Chapter 24- Metabolism Flashcards
Nutrients definition
Any substance the body uses for growth, repair, maintenance
Macronutrients
Carbohydrates, lipids, proteins- make up most of our diet
Micronutrients
Vitamins and minerals- only required in minute amounts
Sources of carbohydrates in the diet
Mostly plants, but also dairy (lactose) and meats (glycogen)
Uses of carbohydrates (3)
- ATP production by body- monosaccharide molecule glucose used
- Nucleic acid synthesis with pentose sugars
- Glycocalyx formation
How much carbohydrates are recommended?
Recommended- 45-60% of daily caloric intake
Complex carbohydrates
Grains and plant based sources that are unprocessed, nutrient rich
Empty carbohydrates
Processed sugars (soda, candy, etc) offers little nutritional value
Types of lipids (2)
- Triglycerides
2. Cholesterol
Types of triglycerides (2)
- Saturated
2. Unsaturated
Where are saturated triglycerides found?
meat, dairy, margarine, etc
Where are unsaturated triglycerides found?
nuts, seeds, olive oil, etc
Where is cholesterol found?
85% produced by the liver regardless of lipid intake. Remaining 15% comes from meat, eggs, dairy, etc
Uses of lipids (4)
- Used to build adipose tissue
- Phospholipids used for cell membranes
- Bile salt, steroid hormones, and other molecule construction
- Absorbing fat soluble vitamins
Functions of adipose tissue (2)
- Insulating, retains body heat- found around internal organs
- A concentrated energy source the body can rely on if you haven’t eaten.
Steroid hormones
Testosterone and estrogen
How much lipids are recommended?
Recommended 20-35% total daily intake
Why should saturated fat and cholesterol intake be limited?
Fats stick to inside of blood vessels, builds up and causes atherosclerosis, forcing the heart to work harder. If it happens in coronary blood vessels, can cause a heart attack
Sources of protein (2)
- Complete proteins- meet all the body’s amino acid requirements
- Incomplete proteins- are short 1 or more amino acid
Where are complete proteins found? (4)
egg, meat, dairy, fish
Where are incomplete proteins found? (3)
seeds, nuts, legumes. Exception- soybeans
Uses of protein (2)
- Structural molecules
2. Functional molecules
Which structural molecules are made of proteins?
Ex- keratin, collagen, elastin, muscle protein- help to build other molecules. Keratin makes the skin tough and dry, elastin lets tissues stretch
Which functional molecules are made of proteins?
enzymes, hormones
How much protein is recommended?
.8 grams per kg body weight, this is on an individual basis. Depends on an individual’s dietary needs and their nitrogen balance
Nitrogen balance
When the rate of protein synthesis equals the rate of protein breakdown in the body
Positive nitrogen balance
When protein synthesis is greater than protein breakdown. Ex- growing children, pregnant women, tissue repair
Negative nitrogen balance
When protein breakdown is greater than protein synthesis. Ex- stress, low protein content or quality in diet, starvation
When are amino acids not used by the body? (3)
- Inadequate dietary intake
- Insufficient amino acid supply
- Hormonal control
How does inadequate dietary intake prevent amino acids from being used?
being short of carbohydrates or fats forces the body to use proteins for energy source (skeletal muscle tissue)
How does inadequate amino acid supply prevent amino acids from being used?
All amino acids must be present to build a particular protein. If one or more is missing, or if there is not enough of one type of amino acid, the rest are used for energy (all or none rule)
How do hormones affect amino acid use?
Anabolic hormones promote protein synthesis and growth, adrenal glucocorticoids promote protein breakdown
Importance of vitamins
vitamins act as coenzymes- assist enzymes in accomplishing various tasks
Sources of vitamins (2)
- Made by the body- vitamin D (in skin), vitamin K and some vitamin B (some bacterial flora)
- Diet
Types of vitamins (2)
- Water soluble (B and C)- have to be absorbed with water because they dissolve in it
- Fat soluble (A, D, E, K)
Sources of minerals
Primary sources- legumes, vegetables, dairy
Function of minerals
Primary function is structural. Others are bound to organic compounds- creates phospholipids, hormones, several different proteins
Why is balance between uptake and excretion necessary with minerals?
Like fat soluble vitamins- toxic overload can occur. Can be poisoned by bringing in too many minerals. Ex- iron overdose, low iodine intake and goiters (swelling of thyroid), high sodium intake and fluid retention
Metabolism definition
The sum of all the chemical reactions occurring in the cells of the body used to provide energy for vital processes synthesizing new material
Anabolic metabolic reactions
building larger, more complex molecules/structures from their smaller subdivisions
Catabolic metabolic reactions
Any reaction that breaks down larger molecules into smaller ones. Cellular respiration is a group of reactions that form ATP from the breakdown of food fuels (glucose).
Oxidation-reduction reactions are attributed to
The breakdown of glucose
Oxidation
The gain of oxygen or the loss of hydrogen (electron). An oxidized substance always loses electrons. Oxygen is electronegative and will attract electrons
Reduction
The gain of electrons. This process is coupled with oxidation- when one substance loses an electron, another must gain the electron. A reduced molecule becomes more negative
Redox reactions are catalyzed by
Enzymes and coenzymes- they are specific to the reaction being carried out. Most enzymes derived from B complex vitamins
Importance of coenzymes in redox reactions
Enzymes can remove hydrogen atoms, but they cannot hold it or bond it- removed hydrogens transferred to coenzymes
Important coenzymes in redox reactions (2)
- Nicotinamide adenine dinucleotide (NAD+)- derived from niacin
- Flavin adenine dinucleotide (FAD)- derived from riboflavin (B complex vitamin)
What source is preferred for ATP production?
Glucose. All carbohydrates brought into the body will eventually be converted into glucose
Once inside the cell, glucose is converted to
glucose-6-phosphate
Normal glucose level
90-120 grams per deciliter of blood
Substrate level phosphorylation
The direct transfer of a phosphate group to an ADP molecule. Glycolysis and citric acid cycle- net gain of 4 ATP
Oxidative phosphorylation
The transfer of a phosphate group to an ADP molecule by the oxidation of food fuels and transfer of electrons. Electron transport chain- 28 ATP
A single glucose molecule yields how many ATP?
32
Glucose oxidation reaction
C6H12O6 + 6O2 yields 6H2O + 6CO2 + 32 ATP + heat
3 sequential pathways of glucose breakdown
- Glycolysis
- Citric acid cycle (aka Krebs cycle)
- Electron transport chain (ETC) and oxidative phosphorylation
Where does glycolysis occur?
Cytosol of the cell
Glycolysis reactants
Glucose. This is an anaerobic process- oxygen is not necessary for this reaction to take place
Glycolysis products (3)
- 2 pyruvic acid
- 2 NADH and hydrogen
- Net gain of 2 ATP
Glycolysis phase 1
Glucose is phosphorylated to produce fructose 1,6-bisphosphate, 2 ATP are used for this conversion
Glycolysis phase 2
Fructose 1,6 bisphosphate is split to form 2 carbon fragments
Glycolysis phase 3
4 ATP molecules are produced by oxidizing carbon fragments. 2 NAD pick up hydrogen- forms 2 NADH. 2 pyruvic acids produced
What happens to pyruvic acid formed during glycolysis?
Depends on oxygen availability. If oxygen is available- pyruvic acid pumped into the next pathway (citric acid cycle). If oxygen is not available- pyruvic acid converted to lactic acid. Some lactic acid pumped out of the cell, transported to liver for processing. Once oxygen becomes available again, lactic acid oxidized back to pyruvic acid and used in citric acid cycle
Where does the citric acid cycle occur?
The mitochondrial matrix
What occurs during the citric acid cycle?
One glucose molecule causes 2 turns of the citric acid cycle. Aerobic process- reaction requires oxygen to be completed. This reaction does not directly utilize oxygen, but products from citric acid cycle are used in ETC
Citric acid cycle reactants (4)
- Acetyl CoA (derived from pyruvic acid)
- Pyruvic acid is oxidized to form acetyl CoA
- 1 CO2 produced
- NAD+ converted to NADH
Citric acid cycle products (3- after one turn)
- 3 carbon dioxide molecules
- 5 reduced coenzymes: 4 NADH and hydrogen, 1 FADH
- 1 ATP
Where does the electron transport chain and oxidative phosphorylation occur?
Occurs in the inner mitochondrial membrane. Aerobic process- reaction directly utilizes oxygen
ETC/oxidative phosphorylation reactants (2)
- NADH + H and FADH from citric acid cycle
2. Oxygen
ETC/oxidative phosphorylation products (2)
- 28 ATP molecules
2. 6 water
What occurs during ETC/oxidative phosphorylation? (3 things)
- NADH and FADH are relieved of their hydrogen ions- NAD+ and FAD available again
- H+ pumped into intermembrane space to create a proton gradient
- H+ from proton gradient created by complex 5 (ATP synthase) to create ATP molecules
Why can’t your body utilize endless amounts of glucose to produce large quantities of ATP?
Rising intracellular ATP inhibits glucose breakdown- glucose is either stored as fat or converted. Three processes allow for glucose storage and access- glycogenesis, glycogenolysis, and gluconeogenesis
3 ways the body can store/access glucose
- Glycogenesis
- Glycogenolysis
- Gluconeogenesis
Glycogenesis
Glucose is converted to glycogen and stored in animal tissue. Skeletal muscle and liver most active in glycogen production and storage
Glycogen
polysaccharide stored in animal tissue (muscle tissue cells)
Glycogenolysis
Glycogen is converted to glucose 6 phosphate to be used for glycolysis. In skeletal muscle, glucose 6 phosphate cannot be released. In liver tissue, hepatocytes convert glucose 6 phosphate to free glucose. Liver can quickly release glucose to blood for use by other body tissues
Gluconeogenesis
Formation of glucose molecules from noncarbohydrate sources. Conversion of glycerol and amino acids to glucose
Importance of gluconeogenesis
Protective measure- prevents important, glucose hogging organs from experiencing low blood sugar. ATP synthesis can occur even in the absence of carbohydrate sources
Purpose of lipid metabolism
Use for energy production. Glycerol and fatty acids can be oxidized for energy- fat stores are concentrated sources of energy
During lipid metabolism, what are fatty acids and glycerol converted to?
Glycerol is converted to glyceraldehyde 3 phosphate-glyceraldehyde yields about 15 ATP. Fatty acids are converted to acetyl CoA
2 ways in which the body can store/access lipids
- Lipogenesis
2. Lipolysis
Lipogenesis
Synthesis of triglycerides (glycerol and fatty acid chains). Acetyl CoA and glyceraldehyde 3 phosphate accumulate, begin triglyceride synthesis to prevent excessive build up. Acetyl CoA join to form fatty acid chains and glyceraldehyde 3 phosphate to converted to glycerol
Lipolysis
Break down triglycerides to glycerol and fatty acids. Glycerol and fatty acids released to blood to be used for pathways
Amino acids can produce energy by (2)
- Degrading them into molecules that can be used in the citric acid cycle
- Converted to glucose
For the body to use amino acids for energy, what has to happen?
they must first have their amine group (NH2) removed
3 processes that can convert amino acids into useable energy source
- Transamination
- Oxidative deamination
- Modification of keto acids
Transamination
The transfer of an amine group to alpha ketoglutaric acid. Alpha ketoglutaric acid transformed to glutamic acid, amino acid transformed to a keto acid
Oxidative deamination
Amine group of glutamic acid from 1 is removed as ammonia. Ammonia is combined with carbon dioxide to form urea- excreted by kidneys. This step can regenerate alpha-ketoglutaric acid
Modification of keto acids
Keto acids formed in step 1 are altered. The products of this step can be used in the citric acid cycle- creates energy
Anabolic-catabolic balance
Molecules are constantly broken down and rebuilt
Absorptive state
Anabolic activity is greater than catabolic activity in the body, nutrient storage is occurring. Lasts about 4 hours after eating a meal- nutrients enter bloodstream from GI tract. Large amounts of glucose available for energy needs, amino acids used to build new protein molecules, fats used to build new triglycerides (adipose tissue) and other lipid molecules
Hormonal control of absorptive state
Insulin. Need hormonal controls, don’t want blood glucose to drop very quickly.
Effects of insulin (3)
- Diffusion of glucose into body cells increases (hypoglycemic hormone- lowers blood glucose levels).
- Uptake of amino acids increases- stimulates protein synthesis
- Prohibits gluconeogenesis and glucose export by liver. Have a lot of glucose coming in already, don’t need the liver to help. Blood glucose would increase drastically.
When is insulin released?
Beta cells of pancreas release insulin in response to increasing blood glucose and amino acid levels
Postabsorptive state
Catabolic activities are greater than anabolic activities in the body. Nutrients used to create energy, occurs when GI is completely empty- no absorption occurring. Importance- maintains blood glucose levels at a desirable level (about 110 g glucose/dL blood)
Sources of glucose in postabsorptive state (4)
- Liver- glycogenolysis begins
- Skeletal muscle- glycogenolysis begins
- Adipose tissue and the liver- lipolysis begins
- Cellular proteins (the last resort)
How are cellular proteins used as a source of glucose as a last resort?
Amino acids deaminated and converted to glucose in liver, kidneys eventually begin gluconeogenesis
Hormonal controls of the postabsorptive state (2)
- Glucagon
2. Epinephrine
Glucagon
Alpha cells of pancreas release glucagon in response to drop in blood glucose levels (hyperglycemic hormone- raises blood glucose levels). Glycogenolysis and gluconeogenesis in liver, adipose releases fatty acids and glycerol to blood
How does epinephrine influence the postabsorptive state?
The adipose tissue is supplied with sympathetic fibers. Epinephrine release mobilizes adipose tissue- promotes glycogenolysis
Metabolic functions of the liver
Glycogenolysis, gluconeogenesis, glycogen storage, fat storage, vitamin and mineral storage, and cholesterol metabolism
Transport of cholesterol
Cholesterol is insoluble in water. Cholesterol and lipoproteins aren’t the same thing- lipoproteins act as transport molecules for cholesterol. They transport cholesterol to and from body tissues
Lipoproteins
Transport cholesterol to and from body tissues, contain both fats and proteins. High lipid content= low density. High protein content= high density. There are 3 types
Very low density lipoproteins (VLDLs)
Most come from liver, transport triglycerides from liver to peripheral tissues
Low density lipoproteins (LDLs)
What remains after triglycerides are unloaded from VLDLs, transport cholesterol from liver to peripheral tissues. High LDL is not desirable (keep LDL low). 160+ mg/dl is not good
High density lipoproteins (HDLs)
Transport cholesterol from peripheral tissues to liver. Cholesterol is broken down in liver, used for bile. Provides steroid producing organs with cholesterol for hormone production. HDL is healthy, 60+ mg/dL is desirable
Regulation of blood cholesterol
Negative feedback loop between diet and liver. Intake of saturated and unsaturated fats influences cholesterol levels. Saturated fat intake stimulates cholesterol production by liver and inhibits its excretion- high saturated fat intake= higher blood cholesterol levels. Unsaturated fats stimulate catabolism to bile salts and its excretion- high unsaturated fat intake= lower blood cholesterol levels. Trans fat intake increases LDL and decreases HDLs
Other influences on blood cholesterol (3)
- Stress and smoking will lower HDL levels
- Regular exercise and estrogen will lower LDL- people with XX chromosomes produce more estrogen
- Body shape- “apple” shape prone to higher LDL and cholesterol levels than “pears”- apple shape means more fat along waistline, unclear why this happens
Energy balance
Energy released by catabolizing food molecules must be balanced by the total energy output of the body. In the body, energy intake= energy output. Each must be regulated to ensure this balance
Energy intake
energy liberated during food oxidation
Energy output
Energy used to do work, energy stored as fat or glycogen, or energy lost as heat. Heat cannot be used by the body for energy source, but it’s useful for warming tissues and blood and maintaining internal body temperature
Which region of the brain regulates and influences feeding behaviors?
Hypothalamus
Hunger promoting regions of hypothalamus
Arcuate nucleus (ARC)- NPY/AgRP neurons release neuropeptide Y and agouti-regulated peptide (AgRP)
Satiety promoting regions of hypothalamus
Arcuate nucleus- POMC (pro-opiomelanocortin)/CART (cocaine and amphetamine regulated transcript) neurons release peptides. These peptides cause the ventromedial nucleus (VMN) to release corticotropin releasing hormone.
Factors that provide short term regulation of food intake (3)
- Neural signals from digestive tract
- Blood levels of nutrients
- GI tract hormones
How do neural signals from the digestive tract regulate food intake in the short term?
Vagal nerve fibers carry information between brain and gut- allow brain to tell content of ingested foods and suppression of appetite via activation of stretch receptors
How do blood levels of nutrients regulate food intake in the short term?
Nutrient signals that suppress appetite include rising blood glucose, rising amino acid levels in blood, and fatty acid content of blood. Protein makes the vagus nerve send impulses to hypothalamus for longer, makes you feel food for a longer period of time
Appetite suppressing GI tract hormones (2)
- Insulin
2. Cholecystokinin (CCK)- blocks effects of NPY
Appetite stimulating GI tract hormones (3)
- Glucagon
- Epinephrine
- Ghrelin (Ghr)- hormone produced by stomach during fasting periods
Leptin
Hormone released long term by adipose tissue in response to increasing body fat stores. Allows the brain to keep track of how much total energy is stored in fat tissue. Rising leptin levels bind ARC, NPY release is inhibited, and stimulates CART. Leptin’s role is to prevent weight loss during a time of nutrient deprivation
Is leptin the solution to obesity?
No. Obese individuals have higher than normal leptin levels, but appear to be resistant to its effects. Leptin’s main role is to prevent weight loss during times of nutritional deprivation
Metabolic rate
The body’s rate of energy output, including the total heat produced by all chemical reactions and mechanical work of the body
Basal Metabolic Rate (BMR)
The energy the body needs to perform only its most essential activities. Includes breathing and resting level of organ function. Approximate BMR many different ways
Factors affecting BMR (5)
- Age- younger individuals tend to have higher BMR
- Gender- BMR is higher in males
- Body temperature- high body temp= higher BMR
- Stress- higher stress= higher BMR
- Thyroxine
How does thyroxine affect BMR?
Higher thyroxine release= higher BMR. Thyroxine causes increased oxygen consumption and heat production by accelerating ATP use. Thyroid hormones impact the metabolic rate
Total metabolic rate
The rate of calorie consumption needed to fuel all ongoing activities (involuntary and voluntary). Most of TMR comes from BMR
Factors influencing TMR (2)
- Skeletal muscle use can cause dramatic increases in TMR and heat production- TMR increases during physical activity, remains elevated several hours after
- Ingesting food increases TMR- food induced thermogenesis- heightened metabolic activity of digestive organs
Normal body temperature range
Normal body temperature ranges from 96-101. Fluctuates no more than 2 degrees during the day, lowest in morning, highest in early evening
How is most body heat generated?
At rest, most heat generated by liver, brain, heart, kidneys, endocrine organs. When active, skeletal muscle tissue can produce 30-40 times more heat than the rest of the body
Importance of maintaining body temperature
Metabolism and enzyme activity are linked to body temperature. Increasing body temperature increases metabolic rate and enzyme activity, while decreasing body temperature decreases metabolic rate
Core temperature
Temperature of organs within the skull and thoracic and abdominal cavities. This is the highest temperature of the body. Must be precisely regulated- if heat needs to be conserved, vasoconstriction occurs so that blood bypasses the skin
Shell temperature
Temperature of the skin- lowest temperature of the body. When blood bypasses the skin, shell temperature falls toward environmental temperature. This temperature varies substantially and doesn’t have an impact on internal body processes.
Heat exchange mechanisms (4)
- Radiation
- Conduction
- Convection
- Evaporation
Radiation
Loss of heat in the form of infrared rays- 50% of heat lost by body is by radiation. Heat can also be gained by radiation (via sunlight, etc)
Conduction
Transfer of heat between two objects that are in direct contact
Convection
Transfer of heat that occurs due to circulating air. Warm air expands and rises, cooler air is dense and falls. Air immediately surrounding the body is warmed, which then rises- continuously replaced by cooler air
Evaporation
The body is cooled as heat is absorbed by water to escape as gas. Insensible water loss- basal level of body heat due to continuous evaporation of water from the lungs, mouth, and skin. Sensible water loss- sweating
Thermoregulatory center of the hypothalamus is composed of (2)
- Heat promoting center- promotes creation of heat to increase body temperature
- Heat loss center
How does the hypothalamus receive information?
Peripheral thermoreceptors and central thermoreceptors send information about temperature to anterior portion of hypothalamus
Peripheral- found in the shell. Central- found in core, more important, send info about internal organ temp
When are heat promoting mechanisms stimulated?
Stimulated when blood temperature falls or external temperature is low
Heat promoting mechanisms (4)
- Vasoconstriction of cutaneous blood vessels- blood bypasses the skin
- Shivering- involuntary muscle contractions. Most important, provides the most heat overall
- Increase in metabolic rate- sympathetic stimulation increases. Epinephrine and norepinephrine enhance heat production by increase metabolic rate
- Thyroxine release
How does thyroxine release increase body temperature?
Increases metabolic rate- increases heat produced. Effect usually seen only in infants
When are heat loss mechanisms stimulated?
Stimulated when core temperatures rise
Heat loss mechanisms (2)
- Vasodilation of cutaneous vessels- blood floods to skin. Body loses heat by radiation, conduction, and convection
- Noticeable sweating- evaporation. Sympathetic fibers activate sweat glands to pour out larger volumes of sweat. This only works well in a “dry heat”- sweat won’t evaporate well in a humid environment
