passes via facilitated diffusion
The rate of carb utilization in most cells is controlled by:
the amount of circulating insulin
What chemical process allows cells to capture glucose?
Phosphorylation
As soon as glucose enters most cells it combines with a phosphate radical via
Glucokinase or hexokinase
This bond is usually irreversible
In specialized cells (liver, kidneys, intestines) flucose phosphatase attaches the phosphate group in a reversible bond
Why is it so beneficial to store glucose as glycogen rather than as loose glucose?
High concentrations of low molecular weight soluble monosaccharides would wreak havoc on the osmotic relationship of the ICF and ECF
One large high molecular weight insoluble polysaccharide will not
Which two hormones can activate phosphorylase?
Epinephrine and Glucagon
Phosphorylase breaks down glycogen and releases glucose
What does “glycolysis” mean?
Splitting of a glucose molecule to form two molecules of pyuvic acid
The net gain in ATP molecules from the glycolytic process is:
2 moles of ATP for every 1 mole of glucose utilized
1 ATP = ________ calories
12,000
Only 47% of the energy expended in glycolysis results in ATP. What happens to the other 57%?
Released as heat
Glycolysis yields two molecules of pyruvic acid. What comes next?
Pyruvic acid is converted into two molecules of Acetyl CoA
The Krebs Cylce begins and ends with ________, allowing it to repeat over and over again
Oxaloacetic acid
What happens in the Kreb’s Cycle?
The Acetyl portion of Acetyl CoA is degraded to CO2 and H+ by the addition of H2O
2 ATP are formed
Why does cellular respiration result in CO2 formation?
At three points in the Decarboxylases cut CO2 from a substrate to release
For each two electrons that pass through the entire electron transport chain, up to _____ ATP molecules are synthesized
three
Fill in the numbers:
_____ hydrogen atoms are released during glycolysis and the citric acid cycle. _____ of these are oxidized, with the release of ____ ATP molecules per ____ atoms of hydrogen metabolized, yielding ______ ATP molecules
24
20
3
2
30
How many ATP are formed from each molecule of glucose degraded to carbon dioxide and water?
38
How does ATP control energy metabolism?
How do ADP and AMP?
It inhibits phosphofructokinase, which catalyzes one of the initial steps in the glycolytic cycle
ADP/AMP have the exact opposite effect on phosphofructokinase
What is the law of mass action?
As the end products of a chemical reaction build up in a reacting medium, the rate of the reaction decreases, approaching zero
What are the two end products of glycolysis?
What happens when they build up?
pyruvic acid
hydrogen (as H+ and NADH)
When they build up they bind react with eachother to form lactic acid
Why is it important that NADH and Pyruvic Acid react to form lactic acid in anaerobic states?
It allows for clearance of the end products of glycolysis in anaerobic states, when those products aren’t going on to be used by the Kreb’s Cycle
If they didn’t form lactic acid they would just sit there, and glycolysis reactions would come to a hault
What happens to lactic acid once oxygen is available again?
Where does this occur?
It’s reconverted to pyruvic acid + NADH + H
It’s immediately oxidized to form ATP
Once there’s excess ATP, the remaining pyruvic acid is converted back into glucose
IN THE LIVER
Which organ is particularly capable of converting lactic acid to pyruvic acid for energy?
the heart
occurs to a great extent during heavy exercise
when lactic acid is released into the blood from the skeletal muscles, the heart uses it as an extra energy source
What is the pentose phosphate pathway?
An alternative oxidation pathway that can provide energy independently of all the enzymes in the citric acid cycle
During pentose phosphate oxidation, hydrogen joins to _____ instead of NAD.
Why does that matter?
NADP
Only hydrogen bound to NADP can be used for the synthesis of fats from carbohydrates
The Pentose Phosphate Pathway uses the energy in the glucose molecules not for the formation of ATP, but for:
the formation and storage of fat in the body
The body stores enough glycogen to last how long?
What happens to the rest?
12-24 hours
converted to fat in the liver and stored as fat in fat cells
What happens when normal quantities of carbs are not available to the cells?
Anterior pituitary secretes ACTH
adrenal cortex releases cortisol
cortisol mobilizes proteins from all the cells of the body, making these proteins available in the form of amino acids
these amino acids are deaminated in the liver and are converted into glucose
Neutral fats are also known as:
triglycerides
There are three kinds of lipids. Which ones contain fatty acids?
Triglycerides and phospholipids
cholesterol does not
Triglycerides are primarily used for ______
Cholesterol and phospholipids are used for ______
provide energy for metabolic processes
form the membranes of all cells and perform cellular functions
A triglyceride is three _____ bound to one ______
long-chain fatty acids
glycerol
What are the three most common human triglycerides?
Stear acid
Oleic Acid
Palmitic Acid
Describe the transport of triglycerides from the GI tract to the blood
broken down into monoglycerides and fatty acids
converted back into new molecules of triglycerides in the epithelial cells
Formed into chylomicrons
transported through the lymph into thoracic duct and into the venous circulation
What is the half life of a chylomicron?
Less than an hour
How are most chylomicrons absorbed from the blood stream?
removed by adipose tissue, skeletal muscle, and cardiac muscle
tissues produce lipoprotein lipase which sits on the surface of capillary endothelial cells and sticks to any circulating chylomicrons
How do adipose cells know when to release fatty acids into the blood stream?
- alpha glycerophosphate is a breakdown product of glucose that is requred to maintain triglycerides. When glucose is low, this product is also low and triglycerides start to fall apart (hydrolyze).
- Endocrine activation can cause cellular lipase to hydrolyze triglycerides
What happens when fatty acids enter the plasma?
They ionize
ionic portion binds with albumin (these are called free fatty acids)
other fatty acids circulate as esters of glycerol, cholesterol, or others
Any condition that increases the rate of fat utilization also increases ___________ in the blood.
What conditions would this include?
free fatty acid concentration
DM, starvation
When all the chylomicrons have been cleared from the plasma, 95% of all lipids in the plasma are in the form of _________
small lipoprotein
particles containing triglycerides, cholesterol, phospholipids and protein
(Chylomicrons are very, very large lipoproteins)
How are lipoproteins classified?
By their density
Define the following:
VLDL
IDL
LDL
HDL
VLDL: mostly triglycerides
IDL: VLDLs from which some triglycerides have been removed, so the concentrations of cholesterol and phospholipids are increased
LDL: almost all triglycerides removed, leaving especially high concentration of cholesterol and phospholipids
HDL: high concentration of protein and very little cholesterol and phospholipids
Where are lipoproteins (other than chylomicrons) formed?
In the liver
Large quantities of fat are stored in which two tissues?
Adipose and the liver
How are fatty acids and glycerol used for energy in cells?
Fatty acids are broken down and oxidized in the mitochondria, formed into Acetyl CoA which enters the citric acid cycle
Glycerol is converted to glycerol-6-phosphate and enters glycolysis
Why does fat oxidation produce so much more ATP than glucose?
Way more hydrogen is released during the breakdown of stearic acid into acetyl coA
A total of 148 molecules of ATP are formed during the complete oxidation of 1 molecule of stearic acid
The net gain is 146
When the liver breaks down lipids and produces more acetyl CoA than it can use, what happens?
Two molecules of the Acetyl CoA condense to form on molecule of acetoacetic acid
Acetoacetic acid is transported in the blood to other cells that can use it for energy
Some of the acetoacitic acid produced in the liver is converted to ______ and _____
Beta hydroxybutyrate
Acetone
Acetoacetic acid is a _______ acid
keto
made of three ketone bodies
What is the rate limiting reaction in cellular ketone usage?
oxaloacetate is required to bind acetyl-CoA before it can enter the citric acid cycle
oxaloacetate is derived from carb breakdown
deficiency of oxaloacetate limits how much acetyl CoA can be used in the the citric acid cycle
Why is it so important that the body be able to store excess glucose as fat?
cells don’t have that much capacity to store glycogen (a few hundred grams)
But adipose tissues can store pounds and pounds of fat
In the average person, the amount of energy stored as fat is _______ that the amount of energy stored as carbohydrates
150x greater!
How does insulin impact fat synthesis?
If insulin is absent, fats are poorly synthesized
glucose can’t enter the fat and liver cells
lack of alpha glycerolphosphate makes it diffuclt to form triglycerides
Why is hyperglycemia fat sparing?
Excess alpha glycerophosphate makes hydrolysis of fats almost impossible
when carbs are available in excess, fatty acids are synthesized more rapidly than they are degraded
The most darmatic increases in fat utilization is seen when?
During exercise, due to norepi and epi from adrenal medullae
activate hormone-sensitive triglyceride lipase
Non-exercise stress has the same effect
Which two hormones are said to have a ketogenic effect?
Why?
Increases lipolysis by releasing ACTH
ACTH stimulates glucocorticoid release from adrenal cortex
Both ACTH and glucocorticoids activate the same hormone sensitive triglyceride lipase that NE and Epi do
In Cushings, when ACTH and glucocorticoids are extremely high, fats are mobilized to the point of ketosis
All phospholipids bear what characteristics?
all lipid soluble
all transported in lipoproteins
all used throughout the body for structural purposes
Phospholipids always contain ____ and ____
one or more fatty acid molecules
one phosphoric acid radical
usually also contain a nitrogenous base
Where are phospholipids synthesized?
essentially all cells in the body, but 90% in the liver
What are the uses of phospholipids? (5)
- essential component of lipoproteins
- Thromboplastin is composed of cephalin
- Sphingomeylin is an electrical insulator in myelin sheaths
- donate phophate radicals for chemical reactions in tissue
- structural formation in the cell
What happens to lipid transport when phospholipids are absent?
seriously abnormal
lipoproteins can’t form without phospholipids
The basic structure of cholesterol is:
sterol nucleus
multiple molecules of acetyl-CoA
Why doesn’t plasma cholesterol increase dramatically with cholesterol ingestion?
high levels of cholesterol inhibit
3-hydroxy-3-methylglutaryl CoA synthase
if plasma cholesterol is high, liver synthesis of cholesterol is inhibited
A diet high in cholesterol doesn’t spike cholesterol levels. A diet high in ______ does.
saturated fats
increased fat deposition means more acetyl-CoA for production of cholesterol, bypassing the normal feedback
Ingestion of ________ fat actually depresses blood cholesterol concentration
unsaturated
we actually have no idea why
Lack of which hormones increases blood cholesterol concentration?
insulin and thyroid hormone
What is the function of cholesterol in the body?
Forms cell membranes
80% is converted into cholic acid in the liver, which is conjugated to form bile salts
Hormone formation
Deposits in skin to help protect the skin from water evaporation
The ratio of _________ determines the fluidity of cell membranes
cholesterol to phospholipids
What’s the difference between arteriosclerosis and atherosclerosis?
atherosclerosis is the deposition of fatty lesions in large and intermediate arteries
arteriosclerosis is the thickening and stiffening of any blood vessel, regardless of size
When vascular endothelium is injured, ________ cells aggregate on the blood vessel and form fatty streaks
macrophage foam
What is the pathogenesis of familial hypercholesterolemia?
defective genes for formation of LDL receptors on cell membranes
Without these receptors the liver can’t absorb IDLs or LDLs
Since these lipoproteins can’t be detected by the liver, it cranks out VLDLs because the liver thinks fat levels are low
What kills people with familial hypercholesterolemia?
if untreated, die by age 30 of atherosclerosis MI
How do HDLs protect against atherosclerosis?
may absorb cholesterol crystals that would otherwise be deposited
may inhibit oxidative stress and prevent inflammation
when a person has a high ratio of ______ to ____ the likelihood of developing atherosclerosis is reduced
HDL
LDL
BUT exogenously increasing HDLs doesn’t really reduce the risk of cardiovascular disease
How are amino acids taken up by cells?
They are too large to diffuse
have to have facilitated or active transport
When are amino acids excreted?
When there are more amino acids in the kidney that there are active transport proteins
How are amino acids stored in cells?
As rapidly-exchangeable proteins, never as free amino acids
_____ and ____ hormones increase the formation of tissue proteins
_____ hormones increase the concentration of plasma amino acids
GH and insulin
adrenocortical glucocorticoids
The major types of protein present in the plasma are:
Albumin
Globulin
Fibrinogen
What are essential and non-essential amino acids?
Amino acids that cannot be synthesized by the cells
refers to amino acids that are essential to the diet
Non-essential amino acids are essential to cellular function, but not essential in the diet because they can be synthesized
Without Vitamin ______, amino acids are poorly synthesized and protein formation cannot proceed
Vit B6 (pyridoxine)
Degradation of amino acids occurs in the ________ by a process called _______
liver
deamination
Describe deamination
amino group from amino acid is transferred to alpha ketoglutaric acid
this forms glutamic acid
flucatmic acid transfers the amino group to another substance or releases it as ammonia
when the amino group is removed, glumatic acid because alpha ketoglutaric acid again and can pick up another amino acid
All urea formed in the body is formed in the ________ by _______
liver
deamination
Why is it important to check an ammonia level, not just BUN?
The BUN only tells you excretion (if something is wrong with the kidney)
If the liver is malfunctioning, ammonia isn’t being processed into urea, so the BUN may not be that elevated
Deaminated alanin is ______
why is this important?
pyruvic acid
This is how the body uses proteins to make energy
The conversion of amino acids into glucose is called ______
the conversion of amino acids into keto acids is called ______
gluconeogenesis
ketogenesis
How many types of amino acids are there?
20
10 essential
10 nonessential
18 can be converted into glucose
19 can be converted into fatty acids
A minimum of 60-75 g proteins is recommended each day. Why?
When you don’t eat protein, body proteins will be degraded
the body has an obligatory loss of about 20-30 g protein each day, so you have to eat more than that to make sure you’re not losing net proteins
Growth hormone _______ the synthesis of proteins
increases
What is the effect of insulin deficiency on protein synthesis?
Insulin is required for protein synthesis
accelerates the transport of amino acids into the cell and reduces protein degradation by increasing the availability of glucose
total lack of insulin reduces protein synthesis to zero
Cortisol ________ plasma amino acid concentration
increases
encourages the breakdown of cellular proteins
ATP is generated by _______
combustion
What is the role of phosphocreatine in the body?
It holds high-energy phosphate bonds (more so even than ATP)
It can’t interact with cellular functions directly, but it can interact with ADP
When there’s excess ATP, phosphate is bound to phosphocreatine
When ATP stores are low, phosphocreatine releases these phosphate to form ATP+creatine
The best source of energy during anaerobic conditions is:
stored glycogen, NOT circulating glucose
Glucose brought into the cell has to be phosphorylated before it can be put into glycolysis, using ATP and decreasing the net ATP gain. Glycogen does not.
Anaerobic exercise is derived from:
glycolysis
What happens to lactic acid once exercise is over?
4/5 of it is converted into glucose
the rest becomes pyruvic acid and is sent into the citric acid cycle
After we quit exercising, we still breathe hard for quite a while. Why?
Your body is “repaying the oxygen debt”:
the extra oxygen is used to convert lactic acid into glucose
convert AMP/ADP to ATP
Convert creatine and phosphate to phosphocreatine
re-establish normal concentrations of Hgb binding
raise O2 concentration in the lungs to its normal level
What is the major rate-limiting factor for almost all energy metabolism in the body?
ADP concentration
How is metabolic rate normally expressed?
In terms of the amount of heat liberated during chemical reactions
How much energy in the body is eventually converted to heat?
Pretty much all of it
Even energy that’s expended as muscle movement causes friction between muscles, which generates heat
What is a calorie?
What is a Calorie?
quantity of heat required to raise the temperature of 1g of water by 1 degree C
a kilocalorie (1000 calories)
What are the four categories of energy output?
- Basal metabolic rate
- physical activity
- digestions
- maintaining body temp
At rest, skeletal mm accounts for __% of BMR
20-30
