Lecture 10 : Gastrointestinal System IV : Nutrition and Metabolism I Flashcards
Nutrient =
substance in food the body uses to promote normal growth, maintenance and repair
Categories of nutrients (5):
Macronutrients = fats, carbohydrates and proteins (make up most of what we eat)
Micronutrients = vitamins and minerals (required in smaller quantities)
Essential nutrients =
body can’t make as fast as we need – must be obtained through diet
Nonessential nutrients =
also vital for normal functioning, but body can synthesize through interconversions of one type of molecule to another
The ______ regulates the Nutrition Facts label
U.S. Food and Drug Administration (FDA)
Nutrition labels help us understand:
types of nutrients included in a packaged food
recommended serving size
number of calories per serving
whether we’re getting enough of the nutrients our bodies need
(% daily recommendations)
Nutrition labels are based on basal metabolic needs of an average person =
~2000 Calories/day
The energy value of foods is measured in _____
kilocalories
1 kilocalorie =
energy to raise temperature of 1 kg water by 1 degree C
1 kcal = 1 calorie (from nutrition labels)
Nutrient content of foods:
Carbohydrates = 4 kcal/gram
Protein = 4 kcal/gram
Fats = 9 kcal/gram
Metabolic rate =
number of kcal used per hour
varies depending on multiple factors:
activity, hormones, age
Carbohydrates
Dietary Sources:
sugars
starch
glycogen
Sugars =
(mono- and disaccharides) - most from plants
Fruits, sugar cane, sugar beets, honey, (exception: milk sugar)
Starch =
(polysaccharides)
Grains & vegetables
Glycogen =
negligible amount from meats
GLUCOSE
the body’s main fuel source for ATP production
Brain and red blood cells use glucose for energy
Either used or stored (glycogen and/or fat)
Other monosaccharides converted to glucose in liver
Pentose sugars in RNA, DNA, sugars in glycocalyx
POLYSACCHARIDES as sources of fiber:
Insoluble fiber – cellulose from vegetables (roughage) : increase bulk of stool
Soluble fiber – pectin from apples, citrus : balances blood cholesterol, sugar
Dietary Considerations =
____ of total calorie intake – ideally complex carbohydrates
45-65%
Dietary Considerations =
Get plenty of fiber _____
(25-30 gm/day)
Dietary Considerations =
Highly processed carbohydrates (candy, soda) – concentrated energy source without ______
benefits of other nutrients (empty calories)
Proteins
Made from 20 amino acid building blocks
9 out of the 20 proteins are _______ because we can’t synthesize them
essential amino acids
Dietary Sources:
Complete proteins =
contain all the essential amino acids for tissue maintenance and growth
Eggs, milk, fish, most meats, soybeans
Dietary Sources:
Incomplete proteins =
(lack one or more essential aa)
Legumes (peas & beans), nuts, cereal grains
Use amino acids to build proteins or burn for energy depending on:
All or none rule – all necessary amino acids must be present to make a protein – unused aa oxidized for energy or converted to carbs or fats
Used for ATP production if not enough carb or fat calories in diet
Anabolic hormones stimulate protein synthesis & growth, stress hormones (cortisol) break down protein and convert amino acids to glucose
Nitrogen balance =
rate of protein synthesis equals rate of protein breakdown and loss (healthy adults)
Positive balance during growth, pregnancy; negative balance during stress, starvation
Will vary based on age, size, metabolic rate and need (state of nitrogen balance); generally _____ – need to get essential amino acids from diet
~0.8 gm/kg body weight
Gluten sensitivity – Celiac disease (genetic) =
gluten breakdown products stimulate immune cells that attack intestinal epithelium – damage villi, decrease surface area for absorption - leads to malabsorption
_____ the most abundant dietary lipid
Triglycerides
Structure of _____ determines whether are solids or liquids at room temperature
fatty acid chain
Body’s most efficient and compact form of stored energy
lipids
Saturated fats =
(more H atoms, single bonds, solid at room temp)
Meat, dairy, coconut, hydrogenated oils
(trans fats: margarine or solid shortening)
Unsaturated fats =
(one or more double bonds, oils – liquid at room temp)
Seeds, nuts, olive oil, vegetable oils
Cholesterol =
(not used for energy)
Egg yolk, meat, organ meat, shellfish, milk products
____ are good fuel sources and are critical for normal cell physiology
Lipids
lipid uses in the Body:
Protect from heat loss, cushion body organs, energy store
____ create myelin and cell membranes
Phospholipids
___ precursor to hormones, stabilizes cell membranes
Cholesterol
Triglycerides are major fuel source for ______
skeletal muscle & hepatocytes
Presence of fats in diet aids in absorption of_____
fat-soluble vitamins
Dietary Considerations:
____of total calorie intake should be lipids
20-35%
Saturated should be less than ___ of total fat intake
10%
Limit cholesterol in diet – _____ makes 85% of what we use
liver
Liver can’t make 2 essential FA:
linoleic acid (omega-6 FA)
linolenic acid (omega-3 FA)
___ is vital for the proper function of the human body
Cholesterol
Cholesterol -
Not used as energy source, but is important precursor molecule for:
- Bile salts
- Steroid hormones including:
testosterone
estrogen
aldosterone
cortisol - Vitamin D
Cholesterol is an integral part of __________
plasma membranes
15% of blood cholesterol comes from _____
diet
85% of blood cholesterol is synthesized by _____
liver
Cholesterol is broken down by liver and excreted in ____
bile
Recommended total blood cholesterol =
< 200 mg/dl
high cholesterol is correlated with:
atherosclerosis, strokes and heart attacks
how cholesterol is packaged in blood is more important clinically as predictor of ______
cardiovascular health
“good” cholesterol
HDL > 60 mg/dl is protective
“bad cholesterol”
LDL > 160 mg/dl is undesirable
_____ are considered a better predictor of cardiovascular disease
LDL levels
_____ :cholesterol lowering drugs routinely prescribed for cardiovascular health
Statins
Lipoproteins =
triglycerides and cholesterol are both insoluble in water, so transported in blood by lipid-protein complexes called lipoproteins which vary in structure and function
have varying amounts of phospholipids & proteins in their structure – accounts for “density”
Chylomicrons =
transport digested fats to liver
Very low-density lipoproteins – carries triglycerides from liver to adipose tissue
Low-density lipoprotein (LDL) =
carries cholesterol from liver to tissues
High-density lipoprotein (HDL) =
carries cholesterol from tissues to liver for breakdown; also prevents cholesterol from accumulating on artery walls
Diet and lifestyle can influence ____ levels
cholesterol
___ continues to make cholesterol, even when present in diet
Liver
________ in diet stimulate liver synthesis of cholesterol and inhibit its excretion from body
Saturated fats
_____ enhance excretion of cholesterol and conversion to bile salts, so decrease total cholesterol levels
Unsaturated fats (olive oil, most vegetable oils)
Trans fats (hydrogenated oils) _____ LDLs and _____ HDLs
increase
decrease
Cigarette smoking and stress ___ HDL levels
lower
Aerobic exercise ____ HDL levels
increases
Vitamins =
Required in small amounts for growth and good health
Serve as co-enzymes in metabolic reactions
Balanced diet best way to ensure adequate intake
Co-enzymes =
act with enzymes to accomplish a chemical task
Most vitamins are not made by body – must be ingested through food or supplements:
Exceptions: vitamin D made in skin; some B vitamins & vitamin K – gut bacteria
Body can convert beta-carotene into vitamin A
Water soluble vitamins =
B complex vitamins and vitamin C
Absorbed in intestines
Exception: Vitamin B12 – intrinsic factor complex binds to receptor
Not stored, excess excreted in urine
Fat soluble vitamins =
Vitamins A, D, E and K
Absorbed with dietary lipids in gut
Are stored in body (except vitamin K)
Excess can result in toxicity
Most minerals are ionized in body fluids or bound to organic compounds to form _____
phospholipids, hormones and various proteins
Best sources of minerals:
legumes, vegetables, milk, some meats
____ is the sum of all biochemical reactions in the body
Metabolism
Two classes of Metabolic Processes :
Anabolism
Catabolism
Anabolism =
reactions that build larger molecules from smaller ones
e.g. combining individual amino acids to make proteins
Catabolism =
processes that break down complex structures to simpler parts
e.g. hydrolysis of foods in GI tract
e.g. glycolysis : breakdown of glucose for ATP production
Nutrients are involved in ______ reactions
both anabolic and catabolic
Anabolic processes build:
Proteins
Glycogen
Triglycerides
Catabolic processes include:
Glycolysis
Citric Acid Cycle
Oxidative Phosphorylation
_____ is the pivotal fuel molecule in the ATP producing pathways
Glucose
1) Glycolysis
Glycolysis, in the cytosol, breaks down each glucose molecule into two molecules of pyruvic acid
2) Citric Acid Cycle
Pyruvic acid then enters the mitochondrial matrix, where the citric acid cycle oxidizes it to CO2
substrate-level phosphorylation forms small amounts of ATP
3) Electron Transport Chain & Oxidative Phosphorylation
Energy-rich electrons picked up by coenzymes are transferred to the electron transport chain, built into the inner mitochondrial membrane
electron transport chain carries out oxidative phosphorylation, which generates most of the ATP in cellular respiration
Two techniques are used for ATP synthesis:
substrate-level phosphorylation
oxidative phosphorylation
substrate-level phosphorylation:
a high-energy phosphate group is transferred directly from a substrate to ADP to form ATP
occurs in the cytosol and mitochondrial matrix
oxidative phosphorylation:
electron transport proteins “pump” protons = creating a proton gradient
ATP synthases uses the energy of the proton gradient to bind phosphate groups to ADP
occurs only in the mitochondrial matrix
_____ play a key role in metabolism
Coenzymes
Two key coenzymes (derived from the B vitamins niacin and riboflavin) serve as carriers of high energy electrons for oxidative phosphorylation:
Nicotinamide adenine dinucleotide (NAD+)
Flavin adenine dinucleotide (FAD)
Coenzymes play a role in Oxidation-Reduction (Redox) Reactions:
Oxidation –can be defined as the gain of oxygen or loss of hydrogen; when a substance is oxidized, it loses electrons (loses energy) as they move to a substance that more strongly attracts them
Reduction – when a substance gains electrons (gains energy) it is said to be reduced
Glycolysis converts one glucose molecule into
______
2 pyruvic acid molecules
____ does not require oxygen: ____ process so occurs whether or not oxygen is present
Glycolysis
anaerobic
Glycolysis phases =
Phase 1 uses energy (2 ATP):
Phase 2 forms 2 3-carbon molecules
Phase 3 transfers hydrogen with high energy electrons to coenzyme carriers and forms 4 ATP
Yield from 1 glucose molecule:
2 pyruvic acid molecules (C3H4O3)
2 net ATP molecules
2 reduced coenzymes: 2 X (NADH + H+)
Anatomy of a mitochondrion
Two “compartments”:
Intermembrane space : between inner and outer membranes
Mitochondrial matrix : inside inner membrane
The ____ occurs in the mitochondrial matrix
citric acid cycle
also called TCA cycle or Kreb’s cycle
citric acid cycle
If oxygen present, pyruvic acid enters the mitochondria
Pyruvic acid converted to acetyl CoA
Coenzyme A is another coenzyme derived from a B vitamin – it is used to shuttle 2-carbon acetic acid into citric acid cycle
Reactions during this process (citric acid cycle):
removal of carbon which is released as carbon dioxide (CO2 )
formation of more reduced coenzymes
PO4 passed from GTP to ADP (substrate level phosphorylation)
Glucose formed 2 pyruvic acid molecules and each goes through the cycle, so total yield from 1 glucose:
6 CO2
10 reduced coenzymes
2 ATP molecules
Energy carried by reduced coenzymes is harvested at the _____
electron transport chain
The electron transport chain is a series of______
proteins on the inner mitochondrial membrane
Coenzymes from glycolysis and the citric acid cycle get ____ here when their hydrogen is stripped off at electron transport chain
oxidized
Each hydrogen atom is then split into a _____
proton (hydrogen ion, H+) and an electron
electron transport chain =
Electrons are passed down the chain, with a stepwise reduction in energy along the way
The released energy is used to pump protons into the intermembrane space
Electrons are combined with oxygen and hydrogen ions to form water
Oxygen is required for this to happen
Activity of the electron transport chain leads to the creation of a:
proton gradient across the inner membrane
Proton movement down its gradient drives _____
ATP synthesis
protons move down their gradient through a membrane protein coupled to a rotary motor called _____
ATP synthase
The spinning rotor catalyzes the binding of ADP and Pi to form ___
ATP
Oxidative Phosphorylation:
Oxidation of coenzyme carriers is coupled to phosphorylation of ADP to create ATP
Oxidative Phosphorylation
Steps:
1) Reduced coenzymes (NADH+ H+ FAH2) deliver electrons to respiratory enzyme complexes I and II
2) the electrons are transferred from one complex to another in the membrane (each complex is reduced and then oxidized)
3) at respiratory enzyme complex IV, electron pairs combine with two protons (H+) and a half molecule of O2, forming water
4) ATP synthase (complex V) harnesses the energy of the proton gradient to synthesize ATP.
As H+ flows back across the membrane through ATP synthase, the synthase rotor spins, causing Pi to attach to ADP, forming ATP
one glucose molecule yields about ____ following oxidative phosphorylation
30 ATP
To fully utilize protein or fat as an energy source, we have to convert it into a substrate utilized by the ____
mitochondria
