Metabolism Flashcards
What are the two control centres in the hypothalamus in terms of feeding?
- feeding centre
- satiety centre
What is the Glucostatic theory?
Regulation of food intake
- Glucose metabolism by hypothalamic centers regulates food intake
What is the lipostatic theory?
- signals from fat stores to the brain modulate eating behaviour to maintain a particular weight
- Leptin, neuropeptide Y, ghrelin, CCK, GLP-1, orexins
What is sensory input from the nervous system in regards to food intake?
Psychological factors, stress
What is direct calorimetry?
- measures energy content of food in kilocalories
- metabolic energy slightly less because foods not fully digested
What is indirect calorimetry?
- estimates metabolic rate as a measure of energy expenditure: oxygen consumption, CO2 production, ratio of CO2 to O2 (Respiratory quotient RQ, respiratory exchange ration (RER)
What six factors affect metabolic rate?
- Age and sex
- Amount of lean muscle mass
- Activity level
- Diet and diet-induced thermongenesis
- Hormones
- Genetics
What are the three places digestion and metabolism take place?
- GI tract
- Tissue cells
- Mitochondria
What are the three possible uses for ingested biomolecules
- Energy to do mechanical work
- Synthesis for growth and maintenance
- Storage as glycogen or fat
What are nutrient pools?
- available for immediate use in plasma
- Free fatty acids pool
- Glucose pool
- amino acid pool
How is the glucose pool regulated?
- tightly regulated
- Glycogenesis and lipogenesis
What is glycogenesis?
- synthesis of glycogen from glucose
- occurs when glucose supplies exceed demand for ATP
what is gluconegenesis?
synthesis of glucose from a precursor other than carbohydrate
How do enzymes control the direction of metabolism?
Through push-pull control
What is the livers role in metabolism?
- intestinal blood supply flows directly to liver: gets all nutrients/metabolites
- Linked closely to pancreatic blood supply: insulin/glucagon hormones exert their effects in the liver first
- stores glucose as glycogen
- can synthesise “new glucose”
- can synthesise ketones
- can synthesise lipids
What is glycongenolysis
- breaks down glycogen to release glucose
- stimulated by low blood glucose
How does muscle tissue affect metabolism?
- utilises glucose as energy source during fed state and activity, utilises lipids as energy source during fasting
- stores glucose as glycogen - only be used by muscle cells
What is adipose tissues effect of metabolism
Key metabolic regulator of lipid storage and release
- stores fatty acids as triglyceride
- releases fatty acids
What is the brains effect on metabolism?
HIGH METABOLIC RATE
- high blood supply
- depends almost entirely of glucose
- oxidises about 120g of glucose per day
Describe the kidneys role in metabolism
- produce urine, maintaining osmolarity and pH of the body fluids
- consume 10% of oxygen used in cellular respiration = needed for reabsorption
- filters urea out
- recovers metabolites such as glucose
Explain the three factors of push-pull control
a) without regulation of enzymatic activity, the pathway will simply cycle back and forth. There is no ney synthesis of substrate A or B
b) in fed-state metabolism under the influence of insulin, enzyme activity for the forward reaction increases. Enzymes for glycogen breakdown are inhibited. Net glycogen synthesis results
c) in fasted-state metabolism under the influence of glucagon, ensymes that break down lgycogen are more active, and enzymes for glycogen synthesis are inhibited. Net glucose synthesis results.
What are anabolic pathways?
ENDERGONIC REACTION
Anabolic pathways synthesise larger molecules from smaller constituent parts, using ATP as the energy source
- fed state, or absorptive state
What are catabolic pathways?
EXERGONIC REACTION
Catabolic pathways are break larger molecules such as carbohydrates, lipids and proteins from ingested food into smaller parts
- fasted state, or postabsorptive state
What are exergernic reactions?
reactions that release energy because the products have less energy than the reactants
What is metabolism?
the sum of all reactions in the body:
metabolism = catabolic reactions + anabolic reactions
What are enzymes
- Enzymes speed up the rate of chemical reactions
- catalysts
- reactants are called substrates
- mostly proteins
- Isozymes
- catalyze same reaction, but under different conditions
- diagnostic enzymes
- may be activated or inactivated or modulated
- coenzymes (e.g. vitamins)
- chemical modulators > temperature and oH
- enzymes lower the activation energy of reactions
How do cells regulate their metabolic pathways?
- Controlling enzyme concentrations
- Producing modulators that change reaction rates: feedback inhibition
- Using different enzymes to catalyze reversible reactions
- Compartmentalizing enzymes within organelles
- Maintaining optimum ratio of ATP to ADP
What controls reversibility of metabolic reactions?
Enzymes
Explain some factors of reversible reactions
- some reversible reactions use one enzyme for both directions
- reversible reactions requiring two enzymes allow more control over the reaction
Explain a factor of irreversible reactions
- irreversible reactions lack the enzyme for the reverse direction
Explain how ATP transfers energy between reactions
- high-energy phosphate bond
- aerobic metabolism
- anaerobic metabolism
- catabolic pathways produce ATP: glycolysis, citric acid cycle, electron transport chain
What does ATP supply energy for?
- Synthesis to make macromolecules
- Transport
- Muscle contractions and cellular motility
How does cellular respiration to ATP
Oxidises glucose molecules to produce ATP through:
- glycolysis
- krebs cycle
- oxidative phosphorylation
How much ATP approx. comes from glucose?
30-32
What type of cellular respiration occurs outside the mitochondria?
Glycolysis
* glucose -> pyruvic acid
What types of cellular respiration occur inside the mitochondria
- citric acid cycle
- electron transport chain
Why does glucose produce more ATP than fat despite fat having higher calories?
It enters the metabolic reaction at a later state then glucose so produces less ATP
How many steps are there in a normal metabolic reaction?
3
Explain fed state metabolism in regards to carbohydrates and proteins
- glucose makes ATP
- excess is converted to: glycogen for short term storage, fat for long term storage
- amino acids assembled into proteins, amine hormones, neurotransmitters
- excess amino acids are converted to fat
Explain fed-state metabolism in regards to fats
- Chylomicrons leave intestine by the lymphatic vessels
- contains: cholesterol, triglycerides, phospholipids, apoproteins
- lipoprotein lipase convert triglycerides into glycerol and fatty acids
- excess cholesterol secreted in bile and blood as a lipoprotein complex
- complex with more protein is denser
- complexes enter cells by receptor mediated endocytosis
- cholesterol and other lipids can be synthesised from non-lipid precursors in fed-state metabolism
Explain the steps of the transport and fate of dietary fats
Fat comes into the lymph, when its in the blood, it can follow different pathways:
- Glycerol react as storage for adipose cells
- Free fatty acids can be diffused into cells where they are oxidised for energy - produce ATP
- Cholesterol can metabolise into bile cells for reuse or become lipo-protein
What does LDL-C do?
brings cholesterol from liver to most cells - lethal cholesterol
What is HDL-C
transports cholesterol out of plasma - healthy cholesterol
What do abnormal plasma levels of lipids do?
Increase risk of atherosclerosis and coronary heart disease: high LDL-C or low LDL-C
Explain the major things that occur in fasted-state metabolism
- Glycogen converts glucose in glycogenolysis
- proteins used to make ATP:
- Deamination of amino acids to organic acids, pyruvate, acetyl coA and intermediates of the citric acid cycle
- Broken down with production of ATP
Explain fasted-state metabolism in regards to lipids
Lipids broken down through lipolysis
- glycerol feeds into glycolysis
- fatty acids undergo beta-oxidation to produce acetyl coA
- excess acetyl coA become ketone bodies: strong metabolic acids lead to ketoacidosis; ketogenic diets rich in proteins and fats low in carbohydrates
What is deamination?
removal of the amino group from an amino acid creates ammonia and an organic acid
What must happen to ammonia and why?
Its toxic so must be converted to urea
How is insulin and glucagon released?
Endocrine pancreas secretes hormones insulin by beta cells and glucagon by alpha cells in the islets of langerhans
What endocrine hormone dominates the fed state?
Insulin
What endocrine hormone dominates in the fasting state?
glucagon
What does insulin do to the metabolism?
inc. glucose oxidation
inc. glycogen synthesis
inc. fat synthesis
inc. protein synthesis
What does glucagon do to the metabolism?
inc. glycogenolysis
inc. gluconeogenesis
inc. ketogenesis
How does insulin promote anabolism?
- increases glucose transport into most insulin-sensitive cells
- enhances cellular utilization and storage of glucose
- enhances utilization of amino acids
- promotes fat synthesis
- glucagon prevents hypoglycemia
- antagonist to insulin
Explain why insulin is so important
Insulin determines the whole of metabolic pathways happening in each cell
what is type 1 diabetes
Characterised by insulin deficiency from beta cells destruction
- without insulin, cells go into fasted-state metabolism: protein, fat breakdowns, hyperglycemia, excessive eating, glucose in urine, excessive urination and thirst
- metabolic acidosis
What is type 2 diabetes?
known as insulin-resistant diabetes
how is body temperature homeostatically regulated?
- normal metabolism generates enough heat to maintain body temperature in the thermoneutral zome
- alterations in cutaneous blood flow conserve or release heat
- sweat contributes to heat loss
