Metabolism Flashcards
(147 cards)
What’s the significance for biological systems of the first law of thermodynamics?
Living organisms can convert chemical energy into mechanical energy and heat, but cannot destroy it.
- Thus, excess energy intake can only be stored as fat.
What are the units of energy?
Joule, but usually expressed as MJ or kJ
How can you measure the energy content of foods?
- Inc. steps taken to do this
By oxidising food samples in a bomb calorimeter.
- A measured amount of dry food is placed inside the calorimeter in an atmosphere of oxygen, and ignited
- The amount of heat released is measured by the increase in temperature of the water jacket and thus the heat of combustion is calculated
What are the Atwater Factors of the 4 fuel sources?
- Fat = 38kJ/g
- Carbohydrate = 17kJ/g
- Protein = 17kJ/g
- Ethanol = 29kJ/g
What are the 2 ways of measuring energy expenditure?
- How do they work?
- What do they use?
- Direct calorimetry
- Relies on measuring heat output from a person in a whole-body calorimeter - Indirect calorimetry
- Based on Oxygen consumption and CO2 Production
(certain amount of energy associated with every litre of O2 consumed)
- Measured using a respirometer
- Can calculate RER
What is RER?
- Equation
- Allows determination of?
- RER of carbs and fatty acids
- Respiratory exchange ratio
- CO2 produced / O2 consumed
- Allows determination of which fuel the body is using
- Carbs: RER = 1
- Fatty acids: RER = 0.7
What is basal metabolism?
What does it differs b/w individuals depending on?
- Energy required for maintenance of life; energy expenditure at rest
- Differs b/w individuals depending on:
Gender
Age
Body size/composition
Genetics
Hormonal status
Stress levels
Disease status
Certain drugs
Factors affecting basal metabolism?
Increased by: - Athletic training - Late pregnancy - Fever - Drugs (e.g. caffeine) - Hyperthyroidism Decreased by: - Malnutrition - Sleep - Drugs (i.e. B-blockers) - Hypothyroidism
Function of salivary glands
Produce saliva, which contains mucous and amylase which STARTS THE DIGESTION of CARBOHYDRATES
Functions of the stomach
- incl. what it secretes
- Storage and mixing of food w/ gastric juices
- Slow release of chyme into intestine
- Secretes acid (denaturing), pepsinogen (protein digestion) and mucous (protection)
Function of the pancreas
Secretes most digestive enzymes, incl. amylase, lipase, proteases
Function of the liver
Synthesis of bile salts/acids important for fat digestion
Function of small intestine
Final stage of digestion and absorption
2 general phases of digestion
- Hydrolysis of bonds connecting monomer units in food macromolecules (glycosidic, peptide, ester)
- Absorption of products from gut into body
Carbohydrate digestion process
- Intake of carbohydrates
- Salivary amylase catalyses the hydrolysis of the glycosidic bonds
- Pancreatic amylase completes the digestion of the starch molecule
- Enzymes hydrolyse disaccharides into monosaccharides (in SI) to be absorbed by intestinal epithelial cells
- Maltose and isomaltose —> glucose x2
- Sucrose —> glucose + fructose
- Lactose —> glucose + galactose - Fibre is excreted as faeces
Carbohydrate absorption process
- Glucose is absorbed through apical surface via symport with Na+ (secondary active transport)
- Glucose moves through basal membrane via facilitative transporter (conc. gradient)
The intracellular conc. of Na+ is kept low by Na+/K+ ATPase
Lactose intolerance:
- What is it?
- Caused by?
- What does it cause? why?
- How to manage
- Disorder affecting carbohydrate digestion
- Caused by a lactase deficiency
- Causes bloating, flatulence and diarrhoea, due to fermentation of lactose by intestinal bacteria
- Need to avoid lactose in diet
Coeliac Disease:
- What is it?
- Where in the body does it affect?
- Cause?
- Symptoms?
- Disorder affecting carbohydrate digestion
- SI
- Body reacts against gluten (wheat protein); antibodies react w/ transglutaminase; villi flattened, nutrients not absorbed
- GI symptoms (variable)
Why do we need dietary protein?
- Supplies AAs to make body proteins
- Source if Nitrogen for purines, pyrimidines and haem
- C skeletons can be used as fuel
General function of GI hormones
Control the secretion of digestive enzymes
What are the 3 main GI hormones and their function?
- Gastrin - stimulates the secretion of gastric juices
- Secretin - stimulates secretion of alkaline bile and pancreatic fluids (bicarbonate)
- Cholecystokinin (CCK) - stimulates the release of pancreatic enzymes and release of bile from the gallbladder
What is protease specificity determined by?
In terms of hydrolysis of proteins
AA side chains
Endopeptidases vs exopeptidases
Endo- attack peptide bonds w/in the peptide chain
Exo- attack peptide bonds at the end of the chain
Pepsin
- What is it
- Source
- Substrate
- Site of action
- Endopeptidase or exopeptidase?
- Enzyme involved in protein digestion
- Stomach
- Proteins and pepsinogen
- Stomach
- Endo